An Implantable Piezofilm Middle Ear Microphone: Performance in Human Cadaveric Temporal Bones

Area of Science:

• Biomedical Engineering
• Acoustics
• Otolaryngology

Background:

• Totally implantable cochlear microphones are limited by the lack of suitable implantable microphone technology.
• An implantable microphone offers potential benefits including enhanced filtering, improved cosmetics, and all-situation usability for cochlear implant users.

Purpose of the Study:

• To evaluate the performance of a piezofilm microphone concept, the DrumMic, designed to sense umbo motion for potential use in implantable cochlear implant systems.
• To assess the feasibility of the DrumMic as a component for future implantable microphones.

Main Methods:

• Five DrumMics were tested in four human cadaveric temporal bones.
• Key performance metrics including sensitivity, linearity, bandwidth, and equivalent input noise were measured using a standardized sound stimulus and measurement setup.

Main Results:

• DrumMic sensitivity was consistently clustered across different microphones and ears, irrespective of anatomical variations.
• The microphones demonstrated linear behavior over a broad dynamic range (46-100 dB SPL) and wide bandwidth (100 Hz - 8 kHz).
• Equivalent input noise was measured at approximately 54 dB SPL in experiments and estimated at 46 dB SPL with outer ear pressure gain accounted for.

Conclusions:

• The DrumMic exhibits robust performance across various ears and fabrication batches.
• Its equivalent input noise performance is comparable to commercial hearing aid microphones.
• Further development requires addressing encapsulation, biocompatibility, and connectorization for human implantation.