100pf capacitor code

Some design guidelines for PCBs don't make much sense, and some practices seem to be too redundant. Usually, these are caused by the black magic of radio frequency transmission. This is either the unfortunate and unexpected consequence of the electronic circuit, or the magic and useful function of the electronic circuit, and a lot of design time is spent on reducing or eliminating these effects or adjusting them.

You want to know how important this is to your project and whether you should worry about accidental radiation. In terms of Baddeley importance level:

When the signal moves down the wire, an electric field is generated in the space around it. If it is a DC signal, the magnetic field will not change, so nothing exciting happens in the RF field, but all remain unchanged. Pure direct current is very rare. The battery can do this unless you perform any switching voltage regulation, but anything plugged into the wall power supply will generate a 50 or 60 Hz sine wave, which is then rectified, transformed, smoothed, poke and pushed into a DC voltage or the like s things. . In fact (depending on the quality of the power supply), the power supply will produce ripples and produce small changes in the DC voltage, thereby effectively generating a small varying electric field. Other things such as crystal oscillators, signal lines between chips, and memory buses all have constantly changing voltage signals that travel from one place to another along the wires. Therefore, electronic equipment is flooded with signals and changes the electric field. It is through the constantly changing electric field, through a large number of mathematical operations (mainly discovered by Maxwell, Faraday and Gauss), that the electric field becomes electromagnetic radiation.

The frequency of radiation is the frequency at which the electric field changes, and there are many factors that affect this. One is the shape of the wire through which the electric field propagates. If you have something called a differential pair, the electric fields falling along the wires cancel each other out, resulting in almost no transmission. If you do not have a wire connected to the other end, the signal will drop along the length and reflect back. If the length of the wire is adjusted so that it can amplify rather than cancel out when reflected, your antenna is good. Back to frequency, it is by no means a perfect sine wave. It is a combination of waves of different frequencies. The antenna receiver has an electronic device that will deconstruct those frequencies in a certain range to extract the signal. Modern things are mainly FM, so there is a main carrier frequency, and will change slightly with the change of the data signal.

The tracking antenna is an antenna made of a small copper wire on the PCB, which happens to resonate at certain frequencies. This may be intentional, such as the F antenna design used in a 2.4 GHz transceiver, or it may be accidental, such as causing a long ground wire to fall in. To avoid this, please carefully check the poured ground for any traces. Either eliminate them or put in a via so that the trace does not resonate. Keep the ground as old as possible. The more fingers you have, the more times you slice, stretch and separate them, and the more unintentional radiation you will suffer. Generally, unless an antenna is intentionally manufactured, do not have any wires connected to both ends. This can be applied to unconnected board IO. After all, if nothing is plugged into the IO connector, it is just a trace leading to nowhere. If your microcontroller is smart enough to detect when the cable is unplugged, please do not send any signals along the cable. Bind all unused IO to the end.

Traces near the edge of the circuit board and farther from the ground plane will radiate more electromagnetic interference. Through-hole stitching refers to placing the through-hole ring always (or as much as possible) around the PCB edge to the ground plane. You can also add through holes on the side of the signal trace to reduce the EMI of the trace. In addition, a certain dose of through holes should be used to connect the ground holes to the ground plane (if you have a separate ground plane on a 4-layer board, or your 2-layer board is mostly grounded at the bottom). This prevents accidental antennas and also ensures that the entire ground remains at the same potential.

Data sheets for microcontrollers and power conditioners have decoupling or bypass capacitors connected to the power supply pins. These chips do not often consume the same amount of power. They vary slightly with the work of the chip, sometimes requiring a brief increase in power. On the power pin, this looks like a rapidly changing signal. The purpose of the decoupling capacitor is to have a small power reserve next to the power pin, so that when the chip fluctuates violently and rapidly, the capacitor can eliminate those power requirements without spreading rapid changes across the power trace . Ferrite beads are usually used when connecting a switching power supply to a power supply board, because it can isolate noise from the power supply, so place it (along with a decoupling capacitor) next to the power supply output.

Why do you want to make wires that take longer than necessary? Sometimes you need to force tracking to take a fairly circuitous route (heehee) to get from one contact to another. The rule is more about prioritizing which routes will become shorter and which routes may be longer. Generally, the faster the signal travels on the wire, the higher the priority, and the shorter the ideal trace length. The crystal oscillator should be as close as possible to the microcontroller, and the wire should be directly between the two. With every increase of 1 millimeter, the greater the change in electric field and the greater the emissions. The UART can have longer wires because the signal does not change at such a fast speed and the positive voltage rail may meander all over the place. This is also a good habit, because faster signals mean you want shorter distances between components to minimize latency, but RF protection is also important.

Since your PCB will have some cable connections, board-to-board connections or chip-to-chip connections, each may have longer traces, so you can add some filtering to the traces to pass series resistance and bypass Capacitors to reduce its noise. The ground should be as close as possible to the noise source (usually a microcontroller).

These are super noisy things, the cheaper they are, the more shortcuts there are. Not only will they explode radio frequency radiation with 50/60 Hz harmonics, but also switching power supplies that usually work at hundreds of KHz will also generate a lot of noise. This output may be unstable, so a lot of noise will spread along the wire and radiate out until it reaches your project, and then the project can work under noisy power. Not to mention

.

One thing that has no effect is the angle of the line. It turns out that even if the speed exceeds 1 GHz, there is no measurable difference between the 90-degree angle in the trace and other angles in the radiated EMI.

If you want a more comprehensive application note

. Also, please see our

@Bob Badley

Thank you for explaining your limited knowledge of SAW, harmonics and FCC guidelines.​​​

The rest of this article is vague and accurate anecdotal advice and follows the advice of most application note publishers.

"Accurate and accurate anecdotal advice" = easy to understand, for more content, like most topics, we must read textbooks.

Suppose this is a way to eliminate "have" and "have". As if they were not enough to hinder the development of publications, it is now an IQ test.

Thank you! My goal is to please!

Can we let the FCC raid broadcast houses?

If they emit enough heat, maybe...

Depending on the situation, I have heard some stories (mainly around here, which is the basis for my comment),

They will knock on your door and ask if you know of any spread.

Then (if you show uncertainty or ignorance), they will (sometimes) help you investigate the source so that you can do some processing on the source, namely replacement and/or repair.

They are generally more useful than savage because they (most people) know that many causes of interference are unintentional (faults).

Even one of the links in the article shows this (neon one).

Usually in the case of maintenance, it is better (and cheaper) to find a HAM for testing interference (assuming they already know how to perform the test, and not a person who is only permitted just because of their own wishes) or contact your communication committee/ contact. Commission (FCC / OFCOM / ETC ..)

It's ham, not ham. Not an acronym.

At least these days, HAM is usually hard to be an asshole. It's like testing someone with a ham.

Indeed, 90-degree and 45-degree corners have little effect on EMI, but at 1 GHz, it may be important to maintain a constant impedance of the trace.

Indeed, I thought at the time that a sub-note should be added to the sentence. +1

However, for a constant impedance, 45 degrees is still bad. If you pay special attention to corner reflections, you need to model the miter more accurately than "use a 45 degree corner".

However, what I have seen about 90-degree and 45-degree angles is that the 90-degree angle in lower-quality manufacturing processes can cause traps and lead to acid corrosion. Nowadays, this problem can be alleviated even by photo-activated etchant.

I won’t say that it sucks-better than 90 degrees,-the corner can be modeled as a capacitor connected to the trace, and it is really small (1pF reactance at 1GHz is 160 ohms, I suspect that the corner is close to pF )

Nonsense, 160 ohms would be a disaster. You will see that 20 ohms is easy (it is like 1 dB), which is about 100 fF.

???? You are on the wrong path-at 1GHz, 100fF is 1600 ohm reactance. I understand that the upper limit of 1pF would be bad news at 1GHz, but some engineering decisions need to be made. Any impedance continuity on the transmission line is not good, but it is relative. At GHz frequency, if there is no reasonable size of the trace, the tolerance of the PCB material will not reach the limit, and other variables in the system may submerge the 45-degree angle.

Gah, I stupidly consider that the final impedance of the trace has changed, which is also completely wrong. In any case, if the circuit is tuned, even the extra capacitance of 100 fF may be a problem because you will shift the frequency. I regularly trim the ground plane under the pad to compensate for such small parasitic effects.

However, the "engineering decision" part is stupid: there is no reason to say that PCB design software can't do arcing instead of sharpening 45, and calculating the correct bevel to keep the trace width as constant as possible is just a matter of mathematics. It is not an engineering decision not to compensate. It is just a lack of knowledge or time, and both should be regarded as failures of the tools used.

Nice article, thanks for sharing.

This seemingly 90s website provides a lot of useful information on reducing EMI:

What a great domain name.

He is an authority on EMI, transmission lines, PCB layout rules, etc.

He happens to live in the middle of Jersey.

Let me add: Always, always think in a circular way. As we learned in Circuit Theory 101, a circuit is a closed loop, going from the source to the sink and back to the source. From direct current to daylight, the theory is applicable in all aspects. In order to minimize electromagnetic radiation, the length of the radio frequency circuit must be minimized. This means bypassing as soon as possible, but it is also important to consider how close the bypass capacitor is to the source of the problem (active device). Not only physically close, but also electrically. What does the whole cycle look like? Is there a clear ground loop, especially on two-layer boards? Is the capacitor physically close to the power supply pin? Is there enough activity like ferrite beads to ensure further reduction of EMI?

This is an interesting story in the conference hall. I have a client who failed because of spurious emissions at 150 MHz, which is very bad. All GPIOs sent by the microcontroller are "wet", so it may make sense to try to mitigate EMI on these lines. Do not. I asked where is the Ethernet PHY (50 MHz, harmonics are usually related to Ethernet). To be sure, the terminal connection on the 50 MHz clock line from the PHY to the transceiver is poor.

But the fact is: GPIO did not malfunction. There is a confusing factor here. Poor termination of the clock line leads to the enhancement of ringing and higher harmonics. These harmonics enter the IO ring of the microcontroller.

Bypass the poor.

In order to facilitate the rework of the microchip, the circuit board designer removes the bypass cap from the microchip. It definitely meets the intended purpose and makes the microcontroller easy to replace, but the added series inductance compromises the advantage of the 150 MHz bypass. As a result, the entire IO ring is allowed to have a higher impedance at 150 MHz, thereby introducing noise and transmitting through any IO connected to the power rail.

The mitigation method is twofold: add some serial terminations on the Ethernet clock line and make the microcontroller bypass closer to the IC. Fortunately, we were able to complete these changes within a four-hour observation window and saw substantial improvements. The changes made are folded into the next board rotation, and the product is now compliant.

Sorry, it should read "Bad terminal connection on the 50 MHz clock line from PHY to *microcontroller*."

This is a fascinating anecdote because it points out that a bypass that works on the basic principles may miss harmonics, which is not necessarily obvious to a novice!

Can you clarify the meaning of "IO ring"? Does it refer to the peripherals and connectors around the microcontroller on the board, or the structure inside the microcontroller die? Or something else? (This seems to be one of the terms, such as "power rail", which is so obvious to those who know they have never explained it, but it is confusing for novices who are not yet at this level. )

Sorry, too much time was spent with silicon designers. As you can guess, the IO ring is a structure on the die. The way the manufacturing process works is that all IO pads are on the edge of the die, so the circuits most directly related to IO actually form a ring around other processing circuits. Therefore, the IO ring.

