Broadband Sound Absorption with Low-Perforation Micro-Perforated Panels Coupled with Space-Coiling and Helmholtz Resonators: Numerical and Experimental Study

In this work, a hybrid acoustic material (HAM) is designed for broadband and low-frequency sound absorption based on the combination of two different materials: a porous layer (melamine foam) and a modified Helmholtz resonator with embedded necks (HRENs). Theoretical predictions, numerical simulations, and experimental measurements are conducted to investigate the acoustic characteristics of the HREN. The HAM absorption mechanism is presented to evaluate the broadband sound absorption by the impedance matching effect of the different structures. The results of experimental tests confirmed that the HAM has broadband sound absorption and presented good agreement with an equivalent fluid model and numerical simulations. Broadband sound absorption was comparatively evaluated by the broadband factor (Qα), revealing the advantages due to the possible configurations of HAM in relation to HREN and melamine foam. In addition, the selection and dimensions of the HREN holes and the perforation ratio, in the range of 3%–10%, allow the hybrid sound absorber to achieve one absorption peak between 235 and 582 Hz with quasi-total absorption (α≥0.8). This work contributes to the understanding of sound wave propagation and broadband absorption in acoustic materials composed of different materials combined.

Structures with light weight and broadband sound absorption is of vital importance for noise control applications in engineering practice. Foams exhibit broadband but poor low frequency sound absorption, micro-perforated sandwich structures conversely possess good sound absorption at low frequencies due to resonance, the bandwidth is however limited. Micro-perforated sandwich structures with foam filling are therefore proposed in the paper to obtain wideband low-frequency sound absorption. An integrated analytical, numerical and experimental research is conducted to investigate sound absorption and lightweight characteristics of four commonly used micro-perforated sandwich structures with honeycomb (PHSP), corrugated (PCSP), N hybrid (PNHSP) and honeycomb-corrugated (PHCSP) cores. An analytical model is built to estimate sound absorption coefficient (SAC) based on the acoustic impedance theory and Johnson-Champoux-Allard model. Numerical simulation and experimental measurement methods are conducted simultaneously to validate the analytical model. The influences and underling mechanism of foam filling and filling configurations are explored, and it is found that melamine foam filling can enhance low-frequency sound absorption bandwidth of micro-perforated sandwich structures, and half-filled foam can bring in higher absorption peak values than fully filled foam due to more violent resonance. To overall evaluate both the lightweight and sound absorption performance of varied sandwich cores, a comprehensive evaluation index by the sound absorption and relative mass is developed. Results show that the PCSPs with lower half part filled foam perform best at both sound absorption and lightweight among all sandwich structures. Results of this paper can provide guidance for the application of sandwich structures.

Theoretical investigation on the acoustic performance of Helmholtz resonator integrated microperforated panel absorber

Sonic black hole (SBH) is a kind of broadband sound absorber, which features lightweight and high-efficiency. However, achieving low frequency sound absorption at a deep-subwavelength thickness remains a challenge for conventional SBHs. Herein, a hybrid sonic black hole (HSBH) with gradually varying neck-embedded Helmholtz resonators (HRs) and micro-perforated panels (MPPs) is proposed. The working bands are broaden at low frequencies with sub-wavelength and broadband sound absorption in the mid-and-high frequency range. Such HSBH exhibits excellent potential in broadband sound absorption with sub-wavelength. The transfer matrix method (TMM) is used to analyze the low-frequency sound absorption of HSBH, which is validated by the finite element method (FEM). It is shown that the proposed HSBH exhibits high sound absorption with sub-wavelength (the frequency of first peak is 102 Hz, about λ / 30 ). The enhanced low-frequency sound absorption of the proposed HSBH is also validated by the experiment results. Meanwhile, the influences of various structural parameters on the low-frequency properties and broadband characteristics of HSBHs are also revealed. A fast and elitist nondominated sorting genetic algorithm (NSGA-II) is introduced to optimize the HSBH. Finally, a coplanar HSBHs are also designed to achieve a broadband sound absorption from 100 to 3000 Hz.

Low-frequency broadband sound absorption is a hot topic in the field of acoustics. For the Helmholtz resonator, the low-frequency sound wave can be controlled by adjusting the size of the structure. However, the frequency bandwidth of the sound absorption is narrow. The micro-perforated panel (MPP) absorber predominantly targets mid-to-high frequency noise. To achieve broadband sound absorption, an auxetic star-shaped metastructure (ASM) based on the Helmholtz resonator and MPP absorber is proposed. The ASM employs an auxetic star-shaped structure as a unit cell, wherein triangular cavities formed at the junction of the unit cells are strategically designed to function as MPP resonators. Firstly, the theoretical formula of the ASM is derived by electro-acoustic analogy, and the numerical simulation results are compared with the theoretical results. Besides, the sound absorption mechanism of the ASM is studied by the acoustic pressure distribution, particle vibration velocity distribution, and power dissipation density distribution. Secondly, the sound absorption performance of the ASM is studied by adjusting the structural parameters. Finally, it is proved that when the thickness of the ASM structure is only 40 mm, the average sound absorption coefficient of 0.9 at 580–1150 Hz. In this paper, a novel method is presented for designing a broadband sound-absorbing metastructure.

