A team of scientists from the Universitat Politècnica de València present the design of a structured material supporting complete absorption of sound with a broadband response and functional for any direction of incident radiation. The structure which is fabricated out of porous lamellas is arranged into a low-density crystal and backed by a reflecting support. Experimental measurements show that strong all-angle sound absorption with almost zero reflectance takes place for a frequency range exceeding two octaves. The researchers demonstrate that lowering the crystal filling fraction increases the wave interaction time and is responsible for the enhancement of intrinsic material dissipation, making the system more absorptive with less material.
"Our study tackles one of the most important problems of society today from a new point of view: the design of materials and surfaces able to significantly reduce noise. In view of the results, we believe we have taken an important step toward the perfect absorber. And that has been done just by reconfiguring a known material," says Víctor Sánchez-Morcillo, researcher at the Campus de Gandia of the Universitat Politècnica de València and director of the Master's Degree in Acoustic Engineering, taught at this campus.
The key to understanding this reaction is the following: the new configuration of the material, in periodically distributed panels, allows sound waves to easily enter the material and increases the interaction between it –the wave- and the structure, thereby increasing the absorption.
As for its possible applications, Víctor Sánchez says that the study's conclusions open a new way to design new noise reduction solutions such as the development of new baffles to reduce noise pollution caused by roads, railways, etc.