Acoustic Wave Manipulation Research Articles

Methods of Manipulation of Acoustic Radiation Using Metamaterials with a Focus on Polymers: Design and Mechanism Insights.

The manipulation of acoustic waves is becoming increasingly crucial in research and practical applications. The coordinate transformation methods and acoustic metamaterials represent two significant areas of study that offer innovative strategies for precise acoustic wave control. This review highlights the applications of these methods in acoustic wave manipulation and examines their synergistic effects. We present the fundamental concepts of the coordinate transformation methods and their primary techniques for modulating electromagnetic and acoustic waves. Following this, we deeply study the principle of acoustic metamaterials, with particular emphasis on the superior acoustic properties of polymers. Moreover, the polymers have the characteristics of design flexibility and a light weight, which shows significant advantages in the preparation of acoustic metamaterials. The current research on the manipulation of various acoustic characteristics is reviewed. Furthermore, the paper discusses the combined use of the coordinate transformation methods and polymer acoustic metamaterials, emphasizing their complementary nature. Finally, this article envisions future research directions and challenges in acoustic wave manipulation, considering further technological progress and polymers' application potential. These efforts aim to unlock new possibilities and foster innovative ideas in the field.

Low-frequency Acoustic Collimation Modulation Based on Monopole Mie Resonance Acoustic Metamaterials

Acoustic metamaterials show great flexibility in manipulating acoustic waves and exhibit important applications. However, an increasing number of applications are suitable for the low-frequency range, which makes it challenging to design acoustic metamaterials for low-frequency modulation. Here, we propose a subwavelength monopole Mie resonance acoustic metamaterial that can flexibly control the propagation route of acoustic waves. Compared to the background medium, the designed Mie unit has a higher refractive index and can achieve directional manipulation of low-frequency acoustic waves based on monopole Mie resonance. Furthermore, an array formed by multiple Mie units in a specific arrangement can achieve the acoustic collimation phenomenon. The designed monopole Mie resonance acoustic metamaterial has potential application prospects in fields such as low-frequency filtering, noise suppression, and nondestructive testing.

Brillouin Klein space and half-turn space in three-dimensional acoustic crystals

The Bloch band theory and Brillouin zone (BZ) that characterize wave-like behaviors in periodic mediums are two cornerstones of contemporary physics, ranging from condensed matter to topological physics. Recent theoretical breakthrough revealed that, under the projective symmetry algebra enforced by artificial gauge fields, the usual two-dimensional (2D) BZ (orientable Brillouin two-torus) can be fundamentally modified to a non-orientable Brillouin Klein bottle with radically distinct manifold topology. However, the physical consequence of artificial gauge fields on the more general three-dimensional (3D) BZ (orientable Brillouin three-torus) was so far missing. Here, we theoretically discovered and experimentally observed that the fundamental domain and topology of the usual 3D BZ can be reduced to a non-orientable Brillouin Klein space or an orientable Brillouin half-turn space in a 3D acoustic crystal with artificial gauge fields. We experimentally identify peculiar 3D momentum-space non-symmorphic screw rotation and glide reflection symmetries in the measured band structures. Moreover, we experimentally demonstrate a novel stacked weak Klein bottle insulator featuring a nonzero Z2 topological invariant and self-collimated topological surface states at two opposite surfaces related by a nonlocal twist, radically distinct from all previous 3D topological insulators. Our discovery not only fundamentally modifies the fundamental domain and topology of 3D BZ, but also opens the door towards a wealth of previously overlooked momentum-space multidimensional manifold topologies and novel gauge-symmetry-enriched topological physics and robust acoustic wave manipulations beyond the existing paradigms.

