A COMPARISON OF SQUEEZE-FILM THEORY WITH MEASUREMENTS ON A MICROSTRUCTURE

Mathematical formulations of the effects of squeezed films of gas have been available for some years. We compare the theoretical predictions for two isolated rectangular plates oscillating normal to each other with measurements on a silicon microstructure that approximates such plates. A range of pressure from vacuum to atmospheric, and frequencies from d.c. to 50 kHz are employed, representing squeeze numbers between zero and 1000, and flow regimes from molecular, through transition to substantially viscosity dominated. Generally the agreement with predictions is good, though there is a small but significant difference in effective plate separation between low frequencies (< 10 kHz) and high frequencies (> 10 kHz). Attention is drawn to the high degree of gas trapping between the plates at resonance, for all pressures investigated; the possibility of using this effect as a pressure sensor is noted. Phase measurements at low frequency provide a simple measurement of gas viscosity.