Acoustic Structures Research Articles

Ion acoustic shocks with contribution of higher order effects in a superthermal beam-plasma

This investigation presents the study of ion acoustic (IA) shocks in a plasma comprising warm inertial ions, and superthermal hot electrons penetrated by an electron beam. Using the reductive perturbation method, the Burgers equation is derived. Tanh-method is employed to derive its solution to study the ion acoustic shock structures. Further, by considering the contribution of higher order effects, the inhomogeneous Burgers-type equation is derived and its solution results in the formation of humped-type IA shocks. The combined effects of electron beam and other plasma parameters on the characteristics of different kinds of ion acoustic shock structures are analysed. The findings of this investigation may be useful to understand insight of physics of nonlinear phenomena for studying dynamics of ion acoustic shocks in space as well as astrophysical plasma environments where superthermal electrons and electron beam are present.

Experimental evidence of the Poisson-like effect for flexural waves in thin metallic plates

This Letter reports the feasibility of a structure specifically designed for the control of flexural waves propagating in thin perforated plates. The structure, here denominated as a redirector device, consists of a square array of free holes that splits the impinging beam and transmits sideways their vibrational energy. This behavior is known as a Poisson-like effect, and it was theoretically described in different acoustic structures. This effect is experimentally demonstrated for flexural waves excited in an aluminum perforated plate, and it is explained in terms of a physical mechanism different to that reported for acoustic waves interacting with thin hollow cylinders embedded in water. In addition, a collimator device based also in free holes is designed and validated with the purpose of providing the beam impinging the redirector device. The measurements indicate that the amount of redirected energy is strongly enhanced when a barrier of two-beam resonators is added at the rear side of the redirector. All the designs are validated by an experimental setup employing 1 mm thick aluminum plates.

Bound States in the Continuum in Compact Acoustic Resonators.

We reveal that finite-size solid acoustic resonators can support genuine bound states in the continuum (BICs) completely localized inside the resonator. The developed theory provides the multipole classification of such BICs in the resonators of various shapes. It is shown how breaking of the resonator's symmetry turns BICs into quasi-BICs manifesting themselves in the scattering spectra as high-Q Fano resonances. We believe that the revealed novel states will push the performance limits of acoustic devices and will serve as high-Q building blocks for acoustic sensors, antennas, and topological acoustic structures.

Nonlinear acoustic wave structures to the Zabolotskaya-Khokholov dynamical model

In this study, the abundant families of nonlinear acoustic wave structures are constructed for Zabolotskaya-Khokholov (Z-K) model which provides information about the propagation of sound beam or confined wave beam in nonlinear media and studies of beam deformation. These wave structures are observed in single (shock and singular) and mixed shock, (complex solitary-shock, shock-singular and periodic-singular) forms. The rational solutions are also emerged during the derivation. The new modified extended direct algebraic (NMEDA) technique and mathematics software are used to obtain the solutions. Moreover, for different values of parameters, the graphs in 3D and 2D-dimensions are also drawn.

Some novel approaches to analyze a nonlinear Schrodinger’s equation with group velocity dispersion: Plasma bright solitons

Taking two efficient analytical techniques, including the generalized exponential rational function method and the extended sinh–Gordon equation expansion method, into account several optical solutions to a variety of nonlinear Schrödinger’s equation with group velocity dispersion are constructed. We are investigated several families of localized structures (bright solitons) for attractive nonlinearities including localized structures in both angular directions in addition to localized structures in one-directional and homogeneous in the other. To provide a better understanding of the obtained results, some numerical simulations for the obtained solutions are carried out. Further, the obtained solutions are represented graphically in order to clarify the vision and deep understanding of the mechanism of all nonlinear phenomena described by these solutions. The acquired results in this survey are new and have not been obtained in previous literature. Moreover, both utilized techniques can be assumed as an important tool for the explanation of some nonlinear physical phenomena such as the modulated envelope localized structures in plasma physics and fluid mechanics. Also, the obtained solutions can help researchers interested in studying the acoustic nonlinear modulated structures in different plasma models especially bright envelope solitons.

