Finding treasures with physics: the fingerprint matrix

Summary

How do you find objects buried in sand or hidden in thick fog? A team from the Institut Langevin (Paris) and TU Wien (Vienna) has developed an astonishing method. Can we reveal objects that are hidden in environments completely opaque to the human eye? With conventional imaging techniques, the answer is no: a dense cloud or layer of material blocks light so completely that a simple photograph contains no information about what lies behind it.However, a research collaboration between the Institut Langevin and TU Wien has now shown that, with the help of innovative mathematical tricks, objects can be detected even in such cases – using what is known as the ‘fingerprint matrix’. The team tested the newly developed method on metal objects buried in sand and in applications in the field of medical imaging. A joint publication on this topic has just appeared in the journal Nature Physics.Seeing and hearing means wave scatteringWhether we take a normal photo or use ultrasound to look inside the body – from a physical point of view, the same thing always happens when we create an image: a wave is sent to an object, the object reflects part of the wave, and the reflected portion reaches our eye – or a measuring device. This reflected wave can be used to determine where the object is located.However, this normally only works if the object's surroundings are sufficiently transparent. “Otherwise, for example in a dense cloud or in murky water, the phenomenon of multiple scattering occurs,” explains Prof. Stefan Rotter from the Institute of Theoretical Physics at TU Wien. The wave is scattered not only by the object to be imaged, but also by the surrounding environment – often many times over, so that only a greatly altered wave can be registered, in which the object being sought can no longer be recognised.“Instead of the object, all you see is a diffuse fog – this is a fundamental problem of imaging techniques, from sonar in submarines to imaging techniques in medicine,” says ...