by Staff Writers
Beijing, China (SPX) May 08, 2017
Researchers at the Institute of Acoustics (IOA) of the Chinese Academy of Sciences have designed and fabricated an underwater acoustic carpet cloak using transformation acoustics, a scientific first.
An acoustic cloak is a material shell that can control the propagation direction of sound waves to make a target undetectable in an acoustic system. The carpet cloak modifies the acoustic signature of the target and mimics the acoustic field obtained from a reflecting plane, so that the cloaked target is indistinguishable from the reflecting surface.
The field of transformation acoustics focuses on the design of new acoustic structures. It shows how to control the propagation of acoustic waves. The parameters of the cloak shell can be given by transformation acoustics.
However, in most cases, these parameters are too complex for practical use. To solve this problem, YANG Jun and his IOA team adopted a scaling factor and simplified the structure of the carpet cloak with only modest impedance mismatch.
The research team then used layers of brass plates featuring small channels filled with water to construct the model cloak. This material possesses effective anisotropic mass density in long-wavelength regimes.
The structure of the carpet cloak, comprised of layered brass plates, is therefore simplified at the cost of some impedance match. "The carpet cloak has a unit cell size of about 1/40 of the wavelength, making it able to control underwater acoustic waves in the deep subwavelength scale," said YANG Jun.
The proposed carpet cloak has shown good performance in experimental results across a wide frequency range. In tests, a short Gaussian pulse propagates towards a target bump covered with the carpet cloak; the scattered wave then returns in the backscattering direction. The cloaked object successfully mimics the reflecting plane and is imperceptible to sound detection.
Previously, the IOA researchers had designed and fabricated a carpet cloak in air. The results of this earlier research were published in the Journal of Applied Physics (Volume 113, Issue 2, January 2013).
The research was published online in Scientific Reports on April 6. Research paper
Washington (UPI) May 2, 2017
Raytheon has received a contract modification for $327.1 million for the low-rate production of the Air and Missile Defense Radar system. The contract will cover the procurement of three initial systems, including the equipment and engineering systems needed to produce, the Department of Defense announced Monday. The systems will be completed at a plant in Marlborough, Mass., and are ex ... read more
Chinese Academy of Sciences Headquarters
Space Technology News - Applications and Research
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