Toy-inspired acoustic lens creates 'sound bullets'

Posted By: Staff
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Washington, Apr 22 (ANI): Inspired by a popular executive toy ("Newton's cradle"), researchers at the California Institute of Technology (Caltech) have built a device-called a nonlinear acoustic lens, which produces highly focused, high-amplitude acoustic signals dubbed "sound bullets."hiara Daraio and colleagues crafted their acoustic lens by assembling 21 parallel chains of stainless steel spheres into an array.

Each of the 21 chains was strung with 21 9.5-millimeter-wide spheres. (Daraio says particles composed of other elastic materials and/or with different shapes also could be used.)

The acoustic lens and its sound bullets (which can exist in fluids-like air and water-as well as in solids) have "the potential to revolutionize applications from medical imaging and therapy to the nondestructive evaluation of materials and engineering systems," said Daraio.

The device is similar to the Newton's cradle toy, which consists of a line of identical balls suspended from a frame by wires in such a way that they only move in one plane, and just barely touch one another.

The chains of particles in the new acoustic lens are like a longer version of a Newton's cradle.

In the lens, a pulse is excited at one end by an impact with a striker, and nonlinear waves are generated within each chain.

These chains "are the simplest representation of highly nonlinear acoustic waveguides, which exploit the properties of particle contacts to tune the shapes of the traveling acoustic signals and their speed of propagation, creating compact acoustic pulses known as solitary waves," said Daraio.

The chains are squeezed closer together-or "precompressed"-using fishing line.

By changing the amount of precompression, the researches could vary the speed of the solitary wave.

When a series of those waves exit the array, they coalesce at a particular location-a focal point-in a target material (which can be a gas, like air; a liquid; or a solid).

This superposition of solitary waves at the focal point forms the sound bullet-a highly compact, large-amplitude acoustic wave.

Varying the parameters of the system can also produce a rapid-fire barrage of sound bullets, all trained on the same spot.

"Our lens introduces the ability to generate compact, high-amplitude signals in a linear medium, and also allows us to dynamically control the location of the focal point," said Daraio.

That means it isn't necessary to change any of the geometric components of the lens to change the location of the focal point.

"All we do is adjust the precompression for each chain of spheres," she said. (ANI)

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