Transmission Of Acoustic Waves Research Articles

Stepless space-regulation of topological acoustic controller with high fault tolerance

In this paper, the stepless space-regulation of topological acoustic transmission channels with high fault tolerance is proposed through introducing structural defect dislocations into a topological acoustic controller. Due to the stability of topological order against local disturbance, the acoustic wave transmission is immune to dislocation boundaries with strong stability, and thus the topological acoustic controller has high fault tolerance. By continuous changing the dislocation, the position relationship between the outgoing and incident acoustic signals no longer limited to the integer multiple distance related to the lattice size, and can realize the efficient acoustic energy transmission without energy loss at the fractional multiple distance, that is, the topological controller can realize lossless acoustic energy transmission and reception in arbitrary position relationship. Furthermore, the coupling relationship between the defect dislocation and the topological acoustic channel is explored, which can realize the stepless space-regulation of the lossless channel in the wide band range. In addition, by further introducing multi-layer continuous dislocations, this high-fault-tolerant topological acoustic controller still has strong stability, and multiple error factors do not affect the transmission results, which greatly reduces the difficulty of manufacturing. Finally, the stepless space-regulation of topological acoustic channels and the high-fault-tolerant topological acoustic controller that are easy to manufacture are verified by our experiments. This research paves the way for the engineering applications of acoustic micro-control, micro-nano fabrication, remote acoustic energy transmission manipulation, acoustic measurement, weak signal processing, acoustic flexible control and other micro-shape and multi-functional acoustic devices, and will bring more inspiration to other classical wave communication fields such as light wave, electromagnetic wave and so on.

Nonreciprocal Intelligent Soundproof Barrier with Active Nonlocal Acoustic Metastructure

Sound insulation is an important issue in daily life and has applications in various scenarios. Conventional acoustic passive metamaterial barriers are designed as a reciprocal sound insulation. However, for some specific application scenarios, unidirectional acoustic insulation is required, which is an enormous challenge for breaking the reciprocity of sound transport with conventional passive metamaterials. Here, a soundproof barrier with nonlocal acoustic metastructure is proposed, which consists of a microcontroller to connect a pair of spatially separated microphones and speakers, to tailoring the acoustic wave transmission for realizing nonreciprocal acoustic insulation. The theoretical calculation and experiment measurement indicated that the active acoustic barrier with a selectable working frequency can realize the suppressive effect in one direction and the enhancive effect in the other direction for an incident acoustic signal. Particularly, the function of an active soundproof barrier can be freely switched to forward, backward, and bidirectional sound insulation by tailoring the nonlocal distance of the digital meta‐atom. Furthermore, this acoustic metastructure is extended from a one‐dimentional waveguide to a two‐dimentional plane to illustrate that it is still valid in an open‐field environment. The proposed customizable nonreciprocal soundproof barriers provide an avenue for many applications in the specific scenarios that require unidirectional sound insulation and high air permeability.

Acoustic vortex filter based on tunable metasurfaces

In this paper, we present an acoustic vortex filter (AVF) based on tunable metasurfaces, which can selectively filter the incident multiplexed vortices that carry different orbital angular momentum (OAM). Our metasurface-based AVF is composed of an upper acoustic metasurface (UAM) and a lower acoustic metasurface, of which the intrinsic topological charge (ITC) can be tuned by mechanically rotating the UAM along its central axis. Due to the critical order of the propagating vortex modes in waveguide, controlling the ITC of the AVF allows for the selective filtering of incoming multiplexed acoustic vortex beams based on the sound vortex diffraction in phase-gradient metasurface, which endows the vortex filter the capability that let the incident vortex of specific OAM pass through it. In the following demonstration, both in theory and experiment, we design the AVF and effectively filter the acoustic vortices with two opposite topological charges by simply altering the orientation angle of the UAM. Based on this, we further demonstrate its application in asymmetric acoustic wave transmission. Our work offers an approach to selectively filter the incident acoustic vortex, which improves the capability to control the acoustic OAM via metasurfaces.

