Michihito Aoki

Development of an implanted bone-conduction hearing aid using giant magnetostrictive material

To circumvent some of the disadvantages of conventional hearing aids such as sound distortion, feedback, and cosmetic factors, implantable hearing devices have been developed. However, these hearing devices also have problems such as insufficient output at high frequencies and inflammation. In this study, a new subcutaneously implanted bone-conduction hearing aid with an external unit and an internal unit is proposed. The external unit consists of a microphone, a speech processor, and a transmitting coil, which send the sound signals and energy to the internal unit by generating a magnetic field. The internal unit consists of a receiving coil, a driving coil, and a vibrator made of giant magnetostrictive material (GMM), which deforms its body by changing the magnetic field. The internal unit is surgically embedded in the temporal bone under the skin and vibrates the skull when the magnetic flux is applied by the external unit. For the first stage in the development of the new bone-conduction hearing aid, a prototype was made and its fundamental properties were examined. The GMM vibrator has a good linear response and high output especially at high frequencies. In contrast, the output at low frequencies is relatively lower than that at high frequencies. To enhance the output of the implanted bone-conduction hearing aid at low frequencies is an issue in the future.