Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Making opaque materials totally transparent

03.07.2018

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.


Sound waves can travel across a complex medium with no distortion.

Credit: @Jamani Caillet / EPFL

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 an 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.

###

References: E. Rivet, A. Brandstötter, K. G. Makris, H. Lissek, S. Rotter and R. Fleury, "Constant-pressure sound waves in non-Hermitian disordered media," Nature Physics, in press (2018).

K. G. Makris, A. Brandstötter, P. Ambichl, Z. H. Musslimani, and S. Rotter, "Wave propagation through disordered media without backscattering and intensity variations", Light Sci. Appl. 6, e17035 (2017).

E. Rivet, "Room modal equalisation with electroacoustic absorbers," EPFL Ph.D. thesis No. 7166, (2016).

Media Contact

Romain Fleury
romain.fleury@epfl.ch
41-216-935-688

 @EPFL_en

http://www.epfl.ch/index.en.html 

Romain Fleury | EurekAlert!
Further information:
http://dx.doi.org/10.1038/s41567-018-0188-7

Further reports about: EPFL Polytechnique acoustic opaque materials sound waves waves

More articles from Materials Sciences:

nachricht Turning up the heat to create new nanostructured metals
21.11.2019 | DOE/Brookhaven National Laboratory

nachricht Small particles, big effects: How graphene nanoparticles improve the resolution of microscopes
20.11.2019 | Max-Planck-Institut für Polymerforschung

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Machine learning microscope adapts lighting to improve diagnosis

Prototype microscope teaches itself the best illumination settings for diagnosing malaria

Engineers at Duke University have developed a microscope that adapts its lighting angles, colors and patterns while teaching itself the optimal...

Im Focus: Small particles, big effects: How graphene nanoparticles improve the resolution of microscopes

Conventional light microscopes cannot distinguish structures when they are separated by a distance smaller than, roughly, the wavelength of light. Superresolution microscopy, developed since the 1980s, lifts this limitation, using fluorescent moieties. Scientists at the Max Planck Institute for Polymer Research have now discovered that graphene nano-molecules can be used to improve this microscopy technique. These graphene nano-molecules offer a number of substantial advantages over the materials previously used, making superresolution microscopy even more versatile.

Microscopy is an important investigation method, in physics, biology, medicine, and many other sciences. However, it has one disadvantage: its resolution is...

Im Focus: Atoms don't like jumping rope

Nanooptical traps are a promising building block for quantum technologies. Austrian and German scientists have now removed an important obstacle to their practical use. They were able to show that a special form of mechanical vibration heats trapped particles in a very short time and knocks them out of the trap.

By controlling individual atoms, quantum properties can be investigated and made usable for technological applications. For about ten years, physicists have...

Im Focus: Images from NJIT's big bear solar observatory peel away layers of a stellar mystery

An international team of scientists, including three researchers from New Jersey Institute of Technology (NJIT), has shed new light on one of the central mysteries of solar physics: how energy from the Sun is transferred to the star's upper atmosphere, heating it to 1 million degrees Fahrenheit and higher in some regions, temperatures that are vastly hotter than the Sun's surface.

With new images from NJIT's Big Bear Solar Observatory (BBSO), the researchers have revealed in groundbreaking, granular detail what appears to be a likely...

Im Focus: New opportunities in additive manufacturing presented

Fraunhofer IFAM Dresden demonstrates manufacturing of copper components

The Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM in Dresden has succeeded in using Selective Electron Beam Melting (SEBM) to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

First International Conference on Agrophotovoltaics in August 2020

15.11.2019 | Event News

Laser Symposium on Electromobility in Aachen: trends for the mobility revolution

15.11.2019 | Event News

High entropy alloys for hot turbines and tireless metal-forming presses

05.11.2019 | Event News

 
Latest News

Scientists first to develop rapid cell division in marine sponges

21.11.2019 | Life Sciences

First detection of gamma-ray burst afterglow in very-high-energy gamma light

21.11.2019 | Physics and Astronomy

Research team discovers three supermassive black holes at the core of one galaxy

21.11.2019 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>