A team of researchers has found a way to make objects invisible using sound waves.
In their study, published in the journal Nature Physics, researchers explained how they used sound waves to make ordinarily opaque objects completely transparent. Their new technology reportedly involves placing acoustic relays at strategic locations so the waves of sound can continuously spread even if there’s an object in their path.
By nature, waves tend to bounce and disperse if they come into contact with any object. This causes the energy waves to scatter in a “highly complex interference pattern,” making them less intense as they move away from the object. Furthermore, this makes transmitting data or energy using wave-scattering media virtually impossible.
However, researchers from Ecole Polytechnique Fédérale de Lausanne in collaboration with TU Wien and the University of Crete have developed a system that could let sound waves travel across such media without any distortion.
To do this, the researchers utilized tiny speakers as acoustic relays to offset the wave scattering. The speakers could be controlled to attenuate, amplify, or change the phase of the sound waves.
“We realized that our acoustic relays had to be able to change the waves’ amplitudes and phases at strategic locations, to either magnify or attenuate them,” Romain Fleury, EPFL’s Laboratory of Wave Engineering head, said in a statement.
“We’ve been working on using controlled speakers as active sound absorbers for years, so it made sense to use them for this new application too,” Hervé Lissek, EPFL’s Signal Processing Laboratory 2 acoustic research group head, added.
The system was tested using a 3.5-meter long air-filled tube that the researchers built. They placed different kinds of obstacles like walls, chicanes, and porous materials into it to create a disordered medium where sound waves won’t be able to pass. They then put their tiny speakers between the obstacles, setting up electronic controls so they could adjust the acoustic properties of the speakers.
“Until now, we only needed to attenuate sound waves. But here we had to develop a new control mechanism so we could also amplify them, like how we can already amplify optical waves with lasers,” Etienne Rivet, co-author of the study, went on to say.
The new technology could one day be used to hide submarines, according to researchers.