Experimental assessment of the performance of an electromagnetic hearing aid in human temporal bones

To circumvent some of the problems inherent in conventional hearing aids such as low gain at high frequencies due to acoustic feedback, discomfort in occlusion of the external ear canal and so on, implantable hearing aids have been developed over the past two decades. The most prominent feature of implantable hearing aids is that a transducer is directly coupled to the one of the middle-ear ossicles. However, since invasive surgery is necessary for implantation of these hearing aids, they have not as yet been widely employed. We therefore constructed a prototype of a non-implantable hearing aid which is mainly composed of a microphone amplifier system and an electromagnetic transducer developed in our previous study. It can generate an excitation force to vibrate the ossicles by a coil adhered to the tympanic membrane. In this study, the excitation force generated by this hearing aid was evaluated using human temporal bones. The best result of experiments using three bones indicates that the newly developed hearing aid can generate an excitation force of more than 80 dB SPL in terms of sound pressure at frequencies between 0.8 and 3.2 kHz.