Electromagnetic compatibility tests on hearing aids

Radio transmitter emissions that have intensity variations in audio frequencies cause interference on sensitive electronic equipment. Hearing aid user complaints caused by this kind of interference were increased by the introduction of digital mobile phones in recent years. In order to understand this interaction, the electromagnetic compatibility of 16 different hearing aid types was measured for high-frequency electromagnetic fields, particularly for those emitted by digital mobile phones. An automated PC-controlled test setup was developed for testing. The setup consisted of a GTEM cell where high frequency fields were generated. Draft version of IEC 118-13 standard was utilized as a basis for the test methodology. All of the hearing aids showed susceptibility to some degree. Six of the hearing aids were found to produce levels above the level proposed by the standard. Additionally, increasing levels of the electric field strength were found to cause a quadratic increase in sound pressure levels produced at the hearing aid output.