Data sheets usually show simplified diagrams of IO pins, but I will briefly describe them here. There is usually a driver that includes a pair of "totem pole" FETs from a dedicated VDDIO power supply to VSS, an input buffer connected to the internal power supply, and some ESD management, usually as simple as a pair of diodes on the IO pins. , One to VDDIO and the other to VSS.

This is the beginning of the trouble. VDDIO must show low impedance to VSS in a wide frequency range, not just VSS VSS, which is most closely related to the IO circuit. If this does not happen, the noise will be coupled to the VDDIO power rail, and once there, it will propagate beyond any IO pins.

So how to get there? Multiple methods. The culprit is the IO driver itself. Whenever one of these drivers is turned on and off, it will draw current from the VDDIO power supply. The higher the impedance of the power supply, when used again* (please note that many microcontrollers have multiple VDDIO pins, each *must* must be independently bypassed), the power supply will cause more voltage ripples, And there will be more noise. Is coupled.

The auxiliary mechanism is a bit tricky and may be what happened in the above situation. Remember all these output drivers, input buffers and ESD structures? Well, each has a parasitic capacitance. It may be small, 1-2pF, but even so, what is the capacitive reactance at 150 MHz? 500-1000 ohms. This means you can effectively model the clock input as having a small resistance of 500-1k on the power rail. Similarly, once the noise enters the power rail, it can be propagated to any other IO pins with the help of active high-side drivers or simply through the same parasitic capacitance path as the power supply. The only way to avoid this situation is to carefully bypass the supply.

150MHz, right?

If bypassing is really critical to your design, you can try using embedded capacitor materials.

Please also refer to:

Thank you for citing these content, it is good to review it from time to time.

For most designs, bypassing is critical, but it doesn't need to be difficult, expensive or intrusive. In most cases, 1-2 0402 ceramic caps of 0.1-0.5 cents per supply pin are sufficient. The trick is to make sure you don't shoot in the foot. When I did the layout, the first step was to place the active components, followed by the bypass and any EMI or SI key components (ferrite, termination). When wiring is required, power and high-frequency signals are always the most important. Usually when this method is not adopted, I still call me, either a designer (unfortunately not recently) or an EMI consultant.

"I want to add: always, always think in a circular way."

Yes. absolute. What I want to say is "Remember that the current is circulating. You can see the signal path, but *you have to imagine the return path below it*."

In higher layer designs, many times you end up with multiple ground layers (not isolated grounds, but multiple layers), because if you stack signal layers on a single ground layer, crosstalk will occur. Also, sometimes you need stripline signals or CPWG, so there will be multiple ground planes there.

In these cases, it is often forgotten that when a signal passes from a layer where the ground loop is on *one* plane through a layer where the ground loop is on a *different* plane, the return current also requires a via to switch the layer. If you don't, that layer of switches can "completely" * mess up the impedance of the trace. Since the signal loop is now larger than you think, it will also cause an increase in EMI from this trace.

This is why the super fancy pants layout pack now has

Specifications, so they are automatically added during routing.

It is also important to remember that power planes also often return signals-therefore, when they are adjacent layers, it is best to avoid using high-switching wiring to span different power planes. For example, if layer 3 is a power layer and there are multiple planes there, try to avoid any traces on layer 4 going through these gaps.

If you have a signal to pass there, please place a coupling capacitor on the right side of the trace to couple the two planes (for example, 3.3V->5V in the simplest case), sometimes called "plane jumper" ". However, it would be better to avoid it completely.

"In this case, what is usually forgotten is that when the signal passes from a layer where the ground loop is on *one* plane to a layer where the ground loop is on a *different* plane, the return current also requires a via to switch the layer. If You don’t, that layer of switches can "completely" * mess up the impedance of the trace. Since the signal loop is now larger than you think, this will also cause the EMI of the trace to increase.”

I encountered this situation, routing the signal from the top layer to the bottom layer on a 4-layer PCB, and there were no bypass capacitors connected to the ground and power planes. What makes me more distressed is that I also did not consider the signal split across the power plane... well, the current loop of the signal might look like spaghetti:')

I'm already familiar with the current loop/current return path, but after making this mistake, the theory becomes "real" enough that I will no longer make this mistake in the near future.

Yes, the loop area should be the first, second and third points of this article, maybe to keep up with the unexpected stub antenna. Most things come from the loop area. Why use decoupling capacitors? Provide a low impedance path for the return signal to minimize the loop area. Why do we have a solid ground with almost no cuts? Provide a low impedance return path for the signal. and many more. Compared with the loop area, through-hole stitching is a very small thing.

Yes, something that emits 90 degrees is a myth, but I still make 45 pairs, just because I think it looks better.

Compared with 45s, 90-degree bending is more likely to become thinner when making PCBs, especially on household etching boards.

I have seen 90* elbows used in the Cisco WiFi card and they look like PCB etched "air core" inductors.

Although bending is more likely than the transmission capacity of the tracking track, it is more likely to define the track length that exists in the scene where the inductive coupling is performed (if any, so far, this is my guess).

Don't you do ESD / EFT testing?

Does IEC 61000-4-2 not apply to your product?

No, not at all.

Great article.

My master's degree has inspired me a lot, but PCB design has never involved any aspect. It turns out that this is the most critical aspect of my work since graduation. I have learned some of these things hard with failed prototype PCBs. I used to sew to solve thermal problems before, but I never considered RF.

>I have solved the thermal problem through sewing before, but I never thought about radio frequency.

OMG! Just search for "RF PCB" on the image, then go through the fence to see all the cute things.

Via stitching is usually performed to manufacture coplanar waveguides for stripline transmission lines.

The goal of PCB layout is to minimize the circuit loop area.

All traces not on the ground plane are antenna structures.

Antenna reciprocity. You generate a lot of emi at a certain frequency, and you like to receive it there.

The reason why radiation is radiated near the edge of the circuit board is that the transmission line generates a signal, so that the ground line width of the electric field line is 5 times that of the ground layer. Generally, you want the ground plane to be very close to the edge of the PCB and back to the signal plane when the signal plane contains high-speed or high-transition traces.

When you set STM32 to fast GPIO mode, ask yourself, does this really need to be fast? If the span is fast, so are its harmonics.

Find,

I see the working principle of high-quality PCBs, where there is no way to route any traces between layers for some reasons:

These traces (especially LVDS pairs) maintain very close spacing, and the PCB spacing between the traces and the ground plane is about 1/2 inch or 10mm.

Generally, the PCB is located in a metal housing, and all non-radio influence channels are located near the vents and connectors. (Even before, I have seen this structure in decent laptops)

>All traces not on the ground plane are antenna structures.

This is a problem because I usually only use two-layer PCBs.

Zero ohm resistors are your friend! You can get a cheap 1206 0 ohm resistor, and then whenever you need to wire, just put a resistor. Remember, despite this, you will cause some crosstalk between two crossing signals because their return current flows through the same part of the ground plane.

My guess is that it’s better to skip the signal overpower (or signal overpower) instead of skipping the signal over-signal, because in any case, the power supply will be high-frequency decoupled on the IC, so the actual physical connection back to the power supply is At low frequencies, however, the return current will be distributed across the board.

Another thing you can do is to put in more effort, but it can actually be better, it is a jumper (the smaller the size, the better, so you can make the pads as small as possible), And *install a jumper* at medium frequencies, the two sides of the ground plane are *different planes* (electrically connected everywhere), so the return current on one side of the plane cannot even see the other The side of the plane returning current.

The 0 ohm 1206 on the back can also be used, but unless you put the via on the pad, it will take up more space, which is usually difficult to construct. As long as you make sure that you don't run wires on top of the pads on the ground plane, the actual space on the ground plane is not a big issue. Just run the wire through the gap between the jumpers.

I often make 2-layer boards, and the 0 ohm jumper is completely my friend. The jumper on the back is a trick, one can say at once: "Hey, you are breaking the ground" and then point out no, no, you are just using the other side of it.

I never thought of using 0 ohm resistors as jumpers. Thank you for your suggestion!

Don't panic, just keep the loop area small. Imagine that the return signal should be as close as possible to the trace, but on the ground plane. For each cut, it must move outward. You can reduce the distance according to the cross stitch stitches I think. Pop your far trajectory up to the top, and then swipe down. This creates an additional path for the ground plane. If you trace the loop area, you can find many areas in which you can manipulate the ground plane without much impact, especially under the IC. Creating a two-layer board with a good low-inductance ground* and* power plane is a bit of an art form, especially when you have a lot of signals.

A few examples:

Thanks for your suggestions and examples.

My most recent job is to obtain medical equipment through radiation and emission tests.

Regarding conduction emissions from power supplies: We tried many power supplies from large (not so major) manufacturers, all of which claimed to comply with conducted emission limits. Guess what? Without external line filters, none of them will pass. Plan to install one.

Another area of ​​difficulty is the appearance of a broad peak around 150 MHz. This is due to the color display being fixed in a metal mount (but not screwed or otherwise fixed, as this is a high-quality display designed to be packaged in consumers) ) Plastic clamshell shell). It does have a metal case, but that is not enough, we have to use copper tape to glue the display case to the metal bracket.

The RFI test is fun! ! ! (Because you learned a lot, and when you got the "pass", the boss thought you were smart)

We paid a lot of money to a guy equipped with all the equipment and antennas for our CE test...I want his job. ;)

He just pointed out the problems, and didn't have to solve them...

Although knowing the location of the impersonation in a 100pf capacitor can "eliminate the edges" and squeak within the limits, it does make you look like a practitioner of black RF technology. ;)

"Regarding conducted emissions from power supplies: We tried many power supplies from large (not so major) manufacturers, all of which claimed to comply with conducted emission limits. Guess what? Without external line filters, none of them would pass . Plan to install one."

Check your PCB layout/grounding. If the device passes CFR Title 47 Part 15B, you may have done it.

We have similar experience in purchasing power modules from well-known manufacturers. Finally, we got a report from the lab telling them that the device failed the emission test, they went and redesigned their power supply to actually meet the specifications announced in the data sheet. It's not that we are a customer who buys 100,000 products every year, they bend back to continue doing business with us. If we buy 1,000 dollars a year, we have already had a bumper year.

When I re-read the beautiful picture on their data sheet, it said "When installed in a compatible device"

Now, both you and I know that there is almost nothing except the power supply itself which causes conducted emission, but I think that sentence is their "swinging room".

Oh, and all consumables are "medical grade", which means that in addition to emissions, they should also meet the leakage requirements of IEC 60601-1. That way, they did it. Silly me I think that if they can solve the problem correctly, then emissions will be a breeze.

Possible explanation: first look at the size of the power supply filter, and then look at the size of the switching power supply. There is not enough space to install these filter components in a switching power supply... and competitors are constantly applying pressure to reduce the size of the power supply.

IEC60601 means that because the products are connected by cables, the requirements for leakage current are very strict.

Leakage current is easily coupled through the large-capacity Y capacitor on the input AC-DC EMI filter. Other sources are grounded heat sinks, which capacitively couple noise into the grounded conductor.

Note that many power supplies have a Y capacitor between the secondary DC output ground and the primary side common. This is to reduce the loop area as much as possible to avoid radiating too much EMI.

For hard switching (fixed frequency, non-resonant) power supplies, it is difficult to work without or without Y capacitors. These types of supply can be said to be more stable, but this may be because they are easier to understand and model.

Y caps are used as filters for common mode noise and common mode chokes

If the method of grounding the power supply of the product enclosure is bad, be prepared for filtering.

