Self Calibration by ON/OFF Sensitivity Switching - Feasibility Study of a Resonant Accelerometer

This research provides the theoretical feasibility study of a novel architecture of a MEMS differential resonant accelerometer, with switchable and tunable electrostatic transmission between the proof mass and the vibrating sensing beams. The same beams are used for sensing of the inertial force, while the transmission is switched ON, and for the device's calibration, when the transmission is OFF. Therefore, the beams' response in the OFF state is affected by the same factors (temperature, electronics, packaging) as in the ON state, with the only exception for the acceleration. This unique ability to physically disconnect the inertial force from the sensing elements opens possibilities for new schemes of the signal processing, including sensitivity tuning, zero-bias correction and on-the-fly self-calibration of the sensor. The device includes a proof mass (PM) and two force-transmitting frames that are attached to the substrate by the suspension springs, such that there is no direct mechanical connection between the PM and the frames. Two identical sensing beams are attached at their ends to the frames and the substrate. When the electrostatic transmission is switched ON by applying a voltage between the PM and frames, the force is transmitted from the PM through the frame to the beams. Disturbance in the electrostatic field, due to the acceleration-dependent displacement of the PM, results in the shift in the beam axial force and, therefore, in its resonant frequency, assuring the device's acceleration sensing. Furthermore, the change in the control voltage tunes the transmission of the input signal, and therefore the scale factor and the dynamic range of the sensor. An analytic model of the generic device is formulated and verified using finite elements analysis. The tunability of the device and the compensation of the scale factor thermal sensitivity are demonstrated using the model.