Low-frequency Sound Waves Research Articles

Viscoelastic material enhancement of underwater sound absorption in higher-order resonators: from low-frequency to ultra-broadband

Underwater noise control is crucial for improving the marine acoustic environment. This study introduces a novel underwater acoustic absorber design that integrates viscoelastic materials with higher-order resonance structures to enhance the absorption efficiency of low-frequency sound waves. By embedding a thin layer of rubber within a conventional second-order Helmholtz resonator, the rubber's viscoelastic and damping properties significantly improve this structure's underwater low-frequency acoustic performance. Theoretical and simulation calculations have shown that the structure has two perfect absorption peaks in the low-frequency range. The simulation results show that in the frequency range of 415-1848 Hz (Simulation), only four units are needed to effectively absorb up to 90% of noise energy, and the total volume is only. Moreover, the absorber maintains excellent absorption performance over a wide range of incidence angles from 0 to 60 degrees. This work is helpful to design ultra-thin low-frequency underwater absorbers.

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.

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.

Calibration-free temperature monitoring of pulverized coal powder based on the dual-mode acoustic tomography

Accurate temperature measurement of the pulverized coal powder is crucial in detecting and preventing coal spontaneous combustion. Compared to other temperature measurement techniques, acoustic tomography using low frequency sound waves has the advantage of high penetration ability for non-intrusive temperature measurement inside the pulverized coal powder. Additionally, by employing an array of acoustic transducers mounted around the coal powder, the entire sensing area can be covered, enabling a comprehensive temperature distribution analysis through tomographic reconstructions. However, the main drawback of the acoustic temperature measurement is the model complexity in describing the dependence of acoustic sound speed on temperature in the porous pulverized coal powder. Accurate calibration is required to determine the model parameters for temperature retrieval, however, which is difficult for in situ industrial application. To solve this problem, we proposed a calibration-free temperature monitoring method based on the dual-mode acoustic tomography for pulverized coal. The three-parameter JCAL model is used to characterize the acoustic propagation in coal powder. The temperature and micro-structure parameters can be jointly retrieved from the reconstructed sound slowness and attenuation distributions at different frequencies. The feasibility and effectiveness of the proposed method are validated in the simulation study. Results show that the dual-mode acoustic tomography can provide calibration-free simplicity for pulverized coal temperature measurement, which has a great potential for industrial applications.

Design and Optimization of One Special Microperforated Plate-Labyrinth Coupled Structure (MPPS-LS): From the View of Numerical Simulation

Controlling large-wavelength acoustic waves via small-size structures is an important direction for the field of noise control. Since porous acoustic material can only absorb low-frequency sound waves when their thickness is approximately one-fourth of the wavelength, such acoustic material is not effective when controlling the large-wavelength acoustic waves with small-size structures. Therefore, the resonant acoustic material has been usually chosen to absorb low-frequency sound waves instead. As a typical resonant acoustic material, microperforated plate structures (MPPS), need one large cavity with low space utilization to absorb the low-frequency acoustic waves. The microperforated plate-labyrinth coupled structure (MPPS-LS) has been proposed with the goal of improving low-frequency sound absorption ability, which is consisted of a MPPS and three separated second-order LS coupled together. The mathematical model has been established using the acousto-electric analogy method and transfer matrix method to examine the impact of the structural parameters of each part on the acoustic characteristics. According to this study, the coupled structure is compact in size and has a good low and medium-frequency acoustic absorption effect, combining low and medium-frequency acoustic absorption characteristics of both the MPPS and LS. The sound absorption of the structure after optimized design is testing using impedance tube.