For traces that deliberately carry RF or HF signals, circular traces are better than slanted traces, because this can reduce signal impedance and reduce ringing. Looking at things like WiFi or even ZigBee recently used, you may find that the trajectory of the antenna feeder is circular and has a flowing curve instead of a sharp 90 degree bend. You want to send as much signal as possible to the antenna and radiate in that direction in the desired direction. Looking at the impedance matching traces on the board with USB, PCIe or other buses with differential pairs, you will find that the corners are rounded instead of 90 degrees.

The reason (according to Johnson, high-speed digital design) is that the width of the transmission line increases slightly at right-angle corners. Therefore, keep the trace width constant and minimize the impedance discontinuity, because the impedance discontinuity will cause reflection.

I believe the reason for this is that it is easier to calculate impedance, not better.

In fact, you can still use right-angle traces, you only need to cut off the outer corners to keep the impedance roughly the same. 2.4GHz is definitely the range where the signal begins to appear such impedance discontinuities. Another trick is to cut holes in the ground plane below. This is usually used under filter covers or series resistors because the width of the pad is significantly larger than the trace.

If your project is not a deliberate radiator, but puts it in a metal box, there may be any debris you want inside, right? Nothing works out of the box.

As long as there is no opening in your box, or the connectors and cables connected to the next box are 100% shielded, it's fine. ;)

Radio frequency is like water, it will leak out from any joints or non-metallic connectors.

If it's that simple.

The noise is coupled with the wiring through the outside. The plastic switch "leaks" and the LED is plastic.

Your metal box can also be a radiator.

> Everything is unlimited.

What does it do? If there is no I/O and UI.... I can imagine that this will work for temperature and acceleration data loggers, nothing more!

Once you have power input, any type of I/O, switches, indicators, displays, your box is no longer sealed. Keyboard matrix scanning can be incredibly noisy, especially if you use GPIO to scan without limiting the slew rate of the signal. (Slew rate = speed of voltage change = sharpness of square wave edge = rich harmonic content of generated EMI.)

Similarly, LED matrix scanning. MAX7219 is a popular chip without slew rate limitation. It is the same as MAX7221, but adds this function. If you are worried about EMI, please guess which one to use!

This is not just for commercial products. If you use radio signals yourself, the noise from your own equipment may be the biggest problem. Because it is so close, it can solve the problem without being particularly loud.

If you have field wiring, it will couple the noise you generate in the box and radiate/conduct out of the box.

FWIW, in the presence of millivolt (sometimes smaller) signals, I will deal with very large RF interference, no, you can’t make the box that tight. You just can't. The exact number makes me incomprehensible, but the performance of about 60dB is good (washer, not an accidental slot antenna, no corrosion, perfect conductor, braided coaxial cable soldered to the copper box, passing through the decoupling ferrite/capacitor, Then it flows continuously through –

When I use the various parasitic capacitances of 50kv (from coaxial cable to ordinary air) on the HV line, the Q value tends to be very high, even if the power supply has an internal "assumed resistive" ballast, the peak current will be unexpected The arc can easily reach kiloamps-kilovolts. For example, megawatts. Now, it is a few feet away from us, working in microwatts, and trying to tell the accurate gamma spectrum or the accurately detected neutron count....

Therefore, megawatts/microwatts – 10^12 – exceed 60dB!

The result is that you have to shield both ends, carefully perform power decoupling and everything you can think of, and then make some modifications until the actual effect is good, so as not to fool your own measurement results. By the way, I have been doing RF/EMI since the early 60s. Knowing the theory is not all, although it will help-at least when you find a bug, you know the reason for the fix; ~}

Since I am doing "research grade" work-in a sense, it is more lenient than "production grade" because it only takes long enough to get answers... and the output of my test bench often explodes A few meters of computers even if they are not connected to anything-I do use arduinos and raspies-as Eben said, it is a low-consequence environment, and it is cheap and easy to replace, just in case the EMI incident is greater Beyond plan.

Please note that in real life, a fusion reactor like the one I am using does not need this sensitive instrument near the reactor-this is research! Some things you only need to find out once, and then you can make them bigger.

The sewing example seems to be similar to the old wincor (Nixdorf/Siemens) product we used (1994 to 1999) in structure, PCB grade, soldering quality and power supply layout.

In addition, some of the above products also use VCC (5 and/or 12v) as their PCB shielding LOL

Have enough bypass Vcc to ground, until AC current

Why not use a chip with a socket for an external oscillator? Use SMD tapered clamps and have enough space to accommodate the oscillator.

Board thickness....

In order to connect the two pins to the top, nonetheless, there is still no way to stop them. The unused pins have 10-14pF harmonic/over-oscillation suppression capacitors.

The next problem is that the chip will be used in a decent metal tablet: unless insulated, short-circuit the clock source.

Capton tapes can only be used for so long (like any design failure year?), and then the PC can only "die".

Generally Joe doesn't know how to solve it, but we will at least guess that it is just to replace the Kapton tape.

The thickness of the board depends on the laminate design, and it is entirely up to the designer to decide which laminate to use.

Because there is more than one type of external oscillator, the size (including size) of each oscillator is different.

Because the oscillator in the socket will be bulky, take up a lot of circuit board area, relatively expensive, low reliability under high vibration or acceleration, and will increase inductance, parasitic capacitance, etc.

You neglected to block...good for you, good for them. Good for everyone.

The title is wrong! The best headline is: How to not write an article.

I think you inadvertently are the whole article.

You *must* be careful with ferrites! Steve Weir published a great article at DesignCon 2011, but unfortunately, it may seem to be offline.

However, the "Analog" article also introduced this.

Ferrites, together with decoupling capacitors, form a good LC filter, which is why they are used. But why not use ordinary inductors? Because the resonance LC peak *amplifies* the signal, but does not attenuate the signal, and the ferrite has a loss (resistive) at its self-resonant frequency.

Except for your hat* move the LC resonance back to the sensing area! *This means that if you are not careful, the ferrite beads + LC filter can *amplify* the switching noise without attenuating it!

The solution is to simulate it! You may need to add a dominant pole (a capacitor + a small resistor in series, or a cr-pin electrolytic cell with high ESR) to suppress the LC resonance of the ferrite.

For this reason, Wurth Elektronik's ferrites are great because they provide a complete set of LT Spice simulations for all ferrites. Therefore, you can determine the best solution very, very quickly.

I found this article and it looks great;

Ah, Wayback Machine! His introduction to the ferrite bead part is

, This is a simple quick reading and instructions on how to deal with them.

I like it and i will join

This is a very timely article for me, because I am currently taking a course on radio receivers. The last class discussed pcb design. I seem to think of something that takes about 1/10 of the frequency wavelength distance. A wire Become a feeder? In any case, don't listen to those who hate the article, thank you for your article.

According to experience, we say that any trace longer than 1/10 of its transmission frequency distance should be regarded as a transmission line.

Although it is usually only used for sine waves, for square waves we tend to look at the rise and fall times.

There is a white paper (MT-097) for analog devices, they said to multiply the rise time (in nanoseconds) by 2 and use the result as the maximum trace length (in inches), and then suggest to treat it as a transmission line .

If you don't think of it as a transmission line, all signals will degrade, but by applying a rule of thumb, you will be fine in most cases.

"...This is by no means a perfect sine wave; it is a combination of waves of different frequencies."

I think you mean this is by no means a perfect sine wave. It is a combination of multiple sine waves of different frequencies. "

It is also worth noting that inputs (such as ADC pins) can also be noise sources. TI microcontrollers are notorious for this behavior. Regardless of the MUX selection, the ADC clock will be output through the pin.

It sounds wrong.

Are there no separate AVDD and AVDSS or VREF + and VREF- on the chip?

We have sorted out the pages about RF PCB functions, and briefly outlined some commonly recommended RF materials and bonding materials that can be used in various applications and industries, including consumer electronics, military/aerospace and medical.

Check it out here:

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In order to protect the hearing health of HA users, researchers in related fields have been studying the impact of electromagnetic interference (EMI) on the HA. From 1997 to 2011, the International Electrotechnical Commission (IEC) developed international standards that stipulated electromagnetic compatibility (EMC) between HA and mobile devices. The latest versions of these standards have increased user compatibility specifications and expanded high-frequency bands.

From 2001 to 2011, the American National Standards Institute (ANSI) published three versions of the national standards for the measurement principles and methods of EMC compatibility between mobile and HA. In 2010, the American Hearing Loss Association announced the latest version of the Federal Communications Commission (FCC) EMC regulations to regulate the compatibility between the Hospital Authority and mobile phones, which requires mobile phone manufacturers to comply with these regulations before the deadline.

However, these standard documents are comprehensive and target professional engineers. There are few articles and reports on HA's EMC control/design technology. Based on the basic radio frequency (RF) emission and reception principles and years of practice of EMC standards, RF-PCB design technology and the use of a new generation of EM components, this article introduces the causes of EMI failures and applicable EMC measurement and evaluation procedures. This kind of HA equipment proposes several EMC control technologies. Researchers and engineers in related fields and the hearing care industry should benefit from reading these topics.

*The first specification is for bystander compatibility, and the second specification is for user compatibility

**Evaluation in directional mode to improve onlooker compatibility

Figure 1: Front and back layers of PCB layout

Figure 2: EMC performance without capacitor and with capacitor

Figure 3: EMC performance before and after the choke is inserted

The EMC effectiveness of the mid-power all-digital BTE HA with Fermifilm UIP 7 packaged PCB unit was demonstrated. The top and bottom graphs show the IRIL curves of HA in the HB field with and without film, respectively. These curves comply with IEC 60118-132004. The maximum IRIL in the top graph is 70.8 dB; the maximum IRIL is 70.8 dB. The maximum IRIL in the bottom graph is 38.2 dB, an increase of 32.6 dB, making it pass the EMC assessment. The film also shields the slot of the HA housing; otherwise, the EMC performance will not be ideal. Open slots (depending on their size) may cause

EMI leakage. In this case, slots with wavelengths less than one-twentieth may leak. Modern BTEs have several slots on the top of their case, which limits slot leakage. You can assemble the wires in the housing and keep them as far away from the slot as possible to avoid EMI leakage. This technology achieves excellent EMI suppression and eliminates most concerns about EMC control when designing PCBs. However, this method is expensive.

Figure 4: EMC performance with and without membrane

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If you build electronic circuits on a regular basis, you may use capacitors multiple times. They are standard components used with resistors, and their resistance values ​​can be proposed without consideration. We use them for power smoothing and decoupling, DC blocking, timing circuits and more applications.

The capacitor is not a simple spot, it has two wires and two parameters: working voltage and capacitance. Various capacitor technologies and materials have different characteristics. Although almost any capacitor with the correct value can accomplish the task in most cases, you will find that understanding these different devices can help you do things that not only accomplish the task, but also do the best. For example, if you have to pursue thermal stability issues or find these additional dB noise sources, you would be very grateful.

It is best to start with the basics and describe the capacitance from the basic principles before studying the actual capacitor. The ideal capacitor consists of two conductive plates separated by a non-conductive dielectric. Charge will accumulate on the board, but due to the insulating properties of the dielectric, they cannot flow between them. Therefore, the capacitor can store charge.

Capacitance is in farads: a farad capacitor holds a voltage of one volt while holding a coulomb charge. A farad, like many SI units, is impractical in size, so outside the narrow domain of supercapacitors (outside the scope of this article), you are more likely to encounter micro, nano, or picofarads. You can use a formula that may be worthwhile to derive its capacitance from the size and dielectric properties of any given capacitor

. Unless you are studying for a high school physics exam, you don’t need to remember it, but it hides an important point. The capacitance is proportional to the dielectric constant

The increase in the number of dielectric materials used has led to various commercially available capacitors using different dielectric materials to achieve a higher capacitance range or better voltage handling characteristics.

