Design and Analysis of a MEMS Fabry-Perot Pressure Sensor

Abstract

Accurate dynamic pressure measurements in the jet engine compressors are the key point in the detection of instabilities that are often precursors to surge or rotating stall. Localized pressure measurements are also very helpful in vehicles aerodynamics performance optimization. A new MEMS pressure sensor capable of measuring pressures between 14.7 psi to 100 psi is presented in this work. The sensor is based on the effect of the viscous damping force on the frequency response of a micro cantilever beam. The frequency response of a micro cantilever beam is affected by two types of damping, squeeze film damping and air flow damping. Both these effects are modeled here. The airflow damping is dependent on the air pressure and increases with pressure. This sensitivity to pressure is utilized to predict the ambient air pressure. In order to measure the beam frequency response, a Fabry-Perot interferometer is fabricated using the cantilever beam and the substrate. An electro-optical measurement system is setup to measure the frequency response of the sensor. A custom made pressure chamber is designed and fabricated to allow high pressure tests. The measured frequency response of the cantilever beams are compared with the model results. The experimental results are fitted to the model predictions using pressure as the fitting parameter. The estimated pressure is then compared with the applied pressure. The estimated pressure is in good agreement with the actual pressure for pressures below 40 psi. For the PolyMUMPs fabricated sensors, the error is less than 4% for pressure values smaller than 40 psi.