Structural Design and Optimization of Low-Frequency High-Power Electromagnetic Transducer

Crucial equipment for marine engineering and research, high-power ultra-low frequency sound sources have become necessary with the rapid development of seabed resource exploration, marine environment monitoring, underwater remote target detection, and communication technology. The current ultra-low frequency sound source cannot meet the requirements of practical applications. In this paper, both the finite element method and equivalent circuit method are used to improve the electromagnetic acoustic transducer, focusing on solving the structural design of the functional parts of the transducer, as well as the mechanical, electrical, magnetic parametrization of the transducer and other key technologies. The structural parameters and material parameters in the transducer that affect the final performance response are obtained through the optimization of the genetic algorithm. The results show that the electromagnetic acoustic transducer studied in this paper can emit low-frequency sound waves below 50~Hz, and the maximum sound pressure level reaches 138~dB, which meets the requirements of general low-frequency high-power acoustic wave transducers in practical work.

Tympanic membrane metamaterial inspired multifunctional low-frequency acoustic triboelectric nanogenerator

This study introduces the Tympanic Membrane Metamaterial inspired acoustic Triboelectric Nanogenerator (TMM-TENG), which exhibits subwavelength structural dimensions and effective sound absorption within low-frequency ranges. The performance of acoustic energy harvesting is increased by replacing rigid bottom of the acoustic cavity with an elastic part and introducing a point-surface mechanism. Experimental tests employing the proposed mechanism are then conducted. The obtained results show a remarkable 2220 % increase in the output voltage of the TMM-TENG compared with the traditional approach. As for the acoustic energy harvesting performance, for a sound pressure level (SPL) of 95 dB, the peak-to-peak value of the output voltage reaches 500 V, with a measured current of 40 μA and a maximum output power of 3.05 mW. Moreover, the incorporation of an elastic part into the TMM-TENG proves advantageous in the manipulation of low-frequency sound waves. The acoustic performance of the device can also be regulated by adjusting the thickness of the elastic part. In addition, multiple TMM-TENGs with varying elastic part thicknesses are placed on a duct, and band-limited white noise is generated to evaluate the sound reduction ability without limiting the air ventilation. Furthermore, the mounted TMM-TENG allows to perform of self-powered wireless temperature sensing and acoustic telecommunication functionalities.

Low-frequency sound attenuation by coiled-up meta-liner with nonuniform cross sections under grazing flow

We report a kind of coiled-up meta-liners with nonuniform cross sections (CMNC), which can efficiently attenuate low-frequency sound waves under grazing flow with a deep subwavelength thickness (e.g., ∼λ/17 at 500 Hz). At a grazing flow Mach number of 0.26, the average transmission loss of the meta-liner is 12.6 dB at 500–1000 Hz, which is twice as much as that of a double-degree-of-freedom acoustic liner of the same size. Physically, the nonuniform cross-sectional distribution and significant cross-sectional area ratio enhances vortex shedding, thus resulting in severe acoustic energy dissipation. The excellent low-frequency acoustic attenuation performance of CMNC is investigated thoroughly with experimental, theoretical, and numerical methods. This work provides an avenue for low-frequency noise reduction in grazing flow scenarios (e.g., in a high bypass ratio turbofan engine).

Review of Underwater Anechoic Coating Technology Under Hydrostatic Pressure

AbstractThe underwater anechoic coating technology, which considers pressure resistance and low-frequency broadband sound absorption, has become a research hotspot in underwater acoustics and has received wide attention to address the increasingly advanced low-frequency sonar detection technology and adapt to the working environment of underwater vehicles in deep submergence. One the one hand, controlling low-frequency sound waves in water is more challenging than in air. On the other hand, in addition to initiating structural deformation, hydrostatic pressure also changes material parameters, both of which have a major effect on the sound absorption performance of the anechoic coating. Therefore, resolving the pressure resistance and acoustic performance of underwater acoustic coatings is difficult. Particularly, a bottleneck problem that must be addressed in this field is the acoustic structure design with low-frequency broadband sound absorption under high hydrostatic pressure. Based on the influence of hydrostatic pressure on underwater anechoic coatings, the research status of underwater acoustic structures under hydrostatic pressure from the aspects of sound absorption mechanisms, analysis methods, and structural designs is reviewed in this paper. Finally, the challenges and research trends encountered by underwater anechoic coating technology under hydrostatic pressure are summarized, providing a reference for the design and research of low-frequency broadband anechoic coating.

