Modelling the Influence of the Electromagnetic Field on a User of a Bone Conduction Hearing Medical Implant

Abstract

The electromagnetic field (EMF) may have a direct influence on the functions of human body, for example through the electrostimulation of the nervous system or tissue heating. The spatial distribution and the level of such influence, estimated by induced electric field strength (Ein) or specific energy absorption rate (SAR), are different in body tissues close to a medical implant, compared to the body without an implant during the same exposure. Numerical models of EMF sources (loop antennas) with dimensions typical for magnetotherapeutic applicators and high frequency radiofrequency identification (RFID HF) readers, and the user of a hearing implant (Bonebridge type – HI-BB) were worked out. The values of Ein and SAR were analyzed in the head of an HI-BB user exposed to EMF in the worst case scenario – at the shortest distance of 2 cm from EMF sources (at the side or at the edge in front of them). It was demonstrated that the use of HI-BB significantly increases the level of direct exposure effects caused by EMF – in low frequency EMF (Ein up to 3.4 times higher), and in radiofrequency EMF (SAR (1 g) up to 4.5 times higher). The level of such hazards depends on the dimensions of the EMF source and the location of the head against the source (i.e. the field polarization). It was shown that low and radiofrequency EMF is a direct environmental hazard for the hearing implant users, but the analysis of the individual sensitivity of particular users still required further studies involving more detailed models of implants and users’ bodies, as well studies covering the indirect EMF influence on the electronic circuits of HI-BB, recognized as electromagnetic compatibility (EMC).