Phase variation of Laguerre-Gaussian vortex beams in a homogeneous atmospheric medium under finite amplitude acoustic wave perturbation

In this article, we have derived the acoustic pressure and medium refractive index expressions in a homogeneous atmospheric medium perturbed by a planar finite amplitude acoustic wave. In a planar finite amplitude acoustic wave perturbation, we developed a Laguerre–Gaussian vortex beam transmission model in a homogeneous atmospheric medium. We investigated the effects of different acoustic source parameters on the phase of the Laguerre–Gaussian vortex beam transmission, considering the atmospheric medium’s viscous effect. The results show that acoustic waves of finite amplitude distort the refractive index distribution of a homogeneous atmospheric medium. At a given distance, the amplitude of the refractive index gradually increases with increasing acoustic wave transmission distance. At the same time, the phase of the Laguerre–Gaussian vortex beam is rotated by the perturbation of the finite-amplitude acoustic wave, and the phase always returns to its initial position. Unlike linear acoustic waves, changes in the homogeneous atmospheric refractive index distribution and the homogeneous phase of the Laguerre–Gaussian vortex light no longer satisfy the periodic variation when perturbed by finite-amplitude acoustic waves. Under the same conditions, the effect of finite-amplitude acoustic waves on the phase of the Laguerre–Gaussian vortex light is stronger than that of linear acoustic waves. Finally, the effects of different acoustic pressure and frequency of the source on the phase of the Laguerre–Gaussian vortex beam transmission are calculated. The results show that different acoustic parameters at the source can be used to achieve phase modulation at different distances and intensities.

Reflections and transmissions from a porous layer sandwiched between seawater and solid substrate

Ocean sediments are composed of a porous layer sandwiched between seawater and a solid elastic base. The reflection and transmission of acoustic waves from ocean sediments are essential in ocean engineering, seafloor seismology, etc. The existing reflection and transmission (R/T) formulas are determined by complex matrix equations in the order of 9 × 9 or higher. To obtain more concise R/T coefficient formulas, we established the propagator matrix of the coupled water-porous-layer-solid elastic system, wherein the above-water is ideal and the middle porous marine sediment is defined by the Biot–Stoll model. Based on the propagator matrix, the displacement R/T coefficients were given by a 3 × 3 matrix equation for two P-wave incidence cases: the down-going case from the water, and the up-going case from the ocean floor. For zero-frequency or zero-thickness limitation, the proposed R/T coefficient formulas are the same as the displacement R/T coefficients at a single fluid–solid interface. The numerical results of the reflected or transmitted waves in the above-water show that the R/T coefficients exhibit regular variations at frequencies far lower than the characteristic frequency. The R/T coefficient amplitudes decreased with increasing frequency at a fixed incidence angle and ratio between the thickness and wavelength.

Acoustic cloaking design based on penetration manipulation with combination acoustic metamaterials

The acoustic wave transmission manipulation ability is the most important performance for the acoustic metamaterials. To manipulate the acoustic transmission, the combination acoustic metamaterials structures are involved, and the two-directional acoustic penetration cloaking scheme are constructed. The combination acoustic metamaterials include chiral metamaterials and self-collimation metamaterials, the acoustic wave transmission path are manipulated to bypass from the acoustic scattering target in the penetration cloaking, and the target scattering stealth problem are effectively solved. In the end, the acoustic transmission manipulation performances are verified by numerical analysis with a finite-width acoustic metamaterial structure plates. The results provide technical support for design and application for acoustic transmission manipulation with acoustic metamaterials.

