Mechanical Spectrum Analyzer in Silicon using Micromachined Accelerometers with Time-Varying Electrostatic Feedback

Capacitive accelerometers with electrostatic force feedback are widely employed, because of performance and robustness. The force feedback acts as a means for electronic modulation of the spring constant of the suspension. Commonly, the electrostatic feedback is employed for null-based acceleration measurement. A suitable electrostatic time-varying actuation could instead be used to make the accelerometer selectively sensitive to a coherent mechanical frequency component. By sweeping the frequency of the drive voltage over a selected range, the mechanical spectrum is analyzed in the mechanical domain. The resulting spectrum analyzer features many advantages compared to conventional techniques for condition monitoring of mechanical machines. An inverted pendulum type of accelerometer structure has been fabricated in silicon using micromachining techniques and operated using electrostatic momentum feedback.