Noise Control Applications Research Articles

Biomimetic Coupling Structure Increases the Noise Friction and Sound Absorption Effect.

Environmental noise pollution is a growing challenge worldwide, necessitating effective sound absorption strategies to improve acoustic environments. Materials that draw inspiration from nature's structural design principles can provide enhanced functionalities. Wood exhibits an intricate multi-scale porous architecture that can dissipate acoustic energy. This study investigates a biomimetic sound-absorbing structure composed of hierarchical pores inspired by the vascular networks within wood cells. The perforated resonators induce complementary frequency responses and porous propagation effects for broadband attenuation. Samples were fabricated using 3D printing for systematic testing. The pore size, porosity, number of layers, and order of the layers were controlled as experimental variables. Acoustic impedance tube characterization demonstrated that optimizing these architectural parameters enables absorption coefficients approaching unity across a broad frequency range. The tuned multi-layer porous architectures outperformed single pore baselines, achieving up to a 25-35% increase in the average absorption. The bio-inspired coupled pore designs also exhibited a 95% broader working bandwidth. These enhancements result from the increased viscous losses and tailored impedance matching generated by the hierarchical porosity. This work elucidates structure-property guidelines for designing biomimetic acoustic metamaterials derived from the porous morphology of wood. The results show significant promise for leveraging such multi-scale cellular geometries in future materials and devices for noise control and dissipative engineering applications across diverse sectors.

Measurement of Compound Sound Sources with Adaptive Spatial Radiation for Low-Frequency Active Noise Control Applications

The proposed compound sound sources for low-frequency noise control applications are composed of dipole sources. Their spatial radiation, which is critical in the modal field of small, closed spaces, is intended to be controlled with independent driving signals of each dipole. The need for small and efficient low-frequency elementary monopole sources led to the proposed vented sub-woofer loudspeaker design with low force factor (low-Bl) drivers. The investigated sources are set up in quadrupole configurations and measured in terms of polar near field response patterns to verify the theoretical predictions. The measurement results consist of the validation of the proposed compound sound sources on the implementation of active noise control problems in the low-frequency range. Also, their small size and modular construction make them interesting for use in other applications.

Series and parallel coupling of 3D printed micro-perforated panels and coiled quarter wavelength tubes

Micro-perforated panel sound absorbers are widely used in noise control applications in the fields of architectural acoustics and transport acoustics. Combining micro-perforated panels with other resonant or sound absorbing systems may broaden the frequency range in which they absorb sound while ensuring that large sound absorption values are reached. In this work, a hybrid sound absorber that combines a micro-perforated panel and a coiled quarter wavelength tube is proposed. Series and parallel configurations of these two systems are studied from analytical, numerical, and experimental point of views. A comparison of two three-dimensional (3D) printing techniques for the production of samples highlights the main challenges for the practical implementation of the proposed design. The advantages and limitations of series and parallel arrangements are discussed and while the parallel configuration is more complex to setup in practice, it provides an improved sound-absorbing performance compared with the series configuration. Finally, the reproducibility of the hybrid absorber in parallel configuration is confirmed by testing samples that were produced with two different 3D printers and in two different laboratories.

Application of Noise Control Combined with Relaxation Training in Patients with Skin Laser Cosmetology: A Single-center Retrospective Study.

Noise pollution has been listed as one of the three major types of pollution, along with air and water pollution. Hospitals should pay attention to noise control, which is of great importance for the treatment and rehabilitation of patients. This study focuses on the application value of noise control and relaxation training. This study retrospectively collected and analyzed the clinical data of 184 patients who underwent skin laser cosmetology in Ningbo Yinzhou No. 2 Hospital from January 2021 to December 2022. Twelve patients who did not meet the criteria were excluded, and the remaining 172 patients were divided based on the type of intervention into the control group (CG, n = 82) and the study group (SG, n = 90). The CG received relaxation training and routine noise management, while the SG received noise control combined with relaxation training. The intervention effect was discussed from the aspects of noise, psychology, and satisfaction. After the intervention, the SG had overtly lower noise levels and lower scores of anxiety and depression compared to the CG (all P < 0.001). Correlation analysis showed that noise levels were positively correlated with scores of anxiety and depression (r = 0.553, r = 0.592, P < 0.001). The two groups had no significant difference in total satisfaction (P > 0.05). Noise poses a significant threat to the human body. Strengthening noise control in hospitals is beneficial for patients' recovery. Combining noise control with relaxation training is an intervention method worthy of clinical application. It can improve the hospitalization environment and reduce the noise levels to a great extent, thereby improving the psychological state of patients and enhancing the medical satisfaction.

