This paper presents experimental and theoretical investigation of a new concept of switches (triggers) that are actuated at or beyond a specific level of mechanical shock or acceleration. The principle of operation of the switches is based on dynamic pull-in instability induced by the combined interaction between electrostatic and mechanical shock forces. These switches can be tuned to be activated at various shock and acceleration thresholds by adjusting the DC voltage bias. Two commercial off-the-shelf capacitive accelerometers operating in air are tested under mechanical shock and electrostatic loading. A single-degree-of-freedom model accounting for squeeze-film damping, electrostatic forces, and mechanical shock is utilized for the theoretical investigation. Good agreement is found between simulation results and experimental data. Our results indicate that designing these new switches to respond quasi-statically to mechanical shock makes them robust against variations in shock shape and duration. More importantly, quasi-static operation makes the switches insensitive to variations in damping conditions. This can be promising to lower the cost of packaging for these switches since they can operate in atmospheric pressure with no hermetic sealing or costly package required.
A differential microphone is described that has been designed to employ similar operating principles to that of the ears of the parasitoid fly, Ormia ochracea. The ears of this fly have been shown to be highly directional even though they are only about 1 mm across [R. N. Miles, D. Robert, and R. R. Hoy, J. Acoust. Soc. Am. 98, 3059–3070 (1995)]. Analyses of the mechanics of this biological system suggest novel approaches to the design of miniature directional microphones. Finite element analysis results for the acoustic resonse of a 1 mm by 2 mm silicon nitride microphone diaphragm are presented. The diaphragm responds to pressure gradients in a manner that is inspired by Ormia’s ears. Predicted results for the natural frequencies, mode shapes, frequency response and directivity of our design are shown to compare closely with measured data obtained for a prototype silicon nitride diaphragm. [Work supported by NIH and DARPA.]
A miniature differential microphone is described having a low-noise floor. The sensitivity of a differential microphone suffers as the distance between the two pressure sensing locations decreases, resulting in an increase in the input sound pressure-referred noise floor. In the microphone described here, both the diaphragm thermal noise and the electronic noise are minimized by a combination of novel diaphragm design and the use of low-noise optical sensing that has been integrated into the microphone package. The differential microphone diaphragm measures 1 ϫ 2 mm 2 and is fabricated out of polycrystalline silicon. The diaphragm design is based on the coupled directionally sensitive ears of the fly Ormia ochracea. The sound pressure input-referred noise floor of this miniature differential microphone has been measured to be less than 36 dBA.
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