RF interference in hearing aids from cellphones Part 2: Comparing in-use RF coupling to predictions

Cellphones and hearing aids are presently tested for their near-field RF emissions and RF immunity, respectively, to predict their mutual compatibility when used together. In the concluding part of this two-part series, we examine the relationship between these independent device measurements and the resultant in-use coupled RF interference, which may be heard as audio frequency noises by the hearing aid wearer. The established standards are seen to be generally reasonable in meeting the compatibility goals (i.e., ensuring a low level of perceived audio interference), but the combined effects of the relative device positioning, the hand, and especially the head add a high degree of uncertainty to the relationship between the actual in-use RF interference coupling and predictions based on individual emissions and immunity measurements.