Fabrication and characterization of a force coupled sensor–actuator system for adjustable resonant low frequency vibration detection

Micromechanical resonators for vibration sensing are typically limited to frequencies above 1 kHz [D. Scheibner, J. Mehner, D. Reuter, T. Gessner, W. Dötzel, A spectral vibration detection system based on tunable micromechanical resonators, Sens. Actuators A 123–124 (2005), 63–72]. A novel method for resonant vibration detection at lower frequencies is introduced in the literature [R. Forke, D. Scheibner, J. Mehner, T. Gessner, W. Dötzel, Electrostatic force coupling of MEMS oscillators for spectral vibration measurements, Sens. Actuators A: Phys. (2007), doi:10.1016/j.sna.2007.04.004]. The micro-electro-mechanical-system (MEMS) operates at standard pressure and utilizes the superheterodyne principle well known from information technologies. By mixing the low frequency vibration with a high frequency carrier, the information of the vibration is transformed into a higher frequency range. A resonant oscillator amplifies and filters the information. This paper reports on the characterization and the silicon technology of the force coupled oscillator system (FCOS).