Planes, trains, and automobiles — as well as many other machines in our world — make noise. Enclosing the engines of these machines with specially designed materials could help reduce acoustic pollution. Kheybari et al. realized a tunable metamaterial that can simultaneously block sound waves and mechanical vibrations in all directions.

Metamaterials are made of repeating arrangements of unit cells. The authors’ design uses air chambers connected by narrow slits to control sound, and elastic regions to control vibrations. Through simulation and experiment, they found applying a load to this metamaterial changes the unit cells’ shape, which can shift the attenuated frequency ranges for sound and vibrations independently.

“When you are designing a product or picking a material, you want to pack as many functionalities as possible in as small of a space as possible,” said author Osama R. Bilal. “One of the reasons we are excited about this material is that it can control both airborne sound and mechanical vibrations while being adjustable in operational frequency.”

This type of tunable material means users can alter which frequencies are blocked after the material is incorporated in a device. The authors hope this work brings tunable materials closer to “built-in intelligence” applications, in which these materials would sense the need to block a certain frequency of sound or vibration and then do it.

Next, they will test this material outside of the lab.

“We showed that it works in experiments, which is great, but we want to implement this in real products and see it impacting our society at large,” Bilal said. “With everything going on, it is time for a quieter world.”

Source: “Tunable auxetic metamaterials for simultaneous attenuation of airborne sound and elastic vibrations in all directions,” by Majid Kheybari, Chiara Daraio, and Osama R. Bilal, Applied Physics Letters (2022). The article can be accessed at

This paper is part of the Acoustic and Elastic Metamaterials and Metasurfaces Collection, learn more here.