One-way transmission system for sound waves

Jul 26, 2011
The nonlinearity and asymmetry present in this chain of compressed spheres can transform vibrations of one frequency, applied at one end of the chain, to vibrations with broadband frequency content leading to rectification. The amplitude of the vibrations are shown by the height of the peaks. Credit: Chiara Daraio / Caltech

While many hotel rooms, recording studios, and even some homes are built with materials to help absorb or reflect sound, mechanisms to truly control the direction of sound waves are still in their infancy. However, researchers at the California Institute of Technology (Caltech) have now created the first tunable acoustic diode-a device that allows acoustic information to travel only in one direction, at controllable frequencies.

The mechanism they developed is outlined in a paper published on July 24 in the journal .

Borrowing a concept from electronics, the acoustic diode is a component that allows a current—in this case a sound wave—to pass in one direction, while blocking the current in the opposite direction. "We exploited a physical mechanism that causes a sharp transition between transmitting and nontransmitting states of the diode," says Chiara Daraio, professor of aeronautics and applied physics at Caltech and lead author on the study. "Using experiments, simulations, and analytical predictions, we demonstrated the one-way transmission of sound in an audible frequency range for the first time."

This new mechanism brings the idea of true soundproofing closer to reality. Imagine two rooms labeled room A and room B. This new technology, Daraio explains, would enable someone in room A to hear sound coming from room B; however, it would block the same sound in room A from being heard in room B.

"The concept of the one-way transmission of sound could be quite important in architectural acoustics, or the science and engineering of sound control within buildings," says Georgios Theocharis, a postdoctoral scholar in Daraio's laboratory and a co-author of the study.

The system is based on a simple assembly of elastic spheres—granular crystals that transmit the sound vibrations—that could be easily used in multiple settings, can be tuned easily, and can potentially be scaled to operate within a wide range of frequencies, meaning its application could reach far beyond soundproofing.

Similar systems have been demonstrated by other scientists, but they all feature smooth transitions between transmitting and nontransmitting states instead of the sharp transitions needed to be more effective at controlling the flow of . To obtain the sharp transition, the team created a periodic system with a small defect that supports this kind of quick change from an "on" to an "off" transmission state. According to Daraio, this means the system is very sensitive to small variations of operational conditions, like pressure and movement, making it useful in the development of ultrasensitive acoustic sensors to detect sound waves. The system can also operate at different frequencies of sound and is capable of downshifting, or reducing the frequency of the traveling signals, as needed.

"We propose to use these effects to improve energy-harvesting technologies," she says. "For example, we may be able to scavenge sound energy from undesired structural vibrations in machinery by controlling the flow of sound waves away from the machinery and into a transducer. The transducer would then convert the sound waves into electricity." Daraio says the technology can also shift the undesired frequencies to a range that enables a more efficient conversion to electricity.

The team plans to continue studying the fundamental properties of these systems, focusing on their potential application to energy-harvesting systems. They also believe that these systems may be applicable to a range of technologies including biomedical ultrasound devices, advanced noise control, and even thermal materials aimed at temperature control.

"Because the concepts governing wave propagation are universal to many systems, we envision that the use of this novel way to control energy might enable the design of many advanced thermal and acoustic materials and devices," says Daraio.

Explore further: Defining a national standard for dynamic pressure waves

More information: The Nature Materials paper is titled "Bifurcation-based acoustic switching and rectification."

Related Stories

Graphene meets heat waves

Mar 06, 2015

EPFL researchers have shed new light on the fundamental mechanisms of heat dissipation in graphene and other two-dimensional materials. They have shown that heat can propagate as a wave over very long distances. ...

Phone snooping via gyroscope to be detailed at Usenix

Aug 15, 2014

Put aside fears of phone microphones and cameras doing eavesdropping mischief for a moment, because there is another sensor that has been flagged. Researchers from Stanford and defense research group at Rafael ...

Charging with ultrasound: uBeam has functional prototype

Aug 08, 2014

uBeam on Wednesday announced its first "fully functional prototype," ready to build for consumers. This is a company that on its Careers page tells visitors, "We're on a mission to untether the world," and ...

Recommended for you

Defining a national standard for dynamic pressure waves

8 hours ago

In recent years, the physical damage done by pressure waves – such as traumatic brain injuries from explosives sustained by military personnel in the Middle East – has become an increasingly urgent public ...

User comments : 5

Adjust slider to filter visible comments by rank

Display comments: newest first

Temple
5 / 5 (1) Jul 27, 2011
Why have I never heard of this technology before?
Jimbaloid
5 / 5 (1) Jul 27, 2011
Why have I never heard of this technology before?

Because you were in Room B!
A_Paradox
5 / 5 (1) Jul 27, 2011
Because you were in Room B!


High five Jimbaloid! :-)
Temple
5 / 5 (1) Jul 28, 2011
My joke was better. ;)
hush1
5 / 5 (1) Aug 03, 2011
lol
Best thread award.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.