  Objective: We present the "UmboMic," a prototype piezoelectric cantilever
microphone designed for future use with totally-implantable cochlear implants.
Methods: The UmboMic sensor is made from polyvinylidene difluoride (PVDF)
because of its low Young's modulus and biocompatibility. The sensor is designed
to fit in the middle ear and measure the motion of the underside of the eardrum
at the umbo. To maximize its performance, we developed a low noise charge
amplifier in tandem with the UmboMic sensor. This paper presents the
performance of the UmboMic sensor and amplifier in fresh cadaveric human
temporal bones. Results: When tested in human temporal bones, the UmboMic
apparatus achieves an equivalent input noise of 32.3 dB SPL over the frequency
range 100 Hz to 7 kHz, good linearity, and a flat frequency response to within
10 dB from about 100 Hz to 6 kHz. Conclusion: These results demonstrate the
feasibility of a PVDF-based microphone when paired with a low-noise amplifier.
The reported UmboMic apparatus is comparable in performance to a conventional
hearing aid microphone. Significance: The proof-of-concept UmboMic apparatus is
a promising step towards creating a totally-implantable cochlear implant. A
completely internal system would enhance the quality of life of cochlear
implant users.
