Scientists have designed an acoustic metamaterial, which allows air to pass through, but cuts off sounds of a given frequency, the invention they describe in an article posted in the electronic library of Cornell University.
the Sound is always propagated in any medium, such as water or air. San-Hoon Kim (Sang-Hoon Kim) from State Maritime University of Mokpo city and son Hyun Lee (Seong-Hyun Lee) from the Korea Institute of machinery and materials in Daejeon were able to separate the sound waves from the air and to extinguish them.
Their “zvukopronitsaemost” it consists of two transparent plastic panels, the space between which is divided into many compartments-resonators. To direct sound waves in resonators help made holes in them.
Scientists have achieved negative values of the bulk modulus of the resonators. This parameter determines how much the material resists compression. Items with negative modulus increases in response to pressure. In nature they don't exist. However, Korean scientists have designed the resonators so that the sound waves resonating inside, resisting the pressure of the same sound waves from the outside, and the sound wave is damped.
However, this metamaterial is designed not for total soundproofing, and for clipping waves of certain frequencies. The frequencies that will “work” window, depend on the parameters of resonators that can be configured. Scientists created the prototype reduces the volume of high frequency sounds 700-2200 Hz, which roughly corresponds to human speech, in 100-3162 time (20-35 dB).
the Scientists believe that their invention can be used to trim unwanted sounds in the total noise picture. For example, if any high pitched sounds disturbing to enjoy the sea, the window can “cut” them and leave only the sound of the sea. The inventors believe their design will work in the water, absorbing the noise of industrial plants, which affects fish and other sea animals.
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