Noise Control Applications Research Articles

MEEF criterion-based spline adaptive filtering algorithm and its application

This paper presents an innovative the minimum error entropy with fiducial points (MEEF)-based spline adaptive filtering (S-AF) algorithm, called SAF-MEEF algorithm, which outperforms the conventional SAF algorithms that use the mean square error (MSE) criterion in reducing non-Gaussian interference. To overcome the limitation of the fixed step-size, a variable step-size strategy is also developed, resulting in the SAF-VMEEF algorithm, which improves the convergence speed and steady-state error performance. Furthermore, the computational complexity and convergence analysis of the SAF-MEEF are discussed. Nonlinear system identification simulations test the performance of the presented algorithms. Furthermore, this article accomplishes the application of nonlinear active noise control (ANC). Their effectiveness and robustness against non-Gaussian noise are demonstrated in different experimental scenarios, including α-stable noise, real-world functional magnetic resonance imaging (fMRI) noise, and real-life server room (SR) noise.

Numerical investigation of noise reduction of a pump-jet propulsor using porous metal

A novel strategy for noise reduction in pump-jet propulsor (PJP) is proposed through the design of porous metal trailing edges on stator blades. The interference between stator wake vortices and rotor blades is one of the primary mechanisms for noise generation in PJP. The goal is to use a porous medium to diminish the intensity of turbulent vortices behind the stator blades, control the interaction between these shedding vortices and the rotor blades downstream of the stator, and ultimately suppress the rotor noise generation source. Large eddy simulation and acoustic analogy analysis of the entire propulsion system based on the Ffowcs-Williams and Hawkings equation are performed. It is found that with the use of porous stator trailing edges, the wake flow pattern of the stator is notably altered, the strong impact of the turbulent vortices on the rotor blades is weakened, and the wall pressure fluctuations on the rotor blades and duct are significantly reduced. As a result, the far-field radiation noise and tonal noise are both effectively reduced, with the maximum reduction in total and tonal sound pressure levels reaching 3.8 dB and 12.53 dB, respectively, corresponding to percentage reductions of 6.0% and 21.69%. These findings demonstrate that porous media have great potential for practical engineering applications in PJP noise control.

Utilization of spent graphite from lithium-ion batteries waste as sustainable reinforcing filler for thermal, vibration-damping, and noise control applications

This study explores the practical application of using spent graphite (SG) derived from lithium-ion battery waste as a sustainable reinforcing filler for fabricating rubber composites. Two types of rubber, natural rubber (NR) and butyl rubber (BR), were employed as matrices, and eight composites were fabricated by increasing SG loadings [0, 10, 20, and 30 parts per hundred rubber (phr)]. The effects of these SG loadings on the composites' morphological, physical, thermal, wettability, mechanical, dynamic mechanical, vibration-damping, and acoustic properties were thoroughly investigated. The findings demonstrate significant improvements with increasing SG loading, particularly in the BR/SG30 composite. By reinforcing 30 phr of SG into the BR matrix, the density, hardness, thermal degradation, and sound-insulating properties improved by approximately 3.50%, 15.64%, 6.05%, and 5%, respectively, compared to the NR/SG0 composite. The damping ratio (ξ) of MSBB + BR/SG30 was approximately 18.04 at the second vibration mode, and the overall sound power level of MSBB was reduced by about 12.20 dB(A) when the BR/SG30 composite layer was applied, highlighting its potential for real-world vibration and noise control applications. These results underscore the significant role of SG as a sustainable reinforcing filler in enhancing the properties of rubber composites, particularly in the BR matrix, making it a promising option for applications requiring effective vibration and noise control. This research opens new possibilities for using SG in various engineering applications, inspiring further exploration and innovation.

Uncertainty and sensitivity analysis of non-acoustic parameters on acoustic characteristics prediction models for porous foam materials

Porous foam materials are widely used in noise control applications. Their acoustic performance can be predicted by acoustic models composed of non-acoustic parameters such as flow resistivity, porosity, tortuosity, viscosity, and characteristic length. However, the influence of these parameters on model outputs varies across different frequency ranges. Therefore, when using a single model for predictions across the entire frequency range, parameters may not fully act within the frequency range where their influence is greatest. To reduce prediction errors and improve the correlation between predicted numerical results and experimental data, uncertainty and sensitivity analyses can be conducted to determine the extent of each parameter's influence at different frequency ranges. In this study, polyurethane foam materials are investigated, and uncertainty and sensitivity analyses are performed on two acoustic models. Firstly, the uncertainty of parameters is assessed using the Monte Carlo method. Secondly, Sobol index method is employed to reveal the influence of parameters across various frequency ranges. Finally, by comparing the results of both analyses, the optimal frequency ranges for each parameter can be summarized. This provides valuable reference for enhancing the accuracy of acoustic model predictions.

