A new acoustic cloak can make objects invisible to SONAR.
Led by mechanical science and engineering professor Nicholas Fang, Illinois researchers have demonstrated an acoustic cloak, a technology that renders underwater objects invisible to sonar and other ultrasound waves.
The cloak is made of metamaterial, a class of artificial materials that have enhanced properties as a result of their carefully engineered structure.
A two-dimensional cylindrical cloak made of 16 concentric rings of acoustic circuits is structured to guide sound waves. Each ring has a different index of refraction, meaning that sound waves vary their speed from the outer rings to the inner ones.
The acoustic circuits actually bend the sound waves around the outer layers of the cloak so that the object within is no longer detectable.
An advantage of the acoustic cloak is its ability to cover a broad range of sound wavelengths. The cloak offers acoustic invisibility to ultrasound waves from 40 to 80 KHz, although with modification could theoretically be tuned to cover tens of megahertz.
Researchers at Duke University have been working on a similar device for microwaves and Japanese researchers have demonstrated optical invisibility cloaking devices.
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