Study on Surface Active Bubble Dynamics Properties under Strong Low-Frequency Sound Waves

Study on Surface Active Bubble Dynamics Properties under Strong Low-Frequency Sound Waves

Piezoelectric Peptide Nanotube Substrate Sensors Activated through Sound Wave Energy.

The use of sustainable and safe materials is increasingly in demand for the creation of photonic-based technology. Piezoelectric peptide nanotubes make up a class of safe and sustainable materials. We show that these materials can generate piezoelectric charge through the deformation of oriented molecular dipoles when the tube length is flexed through the application of sound energy. Through the combination of peptide nanotubes with plasmon active nanomaterials, harvesting of low-frequency acoustic sound waves was achieved. This effect was applied to boost surface-enhanced Raman scattering signal detection of analytes, including glucose. This work demonstrates the potential of utilizing sound to boost sensing by using piezoelectric materials.

Automated approach for recovering modal components in shallow waters.

This paper proposes a fully automated method for recovering modal components from a signal in shallow waters. The scenario involves an unknown source emitting low-frequency sound waves in a shallow water environment, and a single hydrophone recording the signal. The proposed automated algorithm is based on the warping method to separate each modal component in the time-frequency space. However, instead of manually choosing a single arrival time for extraction, the method performs successive extractions with automated time selection based on an explicit quality factor. Modal component separation is achieved through a watershed algorithm, streamlining the process and eliminating the need for manual intervention. The proposed method is tested on experimental data of a right whale gunshot, a combustive sound source, and a bowhead whale upsweep, demonstrating its effectiveness in real-world scenarios.

Experimental study on the effect of sound waves on the heat transfer characteristics of heated pipes

This study has experimentally investigated the heat transfer characteristics of a heated steel pipe (diameter = 20 mm) placed horizontally in a vertical experimental cylindrical pipe under longitudinal sound waves. The ranges of sound parameters used in this study are as follows: sound frequency f = 210–1000 Hz, and sound pressure level SPL = 125–135 dB. The heat transfer coefficient and Nusselt number of the cross- section of the heated pipe are used to describe the influence of different sound parameters on the heat transfer behavior of the heated pipe. The results show that under the action of low-frequency strong sound wave (f < 230 Hz), the distribution of local Nusselt number of heated pipe decreases (0-90°) at first and then increases (90-180°), while under the action of high-frequency strong sound wave (f > 500 Hz), the distribution of local Nusselt number first increases and then decreases. The relative Nusselt number decreases exponentially with the increase of the Strouhal number. In addition, the oscillating flow induced by sound waves is greatly influenced by the natural convection. The local enhancing or weakening effects of strong sound waves with different parameters on the heat transfer in a hot steel pipe are related to the characteristics of local flow.

Acoustic metasurface embedded with thin-walled plate based on phase modulation for multi-angle broadband sound absorption

The design of low-frequency broadband acoustic absorbers with thin thicknesses is a longstanding and challenging problem. This work proposes an acoustic metasurface consisting of macro-perforated porous, thin-walled perforated plate, and meta-porous layers embedded by thin-walled plate (MPM) to combine the advantages of porous material and resonator. MPM is formed by four subunits with a phase gradient. The acoustic properties of an MPM unit cell are investigated by a theoretical model based on homogenization theory and transfer matrix methods, and the theoretical model is verified by a numerical model. Then, the sound absorption mechanism of MPM unit cell is explored, and it is revealed that the mid-frequency and low-frequency sound waves are mainly dissipated by thin-walled perforated plate and meta-porous layers, and the macro-perforated porous structure target high-frequency absorption. In addition, the dependence of geometric parameters of MPM unit cell on acoustic performance and reflected phase is investigated. Furthermore, the geometric parameters of each subunit in acoustic metasurface are carefully designed, and excellent absorption in target frequency is obtained by the hybrid resonance of a single unit cell and the surface wave conversion of MPM with reflected phase gradient. Also, the appearance of perfect sound absorption comes from the far-field interference between reflected waves and the wave-trapping phenomenon near the periodic structure. A thin (λ/20) absorption panel MPMs is designed to achieve multi-angle low-frequency broadband absorption and an effective normal sound absorption (>50 %) band over 344–3000 Hz. This work proposes a novel design idea and opens possibilities for acoustic metasurface practical applications in noise mitigation of various scenarios.

