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MEMS accelerometer is one of the most popular sensors which is widely used in resource explorations, seismic measurements, structural monitoring, and consumer electronics as its good performance and low cost. However, the stiffness of the conventional accelerometers is fixed, which limits the bandwidth of the sensor, so that they are just used in specific applications. In this paper, a stiffness adjustable optical MEMS accelerometer based on electro-thermal actuator is proposed, whose stiffness can be adjusted over a large range by the electro-thermal actuator. The stiffness adjustment is just depending on the voltage applied on the electrodes, which changes the geometrical characteristic of the spring beams by exerting an axial compression displacement on them, enabling the device to neutralize its intrinsic positive stiffness, thus a neutrally stable quasi-zero stiffness region is obtained. The test results show that the first order resonant frequency of the accelerometer can be tuned to below 19 Hz from the unloaded state value of 500 Hz, which greatly changes the working bandwidth of the accelerometer. Combined with the high-resolution optical read-out scheme, the theoretically achievable system resolution can be μg levels. Therefore, the designed stiffness adjustable accelerometer can be used in different bandwidths application fields.
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