Micromachined SiC Accelerometers.(Brief Article)

Silicon micromachined silicon carbide accelerometers are undergoing development for use in high-temperature environments like those inside turbines, internal combustion engines, and other machines. These accelerometers would be used to measure vibrations indicative of deterioration of mechanical components. As such, they would be valuable diagnostic tools that could give advance warnings of failures, indicating the need to perform maintenance. They would even be small enough to fit into turbine blades. Work on this project is being done by Russell G. DeAnna of the U.S. Army Research Laboratory for Glenn Research Center (21000 Brookpark Rd., Cleveland, OH 44135; Tel: 216/433-3484).

Like similar accelerometers micromachined out of silicon, these micromachined silicon carbide accelerometers are based on the concept of displacements as proof masses suspended on springs. They include electrodes for capacitive sensing of displacements of proof masses, and electrostatic feedback for centering and for nulling displacements caused by relatively steady forces like those caused by gravitation and centripetal acceleration. In an experimental silicon carbide device, the proof mass is suspended at opposite ends by springs in the form of folded beams. At each end, the outer two beams are attached to a substrate at four anchor locations.

The particular folded-beam structure offers low stiffness (and thus high sensitivity to acceleration) along both directions perpendicular to the nominal longitudinal axes of the beams and high stiffness (and thus low sensitivity to acceleration) parallel to the nominal longitudinal axes of the beams. If an accelerometer of this or similar configuration were to be used to measure turbine blade vibrations, then ...