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Analytical Evaluation of Squeeze Film Forces in a CMUT With Sealed Air-Filled Cavity

Ahmad, Babar and Pratap, Rudra (2011) Analytical Evaluation of Squeeze Film Forces in a CMUT With Sealed Air-Filled Cavity. In: IEEE Sensors Journal, 11 (10). pp. 2426-2431.

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Abstract

The presence of vacuum inside the cavity of a capacitive micromachined ultrasonic transducer (CMUT) causes the membrane of the device (which is the main vibrating structural component) to deflect towards the substrate, thereby causing a reduction in the effective gap height. This reduction causes a drastic decrease in the pull-in voltage of the device limiting the DC bias at which the device can be operated for maximum efficiency. In addition, this initial deflection of the membrane due to atmospheric pressure, causes significant stress stiffening of the the membrane, changing the natural frequency of the device significantly from the design value. To circumvent the deleterious effects of vacuum in the sealed cavity, we investigate the possibility of using sealed CMUT cavities with air inside at ambient pressure. In order to estimate the transducer loss due to the presence of air in the sealed cavity, we evaluate the resulting damping and determine the forces acting on the vibrating membrane resulting from the compression of the trapped air film. We take into account the flexure of the top vibrating membrane instead of assuming the motion to be parallel-plate like. Towards this end, we solve the linearized Reynolds equation using the appropriate boundary conditions and show that, for a sealed CMUT cavity, the presence of air does not cause any squeeze film damping.

Item Type: Journal Article
Additional Information: Copyright 2011 IEEE. Personal use of this material is permitted.However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.
Keywords: Capacitive micromachined ultrasonic transducers (CMUTs); Green's function;Knudsen number;MEMS;pull-in voltage; Reynolds equation;squeeze film damping
Department/Centre: Division of Mechanical Sciences > Mechanical Engineering
Date Deposited: 08 Sep 2011 11:31
Last Modified: 08 Sep 2011 11:31
URI: http://eprints.iisc.ernet.in/id/eprint/40397

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