The $7 million Multi-University Research Initiative, or MURI, is led by North Carolina State University and funded by the U.S. Office of Naval Research. Purdue will receive $2 million over five years.

The researchers will study how to use sound and radio waves to irradiate objects, producing a new set of waves that bounce back to identify underlying materials. Computational models and mathematical equations will be developed to enable the technique to work in real time to quickly detect explosives. 

"You want to get energy into the material, have it move around to pick up information and then be reradiated so that we can sense what's inside," said Douglas Adams, Purdue's Kenninger Professor of Mechanical Engineering.

A central challenge is learning how to interpret signatures created when high-amplitude waves, like those emitted by loudspeakers, pass through objects made of several layers or components containing different materials.

"Most materials are relatively linear, meaning they respond in an easily predictable way when excited by low-amplitude waves," Adams said. "But with high-amplitude waves, material behavior is much more complicated, or nonlinear, so we can't use the same mathematical equations and models to describe how the waves propagate inside the materials."

The project is led by Michael B. Steer, Lampe Distinguished Professor in NC State's Department of Electrical and Computer Engineering.

The Purdue portion of the work is led by Adams, who will be working with J. Stuart Bolton, a professor of mechanical engineering; Jeffrey F. Rhoads, an assistant professor of mechanical engineering; and Patricia Davies, director of the Ray W. Herrick Laboratoriesand a professor of mechanical engineering. The Purdue team also is working with Mohammed A. Zikry, a professor in the NC State Department of Mechanical and Aerospace Engineering.

Purdue was chosen for the effort in part because of specialized acoustic facilities at the Herrick Laboratories, Adams said.

A major challenge is integrating systems that use both radio and sound waves, which travel at far different speeds. Because the two types of waves have different frequency ranges, they will reveal different kinds of information about an object to more accurately detect improvised explosive devices, or IEDs.

Researchers will use a device called a three-dimensional laser vibrometer to study the behavior of sound waves passing through materials. They also will use "acoustic holography" to show precisely how different materials react to sound waves and embed miniature sensors inside test materials to record data.

Experiments will be conducted at the Herrick Laboratories, the Center for Systems Integrity and Birck Nanotechnology Center.

The research will involve several Purdue doctoral students.