Non-destructive Damping Measurement for Wafer-level Packaged Microelectromechanical System (MEMS) Acceleration Switches

Report No. ARL-TR-7094
Authors: Ryan Knight and Evan Cheng
Date/Pages: September 2014; 38 pages
Abstract: Microelectromechanical systems (MEMS) three-axis acceleration threshold sensors have been developed to measure acceleration threshold levels using voltage switching when the threshold is reached. Determining damping coefficients is important for categorizing how each threshold sensor or switch operates. Switches with different damping coefficients result in different mechanical impedances and response times. Analytical and numerical methods to model damping coefficient values based on empirical data are needed to characterize three-axis acceleration sensors; traditional methods use the displacement of an underdamped system to calculate the damping ratio. Mechanical switches are single output devices that distinguish whether closure occurs or not and lack a transduction mechanism to turn acceleration into a readable displacement signal. Thus, we have devised a more inventive technique to analyze a closed switch. A shock table and vibration testing produces a deterministic acceleration input to close an acceleration switch, which has a defined switch gap distance, and mathematical fitting using these deterministic values allows one to determine damping coefficients. By using both an analytical equation fit method and a numerical optimization program, the damping coefficients for MEMS three-axis threshold acceleration sensors were calculated from the results of the tests and design dimensions of the switches.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2014