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As silicon-chip designers have been packing more electrical elements into smaller packages to make faster computers, others have been building mechanical, chemical, and optical devices on this same silicon. When machines and electronics are combined on a single chip and batch fabricated, the result is a Micro-Electrical-Mechanical-System (MEMS). MEMS allows sensors, electronics, and actuators to be batch fabricated on a single chip. This technology uses the traditional IC fabrication processes and materials along with new techniques and materials to achieve a wide variety of devices. MEMS sensors and actuators have lower mass and higher resonant frequencies than conventional devices. They are typically less than 1mm x 1mm in cross section and 0.4 mm thick, and can be attached to a surface with minimal disruption of the flow field. Their high resonant frequencies allow excellent high-frequency response.
Small sensors are usually good, but small actuators have limitations. Aircraft for example, can't be miniaturized and still carry people, cargo, weapons, and instruments. In these situations, microsize actuators may prove to be prohibitively expensive or impractical. This dilemma is reflected in the current prominence of MEMS sensors and the lack of practical applications for MEMS actuators. (Though microactuators do show promise in medical, biological, and chemical applications.)
Most aerospace applications face packaging challenges because aircraft are exposed to natural elements: rain, sun, ice, insects, and dirt; and human interference: deicing and cleaning fluids, and maintenance crews. Internal surfaces likely to benefit from MEMS are usually part of the propulsion system. Hence, they must operate in environments containing gases with very high temperatures, abrasive particles, and combustion products.
Silicon Carbide (SiC) and nickel-coated MEMS are being pursued at NASA Lewis for high-temperature and harsh-environment applications. Specifically, a microfabricated fuel atomizer is under development. This atomizer offers better performance and is less expensive than conventional metallic devices and may be used in future gas-turbine combustors. Low-temperature MEMS under development at NASA Lewis include pressure-, heat-flux-, and strain- sensor arrays on flexible substrates. These flexible substrates include interconnects and signal- conditioning electronics and can be easily bonded to curved surfaces to enable quick and easy installation and testing. Another important MEMS sensor being developed at Lewis is for ice-detection. This sensor is small enough to be embedded in aircraft wings and in helicopter rotor blades. It will provide icing data on surfaces which were impossible to monitor with conventional sensors. The Vehicle Technology Center is the NASA point of contact for the "Flexible Manufacturing of Application Specific MEMS" program. This is a DARPA-funded program led by Advanced Micro Machines Incorporated and includes CWRU, BF Goodrich, Parker Hannifin, and Wright Labs. The program will begin in 1997.
POC: Dr. Russell G. DeAnna
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