Subwavelength acoustic topology frequency band regulation based on symmetric site-space folded resonant cavities

Acoustic topological insulators, as a type of acoustic metamaterial, possess special acoustic wave manipulation capabilities. However, an acoustic topological insulator based on Bragg scattering requires its lattice constant to be equivalent to the wavelength. This means that constructing acoustic topological insulators efficiently in the low-frequency range is a challenge. To this end, this paper proposes a method to construct sub-wavelength acoustic topological insulators by adding spatially folded resonant cavities at symmetric locations. It can easily reduce unidirectional transmission frequency bands with topological protection to subwavelength scales. On this basis, it is even possible to realize effective control of the unidirectional transmission band over a great range by adjusting the length parameter of the folded resonant cavity. The control range can reach more than 4000Hz. Experimental results from finite element simulations further verify that this approach does not affect the topologically protected edge states and the topologically unidirectional acoustic transmission properties. This work provides a method for the construction of low-frequency acoustic topological insulators, as well as an efficient method for the accurate regulation of unidirectional transmission frequency bands over a wide range of frequencies.

Study of defect mode characteristics in acoustic metamaterials

The development of novel material architectures incorporating unconventional geometric designs (e.g., microstructural instabilities, multi-length scale geometries), or adaptive constituent elements (e.g., piezo electrics) has created a powerful tool to design metamaterials for efficient dispersion manipulation and precise control of acoustic waves. Various aspects of the acoustic dispersion (e.g., wave speed, damping ratio, band gap position and widths) have been investigated with a primary focus on wave characteristics in the acoustic pass bands, promoting their utility in applications, e.g., wave guiding, energy harvesting. However, recent studies on topological waves, truncation and bandgap resonances have highlighted potential benefits of leveraging acoustic waves in the bandgap, e.g., signal propagation, passive flow control. Motivated by this, we explore the dispersion behavior of finite mass-spring-damper acoustic metamaterial models with material defects. The eigen analysis reveals a (defect) resonance in the acoustic band gap, producing a highly localized defect mode. The dependence of this resonance frequency, the degree of localization and phase response of the eigenmode, on the defect parameters are explored. Subsequently, the potential utility of these defect modes in flow control applications is also explored and presented.

Integration of microfluidics in smart acoustic metamaterials

AbstractMicrofluidics has achieved a paradigm-shifting advancement in life sciences, automation, thermal management, and various other engineering streams. In recent years, a considerable amount of research has been conducted on the use of microfluidics in designing novel systems and fabricating next-generation smart materials that are capable of outperforming historical barriers and achieving unprecedented qualities. One such innovative development is the integration of fluidics into building artificially structured smart materials called acoustic metamaterials to achieve active tunability for a real-time controllable manipulation of acoustic waves. Leveraging the capability of microfluidics to automate the manipulation of liquid droplets, fluid streams, or bubbles in a required arrangement has revolutionised the development of actively tunable fluidics-integrated acoustic metamaterials for widescale applications. This review first discusses the prominent microfluidic actuation mechanisms used in the literature to develop fluidics-integrated smart acoustic metamaterials, and then it details integrated metamaterial design and extraordinary applications such as active acoustic wave manipulation or building tunable acoustic holograms etc. The following review concludes by providing the importance and future perspective of integrating microfluidic techniques with novel metamaterial designs, paving the way for innovative futuristic applications.

Band gap of shear horizontal waves for one-dimensional phononic crystals with chiral materials.

Extensive applications of chiral lattice structures in the field of acoustic wave manipulation and vibration modulation show the effectiveness of chirality route to the design of phononic crystals. However, how and to what extent the material chirality affects the band gap properties of phononic crystals remains unclear. In this study, one-dimensional phononic crystals made of chiral materials is proposed, and a theoretical model of shear horizontal (SH) wave propagation in the chiral phononic crystals is developed based on the noncentrosymmetric micropolar elasticity theory. Through the transfer matrix method, the dispersion relationship of SH wave propagation is obtained and the effects of material chirality on the band-gap properties are investigated. Our work demonstrates that the change of material chirality can significantly affect the dispersion relationship of phononic crystals, leading to the wide band gap and low frequency. In a unit cell, when the chiral coefficients of the two parts have opposite signs but the same magnitude and the chiral directions are consistent with the vibrational direction, it is the most favorable for the phononic crystals to achieve the lowest frequency and widest band gap. This study suggests that the material chirality can be harnessed to effectively tune the band-gap properties of phononic crystals. The present study provides insight for the chirality route to the design of phononic crystals.

