Acoustic metamaterials can manipulate and control sound waves in ways that are not possible in conventional materials. Metamaterials with zero, or even negative, refractive index for sound offer new possibilities for acoustic imaging and for the control of sound at subwavelength scales. The combination of transformation acoustics theory and highly anisotropic acoustic metamaterials enables precise control over the deformation of sound fields, which can be used, for example, to hide or cloak objects from incident acoustic energy. Active acoustic metamaterials use external control to create effective material properties that are not possible with passive structures and have led to the development of dynamically reconfigurable, loss-compensating and parity–time-symmetric materials for sound manipulation. Challenges remain, including the development of efficient techniques for fabricating large-scale metamaterial structures and converting laboratory experiments into useful devices. In this Review, we outline the designs and properties of materials with unusual acoustic parameters (for example, negative refractive index), discuss examples of extreme manipulation of sound and, finally, provide an overview of future directions in the field. Acoustic metamaterials can be used manipulate sound waves with a high degree of control. Their applications include acoustic imaging and cloaking. This Review outlines the designs and properties of these materials, discussing transformation acoustics theory, anisotropic materials and active acoustic metamaterials.

Controlling sound with acoustic metamaterials

Dynamics of Phononic Materials and Structures: Historical Origins, Recent Progress, and Future Outlook

This review provides a perspective on the recent developments in the transmission of light through subwavelength apertures in metal films. The main focus is on the phenomenon of extraordinary optical transmission in periodic hole arrays, discovered over a decade ago. It is shown that surface electromagnetic modes play a key role in the emergence of the resonant transmission. These modes are also shown to be at the root of both the enhanced transmission and beaming of light found in single apertures surrounded by periodic corrugations. This review describes both the theoretical and experimental aspects of the subject. For clarity, the physical mechanisms operating in the different structures considered are analyzed within a common theoretical framework. Several applications based on the transmission properties of subwavelength apertures are also addressed.

http://digital.csic.es/bitstream/10261/47904/1/Light%20passing.pdf

Light passing through subwavelength apertures

Within a time span of 15 years, acoustic metamaterials have emerged from academic curiosity to become an active field driven by scientific discoveries and diverse application potentials. This review traces the development of acoustic metamaterials from the initial findings of mass density and bulk modulus frequency dispersions in locally resonant structures to the diverse functionalities afforded by the perspective of negative constitutive parameter values, and their implications for acoustic wave behaviors. We survey the more recent developments, which include compact phase manipulation structures, superabsorption, and actively controllable metamaterials as well as the new directions on acoustic wave transport in moving fluid, elastic, and mechanical metamaterials, graphene-inspired metamaterials, and structures whose characteristics are best delineated by non-Hermitian Hamiltonians. Many of the novel acoustic metamaterial structures have transcended the original definition of metamaterials as arising from the collective manifestations of constituent resonating units, but they continue to extend wave manipulation functionalities beyond those found in nature.

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Acoustic metamaterials: From local resonances to broad horizons.

This article reviews acoustic microfiuidics: the use of acoustic fields, principally ultrasonics, for application in microfiuidics. Although acoustics is a classical field, its promising, and indeed perplexing, capabilities in powerfully manipulating both fluids and particles within those fluids on the microscale to nanoscale has revived interest in it. The bewildering state of the literature and ample jargon from decades of research is reorganized and presented in the context of models derived from first principles. This hopefully will make the area accessible for researchers with experience in materials science, fluid mechanics, or dynamics. The abundance of interesting phenomena arising from nonlinear interactions in ultrasound that easily appear at these small scales is considered, especially in surface acoustic wave devices that are simple to fabricate with planar lithography techniques common in microfluidics, along with the many applications in microfluidics and nanofluidics that appear through the literature.

/pdf/microscale-acoustofluidics-microfluidics-driven-via-5bet39j13p.pdf

Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

Here we report an experimental observation of the self-organization effect of polystyrene particles formed by acoustically induced interaction forces. Two types of stable configurations are observed experimentally: one is mechanically equilibrium and featured by nonzero interparticle separations, and the other corresponds to a closely packed assembly, which is created by strong attractions among the aggregated particles. For the former case involving two or three particles, the most probable interparticle separations (counted for numerous independent initial arrangements) agree well with the theoretical predictions. For the latter case, the number of the final stable configurations grows with the particle number, and the occurrence probability of each configuration is interpreted by a simple geometric model.

Sound-mediated stable configurations for polystyrene particles.

A sound splitter using the orbital angular momentum (OAM) of acoustic vortices is proposed and experimentally demonstrated. We show that a helical waveguide with a periodic array of shunted tubes can be used to achieve different transmission spectra for the acoustic vortices with opposite OAM topological charges due to their different Bragg scattering type bandgaps. By symmetry, the transmission spectra will reverse if the handedness of the helical waveguides is changed. Therefore, two such composite waveguides with opposite handedness can be combined to separate the OAM-dependent flow of sound. Our study of the acoustic vortex splitter may provide a route for demultiplexing in acoustic OAM-based communication.

Acoustic waves splitter employing orbital angular momentum

Experimental investigation of negative refraction and imaging of 8-fold-symmetry phononic quasicrystals

Unlike the well-known Airy beams that can be deformed beyond paraxial angles, the half-Bessel (HB) Beams can bend to steeper angles. Here we propose an effective metasurface design for constructing two-dimensional acoustic HB beams. The design is based on an array of spatially varied coiling-slit units, each of which mimics the wave responses derived from the analytical expression of the acoustic HB beam. A tradeoff method is utilized here to simplify the variable amplitude responses. The full-wave simulations and experimental measurements consistently manifest the effectiveness of this design process. Potential applications, such as the large-angle bending transport of particles, can be anticipated.

https://iopscience.iop.org/article/10.7567/JJAP.55.110302/pdf

Making acoustic half-Bessel beams with metasurfaces

Strong enhancement of sound scattering is important for some applications of acoustic metamaterials, such as sensing and acoustic antennae. Here the authors create a meta-rod structure to achieve the $s\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}d$ $s\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}g$ effect. The near-degeneracy of resonances in multiple channels of the meta-rod can break the so-called single-channel limit of subwavelength structures, and thus achieve extremely strong sound scattering, even in the deeply subwavelength regime. The mechanism behind superscattering of sound turns out to be more robust than that for light, so there are not stringent fabrication requirements for the proposed structure, which is important for practical applications.

Manzhu Ke

Papers

Sound-mediated stable configurations for polystyrene particles.

Acoustic waves splitter employing orbital angular momentum

Experimental investigation of negative refraction and imaging of 8-fold-symmetry phononic quasicrystals

Making acoustic half-Bessel beams with metasurfaces

Superscattering of Sound by a Deep-Subwavelength Solid Mazelike Rod