Scientists Demonstrate New Possibilities For Soundproofing
Scientists believe they have developed plans for new technology that could make sound proof homes a reality.
Reported in the New Journal of Physics, the blueprints for an “acoustic cloak” could make objects impervious to sound waves.
“The mathematics behind cloaking has been known for several years," said Professor John Pendry of Imperial College London, UK, an expert in cloaking.
"What hasn’t been available for sound is the sort of materials you need to build a cloak out of."
Scientists had previously showed that objects could be cloaked from microwaves, rendering them “invisible”.
Now a Spanish research team believe the key to the sound proof device can be found in so-called “sonic crystals”.
These artificial composites – also known as "meta-materials" – can be engineered to produce specific acoustical effects.
"Unlike ordinary materials, their acoustic properties are determined by their internal structure," Professor Pendry said.
These would be used to channel any sound around an object, like water flowing around a rock in a stream.
"The idea of acoustic cloaking is to deviate the sounds waves around the object that has to be cloaked," said Jose Sanchez-Dehesa of the Polytechnic University of Valencia, one of the researchers behind the new project.
Dr. Sanchez-Dehesa believes a material made of tiny cylinders would achieve this effect.
Simulations showed that 200 layers of this metamaterial could effectively shield an object from noise.
Thinner stacks would shield an object from certain frequencies.
"The thickness depends on the wavelength you want to screen," he said.
Researchers, such as Professor Pendry, believe the initial work is already an important first step.
"It’s not an unrealistic blueprint – it doesn’t demand that we do extraordinary things," he said. "This is something that can easily be manufactured."
Researchers believe if such a device existed, it would be practical in many situations, such as creating materials to soundproof houses or to enhance acoustics in concert halls.
There may also be military applications for the device. Researchers believe the technology could be used to conceal submarines from sonar detection.
However, the material may need to be optimized first.
"You don’t want to wrap a submarine in something that is heavy and several inches thick," said Professor Pendry. "It would add quite a lot to the Navy’s fuel bill, I think."
Earlier this year, independent teams of scientists from Duke University and the Hong Kong University of Science and Technology demonstrated the mathematics necessary to create an acoustic cloak.
Also, in 2006, a team of scientists from Duke University used a metamaterial consisting of 10 fiberglass rings covered with copper elements to deflect the microwaves around the object and restore them on the other side.
Other researchers hope to build the holy grail of cloaking: an invisibility device that would channel light at wavelengths normally visible to the eye.
However, this technology is in a more primitive state, according to Dr Sanchez-Dehesa.
"We believe the acoustic cloak is more feasible than a similar device for light," he said.
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Image Caption: A working device could be used to enhance the acoustics of concert halls
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