General Description

The ground surface, to a depth of a few meters, is a granular fluid-filled porous material. Acoustic methodologies describe soils through parameters such as velocity, attenuation, impedance, bulk modulus, and flow resistivity. The Porous Materials Group investigates physical phenomena relating to the interactions of acoustic waves with these porous media. This group has significantly advanced acoustic technologies for land mine detection and the measurement of soil properties. The need to accurately measure minute vibrations of the ground when acoustically excited has led to the development, in conjunction with industry partners, of advanced Doppler vibrometry technologies for rapid area measurements. Consequently, the research in the porous materials group falls into three broad areas: landmine detection under the aegis of the Institute for Humanitarian De-Mining, characterization of soil properties, and vibrometry.

Importance of Research

The Porous Materials Group conducts research to better comprehend the complex interactions between sound and the earth’s surface. It is impossible to overstate the importance of the ground: among many other applications, we grow food in it, build structures and roads on it, and bury things in it. A thorough understanding of the local properties of the ground is required to optimize performance of these activities. The foundational research in the group, then, is development of acoustic techniques for the characterization of soil properties. Existing techniques for characterizing the ground are labor intensive and use invasive type probing or destructive sampling. Acoustic methodologies provide new and improved methods of characterizing soil physical properties by non-invasive, in-situ techniques. The proliferation of landmines in many regions of the world without a corresponding improvement in the means for locating and eliminating them led to the application of the acoustic soil characterization research for landmine detection. The research associated with both of these thrusts indicated a need for advanced instruments and techniques for their use in measuring very small vibrations over a relatively large area, resulting in a new research thrust for vibrometry. The instruments and techniques,

developed in conjunction with industry partners, have countless applications in areas such as non-destructive testing, monitoring of structures, detection of vibrating or moving objects, and others.

Soil sealing and crusting studies
in the NCPA anechoic chamber

Confirmation Sensor

Major Accomplishments

Past and current research efforts have provided a better comprehension of the effects resulting from sound interacting with the surface of the earth. New methods or improved existing ones to measure or evaluate soil physical properties, to prevent soil loss and erosion, and to enhance precision agriculture are being developed. Successful acoustic and seismic research for landmine detection is being conducted with results demonstrating a very high probability of detection and low false alarm rate. Major advances have been made in the signal processing and the use of multiple laser beams to significantly increase the speed of vibration measurement over relatively large surface areas. NCPA personnel used laser Doppler vibrometers (LDVs) in New York's World Trade Center complex immediately following the September 11, 2001 terrorist attack to monitor building vibrations to ensure worker safety from collapse during debris removal.

Future Goals

Future research interests of the Porous Materials Group include the fusion of acoustic sources and advanced vibrometry for applications such as non-destructive inspection and monitoring of structures for commercial and safety applications, and detection and identification of buried facilities, vehicles, and improvised explosive devices for the military. Research interests continue in characterization of soil properties for precision agriculture and civil engineering and in the refinement and continued development of buried object detection.

Many-beam vibrometer vehicle-borne
explosive detection concept

News

ARMY ADVANCED CONCEPT WORKSHOP ON SHALLOW TUNNEL DETECTION.  Under the sponsorship of the Army Research Office, CERDEC-NVESD Countermine Directorate, and RDECOM CIED/CM IPT, the University of Mississippi hosted a workshop on the "Real-Time Detection of Clandestine Shallow Tunnels" at NCPA on February 14-17, 2006.  Shallow tunnels present both military and homeland security threats.  Although many technical approaches to tunnel detection have been proposed and research, a practical, reliable and easily-deployable solution to the problem for military and homeland security applications remains a severe technical challenge.  The objective of the workshop was to bring together key members of the academic and government research commu ities, technologists from industry, and military representatives famliar with specific current iddues to conceptualize both a short-term technology development program and a long-term basic research program to address the problem.