The UmboMic: Characterization and Testing of a Middle Ear Microphone

We report developments on the "UmboMic," a piezoelectric microphone for fully implanted cochlear implants. Internal implantation of the microphone for fully implantable cochlear implants is the goal of future technology, as it has the potential to significantly improve the device performance and user experience.

The UmboMic is designed for implantation in the middle ear cavity, where it detects the motion of the umbo via the piezoelectric effect. The UmboMic sensor is made from two layers of the piezoelectric material called polyvinylidene difluoride (PVDF). Steps towards biocompatibility necessitated material changes to the device structure, including the conducting and glue layers. Seven individual UmboMic sensors are characterized on the bench and implanted in five human cadaveric ears (1 female and 4 male).

Extensive UmboMic testing and characterization demonstrates high sensitivity across frequencies, low noisefloor, shielding from electromagnetic interference, and good linearity. The UmboMic's performance is comparable to a Knowles external hearing-aid microphones, with an equivalent input noise of 32.4 dB SPL from 100 Hz to 7 kHz. Less than a 6 dB difference between UmboMic sensor sensitivity indicates fabrication repeatability. Studies on UmboMic sensor positioning demonstrate the design's resilience to implantation variations.

This UmboMic design represents a promising advancement towards a viable microphone for fully implanted cochlear implants. With very good microphone performances on the bench and in cadaveric human ears, research can turn towards complete device biocompatibility, fixation hardware, and testing for long-term implantation.