Experimental assessment of miniature accelerometers designed for sensing middle ear motion

Abstract

Sensing human middle ear motion requires miniature, low-noise sensors to detect low-amplitude vibration of the ossicle bones to replace the external microphone in a cochlear implant system. Specifically, a 35 μg/√Hz sensor resolution is needed measure motion at 500 Hz (Young et al., 2012). Motivated by sensing middle ear motion without irreversible alteration to the ossicular chain, a small, piezoelectric accelerometer is considered. Our detailed low-frequency analytical model is used to identify promising micromachined, piezoelectric bimorph cantilever accelerometer designs. We fabricated a first generation of accelerometers using a conservative microfabrication approach, taken to enhance the yield of devices rather than to minimize the input referred noise (IRN). The mathematical model was validated by voltage actuation testing of these accelerometers. The device sensitivity to acceleration is tested, and the resulting IRN is desired to assess the viability of the sensor for the middle ear motion application. The first generation experimental results are compared to the mathematical model to determine the accuracy of the model and the efficacy of the fabrication methodology. This knowledge will influence future sensor designs optimized for minimal IRN.Sensing human middle ear motion requires miniature, low-noise sensors to detect low-amplitude vibration of the ossicle bones to replace the external microphone in a cochlear implant system. Specifically, a 35 μg/√Hz sensor resolution is needed measure motion at 500 Hz (Young et al., 2012). Motivated by sensing middle ear motion without irreversible alteration to the ossicular chain, a small, piezoelectric accelerometer is considered. Our detailed low-frequency analytical model is used to identify promising micromachined, piezoelectric bimorph cantilever accelerometer designs. We fabricated a first generation of accelerometers using a conservative microfabrication approach, taken to enhance the yield of devices rather than to minimize the input referred noise (IRN). The mathematical model was validated by voltage actuation testing of these accelerometers. The device sensitivity to acceleration is tested, and the resulting IRN is desired to assess the viability of the sensor for the middle ear motion applic...