Electromagnetic interference from a cellular telephone with a hearing aid

As an extension of previous work, we report a collaborative effort related to EMI with hearing aids. This research is aimed at a comparison of the electromagnetic fields and levels of acoustic interference for a hearing aid placed in the ear. Laboratory measurements of the electric and magnetic fields are obtained, and extensive numerical modeling of fields in free space and in the ear canal is performed. Acoustic measurements, also in free space and in the ear canal of a few volunteers, are obtained. All investigations are for the same GSM telephone. Very good correlation between the electromagnetic and acoustic data has been observed. Our data point out that it may be possible to predict hearing aid sound pressure level (SPL), based on magnetic field strength. However, other factors must be considered before any general conclusions can be drawn. These include the gain setting of the hearing aid, the absolute SPL produced by the hearing aid, and the absolute RF power level at a location of the hearing aid