Defense, homeland-security, military, communications, and aerospace applications are on the prowl for MEMS/nano sensor innovations.
Judging from this year's 2005 Sensors Expo & Conference, held June 6-9 in Chicago, Ill., microelectromechanical-system (MEMS) and nano technologies are poised to meet the needs of many industry sectors. Promising presentations covered homeland-security, reliability, military armaments, composite materials, and communications issues.
One of the most interesting presentations came from Wayne State University. Researchers there are developing rapid sensing platforms for defense, aerospace, and homeland-security applications using real-time biological and chemical sensing systems as well as radiation means.
They developed an array of biosensors that use optics, chemical interactions, and various fluorescence schemes based on surface-acoustic-wave (SAW) sensing technology and an aluminum-nitride compound. They're now working on a prototype real-time testbed with Bluetooth capability and a disposable, easily exchangeable sensor array (Fig. 1).
Wayne State also is working on a portable laboratory that would determine the effects of radiation on the human body by examining marker mRNA abnormalities. The Rapid Assessment Device for Radiation Exposure and Dosimetry (RAD-READ) samples a small drop of blood, segregates the red blood cells from white blood cells, and lyses the white blood cells in a primary reaction chamber(Fig. 2). A second reaction chamber then processes the genetic material.
EXPANDING THE USE OF SAWs
SAW devices are key factors in "labs-on-a-chip" for Nanodetex's homeland-security applications. These devices detect biological, chemical, and explosive agents. Originally developed at Sandia National Laboratories, the MicroChem Lab consists of a pre-concentrator, a micro gas chromatograph, and a four-channel SAW detector (Fig. 3).
In the next two years, Nanodetex hopes to have the MicroChem Lab ready to detect nerve and blister agents in commercial applications. These devices won't include the gas chromatograph, which reduces the system's ability to determine specific concentrations of contaminants. They do, however, speed up the detection process by giving the system a faster response time. Future versions of the MicroChem Lab will detect toxic industrial chemicals, explosives, and biological agents.
The AirSentinal sensor developed by MesoSystems Technology also evaluates biological threats. The first-generation prototype uses a combination of micro-impaction and state-of-the-art ultraviolet (UV) LEDs to generate a fluorescence signal from bioaerosols. It employs an innovative aerosol concentration technology that enables continuous sampling and detection using low-cost components, with data-flow and response times of approximately one minute.
Military-defense and aerospace applications also benefit from advances in microtechnology. Until now, non-MEMS-based technologies have formed the technological basis for inertial guidance mechanisms. But according to Honeywell, a migration to MEMS technology is under way to build inertial measurement units (IMUs) that function as complete gyroscopes. MEMS will enable inertial guidance systems with lower power dissipation, smaller sizes, and lighter weights.
IMPROVING RELIABILITY
Obviously, reliability is critical in MEMS applications. Yet the proprietary nature of MEMS technology and the general immaturity of the MEMS industry have resulted in a lack of long-term performance data and test methods for MEMS devices, says Concurrent Technologies.
To address the problem, the U.S. Army Corrosion Office initiated its MEMS Reliability Assessment Program at Picatinny Arsenal, located in New Jersey. This program will develop long-term reliability-testing and test-capability standards for the Department of Defense (DoD) in both unpackaged and packaged MEMS devices.
Because corrosion-related MEMS failures represent a significant problem, Freescale Semiconductor uses laser-trimmed resistors on its MEMS pressure sensors. These resistors are coated with a fluorsilicone gel as a barrier between the silicon die and environmental influences to combat moisture penetration.
To improve the reliability of composite materials like those used in the aerospace industry, Blue Road Research came up with a fiber-grating sensor technology that determines material structural health. The grating is embedded between the various layers of the composite materials. It then locates and assesses damage from fiber breakage and delaminations.
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