Exceptional points for sound control with non-Hermitian acoustic metasurfaces

Sponsor: NSF CMMI

This project focuses on creating a new class of non-Hermitian diffractive acoustic metasurfaces. Acoustic metasurfaces are thin artificial materials that can control sound waves. These two-dimensional materials are empowered with extraordinary control over the reflected and transmitted sound, which enables the unprecedent shaping of acoustic wavefronts. This research establishes analogies between non-Hermitian quantum mechanics and acoustics that would result in a paradigm shift in the design of acoustic metasurfaces. The project will broadly advance the field of acoustic metasurfaces through discovering new mechanisms for designing materials with novel functionalities, which will have applications in noise control, architectural acoustics, and communication. The outcome of this research will also encourage future fundamental research where acoustics could serve as a platform to materialize quantum mechanics concepts.

Composite honeycomb metasurface panel for broadband sound absorption

We have recently developed a novel honeycomb composite panel [1] that entails minimum modifications of the conventional honeycomb panel, while drastically improving its sound absorption for low-frequency noise. Our design exploits a perforated face-sheet with non-uniform but periodically arranged pores (Fig.  1(a)). Our preliminary study on a prototype reveals that this seemingly trivial change on the face-sheet can significantly increase the sound absorption of the honeycomb composite panel to over 90% (100% being perfect absorption) over 600-1000 Hz, therefore considerably improving the noise-reduction performance. (Fig.  (b)) Remarkably, this excellent noise-reducing performance is achieved at a thickness of 30 mm which is only 1/20 of the largest working wavelength, meaning such a novel material only occupies a small space. This is a crucial advantage for applications where space is extremely limited, such as in automobile and aircrafts. Briefly, this excellent sound absorption arises due to unit cells (each with a different pore size) working synergistically and collectively through their mutual acoustic coupling effects. Our technology could potentially revolutionize the way noise is reduced in automobiles, aircrafts, and other places where noise is of significant concern and could have far-reaching environmental and economic impacts. Furthermore, our technology, when applied to reducing aircraft engine noise, could lower airlines’ expenditure on landing fees at airports (a recurring expense), increase fleet flexibility and reduce the noise pollution in residential areas. Our technology can also be used to solve noise problems beyond those in the transportation sector, such as to reduce HVAC noise.

Fig. 1

[1] X. Peng, J. Ji, and Y. Jing, “Composite honeycomb metasurface panel for broadband sound absorption,” J. Acoust. Soc. Am., vol. 144, no. 4, pp. EL255–EL261, Oct. 2018, doi: 10.1121/1.5055847.