Abstract Acoustic metamaterials have been widely investigated over the past few decades and have realized acoustic parameters that are not achievable using conventional materials. After demonstrating that locally resonant acoustic metamaterials are capable of acting as subwavelength unit cells, researchers have evaluated the possibility of breaking the classical limitations of the material mass density and bulk modulus. Combined with theoretical analysis, additive manufacturing and engineering applications, acoustic metamaterials have demonstrated extraordinary capabilities, including negative refraction, cloaking, beam formation and super-resolution imaging. Owing to the complexity of impedance boundaries and mode transitions, there are still challenges in freely manipulating acoustic propagation in an underwater environment. This review summarizes the developments in underwater acoustic metamaterials over the past 20 years, which include underwater acoustic invisibility cloaking, underwater beam formation, underwater metasurfaces and phase engineering, underwater topological acoustics and underwater acoustic metamaterial absorbers. With the evolution of underwater metamaterials and the timeline of scientific advances, underwater acoustic metamaterials have demonstrated exciting applications in underwater resource development, target recognition, imaging, noise reduction, navigation and communication.
N. Apetre, John G. Michopoulos, A. Iliopoulos
et al.
The continuous progress of additive manufacturing techniques has enabled engineers and designers to build complex geometries at various length scales with minimal setup time, reduced need for skilled labor, and minimal material waste. One important subset of structures endowed with complex geometrical features is formed by periodic and non-periodic metamaterials that enable engineering applications where certain combinations of performance features are desirable. For example, these structures could be used in naval engineering applications where light-weight, large surface area, energy absorption, heat dissipation, and acoustic bandgaps are critical. Nevertheless, to deploy these complex geometry structures, their multiphysics response must be well understood and characterized. The current effort aims to describe an initial approach for designing and deploying graded triply periodic minimal surface (TPMS) architectures. The work focuses on three TPMS systems: (a) Neovius, (b) Schoen’s gyroid, and (c) Schoen’s F-RD made of Ti-6Al-4V alloy. These three geometries are enhanced using variable wall thickness to obtain the so-called graded TPMS. Three problems are explored: (1) evaluation of the elastic equivalent material properties of various unit cells with graded thickness; (2) investigation of acoustics dispersion properties of three cells and (3) a thermo-structural response of a complex geometry made of twelve graded representative volume elements (RVE). Finite element results of the relevant thermo-structural partial differential equations for the case of a gyroid triply periodic cylindrical sandwich structure are presented.
The analysis of known analytical solutions to the problem of calculating transmission the sound insulation of one- two- and three-layer glazing in comparison with the results of laboratory measurements is presented. The wave theory of sound transmission through single-layer and multi-layer enclosing structures with air gaps is used. Based on calculations of sound insulation of single-layer glazing, it is shown that the theory underlying the methodology of GOST R EN 12354-1–2012 “Acoustics of buildings. Methods for calculating the acoustic characteristics of buildings based on the characteristics of their elements. Part 1. Sound insulation of air noise between rooms”, most adequately takes into account the processes of non-resonant and resonant sound transmission. Its use in the formulation of models of sound transmission through double and triple glazing, taking into account internal losses and the influence of resonant processes, made it possible to obtain analytical solutions to the problem of sound insulation of single-chamber and double-chamber double-glazed windows, which showed good convergence with the experimental results. The proposed method for calculating sound insulation through single- and double-chamber double-glazed windows can be used in engineering calculations after additional studies of internal losses in multilayer glazing, as well as additional measurements of a number of “standard” types of glazing to verify the methodology.
