Field Of Noise Control Research Articles

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.

Research on noise reduction methods for indoor substations based on resonant sound absorption

Aiming to reduce the impact of substation noise on the lives of surrounding residents, improving the low and middle frequencies acoustic performance of traditional resistive mufflers in indoor substations is significant. The paper is based on the resonance sound absorption mechanism, and for the first time applies multi-frequency resonance noise reduction technology to the research field of indoor substation noise control, proposing a multi-frequency resonant muffling structure. The acoustic performance of the proposed muffler unit is investigated through theoretical and numerical analysis. The measured noise data of the indoor substation is used as sound excitation in the numerical analysis. The results show that at frequencies of 100 Hz, 200 Hz, 300 Hz, 400 Hz, and 500 Hz, the noise in indoor substations is significantly reduced by the multi-frequency resonant muffling structure. The paper provides references for the application of multi-frequency resonant mufflers in the field of noise control of indoor substations.

Measuring the radiation of sound sources with the radiation mode method: Towards realistic problems.

The measurement of the pressure field radiated by a sound source has many applications in the fields of noise control and loudspeaker system design. In this paper, the radiation mode method is used to measure the field radiated by a complex acoustic source whose surface impedance is arbitrary and does not correspond to the Neumann boundary condition used for the calculation of radiation modes. The most effective radiation modes are used as test functions to calculate a pressure expansion around the source under test, an expansion that matches the measured pressure at a limited number of points close to the source. This expansion is then used to calculate the radiated pressure at a greater distance at unmeasured locations. In a first step, numerical simulations are performed to evaluate the method's most influential parameters. Then, measurements are performed in a semi-anechoic room on two real sources of increasing complexity. Obtained results show that the radiation mode method allows an accurate evaluation of the pressure field radiated by the test object over a fairly wide frequency band (between 100 Hz and 2 kHz) even for complex sources.

Research progress of piezoelectric polymer PVDF in sound absorption technology

Owing to its impedance properties and piezoelectric effect, the piezoelectric polymer polyvinylidene fluoride (PVDF) finds application in the field of noise control. Traditional sound-absorbing materials have gradually fallen short of the demands of sound-absorbing functionality and environmental adaptability in today’s increasingly acute noise pollution environment. When PVDF is added to sound absorption, materials or structures have an additional loss path for the conversion of sound energy to electric energy. This helps to increase the low-frequency sound absorption band and improve low-frequency sound absorption performance. Through the action of viscosity, friction, relaxation, piezoelectric effect, and dielectric loss, the sound energy in the passive sound-absorbing material containing PVDF is transformed into energy dissipation in the form of heat energy, electric energy, and so on under the matching of PVDF low impedance. In active control, secondary sound and force sources can be supplied by PVDF-based transducers and actuators to reduce noise. This paper first provides an overview of the piezoelectric characteristics of β-phase PVDF and its optimization techniques. It then goes on to discuss the use of PVDF in passive sound-absorbing materials, active controls, and hybrid sound absorption systems. Finally, it summarizes the benefits, issues that still need to be resolved, and future directions for these three noise reduction techniques.

Semi-self-similar fractal cellular structures with broadband sound absorption

Honeycomb core materials, recognized for their excellent sound absorption and load-bearing capabilities, are widely employed in engineering applications. The back cavity shape of honeycomb structure absorbers plays a crucial role in their sound absorption performance. In this study, the honeycomb structure absorbers are re-designed using fractal design principles, enabling a modification of the acoustic properties of traditional honeycomb-type absorbers and a significant enhancement in the sound absorption frequency band. The theoretical predictions of the semi-self-similar fractal honeycomb absorber structure are validated through finite element simulations and experimental studies, exhibiting remarkable consistency. The findings indicate that compared to single-layer first-order structures, the performance of dual-layer second-order fractal element Helmholtz resonators is significantly improved. Relative to conventional honeycomb panel structures, the fractal design approach markedly enhances the semi-absorption bandwidth of the absorbers, with an increase in the fractal order further broadening the sound absorption frequency band. The innovation of achieving broadband absorption through fractal resonators not only represents a new direction in the design of advanced honeycomb core materials but also holds substantial promise in the field of noise control.

