Acoustic Metamaterial Panel Research Articles

Improving Sound Insulation in Low Frequencies by a Three-Component Cladding Acoustic Metamaterial Panel

In this paper, a three-component cladding acoustic metamaterial panel with good sound insulation effect in the low-frequency range is proposed. The sound transmission loss of metamaterial panels under different structural configurations and different material parameters is investigated by combining finite element simulation calculations with experimental research. The results show that the closer the center of gravity of the scatterer is to the substrate, the better the stability of the resonance unit, the wider the range of effective sound isolation frequencies, and the higher the degree of normalization. The filling rate of the scatterer is maintained at about 0.5 to obtain a better sound insulation effect. At the same time, choosing lower density materials for the substrate and metal materials with high density and high modulus of elasticity for the scatterer can maximally widen the bandgap and allows for low-frequency sound insulation below 600 Hz. This approach improves the low-frequency sound insulation efficiency of acoustic metamaterials. The results provide important explanations and references for a deeper understanding of the sound insulation mechanism and the effects of different parameters on sound insulation.

Lightweight panels based on Helmholtz resonators for low-frequency acoustic insulation

In this study, we propose a novel lightweight acoustic metamaterial panel composed of coupled Helmholtz resonators, designed to insulate low-frequency broadband noises effectively. Through finite element analysis, we observe the emergence of band gaps with varying widths, depending on the unit cell dimensions, the band gaps start at 100 Hz, and as the scale decreases, the band gaps shift to higher frequencies within specific ranges. These band gaps arise from the coupling of two Helmholtz resonators with different volumes but a common neck. For our work, we use ABS materials, which facilitate easy panel manufacturing. Moreover, we also explored the potential of other materials to enhance the low-frequency broadband sound insulation performance of the system. The results obtained from this research provide promising insights into developing lightweight panels for efficient low-frequency broadband sound insulation.

Sound transmission loss of a novel acoustic metamaterial sandwich panel: Theory and experiment

A novel acoustic metamaterial (AMM) sandwich panel with enhanced sound transmission loss (STL) is proposed and designed by periodically distributing the local resonators in the stiffened core. The vibro-acoustic coupling is considered by the continuity of velocity at the fluid–structure interfaces. The effective dynamic mass density method is used to investigate the influences of the local resonators on the reinforced STL of the sandwich panel. The space harmonic expansion method and the virtual work principle are applied to derive the dynamic equations. An acoustic experiment is carried out and compared with the theoretical result. Experimental and theoretical results show that the STL curve has a peak near the objective frequency of the local resonator. The vibro-acoustic behaviors are further investigated using the finite element method (FEM). The peaks and dips in the STL curves are explained by the vibration modes and stress distributions obtained by the FEM. The proposed AMM sandwich panel possesses improved sound insulation performance around the mass-air-mass resonance frequency. For specific working conditions, the present method can be used to improve the STL of sandwich plates by adding resonators.

Computational homogenization of locally resonant acoustic metamaterial panels towards enriched continuum beam/shell structures

Locally resonant acoustic metamaterial (LRAM) panels are excellent candidates for the low-frequency flexural wave attenuation in thin structures. To enable the efficient analysis and design of LRAM beam/shell structural elements for practical applications, a computational homogenization method for modelling wave propagation phenomena in LRAM panels is presented in this work. The approach is based on the notion of a relaxed separation of scales, which tailors the methodology to the phenomena governed by local resonators embedded in a host medium. The macroscopic LRAM panel is modelled as a thin continuum beam/shell described by proper structural kinematics and momentum balance relations. At the microscale, a LRAM unit cell is considered with lamina-wise in-plane boundary conditions and zero out-of-plane tractions, representing the free top and bottom surfaces of the macroscopic LRAM panel. Under the assumption of linear elasticity, in the relaxed separation of scales regime, the microscale unit cell problem can be represented by the superposition of a static and a dynamic problem, hereby enabling a significant model reduction. As a result, the macroscale effective material properties can be computed once and for all off-line for a given unit cell. In addition, a new macroscale evolution equation emerges describing the effect of the microscale internal dynamics on the macroscopic fields through the introduction of new macroscale enrichment variables, which reflect the modal amplitudes of localized microscale modes. The proposed homogenization methodology reveals a high level of accuracy and numerical efficiency compared to the reference direct numerical simulation (DNS) for all relevant analyses: computation of real and complex dispersion spectra for an infinite LRAM panel, as well as steady-state frequency response and transient behaviour for a finite LRAM panel.

