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Most natural materials have a disordered atomic structure that interferes with the propagation of sound and electromagnetic waves. When the waves come into contact with these materials, they bounce off and disperse – and their energy dissipates in a very complex pattern of interference, the intensity of which decreases. This means that it is virtually impossible to transmit data or untouched energy through broadcast media and take full advantage of the potential of wave technology.
For example, you do not need to watch your smartphone. where radiofrequency waves disperse in all directions. Other potential applications include biomedical imaging and geological study, where it is important to be able to send waves through highly disordered media.
A team of researchers from two EPFL laboratories, in badociation with TU Wien and the University of Crete, developed a system that allows sound waves to travel through such media without distortion. It uses tiny speakers as acoustic relays to compensate for wave diffusion, and has been successfully tested on a true acoustic system. Their work has just been published in Nature Physics .
Using Speakers to Remove Obstacles
In the researchers' system, tiny speakers can be controlled to amplify, attenuate, or shift the phase of sound waves. This allows them to compensate for the diffusion that occurs when the waves hit obstacles, thus reproducing the original sound exactly on the other side of the messy medium.
How does it work? "We realized that our acoustic relays should be able to modify the amplitudes and phases of the waves at strategic locations, either to amplify or to attenuate them," explains Romain Fleury, head of the Wave Engineering Laboratory (LWE) and co-ordinator. author.
Researchers tested their system by building a tube filled with air and placing various types of obstacles such as walls, porous materials and baffles, to create a highly messy environment at through which no sound wave could pbad. They then placed their tiny speakers between the obstacles and set up electronic controls to adjust the acoustic properties of the speakers. "We have been working for years to use loudspeakers controlled as absorbers of its badets, so it makes sense to use them for this new application," says Hervé Lissek, head of the Sound Processing Group at Signal Processing Laboratory 2 (LTS2). from EPFL. and a co-author of the study. "Until now, we only needed to attenuate the sound waves, but we had to develop a new control mechanism in order to amplify them, as we can already amplify the optical waves with lasers," he adds. Etienne Rivet, another co-author. EPFL who wrote a thesis on the subject. Their new method – unique in acoustics – uses programmable circuits to control multiple speakers simultaneously and in real time.
Making Objects Invisible
The Researchers' Method for Active Acoustics The control is similar to that used in hearing aids and could potentially be used for sounds containing ambient frequencies municipalities. It could also be used to eliminate waves that bounce off objects like submarines, making them undetectable by sonar. In addition, the theory underlying their work is universal and could have parallel applications in optics or radiofrequency, to make objects invisible or to take images through opaque materials
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