Mechanism analysis and optimal design of sound-absorbing metastructure constructed by slit-embedded Helmholtz resonators

<sec>Low-frequency noise has always been a thorny problem in the field of noise control. In recent years, the development of sound-absorbing metastructures has provided new ideas for controlling low-frequency noise. In this work, we propose a low-frequency sound-absorbing metastructure constructed by Helmholtz resonators with embedded slit. Analytical and numerical models are established to analyze the sound absorption performance and mechanism of the proposed sound-absorbing metastructure, and optimization design is conducted to achieve low-frequency wideband absorption performance. The analytical modeling method and the performance of the proposed sound-absorbing metastructure are also experimentally verified. The main conclusions are summarized as follows.</sec><sec>1) By using transfer matrix method and finite element method, analytical and numerical models for calculating sound absorption coefficient are established. It is shown that analytical predictions are in good agreement with numerical calculations. It is demonstrated that a typical design of a 30-mm-thick single-cell metastructure can achieve a sound absorption coefficient of 0.88 at 404 Hz. Typical designs of two-cell parallel structure and the four-cell parallel structure (both with a thickness of 50 mm) can achieve two and four nearly perfect low-frequency sound absorption peaks in a frequency band of 200–400 Hz, respectively.</sec><sec>2) The low-frequency sound absorption mechanisms of the proposed metastructures are explained from four aspects: simplified equivalent model parameters, normalized acoustic impedance, complex-plane zero/pole distribution, and sound pressure cloud image and particle velocity field distribution. It is demonstrated that the main sound absorption mechanism is related to the thermal viscous loss of sound waves, caused by the inner wall of embedded slit.</sec><sec>3) The design for broadband low-frequency absorption performance is optimized by using differential evolution optimization algorithm. An optimized parallel-multi-cell coupled metastructure with multiple perfect sound absorption peaks below 500 Hz is realized. For a thickness of 90 mm, the sound absorption coefficient curve of an optimized metastructure exhibits 8 almost perfect sound absorption peaks and an average sound absorption coefficient of 0.86 in a frequency range of 170－380 Hz.</sec><sec>4) Experimental samples are fabricated to test sound absorption. Experimental results are basically consistent with the analytical predictions. The results from analytical model, numerical calculations and experimental measurements are mutually verified.</sec><sec>In summary, the sound-absorbing metastructures with a thickness of sub-wavelength, proposed in this work, exhibit outstanding sound absorption performance at low frequencies. We demonstrate that they are suitable for low frequency broadband sound absorption below 500 Hz. Owing to their thin thickness and relatively simple construction, they have broad application prospects in practical noise control engineering.</sec>

Sound field control in a rectangular closed space using multiple selected room modes

Sound field control using multiple loudspeakers is essential for many applications such as sound field reproduction for delivering an immersive sound experience and noise control. These sound field controls are generally required in closed spaces, such as living rooms or factories, where eigenmodes are prominent at low frequencies. Many studies on the control of a few modes in closed spaces have been conducted in the field of noise control. In this study, we attempted to reproduce arbitrary sound fields, such as plane and spherical waves, from virtual sound sources using simultaneous multiple eigenmodes based on room-mode matching (RMM). Because most rooms are generally considered rectangular at low frequencies, we expanded the target sound field with discrete cosine transform (DCT) by approximating the eigenmodes as cosine functions. We proposed a method for extracting the control modes necessary to reproduce the desired sound field considering the mode strength at a target frequency. The simulation results verified that the proposed method can reproduce propagating plane waves with loudspeaker arrays placed on both sides of the closed space while maintaining the loudspeaker filter gains at appropriate values.

Near-perfect low-frequency sound absorption in subwavelength H-fractal metamaterials

We designed and demonstrated the near-perfect low-frequency sound absorption in subwavelength H-fractal metamaterials, in which the absorption peak frequency can be continuously tuned by changing the opening positions. Moreover, the total thickness of the acoustic metamaterial can be decreased to λ/92.2 by increasing the number of openings. The underlying mechanism is ascribed to the impedance matching due to additional couplings from new openings. The experimental results agree well with the numerical analyses, and the proposed method provides a new route for reducing the thickness of sound-absorbing materials, which may find large application demands in the noise control field.

