In high-efficient MMA-accelerometers the capacitive principle of measurement is used. In addition, in this connection a low level of noises and energy consumption, economical efficiency and reliability are provided. The capacitive sensitive elements, based on changing the clearance, require, as a rule, the control with feedback, which increases the complexity of the measurement circuit and energy consumption. The capacitive sensitive elements with changing the area of the electrodes overlapping have a good linearity of the capacitance dependence on movement and large range of measurements, but their fabrication is more complicated. In the paper a model of a sensitive element of a microelectromechanical capacitive accelerometer with sandwich construction has been presented and analyzed. The operation of the sensitive element is based on using the changes in the relative permittivity of the dielectric capacitors due to the introduction of a moving inertial mass between the moving capacitor electrodes under the action of acceleration. As a result, there is a change of capacitance in the output measuring circuit. It has been shown that the model considered provides high sensitivity to acceleration, resistance to temperature changes and low residual mechanical stress in the sensitive element. Modeling and calculations have been performed with using the Ansys and SolidWorks programs. It has been obtained that the movement of movable mass along the axis of sensitivity X 5 times exceeds the movement of the movable mass along the non-working axes, and the capacitance changes between the electrodes along the X-axis is 2500 times greater than the capacitance changes between the electrodes on the non-working axes Z and Y. The calculations have shown that for all values of acting acceleration (up to 30 g) the mechanical stress in the sensitive element is significantly less than the strength limit of silicon, equal to 440 MPa. It has been determined that the temperature variations in the range from -40 to +85 C have led to insignificant changes of capacitance along the working axis (0.0025 - 0.003pF). This demonstrates the temperature stability of work of the sensitive element. The analysis has shown that the developed and studied model of the sensitive element sandwich construction provides the high sensitivity of MMA accelerometer and stability of its parameters.
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