EPFL researchers have found a way to make materials that are normally opaque to sound waves completely transparent. Their system involves placing acoustic relays at strategic locations so that sound waves can propagate at a constant amplitude – regardless of what may lie in their path. This method could eventually be used to make it possible to hide objects like submarines.
Most naturally occurring materials have a disordered atomic structure that interferes with the propagation of both sound and electromagnetic waves. When the waves come into contact with these materials, they bounce around and disperse – and their energy dissipates according to a highly complex interference pattern, diminishing in intensity. That means it’s virtually impossible to transmit data or energy intact across wave-scattering media and fully leverage the potential of wave technology.
For an example, you need look no further than your smartphone – the geolocation function works less well inside buildings where radiofrequency waves scatter in all directions. Other potential applications include biomedical imaging and geological surveying, where it’s important to be able to send waves across highly disordered media.
A team of researchers from two labs at EPFL’s School of Engineering, working in association with TU Wien and the University of Crete, has developed a system that allows sound waves to travel across such media with no distortion. It uses tiny speakers as acoustic relays to offset the wave scattering, and has been successfully tested on a real acoustic system. Their work has just been published in Nature Physics.
Using speakers to eliminate obstacles
In the researchers’ system, the tiny speakers can be controlled to amplify, attenuate or shift the phase of the sound waves. That lets them offset the diffusion that results when the waves hit obstacles, and thereby reproduce the original sound exactly on the other side of the disordered medium.
How does it work? “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,” says Romain Fleury, head of EPFL’s Laboratory of Wave Engineering (LWE) and a co-author of the study.
The researchers tested their system by building a 3,5 meters long air-filled tube and placing various kinds of obstacles such as walls, porous materials and chicanes into it, in order to create a highly disordered medium through which no sound waves could pass. They then placed their tiny speakers between the obstacles and set up electronic controls to adjust the speakers’ acoustic properties. “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,” says Hervé Lissek, head of the acoustics research group at EPFL’s Signal Processing Laboratory 2 (LTS2) and a co-author of the study. “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,” adds Etienne Rivet, another co-author at EPFL who wrote a thesis on the subject. Their new method – the only one of its kind in acoustics – uses programmable circuits to control several speakers simultaneously and in real time.
Making objects invisible
The researchers’ method for active acoustic control is similar to that used in noise cancelling headphones and could potentially be used for sounds containing common ambient frequencies. It could also be used to eliminate the waves that bounce off objects like submarines, making them undetectable by sonar. Moreover, the theory underlying their work is universal and could have parallel applications in optics or radiofrequencies, to make objects invisible or to take images through opaque materials.
The Latest on: Acoustic invisibility cloak
via Google News
The Latest on: Acoustic invisibility cloak
- World's first 3D acoustic cloaking device created on March 11, 2019 at 5:00 pm
Metamaterials are already being used to create invisibility cloaks and "temporal cloaks," but now engineers from Duke University have turned metamaterials to the task of creating a 3D acoustic cloak. ... […]
- 3D metamaterials on January 30, 2019 at 4:00 pm
mechanical and acoustic, and transport metamaterials. We leave out designed inhomogeneous metamaterial distributions, which, for example, enable invisibility cloaks and counterparts thereof, as this ... […]
- Plasmonic metamaterials: From microscopes to invisibility cloaks on December 22, 2018 at 3:53 pm
and even an invisibility cloak. In a Perspectives piece in this week's issue of the journal Science ("Low-Loss Plasmonic Metamaterials"), Caltech's Harry Atwater and Purdue University colleague ... […]
- Scientists twist sound with metamaterials on December 22, 2018 at 3:52 pm
In the journal Applied Physics Letters ("Broadband field rotator based on acoustic metamaterials"), the team ... with fascinating wave-control capabilities such as invisibility or illusion cloaks," ... […]
- A step closer to Star Trek-style cloaking device on May 12, 2018 at 6:01 am
Scientists have developed a material that makes an underwater object invisible to sonar detectors, an advance that brings us a step closer to Star Trek-style invisibility cloaks ... steps to make ... […]
- Scientists Made a Working Invisibility Cloak (But There's a Catch) on May 10, 2018 at 8:30 am
Whether the invisibility cloak in Harry Potter, the cloaking device in Star Trek, or the various government agencies investing in invisibility R&D, humans have long fantasized about technology capable ... […]
- Creating Harry Potter-style invisibility cloaks that hide objects from sound on March 28, 2018 at 4:51 am
which could lead to improved acoustic technology, including better imaging under water, and biomedical applications, such as better imaging of tissue. Cloaking is sort of synonymous with invisibility, ... […]
- Creating Invisibility Cloaks that Hide Objects from Sound on March 27, 2018 at 7:49 am
Using his own version of Harry Potter's cloak of invisibility, Rutgers professor Andrew Norris ... which could lead to improved acoustic technology, including better imaging under water, and ... […]
- The world’s first acoustic invisibility cloak has been created by Duke University on December 20, 2017 at 5:14 am
Duke University has built the first 3D omnidirectional acoustic invisibility cloak. The cloaking device, which takes the form of a pyramid of perforated plastic, is hidden from sound waves striking it ... […]
via Bing News