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Sound shifters!

NSF-funded researchers at Duke University have discovered how uniquely shaped artificial or metamaterial can control the transmission, redirection and reflection of sound waves with almost perfect efficiency. Made of 3-D printed plastic, itís not the plasticsí properties but the actual shapes of the metamaterialís structural features as well as the space around them, that allow it to manipulate sound waves. So think of someone blowing air across the top of a glass bottle-the pitch the bottle makes depends on how much liquid is in the bottle. Similarly, as a sound wave travels through the structure, each column resonates at a different frequency depending on how much of it is filled in with plastic. As a sound wave travels through the device, each cavity resonates at its prescribed frequency. This vibration not only affects the speed of the sound wave but interacts with its neighboring cavities to influence both transmission and reflection. The team used this mechanism to manipulate the sound in the desired direction and also limit any redirection in unwanted paths.
They hope to transfer these ideas to the manipulation of sound waves in water to improve applications like sonar. For more information:

Credit: Steve Cummer & Junfei Li, Duke University

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