Does material matter in designing better acoustic metasurfaces?

The emerging capabilities of acoustic metasurfaces to control and shape sound waves are attracting a lot of interest for their applications in particle manipulation, holography and architectural acoustics. The metasurfaces, which consist of unit cells of various structural designs, are usually fabricated with 3-D printing of plasticlike materials and some have even been designed for do-it-yourself construction at home. The particular architectural design can tailor the resulting sound profile, but the role of material properties is still not fully understood.

In the Journal of Applied Physics, investigators report numerical computations, based on finite element analysis, of acoustic metasurface models that take into account their constituent material properties. They used model parameters similar to both steel and plastic to investigate the fabrication materials’ role in metasurface performance.

Steel had been assumed to be a better material for fabricating these devices because its acoustic impedance is larger. However, the current study revealed that this is not necessarily the case. Using either steel or plastic can lead to problems if the design is not done properly. If the design is, however, done properly, plastic turns out to be as good a choice as steel. This is good news, since it is much easier to use plastic than steel for 3-D printing of the metasurfaces.

The authors also investigated the role of visco-thermal losses. They found this phenomenon to have a more pronounced effect on the behavior of acoustic metasurfaces than the structural interaction — in other words, the material used — did.

It is still important, however, to incorporate material properties in models to account for structural interaction when designing these metasurfaces. This aspect has been largely ignored until now. In future work, the authors plan to look for ways to make structural interaction useful, rather than merely a hindrance, and to consider the design of more elaborate metasurfaces.

Source: “Investigation of acoustic metasurfaces with constituent material properties considered,” by Nikhil JRK Gerard, Yong Li, and Yun Jing, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5007863 .