There are obstacles to the use of dielectric materials in capacitors, and the ideal properties of dielectrics also bring many unpleasant side effects. All capacitors in the real world have internal parasitic resistance and inductance. Although small, they sometimes affect the operation of the capacitor. The dielectric constant changes with temperature or voltage, piezoelectricity or noise. Different types of capacitors may have shocking failure modes, and even amazing prices. Therefore, we have entered the main part of this section. In this section, we will take you to understand some types of capacitors you may encounter and list their various characteristics, including good and bad. We will not claim to cover all possible capacitor technologies, but we will introduce common capacitor technologies and check any subtypes you might find.

An aluminum electrolytic capacitor uses an anodic oxide layer on an aluminum plate as a dielectric, and the electrochemical battery electrolyte that forms it is used as another aluminum electrolytic capacitor. Because they are electrochemical cells, they are polarized, in other words, any DC potential passing through them must always be in the same direction as the anode plate (!) or the positive terminal as the anodized plate.

The pole plates of practical electrolytic capacitors in the form of aluminum foil sandwich plates are rolled into a cylinder and contained in an aluminum can. Their quoted working voltage depends on the depth of the anodized layer.

Electrolytic capacitors have the largest capacitance you will encounter in normal use, ranging from 0.1 to thousands of µF. Due to the tightly wound electrochemical cells, they have a high equivalent series inductance, so they are not suitable for use at high frequencies. In general, you will find them useful for power smoothing and decoupling and audio coupling.

Tantalum electrolytic capacitors are in the form of sintered tantalum anodes, which have a very high surface area, on which a thick oxide layer is grown, and a manganese dioxide electrolyte is applied on it as the cathode. The combination of high surface area and the dielectric properties of tantalum oxide dielectric means that the capacitance per unit volume of tantalum capacitors is very high, so tantalum capacitors are much smaller than aluminum electrolytic capacitors with the same capacitance. Like aluminum electrolysis, tantalum capacitors must also be polarized, and the DC potential at both ends must always be in the same direction.

The value of tantalum capacitor is about 0.1 to hundreds of µF. Compared with similar aluminum products, their leakage resistance and equivalent series resistance are much lower, so you can find them in test and measurement, high-end audio, and other advantageous applications.

Tantalum capacitors have a failure mode that requires attention. They are known to catch fire. Amorphous tantalum oxide is a good dielectric, while the crystalline form of tantalum oxide is a good conductor. Misoperation of tantalum capacitors by applying excessive surge currents to tantalum capacitors may cause the dielectric to change from one form to another, resulting in a substantial increase in the current flowing through the capacitor. Fortunately, not all news is bad news. Their reputation in the fire comes from earlier tantalum capacitors, and improved manufacturing technology has delivered more reliable products.

There are entire series of capacitors that use polymer films as dielectrics, which are sandwiched between coiled or staggered layers of metal foil, or have a metalized layer deposited on the surface. The rated voltage of these capacitors can be around 1000V, but they are not suitable for large-capacity capacitors. You will find that their capacitance ranges from about 100pF to single-amplitude µF. Each different polymer dielectric used has its own advantages and disadvantages, but the equivalent series capacitance and inductance of the entire capacitor series are lower than the electrolytic capacitors discussed so far. Therefore, you will see their use in higher frequency applications, as well as power supply decoupling in electrical noise environments and general applications.

Capacitors are used in circuits that require good temperature and frequency stability. You will also find that they are used in power supply suppression and other power circuits, especially for rated versions for high-voltage AC use.

Capacitors do not have the temperature and frequency characteristics of polypropylene, but they are inexpensive and can withstand the high temperatures of SMD soldering. Therefore, you will find them used as general purpose capacitors in non-critical applications.

Capacitors still do not have stable temperature and frequency characteristics, but they can withstand much higher temperature and voltage than polyester.

The capacitor has all the temperature and frequency stability of polypropylene and can withstand high temperatures.

You may also encounter

with

Capacitors in old equipment, but these two dielectrics are not commonly used today.

Ceramic capacitors have a long history, and you can find them in devices that span decades from today to the beginning of the last century. Earlier ceramic capacitors were single-layer ceramics plated with metal on either side, while recent examples also include multi-layer designs in which alternating layers of metal and ceramic are constructed to form a set of staggered plates. Depending on the dielectric used, the capacitance ranges from 1pf to tens of µF, and the voltage is kilovolts. You will find single-layer ceramic discs and multilayer ceramic surface mount packages used in a variety of small capacitor applications in all areas of electronic products.

When looking at ceramic capacitors, it is best to consider them in terms of the ceramic dielectric used, because they derive their performance from these capacitors. Ceramic dielectric classification

It is these codes where we will quote the most common codes.

The dielectric has the best capacitance stability in terms of temperature, frequency and voltage. You will find C0G capacitors for resonant high frequency and other high performance circuits.

The dielectric does not have the temperature or voltage characteristics of COG, so it can be used in less important applications. Generally, you will find them for decoupling and general-purpose applications.

The dielectric has a higher capacitance than X7R, but has poor temperature characteristics and a lower maximum voltage. Like X7R, you will find them in general purpose and decoupling circuits.

Since ceramics are also generally piezoelectric, some ceramic capacitors also exhibit micro-sounding. If you are working under high voltage and audible frequencies, such as in a tube amplifier or electrostatic environment, you may sometimes hear this effect because the capacitor may "sing". If you use piezoelectric capacitors to provide frequency stability, you may find that they are modulated by environmental vibrations.

As mentioned earlier, this article does not attempt to cover all capacitor technologies. A quick look at the electronic consumables catalog will show you several technologies not mentioned here, and many others are outdated or have a small niche that you rarely see them. Instead, what we want to achieve is to make some of the common types you might see mysterious and help you make choices when you make your own designs. If we arouse your appetite for more component loss, maybe we can get your attention

.

It doesn't matter, use capacitors that require almost zero inductance in the microwave area.

How about im head capacitors?

Or PCB capacitor?

Variable PCB capacitors?

Yeah, I know. "This article does not attempt to cover all capacitor technologies." I just want to point out that those will be interesting because you can make your own!

Lol, no, they are useful links, not sure if his book lists other uses for large capacitors...

Thank you for linking with variable PCB capacitors. This will come in handy.

I like those links. thanks for sharing.

No mention of the capacitor disaster:

Jenny forgot to mention that Magic Blue Smoke was among them.

No, that's fast magic blue smoke. It escapes faster than ordinary blue smoke.

Thank you for your information! Don't know at all (always think what I see is related to the wrong temperature specification)​​!

Particularly worth reading is the root cause of this huge problem: the perfect example of "good, bad, ugly"-capacitor companies in Japan, China, and Taiwan. Maybe this is the reason why my 2006 iMac power unit failed.

charming! I know this question, but I don't know where there is such a comprehensive understanding. Thank you for contacting us.

The trap for young players is the forced pressure reduction of tantalum... The issue is not often mentioned until the part fails and the manufacturer points you to the white paper.

Other curious traps:

– The capacitance of ceramic capacitors varies greatly with the applied voltage. If a voltage close to 10V is applied, a 100nF rated 10V capacitor may only have a 10nF capacitor.

– Class 2 (not COG NPO) ceramic capacitors decline over time and recover after re-soldering. This is a non-linear thing, which is very eye-catching for newly produced or newly welded caps.

– When a new aluminum electrolytic cover or no voltage is applied for about 6 months, the leakage of the aluminum electrolytic cover is 10 times. They need a few minutes to "reform".

– The leakage of aluminum electrolytic capacitors varies with voltage in a non-linear manner, so general electrolytic capacitors usually self-discharge to about 30% of the rated voltage quickly, and then will not drop below 20% of the rated voltage for months or even years.

-The aluminum electrolytic cover will change proportionally with temperature, and all other factors will change slightly. A good rule of thumb is that for every 10°C increase in operating temperature, it will decrease by half an hour. vice versa. So, if you run 1000 hours at 100C rated capacity at 40C, it will last 64,000 hours.

–Specifies the capacitance value of Class 2 (X7R, Y5U) ceramic capacitors and the tolerance at +25°C. In most cases, the peak is not far away (maybe 20°C). This means that when you stay away from room temperature, the capacitance usually drops. It does not increase one method, nor does it reduce another.

Regarding the first point of the list, the change in capacitance with voltage is only applicable to Type 2 dielectrics. It also particularly affects smaller external dimensions, but does not change much with the rated voltage. This Maxim application note is very interesting:

The C0G/NP0 dielectric is basically flat. But this is something that many people will miss, because most of the ceramic capacitor datasheets I have seen don't even mention it, and there is no e-book I have read, nor is this article.

Same Here. I didn't fully realize the characteristics of DC bias until a few years ago, when a sales representative of a supplier who had just released a series of new bottle caps with "low DC bias function" came to our company to advertise. Makes me wonder what else is under the carpet.

How repeatable/reliable is the effect?

Can you reliably build a VCO by applying different bias voltages?

There are not only type 1 and type 2 ceramic capacitors. A better statement may be that the Class 1 capacitors were not significantly affected.

correct.

Then there are temperature-compensated ceramic capacitors. They are not common in today's cheap crystal oscillators and digital synthesis frequencies, but you will find them in older equipment, and perhaps in some older electronics stores. If you use them by mistake when you expect the temperature, you will feel unhappy. They are usually available in N750 and N1500, if memory is available, P150 and N2200 can also be used. They are used to stabilize the temperature of RF oscillators and filters. The inductance of the inductor will increase with the increase of temperature; therefore, the use of capacitors with a negative temperature coefficient (for N750 type capacitors, 750 parts per million degrees Celsius) will be used to maintain the resonance frequency roughly with temperature changes Constant. They will be used in parallel or in series with NP0 (C0G) capacitors to produce a net temperature coefficient that offsets the net temperature coefficient of the inductor. The use of temperature compensation capacitors can produce surprisingly stable and easy-to-tune tens of megahertz oscillators.

If you can find it, does ETI remember? John Lindsey Hood has written a series of wonderful articles called "True Ingredients." It thinks in the late 1980s. It's worth trying. I have a series somewhere.

John Linsley Hood

I cannot find many online copies.

Thanks for that. If there is enough interest, and I can sort out copywrite, I can scan my article. In 1985, memory was still OK. I know it will be there.

Please I am very interested. When reading in-depth articles about electronics in the 1980s, I got the golden age of electronic atmosphere.

There are copies of old 1950s popular mechanics everywhere on the Internet, and I really like the copies I have. The big business at the time was selling mail-order courses to train people to become TV technicians. The college competition provides more and more things to build themselves, with meters and complete TVs with various screen sizes.

I recently started as an electrical test engineer and started using "professional" parts. The main difference lies in designing and ordering parts for each project. Out of hobby, I picked up a box of old capacitors and pulled it out until there were (close to) matches. Anyway, in my project, I found 10uF (50V) ceramic capacitors in the 1206 case, and I used them to replace the electrolytic capacitors in circuits such as MAX232. In the case of 1206, they rose to 220uF (2,5V)...

That's great!

Now, understand the DC bias effect of each ceramic capacitor whose dielectric is not NP0/COG.

Pro Tip 1:

Your 10uF ceramic capacitor is not 10uF.

Although this is much more detailed than the article, please don't forget to use Mica capacitors to prototype the semiconductor buffer in the switching power supply.

Pro Tip 2:

If you work in engineering and want to keep that job, please visit the manufacturer's website to calculate the life of aluminum electrolytic capacitors in your application. This is especially important in power supply, high temperature, high rms ripple current or high voltage applications.

