JMM 2006c Abstract
Design and characterization of a
micromachined Fabry–Perot vibration
sensor for high-temperature applications
P.M. Nieva, N.E. McGruer and G.G. Adams
Summary
We have designed and characterized a MEMS-based Fabry–Perot device
(MFPD) to measure vibration at high temperatures. The MFPD consists of a
micromachined cavity formed between a substrate and a top thin film
structure in the form of a cantilever beam. When affixed to a vibrating
surface, the amplitude and frequency of vibration are determined by
illuminating the MFPD top mirror with a monochromatic light source and
analyzing the back-reflected light to determine the deflection of the beam
with respect to the substrate. Given the device geometry, a mechanical
transfer function is calculated to permit the substrate motion to be
determined from the relative motion of the beam with respect to the
substrate. Because the thin film cantilever beam and the substrate are
approximately parallel, this two-mirror cavity arrangement does not require
alignment or sophisticated stabilization techniques. The uncooled
high-temperature operational capability of the MFPD provides a viable
low-cost alternative to sensors that require environmentally controlled
packages to operate at high temperature. The small size of the MFPD
(85–175 um) and the choice of materials in which it can be manufactured
(silicon nitride and silicon carbide) make it ideal for high-temperature
applications. Relative displacements in the sub-nanometer range have been
measured and close agreement was found between the measured sensor
frequency response and the theoretical predictions based on analytical
models.
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