Nonwoven fabrics developed from agriculture and industrial waste for acoustic and thermal applications

Numerous researchers in the field of noise control and acoustics have found success in using biomaterials to create a porous sound absorber that is both effective and environmentally friendly. This paper discusses the utilization of fibers extracted from the waste from coffee husk (CH) and waste from the cotton (CO) spinning industry to be an alternative to synthetic-based acoustic materials. The study was conducted within the range of 50–6300 (Hz) frequency. Five well-known mathematical prediction models, namely Delany–Bazley (D–B), Garai–Pompoli (G–P), Miki, Allard Champoux (AC), and Johnson–Champoux–Allard (JCA) models are theoretically used to predict the sound absorption coefficient of nonwoven fibrous materials. When compared with the experimental data, it was discovered that the JCA and AC model is the most acceptable model for predicting the absorption behavior of CH/CO nonwoven fibrous materials. Additionally, the thermal insulation of nonwoven fibrous materials has been experimentally and numerically studied. It is noteworthy that, when compared to the Herman model, the Bhattacharyya model’s results showed slightly greater thermal conductivities. Overall, this work used an environmentally friendly way to turn waste into a valuable product.

Design and study of broadband sound absorbers with partition based on micro-perforated panel and Helmholtz resonator

Micro-perforated panel (MPP) absorber has various merits, so it has great potential for application in the field of noise control. In this paper, the cavity with a variable section partition was designed to solve the broadband sound absorption problem of MPP. Three types of sound absorbers were developed with subwavelength thickness based on the cavity: Micro-perforated panel with built-in Helmholtz resonator (MPPHR), single-layer and double-layer micro-perforated panel backed by the cavity (SL-VMPP and DL-VMPP, collectively referred to as VMPP). The absorption characteristics of three sound absorbers with various partition parameters were investigated by COMSOL Multiphysics software. Furthermore, three types of absorbers were optimized with particle swarm optimization (PSO) algorithm for a superior absorption performance. Finally, the experimental results demonstrate predicted improvements in broadband sound absorption levels when compared to conventional MPP absorber: The MPPHR with a thickness of 32 mm (∼λ/18 at the first resonant frequency) has a half absorption band of up to 1294 Hz, which is nearly 500 Hz wider than the conventional MPP with equal cavity depth. The optimized SL-VMPP and DL-VMPP have an absorption level of at least 80 % in the frequency range of 794–1614 Hz and 632–1954 Hz, respectively.

Experimental study of the Sound Absorption of Nylon Woven Fabric

Nylon is the world's earliest synthetic fiber, it has excellent performance and rich raw material resources, so that it has been used until now. The purpose of this research is to investigate the acoustics of thin fabric. Acoustically, it can be seen as a thin layer composed of porous fibrous materials. Therefore, its sound absorption performance is the combination of at least two kinds of sound absorption mechanisms. The main purpose of this paper is to study the relationship between sound absorption properties and structural parameters of thin fabric by means of experiment . The study concerning the transmission and attenuation of acoustic wave in thin fabrics is helpful for the design of thin fabric, and improving its applications in the field of noise control and indoor acoustics.

Influence of Magnetic Field on Sound Transmission Loss of the Unit Filled with Magnetorheological Fluid.

To explore the feasibility of applying magnetorheological fluids (MRFs) in the field of noise control, the influence of the magnetic field intensity and direction on the sound transmission loss (STL) of a unit filled with MRF (MRF unit) were investigated in this study. First, two types of test sample containing the MRF unit were designed and fabricated. The magnetic field applied to the MRF was provided by the permanent magnets used in pairs. The direction of the magnetic field was perpendicular or parallel to the direction of the sound wave propagation. The distribution of the magnetic field intensity of the two types of test samples was simulated using magnetostatic finite element analysis and validated with the magnetic field intensity measured using a Teslameter. For comparison, test samples containing air and water units were also prepared. Then, the STL of the two types of test samples were measured under different magnetic field intensities using the impedance tube method. Finally, the STL curves of the two types of test samples were presented, and the influence of magnetic field intensity and direction on the STL were discussed. The results demonstrate that the magnetic field direction has a significant influence on the STL of the MRF unit. In addition, when the magnetic field direction is parallel to the sound propagation direction, the STL of the test sample containing MRF unit significantly increases with the increase of the magnetic field intensity at low and middle frequencies.

Deep-subwavelength broadband sound absorbing metasurface based on the update finger coiling-up method

The bulky structure of traditional sound-absorbing materials limits its application to control low-frequency noise, and new deep-subwavelength low-frequency broadband acoustic materials have an urgent need. This paper proposes an update finger coiling-up method, which can improve the sound absorption coefficient and working bandwidth of the unit without increasing the thickness. In addition, the complexity of the structure can be simplified to facilitate manufacturing. The influence of the typical parameters of the unit on the sound absorption performance and the coupling performance of the unit are also studied. Finally, by combining 16 finger coiled-up units, a metasurface with continuous broadband sound absorption in the range of 375 Hz to 855 Hz is obtained, and the average sound absorption coefficient is above 0.85. In particular, the thickness of the metasurface is only 38 mm, which is 1/24 of the corresponding operating wavelength at 375 Hz. The proposed update finger coiling-up method provides a new idea for reducing the thickness of sound-absorbing materials, which will have good application prospects in noise control field.

