New Device Increases Ability to Ricochet Sound Back to its Source

Downtown Raleigh skyline rises up behind the Memorial Belltower. (Credit: North Carolina State University)

An innovative device capable of reflecting sound in the direction it came from, instead of deflecting it at an angle has been built by scientists. The “retroreflector” reflects sound across an operating range of 70 degrees in both directions - more than doubling the operational range of earlier technologies.

“The technology makes use of two engineered materials,” says Yun Jing, an associate professor of mechanical and aerospace engineering at North Carolina State University and co-corresponding author of a paper on the research.

The first layer focuses the incoming sound waves onto a second layer, which then sends the sound waves back to their source. We were inspired by a similar approach used in optics research, but we think we are the first to use this technique in the acoustics field.”

Yun Jing, Co-Author

Earlier methods for developing retroreflective surfaces depended upon rectangular pits arrayed across a material. Sound waves would rebound from the side of the rectangle to the bottom, before ricocheting back in the direction it came from.

Experiments conducted with a prototype of the new technology revealed that it is also fairly efficient. At 0 degrees (when the sound source is perpendicular to the surface), 60% of the sound is reflected back to the source. At 70 degrees (the extreme end of the effective range), 40% of the sound is ricocheted back to the source.

The paper titled “Acoustic planar surface retroreflector” was published in the June 25th issue of the Physical Review Materials journal. The paper’s first author is Gang Yong Song of Southeast University, in Nanjing, China. The paper’s co-corresponding authors are Qiang Cheng and Tie Jun Cui of Southeast University.

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