Pro Tip 2a: Press the ctrl key and click to display the root mean square value of the waveform in LTSpice.

Thanks for the tips. The capacitor rating is 1v DC. The size of the 1206 is better than the smaller size, which is the main reason why the 1206 is selected for low output and easy manual welding (expensive labor).

For me, the most important point mentioned earlier is the effect of temperature on the life expectancy of electrolytic capacitors. In my experience, due to other reasons beyond the rated value, the failure of electronic equipment is almost always caused by the failure of the electrolytic capacitor. If you want to continue using it for 10 years, it is best to keep any electrolyte cool. Keep them away from CPUs and similar chips, etc. Your device may be used for several years.

Don't forget that flux capacitors usually require very high voltages to work.

Rated working time is -30 years

Please don't believe it until you see the data sheet and receive a sample of my product from Rubycon.

I miss capacitors-they can actually condense electricity. Electrical condensate is indeed powerful. You don't want to get anything.

But what can capacitors do? Will they be capacitive? Will they promote capacitation? Do you want to use those words in the sentence?

Abandoning Alessandro, they have not been called condensers for 60 years.

I have been working on motorcycles in the late 1970s, and all service documents refer to condensers wired as required. This means that only 37 years ago, it was still a generic term (at least in this app).

Condenser is a general term in ignition systems and has long been obsolete in other applications. I am sure that the replacement part is still called a condenser.

In Romania, they still call it a "condenser". You can imagine the expressions of an ancient university teacher when students say "capacitor" after reading an English document.

Personally, as long as both sides of the conversation understand what is being said, I don't care how to call them.

In Dutch, the word capacitor is still "capacitor"

And in the French "condenser"

In the automotive industry, they are still called condensers.

I am 60 years old, does that mean I am no longer useful?

If you touch the terminals of the larger terminals, they may make you incapacitated.

The term capacitor was first used in the 1920s. The Navy seems to be an early adopter. The condenser gradually disappeared until it disappeared (almost) in the 1960s. Some people think that capacitors are closer to the resistors and inductors already used, but who knows.

When I was working for Tek in the late 1970s, they discovered that for a particular case size, never use the largest capacitor available. Always go to the next larger box. I can’t start telling you how many caps were removed and replaced with larger cases to improve reliability.

Likewise, not all electrolytic capacitors are the same. Replace a low ESR capacitor with an equivalent value, instead of a low ESR capacitor, you will see the inside of the capacitor.

Mica caps can also be used. See that the CM04 cover can be unsoldered from the RF breadboard. When they moved to CM06, they got warmer, but not hot enough to melt the solder.

For the same capacitance value, the next larger case size has a larger surface area.

Calculate the key value of electrolytic capacitor life.

Unless absolutely necessary, avoid using tantalum capacitors, and then try to check your supplier. The tan tantalite industry has become severely corrupt, causing catastrophic wars and human rights issues.

If we follow this policy globally, none of us will buy anything with rare earth magnets in it, because +90% of the market is controlled by a totalitarian regime with a very bad human rights record.

So, Peter, if there is a hard drive in the computer, please return the computer. Only buy SSD from now on? What about everything else with a compact motor equipped with rare earth magnets?

Yes, if you haven't solved the problem, then I hate an evil person more than a proud evil person. He implies that they are not evil, and everyone else is evil.

Look, when I read the review, I just saw someone trying to light up something, something most people don't know. He did not say "Don't use tantalum capacitors", "If you use them, it would be terrible." He just kindly asked, "Please avoid using tantalum capacitors." All other statements in his comment are statements of fact. You can still use whatever you want in your design. No one accuses you of being evil.

Maybe you just reacted to the previous discussion about tantalum that you participated in before, and the commenter was more demanding than Peter.

Lol, what a hot load. As I implied, hypocrisy.

These days, can you even buy phones that guarantee conflicts and free human rights violations?

no, you can not. Many people do know this, and most of the people in this group really don't care. I care, but boycotting does not stop this practice. The people involved just adapted without actually reducing the harm to the innocent.

If you have questions about the behavior of immoral people, please disband these people, because there is no other way to stop them. Boycott is a very blunt tool, which usually causes a lot of incidental economic losses, and even more innocent people. Bring harm.

Do you honestly believe that you are so wise that you can recommend any form of boycott and can predict the true result? Why not just ask people to donate to NGOs that help those in need to resist harm? Isn't this more destructive, or more sensible?

Sorry if you don't like my opinion, but at least I can prove it strongly!

Regarding the phone, there is currently a project, although I do not claim to own it. As you said, there is no way to guarantee that they will do what they say:

.

I think you are confused-I have never tried to talk about tantalum capacitors since the beginning. Please read my comment again. I just want to point out that Peter is not accusing you of evil. He did not ask for any moral requirements. Yes, he advises you not to use tantalum capacitors, because that is his belief. But does he think he is "better than you" just because he doesn't use tantalum capacitors? I do not think so. This is the point I want to make. Is it hard to believe that this might be ignorance? In this case, the reply you just gave me will be deeply valued by him.

Most of the arguments you put forward in this response sound good, and if you put them in the original comment, I won’t have any questions about it. There is no problem with my opinion. I just want to use "attack your emotional foundation". Yes, if you haven’t solved this problem, the only evil people I don’t like are evil people. He suggested that they are not evil, others Everyone is. "This is not the right choice. In general, your first comment is indeed...not good. Has it become so difficult online?

Like I said, how hot the air is, you can't verify any of them. In any case, what right do you have to regulate the Internet, and that is that, in the eyes of some people, arrogance is just as offensive as in my comments. It looks like you are a self-righteous hypocrite like "Peter". Even if you just don’t dare to question them, your thoughts about “good” always boil down to people who “fit your dogma”.

>Sorry if you don't like my opinion, but at least I can prove it strongly!

This is not your opinion, but your attitude towards the opinions of others.

I'm sorry, Dan. What you are doing is "If we can't fix all the problems at once, then make those who try to fix certain problems proud". I must stand by Peter and Droif. Always pay attention to the problem, choose some problems and try to solve them. Stay vigilant and don't try to solve it (others may try).

Engineers should work like this.

You can choose not to use them in your design.

Yes, you can do what you want to do according to your own design, but don't deceive yourself, because you may actually be hurting others. If you can use them in your design and save money, you can donate the difference in profits to charity (if you really care). Or do you think bad people are better at doing good than bad people? Take a moment to think carefully.

No, I will not.

However, whenever I do not choose a tantalum cap, I will be happy for your rant.

This is not a rant, just a tantrum!

what! Okay, thank you.

I made it. Usually, because they can be used as electronic igniters well.

Obviously, Kemet "guarantees" that the tantalum in its products is conflict-free.

They provided a report listing the sources of tantalum (and other minerals): China, the United States, Thailand, Germany, Kazakhstan, Austria, and Japan. This is required by the US Dodd-Frank Conflict Minerals Regulations-does anyone here know more about this/bell?

AVX and:

All your stuff comes from China,

All your things are contaminated. Cheer up and stop deceiving yourself. The market is like a water container. You take water from one part, but you still increase the demand for all other parts. There is also the fact that once they enter a huge resource base like China, you really cannot track the material. You just want to feel special.

Would have liked to hear more about self-healing polymer capacitors. As far as I know, they are usually used as X or Y filter components in mains voltage applications, but maybe there are other interesting applications where self-healing capacitors are used? How does self-repair work?

Good article, thank you!

Errata:

I think tantalum has a lower leakage than aluminum electrolyte and therefore has a higher leakage resistance.

A typo, not a complete error :) – Every different polymer dielectric used has its own characteristics, has its advantages and disadvantages, but compared to the electrolytic capacitors we discussed, the entire capacitor series has an equivalent series* *Capacitance** and inductance are both low. to date.

Ok

The real conflict with tantalum bottle caps is their failure mode.

Find the safe derating of tantalum capacitors. They are ridiculous because they cannot be used in all applications except for the most absolutely necessary applications (very low ESR and high capacitance).

Safety is the reason to avoid them.

If your voltage converter happens to be 500w, what capacitor would you use?

:)

Some good things about iequalscdvdt.com

"Although not all news is bad news, their reputation in the fire comes from earlier tantalum capacitors, and improved manufacturing technology has provided more reliable products."

Do not. You may be confused by the existence of multiple "tantalum" caps.

. The sturdy tantalum cover has a fire failure mode. This is not surprising: the electrolyte is MnO2, so you have many easy-to-access oxygen tanks, and they will flourish. However, the sturdy tantalum capacitor caps can also be self-repairing and can withstand less pressure, so under the right conditions, they are very reliable and can be stable for a long time (no service life). However, they are still not inherently safe. The sturdy tantalum caps will not burn because of short-term failure, but because they "ignite" and burn.

However, the tantalum polymer cap does not have an ignition failure mode because the electrolyte is not MnO2, but a polymer. They also have lower ESR, but lower long-term reliability (due to polymer degradation). However, they will not catch fire on their own. However, they do experience short-circuit faults, so they can still take out systems that are not limited by current.

Niobium oxide caps are basically solid tantalum caps without an ignition device (long-term stable), so you would consider them ideal-but they are also expensive and uncommon.

For young players, the trap of solid polymer aluminum capacitors and electrolytic aluminum capacitors:

"Because the polymer is a solid, it also has a longer service life, and does not follow the classic Arrhenius formula. The temperature will not double every 10°C, and every 20°C drop in temperature, the life will be 10 times longer."

Translation: Every 20°C increase in temperature will shorten the life span by 10 times.

It's a bit different, isn't it?

A small mistake:

The equivalent series capacitance and inductance of the entire capacitor series are low

Should be "equivalent series

(ESR)"

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Soft robotics technology can realize many new technologies for the physical interaction between humans and robots, but the necessary high-performance soft actuators still do not exist. The best soft actuator must be fast, powerful, and have programmable shape changes. In addition, they should have high energy efficiency in unfettered applications and be easy to manufacture. Here, we have combined the ideal characteristics of two completely different active material systems: the fast and efficient drive of dielectric elastomers and the directional shape programmability of liquid crystal elastomers. Through the top-down photo-orientation method, we program the molecular orientation and local huge elastic anisotropy into the liquid crystal elastomer. The linearly driven liquid crystal elastomer monolith achieves a strain rate of more than 120% per second with an energy conversion efficiency of 20% per second, while the moving load exceeds 700 times the weight of the elastomer. Electric actuators provide unprecedented opportunities to achieve miniaturization, shape programmability, efficiency and greater freedom, suitable for soft robots and subsequent fields.

In traditional robotics technology, the basic rigid actuation mechanism of electric motors or hydraulic and pneumatic actuators hinders the miniaturization of robots, and more importantly, hinders the use of robots in human collaboration environments. The compatible actuator is to make the robot and the man-machine interface (

). The ideal compliant actuator will have high efficiency, strength-to-weight ratio, work capacity and shape programmability to perform complex functions. Like artificial muscles, soft actuators with these characteristics will greatly promote technology in aerospace, robotics, medical equipment, energy harvesting equipment and wearable devices (

-

). Among the many soft actuators that have been explored, the dielectric elastomer (DE) seems promising in some respects, even surpassing skeletal muscle (

). In addition, the liquid crystal elastomer (LCE) exhibits reversible large mechanical deformation (

,

). The latest advances in optical alignment and microfabrication technologies have enabled the pre-programming of liquid crystal alignment in microscopic areas to achieve complex shape deformations (

). However, both actuators have their shortcomings: DE membrane needs to be macroscopically pre-strained (

) Or requires a multi-step manufacturing method, which makes it difficult to program small actuators with local shape changes (

). At the same time, due to the small strain generated, the direct conversion of electrical energy to mechanical work using LCE is still limited (

). However, we proved the ability to pattern the LCE molecules in a locally varying arrangement, thereby adjusting the spatial variation of mechanical compliance, so that a more efficient DE driver can be realized with a pre-programmed drive degree and direction.

