Synopsis: Sound Switch

A novel type of acoustic metamaterial made of rubber and metal absorbs or transmits sound waves, depending on how the material is squeezed.
Synopsis figure
P. Wang et al., Phys. Rev. Lett. (2014)

Acoustic metamaterials are composite systems that can be used to control the propagation of sound waves in ways impossible with natural materials, with potential applications in noise reduction and in “stealth” technologies. A new design, combining an elastic matrix, structural elements, and metallic cores, features an adjustable acoustic response that can be tuned through squeezing. Experiments with this metamaterial—detailed in Physical Review Letters—show that it behaves like a switch that blocks or lets pass a certain band of sound frequencies, depending on how much it is squeezed.

Similarly to optical metamaterials, acoustic metamaterials combine structural elements that tailor the propagation of waves thanks to band gaps—frequency ranges of strong attenuation. Currently, most acoustic metamaterial configurations are passive and operate at fixed frequencies. But the ability to make them tunable would boost the spectrum of possible applications.

Katia Bertoldi and her colleagues from Harvard University have developed a new tuning strategy based on the mechanical deformation of the structure as a whole. Their acoustic metamaterial is a 50-millimeter-thick silicon rubber block perforated with an array of holes. Inside each hole is a copper core, held in place by four elastic beams. As shown in simulations and experiments, the core-beam microstructures act as acoustic resonators that absorb sound waves with frequencies around 100 hertz. However, when the system is compressed by a few percent in the vertical direction, the elastic beams buckle, causing the resonant absorption band to drop in frequency. When further squeezed, the metamaterial no longer absorbs sound waves at all, like a switch being flipped open. An acoustic switch could play a role in smart systems for vibration/noise reduction, guiding of sound waves, frequency modulation, as well as acoustic imaging. – Michael Schirber


More Announcements »

Subject Areas


Previous Synopsis

Particles and Fields

Gluons Chip in for Proton Spin

Read More »

Next Synopsis

Atomic and Molecular Physics

Simple Molecules for Accurate Clocks

Read More »

Related Articles

Synopsis: Enter the Metacage

Synopsis: Enter the Metacage

An array of equally spaced nanowires, dubbed a metacage, could block optical radiation from entering or escaping a region of arbitrary shape. Read More »

Synopsis: Connecting Qubits with Sound
Quantum Information

Synopsis: Connecting Qubits with Sound

Surface acoustic waves may work as a “quantum bus” that carries information to different parts of a quantum computer. Read More »

Synopsis: The Helical Factor

Synopsis: The Helical Factor

An array of helical elements absorbs radiation of a certain frequency while casting no shadow in light over a range of other frequencies. Read More »

More Articles