Investigation on high temperature point detection of spontaneous combustion of loose coal based on optimal acoustic signal

Selecting sound source signals in acoustic temperature measurement technology is particularly important and is a key to improving the accuracy of acoustic temperature measurements. Pseudorandom, linearly swept, and pulsed signals are selected as research objects for this study. The decay of the three signals as they propagate through a loose coal, the frequency band and the period of the linearly swept signal are analyzed. The results showed that the attenuation coefficient of the linear sweep signal is less sensitive to temperature, and the attenuation coefficient of the low-frequency sound wave is smaller. When the lower limit of the frequency band of the sweep signal is closer to the upper limit of the frequency band, the main peak value of the cross-correlation coefficient is smaller. The main peak of the cross-correlation curve of low-band narrowband signals is greater than that of high-band narrowband signals. The cross-correlation effect is more significant for the 600–1000 Hz sweep signal. Moreover, the strongest effect is determined when the period is 0.1 s. Finally, the temperature of anthracite loose coal was measured according to the optimal signal. The maximum absolute error in the measurement results was 1.23 °C, and the maximum relative error was 4.22%.

Mycelium-Based Composites as a Sustainable Solution for Waste Management and Circular Economy.

The global population is expected to increase by nearly 2 billion individuals over the next three decades, leading to a significant surge in waste generation and environmental challenges. To mitigate these challenges, there is a need to develop sustainable solutions that can effectively manage waste generation and promote a circular economy. Mycelium-based composites (MBCs) are being developed for various applications, including packaging, architectural designs, sound absorption, and insulation. MBCs are made by combining fungal mycelium with organic substrates, using the mycelium as a natural adhesive. Mycelium, the vegetative part of fungi, can be grown on various organic feedstocks and functionalized into a range of diverse material types that are biobased and thus more sustainable in their production, use, and recycling. This work aims to obtain mycelium-based composites with acoustic absorption properties, using coffee grounds and agricultural waste as raw materials. The topic approached presents a new method of recovering spent coffee grounds that does not involve high production costs and reduces two current environmental problems: noise pollution and abundant waste. Measurements of the normal-incidence sound absorption coefficient were presented and analyzed. Mycelium-based composites offer an innovative, sustainable approach to developing bio-composite sound-absorbing surfaces for interior fittings. The material by Ganoderma lucidum exhibits exceptional sound-absorbing properties at frequencies below 700 Hz, which is a crucial aspect of creating sound-absorbing materials that effectively absorb low-frequency sound waves. The modular construction system allows for a high degree of flexibility to adapt to short-term changes in the workplace.

A broadband and low-frequency sound absorber of sonic black holes with multi-layered micro-perforated panels

Sonic black hole (SBH) absorber is a promising strategy in noise reduction. However, low-frequency sound waves are difficult to be captured and dissipate due to the terminal truncation and the discontinuity of the admittance for the actual SBH. To make up the disadvantages, this paper incorporates micro-perforated panels (MPP) into the SBH to improve its low-frequency property. The design is realized by inserting the multi-layered MPPs (MLP) into the rings with decaying inner radius inside a SBH duct, termed the MLPSBH duct. The theoretical and numerical results show that the proposed absorber can achieve effective sound absorption in the frequencies above 225 Hz, in which the thickness of the absorber is only λ/15 with the λ being the corresponding wavelength. Mechanism studies indicate that the specific slow wave effect of the SBH can effectively mitigate the requirements for the absorber length. Closer examination reveals that the high acoustic resistance characteristics of the MLP remarkably compensate for the acoustic resistance mismatch of the SBH in low-frequency range. Thus, attributing to the interplay of the SBH and MLP effects, the proposed absorber achieves broadband and low-frequency sound absorption. Based on the deduction and validation of the transfer matrix method (TMM), the influence of the structural parameters on the sound absorption is investigated. The analysis indicates that the absorption performance of the proposed absorber barely depends on the damping and the number of rings, which allows the MLPSBH duct to maintain the excellent performance without abundant rings and extra absorbent material. The proposed strategy is an inspiration for the application of the SBH-based structures.

