New underwater acoustic invisibility cloak. Free Technical Library News

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New underwater acoustic invisibility cloak

19.05.2018

A team of researchers from the University of Pennsylvania has developed a concealment device that works effectively underwater. This new "metamaterial invisibility cloak" is able to intercept and refract acoustic waves propagating under water, which probe the surrounding space with sonars. At the same time, all this happens without the slightest reflection or scattering of sound waves, due to which the sonar will not be able to know that any object is within its reach.

We remind our readers that metamaterials are artificial materials with a complex structure and structure of their surface, due to which they have properties that are completely absent from any materials of natural origin. Typically, metamaterials are composite materials based on various metals, ceramics, and plastics.

In the case of an underwater acoustic invisibility cloak, the problem of creating an effective concealment device is complicated by the fact that water is denser and less compressible than air, which limits the number of possible options. The material of the new invisibility cloak consists of cells whose dimensions are smaller than the wavelength of acoustic vibrations. After testing various options, the researchers settled on a device in the form of a pyramid, 90 centimeters high, made of metal plates perforated in a special way.

The tests of the device were carried out in a tank filled with water, equipped with a source of sound waves with a frequency of 7 to 12 thousand Hertz and a variety of hydrophones that controlled the entire picture of sound vibrations in the tank. It was found that the pyramid still reflected sound waves back, however, the phase, amplitude and some other parameters of the sound waves did not correspond to the parameters of the waves reflected from the surface of an object. And this, in turn, makes it impossible for the normal operation of instruments such as sonar.

According to the researchers, the technology they have developed, in addition to its use as sonar hiding devices, has a number of possible applications. And such areas, first of all, include long-range underwater communications, the operation of which is based on acoustic range signals.

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