Acoustic wave manipulation with artificial metasurfaces

Abstract

Metasurfaces are a family of thin, 2D artificial materials in the subwavelength scales. These engineered surfaces have shown incredible abilities and functionalities in wavefront modulation applications during the last two decades. The effective properties of the metasurface are dictated by structure shape rather than composing material. In these structures, the structure's effective properties such as stiffness and impedance are the function of their shape and pattern. Researchers have designed and built several metamaterials and metasurfaces to realize and target certain properties, which are not easy to find in nature and available material libraries. These new surfaces and materials can be used in many applications and different fields like soft robotics, biomedical imaging, and energy harvesting. In the first part of this work, an acoustic metasurface is proposed, combining the coiling and cavity concepts. It is assumed that the proposed acoustic metasurface has 12 independent geometrical parameters. Then, the effect of each parameter on sound transmission and reflection is investigated, and a design methodology is presented. It is shown that the proposed metasurface can modulate the phase of the incident acoustic wave in a 2-span while preserving its amplitude. This feature enabled the applicability of the proposed acoustic metasurface in designing some structures to redirect, split and focus the incident acoustic wave without losing the wave energy. In the second part of this work, the proposed metasurface is developed to address the problem of simultaneous sound silencing and air ventilation in low frequencies. It is shown that the proposed metasurface reduces the sound transmission up to 18 dB in a broad band while covering low-frequency ranges. The presented numerical studies indicate that the proposed thin acoustic metasurface has an insignificant effect on air ventilation and heat transfer. It is shown that this feature makes the proposed metasurface an ideal case for designing silent spaces. Finally, in the third part of this work, an analytical solution is developed to study and extract the effective properties of acoustic metamaterials from the impedance tube measurements. This solution extends the previous methods and facilitates the study of acoustic metamaterials when the impedance tub and sample do not have the same sizes. It is shown that the proposed solution is able to extract the effective properties of acoustic metamaterials with high accuracies.--Author's abstract