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

The proposed work enumerates a hybrid thin, deep-subwavelength (2 cm) acoustic metamaterials acting as a completely new type of sound absorber, showing multiple broadband sound absorption effects. Based on the fractal distribution of Helmholtz resonator (HRs) structures, integrated with careful design and construct hybrid cross micro-perforated panel (CMPP) that demonstrate broad banding approximately one-octave low-frequency sound absorption behavior. To determine the sound absorption coefficient of this novel type of metamaterial, the equivalent impedance model for the fractal cavity and the micro-perforated Maa’s model for CMPP are both used. We validate these novel material designs through numerical, theoretical, and experimental data. It is demonstrated that the material design possesses superior sound absorption which is primarily due to the frictional losses of the structure imposed on acoustic wave energy. The peaks of different sound absorption phenomena show tunability by adjusting the geometric parameters of the fractal structures like cavity thickness ‘t’, cross perforation diameter of micro perforated panel, etc. The fractal structures and their perforation panel are optimized dimensionally for maximum broadband sound absorption which is estimated numerically. This new kind of fractals cavity integrated with CMPP acoustic metamaterial has many applications as in multiple functional materials with broad-band absorption behavior etc.

In this study, a broadband sound absorber was developed using a double-layered irregular honeycomb microperforated panel (MPP) structure and a particle swarm optimization (PSO) algorithm to address the issue of broadband sound absorption of MPPs. An acoustic impedance model of the designed sound absorber and an optimization algorithm were implemented to obtain the structural configuration parameters for quasi-perfect sound absorption. The coupling effect between the resonant elements and the optimized structural configuration parameters enabled broadband and high-efficiency sound absorption. The impedance tube experimental results demonstrated an excellent broadband sound absorption level within the range of linear acoustics, and the designed triad and tetrad structures exhibited more than 70% absorption efficiency in the range of 609–4 002 Hz and 518–5 162 Hz, respectively. This study provides a design method and insights into the design, promotion, and application of broadband sound absorbers.

An acoustic metasurface gives a broadband sound absorption by a planar periodic array combining small resonant modules tuned at different frequencies. The resonant module is often applied by a Helmholtz resonator, a membrane backed by an airtight cavity and a quarter wavelength closed tube, which have equivalent small area to a fraction of the wavelength. The author has studied the sound absorption of resonators by applying a multiple folded long neck and an airtight cavity for a thin sound-absorbing structure with high sound absorption at low frequencies below 100 Hz. In this paper, the author prototypes an acoustic metasurface by planar periodic array of Helmholtz resonators at various resonant frequency tuned by this neck and cavity of the resonator as a unit cell, and discusses the sound absorption characteristics. The prototyped acoustic metasurface gives a 40 % - 70 % sound absorption from 125 Hz to 250 Hz when it is combined with a 6.4 mm thickness of top plate including a 24 mm - 96 mm length of the multiple folded long neck and a 43.2 mm depth of the airtight cavity. And, more broadband sound absorption will be discussed by a theoretical analysis.

Perfect, broadband and asymmetric sound absorption is theoretically, numerically and experimentally reported by using subwavelength thickness panels in a transmission problem. The panels are composed of a periodic array of varying crosssection waveguides, each of them being loaded by Helmholtz resonators (HRs) with graded dimensions. The low cut-off frequency of the absorption band is fixed by the resonance frequency of the deepest HR, that reduces drastically the transmission. The preceding HR is designed with a slightly higher resonance frequency with a geometry that allows the impedance matching to the surrounding medium. Therefore, reflection vanishes and the structure is critically coupled. This results in perfect sound absorption at a single frequency. We report perfect absorption at 300 Hz for a structure whose thickness is 40 times smaller than the wavelength. Moreover, this process is repeated by adding HRs to the waveguide, each of them with a higher resonance frequency than the preceding one. Using this frequency cascade effect, we report quasi-perfect sound absorption over almost two frequency octaves ranging from 300 to 1000 Hz for a panel composed of 9 resonators with a total thickness of 11 cm, i.e., 10 times smaller than the wavelength at 300 Hz.