Generalized acoustic impedance metasurface

Impedance theory has become a favorite method for metasurface design as it allows perfect control of wave properties. However, its functionality is strongly limited by the condition of strict continuity of normal power flow. In this paper, it is shown that acoustic impedance theory can be generalized under the integral equivalence principle without imposing the continuity of power flow. Equivalent non-local power flow transmission is instead realized through local design of metasurface unit cells that are characterized by a passive, asymmetric impedance matrix. Based on this strategy, a beam splitter loosely respecting local power flow is designed and demonstrated experimentally. It is concluded that arbitrary wave fields can be connected through arbitrarily shaped boundaries, i.e. transformed into one another. Generalized impedance metasurface theory is expected to extend the possible design of metasurfaces and the manipulation of acoustic waves.

Sustainable Solutions in Sound Shielding: Harnessing Metamaterials for Acoustic Cloaking

The development of metamaterials promises to enable smallscale, worldwide industry-wide acoustic, electromagnetic, mechanical, and solar energy harvesting. Engineered structures surpass natural material limitations, offering capabilities unattainable in traditional counterparts. This paper explores metamaterials' manipulation of acoustic, electromagnetic, mechanical, and solar energy. Mechanical metamaterials convert strain into electrical energy, applicable from interstellar travel to terrestrial infrastructure. Precision-configured acoustic metamaterials efficiently harness dispersed acoustic energy, improving renewable energy methodologies. Integration into photovoltaic cells showcases metamaterials' solar potential, with innovative designs enhancing solar energy conversion efficiency. “Metamaterials” is a word used to describe artificial structures whose properties are based on the aggregate expression of individual components. Acoustic metamaterials are the term used for such constructions intended for the manipulation of acoustic waves. Controlled wave propagation is made possible by acoustic metamaterials, which is frequently not possible with bulk materials created chemically. This indicates that the wave propagation in acoustic metamaterials is directed and produces desired acoustic effects, independent of the mass-density properties of the material. The distinct properties of acoustic metamaterials have paved the way for the creation of practical solutions for a variety of uses, such as passive destructive interference, acoustic cloaking, sound focusing, low-frequency sound insulation, and biomedical acoustics. The kind of sound modification determines the general properties of an acoustic metamaterial. The properties of several of the most promising acoustic metamaterials from passive to active are introduced in this work. In order to achieve a sustainable future, it is necessary to combine environmentally friendly technologies with renewable energy sources for their final application. This is demonstrated by highlighting both the fundamental concepts and the physical models that were assessed.

Asymmetric conversion of arbitrary vortex fields via acoustic metasurface

Asymmetric manipulation of acoustic waves has gained significant attention due to its rich physical properties and potential application prospects. In this study, we design and demonstrate a planar acoustic metasurface (AM) that enables asymmetric conversion for vortex fields with arbitrary orbital angular momentum (OAM) to different plane waves by placing the same vortex source at different focusing points of above and below. This asymmetric effect is caused by the spatial asymmetry of vortex wave, and AM achieves the conversion of two types of waves through directional compensation of phases. Numerical demonstrations and acoustic experiments further validate this asymmetric phenomenon, and the deflection angle of converted plane waves is qualitatively and quantitatively confirmed by a more general formula. Our work enriches the research meta-system of acoustic wave physics and holds potential applications in underwater acoustic communication and OAM-based devices.

Recent Progress in Resonant Acoustic Metasurfaces.

Acoustic metasurfaces, as two-dimensional acoustic metamaterials, are a current research topic for their sub-wavelength thickness and excellent acoustic wave manipulation. They hold significant promise in noise reduction and isolation, cloaking, camouflage, acoustic imaging, and focusing. Resonant structural units are utilized to construct acoustic metasurfaces with the unique advantage of controlling large wavelengths within a small size. In this paper, the recent research progresses of the resonant metasurfaces are reviewed, covering the design mechanisms and advances of structural units, the classification and application of the resonant metasurfaces, and the tunable metasurfaces. Finally, research interest in this field is predicted in future.

