Digital Hearing Aids: Designing for EMC Compliance - In Compliance Magazine

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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