Lithium niobate (LiNbO3) crystals are important dielectric and ferroelectric materials, which are widely used in acoustics, optic, and optoelectrical devices. The physical and chemical properties of LiNbO3 are dependent on microstructures, defects, compositions, and dimensions. In this review, we first discussed the crystal and defect structures of LiNbO3, then the crystallization of LiNbO3 single crystal, and the measuring methods of Li content were introduced to reveal reason of growing congruent LiNbO3 and variable Li/Nb ratios. Afterwards, this review provides a summary about traditional and non-traditional applications of LiNbO3 crystals. The development of rare earth doped LiNbO3 used in illumination, and fluorescence temperature sensing was reviewed. In addition to radio-frequency applications, surface acoustic wave devices applied in high temperature sensor and solid-state physics were discussed. Thanks to its properties of spontaneous ferroelectric polarization, and high chemical stability, LiNbO3 crystals showed enhanced performances in photoelectric detection, electrocatalysis, and battery. Furthermore, domain engineering, memristors, sensors, and harvesters with the use of LiNbO3 crystals were formulated. The review is concluded with an outlook of challenges and potential payoff for finding novel LiNbO3 applications.
Multi-reflection interference of sound waves is ubiquitous in our daily life, and suppressing any such distortions of a wave’s free propagation and achieving counter-directional adaptation is a challenging task, with many applications in acoustics. Here, we propose a non-Hermitian Fabry–Perot resonance unit, which demonstrates unidirectional invisibility in opposite directions at the so-called exceptional points by adjusting its geometric configuration and intrinsic acoustic parameters. Then, we extend the principle and design a waveguide containing six inclusion–membrane pairs in which a unique property of step-wise constant-amplitude waves in two opposite directions has been realized, irrespective of whether the distribution of inclusions is periodic or random. Our method breaks through the limitation of the impedance, amount, position of the inclusions, and the incident direction of the waves, revealing potential applications in acoustic sensing, noise control engineering, and other related wave disciplines.
Efficiently receiving underwater sound remotely from air is a long-standing challenge in acoustics hindered by the large impedance mismatch at the water-air interface. Here we introduce and experimentally demonstrate a technique for remote and efficient water-to-air eavesdropping through phase-engineered impedance matching metasurfaces. By judiciously engineering an ultrathin mechanically-rigid boundary, we make the water-air interface acoustically transparent and at the same time we are able to pattern the transmitted wavefront, enabling efficient control over the effective spatial location of a distant airborne sensor such that it can measure underwater signals with large signal-to-noise ratio as if placed close to the physical underwater source. Such airborne eavesdropping of underwater sound is experimentally demonstrated with a measured sensitivity enhancement exceeding 38 dB at 8 kHz. We further demonstrate opportunities for orbital-angular-momentum-multiplexed communications and underwater acoustic communications. Our metasurface opens new avenues for communication and sensing, which may be translated to nano-optics and radio-frequencies.
Wave demultiplexers transporting desired wavelengths towards proper directions or ports are attracting numerous interests and applications in both physical and engineering areas. In acoustics, there is still a lack of compact and simple designs to achieve demultiplexers in three-port systems. In this work, we propose such a design using Helmholtz resonators where the frequency selection is based on the phenomenon of acoustically induced transparency (AIT). First, a modified transfer matrix method is derived to analytically describe and analyze the AIT effect with Helmholtz resonators. Then, the good performances of wave routing in these designs are further demonstrated by both simulation and experiment. These AIT based demultiplexers are subwavelength and simple in their designs. Therefore, they are promising for various potential applications such as signal processing, information communication and sensing.
Abstract Metallic foams are among the most promising class of materials due to their unique mechanical properties combining low mass with high stiffness, excellent energy absorption, and vibroacoustic damping. Consequently, noise control using methodically engineered metallic foams has received increased attention from both industrial and scientific community. Accordingly, this paper aims to present the mechanism of sound absorption along with the experimental and theoretical procedure that can be used to classify metallic foams. Additionally, the influence of design parameters on the resulting sound absorption coefficient of closed and open-cell metallic foams are explored. While Aluminium foams used to dominate the literature when it comes to acoustics, recent studies have reported Nickel-Inconel superalloy and Copper foams as having superior sound absorption coefficients.