1-bit absorption-diffusion acoustic coding metasurface

Acoustic metasurfaces demonstrate unprecedented potential for flexible capabilities of the acoustic wavefront manipulation. Especially, acoustic diffusers and absorbers via acoustic metasurfaces have garnered significant attention of researchers due to the excellent performance. However, although these diffusers and absorbers have achieved excellent acoustic scattering suppression, it still remains a significant challenge to obtain higher scattering suppression. Here, a 1-bit absorption-diffusion acoustic coding metasurface (ADM) is proposed, which can achieve high-performance acoustic backward scattering reduction in the operating frequency by combining the advantages of acoustic diffusers and absorbers. In order to realize the proposed ADM, two kinds of subwavelength dual-layer unit cells with opposite reflection phases and low amplitudes are introduced. Both simulated and experimental results demonstrate that the proposed ADM can achieve the pre-designed backward acoustic scattering reduction. The proposed integrated mechanism can provide a new method for designing high-performance acoustic metasurfaces, which can have potential applications in stealth technology, noise control and other relevant applications.

Generalization of noise insulation afforded by common window designs with active noise control exposed to moving noise source

A window device that can provide noise insulation while maintaining natural ventilation is highly desirable and is especially sought after in heavily noise-polluted and hot-humid climates cities, such as Southeast Asian cities. However, a solution to provide such a window is non-trivial because the design principles guiding acoustics and ventilation are diametrically opposed. While louvre windows have traditionally been used in communal, healthcare, and some educational setting to provide a balance between acoustics and ventilation benefits, it is still sorely lacking to provide sufficient insertion loss without sacrificing ventilation entirely. A new plenum window design has recently garnered research and market interest to tackle the dichotomous problem. Additionally, the application of active noise control (ANC) in windows is gaining popularity and offers potential solutions to improve noise control without compromising ventilation. However, it remains unclear how different traditional and modern window designs compare in terms of their acoustic performance, especially when exposed to non-stationary noise sources such as urban traffic, a major noise pollutant. Thus, the present study seeks to provide a generalization of insertion loss provided by different window designs exposed to moving sources including a tangent study on ANC implementation via a time-domain approach.

Hygroscopic effects on sound absorption of multiscale bio-based porous materials

Hygroscopicity is the tendency of a material to absorb moisture from the surrounding environment. This work investigates hygroscopic effects on the sound absorption properties of multiscale bio-based materials. It is shown how moisture can significantly alter their acoustic performance as well as how to recover their original dry-material performance by means of heat treatment, akin to thermal reactivation commonly used in the chemical engineering industry. The results of an experimental campaign, conducted over an extended period of time, is reported. Possible theoretical explanations on the reduced acoustic performance of activated carbons by hygroscopic effects and the achieved improvement, obtained after heat treating the material, are also presented. The results of this work provide useful insights on the long-term acoustic behaviour of multiscale bio-based materials for noise control applications.

A tunable high-order micro-perforated panel metamaterial with low-frequency broadband acoustic absorption

We proposed a tunable high-order micro-perforated panel metamaterial for broadband absorption, in which the energy dissipation modes is reconstructed by the cavity partition plates. Owing to the more degrees of freedom in impedance design, the metamaterial not only obtains multiple perfect absorption peaks with broader bandwidth, but also allows for flexible frequency regulations. By coupling 12 high-order cells, the metamaterial finally achieves a smooth spectrum with 94% average absorption across the range of 300–3200 Hz, which is verified by the simulation and experiment. This metamaterial could have great applications in noise control engineering owing to the extraordinary performance.

