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Invisibility is perhaps one of the most intriguing of notions that have captured our imagination.
Shu Zhang, Chunguang Xia, and Nicholas Fang from the University of Illinois at Urbana-Champaign, report the successful design and realization of an acoustic cloak for underwater ultrasound. This metamaterial cloak is constructed with a network of acoustic circuit elements, namely, serial inductors and shunt capacitors. Metamaterials are artificially structured materials whose patterns and shapes give it properties those materials might not otherwise have.
The acoustic cloak can bend ultrasound waves around an area so that anything inside that area becomes "invisible." The cloak is effective for a broad frequency range with low loss due to reduced scattering and shadow.
Image credit: Shu Zhang The acoustic cylindrical cloak for ultrasound waves is the size of a DVD. The larger grooves act as shunt capacitors, while the narrow channels connecting the grooves act as serial inductors.
"Invisibility cloak for ultrasonic waves," Physics. 4, 2 (2011)
"Broadband Acoustic Cloak for Ultrasound Waves," Phys. Rev. Lett. 106, 024301 (2011)