Defect‐Adjusted Valley Edge States and Rainbow Trapping of Elastic Waves in 2D Topological Phononic Crystals

Topological phononic crystals (PnCs) with topologically protected boundary states have important applications in the fields of acoustic wave transmission and control. However, previous studies based on solid‐state PnC systems are mostly limited by fixed structures, resulting in the difficulty to deform the edge states, which partly limits its practical applications. Herein, a 2D solid topological PnC coupled with the defect is designed to achieve the adjustable valley edge state and rainbow trapping. First, by breaking the spatial inversion symmetry, the valley Hall phase transition of elastic wave is realized and valley edge states are obtained. Next, by introducing defects of different widths between the two different valleys’ topological PnCs, both the defect‐adjusted valley edge state and defect state are achieved. Then, by designing different topological PnCs waveguides, the robust transport characteristics of the two above states are compared. Subsequently, a new power divider based on the defect‐adjusted valley edge state is designed, which is found to possess various manners of operation such as equal and unequal power divisions. Finally, based on defect adjustment of the edge states, a rainbow trapping is implemented. This research provides an important guidance for ultrasonic devices, such as waveguides, energy harvesters, and power dividers.

Theoretical Investigation on Thermal, Mechanical and Ultrasonic Properties of Zirconium Metal with Pressure

Zirconium (Zr), a metal with an hcp structure, has been investigated for the transmission of acoustic wave in the 0 to 25 GPa operating pressure. For this, the Lennard-Jones interaction potential approach has been used to estimate the higher order elastic coefficients (SOECs and TOECs). This model is used to calculate the 2nd and 3rd order elastic parameters for zirconium metal. With the help of SOECs, other elastic moduli such as bulk modulus (B), Young’s modulus (Y) and shear modulus (G) have been calculated for Zr metal using Voigt-Reuss-Hill (VRH) approximations. Later, applying SOECs as well as zirconium density under the same pressure range, three orientation dependent acoustic velocities, comprising Debye average velocities, have been studied. Basic thermal characteristics such as specific heat at constant volume, thermal conductivity associated with lattice, thermal energy density, thermal relaxation time as well as acoustic coupling coefficients of zirconium metal have been also calculated at same pressure range. The computation is also satisfactory in estimating the ultrasonic attenuation coefficients, arises due to the interaction of phonons, hardness as well as melting temperature under various pressures in this research work.

Time-domain multiple traces boundary integral formulation for acoustic wave scattering in 2D

We present a novel computational scheme to solve acoustic wave transmission problems over two-dimensional composite scatterers, i.e. penetrable obstacles possessing junctions or triple points. The continuous problem is cast as a local multiple traces time-domain boundary integral formulation. For discretization in time and space, we resort to convolution quadrature schemes coupled to a non-conforming spatial spectral discretization based on second kind Chebyshev polynomials displaying fast convergence. Computational experiments confirm convergence of multistep and multistage convolution quadrature for a variety of complex domains.

Roton-Enabled Mechanical Diode at Extremely Low Frequency

Abstract This paper presents a refined model for a mechanical diode based on a mass-spring system. The proposed model utilizes a bilinear spring to construct a frequency converter, which effectively disrupts the reciprocal transmission of acoustic waves. By employing a mass-spring-mass system as a filter, a nonlocal connection is introduced to generate an extremely low-frequency band gap (2–4 Hz), thereby achieving a mechanical diode with a lower operating frequency. The feasibility of these low-frequency mechanical diodes is demonstrated through comprehensive numerical simulations and experimental analyses. In addition, we evaluated the effect of bilinear springs and nonlocal connection parameters on the diode performance.

Ultra-broad low-frequency forbidden bands in 1D solid–fluid acoustic superlattices with multiple solid constituents

In this paper, a theoretical model of underwater acoustic wave propagation, based on the transfer matrix method, is employed to calculate acoustic wave transmission through a 1D solid–fluid superlattice (SFSL) with multiple solid constituents. The band structure of infinite multi-element SFSL and the transmission coefficient of finite one are obtained, both of which reveal the existence of multiple separated ultra-broad low-frequency forbidden bands, even in the case of solid constituents with very close acoustic parameters. Simulations about the finite multi-element SFSL are carried out to verify the correctness of these findings. In addition, the influence of the acoustic parameters and the structural parameters on the low-frequency forbidden bands (LFBs) of SFSL with two solid constituents (m = 2) is also investigated. It is found that the required two separated LFBs can be achieved by choosing appropriate material parameters. For the situation of m ≥ 2, it is expected to provide more possibilities to engineer low-frequency bandgaps. Our results infer that multiple separated LFBs in multi-element SFSL can be quite useful for making highly performing low-frequency acoustic filters in selective angle ranges, which are useful for the elimination of the side lobes of low-frequency acoustic transducers.