Guiding acoustic waves via a gradient index meta-layer

In this work, we propose an efficient approach for controlling acoustic waves through guided mode conversion within a single meta-layer comprised of gradient index metamaterials. By harnessing the subwavelength localization characteristics of acoustic surface waves, the meta-layer can be properly shaped to accommodate arbitrary and prospective trajectories, thus enabling flexible guidance and routing of acoustic waves. Utilizing such a mode conversion mechanism, the acoustic directional transmitter and beam splitter have been devised and numerically demonstrated based on Archimedean spiral structures. These acoustic devices can exhibit a broadband response, achieving transmission efficiency exceeding 80% over a specific bandwidth that can be controlled by the geometry design. The proposed gradient index meta-layer may open new possibilities for acoustic wave manipulation, enabling some promising applications in noise control, information transmission, and energy harvesting.

A Stable IIR Filter Design Approach for High-Order Active Noise Control Applications

In commercial non-adaptive active noise control (ANC) applications, an IIR filter structure is often used to reduce real-time computations. On the contrary, an FIR filter structure is usually preferred in the filter design phase because the FIR filter design formulation can be convex and is simple to solve. To combine the benefits of both FIR and IIR filter structures, one common approach in ANC applications is to use an IIR filter structure to fit a pre-designed FIR filter. However, to ensure stability, most of the common IIR filter fitting approaches involve the computation and relocation of poles which can be difficult for high-order cases. In this current work, a stable IIR filter design approach that does not need the computation and relocation of poles is improved to be applicable in ANC applications. The results demonstrate that the proposed method can achieve better fitting accuracy and steady-state noise control performance in high-order non-adaptive applications when the pre-designed noise control FIR filter is fitted. Besides fitting the noise control filter, the proposed method can also be used to fit the secondary path and acoustic feedback path to reduce the required real-time computations if adaptive controllers are applied.

Flexible wavefront manipulations via amplitude-phase joint coding acoustic metasurfaces

Acoustic coding metasurfaces (ACMs) with limited kinds of meta-atoms have attracted much attention due to flexible wavefront manipulations of acoustic waves. However, the previously reported ACMs are mainly encoded by phase responses, limiting their functions and applications. For complete manipulation of the propagation of acoustic waves, it is beneficial to control both amplitude and phase responses. In this paper, amplitude-phase joint coding acoustic metasurfaces (APCMs) are proposed, which enable simultaneous realization of acoustic wavefront engineering and energy allocation. In particular, by adjusting the geometrical parameters of the proposed dual-layer meta-atoms, the reflection amplitude can be continuously controlled from approximate total absorption to total reflection, and the full reflection phase coverage can be realized. Two examples are proposed to verify the abilities of APCMs. The direction and intensity of the reflected beam can be manipulated. Meanwhile, the position and intensity of focal spots can be arbitrarily modulated by different amplitude-phase sequences of coding elements. The full-wave numerical simulation results confirm the effectiveness of the proposed APCMs, which have potential applications in noise control and advanced field-manipulation systems.

Broadband sound attenuation and absorption by duct silencers based on the acoustic black hole effect: Simulations and experiments

Wideband reduction of both sound reflection and transmission using compact non-intrusive liners remains a challenging issue for duct noise control applications. This work focuses on the acoustical performance limitations of cylindrical silencers made up of annular ring resonators with axial gradient of their cavity depths. It is shown from theoretical, numerical and experimental studies that a sub-wavelength silencer with optimized acoustic black hole (ABH) properties can be designed through which incident sound waves are retarded and fully dissipated within the activated resonant cavities. Such ABH-type silencer requires a suitable interplay between the wall impedance axial variations and the visco-thermal losses within the cavities. Key parameters that influence this balance are the axial growth of cavity depths and the wall porosity. A causal-based criterion has been proposed that maximizes the total integrated dissipated power, thereby leading to the optimal value of the wall porosity and to the ultimate bandwidth-to-length ratio that can be achieved by an ABH-type silencer given a target dissipation value. A space-frequency region has been numerically and experimentally identified over which the ABH effect is prominent. The causal-based criterion has been extended to account for the low-frequency ultimate performance of ABH silencers with coiled cavities and for the effects of a low-speed grazing flow.

