Sound Waves Research Articles

Beam–plasma dynamics in finite-length, collisionless inhomogeneous systems

This study investigates the streaming instability triggered by ion motion in a plasma system that is finite in length, collisionless, and inhomogeneous. Employing numerical simulations using particle-in-cell techniques and kinetic equations, the study examines how inhomogeneity emerges from integrating a cold ion beam with a background plasma within a confined system. The findings suggest that steady ion flow can modify ion sound waves through acoustic reflections from system boundaries, leading to instability. Such phenomena are known to be a hydrodynamic effect. However, there are also signatures of the beam-driven ion sound instability where kinetic resonances play a pivotal role. The main objective is to understand the impact of a finite-length system on beam–plasma instability and to identify the wave modes supported in such configurations.

A stable decoupled perfectly matched layer for the 3D wave equation using the nodal discontinuous Galerkin method

In outdoor acoustics, the calculations of sound propagating in air can be computationally heavy if the domain is chosen large enough for the sound waves to decay. The computational cost is lowered by strategically truncating the computational domain with an efficient boundary treatment. One commonly used boundary treatment is the perfectly matched layer (PML), which dampens outgoing waves without polluting the computed solution in the inner domain. The purpose of this study is to propose and assess a new perfectly matched layer formulation for the 3D acoustic wave equation, using the nodal discontinuous Galerkin finite element method. The formulation is based on an efficient PML formulation that can be decoupled to further increase the computational efficiency and guarantee stability without sacrificing accuracy. This decoupled PML formulation is demonstrated to be long-time stable, and an optimization procedure for the damping functions is proposed to enhance the performance of the formulation.

The acoustic properties of FDM printed wood/PLA-based composites

The acoustic properties of the Fused Deposition Modelling (FDM) printed PLA wood composite was investigated. Initially tensile and flexural of wood PLA composite was studied with respect to varying layer thickness (0.15 mm, 0.20 mm, and 0.30 mm), infill density (30%, 60%, and 90%), and pattern (Layer, Triangle, and Hexagon). The outcomes demonstrated that the specimen produced with a hexagonal pattern, 90 % infill density, and 0.2 mm layer thickness had the highest tensile (16 MPa) and flexural strength (16 MPa). Utilizing this optimized parameter, micro-perforated panels were printed and acoustic properties were studied. Five specimens with a 3 mm thickness, various perforation diameters (5 mm, 4 mm, and 3 mm), and architecturally tapered perforations were fabricated. Using the impedance tube approach, the sound transmission loss and sound absorption coefficients were measured. The findings indicate that, in comparison to all the printed specimens, tapered type perforation with an exterior diameter of 5 mm and an internal diameter of 4.7 mm showed highest sound absorption coefficient of 0.60 Hz. A viscous loss is obtained by its convergent hole diameter reduction, which results in sound attenuations and is easily absorbed in the micro-perforated panel. Similar to this, the specimen printed with smaller perforation diameters (3 mm) had a high sound transmission loss of 79 dB. The small diameter of the perforations prevented the passage of sound waves. The current study is anticipated to lay the groundwork for extensive future research on these classes of materials, potentially serving as a catalyst for advancements in FDM based polymeric materials research and development.

Estimating direction of arrival in reverberant environments for wake-word detection using a single structural vibration sensora).

The vibrational response of an elastic panel to incident acoustic waves is determined by the direction-of-arrival (DOA) of the waves relative to the spatial structure of the panel's bending modes. By monitoring the relative modal excitations of a panel immersed in a sound field, the DOA of the source may be inferred. In reverberant environments, early acoustic reflections and the late diffuse acoustic field may obscure the DOA of incoming sound waves. Panel microphones may be especially susceptible to the effects of reverberation due to their large surface areas and long-decaying impulse responses. An investigation into the effect of reverberation on the accuracy of DOA estimation with panel microphones was made by recording wake-word utterances in eight spaces with reverberation times (RT60s) ranging from 0.27 to 3.00 s. The responses were used to train neural networks to estimate the DOA. Within ±5°, DOA estimation reliability was measured at 95.00% in the least reverberant space, decreasing to 78.33% in the most reverberant space, suggesting an inverse relationship between RT60 and DOA accuracy. Experimental results suggest that a system for estimating DOA with panel microphones can generalize to new acoustic environments by cross-training the system with data from multiple spaces with different RT60s.