The acoustic streaming effects and transmission mechanisms of a micro-cavity acoustic black hole structure with an abrupt cross-section

This paper investigates the acoustic streaming effects (ASEs) and mechanisms behind the transmittance of sound in a metallic micro-cavity acoustic black hole (ABH) structure with an abrupt cross-section and examines the sound field flow characteristics inside the micro-cavity ABH under the sound excitation, such as the velocity, acceleration and pressure fields. And the sound transmission mechanisms are characterized by the ASEs which can be obtained by solving Navier–Stokes equations. The numerical results show that the sharp increase in the velocity and acceleration at the ABH tip position is the main reason for the focusing of the sound energy. And the dramatic increase in the tip cross-section reduces the acoustic streaming velocity, which is the main reason for the attenuation of the sound energy. Additionally, the thermoviscous effect of the acoustic boundary layer can also dissipate the low-frequency sound energy. The sound insulation experiment shows that the proposed micro-cavity ABH structure has a sound transmission loss (STL) of over 15[Formula: see text]dB in the low-frequency regime. This research reveals the mechanisms of the ASE’s work on the sound transmission properties of the micro-cavity ABH and provides new insight into low-frequency sound wave suppression. The ABH structure proposed in this paper has excellent strength, bearing capacity and long lifecycle, so it can be applied in the construction industry through its integrated design of structure and performance.

On the potential of using Distributed Acoustic Sensing (DAS) to build teleseism based ocean-tomography network

The sound from marine teleseisms rank among some of the loudest in Earth’s Oceans, typically radiated into the ocean near the epicenter and propagating across the entire ocean basin. Acoustic sensing on ocean observatories provide a critical path to better understand origins of these low-frequency sound waves known as T-phases, and structure of the ocean over the megameter propagation through the ocean. Of the emerging technologies implemented on these observatories, distributed acoustic sensing (DAS) has the potential to revolutionize marine seismoacoustics. DAS can be implemented on unused oceanic fibers on the continental slopes surrounding an ocean basin could readily enable a teleseism based ocean-tomography network with surprisingly little new infrastructure. In November 2021, a DAS system installed on two runs of fiber optic cable that connect to an ocean observatory measuring offshore volcanic activity, detected a few examples of teleseismic T-phases. Combined with other hydroacoustic ocean observatories in the Pacific Ocean, the T-phase origins are localized to bathymetric features over 100 km from the epicenter, an important consideration when utilizing these T-phases as sources of opportunity to study the ocean.

Design a special micro-perforated plate coupled with the labyrinth metamaterial with improved sound absorption properties at medium and low frequencies

The micro-perforated panel structure has good sound absorption performance in medium and high frequencies, and the labyrinth metamaterial structure has good low-frequency sound absorption performance. Both the two structures are relatively simple, and can be obtained by simple processing with resin material, which is convenient for batch production. In order to enhance sound absorption ability for the sound absorption structure within low frequency, this research work has put forward one coupled structure via the micro-perforated panel and three second-order maze metamaterials structure, resulting in a coupled structure with a low-frequency sound absorption performance. Combination of equivalent circuit method calculates acoustic resistance and absorption coefficient for the sound absorption structure, and genetic algorithm has been employed to optimize the parameters of this sound absorption structure. Finally, the theoretical calculations analysis results have been verified by finite element simulation, which shows the trend of the curve of sound absorption coefficient of the two structures was basically consistent. And the sound absorption coefficient of the three peaks is all above 0.7, and the mean value of the sound absorption coefficient is above 0.6 at the acoustic frequency of 0–1500[Formula: see text]Hz, indicating that the coupled structure has a good performance of absorbing medium- and low-frequency sound waves.