Efficient implementation of the functional links artificial neural networks with cross-terms for nonlinear active noise control

This paper proposes an efficient extension of functional links artificial neural networks (EE-FLANN) for the active noise control (ANC) application. The developed EE-FLANN controller can upgrade the model accuracy with the actual system thanks to adding the cross-terms to the trigonometric function. Unlike the method in the generalized FLANN (GFLANN) controller, the EE-FLANN exploits include cross-term symmetry. However, this causes the computational burden to increase remarkably. To reduce this disadvantage, we truncate the cross-terms appropriately based on the simplified strategy. Furthermore, the adaptive algorithm is designed to partially update the filter coefficients appropriately. Specifically, the cross-terms that do not satisfy certain magnitude conditions will be omitted during the update process to reduce costs. Experiments have shown that the proposed EE-FLANN controller can achieve comparable performance to the GFLANN controller but the complexity is reduced by up to 20%.

Noise control strategies: Options beyond sound walls

As noise control requirement needs expand into different and new industries, traditional "sound walls" are becoming less utilized and there is a focus more on treating source noise with products specifically designed for various applications considering frequency content, low frequency impacts, intermittent noise and tonal content. This presentation will explore feasible and efficient noise control strategies and applications, focusing on both temporary and permanent solutions that address a variety of industries, along with new product lines that are available to provide solutions where either "sound walls" are not applicable or site constraints require an outside the box approach to provide solutions. Attendees will learn about engineered applications for both environmental and interior industrial impacts across various industries and challenges and what solutions are available that consider feasibility, safety, access and performance while also considering cost implications.

Development of a low-frequency broadband sound absorber based on a micro-perforated panel coupled with the Helmholtz resonator system

In the field of vibration and noise reduction, micro-perforated panel (MPP) structures and Helmholtz resonators (HR) play crucial roles as common sound-absorbing elements. However, independently applied MPP and HR structures cannot provide sufficiently wide absorption bandwidths at low frequencies. To achieve low-frequency broadband sound absorption, this study proposes a novel low-frequency broadband sound absorption structure (EMH) based on MPP and HR with a thickness of 40 mm to achieve a subwavelength, efficient, and compact design. We establish theoretical models of MPP and HR coupled systems, systematically analyze the sound absorption performance of same-element and different-element coupled structures, and employ the particle swarm optimization (PSO) algorithm to obtain structural parameters for efficient coupled sound absorption. Furthermore, we compare the sound absorption performance of three optimized coupled structures (MPP-coupled (SM), HR-coupled (SH), and MPP and HR-coupled) from the perspective of the theoretical calculation of the sound absorption coefficient and finite element analysis of the sound absorption mechanism. Finally, samples fabricated using 3D printing technology are tested in an impedance tube. The results demonstrate that efficient coupled sound absorption of MPP and HR can be achieved through parameter optimization. SH and SM exhibit nearly perfect sound absorption in the frequency ranges of 323–495 Hz and 615–1600 Hz, respectively, whereas the effective absorption bandwidth of EMH can reach 1225 Hz in the range of 200–1600 Hz. EMH shows superior low-frequency broadband sound absorption performance with a lightweight and simple structure, which holds the potential for application in low-frequency noise control.

Absorption–diffusion integrated acoustic metasurface for scattering reduction

Absorption and diffusion are expected to reduce the energy intensity of reflected waves, while combining the advantages of both can further disperse incoming energy and improve acoustic stealth performances. In the paper, an absorption-diffusion integrated acoustic metasurface (ADM) is proposed, achieving high-performance acoustic backward scattering reduction in the operating bandwidth ranging from 6550 Hz to 6950 Hz. In order to obtain the proposed ADM, two kinds of subwavelength dual-layer unit cells with phase differences of 180° and low amplitudes (<0.4) are introduced. The highly efficient absorption of acoustic waves is achieved by extending the acoustic wave propagation path of the proposed unit cells. Meanwhile, the destructive interference between the pre-designed unit cells also contributes to diffusion-like scattering, which contributes to further suppression of specular reflection. Both simulated and experimental results demonstrate that the proposed ADM can achieve excellent acoustic backward scattering reduction. The proposed integrated mechanism can provide a method for achieving high-performance acoustic wavefront manipulation, which has potential applications in stealth technology, camouflage, noise control, and other relevant applications.

