Detectors use sound waves to irradiate IEDs

Purdue University is developing detectors that use sound and radio waves to penetrate shielding materials of IEDs and hidden bombs.

The work is being conducted as part of the $7m (£5m) Multi-University Research Initiative (MURI), led by North Carolina State University and funded by the US Office of Naval Research. Purdue will receive $2m over five years.

The researchers will study how to use sound and radio waves to irradiate objects, producing a new set of waves that reflect 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, such as 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,’ said Adams. ‘But with high-amplitude waves, material behaviour is much more complicated, or non-linear, so we can’t use the same mathematical equations and models to describe how the waves propagate inside the materials.’

A major challenge involves integrating systems that use 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 (IEDs).

Researchers will use a device called a three-dimensional laser vibrometer to study the behaviour 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.