Deep auto-encoder network in predictive design of Helmholtz resonator: On-demand prediction of sound absorption peak

In this paper, a large sample database is established by using a classical Helmholtz resonator, and the acoustic performance parameters and geometric structural parameters are trained by using the deep auto-encoder (DAE) model based on machine learning. Next, 20 groups of target peak points (αE, fE) are arbitrary selected inside and outside the sample database, and the corresponding geometric structural parameters (dn, dc, hp, hn) are obtained by training the DAE model, and the predicted peak points (αD, fD) are obtained. By comparing the target peak points (αE, fE) with the predicted peak points (αD, fD), the verification results show that the DAE model has very high prediction accuracy for samples from the database, while the prediction accuracy for samples out of the database is slightly lower. The proposed method represents a transformation of the design paradigm of functional acoustic devices, which can be further applied to the predictive design of more complex acoustic structures, and has great application potential in the field of vibration and noise reduction.

Parity–time symmetric acoustic system constructed by piezoelectric composite plates with active external circuits

Researches on parity-time (PT) symmetry in acoustic field can provide an efficient platform for controlling the travelling acoustic waves with balanced loss and gain. Here, we report a feasible design of PT-symmetric system constructed by piezoelectric composite plates with two different active external circuits. By judiciously adjusting the resistances and inductances in the external circuits, we obtain the exceptional point due to the spontaneous breaking of PT symmetry at the desired frequencies and can observe the unidirectional invisibility. Moreover, the system can be at PT exact phase or broken phase at the same frequency in the same structure by merely adjusting the external circuits, which represents the active control that makes the acoustic manipulation more convenient. Our study may provide a feasible way for manipulating acoustic waves and inspire the application of piezoelectric composite materials in acoustic structures.

Impedance theory of wave propagation on infinite periodic structures

For linear acoustic and mechanical periodic structures from cells made of lumped and continuous elements introduced is the concept of the group impedance as a universal quantity through which all the basic wave characteristics of the structure (dispersion, energy, orthogonality, forced vibration) are expressed. Presented are the necessary expressions. Based on the unique properties of the group impedance, a new homogenization method is proposed useful for analysis and design of mechanical and acoustic metamaterials with prescribed wave properties.

Acoustic-level and language-specific processing of native and non-native phonological sequence onsets in the low gamma and theta-frequency bands

Acoustic structures associated with native-language phonological sequences are enhanced within auditory pathways for perception, although the underlying mechanisms are not well understood. To elucidate processes that facilitate perception, time–frequency (T–F) analyses of EEGs obtained from native speakers of English and Polish were conducted. Participants listened to same and different nonword pairs within counterbalanced attend and passive conditions. Nonwords contained the onsets /pt/, /pət/, /st/, and /sət/ that occur in both the Polish and English languages with the exception of /pt/, which never occurs in the English language in word onset. Measures of spectral power and inter-trial phase locking (ITPL) in the low gamma (LG) and theta-frequency bands were analyzed from two bilateral, auditory source-level channels, created through source localization modeling. Results revealed significantly larger spectral power in LG for the English listeners to the unfamiliar /pt/ onsets from the right hemisphere at early cortical stages, during the passive condition. Further, ITPL values revealed distinctive responses in high and low-theta to acoustic characteristics of the onsets, which were modulated by language exposure. These findings, language-specific processing in LG and acoustic-level and language-specific processing in theta, support the view that multi scale temporal processing in the LG and theta-frequency bands facilitates speech perception.

Padé近似を用いた音響透過率の角周波数平均の予測とそのトポロジー導関数

We propose a topology optimisation of wideband periodic acoustic structures using the Padé approximation. The frequency of incident waves largely influences the performance of acoustic devices. We thus need to care about the performance deviation due to possible changes in the frequency when designing a practical acoustic structure. To this end, we may define the objective function for the topology optimisation as the frequency average of the performance index to take the frequency fluctuation into account. In the previous research, we proposed a topology optimisation with such an objective function, where the Padé approximation is used to efficiently estimate the frequency average of the sound pressure. The current research aims to apply the method to the optimisation of periodic structures. In this research, we use the energy transmittance across a structure as the performance index and define the frequency average of it as the objective function. The frequency average of the transmittance is derived via the Padé approximated far-field patterns in a certain frequency band. The topological derivative of the estimated objective function is also derived with the adjoint variable method. We confirm the correctness of the proposed method through a numerical test.

Acoustic ring resonator: Experiments and simulations

The application of acoustic ring resonator structures for the manipulation of audio frequency acoustic waves is demonstrated experimentally and via numerical simulation. Three ring resonator systems are demonstrated: a simple single ring structure that acts as a comb/notch filter, a single ring between two parallel waveguides that acts as an add-drop filter, and a sequential array of equally spaced rings that creates acoustic bandgaps. The experiments are conducted in linear waveguides using an impulse response method. The ring resonators were created via 3D printing. Finite element numerical simulations were conducted using COMSOL.

