Chemical weapons sensor designed with COTS software

Aug. 1, 1998
LOS ALAMOS, N.M. - Government scientists have designed a method to detect chemical weapons, and used a commercial-off-the-shelf (COTS) software tool to analyze the data.

Chemical weapons sensor designed with COTS software

By John McHale

LOS ALAMOS, N.M. - Government scientists have designed a method to detect chemical weapons, and used a commercial-off-the-shelf (COTS) software tool to analyze the data.

Experts at the Electronic and Electrochemical Sensors & Devices Group at Los Alamos National Laboratories in Los Alamos, N.M., used Origin data analysis software, from Microcal Software Inc. in Northampton, Mass., to analyze the data gen-erated by the Swept- Frequency Acoustic Interferometry (SFAI), a noninvasive method that shoots sound waves through liquid to measure its sound speed, sound atten-uation, density, and viscosity.

SFAI will make it possible for inspectors to determine whether artillery shells and other sealed containers are filled with chemical warfare compounds without the time and expense of opening or drilling a hole in them, says Dipen Sinha, director of the SFAI program at Los Alamos. Developing the method were researchers using data analysis and technical graphics software to correlate the characteristics of the resonance peaks of sound waves to the liquid`s physical properties, he says.

Los Alamos experts selected Origin because the company provided all the advanced data analysis routines required to detect underlying patterns, Sinha explains. "In addition, its ability to easily visualize data turned out to be critical to this work," he says.

The U.S. Defense Special Weapons Agency in Alexandria, Va., funded SFAI for use in compliance with the Chemical Weapons Convention treaty, which calls for the eventual destruction of all chemical weapons, Sinha says.

The Los Alamos technique has been successfully tested on a large variety of chemical munitions at government storage depots, with a developer of the system on hand to assist in the demonstration, he says. Operators who have had no previous experience with the technology will perform the next stage of field trials.

SFAI is an adaptation of an old ultrasonic interferometry technique for determining sound velocity and absorption in liquids and gases, Sinha says. The underlying principle is the establishment of a standing acoustic wave inside a resonator cavity, using external excitation and simultaneous detection, he explains.

It works through the application of swept frequency electric excitation - in a frequency range from 1 kHz to 15 MHz - to a piezoelectric transducer attached to the outside of the container, Sinha says. At certain frequencies, the signal produces acoustic resonance in the liquid inside the container. The result is a series of resonance peaks in a spectrum. A second piezoelectric transducer that works as a receiver detects these, he says.

"Information about the contents is derived from an analysis of the spectrum of resonance peaks," Sinha continues. A single sweep measurement can be used to derive liquid properties that include sound speed, sound absorption, frequency dependence of sound absorption, and liquid density, he adds.

"In SFAI, deriving so much information from the one measurement is important, particularly in the area of chemical diagnostics," Sinha explains. "Many chemical compounds can have the same sound speed, for example, but none is identical across all four parameters."

In the development of the SFAI process, the task for researchers was to create algorithms that would derive sound velocity, attenuation, density, and viscosity from the spectrum, Sinha says. "To do this, literally thousands of data sets from tests were plotted against theoretical predictions," he continues. "Each new data set had many subtle variations, some of which hid patterns that could be used to determine the properties of the fluid inside the sealed container.

"With Origin, it was possible to adjust virtually any component of a plot through interactions with the mouse and dialog boxes," Sinha says. "As a result, instead of poring over tables of data or rudimentary plots and missing important information, researchers were able to easily create thousands of highly informative plots, some of which uncovered vital aspects of the SFAI process," he explains.

"In the development of SFAI, nearly every capability of Origin was used on a daily basis. When the software did not contain a certain analysis, it was either created in-house through Origin`s built-in scripting language or Microcal Software provided it," Sinha continues. "Without Origin, it would have been very difficult to develop the algorithms for this technique," he adds.

After all the required algorithms for SFAI were determined, they were rewritten as FORTRAN or Quick BASIC programs for use in the detector that is used in the field, Sinha explains. The instrument weighs about six pounds, and feeds data into a 486 PC with a customized digital synthesizer and analyzer board from Neel Electronics, in Laguna Niguel, Calif.

The computer memory contains a database of the physical properties of all primary chemical warfare compounds. An operator runs the system by placing the transducers on the item to be tested and pressing a button. All measurements and analysis are done automatically.

The detector can safely analyze a container in approximately 20 seconds, a significant improvement over early monitoring systems, Sinha claims.

SFAI also is used in characterizing petroleum products and for detecting spoiled milk in sealed containers such as paper cartons, plastic bottles, and Tetra Pak pouches.

For more information on Origin contact Microcal Software by phone at 800-969-7720, by fax at 413-585-0126, by mail at One Roundhouse Plaza, Northampton, Mass. 01060, or on the World Wide Web at

For more information on SFAI contact Sinha by phone at 505-667-0062, by mail at Electrochemical Sensors & Devices Group, Los Alamos National Laboratories, Los Alamos, N.M. 87545, or on the World Wide Web at

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The Swept-Frequency Acoustic Interferometry method developed by experts at Los Alamos National Laboratories detects chemical compounds in weapons by shooting sound waves through liquid to measure its sound speed, sound attenuation, density, and viscosity.

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