Step-by-step structural design methods for adjustable low-frequency sound insulation based on infinite plate-type acoustic metamaterial panel

With the development of acoustic metamaterials (AMM), more and more researchers focus on the study of plate-type acoustic metamaterial panel (PAMMP). With the goal of industrial applications, the structural design methods of large-scale PAMMP are important. In this research, we establish an infinite plate-type acoustic metamaterial panel (IPAMMP) model, and experimental and simulation results show that the sound transmission loss (STL) curves of IPAMMP and large-scale PAMMP have good consistency in an interested range. On this basis, a set of step-by-step structural design methods for single-frequency and multi-frequency sound insulation are proposed. By adjusting the structural parameters of IPAMMP, the single-frequency STL peak could be shifted. Further study shows that multiple STL peaks could be realized in the low-frequency range by placing different masses on IPAMMP. Finally, taking transformers 100 Hz, 200 Hz, 300 Hz, 400 Hz and 500 Hz as examples, the feasibility of the structural design methods is verified by simulation. Consequently, the proposed step-by-step structural design methods could address the single-frequency and multi-frequency sound insulation at a specific frequency, demonstrating adjustability.

Ventilated acoustic metamaterial window panels for simultaneous noise shielding and air circulation

The conflict between the acoustical performance and ventilation efficiency in conventional noise barriers limits their application potentials in several settings. To address this challenge, we design and experimentally demonstrate a ventilated tunable acoustic metamaterial for noise mitigation at targeted frequencies. Through the structure, a peak normal incidence sound absorption coefficient of more than 0.96 at 1000 Hz and the peak normal incidence sound transmission loss of 18 dB is achieved while maintaining the air circulation with a 45% open area of ventilation. Such a high absorption near the resonant frequency under the ventilation condition originates from high impedance matching between the metastructure and air. Next, we present a proof-of-concept for the fabrication of acoustic metapanels for large scale applications. A simple jigsaw puzzle-like assembly technique is used to interconnect the multiple unit cells, leading to the production of integrated metapanels. The experimental findings validate the potential applications of the proposed metapanels for low-to-mid frequency noise control in a small ventilated spaces.

Synergetic coupling large-scale plate-type acoustic metamaterial panel for broadband sound insulation

In the field of low-frequency noise control, the locally resonant membrane and plate-type acoustic metamaterials (PAMMs) have received extensive attention from researchers due to its sub-wavelength thickness and low surface density properties. However, the existing research works mainly focus on the sound transmission loss (STL) of small-sized unit cells with the fixed boundary, resulting in that the sound insulation performances are great different from those of the large-scale structures used in engineering applications. For this reason, a square large-scale PAMM panel with side length of 0.704 m, which consists of a periodic array of square unit cells, is numerically studied under the normal incidence condition. The results show that the large-scale PAMM panels appear the obvious STL peak (~38 dB) in the low-frequency range. Moreover, the goal of broadband sound insulation based on the multi-cells synergetic coupling is realized by reasonably arranging the masses on the metamaterial panels. Numerical results indicate that a broadband insulation with average STL higher than 20 dB is obtained in the range of 300–900 Hz. Finally, a simplified experimental setup based on the box and semi-anechoic chamber is designed to verify the sound insulation performance, and the experiment under standard reverberation chamber and semi-anechoic chamber is performed in order to evaluate the sound insulation capability in the actual reverberation noise environment. The ideal periodic boundary is used in the numerical calculations, which is obviously different from the boundary condition in experiments. Therefore, the influence of the boundary condition on the STL is discussed and analyzed by calculating the STL of the metamaterial panels with different number of cells. The proposed design methods and results can provide some guidance for the application of the PAMM panels in practical engineering.

Honeycomb locally resonant absorbing acoustic metamaterials with stop band behavior

This study presents the design of a locally resonant absorbing metamaterial in the form of cubes and rectangular cubes, formed from square and honeycomb shaped unit cells. In this context, we fabricated a box consisting of acoustic metamaterial panels to validate our numerical simulation model. Then, we developed simulation models of acoustic metamaterials with square and honeycomb unit cells, forming cubic and rectangular cube sound barriers. Our purpose was to verify the operating frequency range of the designed metamaterial and then, compare the behavior of the different acoustic metamaterial structures in the specified frequency range. The acoustic metamaterials proved to be significantly effective in sound wave absorption providing transmission losses of up to 17.5 dB, more or less similarly in the three different structures, due to the identical resonators used in all of the structures, despite difference in unit cell shapes, number of resonators in the unit cell, and geometry of the barrier structure (cube or rectangular cube). These perforated metamaterial structures were then, tested in a waveguide consisting of panels of locally resonating metamaterials. Simulation results indicated that significant stop band behavior appeared for both square and honeycomb structures in the frequency of 750–1200 Hz, with a transmission loss of up to 60 dB. A clear comparison with a regular plate sound insulator tuned to the same resonance frequency is made, and the bandwidth and transmission loss is compared under the constraints of same occupied space and same material type. According to the procedure described in this paper, it is possible to design stop bands with excellent performance in a certain targeted frequency range.