Generally, the DE actuator forms a variable resistor-capacitor through electrostatic attraction between two compliant electrodes coated on opposite sides of the isotropic DE (

) (

). The high voltage applied to the compliant electrode induces electrostatic pressure, the so-called Maxwell stress, which deforms the DE. Compared with LCE, electric actuation mechanism can produce higher working efficiency (ratio of mechanical work to input electric energy) and higher actuation speed (

). In addition to acting as a soft linear actuator, DE actuators can also be applied to fixtures, haptic devices or optical devices, but they require complex shape changes (

). Despite some impressive demonstrations, DE actuators have not yet been widely used in soft robots, partly because of the need for pre-straining or the challenges of manufacturing equipment with complex deformation profiles (

). Overcoming these challenges and expanding the application range of DE actuators requires material innovation for the next generation of high-performance DE with shape programmability (

).

(

) Schematic diagram of traditional isotropic DE actuator in closed and open state. (

) Schematic diagram of a single-axis aligned dielectric LCE actuator (DLCEA) in closed and open states. Liquid crystal molecular orientation; director

Use double-headed arrows to indicate the harder direction of the LCE. When driven by voltage,

, The material will become thinner and stretch perpendicular to the alignment direction, greater than the direction parallel to the director. (

) DLCEA mechanical stress and normalized capacitance (

) The strain response in the linear range of DLCEA is characterized by a strain rate of 0.1% per second.

LCE is a polymer with rubber elasticity, and its molecular anisotropy gives it anisotropic overall properties. Most previous work on LCE actuation has focused on thermal or light drive mechanisms. Heat or light will temporarily disrupt the order of anisotropic molecules, called the guiding field (

), resulting in internal stress and anisotropic overall deformation (

). The local LCE director field can be pre-programmed to create complex shape changes at startup. However, light actuation is inefficient, while thermal actuation is slow and inefficient. Therefore, they are not suitable for applications that require high energy efficiency and fast startup, such as robotics. The direct electric drive of LCE is a highly sought after technology (

). Some previous studies have demonstrated that by coupling the electric field to the molecular dielectric anisotropy or sometimes to the intrinsic polarization of the LCE or LCE composite, the electrical drive of the LCE can be achieved. Therefore, the electric field drives the molecules to reorient to produce overall strain. However, these methods require high temperatures or the use of carbon nanotubes to enhance electrical response. Otherwise, only a small driving strain will be generated at room temperature (

). In this work, we directly use the large mechanical anisotropy of LCE without relying on molecular rotation in the electric process. We further use the latest developments in the patterning of LCE films to customize local anisotropic elasticity and Poisson's ratio to achieve an efficient and shape-programmable DE, which we call a dielectric LCE actuator (DLCEA;

). By arranging the LCE molecules in the local domain, we achieved electric drive and shape deformation at room temperature, and showed large, rapid and powerful strain.

LCE film is manufactured by a two-step process recently developed by some authors (

). In short, before preparing the LCE film, oligomers were synthesized through the thiol acrylate click reaction. Ordinary diacrylate reactive liquid crystal monomers are chain extended by Michael addition of dithiol linking molecules. The exact component ratio, monomer selection and dithiol linking group can all be adjusted to adjust the specific mechanical properties of the final LCE film (

). We have produced a large area of ​​ordered uniaxial LCE (Figures S1 and S2), and have huge elastic anisotropy (

). In all experiments, we only activated DLCEA at room temperature in the linear state of the strain (Figure S3). We can also program the LCE director field locally through optical alignment to create a command surface for spatial programming and locate the LCE director locally (

). Finally, we used compatible grease electrodes on both sides of the LCE membrane to create the DLCEA device (Figure S4). Further details can be found in materials and methods.

In order to characterize the basic characteristics of DLCEA, we first produced a single-domain, uniaxially arranged LCE film. The electrode coated on the uniaxial DLCEA can simultaneously measure the capacitance and the stress and strain applied to the LCE film (

). When strain (

) Parallel application with the director,

, Compared with when strain is applied perpendicular to the director, the rigidity of LCE is one order of magnitude higher.

⊥

, Which shows a high degree of elastic anisotropy. Similarly, the difference in the slope of the normalized capacitance between DLCEA devices with different director directions indicates the anisotropy of Poisson's ratio. DLCEA capacitance is directly proportional to the area of ​​the film covered by the electrode and inversely proportional to the film thickness. Therefore, Poisson's ratio anisotropy causes the thickness and area of ​​the film to change at different rates according to the strain direction relative to the LCE director field (Figure S5A). Using a simplified finite element model, we found that for a large elastic anisotropy, the linear expansion strain produced by a given Maxwell stress is almost twice the linear expansion strain observed in an isotropic material, while the elastic The expansion modulus is equal to the soft direction (Figure S5B). Other works with similar chemical properties of LCE have also observed one-dimensional (1D) translational crystallinity, which can explain the particularly large elastic anisotropy observed in this work (

Then, we feature isometric drawings (constant strain; uniaxial DLCEA).

) And isotonic (constant force;

) Configuration. In the isometric test, we applied an initial strain to the DLCEA device and performed a relaxation period before applying high pressure (Figure S6A). Through the reduction of active stress, we observe two relationships between strain, applied voltage and active stress, which are consistent with Maxwell’s stress model.

∝

/

,where is it

Is the applied voltage,

Is the thickness of the LCE film. First, driving with a larger initial strain will produce a higher active nominal stress reduction; the isometric pre-strain will cause the LCE to become thinner, so at a given voltage, a higher Maxwell stress (

). For LCE, it seems that the speed at which the additional strain causes the material to thin is sufficient to offset the increased restoring force, so that a given drive voltage will result in greater activity stress. We also observed that for each fixed strain, the effective nominal stress reduction during isometric measurement increases squarely with the increase in voltage (Figure S6B). At the highest voltage tested, we measured the peak effective nominal stress reduction by more than 50 kPa. However, for devices with directors,

Since the modulus is much higher, the active stress is relatively small. When maintaining isometric strain, DLCEA behaves like a spring with variable stiffness. In this case,

, The initial strain of 5% and the driving voltage of 2 kV, the LCE expansion caused by Maxwell stress almost compensates the stress caused by the entire equidistant strain. We also performed an equipotential test in which DLCEA was strained under a constant voltage. These tests show the expected drive stroke of the DLCEA load when voltage is applied (Figure S7).

) Isometric (constant strain) test. Active nominal stress reduction measured under various initial equidistant strains (

) For equipment assembled with LCE Director

with

‖

And photos of the assembled DLCEA equipment,

. (

Isotonic (constant force) test. The contraction discharge strain trajectory of a high-speed camera with an actuation voltage of 3 kV under various loads. Illustration: Corresponding discharge measurement value. (

) The basic actuator characteristics are based on the contraction trajectory and the discharge current (including strain (

), peak strain rate (

), peak specific power (

), specific energy (

) And efficiency. Image source: Zoey S. Davidson.

Next, we use the same DLCEA and suspend different weights from the free end of DLCEA to generate a constant load force and initial nominal strain for isotonic testing.

(

And figure. S8). DLCEA in

Even at the highest voltage tested, this configuration did not show any appreciable active strain at initial load because their elastic modulus was significantly higher (Movie S1). However, DLCEA and

Under the heaviest load tested, the applied voltage of 3 kV was 0.27 N, which was approximately 790 times the weight of the bare LCE film (35 mg). This configuration showed up to 5% rapid active strain. We performed the isotonic contraction test by suddenly releasing the weighted DLCEA device, and used high-speed video (Figure S8B and Movie S2) to capture the subsequent motion. As the load and initial strain increase, the DLCEA capacitance also increases, which can be seen from the offset discharge curve in the insert diagram.

. In all cases, the discharge time within about 60 ms (approximately 1 ms) is much faster than the discharge time required for DLCEA contraction, which indicates that the system is currently limited by the viscoelasticity of LCE. We also observed a significant viscosity loss in contraction, which is evident from the continuous creep contraction after the initial elastic response (Figure S8B). From the contraction trajectory of DLCEA, we can calculate the basic performance indicators of pure elastic response and expansion creep contraction (

And figure. S8C).

In order to achieve complex shape driving, LCE usually functions by programming the spatially varying in-plane shrinkage strain when heated above the phase change. However, the DE drive mechanism is not based on a thermally induced phase change, but generates an in-plane expansion strain. Therefore, the boundary conditions play an important role in determining the realized DLCEA shape change. In order to better understand the effect of boundary conditions on DLCEA, we have performed a basic characterization of the buckling effect caused by the expansion of the elastic body between the fixed boundary (

, And the movie S3). The buckling amplitude increases with the increase of the voltage, and at 2.5 kV, an out-of-plane peak-to-peak stroke of 1800% of the LCE film thickness greater than about 80 μm is generated, corresponding to a linear strain of about 5% (

And figure. S9A). Actuation speed is another important characteristic of potential DLCEA applications. We applied a sinusoidally varying 1-kV potential to measure the change in drive amplitude with the applied frequency (

And figure. S9B). The excitation amplitude decays exponentially with frequency, but 50μm can still be sensed at 30 Hz and 1 kV.

)with(

) The state of a single-axis DLCEA device with fixed boundary conditions. Expansion in the soft direction will produce out-of-plane bending, thereby displacing the thin lines tightened on the surface. (

) The relationship between the experimental measurement of buckling and the applied voltage. (

The frequency response of 1kV buckling uniaxial DLCEA is 0.1 Hz and the excitation amplitude is about 130μm.

We designed a spatially variable LCE director configuration to prove that it is possible to pre-program complex patterns in 2D and then electrically drive the film into a 3D form (

). According to the programmed director area, the LCE film will be partially positive (

) Or negative Gaussian curvature (

). These shapes are usually called conical and anti-conical. The theory describing this form of deformation in elastic media was previously described in Modes.

). We understand these shape changes by considering a simplified model of an anisotropic DE made of rigid concentric rings embedded in a soft elastomer (

). These rings prevent expansion along the ring, but allow expansion in the radial direction, resulting in frustration and out-of-plane bending. Similar arguments apply to radial rigid elements. Double-headed red arrow in

Indicates the direction of soft expansion. We create a pixelated array of topological defects by spatially programming the light polarization using the pattern of linear thin-film polarizers (

), positioning the LCE supervisor locally as

. Directors form a lattice of radial and azimuthal defect types. When electrically driven, they will bend out of the plane due to incompatible in-plane strain (

And movie S4). We measured discharge (0 V) and start (2.5 kV;

) Status. For this reason, we kept the device in its active shape for more than 3 hours under a voltage of 2.5 kV, while the current consumption was less than 1μA, thus confirming its high stability and low power consumption. From the circular trajectory around the center of the radial defect type, the height change of the local programming and the accompanying Gaussian curvature formation (

). Out-of-plane bending will produce a peak-to-peak height difference of more than 1600 μm, which is an increase of 2000% compared with the initial film thickness of about 80 μm, corresponding to a surface strain of 22%. Bottom right corner of DLCEA enabled

Indicates that the defect may bend up and down.