Evidence of nonlinearity tailoring in static and dynamic responses of honeycomb and auxetic hourglass lattice metastructures

Nature’s morphology and optimal energetic solutions remain the key motivation for designing cellular-based lattice structures. Understanding the nonlinear dynamical behaviors that arise from different lattice topologies of such structures in the metastructure framework is crucial for their successful implementation in various novel designs and technologies related to vibration and shape control. This paper presents a study of the static and dynamic response of auxetic and honeycomb lattices with hourglass or dome-shaped metastructures. The potential tailoring of nonlinearity of such responses through various design parameters that play a vital role in shaping the dynamic properties of such structures is discussed here. The impact of cell design parameters on the resulting macroscopic behavior is assessed using both numerical simulations and experimental studies. The transition from softening to hardening nonlinear dynamic responses is reported with cell topologies ranging from the regular honeycomb to auxetic topologies that are widely used as fundamental cells of cellular materials design. The experimental study is based on the time responses measured to verify the numerical predictions. The experimental system consists of different 3D printed hourglass samples based on the auxetic and honeycomb lattices on which dynamic testing using a laser Doppler vibrometer is performed. The design strategies proposed in this paper can be integrated into a wide range of lattice-based materials for noise and vibration control applications and biomedical devices.

Designing and experimental validation of single-layer mixed foil resonator acoustic membrane to enhance sound transmission loss (STL) within low to medium frequency range

This study presents a novel design for an acoustic membrane structure that employs a parallel-arrangement of mixed foil sound resonators to improve sound absorption and insulation capabilities in the low to medium frequency range. The structure is composed of a single layer of parallel-arranged mixed foil wedge-shaped coffers and a bottom flat panel separated by an air cavity. The mixed thickness-based foil resonators are treated as a combination of independent resonators with unique resonance frequency, resulting in improved sound insulation with broadband efficacy. A comprehensive parametric analysis was carried out using the Finite Element Method (FEM) based COMSOL Multiphysics, yielding the anticipated outcomes. The study revealed that the broadband Sound Transmission Loss (STL) can be tailored by varying the thickness of the top and side walls, the bottom plate thickness, and the depth of the rear air cavity. The findings suggest that existing acoustic membrane design can be highly efficient, achieving, and average STL of over 40 dB ∼ 45 dB across the low to medium frequency range of 500 Hz to 3000 Hz. The experimental validation was conducted in an anechoic chamber, and the results were found to be in close agreement with the FEM simulation results. In comparison to conventional uniform foil sound resonator based acoustic membrane structure, this mixed single-layer square wedge-shaped foil resonator based acoustic membrane exhibits outstanding sound insulation performances in the low to medium frequency range, owing to its lightweight structure and availability of conventional manufacturing techniques. This advanced version of the foil sound resonator based acoustic membrane holds immense promise for the use in acoustics and noise control applications across domestic, commercial, and industrial environments.

Design and low-velocity impact behavior of an origami-bellow foldcore honeycomb acoustic metastructure

The ancient art of origami has inspired the design and fabrication of numerous acoustic and energy-absorption mechanical metamaterials and metastructures. This study introduces an origami-inspired honeycomb acoustic metastructure designed for engineering applications that demand both high impact resistance and effective sound absorption. This acoustic metastructure is formed by bonding a panel containing periodically distributed perforated holes and a panel without perforations to a periodical array of trapezoidal origami-bellow units. Acoustic wave propagation and drop-weight impact simulations are conducted to investigate the acoustic performance and low-velocity impact behavior of the metastructure. The results show that the origami-bellow honeycomb structure exhibits superior sound absorption capacity over two frequency ranges, outperforming the conventional honeycomb-core sandwich structure. Furthermore, it is shown that, in comparison with both the conventional hexagonal honeycomb-core and the Miura-ori foldcore sandwich structures, the proposed acoustic metastructure demonstrates higher levels of impact resistance and energy absorption capacity. We also show that the mechanical performance of the introduced metastructure under low-velocity impact loads can be further enhanced by increasing the story height of the origami-bellow units. Besides, the matrix material of the origami foldcore can be tailored to suit various scenarios, providing noise control and collision robustness for a diverse range of engineering applications.

Acoustic coherent perfect absorption based on a PT symmetric coupled Mie resonator system

Parity-time (PT) symmetric coupled resonator systems have exhibited intriguing and unexpected properties in optics and electronics. Here, we extend it to acoustics and report a coupled Mie resonators (MRs) system respecting PT symmetry. The system is constructed with two parallel waveguides connected by an aperture and two MRs placed symmetrically at both sides of the aperture. Instead of using active elements or complex refractive index modulation without gain, we exploit the incident waves of the waveguide as an effective gain so that PT symmetry with balanced loss and gain is realized by only passive materials. Coherent perfect absorption (CPA), which can completely absorb the in-phase excitations with the same intensity provided from two opposite directions, is observed in the PT symmetric phase and at the exceptional point but not in the broken phase. In addition, by varying the relative phase between the two incident waves, the coherent absorption can be tuned from CPA to zero. Our design may provide a flexible platform to research PT symmetry in acoustics and may have applications in tunable noise control, acoustic modulators, and switches.