Experimental and Theoretical Investigation of the Acoustic Absorbers Fabricated from Natural Kenaf Fibres and Rice Husk

ABSTRACT Fabrication of acoustic absorbers from a combination of natural waste materials is a novel approach in the field of noise control. The aim of this study was to investigate the acoustic absorption performance of several sample sound absorbers made from natural kenaf fibers and rice husk. A new method of fabricating these sample sound absorbers was also employed to study the usability as well as performance improvement via the approach fibro-granular sound absorbers (FGSA). The values of acoustic absorption performance, porosity, and airflow resistivity of the samples were used in the experimental design. The Dunn and Davern (D-D) theoretical model as well as the reversed D-D model with Nelder–Mead Simplex were applied to evaluate the sound absorption as well. According to the obtained values, it was found that at low- and mid-frequency range, the sound absorption value of FGSA is higher than other acoustic materials. The FGSA (with a density of 150 kg/m3) increased noise reduction coefficient value by 31.25% compared to samples fabricated to the rice husk and also by 10.53% compared to kenaf. Based on comparison of the theoretical and experimental results, the model optimized with the Nelder–Mead method had higher accuracy and fitting in predicting the sound absorption values than the D-D model. Finally, it was found that improvement in the sound absorption performance of the natural acoustic absorbers might be achieved through adopting the approach of combining natural materials and fabrication of FGSA.

The review of fiber-based sound-absorbing structures

According to the World Health Organization, noise pollution is second only to air pollution in its impact on health and the environment. Fiber-based sound-absorbing structures have great application potential in the field of sound absorption and noise reduction because they can provide a wider sound absorption range than traditional porous fiber materials, and at the same time have the advantages of light weight, low cost and strong processability. Consequently, significant research interest in the field of noise control has been directed into the study of composite sound-absorbing materials based on porous fiber materials. In this review, we have summarized manifold theoretical structures based on fiber materials, such as multilayer structure, porous micro/nano structure, membrane sound-absorbing structure and perforated resonance structure of fiber-based sound-absorbing structures, aiming to illustrate that the structure must affect the sound absorption performance of the material. The focus is on the research and development of the design concepts, and preparation methods of fiber-based acoustic structures are reviewed. Finally, this review concludes with the prospects and outlook for fiber-based acoustic structures. We hope that this article which reviews the structure design principle and preparation method of fiber-based sound-absorbing structures can give inspirations for readers.

Time to Noise-Induced Hearing Loss among Different Type of Shift Work among Steel Workers: A Survival Study.

Background:There have been few reports on relationships between Shift Work (SW) and time to Noise-Induced Hearing Loss (NIHL). This research explores the relation between SW and time to NIHL among male workers.Methods:Between 1990 and 2015, this historical cohort study was conducted. Two different definitions events (Low Frequency Hearing (LFH) and High Frequency Hearing (HFH)) of NIHL An average pure-tone hearing threshold was thresholds at 1, 1.5 and 2 kHz for LFH(un-normal>20) and 4, 6 and 8 kHz for HFH (un-normal>20) for Air (AC) and Bone (BC) conduction, in both ears, respectively. In this study Kaplan–Meier and Multilevel Cox Model in addition R version 3.2.1 and MLWiN software used to analysis data. P-values less than 0.05 are considered to be statistically significantResults:There were 6632 male workers in the research survey (mean age=35(±5)). Among these subjects, 2678 (40%),278 (4%) and 3676 (56%) were Day Workers (DW), Weekly Rotating Shift workers (WRS) and Routinely Rotating Shift workers (RRS), respectively. The result of this study showed more hazard risk of ear problem in LFH (Hazard=1.55 with 95% CI= (1.06–1.39)) and HFH (Hazard=1.08 with 95% CI= (1.04–1.13)) in RRS rather than day workers. In WRS group ear problem has been seen just in LFH (Hazard=1.55 with 95% CI= (1.2–2.0)).Conclusion:The findings of the 15-year historical cohort study generally support a relationship between SW and time to NIHL. Therefore, more actions in the field of noise control, greater use of safety devices as well as increased staff training on the use of safety devices recommended for shift worker.

