World's first acoustic hyperlens could improve sonar devices

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Washington, October 26 (ANI): Researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory have developed the world's first acoustic hyperlens, which could lead to a big improvement in ultrasound and underwater sonar devices.

The acoustic hyperlens provides an eightfold boost in the magnification power of sound-based imaging technologies.

Clever physical manipulation of the imaging sound waves enables the hyperlens to resolve details smaller than one sixth the length of the waves themselves, bringing into view much smaller objects and features than can be detected using today's technologies.

The key to this success is the capturing of information contained in evanescent waves, which carry far more details and higher resolution than propagating waves but are typically bound to the vicinity of the source and decay much too quickly to be captured by a conventional lens.

"We have successfully carried out an experimental demonstration of an acoustic hyperlens that magnifies sub-wavelength objects by gradually converting evanescent waves into propagating waves," said Xiang Zhang, a principal investigator with Berkeley Lab's Materials Sciences Division and director of the Nano-scale Science and Engineering Center at the University of California, Berkeley.

"Our acoustic hyperlens relies on straightforward cutoff-free propagation and achieves deep subwavelength resolution with low loss over a broad frequency bandwidth," he added.

Zhang and his co-authors fashioned their acoustic hyperlens from 36 brass fins arranged in the shape of a hand-held fan.

Each fin is approximately 20 centimeters long and three millimeters thick.

The fins, embedded in the brass plate from which they were milled, extend out from an inner radius of 2.7 centimeters to an outer radius of 21.8 centimeters, and span 180 degrees in the angular direction.

"As a result of the large ratio between the inner and outer radii, our acoustic hyperlens compresses a significant portion of evanescent waves into the band of propagating waves so that the image obtained is magnified by a factor of eight," said co-author Fok, a graduate student in Zhang's lab.

"We chose brass as the material for the fins because it has a density about 7,000 times that of air, a large ratio that is needed to achieve the strong anisotropy required for a flat dispersion of the sound waves," Fok added.

The current version of the acoustic hyperlens successfully produced 2-D images of objects down to 6.7 times smaller than the wavelength of the imaging sound wave.

Now, Zhang and his team are up-grading their technique to produced 3-D images.

They are also working to make their acoustic hyperlens compatible with pulse-echo technology, which is the basis of both medical ultrasounds and underwater sonar imaging systems. (ANI)

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