Remote Acoustic Detection System Uses Laser Vibrometer to Identify Homemade Bombs

Vanderbilt University engineer Douglas Adams and his team have developed a remote acoustic detection system designed to identify homemade bombs that can determine the difference between those that contain low-yield and high-yield explosives. This research was presented at the American Society of Mechanical Engineers Dynamic Systems and Control Conference on October 23, 2013 in Stanford, CA. The new system consists of a phased acoustic array that focuses an intense sonic beam at a suspected improvised explosive device. At the same time, an instrument called a laser vibrometer is aimed at the object's casing and records how the casing is vibrating in response. The nature of the vibrations reveal a great deal about what is inside the container. "We are applying techniques of laser vibrometry that have been developed for non-destructive inspection of materials and structures to the problem of bomb detection and they are working quite well," Adams said.

Transcript

00:00:01 [Music] the objective of This research is to use non-c contct sensing to characterize the contents of containers the application of This research is in the detection of homemade explosive devices this work is focused on understanding how the signature of a container changes due to its contents

00:00:28 these three 1gallon plastic containers look nearly identical from the outside but each has different contents one is empty one contains water and the third contains a mixture of kitty litter in water to create a clay-like material the containers were excited using an 8 ohm impedance selenium air driver placed approximately 3 in behind the container the signal was a burst

00:00:51 chirp from 100 to 5,000 Hertz in a duration of around half a second the excitation signal was created using this vibr system shown here and then Amplified this portion of the video provides a walk around view of the entire experimental setup the first chirp excitation can be heard in this portion of the video the

00:01:33 sound pressure was approximately 110 DB in amplitude the spot from the laser vibrometer can also be observed to move from point to point on the surface of the container as it measures the velocity response the screen image showns the software interface and the rich nature of the measured velocity response containing a broad range of

00:01:57 frequencies this plot shows the Spectre of the velocity responds measured perpendicular to the surface at one point on the container the black curve corresponds to the empty container while the blue curve corresponds to the container filled with water 25 blocks of data were used to average the Spectrum for each container type it's clear that the Spectrum corresponding to the

00:02:18 waterfill container is much lower in amplitude than the empty container here are the two curves corresponding to The Container again empty and one container containing the clay substance once again the Spectrum for the container with Clay is much lower in amplitude than the empty container these Expressions indicate the analytical relationships that

00:02:42 demonstrate why the amplitude for the containers filled with water and Clay are much lower in velocity than the empty container this final comparison shows the two filled containers one with water one with clay handheld vibrometers are available such as this Keon 1D unit that could be used to acquire the non contct response data

00:03:09 for this type of research a peer- reviewed paper related to this work is being presented at the asme dynamic systems and controls Conference October 21st through the 23rd in Palo Alto California the paper focuses on how the interface between the walls of the container and an explosive surrogate material influenc is the signature that is measured on the

00:03:32 outside of the container the paper demonstrates as shown in this plot that a surrogate material with 75% volume fraction of crystals can be distinguished from a material with 50% volume fraction of crystals using only the response of the container material the shift in resonant frequencies is apparent in the velocity Spectrum plot furthermore the nonlinear

00:03:53 nature of the response to the container is observed due to the presence of the interface we would like to acknowledge our sponsor from the United States Office of Naval Research also our co-author and the principal investigator of This research and other collaborators