Acoustic metamaterial panel for both fluid passage and broadband soundproofing in the audible frequency range

We present the design, including an experimental demonstration, of an acoustic metamaterial panel aimed at reducing incoming broadband noise in the audible frequency range while allowing an incoming fluid to pass through the holes formed in the panel. The noise reduction performance of the proposed acoustic metamaterial panel is attributed to an array of annular cavities enclosing the fluid passage holes. The acoustic behavior of the acoustic metamaterial panel is theoretically analyzed by the transfer matrix method, and an equivalent acoustic impedance of each annular cavity is included with its effective length in the derived transfer matrix. The effective bulk modulus for the acoustic metamaterial panel is then extracted from the transmission and reflection coefficients by using the retrieval method. It is shown that the frequency range of the negative effective bulk modulus coincides with the stop band of the acoustic metamaterial panel. The underlying physical mechanism for the negative effective bulk modulus is attributed to the out-of-phase motion of vibrating particles in adjacent annular cavities. A calculated transmission coefficient curve of the acoustic metamaterial panel is shown to be in good agreement with the measured one. The findings presented in this work should be useful in the design of a holey soundproof panel.

An efficient analytical model for baffled, multi-celled membrane-type acoustic metamaterial panels

A new analytical model for the oblique incidence sound transmission loss prediction of baffled panels with multiple subwavelength sized membrane-type acoustic metamaterial (MAM) unit cells is proposed. The model employs a novel approach via the concept of the effective surface mass density and approximates the unit cell vibrations in the form of piston-like displacements. This yields a coupled system of linear equations that can be solved efficiently using well-known solution procedures. A comparison with results from finite element model simulations for both normal and diffuse field incidence shows that the analytical model delivers accurate results as long as the edge length of the MAM unit cells is smaller than half the acoustic wavelength. The computation times for the analytical calculations are 100 times smaller than for the numerical simulations. In addition to that, the effect of flexible MAM unit cell edges compared to the fixed edges assumed in the analytical model is studied numerically. It is shown that the compliance of the edges has only a small impact on the transmission loss of the panel, except at very low frequencies in the stiffness-controlled regime. The proposed analytical model is applied to investigate the effect of variations of the membrane prestress, added mass, and mass eccentricity on the diffuse transmission loss of a MAM panel with 120 unit cells. Unlike most previous investigations of MAMs, these results provide a better understanding of the acoustic performance of MAMs under more realistic conditions. For example, it is shown that by varying these parameters deliberately in a checkerboard pattern, a new anti-resonance with large transmission loss values can be introduced. A random variation of these parameters, on the other hand, is shown to have only little influence on the diffuse transmission loss, as long as the standard deviation is not too large. For very large random variations, it is shown that the peak transmission loss value can be greatly diminished.

Ultra-thin metamaterial for perfect and quasi-omnidirectional sound absorption

Using the concepts of slow sound and critical coupling, an ultra-thin acoustic metamaterial panel for perfect and quasi-omnidirectional absorption is theoretically and experimentally conceived in this work. The system is made of a rigid panel with a periodic distribution of thin closed slits, the upper wall of which is loaded by Helmholtz Resonators (HRs). The presence of resonators produces a slow sound propagation shifting the resonance frequency of the slit to the deep sub-wavelength regime (λ/88). By controlling the geometry of the slit and the HRs, the intrinsic visco-thermal losses can be tuned in order to exactly compensate the energy leakage of the system and fulfill the critical coupling condition to create the perfect absorption of sound in a large range of incidence angles due to the deep subwavelength behavior.

Subwavelength acoustic metamaterial panels for underwater noise isolation

Acoustically thin metamaterial underwater noise isolation panels have been developed that provide as much as 16 dB of noise isolation for a panel with a thickness just 160th of the wavelength in the host medium (fresh water) at 2.5 kHz. The panels are composed of thin layers of neoprene rubber and polyoxymethylene containing air-filled voids. The level of isolation provided by the panels is shown to correlate positively with the volume fraction of air voids within the panel.

Simulation and experimental study of a metamaterial panel for mechanical wave absorption

Based on the mechanical wave selective absorption principle of mass-spring microstructures by the optical vibration mode, a two-dimensional acoustic metamaterial panel consisting of lumped mass and elastic membrane is presented. The vibration characteristic simulation of the metamaterial equivalent panel representative cell is performed using the finite element method and the results indicate that the presented 2D metamaterial panel behaves just like regular mass-spring microstructures. Under the guidance of the simulation results, a square metamaterial panel is fabricated and its vibration characteristics are examined using a Polytec scanning laser vibrometer. The test results indicate that the metamaterial panel can efficiently absorb mechanical waves of about 157.5 Hz.

Latex could be ultimate domestic soundproofer

Low frequency bass sounds are notoriously difficult to block and a comon form of sound pollution, but they're no match for 15-mm-thick acoustic metamaterial panels

Acoustic metamaterial panels for sound attenuation in the 50–1000 Hz regime

We show experimentally that thin membrane-type acoustic metamaterials can serve as a total reflection nodal surface at certain frequencies. The small decay length of the evanescent waves at these frequencies implies that several membrane panels can be stacked to achieve broad-frequency effectiveness. We report the realization of acoustic metamaterial panels with thickness ≤15 mm and weight ≤3 kg/m2 demonstrating 19.5 dB of internal sound transmission loss (STL) at around 200 Hz, and stacked panels with thickness ≤60 mm and weight ≤15 kg/m2 demonstrating an average STL of >40 dB over a broad range from 50 to 1000 Hz.