Research and design of broadband muffler based on second-order Helmholtz resonators

Noise is always a serious factor affecting people's quality of life. The most common sound-absorbing materials are porous materials, which work based on the principle that sound waves entering into the pores inside the material are subjected to air friction and viscous resistance, thus converting sound energy into heat. Porous materials have excellent performance of absorbing medium-frequency and high-frequency sound , but they are required to be thick enough to control the low-frequency sound waves with large wavelengths, which limits the application of porous materials in low-frequency noise control. In recent years, acoustic artificial structures have become a research hotspot, which can realize exotic effective acoustic parameters based on periodical structure or local resonance. Acoustic artificial structure provides a new material basis for noise control, in which Helmholtz resonator plays an important role because of its simple geometry. In this study, a broadband muffler is designed based on the second-order neck embedded Helmholtz resonator. In order to achieve low-frequency and broadband sound insulation with a limited number of units and structure length, the second-order resonator is chosen as a basic structure unit, which has a stronger low-frequency noise reduction capability and has one high-frequency transmission loss peak more than a conventional Helmholtz resonator. The acoustic characteristics and insulation performance of second-order resonators are analyzed through theoretical calculation, simulation calculation and experimental test. Then, based on the theoretical model and empirical rules, a broadband muffler composed of nine second-order resonators is designed by carefully adjusting the geometry parameters of each resonator. The three-dimensional printed resonators are installed on the side wall of a square standing wave tube for experimental measurement. In the experiment, the transmission loss curve of the muffler is measured by the two-load method. The result shows that the designed muffler has good sound insulation performances in a frequency range of 267–927 Hz, with the whole transmission loss above 20 dB and the maximum sound insulation up to 60 dB. The experimental result is consistent with the calculation result and simulation result. The muffler has simple structure and high practicability, which will have a wide application prospect in noise control engineering.

Robust design of an asymmetrically absorbing Willis acoustic metasurface subject to manufacturing-induced dimensional variations.

Advancements in additive manufacturing (AM) technology are promising for the creation of acoustic materials. Acoustic metamaterials and metasurfaces are of particular interest for the application of AM technologies as theoretical predictions suggest the need for precise arrangements of dissimilar materials within specified regions of space to reflect, transmit, guide, or absorb acoustic waves in ways that exceed the capabilities of currently available acoustic materials. This work presents the design of an acoustic metasurface (AMS) with Willis constitutive behavior, which is created from an array of multi-material inclusions embedded in an elastomeric matrix, which displays the asymmetric acoustic absorption. The finite element models of the AMS show that the asymmetric absorption is dependent on asymmetry in the distribution of materials within the inclusion and highly sensitive to small changes in the inclusion geometry. It is shown that the performance variability can be used to place constraints on the manufacturing-induced variability to ensure that an as-built AMS will perform using the as-designed parameters. The evaluation of the AMS performance is computationally expensive, thus, the design is performed with a classifier-based metamodel to support more efficient Monte Carlo simulations and quantify the sensitivity of the candidate design performance to the manufacturing variability. This work explores combinations of material choices and dimensional accuracies to demonstrate how a robust design approach can be used to help select AM fabrication methods or guide process development toward an AM process that is capable of fabricating acoustic material structures.

A Tunable Open Planar Acoustic Notch Filter Utilizing a Pneumatically Modulated Helmholtz Resonator Array

Acoustic filters provide sound insulation unpleasant noises at a specific frequency only. Ordinary passive acoustic filters made up of acoustic metamaterial structures can work without a power supply. However, their working frequency is not adjustable. This study reports a tunable open planar acoustic notch filter that incorporates a pneumatically controlled Helmholtz resonator (HR) array. The HR array consisted of three layers: cavities, a membrane, and microchannels. The cavities function as the HR chambers, whose volume determines the resonant frequency. The acoustic wave is effectively attenuated at this frequency owing to the HR effect. The HR chamber volume can be varied by displacing the stretchable membrane with air pressure through the microchannels. This helps in adjusting the resonant frequency, thereby realizing a tunable acoustic notch filter. We conducted theoretical, and experimental examinations along with simulations of the frequency response for an HR array with three different cavity thicknesses. The prototype device realized a frequency tuning of approximately 4.1–4.9 kHz with 10 dB filtering. Furthermore, an improved notch frequency tunability was observed for the thinner cavities, along with a decrease in the notch performance. Thus, the proposed HR array filter can be useful for high-frequency noise that is generally uncomfortable for humans.

