Acoustic Metamaterials: A Review of Theories, Structures, Fabrication Approaches, and Applications

Abstract

Acoustic metamaterials (AMs), which are materials composed of subwavelength periodic artificial structures with specific designs, have drawn significant research attention. This is because of the extraordinary abilities of AMs to manipulate acoustic waves compared with those of traditional acoustic materials. In this review, current advances in AM research are comprehensively investigated and summarized. First, major theories regarding AMs, including the acoustic wave equation, crystal lattice and energy band theory, effective medium theory, and general Snell's law, are explained in detail. Existing AM structures are then described and divided into several categories based on their structural characteristics and responses to acoustic waves. Furthermore, to bridge the gap between design and practical application, both conventional and advanced AM manufacturing methods are summarized. The applications of AMs in the fields of acoustic cloaking, acoustic lensing, acoustic absorption, noise reduction, and supernormal sound transmission are particularly delineated. Finally, contemporary challenges, trends, and strategies relevant to AMs are discussed. This review aims to provide a comprehensive collection of AM‐related knowledge, including information regarding physical theories, structures, fabrication approaches, and applications, which will help promote the further development of AMs.

Acoustic wave propagation in permeable lossy metamaterials

“…Metamaterials are artificially structured materials with atypical effective parameters that are primarily determined by the metamaterials' microstructure instead of chemical composition. Research on acoustic metamaterials, reviewed in [1][2][3], has rapidly grown since the works by Liu et al [4] and Fang et al [5] who reported, respectively, acoustic metamaterials exhibiting negative real part of the effective density and compressibility in a narrow frequency band. In both cases, this is due to the resonant behavior of the metamaterial constituents; with consequences being the existence of sub-wavelength bandgaps (i.e.…”

“…Hence, the unconventional acoustic behavior is confined to narrow frequency bands. While this limitation could, at least in part, be overcome by visco-thermal losses, it is known that excessive losses can deteriorate the performance of acoustic metamaterials (see, e.g., [3,38]). This clearly points out the need to properly account for losses in the modelling of acoustic metamaterials.…”

Progress of low-frequency sound absorption research utilizing intelligent materials and acoustic metamaterials

“…[8][9][10] New physical mechanisms, other than viscous dissipation in the vicinity of the solid surface and heat conduction through solids, were introduced to achieve effective low-frequency sound absorption. 11,12 Acoustic metamaterials are articial structural materials with periodic or non-periodic unit arrangements to obtain local resonance and special intrinsic parameters, 13 such as negative effective mass density, negative effective modulus of elasticity, and zero refractive index. [14][15][16][17][18] These unconventional properties are usually difficult to nd in traditional materials.…”

Tunable Asymmetric Transmissions via Anisotropic Acoustic Metamaterials

“…Acoustic metamaterials (AMs) consisting of subwavelength artificial structures have been widely used to manipulate sound waves with specific requirement and realize many novel functionalities, [1][2][3] such as acoustic cloaking, [4,5] acoustic energy harvesting, [6][7][8] acoustic imaging, [9,10] and so on. In recent years, metasurfaces with subwavelength thickness, as 2D counterparts of metamaterials, have been first proposed via the generalized Snell's law in optics.…”