New Analytical Method Helps Verify Chemical Weapons Compliance

Los Alamos National Laboratory

The ability of a new analytical method to measure fluid properties within a closed container will help to verify compliance with the chemical weapons treaty. The new method 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 them. Called Swept-Frequency Acoustic Interferometry (SFAI), the new noninvasive method shoots sound waves through the liquid to measure its sound speed, sound attenuation, density and viscosity. The method was developed by 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.

Figure 1. Extraction of peak-width and peak spacing from experimental data. The red curve shows the fitting of the data from theory using Origin’s peak-fitting module.

SFAI is a novel adaptation of an ultrasonic interferometry technique developed decades ago for determining sound velocity and absorption in liquids and gases. The underlying principle is the establishment of a standing acoustic wave inside a resonator cavity, using external excitation and simultaneous detection. 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. 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. These are detected by a second piezoelectric transducer that works as a receiver.

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