Predicting the Reflection Coefficient of a Viscoelastic Coating Containing a Cylindrical Cavity Based on an Artificial Neural Network Model

A cavity viscoelastic structure has a good sound absorption performance and is often used as a reflective baffle or sound absorption cover in underwater acoustic structures. The acoustic performance field has become a key research direction worldwide. Because of the time-consuming shortcomings of the traditional numerical analysis method and the high cost of the experimental method for measuring the reflection coefficient to evaluate the acoustic performance of coatings, this innovative study predicted the reflection coefficient of a viscoelastic coating containing a cylindrical cavity based on an artificial neural network (ANN). First, the mapping relationship between the input characteristics and reflection coefficient was analysed. When the elastic modulus and loss factor value were smaller, the characteristics of the reflection coefficient curve were more complicated. These key parameters affected the acoustic performance of the viscoelastic coating. Second, a dataset of the acoustic performance of the viscoelastic coating containing a cylindrical cavity was generated based on the finite element method (FEM), which avoided a large number of repeated experiments. The minmax normalization method was used to preprocess the input characteristics of the viscoelastic coating, and the reflection coefficient was used as the dataset label. The grid search method was used to fine-tune the ANN parameters, and the prediction error was studied based on a 10-fold cross-validation. Finally, the error distributions were analysed. The average root means square error (RMSE) and the mean absolute percentage error (MAPE) predicted by the improved ANN model were 0.298% and 1.711%, respectively, and the Pearson correlation coefficient (PCC) was 0.995, indicating that the improved ANN model accurately predicted the acoustic performance of the viscoelastic coating containing a cylindrical cavity. In practical engineering applications, by expanding the database of the material range, cavity size and backing of the coating, the reflection coefficient of more sound-absorbing layers was evaluated, which is useful for efficiently predicting the acoustic performance of coatings in a specific frequency range and has great application value.

Investigation of Warp and Weft Knitted Fabric Acoustic Structures Derived from Garment Waste

The mechanical performance of knitted fabric was significantly affected by loop density and geometries. Knitted fabric composites occupy a special position in the field of engineering materials because of their easy to form complex components and high impact energy absorption. But Knitted fabric composites have low in-plane tensile strength because the yarns are in a loop structure in the materials. Sound insulation requirements in automobiles, manufacturing environments, and equipment, generating higher sound pressure drive the need to develop more efficient and economical ways of producing sound absorption materials. The knitted fabric based acoustic materials were produced from cut wastes from different garment industries for their sound absorption property test as per the method described in ASTM E 1050. The acoustic performance of knitted fabrics was measured by independent tube methods for sound waves of 1000-6000 Hz. It is observed that the knitted fabrics acoustic materials prepared from waste materials showed high sound absorption than woven fabrics made from the same synthetic fibers. Moreover, the test revealed that blended knitted fabric had a better sound absorption property.

Observation of Unidirectional Solitonlike Edge States in Nonlinear Floquet Topological Insulators

A salient feature of solid-state quantum-Hall-type topological materials in two dimensions is the presence of conducting electronic edge states that are insensitive to scattering by disorder. Such unidirectional edge states have been predicted and observed in many other experimental settings, including photonics, mechanical, and acoustic structures. It is of great interest to understand how topological states behave in the presence of interparticle interactions and nonlinearity. Here, we experimentally demonstrate backscatter-immune unidirectional solitonlike nonlinear states on the edge of photonic topological insulators consisting of laser-written waveguides. As a result of the optical Kerr nonlinearity of the ambient glass, the solitonlike wave packet forms a long-lived quasilocalized coherent structure that slowly radiates power into the bulk and along the edge. The realization of solitonlike edge states paves the way to an understanding of nonlinear and interacting topological systems.2 MoreReceived 4 May 2021Revised 18 October 2021Accepted 21 October 2021DOI:https://doi.org/10.1103/PhysRevX.11.041057Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasKerr effectOptical solitonsPhotonicsTopological effects in photonic systemsTopological materialsAtomic, Molecular & OpticalCondensed Matter, Materials & Applied PhysicsNonlinear Dynamics