Multiband ventilation barriers enabled by space-coiling acoustic metamaterials

In this study, space-coiling acoustic metamaterials were employed to achieve multiband sound insulation for ventilation acoustic barriers. Based on the ability of space-coiling metamaterials to manipulate acoustic waves, multiple resonances are introduced by tuning the effective refractive indices of internally curled channels, especially for low-frequency sound. This paper presents an analytical model of the proposed structure and its corresponding band structure, demonstrating that the acoustic barrier reported herein suppresses the transmission of acoustic waves by the band-folding effect as well as local resonance. To confirm the underlying mechanisms, effective parameters and equi-frequency contours were evaluated. The normal sound transmission loss was determined numerically and experimentally, and the effectiveness of the ventilation barrier in a diffuse field was confirmed by conducting numerical simulations.

Multi-dimensional eigenmodes induced by multi-slide dislocations in acoustic metamaterials

Crystal defects, such as line defects and point defects, have been introduced into acoustic metamaterials for waveguiding and localization. Here, the slide dislocations are introduced into the acoustic metamaterials and the multi-dimensional eigenmodes which exhibit as the 2D surface eigenmodes, the 1D hinge eigenmodes and the 0D bound eigenmodes are yielded. The number of eigenmodes is consistent with the number of the air connecting cylinders at the slide interfaces. The experiments results show the highly efficient transmission of acoustic waves along the sliding surfaces and hinges, and verify the high energy localization of acoustic waves at the intersection of multi-sliding interfaces. Due to the high designability of acoustic metamaterials and slide interfaces, the developed multi-dimensional eigenmodes induced by multi-slide dislocations provide great platforms for the sound waveguiding and the energy recovering.

An equivalent lattice-modified model of interfering Bragg bandgaps and Locally Resonant Stop Bands for phononic crystal made from Locally Resonant elements

The design and development of advanced devices based on metamaterials to control the transmission of acoustic waves is a hot topic. An important class of these metamaterials is based on phononic crystals with Locally Resonant Structure, included in those commonly known as Locally Resonant Sonic Materials. In these metamaterials, wave control is basically performed by two mechanisms: internal (or local) resonances in the scatterers that form the phononic crystal, and Bragg bandgaps due to structural periodicity. Their main control feature is the resonance peaks forming additional stop-bands away from the Bragg frequency, mainly in the low frequency regime. For some applications, coupling of the two phenomena is necessary to create a broad transmission gap. However, when both are located in close frequency ranges, some destructive interferences can occur. In this paper, the authors develop a comprehensive numerical model of periodic arrays of Hemholtz resonators, which explains in detail the physical mechanisms of this destructive interference and, simultaneously, allows the reproduction of the consequences of the interference. The numerical results are supported by experimental tests.

Acoustics of Compressed Earth Blocks Bound Using Sugarcane Bagasse Ash and Water Hyacinth Ash

Mechanical compaction is often used to densify building earth blocks by reducing the void between the particles. Compacted stabilised earth involves a binder, which holds the particles of the materials together. The compaction and addition of binders to the earth can modify its transport, mechanical, and acoustical properties. In this study, the acoustic transmission coefficient, porosity, and airflow resistivity were investigated by varying the concentrations of water hyacinth ash (WHA) and sugarcane bagasse ash (SBA) binders. An acoustic test rig comprising an acoustic wave guide made from joined water pipes was employed to analyse the influence of the WHA and SBA binders on the acoustical performance of the earth blocks. It was found out that the measured acoustic wave transmission was sensitive to the variation in the composition of WHA and SBA in the earth blocks. Increasing the WHA concentration led to an increase in the acoustic transmission coefficient and porosity, but reduced the airflow resistivity of the compressed earth blocks; while increasing the SBA reduced the transmission coefficient and porosity, but increased the airflow resistivity. This shows that SBA has a stronger binding property than WHA, which is ideal for the manufacture of stronger earth blocks, while the higher porosity of the earth blocks obtained with WHA is good for the construction of porous walls, which is good for maintaining the airflow between the inside of buildings and the surrounding.

