Acoustic metamaterial can focus sound like a lens

Technology News |
By Christoph Hammerschmidt

Researchers at the universities of Sussex and Bristol have unveiled how the practical laws used to design optical systems can also be applied to sound through acoustic metamaterials The research has been presented at the ACM CHI Conference on Human Factors in Computing Systems.

The researchers have demonstrated the first dynamic metamaterial device with the zoom objective of a varifocal for sound. The project team have also built a collimator, capable of transmitting sound as a directional beam from a standard speaker.

The breakthrough has the potential to revolutionise the entertainment industry as well as many aspects of communication in public life by creating directional speakers that can reach out to an individual in a crowd.

Acoustic metamaterials are normal materials, like plastic or paper or wood or rubber, but engineered so that their internal geometry sculpts the sound going through. The idea of acoustic lenses has been around since the 1960s and acoustic holograms are starting to appear for ultrasound applications, but this is the first time that sound systems with lenses of practical sizes, similar to those used for light, have been explored.

The technology takes everyday materials like glass, wood and 3D printer plastic and engineers them to control, direct, and manipulate waves in uncommon ways, transforming metasurfaces into behaving like converging lenses for sound.

Metamaterials are smaller, cheaper and easier to manufacture than phased arrays and can even be fabricated in recyclable materials. Metamaterial devices also lead to less aberrations than speaker arrays, even over limited bandwidths.

Using a single speaker, it will be possible to deliver alarms to people moving in the street, like in the movie Minority Report. Using a single microphone, the technology can be used to listen to small parts of a machinery to decide everything is working fine.

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