Phononic crystal-based acoustic demultiplexer design via bandgap-passband topology optimization

The wave demultiplexer, which selectively transports specific frequencies from incident waves, has garnered considerable interest for its applications across various engineering disciplines. This study introduces a new customizable design method for acoustic demultiplexers based on the topology optimization of phononic crystals (PnCs). To achieve an acoustic demultiplexer capable of filtering multiple frequencies, a topological design model for PnCs that simultaneously considers bandgaps and passbands is proposed. By assembling the optimized PnCs within the structure, the demultiplexer can separate sound waves of different frequencies into distinct output channels. In the optimization model, an objective function based on transmission rates is proposed to determine whether specific frequencies fall within the specified bandgap or passband. To solve this complex topology optimization problem, the Kriging-based material-field series expansion (KG-MFSE) approach is used to describe the material distribution and optimization of PnCs. The designed PnC unit cells can be directly integrated into the demultiplexer without requiring additional space. Based on specified combinations of passbands and bandgaps, different PnCs are designed to realize a programmable acoustic demultiplexer capable of filtering various sound waves. Numerical analyses demonstrate that the constructed acoustic demultiplexer effectively separates the specified frequencies. Finally, experimental validation of the 3D printed acoustic demultiplexer model confirms the effectiveness of the proposed optimization method.

Bifurcation, quasi‐periodic, chaotic pattern, and soliton solutions for a time‐fractional dynamical system of ion sound and Langmuir waves

This paper strives to investigate the time fractional system that characterizes the ion sound wave influenced by the ponderomotive force induced by a high‐frequency field, as well as the Langmuir wave in plasma. Initially, based on the qualitative theory for planar integrable systems, four‐phase portraits are found in the phase plane under certain conditions on the physical parameters. These conditions are used to prove analytically the existence of solitary, kink (anti‐kink), periodic, super‐periodic, and unbounded wave solutions. The correspondence between the energy levels, phase orbits, and consequently the type of the solution is announced. We derived the bounded wave solutions associated with the phase orbits, which are shown to be consistent with the qualitative analysis of the types of solutions. Moreover, we studied the consistency between the obtained solutions by investigating the degeneracy of the solutions through the transmission between the phase orbits, or equivalently, through the dependence on the initial conditions. With the presence of perturbed periodic terms, the quasi‐periodic behavior and chaotic patterns are investigated.

Dynamics of rain-triggered lahars and destructive power inferred from seismo-acoustic arrays and time-lapse camera correlation at Volcán de Fuego, Guatemala

AbstractLahars, or volcanic mudflows, are one of the most devastating natural, volcanic hazards. Deadly lahars, such as the one that occurred after the Nevado del Ruiz, Columbia eruption in 1985, in which at least 23,000 people tragically lost their lives, threaten the safety and well-being of humans, the economy, and the infrastructure of many of the communities living in the vicinity of volcanoes. Due to their complex flow behaviors, lahars remain a major challenge to those studying them. We present an analysis of several rain-triggered lahar events at Volcán Fuego in Guatemala using both seismic and infrasound monitoring to quantify both ground vibrations and low-frequency atmospheric sound waves associated with these mudflows. Geophysical data collected over this field campaign quantifies flow parameters such as velocities, stage and the frequency of these rain-triggered lahars. Time-lapse imagery of lahar flows is compared with filtered seismo-acoustic signal characteristics to ascertain stage predictions and relationship to stage fluxes. Using random forest regression models, we establish moderate correlations (correlation coefficient modes 0.48–0.53) with statistical significance (p value = 0.01–0.02) between signal energetics and respective stage. Compiling a catalog of rain-triggered lahar events in Volcán de Fuego’s drainages over a season permits a dataset amenable to statistical analysis. Our goal is the development of new-generation geophysical monitoring tools that will be capable of remote and real-time estimation of flow parameters.