Numerical simulation on the acoustic wave scattering and fluid perturbations inside confined orifice flow

Acoustic wave scattering and fluid perturbations produced by interactions between incident acoustic wave and confined orifice flow were investigated by a combined numerical solution containing nonlinear flow simulation and linearized acoustic simulation. In flow simulations, the mainstream Reynolds number was fixed at 10,000, which relates to the cooling pipe system of lithography. Turbulent flow fields corresponding to different orifice geometries were solved by an opensource finite volume solver OpenFOAM with Reynolds-averaged Navier–Stokes turbulence model. The turbulence database could efficiently improve the accuracy of subsequent linearized acoustic simulations as the viscosity dissipations were considered. In acoustic simulations, the linearized Navier-Stokes equations were solved by a finite element solver with transformation into frequency domain. The incident acoustic waves with varying frequencies from 500 Hz to 4000 Hz were arranged first at the inlet and then the outlet surfaces, enabling a two-port analysis on the transmission and reflection coefficients of acoustic waves. The numerical setup and the two-port model were well validated by results in literature. Generally, acoustic waves tend to gradually dissipate as their frequencies increase or the opening ratio of the ducted orifice decreases. However, the nonlinear variation in the transmission and reflection coefficients against the frequency variation of the incident acoustic waves could be investigated by increasing the thickness ratio. The acoustically induced fluid perturbations that were characterized by the Q-criterion could form a ring shape vortex structure in the vicinity of the orifice edge and then develop into disk-like packets. When the circumferential shape of the orifice was changed to a square, the attenuation of the incident acoustic waves corresponded to the intensity of the three-dimensionality of the acoustic-induced vortex structures, which indicated a greater energy transfer from the acoustic waves to the fluid perturbations.

Genetic variants and altered expression of SERPINF1 confer disease susceptibility in patients with otosclerosis.

Otosclerosis (OTSC) is a focal and diffuse bone disorder of the human middle ear characterized by abnormal bone growth and deposition at the stapes' footplate. This hinders the transmission of acoustic waves to the inner ear leading to subsequent conductive hearing loss. The plausible convections for the disease are genetic and environmental factors with yet an unraveled root cause. Recently, exome sequencing of European individuals with OTSCrevealed rare pathogenic variants in the Serpin Peptidase Inhibitor, Clade F (SERPINF1)gene. Here, we sought to investigate the causal variants of SERPINF1 in the Indian population. The gene and protein expression was also evaluated in otosclerotic stapes to ameliorate our understanding of the potential effect of this gene in OTSC. A total of 230 OTSC patients and 230 healthy controls were genotyped by single-strand conformational polymorphism and Sanger sequencing methods. Bycomparing the case controls, we identified five rare variants (c.72 C > T, c.151 G > A, c.242 C > G, c.823 A > T, and c.826 T > A) only in patients. Four variants c.390 T > C (p = 0.048), c.440-39 C > T (p = 0.007), c.643 + 9 G > A (p = 0.035), and c.643 + 82 T > C (p = 0.005) were found to be significantly associated with the disease. Down-regulation of SERPINF1 transcript level in otosclerotic stapes was quantified by qRT-PCR, ddPCR and further validated by in situ hybridization. Similarly, reduced protein expression was observed by immunohistochemistry and immunofluorescence in otosclerotic stapes that corroborate with immunoblotting of patients' plasma samples. Our findings identified that SERPINF1 variants are associated with the disease. Furthermore, reduced expression of SERPINF1 in otosclerotic stapes might contribute to OTSC pathophysiology.