A model for near-perfect transmission through lossy media with acoustic sources

Acoustic metamaterials exhibit effective material properties not found in naturally occurring media, and, as such, have received considerable attention for their potential applications in noise and vibration control, diagnostic imaging, and nonreciprocal transmission. Complementary acoustic metamaterials have been proposed as a means of compensating for the high impedance mismatches of aberrating layers that disrupt the acoustic field and hence distort acoustic images. More recently, a complementary acoustic metamaterial featuring active components was shown in principal to compensate for both the impedance mismatch and energy attenuation of lossy materials, but a physical realization of the concept has not yet been implemented. Here, we present results from a one-dimensional acoustic model showing how a plane wave incident on a lossy material can be augmented by point monopole and dipole sources to allow for near perfect transmission, thus rendering the lossy medium acoustically transparent. We present general expressions for source magnitudes that are dimensionless with respect to frequency, material thickness, and the background medium. We show that these results are consistent with three-dimensional finite element simulations, where the appropriate monopolar and dipolar forces are generated using finite dimensional velocity sources with real loudspeaker characteristics mounted in an acoustic waveguide.

An adaptive constrained multi-channel active noise control filter design approach using convex cone optimization

In current practical active noise control (ANC) applications, solutions to three main technical challenges need to be sought: the requirement of a stable controller when acoustic feedback paths exist, a larger quiet zone, and adaptation to a time-varying environment. The imposed controller stability constraints can significantly increase the computational requirements and negatively impact the adaptation of ANC filters in real time. Multi-channel systems are usually needed if a larger quiet zone is required while the coupling between different channels can greatly lower the convergence rate of adaptive algorithms. In the current work, a multi-channel adaptive constrained ANC filter design method is proposed. The recently proposed convex cone formulation for ANC design is adopted to reduce the computational time of solving the constrained ANC filter design problem. The optimal filter coefficients are then redesigned continuously using convex optimization when the environment is time-varying. The experimental result shows that, compared with the traditional leaky FxLMS method, the proposed method has a faster convergence rate and a better steady-state noise control performance.

Observation of non-reciprocal harmonic conversion in real sounds

Reciprocity guarantees that in most media, sound transmission is symmetric between two points of space when the location of the source and receiver are interchanged. This fundamental law can be broken in non-linear media, often at the cost of detrimental input power levels, large insertion losses, and ideally prepared single-frequency input signals. Thus, previous observations of non-reciprocal sound transmission have focused on pure tones, and cannot handle real sounds composed of various harmonics of a low-frequency fundamental note, as generated for example by musical instruments. Here, we extend the reach of non-reciprocal acoustics by achieving large, tunable, and timbre-preserved non-reciprocal transmission of sound notes composed of several harmonics, originating from musical instruments. This is achieved in a non-linear, actively reconfigurable, and non-Hermitian isolator that can handle arbitrarily low input power at any audible frequency, while providing isolation levels up to 30dB and a tunable level of non-reciprocal gain. Our findings may find applications in sound isolation, noise control, non-reciprocal and non-Hermitian metamaterials, and analog audio processing.

Vibrational Power Flow Analysis for the Sandwich Cylindrical Shell Structure with a Metal–Rubber Core in the Thermal Environment

This research is designed to investigate the vibrational characteristics of a sandwich cylindrical shell structure with an elastic-porous metal–rubber core in the thermal environment by the power flow method. The finite element models of the homogeneous and sandwich cylindrical shell structures are established for harmonic response analysis completed by the mode superposition method. Further, the structural power flow is calculated and visualized based on the results of the finite element analysis. A comparison is made with the results for a plate available in the literature validating the effectiveness of the power flow visualization method. The effects of some key factors, such as the frequency, the metal–rubber core, the length-to-radius ratio, and the temperature on the power flow of the sandwich cylindrical shell structure, are analyzed using power flow cloud pictures and vector diagrams. The results reveal that the frequency affects the distribution of power flow, and the metal–rubber core can dissipate energy, whereas the length-to-radius ratio and temperature do not have a significant influence on the power flow of the sandwich cylindrical shell structure with a metal–rubber core (SCSMR). This work should be valuable for the noise and vibration control application of the SCS-MR.

