Metamaterial bends sound waves to create loudspeakers only you can hear

Nothing is more annoying than having to listen to someone else’s music when you are trying to do something else. Whether it’s your neighbours having another party or someone blasting music too loud in a public space, it can lead to a lot of frustrations. To combat this problem, researchers at the Universities of Sussex and Bristol have developed a 3D printed metamaterial that can control sound by bending sound waves.

The material consists of 3D printed stacked bricks the size of a fingernail. These bricks coil up space and act to slow down sound. Because of this, the incoming sound waves can be accurately directed to a specific area, meaning that only a person in this spot can hear it.

Each brick has a labyrinth structure that is carefully designed to delay the time it takes for sound to go through the structure. When sound waves enter the brick on one side, it has to go through a maze of obstacles inside the labyrinth structure, before coming out on the other side.

Depending on the set of bricks used, the time delay can be varied. By assembling a mosaic of bricks, the desired sound field can be designed.

As any metamaterial, it is not the actual material that determines the material properties, but rather the structure. Hence, any rigid material can be used to create the sound blocks. The researchers used a polymer.

Large versions of the metamaterial could be used to direct or focus sound in a particular location to form an audio hotspot, while smaller versions could be used to destroy tumours deep inside the body using high intensity ultrasound.

The researchers suggest that one day, you could design your own sound barrier with the bricks as a sort of Lego acoustics kit.

Photos: Universities of Sussex and Bristol