Acoustic Detection of Pipeline Blockages in Gas Extraction Systems: A Novel Approach

Gas extraction is crucial for coal mine safety, yet pipeline blockages by solid slag and water severely hinder efficiency and pose risks. Traditional detection methods are limited by rapid signal attenuation and noise interference. In this study, an acoustic detection technology is introduced for pipeline blockages, utilizing sensors at potential blockage points to collect sound wave data. Experiments with a scaled pipeline model reveal that slag blockages produce characteristic peaks in the 1200 Hz–2000 Hz range, while water blockages show peaks in the 1 kHz–2 kHz and 3.5 kHz–4.5 kHz bands. The longitudinal blockage intensity and extraction pressure significantly affect the sound pressure levels. A reliable fitting model predicts the blockage intensity based on acoustic signals, achieving high accuracy. This novel method enhances blockage identification, offering a non-invasive, cost-effective solution that improves coal mine safety and efficiency.

A pneumatic soft acoustic metamaterial through modular design

Tunable acoustic metamaterials have excellent sound waves control and manipulation properties because of their deformations under different stimuli. Pneumatic actuation has recently attracted the attention due to its low-cost, fast in response and easy to integrate. However, due to the difficulty in fabricating soft enough scatterers and ensuring their airtightness, the experimental realization of pneumatic soft acoustic metamaterials remains a great challenge. In this paper, a pneumatic soft acoustic metamaterial is designed and its tunable band gap has been experimentally demonstrated. The designed pneumatic soft acoustic metamaterial comprises an array of soft inflatable rubber cavities in the background of air. And the scatterer in the soft acoustic metamaterials can deform by adjusting the air pressure, which can switch on or off the band gaps. The effects of scatterer shapes and orientations on the adjustable band gap are studied using numerical simulation methods. Furthermore, the modular design is introduced to ensure the flexibility of the designed soft acoustic metamaterials. And we fabricate modularized pneumatic soft acoustic metamaterials with square scatterers through the casting molding approach. The acoustic experiment results are agreement with the simulation results, which demonstrates that the band gap can be efficiently tuned when applying the air pressure. Additionally, the average transmission drops by about 20.2 dB in the maximum band gap of 3209.7–4639.7 Hz. This study provides a guide for designing and fabricating a pneumatic soft acoustic metamaterial, and confirms the feasibility and application potential of the design of acoustic devices by harnessing pneumatic actuation.

Characterizing Temperature-Dependent Acoustic and Thermal Tissue Properties for High-Intensity Focused Ultrasound Computational Modeling

High-intensity focused ultrasound (HIFU) thermal therapies utilize concentrated sound waves to ablate diseased tissue at precise locations within the body. Computational simulations of HIFU can assist clinicians by predicting the death of target tissues, identifying sensitive healthy tissues that risk thermal damage, and optimizing acoustic power delivery to minimize treatment times and maximize treatment efficacy. Accurate simulations require accurate inputs, and many computational solvers neglect property changes induced by tissue heating during treatment. Additionally, temperature-dependent tissue property data in the literature are relatively scarce. This study presents methodology for characterizing temperature-dependent acoustic and thermal properties in ex vivo porcine muscle tissue. From 20 – 50 °C, speed of sound is found to increase from approximately 1580 – 1620 m/s. The acoustic attenuation coefficient increases for 20 – 50 °C from 0.09 – 0.24 Np/cm at 0.5 MHz and 0.16 – 0.37 Np/cm at 1.6 MHz. Thermal conductivity and thermal diffusivity increase from 0.52 – 0.55 W/m °C and 0.147 – 0.158 mm2/s, respectively, over 20 – 60 °C. Specific heat capacity increases from approximately 3500 – 3800 J/kg °C, over 20 – 80 °C. Each property is consistent with data found in the literature, extends the literature to a larger temperature range, and, for acoustic properties, extends to unique frequencies. Temperature-dependent predictive models are also developed for each of the five properties. This study’s property measurement methodologies can be used to characterize other biological tissues, and the predictive models developed herein will facilitate future efforts in temperature-dependent modeling and uncertainty quantification of HIFU thermal therapies.