Research on Sound Absorption Properties of Tri-Periodic Minimal Surface Sandwich Structure of Selective Laser Melting Titanium Alloy

Triply Periodic Minimal Surface (TPMS) sandwich structure has the characteristics of lightweight, high specific strength, specific stiffness, vibration, and noise reduction. There is relatively little research on its sound absorption performance. TPMS sandwich structure based on selective laser melting (SLM) technology can achieve precise control of structure type, porosity, and so on, and has broad prospects in noise control applications. In this paper, the sandwich structure is designed based on tri-periodic minimal surface implicit function, and the titanium alloy sandwich structure is formed by SLM technology, and the sound absorption performance of titanium alloy TPMS sandwich structure is studied. The effects of volume fraction, panel thickness, and cell layer number on the sound absorption performance of the two TPMS structures were systematically analyzed using the transfer function method. The results show that: The GP10 sandwich structure with the volume fraction of 20%, the thickness of the panel is 1.0 mm, and the number of cell layers is 3C parameter combination has better sound absorption performance and higher sound absorption bandwidth, and the sound absorption coefficient is 0.36. For Ti6Al4V sandwich sound absorption structure, it is not suitable to design too thick panels. When the volume fraction is lesser, the increase of the tortuosity factor τ improves the sound absorption performance of the two structures, and excessive volume fraction leads to a decrease of sound absorption performance. The increase of cell layers can broaden the sound absorption bandwidth of the two structures, and the sound absorption capacity increases and then decreases in the range of 150–6400 Hz. The Gyroid structure mostly exhibits resonance sound absorption mechanism, while the Diamond structure exhibits resonance sound absorption mechanism combined with the viscous loss of sound wave. The work done in this paper can provide a theoretical basis for the study of the sound absorption characteristics of TPMS sandwich structure.

Design and Fabrication of Aerogel Composites for Oil Water Separation and Spilled Oil Cleaning

Aerogel composites are multicomponent highly porous materials with air as the major dispersed phase. There are many kinds of aerogel composites including synthetic and natural aerogel composites. Aerogel composites have found wide applications in sorption, thermal insulation, vibration damping, and noise control. This mini review focuses on the aerogel composites with oil water separation function for spilled oil cleaning. The design and fabrication of various aerogel composites for oil cleaning are emphasized. The commonly used technologies including in-situ reaction, sol–gel spinning, templating, and self-assembling are introduced. The microstructure control through directional freeze casting, bio-inspired approach, coating, etc., are discussed.

Application of active noise control for plenum window in a domestic setting

Plenum windows, also known as ventilation windows allow for natural ventilation in living spaces while providing noise reduction to improve the health and living comfort of occupants, especially in noise polluted and tropical/sub-tropical cities. However, while plenum windows can provide acceptable levels of natural ventilation, the passive noise performance of plenum windows when fully opened is still lacking compared to the conventional closed windows at low frequencies. Active noise control (ANC) has been shown to provide good performance in several applications in low-frequencycontrol. Thus, the application of active noise control through a single-channel and dual-channel ANC implementation is to be developed and demonstrated in a field test for a plenum window set in a domestic home built to reproduce the environment of a high-rise apartment. The experimental application will be based on the optimal configurations for single and dual-channel ANC informed by prior simulation studies.

On optimum speaker placement with a model-based approach for indoor local active noise control applications

In this study, a control system actively canceling the noise will be developed through a model-based algorithm to reduce the noise generated in the room on individuals in an environment as much as possible. The model-based design approach is preferred because it is convenient for optimization and can be applied much more effortlessly than real experiments; it is applied using the finite difference method. The model developed within this scope has been validated by comparing it with the acoustic test data performed in an empty room. The positioning of loudspeakers was accomplished through a heuristic search algorithm to obtain the highest local cancellation of noise originating in the acoustic cavity from any position(s) in the targeted area. The feedforward adaptive control system chosen to drive the control loudspeakers is implemented using the least mean squares algorithm. The efficiency of the designed system under different noise conditions was examined, and two of them were included in the study.

