The effect of squeeze film constriction on bandwidth improvement in interferometric accelerometers

Abstract

This paper studies the effects of a constricted squeeze film on the performance of an optical microelectromechanical system accelerometer. Squeeze films are shown to extend the sensor frequency range (bandwidth) in accelerometers without decreasing the mechanical sensitivity by retarding the resonate response. By restricting the venting of a squeeze film, this preferential behavior is observed at lower frequencies than is expected for ideally vented accelerometers. Due to this effect, constricted squeeze films may be used to improve the bandwidth performance of devices of lower natural frequencies and higher inertial sensitivities. A model, extended from the existing squeeze film theory, is developed for the squeeze film formed between circular plates with generalized mixed boundary pressure conditions to describe the boundary flow resistance. These effects are experimentally observed in a parallel plate Fabry-Pérot interferometric accelerometer through frequency response characterization at mechanical resonance under pressure variation. The analytical results for the constricted squeeze film are used to predict the performance gains due to the frequency-dependent squeeze film parameters. These results are experimentally confirmed by demonstrating improved bandwidth performance due to the constricted squeeze film.

Non-monotonic pressure dependence of resonant frequencies of microelectromechanical systems supported on squeeze films

“…The damping and natural frequency of such MEMS structures are among their most important performance metrics-they dictate the safe bandwidth for operation for non-resonant devices, and for resonant devices they dictate the sensitivity and speed of the device. From the early days of MEMS modeling it has been recognized that the coupling of the vibrating structure with the surrounding gas film modifies significantly its dynamic response [1][2][3][4][5][6][7], especially its effective damping [8][9][10][11]; however, the change of natural frequencies due to gas films has been much less investigated [11][12][13][14].…”