Stabilization mechanisms of various acoustic metasurfaces on the second mode in hypersonic boundary-layer flows

Acoustic metasurfaces have been shown to stabilize the Mack second mode in the hypersonic boundary layer through various acoustic wave manipulations, but the stabilization mechanisms still lack unified clarification. In the present work, momentum potential theory is used to develop a physics-based analysis of the perturbance flow field above three kinds of acoustic metasurfaces: the absorptive, impedance-near-zero, and reflection-controlled metasurfaces. It found the thermal-acoustic source term Pta contributes the most to the instability, and the main differences in the stabilization mechanisms of the various metasurfaces can be derived from the distributions of Pta. The absorptive metasurface largely restrains the negative Pta term near the surface and slightly attenuates it near the critical layer. The impedance-near-zero metasurface generates a positive contour under the critical layer, while the reflection-controlled metasurface induces additional positive Pta intertwining along the critical layer. In addition, a uniform macroslit surface without particular acoustic characteristic is verified to stabilize the Mack second mode because the recirculation zones inside the macroslits attenuate the near-surface negative Pta. By deflecting the reflective waves, additional larger positive Pta could be produced and wrapped along the critical layer and that achieves a more prominent stabilization performance by designing a reflection-controlled macroslit surface.

Underwater acoustic self-focusing and bending in conformal Mikaelian lens by pentamode metafluid

In this paper, we present the design of an arc-shaped Mikaelian lens using conformal transformation acoustics. We have derived the propagation trajectory equation for vertically incident rays within the lens. The ray trajectories inside the designed lens exhibit the feature of self-focusing as well as of deflection of the propagation direction. The microstructure design of the lens is realized using pentamode material unit cells, which provide the necessary property for underwater acoustic wave manipulation. The simulation results demonstrate that the designed lens has a good self- focusing effect and can deflect the propagation direction of incident waves at the same time. The pentamode conformal Mikaelian lens shows potential applications in underwater imaging, detection and communication.

Geometric Phase in Twisted Topological Complementary Pair.

Geometric phase enabled by spin-orbit coupling has attracted enormous interest in optics over the past few decades. However, it is only applicable to circularly-polarized light and encounters substantial challenges when applied to wave fields lacking the intrinsic spin degree of freedom. Here, a new paradigm is presented for achieving geometric phase by elucidating the concept of topological complementary pair (TCP), which arises from the combination of two compact phase elements possessing opposite intrinsic topological charge. Twisting the TCP leads to the generation of a linearly-varying geometric phase of arbitrary order, which is quantified by the intrinsic topological charge. Notably distinct from the conventional spin-orbit coupling-based theories, the proposed geometric phase is the direct result of the cyclic evolution of orbital-angular-momentum transformation in mode space, thereby exhibiting universality across classical wave systems. As a proof of concept, the existence of this geometric phase is experimentally demonstrated using scalar acoustic waves, showcasing the remarkable ability in the precise manipulation of acoustic waves at subwavelength scales. These findings engender a fresh understanding of wave-matter interaction in compact structures and establish a promising platform for exploring geometric phase, offering significant opportunities for diverse applications in wave systems.

Guiding acoustic waves via a gradient index meta-layer

In this work, we propose an efficient approach for controlling acoustic waves through guided mode conversion within a single meta-layer comprised of gradient index metamaterials. By harnessing the subwavelength localization characteristics of acoustic surface waves, the meta-layer can be properly shaped to accommodate arbitrary and prospective trajectories, thus enabling flexible guidance and routing of acoustic waves. Utilizing such a mode conversion mechanism, the acoustic directional transmitter and beam splitter have been devised and numerically demonstrated based on Archimedean spiral structures. These acoustic devices can exhibit a broadband response, achieving transmission efficiency exceeding 80% over a specific bandwidth that can be controlled by the geometry design. The proposed gradient index meta-layer may open new possibilities for acoustic wave manipulation, enabling some promising applications in noise control, information transmission, and energy harvesting.