Design of causal preconditioning filters for adaptive filtering algorithms in real-time multi-channel active noise control applications

Least-mean-square (LMS) algorithm has been widely used in the area of active noise control (ANC). One practical concern of LMS-based algorithms is its slow convergence rate in multi-channel broadband noise control applications. To improve the convergence speed of traditional LMS algorithm, preconditioning filters were added to the LMS system in previous studies to remove the correlation between the reference signals and decouple the plant responses. However, the preconditioning filters implemented previously are usually obtained through singular value decomposition of the cross spectral matrix of reference signals and the plant response matrix, which does not lead to causal preconditioning filters and, thus, it can only be applied in spatial audio applications when delay is not an important concern, but cannot be implemented in real-time active noise control applications. In the current work, a method is proposed to obtain a casual multi-channel preconditioning filter for real-time active noise control applications through a numerically robust algorithm to perform a spectral factor decomposition to the reference signal cross spectral matrix and a minimum-phase and all-pass decomposition to the multi-channel secondary path. Simulation results show that, by applying the proposed preconditioning filter, the convergence speed of the LMS algorithm can be significantly improved.

Application of active noise control based on neural network to vehicle's engine sound

Active noise control(ANC) is a particularly effective system for reducing low-frequency noise to compensate passive noise control. With the recent development of digital signal processor(DSP) performance, ANC has the potential to be developed with various algorithms. Accordingly, several ANC algorithms using various controlloer such as artificial neural network(ANN) are being proposed. In nonlinear system; at many practical applications, the ANC algorithm using a neural network gets more reduction performance compared to the linear ANC. In this study, the methology proposed neural network based FxLMS algorithm to reduce noise for non-linear system by predicting time series data for near future. This proposed algorithm is applied to reduce the engine noise of vehicle to construct silent inner environment and verify the performance by below.

Flat Fresnel-spiral acoustic metamaterials composed of several arms ventilated metamaterials for simultaneous broadband sound absorption and air circulation

With a steep rise in the urban population requiring an increased number of buildings, public and private transport systems, urban noise is posing a serious environmental problem affecting health. To attenuate the effect on the well-being of human health, a variety of conventional sound-absorbing materials suitable at mid and higher-frequency noise absorption are commonly being used but low and mid-frequency noise remains a challenge. These applications are further limited by the acoustic performance and ventilation efficiency in conventional noise barrier limits of their fields. Acoustic metamaterial presents a unique solution as an artificially designed material showing low-frequency noise mitigation. A novel subwavelength device having thickness of 15mm (&lt;2 cm) ,with potential application in noise mitigation and air ventilation solution is presented herein. In this study, the design and fabrication of a small prototype based on a Fresnel-spiral shape composed of several arms are performed. Numerical and experimental investigations were carried out to determine the acoustical properties of the proposed ventilated metamaterial in terms of sound absorption and sound transmission loss. The experimental investigation shows significant sound absorption with a high bandwidth (more than one octave in the range of &gt; 900 Hz ), acoustic properties leading to potential applications in urban noise control for low and mid-frequency ranges.

Numerical modelling of acoustic metamaterial made of periodic Helmholtz resonator containing a damping material in the cavity

Acoustic metamaterials are frequently used in many fields such as aerospace, buildings and ground transportation industries for low frequency noise control applications. Different solutions based on membrane or Helmholtz resonators have been investigated in the past few years. In the present study, a numerical design of acoustic metamaterial made of Helmholtz resonator with a membrane in its cavity is presented. The resonator with a neck extended into the cavity is periodically embedded within a porous material. The membrane inside the resonator cavity is modelled as a linear isotropic elastic material with free and fixed boundary conditions. The transmission loss (TL) of the proposed metamaterial design, predicted by finite element method presents multiple resonant peaks while only one peak is obtained with a conventional resonator. Two TL resonance peaks are observed when the membrane circumferential boundary is free inside the resonator cavity. For fixed boundary conditions, more than two resonance peaks are obtained. The proposed metamaterial design can therefore be used in many industrial applications for low frequency noise attenuation.