[Principle requirements for an electromechanical transducer for implantable hearing aids in inner ear hearing loss....

In order to overcome the disadvantages of hearing aids, a significant amount of research aimed at replacing them by implanted ossicular-coupled electronic hearing devices is being carried out. The technical and audiological demands on the electromechanical transducer of an implantable hearing aid for moderate to severe sensorineural hearing losses include high transmission quality of the equivalent sound-pressure level without significant linear or nonlinear distortion, and an energy balance suitable for implantation. Fundamental specifications for a transducer are a high spectral bandwidth of up to 10 kHz, an elongation amplitude of at least 100 nm within this range, a small ripple of the elongation frequence response of around +/- 3 dB, a total harmonic distortion (THD) of less than 0.5%, and a maximum electric power consumption of 0.1 mW. The demands on construction, such as hermetic sealing, biocompatibility, and biostability, are also discussed in detail. It appears that optimum transducer design is essentially a compromise between the physical requirements which are in part conflicting regardless of the transducer principle employed.