Researchers at the University of California San Diego have developed a stretchable and flexible probe that could make it easier to perform ultrasound imaging on odd-shaped structures such as railway tracks.

The probe consists of a thin patch of silicone elastomer patterned with an ‘island-bridge’ structure; small electronic parts make up the islands and connecting spring-like structures form the bridges.

It is the flexibility of these bridges, made from spring-shaped copper wires, that allows the patch to bend to irregular surfaces, while the islands contain electrodes and piezoelectric transducers which produce ultrasound waves when electricity passes through them.

In contrast, conventional ultrasound devices have a flat and rigid base which prevents them from maintaining good contact when scanning across curved, wavy or angled surfaces.

“Elbows, corners and other structural details happen to be the most critical areas in terms of failure—they are high-stress areas,” said professor of structural engineering at UC San Diego and co-author of the study Francesco Lanza di Scalea.

“Conventional rigid, flat probes aren’t ideal for imaging internal imperfections inside these areas.”

Typically gel, oil or water is used to create better contact between the ultrasound probe and the surface of the object it is examining. However, too much of these substances can filter out some of the signals.

Conventional ultrasound probes are also bulky, making them impractical for inspecting hard to reach parts or transporting across railway tracks.

Researchers tested the new device on an aluminium block with a wavy surface which contained defects 2cm to 6cm beneath the surface. They placed the probe at various spots on the surface, collected data and then reconstructed the images using a customised data processing algorithm.

The probe was successfully able to map the 2mm-wide holes and cracks inside the block.

The device is still at the proof-of-concept stage and cannot yet provide real-time imaging.

Professor of nanoengineering at UC San Diego and the study’s corresponding author Sheng Xu said: “In the future, we hope to integrate both power and a data processing function into the soft ultrasound probe to enable wireless, real-time imaging and videoing.”

The study was published in the 23 March issue of Science Advances.