By Chris Burroughs
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READY FOR FIELD TESTING -- Researchers Graham Yelton (left) and Richard Cernosek (right) watch as Alan Staton conducts a laboratory test using the lightweight portable chemical vapor detection system developed by Sandia. The system is currently being refined in preparation for field testing in a chemical plume in 2001. (Photo by Randy Montoya)
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"There is much interest in this detection technology -- by the military, the Environmental Protection Agency, DOE and other government agencies, and many private enterprises," says Richard Cernosek (1744), project lead. "The technique is adaptable for a variety of applications ranging from environmental monitoring and remediation to industrial process control and from personal health and safety to law enforcement and drug detection."
The seven-pound, battery-powered sensor system, built into a box 10 by 8 by 4 inches, along with its notebook computer is light enough to be hand-carried into the field where it can test for and identify 18 different chemicals in minutes.
Richard says the system's light weight and ability to test for a multitude of chemicals make it a significant step in the area of vapor detection. In the not-so-distant past, chemical samples had to be taken in the field and then returned to the laboratory for testing. This resource-intensive method requires a considerable delay before chemical information is available. Many situations, such as in military applications, demand on-the-spot chemical analyses.
This new system -- which can test for chemical signatures related to the three categories of weapons of mass destruction: nuclear, chemical, and biological -- is part of a new generation of chemical vapor detection technology.
Heart of detection system
"We see this system as possessing many desirable properties of a portable chemical detector," Richard says. "It is sufficiently sensitive to determine chemical concentrations at relevant levels. It can identify chemicals with a high degree of accuracy. It has rapid response for timely determination of information. It isn't affected by changes in temperature and humidity. It is compact and uses low power, making it suitable for field applications. And it can be produced at a low cost."
The heart of the detection system is an array of seven surface acoustic wave (SAW) sensors, each with a different chemically sensitive thin film coating. The substrate of the sensors is quartz, cut at a crystalline angle that supports a surface wave. As a piezoelectric material, the quartz converts electric signals to surface acoustic waves that travel much like waves on water. A thin, selectively absorbing layer is coated on the quartz surface. When specific chemical molecules sorb into or onto this layer, the acoustic waves travel more slowly. This change can be detected by the sensor microelectronics once the acoustic wave is converted back to an electric signal.
Small sealed case
Because each sensor is coated with a distinct chemically sensitive layer, the sensors will respond differently to the same chemical, forming a recognizable pattern. The data from all the sensors are put into a Sandia-developed pattern-recognition algorithm, a computational program called Visual Empirical Region-of-Influence (VERI), which uses a clustering technique to identify the various chemicals. The VERI algorithm has proven to be very good in discriminating among different chemicals. The algorithms can identify 18 different volatile organic compounds over a wide concentration range with a 95 percent accuracy.
The sensor array is contained in a small, sealed, temperature-controlled case with electrical connections and gas flow ports. The array itself can be removed from the case, allowing sensor arrays to be customized for particular applications. A small diaphragm pump pulls vapor samples from the environment through the test cavity. The system uses a Windows-based notebook computer for system control, real-time display, data storage, and pattern recognition.
The researchers have so far tested the system only in a laboratory setting using chemicals in vials and beakers. They are refining its capabilities -- the pattern recognition and sensor array -- to increase performance and prepare for field testing in a chemical plume in 2001. "Then we'll see this system operate in a realistic setting," Richard says. "It's been several years in the development and preparation. We should be ready for this."
The team working on the instrumentation portion of the project includes Richard as project lead, Graham Yelton, Alan Staton, Art Rumpf, Chris Colburn, Larry Anderson (all 1744), and Jimmie Wolf (1738). Gordon Osbourn, John Bartholomew, and Rubel Martinez (all 1118) comprise the VERI development team. Numerous other Sandians contributed to the technology development throughout the project lifetime. External collaborators include several universities -- most notably Texas A&M and New Mexico Institute of Mining and Technology -- other DOE laboratories, and industrial partners. Project funding comes from the DOE Nonproliferation and National Security Office of Research and Engineering.
Last modified: November 3, 2000
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