The Influence of the Project Based Learning Model Assisted by PhET Simulation on Students’ Critical Thinking and Problems Solving Abilities in Sound Wave Material

This research aims to test the effect of the Project Based Learning model assisted by PhET simulations on students' critical thinking and problems solving abilities in sound wave material. The type of research used was a Quasi experiment with a pretest-posttest control group design. The population in this study were all students in class XI Science at SMAN 3 Mataram. The sampling technique used purposive sampling technique, so that XI IPA 1 was obtained as an experimental class which was given treatment using a Project Based Learning model assisted by PhET simulation and XI IPA 2 as a control class using a conventional model. The test instrument used is a description of 12 question items consisting of 7 question items to measure critical thinking abilities and 5 question items to measure problem solving abilities. The hypothesis test used in this research is one-way MANOVA. The results of the hypothesis test show that the significance value of 0.001 is less than 0.05, so H_0 is rejected and H_a is accepted. Based on these results, it was concluded that there was an influence of the Project Based Learning model assisted by PhET simulations on students' critical thinking and problems solving abilities in sound wave material.

Genetic-algorithm-assisted design of chiral honeycomb membrane acoustic metamaterials for broadband noise suppression

Low-frequency sound wave reduction is hardly feasible for traditional sound absorbers such as porous media. In contrast, locally resonant acoustic metamaterials act as spatial frequency filters, effectively reducing low-frequency noise. However, these materials can have narrow bandgaps, add extra mass to the main system, and function only within a specifically adjusted frequency range. Therefore, this paper proposes a methodology for designing three-dimensional (3D) chiral honeycomb membrane-type acoustic metamaterials (MAM) based on acoustic circular dichroism (ACD), negative effective mass, and local resonance mechanisms (LRM). The paper also uses the genetic algorithm (GA) to maximize sound transmission attenuation and widen bandgaps. The accuracy of the simulations is validated with available experimental data. The key idea of the present study is to automatically design a MAM structure using modern optimization tools. A developed GA aims to maximize the average sound transmission loss (STL) across the desired low-frequency range of 0–850 Hz by optimizing the value of structural parameters associated with the configurations of masses, including rotation and linear offset, as well as their geometrical dimensions, including length and width. COMSOL Livelink with MATLAB is employed as a practical co-simulation tool to find an optimum value for structural parameters. Results indicate a 35% improvement in average STL along with an ultra-wide bandgap with a 507% bandgap coverage factor (BGCF) in the frequency range of interest, verifying the reliability of the developed algorithm. In addition, sound mitigation incidence is justified by exploring the negative effective parameters of the unit cell and displacement vector fields. The proposed designs demonstrate superior performance as both initial and optimized models broke the mass law within the investigated frequency range. Finally, the effect of the selected geometrical parameters on the objective function is observed through sensitivity analysis. This study presents the practical use of optimization algorithms to develop MAMs.

Multifunctional metamaterials for simultaneous sound absorption and flexural vibration isolation

Controlling the noise and vibration simultaneously in some engineering scenes is extremely essential to eliminate harmful effects on the humans and equipments. To overcome this challenge, a multifunctional metamaterial plate with both airborne sound absorbtion and flexural vibration isolation simultaneously is investigated theoretically, numerically, and experimentally. The plate consists of a host plate and a Helmholtz resonator, where Helmholtz resonance is used to absorb sound waves and its external solid domain plays as role of a local resonator to isolate the flexural vibrations. The theoretical models were established to characterize the mechanism of the sound absorption and vibration isolation. The experimental results demonstrated that the proposed metamaterial plate can achieve perfect sound absorption at 649 Hz and a flexural wave band gap at 289–470 Hz. Besides, although the sound absorption and vibration isolation functions are integrated in the same component, our theory identifies several critical geometrical parameters which can manipulate the absorption peak and the flexural wave bandgap, allowing us to design its frequency of multiple functions as desired. This work provides a promising solution for noise and vibration reduction in engineering.

