Miniature accelerometers for sensing middle ear motion

Abstract

Acceleration sensors are prevalent in handheld electronics, navigation systems, and physical activity monitors as well as for vibration measurement. There are many measurement applications, such as sensing human middle ear motion, that require miniature, low-noise sensors to detect low-amplitude vibration. Both capacitive and piezoresistive MEMS accelerometers have been used for vibration sensing of the middle ear. Recent capacitive designs are large (base area of 2.5 mm x 6.2 mm) and have a limited bandwidth of 6.44 kHz. Low-noise piezoresistive devices power requirements are high for hearing instruments, greater than 1 mW. Commercial piezoelectric accelerometers are a viable means for vibration detection; while small, they are still large and lacking proper electronic connections for middle ear sensing applications. The aforementioned problems motivate the design of a small, passive, broadband accelerometer with low input referred noise (IRN). In this work, we design a micromachined, piezoelectric bimorph cantilever accelerometer for broadband, low-amplitude vibration sensing. An analytic model is developed to minimize the IRN. The analytic expression allows for rapid design of many system parameters that are verified through finite element analysis.