The best part is that they used conventional porous materials already common in the construction industry. No expensive metamaterials or mathematical wizardry.
The researchers demonstrated how the structure achieves extraordinary sound absorption using what might seem like a contradictory strategy - the sound attenuation increases when the quantity of absorbent material is reduced, so a totally reflective surface becomes a perfect absorbent despite the fact that, for the most part, there is no material that absorbs sound.
The key to understanding the reaction: 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, it 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.
“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.
All the experimental development of this work has been done at the Campus de Gandia of the Universitat Politècnica de València, a center with a wide research and teaching experience related to acoustics.
Citation: J. Christensen, V. Romero-García, R. Picó, A. Cebrecos, F. J. García de Abajo, N. [parcial]Picó, A. Mortensen, M. Willatzen, Christensen, V. J. Sánchez-Morcillo, 'Extraordinary absorption of sound in porous lamella-crystals', Scientific Reports 4, doi:10.1038/srep04674