By patterning the pattern of the director into an azimuth-radial defect lattice, it is possible to perform programmed shape driving, such as dent pattern deformation. (

) The azimuth defect type is deformed into a cone with local positive Gaussian curvature, and (

) The radial defect type deforms into an inverse cone with locally negative (saddle) Gaussian curvature. In (A) and (B), the two-way red arrow indicates the soft direction. (

) Use a polarizing film pixelated array with a designed local direction to pattern defects. (

Observed by crossed polarizers, the finished LCE film has a pixelated uniaxial arrangement (indicated by the white dotted line), forming a defective lattice. (

) When charged to 2.5 kV, there will be a lot of visible deformation on the surface. (

) The height map measured by the grease-coated LCE profiler is almost flat, there is no charge, and the change exceeds 1.6 mm when charged to 2.5 kV. The two-dot-dash line and the dot-dash circle in (F) are (

). The change from an approximately constant height to a sinusoidally varying height represents a sign change of the local Gaussian curvature. Scale bar, 4 mm. Image source: Zoey S. Davidson.

When using DLCEA as a linear actuator, compared with similar isotropic materials, we expect the anisotropy of Poisson's ratio to be larger to produce higher efficiency and require a lower electric field for actuation (

). Compared with other LCE actuators, the execution efficiency reported here is about 20%. As far as we know, due to the low energy conversion efficiency, the actuation efficiency of LCE has not been reported. For example, according to our estimation, the actuation efficiency of thermally induced LCE is lower than 0.001%, according to (

). Note that this estimation is based only on the initial stroke; a constant current is required to keep the LCE in the contracted state. In addition, our DLCEA efficiency is comparable to the latest examples of isotropic DE actuators with highly optimized electrodes, with a reported efficiency of 1.5% (

). We expect to reduce viscosity loss and creep, which is represented here by the hysteresis loop.

And prolong the contraction

, Will further improve the fast and efficient DLCEA situation.

We believe that the high efficiency reported in our system is due to the anisotropy of elastic modulus and Poisson's ratio. Generally speaking, elastomers save volume. Therefore, extension in one direction results in contraction in the other direction. However, the shrinkage of the LCE film is perpendicular to the director. In other words, when the LCE film is tensioned perpendicular to the director, its thickness shrinks. The thickness is also perpendicular to the director, so it shrinks faster than the width parallel to the director. When parallel to the deflector strain, the thickness and width of the LCE are equal (assuming that the cross section is isotropic). It is worth mentioning that the last point is still uncertain: as mentioned earlier, in this type of LCE, the crystallinity of one-dimensional translation is very common (

). In particular, the one-dimensional crystal plane may be at a certain angle to the LCE director, which breaks the symmetry, so that when strain is parallel to the director, the width and thickness are assumed to shrink equally. Adjusting this one-dimensional crystallinity may play an important role in further improving the linear driving capability of DLCEA.

In order to further clarify the advantages of elastic anisotropy, we consider the use of a simplified DE model of an approximate volume-saving elastomer model with approximate Poisson's ratio anisotropy and large Poisson's ratio anisotropy under no load (see figure S5). In this model, almost all compressive strains caused by Maxwell stress will produce tensile strains in the soft direction of the elastomer. In other words, Maxwell strain through the thickness of the material,

=

, Causing strain

And almost no pressure

. In an isotropic elastomer, the same Maxwell strain will only produce half of the strain, because the volume conservation strain will be evenly divided into

. For linear actuators, this is the first advantage of DLCEA. The excitation voltage required to reach a given strain is reduced. The second advantage of the anisotropy of linear actuators comes from the energy considerations of the same system. The elastic energy density of deformation is squared in strain. Therefore, in the simplified model presented here, there will be no energy component from strain.

direction. In addition, for a given required linear extension strain, the input electric field energy (∝

) Will also be less, because the required Maxwell strain is less than the strain in the isotropic DE. Therefore, the anisotropic DE actuator can achieve the same strain as the isotropic DE linear actuator, but with higher efficiency. Both no-load and ideal uniaxial elastic body assumptions can be relaxed, and viscoelastic effects can be added to build a more complete model.

The anisotropy of material Poisson's ratio is also an important feature for realizing programmed shape change drive. The driven (compressed) LCE expands laterally anisotropically to produce the observed shape change. Although in principle the curved shape of DLCEA is multi-stable, we only observe a single driving state for each sample (

). We hypothesized that the gravity during the test or the uneven photocrosslinking of the LCE film during the device manufacturing process may destroy the symmetry that achieves multiple stability. Nevertheless, our demonstration of local changes in Gaussian curvature shows that our method can potentially be extended to achieve various programmable shape changes (

). In addition to programming the direction of the director in the plane, the direction of the LCE director can also be programmed along the film thickness. as the picture shows. For S10, we assembled DLCEA with a twisted LCE configuration, where the guide rotates nearly 90° from the top surface to the bottom surface. When an electric field is applied, the twisted DLCEA will produce a twisting motion, the amplitude of which depends on the inherent characteristics of the material, but also on the geometry of the LCE (

Here, by combining the ideal characteristics of DE and LCE in a single material platform, we demonstrated the excellent driving performance of the electric drive DLCEA, including high energy conversion efficiency (20%), high driving speed (120% per second) and programmable The shape changes from 2D to 3D, and the out-of-plane stroke exceeds 1800%. In order to obtain greater driving force, you can choose a multilayer DLCEA stack, as shown in the LCE and DE multilayer stack (

), although this requires the development of alternative soft electrodes. In addition, even more general shape changes, ie non-local Gaussian curvatures, can be achieved by spatially programming LCE alignment and local crosslink density.

When DLCEA is combined with 3D printing, origami and origami drive strategies, and distributed control systems to create a multifunctional soft robot in a scalable manner, the active materials and top-down microfabrication technology and electric drive introduced here The insights of the integration of mechanisms may provide exciting opportunities. Material and construction costs are low. Electric drive mechanisms can also be applied to other technologies, including energy harvesting and storage, medical equipment, wearable technology, and aerospace. In addition, fast and dynamic modulation can be useful in display and optical applications.

1,5-Pentanedithiol (1,5-PDT; >99%), 1,8-diazabicycloundecaheptene (DBU), butylated hydroxytoluene (BHT) and magnesium sulfate (MgSO)

; Anhydrous powder) purchased from Sigma-Aldrich and used as is. Hydrochloric acid (HCl), dimethylformamide (DMF) and dichloromethane (DCM) were purchased from Fischer Scientific. The photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPA) was purchased from Toronto Research Chemicals. Brilliant Yellow (BY) was purchased from Tokyo Chemical Industry. Liquid crystal monomer 1,4-bis-[4-(4-(6-acryloxy-hexoxyoxy)benzoyloxy]-2-methylbenzene (RM82; >95%) purchased from Wilshire Technologies Inc. can be used without further purification. Conductive carbon grease NyoGel 756G was purchased from Newgate Simms.

We made LCE film through a two-step process recently developed by some authors (

). Before preparing the LCE film, oligomers were synthesized through the thiol-acrylate click reaction. The reactive liquid crystal monomer RM82 is chain extended by Michael addition with 1,5-PDT. In a typical synthesis, 12.5 g RM82 was mixed with 5.06 g 1,5-PDT in 120 ml DCM and three drops of DBU catalyst. After stirring at room temperature for 16 hours, the solution was washed sequentially with 1M HCl, 0.1M HCl and deionized water in a separatory funnel. The DCM product mixture was then dried with 25g MgSO 4

30 minutes, then filter. Before rotary evaporation and direct vacuum, BHT (50 mg) was added to the clear DCM and product mixture until a thick white oligomer remained. The oligomer can be stored at -30°C for up to 2 months.

Deionized water, isopropanol and acetone are usually used in an ultrasonic bath to clean glass slides that are usually 5 cm x 5 cm and 8 cm x 10 cm. Next, the glass slide was dried with nitrogen gas and then treated with oxygen plasma. A mixture of 1 wt% BY dissolved in DMF was spin-coated on a glass slide, and then dried on a hot plate at 120°C. Place a gasket with a thickness of 65 or 75μm, cut from polyimide or polyester film plastic along the edge of the BY coating side of the glass sheet; then, place two slides so that they are coated with BY The coated faces face each other. The large paper clip holds the slide with the polarizing film placed on one side. A customized 447 nm light-emitting diode (LED) light source is used to illuminate the BY-coated glass through a polarizing film, thereby optically programming the orientation of the BY molecules. In order to program the locally varying Gaussian curvature, the polarizer was cut into pixels and then reassembled by hand on a glass slide with the desired orientation (see

). The thin layer of BY molecules is rearranged perpendicular to the incident light polarization to create a spatial light programming command surface, and then the LCE director (

The previously prepared oligomer was melted with additional RM82 and a small amount of photoinitiator to crosslink the oligomer chain into the elastomer network. In more detail, assuming that the oligomer is only composed of a single-unit length RM82 chain with both ends blocked by 1,5-PDT, the LCE oligomer and other RM82 LCE monomers are melted at a molar ratio of 1:1. together(

). Therefore, the mixture is composed of an excess of thiol groups, which may be a large part of the final LCE viscosity loss (see the uniaxial alignment DLCEA characteristics section), but this sparse cross-linking also facilitates the need for greater driving strain The softness. The melt was mixed at 120°C for only 2-3 minutes, and then degassed in a vacuum oven at 90°C for about 3 minutes. Add 1% by weight of DMPA and stir carefully to avoid introducing bubbles again.

Then the isotropic LCE melt was poured onto the BY-coated glass at 80°C, and then carefully clamped on the second hot BY-coated glass substrate. The BY-LCE-BY sandwich is cooled to an oriented (nematic) phase of about 73°C, and then gradually cooled to room temperature, during which time it is consistent with the spatial programming imparted by the BY coating, and the defects are annealed from the phase change. Once the LCE has cooled to room temperature, it can be cured under UV light using the OmniCure S2000 arc source. After being exposed to ultraviolet rays to polymerize LCE in a programmed state, we immersed the BY-LCE-BY sandwich panel in water to release LCE from the BY-coated glass substrate.

The final LCE film thickness (described below) was confirmed from the area cut into the actuator by confocal laser profilometry. Good alignment of LCE and almost no defects are the basic characteristics of the film, which can give maximum elastic anisotropy and obtain the best material properties. The high contrast between the LCE directions between the crossed polarizers can be seen in Figure 5. S1.

After separating the LCE sheets from the glass substrate, they were rinsed with water to remove residual BY, and dried with nitrogen. Put the LCE sheet back on the glass substrate and carefully inspect to identify defects and bubble-free areas to manufacture DLCEA devices. For the single-axis DLCEA device, the most clearly identified area is cut into rectangular slices usually 14 mm by 34 mm, with a typical weight of 35 mg. The membrane of this size was chosen for ease of handling and the electrical actuation constraints described below. The smaller adjacent area (20mm by 5mm) was originally used to characterize the stress-strain behavior and the larger strain behavior of the LCE.

Then check the edge of the laser cut area on the larger film with a laser confocal interferometer (KEYENCE VK-X210) to confirm the processing height of the LCE film. We found that Kapton of nominal 65 microns can produce LCE film of approximately 70 microns, and Mylar of nominal 75 microns can produce LCE film of approximately 83 microns. The thickness of the entire produced LCE board may vary by ±10% (Figure S2).