Is it Time to Demolish Current Mathematics?

Current mathematics in 3D geometric space plus real time t as an external control is incomplete and misleading. The dream of theoretical physicists and mathematicians to demolish all current mathematics and replace it with a single universal numerical statistical law in 4D is now within reach. In this paper, we first focus on the introduction and definition of the proposed unitary 4D space. Next, we introduce and explain what we call the modern Laplacian theorem in 4D unit space. Finally, we explain some unexpected and striking numerical results such as measuring the speed of sound in air at 330 m/s and that of light at 3 E8 m/s. There is an inherent relationship between the speed of sound in air and the diffusivity of sound waves in the sound room, similar to the relationship between the speed of light in a vacuum and the thermal diffusivity of metals when they all live two in a 4D unit. space.

Model for random atmospheric inhomogeneities in engine noise auralization

Modelling the impact of atmospheric turbulence is not often encountered in aircraft noise auralizations despite its relevance to human-ear perception. As sound waves propagating through turbulent media undergo modulations, observable in phase and amplitude fluctuations, the plausibility of aircraft noise auralizations is increased by taking this effect into account. This paper presents an extension of a method first developed by Rietdijk et al., for modelling these fluctuations for spherical sound waves travelling through randomly inhomogeneous media. The extensions of the method presented in this paper are: (1) Height-dependent von Kármán spectra are implemented to model slanted or vertical sound propagation. (2) An overlap-add-method is introduced to model a moving sound source when height-dependent changes of turbulence characteristics are considered. (3) Easier to measure input parameters for the (meteorological) conditions are implemented, like e.g. the day time or relative humidity. The method is integrated into a global framework dedicated to engine noise simulation, propagation and auralization, developed and validated by the German Aerospace Center (DLR). A good match with measured functions of phase and amplitude fluctuations are observed, as well as realistic reproduction of spectrograms, time signals and the psychoacoustic fluctuation strength of the auralizations with respect to real flyovers.

Novel method to determine bedrock from a single sensor based seismic reflection signal using Haar wavelet transform

The determination of bedrock depth is crucial across various earth sciences and related fields. Geophysical techniques, notably the continuous wavelet transform, are increasingly employed to map subsurface bedrock structures. This method allows the transformation of 1D time domain seismic reflection signals into a 2D image, providing time–frequency representations for feature extraction. Leveraging the advantages of wavelet theory, particularly the Haar wavelet known for its simplicity and compact support, this study utilizes continuous Haar wavelet local maxima lines to enhance bedrock analysis. Seismic reflection data is acquired using an extremely sensitive geophone as a receiver along with a high dynamic range data logger. The Common Midpoint (CMP) approach, coupled with optimized offset distances, is utilized to ensure robust data quality and signal strength. Simple sources, such as a sledgehammer, generate sound waves for data collection prior to borehole drilling, correlating acquired data with lithogeological information. This research emphasizes the significance of adjusting parameters like sampling frequency, choice of wavelet, and optimal offset distances. The methodology employed, involving a single geophone, a one-channel data recorder, and a basic sledgehammer as a sound source, offers an inexpensive, straightforward, and non-invasive approach. The study demonstrates the effectiveness of Haar wavelet local maxima lines in accurately determining bedrock depth, producing results closely aligned with both predicted and actual depths.

