MEMS acoustic sensors for totally implantable hearing systems

There is a need for high quality implant microphone for existing semi-implantable hearing aid systems, including cochlear systems and middle ear semi-implant systems. A totally implant hearing aids system, integrates implant microphone, interface electronics, speech processor, stimulator, and cochlear electrodes, can overcome the discomfort, inconvenient, and stigma problems associate with the conventional and semi-implantable hearing aids. This paper presents the results of four years invitro study to use micro-chip acoustic sensors, serving as implant microphones, to directly sense the umbo acoustic vibration, convert it into high quality electrical sound signal at the output. Umbo vibration characteristics were extracted from literatures and laboratory data. A PZT vibration source is built to simulate the Umbo receiving 40 to 100 dB SPL sound input. A laboratory model using commercial electrets-microphone as the sensor was studied in the laboratory and on several temporal bones. Near flat frequency response from 250 to 8,000 Hz was measured with minimum detectable signal about 65 db SPL at 1 kHz, limited by the sensitivity of the microphone and the noise of the amplifier. From these results, an MEMS acoustic displacement sensor chip was designed and fabricated, to increase the sensitivity and to provide a easy mounting method on Umbo. Test results in laboratory and on temporal bones are being cumulated and will be presented.