The frequency response of a floating piezoelectric microphone for the implantable middle ear microphone.

OBJECTIVES/HYPOTHESIS: A piezoelectric sensor, floating piezoelectric microphone, driven by acoustic vibration of the ossicles, is one possible design for a microphone for a totally implantable cochlear implant. The purpose of the article was to study the frequency response of the floating piezoelectric microphone and to identify the ideal feasible position in the ossicular chain. STUDY DESIGN: Basic Research. METHODS: The frequency response of the floating piezoelectric microphone was analyzed by finite-element modeling and in vitro testing of fresh cadaveric heads. The floating piezoelectric microphone, 5.0 mm in length and 1.5 mm by 1.2 mm in rectangular cross section, as a piezoelectric microphone, was placed at various locations on the ossicular chain and stimulated by pure tones of different frequencies. RESULTS: The floating piezoelectric microphone can pick up the vibration of the ossicular chain and effectively convert it into the electronic signals effectively both in the long process of incus and in the malleus. The average sensitivity of the FPM is -44.22 dB rms ref 1V at 1000 Hz in the long process of incus, -53.33 dB rms ref 1V at 1000 Hz in the malleus, and -108.59 dB rms ref 1V at 1000 Hz in the tympanic cavity. CONCLUSIONS: The floating piezoelectric microphone is expected to be used as an implantable middle ear microphone for the totally implantable cochlear implant.

Feasible pickup from intact ossicular chain with floating piezoelectric microphone.

OBJECTIVES: Many microphones have been developed to meet with the implantable requirement of totally implantable cochlear implant (TICI). However, a biocompatible one without destroying the intactness of the ossicular chain still remains under investigation. Such an implantable floating piezoelectric microphone (FPM) has been manufactured and shows an efficient electroacoustic performance in vitro test at our lab. We examined whether it pick up sensitively from the intact ossicular chain and postulated whether it be an optimal implantable one. METHODS: Animal controlled experiment: five adult cats (eight ears) were sacrificed as the model to test the electroacoustic performance of the FPM. Three groups were studied: (1) the experiment group (on malleus): the FPM glued onto the handle of the malleus of the intact ossicular chains; (2) negative control group (in vivo): the FPM only hung into the tympanic cavity; (3) positive control group (Hy-M30): a HiFi commercial microphone placed close to the site of the experiment ear. The testing speaker played pure tones orderly ranged from 0.25 to 8.0 kHz. The FPM inside the ear and the HiFi microphone simultaneously picked up acoustic vibration which recorded as .wav files to analyze. RESULTS: The FPM transformed acoustic vibration sensitively and flatly as did the in vitro test across the frequencies above 2.0 kHz, whereas inefficiently below 1.0 kHz for its overloading mass. Although the HiFi microphone presented more efficiently than the FPM did, there was no significant difference at 3.0 kHz and 8.0 kHz. CONCLUSIONS: It is feasible to develop such an implantable FPM for future TICIs and TIHAs system on condition that the improvement of Micro Electromechanical System and piezoelectric ceramic material technology would be applied to reduce its weight and minimize its size.