Manipulation of reflected acoustic wavefront by a comb-like metasurface

This work proposes a design strategy for an acoustic metasurface with the goal of flexibly modulating reflected waveforms. The metasurface unit is composed of a rigid base and a column of rectangular partitions arranged in a comb-like configuration. A full 2π phase shift of the reflected waves can be achieved by adjusting the height of these rectangular partitions. The utilization of a particle swarm optimization algorithm determines the specific phase shift of the units along the metasurface. As a pragmatic example, it is shown that the comb-like metasurface offers a superior ability to direct the propagation of reflected sound waves in the desired directions, and experiments are performed to verify this anomalous reflection phenomenon. Furthermore, numerical calculations effectively demonstrate the application of the acoustic ground illusion. This work presents an effective and feasible design scheme for acoustic wave manipulation.

Simultaneous manipulation of acoustic waves in the reflected and transmitted regions with the full space metasurface

Acoustic metasurfaces offer great opportunities to realize exceptional functionalities and novel devices. However, most traditional metasurfaces manipulate acoustic waves either in the reflected region or in the transmitted region, leaving half of the space unexplored. Here, we propose a full space metasurface, which can simultaneously manipulate acoustic waves in the reflected and transmitted regions. As a proof of concept, three metadevices are designed and demonstrated: multi-directional scattering, asymmetric acoustic scattering and multi-focal focusing. Our proposal exhibits the full space utilization and may offer opportunities in the capabilities of metasurfaces in sound manipulation.

Pseudospin-layer coupled edge states in an acoustic topological insulator

The acoustic pseudospin edge states characterized by backscattering immunity and unidirectional transport provide a basis for designing devices with unconventional functions. In this Letter, we report pseudospin-layer coupled acoustic topological edge states realized by two layers of coupled honeycomb sonic crystals. With the additional layer degree of freedom, we define two distinctly different topological invariants that collectively determine the direction of the acoustic vortex and the layer polarization. We achieve an interesting phase diagram and explore the edge states between different phases. Additionally, we extend the topological edge states to the heterostructure and experimentally verify its capability to focus acoustic waves and convert layer polarization. Our work may provide a feasible platform for the manipulation of acoustic waves and could have promising applications in various areas, such as acoustic signal transmission and splitting.

Development of a FEM tool to calculate the dispersion curves of 2D phononic structures

AbstractThe control and manipulation of acoustic and elastic waves is an important research topic in engineering sciences. In acoustics, an adequate combination of different materials can contribute to an efficient and broadband sound isolation. The realization of a vibration‐free environment for high‐precision mechanical systems in laboratories and measuring environments is also desirable in many practical cases. Therefore, advanced materials and structures with outstanding acoustic and elastodynamic properties are of great importance in engineering applications. In this paper, a numerical tool based on the finite element method (FEM) is developed for computing the dispersion relations or band structures of two‐dimensional (2D) phononic crystals (PCs) composed of an elastic matrix and periodically distributed cylindrical inclusions.

Efficient digital metasurfaces for full-space manipulation of acoustic waves with low crosstalk between reflection and transmission

Metasurfaces, as a class of emergent platforms, have shown enormous potentials in controlling classical waves. However, achieving simultaneous and dynamic manipulations of reflected and transmitted waves in a low-crosstalk and high-efficiency manner via a single metasurface still remains huge challenges in fact, especially for acoustic waves that lack of available vector degrees of freedom. Here, we propose and experimentally demonstrate an acoustic full-space digital metasurface consisting of arrays of dual-channel elements with variable coding states, and the reflected and transmitted sound waves can be controlled independently and dynamically. Benefitting from the dual-frequency design and the mode suppression effect, the presented element not only attains high efficiency (up to 80% in transmission mode, and nearly 100% in reflection mode), but also enables decoupled modulations of the reflection and transmission coefficients. To illustrate the presented acoustic metasurface, tunable beam deflection and alterable wave focusing are experimentally validated without inter-modal crosstalk on both sides of the platform, respectively. This work opens an avenue to control sound waves in multiple dimensions, which may further promote the development of miniaturized acoustic devices with high integration and versatility.