In this paper, the low frequency sound absorption structure based on Helmholtz resonator (HR) is deeply studied. The influence of hierarchical structure design on the broadband sound absorption is emphatically discussed. Through the introduction of the embedded slits and hierarchical structures, we design a new and efficient hierarchical slit-embedded HR (HSEHR) for sound absorption. This structure not only inherits the advantages of the classic HR, but also realizes the effective sound absorption(α > 0.97) in a lower frequency(225 Hz) range through the interaction of the embedded slit and the hierarchical structure. More interestingly, the thickness of HSEHR is only 1/50 of the corresponding wavelength. In order to verify the sound absorption effect of HSEHR, we have carried out a lot of theoretical analysis and numerical simulation. The results show that HSEHR has excellent sound absorption performance in the low frequency range, and with the introduction of the hierarchical structure, the sound absorption peak moves to a lower frequency, and a higher sound absorption coefficient is obtained. We also found that by adjusting the structural parameters of HSEHR (such as the depth and width of the primary embedded slit.), its resonance frequency can be precisely controlled. So it can better match the target noise frequency and improve the sound absorption efficiency. In addition, genetic algorithm is used to optimize the structural parameters of HSEHR to further improve its sound absorption performance. The optimization results show that HSEHR optimized by genetic algorithm has better sound absorption performance in the broadband low frequency range. It achieves excellent sound absorption at 260–480 Hz. The sound absorption coefficient is up to 0.92, which is infinitely close to perfect sound absorption. It provides an excellent solution to the noise problem.

Low-frequency sound attenuation is often pursued using Helmholtz resonators (HRs). The introduction of a compliant wall around the acoustic cavity results in a two degrees-of-freedom (2DOF) system capable of more broadband sound absorption. In this study, we report the amplitude-dependent dynamic response of a compliant-walled HR and investigate the effectiveness of wall compliance to improve the absorption of sound in linear and nonlinear regimes. The acoustic-structure interactions between the conventional HR and the compliant wall result in non-intuitive responses when acted on by nonlinear amplitudes of excitation pressure. This paper formulates and studies a reduced order model to characterize the nonlinear dynamic response of the 2DOF HR with a compliant wall compared to that of a conventional rigid HR. Validated by experimental evidence, the modeling framework facilitates an investigation of strategies to achieve broadband sound attenuation, including by selection of wall material, wall thickness, geometry of the HR, and other parameters readily tuned by system design. The results open up new avenues for the development of efficient acoustic resonators exploiting the deflection of a compliant wall for suppression of extreme noise amplitudes.

Unlike classical multi-layered micro-perforated panels (MPPs), which rely on sub-millimeter orifices for sound dissipation, we propose a multi-layered porous Helmholtz resonators absorber. It consists of alternately layered perforated porous material panels and perforated rigid panels with millimeter- to centimeter-scale orifices, primarily relying on porous materials for sound energy dissipation. Theoretically, perforated porous material panels are modeled as homogeneous fluid layers using double porosity theory, and the total surface impedance is derived through bottom-to-top impedance translation. A double-layered prototype was tested to validate the theoretical and numerical models, achieving near-perfect absorption peaks at 262 Hz and 774 Hz, with a subwavelength total thickness of 11 cm and a broadband absorption above an absorption coefficient of 0.7 from 202 Hz to 1076 Hz. Simulations of sound pressure, particle velocity, power dissipation, and sound intensity flow confirm that Helmholtz resonances in each layer enhance sound entry into resistive porous materials, causing absorption peaks. Parameter studies show this absorber maintains high absorption peaks across wide ranges of orifice diameters and panel thicknesses. Finally, an optimized triple-layer porous Helmholtz resonators absorber achieves an ultra-broadband absorption above a coefficient of 0.95 from 280 Hz to 1349 Hz with only 16.5 mm thickness. Compared with conventional MPPs, this design features significantly larger orifices that are easier to fabricate and less susceptible to blockage in harsh environments, offering an alternative solution for low-frequency and broadband sound absorption.

In both experiment and simulation, we demonstrate a graded array of Helmholtz resonators (HRs) with cross-linked polypropylene (IXPP) ferroelectret films on the inner walls of cavities, which can realize both sound absorption and energy harvesting within 300–800 Hz. This dual-function graded array contains nine HRs with different sizes, which can offer a broadband working frequency and absorb part of acoustic energy. The unique ability of IXPP ferroelectret films can be used to efficiently harvest sound energy during resonant performances. An electric circuit is designed for collecting electrical signals of each branch individually. The average values of sound absorption coefficient and output power are about 0.81 and 1.43 nW in the range of 300–800 Hz with an input sound pressure level (SPL) of 100 dB in experiment, respectively. Our results enrich the fundamental techniques of both sound absorption and acoustic energy harvesting (AEH), which can pave a way for designing acoustic device in the field of sound absorption and energy conversion for future engineering application.

Helmholtz resonator is considered and widely accepted as a basic acoustic model in engineering applications and research. In this paper, the normal incidence sound absorption characteristics of series and parallel configurations of Helmholtz resonators is studied analytically, numerically and experimentally. The proposed analytical model for series configuration of HRs comprises of Johnson–Champoux–Allard model and transfer matrix method while parallel configuration of HRs is described using parallel transfer matrix method. The results from proposed analytical models fit well with the finite element method (FEM) results obtained from COMSOL multiphysics. Incorporation of parallel configuration and proper tuning of geometric parameters helps to overcome the trade-off between broad band sound absorption and minimum space utilization. Also, the experimental observations of one of the parallel configuration substantiates the FEM results. Moreover, the FEM models are more accountable for the variation in neck position and also provide better visualization of acoustic absorption with frequency.