Looking to block out noise? Try metamaterials

The world is getting noisier. Cricket chirps are drowned out by car horns and bird songs are overwhelmed by the roar of airplanes. Noise pollution is increasingly linked to poor outcomes for both nature and human health, so researchers are looking into ways to block it out.

Traditional acoustic absorbers often have porous surfaces designed to absorb sound through the friction of air molecules against their surfaces. These materials work well but in some applications the sheer volume needed to sufficiently reduce noise is impractical. Instead, researchers and engineers are looking to metamaterials, which rely on high energy densities to absorb sound and can consequentially be much thinner.

Yang and Sheng presented an overview of acoustic metamaterial absorbers and how they can be used commercially to reduce noise. The researchers described the theoretical basis for the design of such materials as well as examples to highlight their effectiveness.

“The most important takeaway of this article is that the narrow frequency band of resonant acoustic metamaterials can be turned into an advantage in realizing the tunable acoustic absorber,” said author Ping Sheng. “In this case, each resonator serves as a Lego piece in forming an optimal absorption spectrum tailored to the noise spectrum, subject to the constraint of limited space available for the noise reduction application.”

The authors presented the benefits and challenges of using metamaterials in selected commercial applications, and provided perspectives on directions for future research.

“Metamaterial absorbers are already commercialized for airborne sound, and I believe similar applications for underwater acoustics will not be far behind,” Sheng said.

Source: “Acoustic metamaterial absorbers: The path to commercialization,” by Min Yang and Ping Sheng, Applied Physics Letters (2023). The article can be accessed at https://doi.org/10.1063/5.0147941 .