In the next step of DLCEA manufacturing (Figure S4), we use conductive carbon grease NyoGel 756G to connect the compliant electrodes to both sides of the LCE membrane. This grease is often used in other DE systems (

). In order to apply the carbon grease, the LCE was first clamped in a 3D printed plastic clip with copper tape leads designed to facilitate the connection of the equipment to the test equipment described below and the "Uniaxial Alignment DLCEA Characteristics" section. A certain degree of misalignment during clamping is inevitable. The tailored LCE is fixed in a laser-cut plexiglass assembly jig and covered with a low-viscosity removable tape, which is placed around the edge of the LCE film. The masking tape forms a boundary area on the edge of the LCE without electrode grease, which prevents short circuits when driving the device under high voltage. It was found that a gap of 2mm around the edge was sufficient to prevent a short circuit under the test voltage (see

). Use a cotton swab applicator to apply grease, and use a straight edge to remove excess grease. Before and after using the grease electrode, weigh the entire Plexiglas fixture with LCE film to find the grease weight. For the two electrodes of DLCEA, the grease weight usually totals 30 mg. Other high-conductivity electrode materials can achieve better performance while adding smaller weight and cross-sectional area (

); Future research on these actuators will study alternative electrode materials.

Throughout the work process, we only tested and activated DLCEA at room temperature under linear conditions where the strain did not cause the LCE guide to reorient. Usually, we find that the onset time of soft mold deformation (pointing to reorientation) is 45% to 50%

As shown. S3.

We performed mechanical and electrical characterization of the laser-cut single-axis DLCEA (

And figure. S2). The tensile test was performed in TA Instruments DHR3, and the capacitance measurement was performed simultaneously using a Hameg 8118 LCR meter. Generally, a uniaxial DLCEA made of 65 μm spacers and electrodes with an area of ​​1 cm x 3 cm coated on both sides has a zero strain capacitance of about 300 pF. We observe the correlation between the capacitance growth rate and the tensile strain direction of the LCE film relative to the director. The capacitance of DLCEA with strain perpendicular to the director grows faster than the capacitance of DLCEA with strain parallel to the director. We can model how strain affects the DLCEA capacitance.

The capacitance of the parallel plate capacitor (or DLCEA) is

ϵ

Is the permittivity of free space, ϵ

Is the relative dielectric constant perpendicular to the liquid crystal director (note that the reactive mesogen RM82 used in this work has negative dielectric anisotropy, ie

> ϵ

). The rectangular area covered by the electrode is

X

, The film thickness is

(For the schematic and coordinate system, please refer to Figure S5). When DLCEA was

(Perpendicular to the director), the thickness decreases

=-

And along the width

cut back

=-

. The thickness and area become (1 +

)

=(1 −

And (1 +

(1 +

=(1 +

) (1 −

, Respectively. Therefore, the capacitance becomes

Next, we normalize by the capacitance under zero strain, and then Taylor expands for small strain, that is, only the linear term

Insert this equation from the relationship between the symmetry of the system and the mechanical anisotropy,

/ν

And assuming

= 0.5, we get

≈0.04 and

≈0.84. Take the modulus of elasticity (

),

, The stiffness tensor is fully defined. These values ​​indicate that LCE is unexpectedly compressible. However, this is impossible, and due to at least the following three reasons: Capacitance

At 20% strain, the coefficient decreases from 32 to 22, and it will inevitably be slightly pre-strained when measuring the modulus.

, Namely LCE. These are in addition to the possibility of partial crystalline order (smectic C phase) mentioned in this article. These factors together lead to errors that may lead to apparent compressibility.

Equidistant testing is performed by quasi-statically increasing the voltage applied to the pre-strained sample. After the capacitance measurement, strain the DLCEA still fixed in the rheometer to a fixed amount (5%, 10%, 15%, and 20%), and then relax for a period of time until the measured stress creep is much smaller than the induced stress (Figure S6A). Starting from 500 V, the driving voltage (Heinzinger LNC-10 kV) increases by 100 V every 15 s. Samples are taken from the middle 5 s of each cycle to measure the active change in stress due to the applied voltage. Following the relationship given by Maxwell's stress equation, the logarithmic effective nominal stress reduction for all equidistant strains has a slope of 2.0 to the logarithmic voltage relationship (Figure S6B).

The equipotential test is done by first straining the DLCEA without applying a voltage, and then applying a voltage of 2 kV (Figure S7). The difference in induced stress between the 0 kV and 2 kV curves represents the expected stroke when DLCEA is used as an actuator under constant load.

In order to characterize the basic characteristics of LCE as a muscle-like actuator, we tested the DLCEA tightened by a constant gravity load.

. The weight suspended by the DLCEA causes the initial strain that makes the material thinner, which contributes to a greater driving force and thus a higher initial load. When voltage is applied to DLCEA

⊥

As the elastic response of LCE has changed, the system adopts a new length. The LCE hardens, so the weight stops when the forces are balanced. However, after the initial elastic response, DLCEA continues to creep due to the viscoelasticity of LCE. The strain gradually increases until it finally reaches a steady state. After a period of time, a short-circuit path is provided to the electrodes of DLCEA through a custom switching mechanism. Therefore, DLCEA is discharged and suddenly contracted elastically, and then continued to contract further slowly due to viscoelasticity (

And figure. S8). if

, Due to the significantly higher stiffness (movie S1), there is no significant drive along the loading direction; therefore, no further testing of this DLCEA configuration was performed.

At the same time as the startup, a high-speed camera (Vision Research v641) was manually triggered. For shrinking data

, The camera captures at 1400 frames per second. The video frame for switching high voltage is identified by a pair of LEDs triggered by the same solid state relay as the high voltage switch. Use an oscilloscope (Tektronix MDO4024C) to measure the discharge current on a resistance divider pair connected in series with DLCEA. A schematic diagram of the high-voltage switching mechanism that measures the discharge current by reading the voltage,

On known resistance

,as the picture shows. S8A. The drive also depends on the applied voltage. For each load, voltages of 2, 2.5 and 3 kV were tested on the same DLCEA (Figure S8C).

Use Tracker Video Analysis (Tracker Video Analysis (

), and then use a custom Python script for analysis. In these tests, the high voltage was switched on for about 20 s before discharging, so that DLCEA reached its active, stable resting length. Mark the initial distance manually in Tracker Analysis, then compare it with the known component size to calculate the distance, and then calculate the energy, power, and efficiency. The oscilloscope data was also analyzed using custom Python code. By measuring the discharge with the switch not connected to DLCEA, the baseline capacitance charge can be subtracted from the measured discharge. The capacitance of the high-voltage cable per meter is about 100 pF.

The mechanical work done by the actuator during discharge is calculated based on the mass of the additional load.

, And the displacement found through the high-speed video, namely

Δ

Is the acceleration due to gravity, 9.8 m/s

And Δ

Is the displacement of mass. Power into the system,

Discovered by integrating the discharge current measured as voltage

, Through the known resistance,

, And then multiply by the applied voltage (for example, 3 kV). Finally, efficiency is calculated based on the ratio of these energies,

.

The finite element simulation was carried out using the structural mechanics module of COMSOL Multiphysics 5.3a (COMSOL, 2008). Several mesh refinement steps were performed to ensure convergence of the results. For the no-load simulation of DLCEA (Figure S5B), the LCE film was modeled as an anisotropic thin plate (width 14 mm; length 30 mm) with an initial thickness of 80 μm. Use five independent elastic constants to calculate the flexibility and stiffness matrix of an anisotropic material using Voigt notation

Assuming "1" is

Nematic guide

In order to demonstrate the effect of anisotropy on the performance of the actuator, we scanned

From 1 to 20 MPa, while assuming Poisson's ratio

= 0.5 and ν

= 0.9-ν

And shear modulus

(Assuming that Young's modulus and bulk modulus are equal). The geometric boundary condition is defined as clamping on one side. By considering the electrode margin as 2 mm, a normal pressure load (100 kPa representing Maxwell stress) was applied to the top side of the LCE plate, and the roller boundary conditions were set to the bottom side of the LCE. A constant force is applied to the free edge of the LCE beam (as opposed to the clamping edge) to induce deflection and simulate gravity load.

In Petsch's work

), insert the filament heater into the aligned LCE. When heated, the device shrinks in its alignment direction. The 90% contraction reaction time reported in this work is 20 to 30 s. In the example reported in this article, they achieved a 1.85 mm stroke with a test load of 2.25 g and an input power of 430 mW. Then the stroke efficiency is

Or about 0.0005% for strokes only. In order to maintain this stroke, a constant current must be applied.

The edge of the uniaxial LCE film is constrained by a laser-cut plexiglass frame. Place the film carefully on top of the frame so as not to cause prestress or leave any slack. Coat the center square carbon grease electrode on both sides of the film through a low-viscosity removable tape mask. The in-plane length of the film grows in the soft direction, but due to the fixed boundary conditions, curved wrinkles are generated. The height of the wrinkle pattern is measured by the laser confocal profiler in the off state and at every 250 V voltage from 500 V to 2.5 kV. In the 2.5kV activation state, the out-of-plane peak-to-peak travel is 1.47 mm or 1800% of the LCE film thickness (approximately 80 μm).

In order to determine the frequency response of the uniaxial buckling DLCEA, we applied the sinusoidally varying 1 kV provided by the Physik Instrumente E-107 piezoelectric high-voltage amplifier. The input signal is generated by a function generator (Tektronix). Observe the movement of the DLCEA film with a Thorlabs Telesto optical coherence tomography microscope. First, manually find the maximum height of the DLCEA film in the DC on state, and then observe various frequencies in the same position (

And figure. S9B).

The defect array is achieved by programming the laser-cut square light polarization of a linear polarizing film that is sewn back into the desired grid on the glass slide using NOA65 ultraviolet curing glue. Due to the defects in the laser cutting step and the difficulty of manual stitching, the stitched polarizers are not perfect with each other. However, the misalignment boundary between the aligned regions in the LCE film is small and obviously does not affect the drive response.

Similar to uniaxial buckling, after manufacturing the LCE and removing it from the BY-coated glass slide, we fixed the LCE film on the laser-cut plexiglass frame and covered the programming area with conductive carbon grease. Due to the mismatch in refractive index between the isotropic and well-aligned areas, it is difficult to distinguish the programming area from the surrounding area under ambient lighting. The curved shape of the film is measured by the KEYENCE laser profiler (VK-X210), and the 10x objective lens is set to ultra-high speed

Scan at a pitch of 4μm. The observation area is a stitched image of many individual images.

For supplementary materials for this article, please visit:

Figure S1 Optical characterization of a uniaxially arranged LCE.

Figure S2 Photograph of LCE laser cutting area and measured height.

Figure S3 Stress and strain characterization of uniaxial LCE.

Figure S4. The assembly process of a typical single-axis DLCEA construction.

Figure S5 Schematic diagram of DLCEA, with coordinate axes and simulation results.

Figure S6. Isometric uniaxial DLCEA relaxation and log-log stress-voltage relationship.

Figure S7 Equipotential test of single axis DLCEA.

Figure S8. A schematic diagram of the high-voltage switching mechanism, isotonic full-cycle actuation, and isotonic actuation characteristics that vary with voltage.

Figure S9. DLCEA uniaxial buckling voltage and frequency response.

Figure S10. Drive for twisted configuration of LCE film.

Movie S1. Single axis DLCEA, director parallel to

Movie S2. Single axis DLCEA, director perpendicular to

Movie S3. Demonstration of uniaxial buckling DLCEA.

Movie S4. Demonstrates programmable shape change buckling DLCEA.

This is an open access article distributed under the following terms

, It allows use, distribution and reproduction in any medium, as long as the final use is

For commercial interest, and provide the original works appropriately cited.

Volume 5, Issue 11

November 01, 2019

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