Contribution of the generalized (r, q) distributed electrons in the formation of nonlinear ion acoustic waves in upper ionospheric plasmas

The properties of ion acoustic solitary and periodic structures are studied in magnetized two-ion component (O+ − H+ − e) plasmas with (r, q) distributed electrons. It is found that two modes of ion acoustic waves, namely, fast and slow modes, can propagate in such a plasma. The nonlinear Zakharov–Kuznetsov equation is derived using the well-known reductive perturbation method. Employing the theory of planar dynamical systems, the system under consideration is found to admit compressive (hump) and rarefactive (dip) solitary structures and periodic wave solutions. It is found that behavior of propagation of nonlinear ion acoustic solitary structures is different for fast and slow modes owing to the difference in physics of the two modes. The effect of the double spectral indices r and q is thoroughly explored. It is shown that altering the shape of the distribution function through these indices radically alter the propagation characteristics of nonlinear ion acoustic waves. The ratio of concentration of heavy (O+) to light ions (H+) is found to change the fast mode, whereas the temperature ratio is observed to alter the slow mode. We have applied our study to the upper ionosphere where bi-ion plasmas and the presence of non-Maxwellian electrons have been observed by various satellite missions.

Machine learning inversion design and application verification of a broadband acoustic filtering structure

Most previous studies on acoustic structure performances have used the geometrical parameters to establish a theoretical model and calculate the acoustic performance to realize the forward design of an acoustic structure. This process strongly depends on the complexity and stability of the theoretical model. The development of machine learning has provided a new idea for the inverse design of acoustic structures, which can significantly improve the efficiency and accuracy of the inverse design of acoustic structures. This paper used the Helmholtz resonator and porous materials as a basic unit and established a theoretical model for the forward calculation of the sound absorption coefficient of the unit. By keeping two geometrical parameters fixed while changing the other four geometrical parameters, a database consisting of 79,730 acoustic performance parameter groups was constructed, and it corresponded to different sound-absorbing units with an absorption coefficient peak α ranging from 0.1467 to 0.9999, and a frequency f ranging from 255 Hz to 1658 Hz. A deep neural network (DNN) model was used to realize the reverse design of acoustic units corresponding to the performance parameters inside and outside the database. Because this paper aimed to achieve the prediction of acoustic performance parameters, and proposed a deep auto-encoder network (DAE) model with higher prediction accuracy after optimization based on DNN model. Using these two models, the prediction of the acoustic units corresponding to ten groups of performance parameters inside and outside the database was performed. The forward calculation results show that the two proposed models can realize the inversion design of acoustic structures, and the prediction accuracy of the DAE model is 2.64 times higher than that of the DNN model. The DAE model is used to realize the reverse design of the acoustic structure with a broadband acoustic filtering function. The reliability of the predicted broadband acoustic filtering structure was verified by the experiments with the predicted center frequency deviation of only 9 Hz. The proposed DNN and DAE models have certain reference significance for realizing the reverse design of acoustic performance and functional acoustic equipment.

Chimpanzee vowel-like sounds and voice quality suggest formant space expansion through the hominoid lineage.

The origins of human speech are obscure; it is still unclear what aspects are unique to our species or shared with our evolutionary cousins, in part due to a lack of a common framework for comparison. We asked what chimpanzee and human vocal production acoustics have in common. We examined visible supra-laryngeal articulators of four major chimpanzee vocalizations (hoos, grunts, barks, screams) and their associated acoustic structures, using techniques from human phonetic and animal communication analysis. Data were collected from wild adult chimpanzees, Taï National Park, Ivory Coast. Both discriminant and principal component classification procedures revealed classification of call types. Discriminating acoustic features include voice quality and formant structure, mirroring phonetic features in human speech. Chimpanzee lip and jaw articulation variables also offered similar discrimination of call types. Formant maps distinguished call types with different vowel-like sounds. Comparing our results with published primate data, humans show less F1–F2 correlation and further expansion of the vowel space, particularly for [i] sounds. Unlike recent studies suggesting monkeys achieve human vowel space, we conclude from our results that supra-laryngeal articulatory capacities show moderate evolutionary change, with vowel space expansion continuing through hominoid evolution. Studies on more primate species will be required to substantiate this.This article is part of the theme issue ‘Voice modulation: from origin and mechanism to social impact (Part II)’.