Active vibration control for window rattling caused by infrasound: Field experiment for one pair of sliding glass doors installed on the test building

We developed an active vibration control system to reduce window vibration caused by infrasound since serious environmental noise problems such as window rattling have remained in Japan. In our previous study, we demonstrated the application of active noise control for the window vibration to reduce the transmitted sound into the room by using the low-frequency sound generator as the secondary source. However, active noise control using sound waves has the problem of increasing the sound pressure level in some areas outside the control window. Therefore, we developed an active vibration control system equipped with self-made inertial vibration exciters and laser displacement gauges to reduce the window vibration caused by infrasound without increasing the sound pressure level. An experiment was conducted to investigate the applicability of the developed active vibration control system to reduce window vibration. The vibration of one pair of sliding glass doors installed in the test building was controlled by the developed systems mounted on windows so that vibration displacement became static. As a result, the displacement of window vibration caused by infrasound was reduced by one-third without increasing the sound pressure level outside the test building. This vibration reduction resulted in the transmitted sound into the room by up to 11 dB within the frequency range below 16Hz.

Application of Active Impulsive Noise Control (AINC) for Excavator Cabin Using Advanced Convex-Combined Normalized step size Algorithm and Verification of Robustness

Conventional Active Noise Control (ANC) algorithms, such as Filtered-x least mean square (FxLMS), is not suitable for Active Impulse Noise Control (AINC). Because it lacks robustness to the impulsive sample input, it is unstable and diverges very easily. Therefore, AINC algorithm must be robust to impulse. The heavy equipment such as excavators often occur frequent impulse noise during operations. Also, in working environment of operating excavator, impulsive noise is prone to occurred by other heavy equipment. Therefore, it is necessary to examine the AINC algorithm that is suitable for excavators and its robustness. In this study, Convex Combined Step Size (CCSS), which is simulated better effects in AINC than conventional ANC algorithms, is tried to AINC of excavator. In addition, the noise reduction performance and robustness to undesirable sound were verified in the simulated experiment environment of the excavator cabin.

A diffusion filtered-x affine projection algorithm for distributed active noise control

The well-known Filtered-x Affine Projection (FxAP) algorithm is usually deemed a better choice than the conventional Filtered-x Least-Mean-Square (FxLMS) algorithm when faster convergence speed is desired in active noise control applications. However, the improvement of its convergence performance is obtained at the expense of increased computational complexity. It is usually unrealistic to regulate multichannel ANC systems using the centralized AP algorithm. Recently, distributed diffusion adaptation schemes over acoustic sensor and actuator networks have been introduced to multichannel ANC systems, such as the Diffusion FxLMS algorithms. Distributed processing based on diffusion cooperation strategy allocates the computation load to the network nodes in a scalable manner. This paper proposes a distributed Diffusion Filtered-x AP (DFxAP) algorithm for multichannel ANC systems. Simulation results and computational complexity analysis show that the DFxAP algorithm outperforms the Diffusion FxLMS algorithm in convergence performance and has lower computational complexity compared to the centralized AP algorithm.

Mechatronic design of a composite vibration isolation system

Composite materials have attracted researchers in vibration and noise control applications due to their significant dynamic characteristics such as high strength and high damping level. In this paper, a Glass Fiber Reinforced Composite material (GFRC) is presented as a vibration isolation system to control vibration levels in industry. In addition, the impact of integration of a mechatronic control system to improve the machining process and increase the control of vibration nature. A prototype of an industrial cam–follower machine is motorized, and the Frequency Response Function (FRF) is recorded using a B&K data acquisition analyzer at five rotational speeds. The transmitted vibrations to the machine foundation are estimated without any isolation system. Then, two optimized GFRC plates of optimum stacking sequences are used as an isolation system to reduce the transmitted vibration. The displacement transmissibility is calculated theoretically and experimentally. The results show that the use of GFRC plates as an isolator reduces the vibration level of the system by 98.46% and 98.5% for [90/90/90/0/0]s and [90/ ± 45/ ± 35/90/ ± 35]s GFRC configurations respectively.