Scattering by Finely Layered Obstacles: Frequency-Explicit Bounds and Homogenization

We consider the scalar Helmholtz equation with variable, discontinuous coefficients, modelling transmission of acoustic waves through an anisotropic penetrable obstacle. We first prove a well-posedness result and a frequency-explicit bound on the solution operator, with both valid for sufficiently-large frequency and for a class of coefficients that satisfy certain monotonicity conditions in one spatial direction, and are only assumed to be bounded (i.e., $L^\infty$) in the other spatial directions. This class of coefficients therefore includes coefficients modelling transmission by penetrable obstacles with a (potentially large) number of layers (in 2-d) or fibres (in 3-d). Importantly, the frequency-explicit bound holds uniformly for all coefficients in this class; this uniformity allows us to consider highly-oscillatory coefficients and study the limiting behaviour when the period of oscillations goes to zero. In particular, we bound the $H^1$ error committed by the first-order bulk correction to the homogenized transmission problem, with this bound explicit in both the period of oscillations of the coefficients and the frequency of the Helmholtz equation; to our knowledge, this is the first homogenization result for the Helmholtz equation that is explicit in these two quantities and valid without the assumption that the frequency is small.

Chirality-selective transmission of acoustic orbital angular momentum through lossy metasurfaces

Wave fields with acoustic orbital angular momentum have drawn greatattention because of its wide range of applications such as acoustic communication and particle manipulation. We designed, fabricated, and experimentally validated a type of lossy metasurface which enables an extremely selective transmission of acoustic wave filed depending on the chirality of its orbital angular momentum. The metasurface is composed of a phase gradient metagrating (PGM) and microperforated panel (MPP). By harnessing the multiple internal reflection of PGM and the carefully engineered loss of MPP, the left-handed incident vortex has a near-zero power transmission while its right-handed counterpart has a 60% power transmission. Such an extremely selective transmission was experimentally validated by retrieving the full scattering matrix using a generalized twelve-microphone method, which shows a good agreement with numerical simulations.

Effect of skull porosity on ultrasound transmission and wave mode conversion at large incidence angles.

Transcranial ultrasound imaging and therapy depend on the efficient transmission of acoustic energy through the skull. Multiple previous studies have concluded that a large incidence angle should be avoided during transcranial-focused ultrasound therapy to ensure transmission through the skull. Alternatively, some other studies have shown that longitudinal-to-shear wave mode conversion might improve transmission through the skull when the incidence angle is increased above the critical angle (i.e., 25° to 30°). The effect of skull porosity on the transmission of ultrasound through the skull at varying incidence angles was investigated for the first time to elucidate why transmission through the skull at large angles of incidence is decreased in some cases but improved in other cases. Transcranial ultrasound transmission at varying incidence angles (0°-50°) was investigated in phantoms and ex vivo skull samples with varying bone porosity (0% to 28.54%±3.36%) using both numerical and experimental methods. First, the elastic acoustic wave transmission through the skull was simulated using micro-computed tomography data of ex vivo skull samples. The trans-skull pressure was compared between skull segments having three levels of porosity, that is, low porosity (2.65%±0.03%), medium porosity (13.41%±0.12%), and high porosity (26.9%). Next, transmission through two 3D-printed resin skull phantoms (compact vs. porous phantoms) was experimentally measured to test the effect of porous microstructure alone on ultrasound transmission through flat plates. Finally, the effect of skull porosity on ultrasound transmission was investigated experimentally by comparing transmission through two ex vivo human skull segments having similar thicknesses but different porosities (13.78%±2.05% vs. 28.54%±3.36%). Numerical simulations indicated that an increase in transmission pressure occurs at large incidence angles for skull segments having low porosities but not for those with high porosity. In experimental studies, a similar phenomenon was observed. Specifically, for the low porosity skull sample (13.78%±2.05%), the normalized pressure was 0.25 when the incidence angle increased to 35°. However, for the high porosity sample (28.54%±3.36%), the pressure was no more than 0.1 at large incidence angles. These results indicate that the skull porosity has an evident effect on the transmission of ultrasound at large incidence angles. The wave mode conversion at large, oblique incidence angles could enhance the transmission of ultrasound through parts of the skull having lower porosity in the trabecular layer. However, for transcranial ultrasound therapy in the presence of highly porous trabecular bone, transmission at a normal incidence angle is preferable relative to oblique incidence angles due to the higher transmission efficiency.