A new electromagnetic hearing aid using lightweight coils to vibrate the ossicles

As the first stage in the development of a noninvasive electromagnetic hearing aid, we made a new transducer that generates a high-excitation force to vibrate ossicles via the tympanic membrane. This transducer consists of a core, driving and induction coils, a rare-earth magnet, and a vibrator coil. We designed the core, the driving and induction coils, and the magnet so as to generate the greatest excitation force possible when installed in the external ear canal of humans. With regard to the vibrator coil, which was attached to the center of the tympanic membrane to vibrate the ossicles, we determined its optimal mass, position, and shape both by finite-element method (FEM) analysis and by experiments using an artificial middle ear. A prototype of the optimally designed transducer can generate an excitation force of more than 95 dB sound pressure level (SPL) in terms of sound pressure at frequencies between 0.1 and 10 kHz. This result indicates that the transducer developed in this study can be used to treat patients with a hearing loss up to 70 dB hearing level (HL).