On the Absorption of γ-Radiation by Absorbers with a Thickness Equal to a Multiple of the Mean Free Path and Analogies with Standing Waves in a Sound Resonance Tube

This article addresses the phenomenon of the decreased absorption of γ-radiation when the thickness of the absorber equals a multiple of the mean free path, as observed in relevant laboratory experiments with various absorbing materials. This phenomenon can be compared with the periodic peaks in intensity in an open-ended sound tube that appear at multiples of half wavelength. This could suggest that there is analogy between the two physical systems that are the γ-ray absorber and the sound wave resonance tube. More similarities between the two systems are also presented.

Discussion on optical solitons, sensitivity and qualitative analysis to a fractional model of ion sound and Langmuir waves with Atangana Baleanu derivatives

Abstract This research explores new soliton solutions to the Atangana–Baleanu derivative (ABD) fractional system of equations for ion sound and Langmuir waves (FISLW). We utilize the fractional ABD operator to convert our system into an ordinary differential equations. In recent years, machine learning (ML) evolves significantly in the context of data analysis and computing different solutions, which typically enables systems to operate wisely. Now, we are going to use numerous ML tools including matplotlib. pyplot as plt, scipy.integrate, mpl toolkits.mplot3d, and Axes3D to generate various types of optical solutions by using complete discriminant of the polynomial method. We will also analyze solutions for the hyperbolic function, trigonometric function, Jacobian elliptic function (JEF), and other solitary wave solutions. Solitons have extensive uses in pure and applied mathematics, including nonlinear partial differential equations: the Boussinesq equation, the nonlinear Schrödinger equation, and the sine-Gordon equation, Lie groups, Lie algebras, and differential and algebraic geometry. In addition, we study the chaotic behaviour, i.e., 2D, 3D, time series, Poincarè maps, and sensitivity analysis of our governing model. Sensitivity analysis explores how changes in a system’s variables affects its behaviour.

Theory and Design of Audio Rooms: Physical Formulation

The time-dependent statistical chains of transition matrix B are successfully used to calculate the reverberation time TR and sound energy density field in audio rooms. This is a real breakthrough in the search for a statistical derivation of Sabines' imperial theory which has never been rigorously proven since 1898. Additionally, we provide proper design and calculations of sound wave energy density in audio rooms via two cuboid room examples. We provide proper design and calculations of sound wave energy density in audio rooms via two cuboid room examples. We also propose some general statistical rules that can be applied to statistical problems of physical phenomena in general, such as the thermal diffusion equation and the theory of sound waves in audio rooms. We also give a description of the theory and design of what we call comfortable sound rooms based on the purpose of their use via well-defined measurables. Finally, we provide a consistent derivation of Sabines' theory without using Ls=4V/A or any other statistical assumptions.

Unprecedented mechanical wave energy absorption observed in multifunctional bioinspired architected metamaterials

In practical engineering, noise and impact hazards are pervasive, indicating the pressing demand for materials that can absorb both sound and stress wave energy simultaneously. However, the rational design of such multifunctional materials remains a challenge. Herein, inspired by cuttlebone, we present bioinspired architected metamaterials with unprecedented sound-absorbing and mechanical properties engineered via a weakly-coupled design. The acoustic elements feature heterogeneous multilayered resonators, whereas the mechanical responses are based on asymmetric cambered cell walls. These metamaterials experimentally demonstrated an average absorption coefficient of 0.80 from 1.0 to 6.0 kHz, with 77% of the data points exceeding the desired 0.75 threshold, all with a compact 21 mm thickness. An absorptance-thickness map is devised for assessing the sound-absorption efficiency. The high-fidelity microstructure-based model reveals the air friction damping mechanism, with broadband behavior attributed to multimodal hybrid resonance. Empowered by the cambered design of cell walls, metamaterials shift catastrophic failure toward a progressive deformation mode characterized by stable stress plateaus and ultrahigh specific energy absorption of 50.7 J/g—a 558.4% increase over the straight-wall design. After the deformation mechanisms are elucidated, a comprehensive research framework for burgeoning acousto-mechanical metamaterials is proposed. Overall, our study broadens the horizon for multifunctional material design.