  Purpose: One of the major reasons that totally implantable cochlear
microphones are not readily available is the lack of good implantable
microphones. An implantable microphone has the potential to provide a range of
benefits over external microphones for cochlear implant users including the
filtering ability of the outer ear, cosmetics, and usability in all situations.
This paper presents results from experiments in human cadaveric ears of a
piezofilm microphone concept under development as a possible component of a
future implantable microphone system for use with cochlear implants. This
microphone is referred to here as a drum microphone (DrumMic) that senses the
robust and predictable motion of the umbo, the tip of the malleus. Methods: The
performance was measured of five DrumMics inserted in four different human
cadaveric temporal bones. Sensitivity, linearity, bandwidth, and equivalent
input noise were measured during these experiments using a sound stimulus and
measurement setup. Results: The sensitivity of the DrumMics was found to be
tightly clustered across different microphones and ears despite differences in
umbo and middle ear anatomy. The DrumMics were shown to behave linearly across
a large dynamic range (46 dB SPL to 100 dB SPL) across a wide bandwidth (100 Hz
to 8 kHz). The equivalent input noise (0.1-10 kHz) of the DrumMic and amplifier
referenced to the ear canal was measured to be 54 dB SPL and estimated to be 46
dB SPL after accounting for the pressure gain of the outer ear. Conclusion: The
results demonstrate that the DrumMic behaves robustly across ears and
fabrication. The equivalent input noise performance was shown to approach that
of commercial hearing aid microphones. To advance this demonstration of the
DrumMic concept to a future prototype implantable in humans, work on
encapsulation, biocompatibility, connectorization will be required.