Absorption performance of nonplanar periodic structures solved by layered rigorous coupled-wave analysis

Porous materials with corrugated surfaces are widely used in the field of noise control, as they can effectively convert sound energy into heat resulting in sound absorption. It is important to predict the absorption coefficients of sound-absorbing devices for the design of appropriate shape and size. In this study, a semi-analytic method of layered rigorous coupled-wave analysis (LRCWA) is proposed to predict the absorption of nonplanar periodic materials. Starting from the division of corrugated surfaces into multiple layers, we process the sound behavior in each layer as in a rectangular periodic modulation structure. By connecting the interlayer boundary continuity conditions, the acoustic coupling equation of the whole structure can be established. The effectiveness and practicability of the LRCWA method is validated based on the comparisons with the experimental data and the simulation of finite element method. Besides the absorption coefficient that is mainly discussed in this work, the proposed method is universal in analyzing the physical properties of nonplanar periodic structures, which can greatly accelerate the delicate design and optimization of such structures.

Utilization and Study of Raw Groundnut Shell as a Source of Sound Absorbing Material

ABSTRACT Natural biodegradable materials have the potential of an alternative traditional sound-absorbing material. These materials have the advantages of low cost, light in weight, easily available, eco-friendly, and nonpolluting. Groundnut shell is a cover of the peanuts and considered an agriculture waste material that can be used in the field of noise control. This study highlights the possibility of the groundnut shell material as a sound absorption material by evaluating the acoustical properties like Air Flow Resistivity (AFR) and Sound Absorption Coefficient (SAC). Three different samples made of groundnut shell with thicknesses 10, 20, and 30 mm have been considered for the analysis. The effect of thickness and the air gap of the different samples on the acoustics parameters have been discussed. The experimental results show that the AFR decreases with increasing thickness of the sample material while a sound absorption coefficient (SAC) is found higher values at medium and high frequency (from 1000 to 4000 Hz). This study will be useful for the development of new sound absorbing material.

Parameter identification of sound absorption model of porous materials based on modified particle swarm optimization algorithm.

Porous materials have been widely used in the field of noise control. The non-acoustical parameters involved in the sound absorption model have an important effect on the sound absorption performance of porous materials. How to identify these non-acoustical parameters efficiently and accurately is an active research area and many researchers have devoted contributions on it. In this study, a modified particle swarm optimization algorithm is adopted to identify the non-acoustical parameters of the jute fiber felt. Firstly, the sound absorption model used to predict the sound absorption coefficient of the porous materials is introduced. Secondly, the model of non-acoustical parameter identification of porous materials is established. Then the modified particle swarm optimization algorithm is introduced and the feasibility of the algorithm applied to the parameter identification of porous materials is investigated. Finally, based on the sound absorption coefficient measured by the impedance tube the modified particle swarm optimization algorithm is adopted to identify the non-acoustical parameters involved in the sound absorption model of the jute fiber felt, and the identification performance and the computational performance of the algorithm are discussed. Research results show that compared with other identification methods the modified particle swarm optimization algorithm has higher identification accuracy and is more suitable for the identification of non-acoustical parameters of the porous materials. The sound absorption coefficient curve predicted by the modified particle swarm optimization algorithm has good consistency with the experimental curve. In the aspect of computer running time, compared with the standard particle swarm optimization algorithm, the modified particle swarm optimization algorithm takes shorter running time. When the population size is larger, modified particle swarm optimization algorithm has more advantages in the running speed. In addition, this study demonstrates that the jute fiber felt is a good acoustical green fibrous material which has excellent sound absorbing performance in a wide frequency range and the peak value of its sound absorption coefficient can reach 0.8.

Broadband ultra-thin acoustic metasurface absorber with coiled structure

We theoretically and experimentally propose two designs of broadband low-frequency acoustic metasurface coiled absorbers (Sample I/Sample II) for the frequency ranges of 460 Hz–972 Hz and 232 Hz–494 Hz (larger than 1 octave), with absorption larger than 0.8 (average is 0.87), and having the ultra-thin thickness of 4.5 cm and 9 cm respectively (λ/17 for the lowest working frequency and λ/8 for the highest frequency). The designed supercell consists of 16 different unit cells corresponding to 16 eigen frequencies for resonant absorptions. The coupling between multiple resonances leads to broadband absorption effect in the full range of the targeted frequency spectrum. In addition, the coiling structure lead to the ultra-thin thickness of the metasurface absorbers. Our conceived ultra-thin low-frequency broadband absorbers may lead to pragmatic implementations and applications in noise control field.