MEMS-based mechanical spectrum analyzer

An ac-operated capacitive accelerometer with electrostatic force feedback is employed for direct mechanical spectrum analysis. Force feedback acts as a means for electronic modulation of the spring constant of the suspension and thus for enhancing the sensitivity. Therefore, a suitable electrostatic time-varying actuation can be used to make the accelerometer selectively sensitive to a coherent frequency component of a mechanical vibration. By sweeping the frequency of the drive voltage over a selected range, the mechanical (vibration) spectrum is analyzed in the mechanical domain. An inverted pendulum type of accelerometer structure has been fabricated in silicon using micromachining techniques and operated using electrostatic momentum feedback. The spectral performance is comparable to fast Fourier transform based systems for spectral analysis on a time series supplied by a conventional accelerometer, while the overall system features a reduced complexity and reduced power consumption.