Acoustic meta-material: a shape that reflects sound but passes light and air

A Boston University team have developed an acoustic, 3D-printed metamaterial whose topology is such that it reflects 94% of human-audible sound; the researchers' demonstration involves inserting a ring of this stuff in a PVC pipe and blasting a speaker down one end: light and air emerges from the other end, but sound does not.

The metamaterial is in contrast to traditional acoustic insulation materials, which absorb sound and convert it to heat energy; this material actualy reflects the sound back.

The researchers muse that their invention could be used to dampen sound from HVAC systems, drones, MRIs, and other hard-to-manage sources of unpleasant sound and noise pollution.

Ghaffarivardavagh and Zhang also point to the unsightliness of the sound barriers used today to reduce noise pollution from traffic and see room for an aesthetic upgrade. "Our structure is super lightweight, open, and beautiful. Each piece could be used as a tile or brick to scale up and build a sound-canceling, permeable wall," they say.

The shape of acoustic-silencing metamaterials, based on their method, is also completely customizable, Ghaffarivardavagh says. The outer part doesn't need to be a round ring shape in order to function.

"We can design the outer shape as a cube or hexagon, anything really," he says. "When we want to create a wall, we will go to a hexagonal shape" that can fit together like an open-air honeycomb structure.

Ultra-open acoustic metamaterial silencer based on Fano-like interference [Reza Ghaffarivardavagh, Jacob Nikolajczyk, Stephan Anderson, and Xin Zhang/Phys Rev] (Sci-Hub Mirror)

Scientists have discovered a shape that blocks all soundeven your co-workers [Mark Wilson/Fast Company]

BU researchers develop 'acoustic metamaterial' that cancels sound [Boston University/Eurekalert]

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