Micro-perforated Panel Absorber Research Articles

Limp microperforated panel finite elements and its application

Microperforated panel (MPP) absorbers provide relatively broadband sound absorption with the superior material properties in durability, recyclability, and flexibility of design, and they can be considered as an attractive alternative of conventional sound absorbers. Recently, with the rapid progress of computer technology, numerical methods such as finite element method (FEM) and boundary element method have become powerful design tools for developing MPP absorbers with the consideration of advantage in handling arbitrary geometries, and there exist some computational models of MPP. This paper presents a simple and computationally efficient limp MPP elements to treat MPP absorbers in finite element analysis and the performance is demonstrated in various problems. First, the theory of MPP elements is presented briefly. Then, the validity is shown using impedance tube problems, in which the absorption characteristics of some MPP absorbers calculated using FEM are compared with the theoretical values. Finally, the applicability to room acoustics simulations is demonstrated by calculating transfer functions and impulse responses of rooms with practical dimensions.

Suppressing Noise for an HTS Amorphous Metal Core Transformer by Using Microperforated Panel Absorber

Noise pollution is an important issue in modern society. This paper is mainly concerned with noise suppressing of amorphous metal alloy core superconducting distribution transformers (AMSDTs). A microperforated sound absorption structure based on the electroacoustical equivalent circuit model was designed and installed in the inner sides of the box circumference. Up to now, there have been few investigations and reports of its application in superconducting transformer. In this paper, single and double microperforated panels (MPPs) were installed in the inner sides of the box circumference when the box was filled with air. To understand the reduction in vibration noise behaviors of AMSDTs installed with MPPs under normal operation, an AMSDT model was used as the test object, and a single MPP, double MPPs, and different backed cavities filled with the air experimentally and compared when rated voltages were applied to the AMSDT model. Tests were also carried out on the AMSDT model with different temperature air cavity and MPPs made with different materials. An attempt was made to find the largest amplitude and its corresponding frequency on the box surface using vibration sensors, which were arranged on the surface of the box. A data-acquisition platform was set up for signal measurement. The results validate the proposition that the MPP absorber effectively reduces the audible noise of the AMSDT, that the performance is improved by partitioning the backed cavity into differently sized sections, and that the performance is affected when the cavities are filled with air and overexcitation currents or voltages are applied to the AMSDT model. The test results are helpful for optimizing the design and reducing the noise of AMSDTs.

Numerical study on the absorption performance of MPP sound absorber installed in small rectangular rooms

Sound absorbers using microperforated panel (MPP) are one of the most promising alternatives of the next-generation sound absorbing materials, thanks to the superior material performances in durability, weatherability, recyclability, and flexibility of design, as well as the attractive broadband sound absorption characteristics. Many previous researches focus on the development of absorbers itself. However, in order to bring out the absorption performance sufficiently or to use it appropriately in room acoustics applications, it is important to understand the absorption effect of MPP absorbers on sound fields in rooms. For the purpose, recently, highly accurate wave-based acoustics simulation techniques such as FEM can be used to analyze sound fields in practical sized rooms with MPP absorbers. This paper presents the absorption performance of MPP absorbers installed in a small rectangular room of 91 m3 using 3D-FEM in frequency domain. Both the steady-state and the unsteady-state sound fields are calculated up to 1 kHz under the various absorber locations. The unsteady-state sound fields are calculated using inverse Fourier transform of transfer functions of rooms. The results are compared to explore the optimum sound absorber locations.

A design method of fairing acoustic noise mitigation for Korean space launcher

In this presentation, fairing acoustic protection system (APS) for Korean space launcher is introduced. The design of APS for payload fairing of KSLV-II is summarized. The current APS consists of acoustic blankets for midfrequency range absorption and acoustic resonators for low frequency noise absorption. Detailed design procedures of APS, which include external acoustic loading prediction based on the modified NASA SP-8072 monograph and fairing system vibro-acoustic analysis, are presented. An acoustic test of a cylindrical composite structure with APS is also presented. The effect of spatial correlation of external acoustic excitation on the vibro-acoustic response of fairing structure and its interior volume is discussed. The concept of future APS by using the micro-perforated panel absorber combined with Helmholtz resonators is also introduced. Effects of high pressure environment on the acoustic absorption of micro-perforated panel is discussed.

Modeling and formulation of microperforated panels in the finite-difference time-domain method

A microperforated panel (MPP) was first developed by Maa and is recently regarded as one of the most promising absorption materials for next generation. Considering the approximation formula suggested by Maa, impedance of the perforations cannot be directly implemented in time-domain calculations because the impedance depends on frequency. Some new ideas are therefore necessary to take into account the effects of an MPP in time-domain analyses. Herein, a method to consider effects of an MPP in the finite-difference time-domain (FDTD) analyses is proposed. An MPP is considered as a boundary condition and the frequency dependence in the calculation is removed by replacing the frequency-dependent terms with constant values which are derived based on the multiple regression analysis. Additionally, the stability condition of the MPP boundary for one-dimensional sound field is developed. Absorption characteristics of MPP absorbers with back air layers of various depths are calculated numerically and compared with analytical ones. Consequently, stable calculations are achieved by satisfying both the CFL condition and the stability condition of the MPP boundary and the high prediction accuracy and wide applicability are confirmed.

Improving low-frequency sound absorption of micro-perforated panel absorbers by using mechanical impedance plate combined with Helmholtz resonators

The traditional Micro-perforated plate (MPP) is a kind of clean and non-polluting absorption structure in the middle and high frequency and has been widely used in the field of noise control. However, the sound absorption performance is dissatisfied at low frequencies when the air-cavity depth is restricted. In this paper, a mechanical impedance plate (MIP) is introduced into the traditional MPP structure and a Helmholtz resonator is attached to the MIP. Mechanical impedance plate (MIP) provides a good absorption at low frequency by using mechanism of mechanical resonance and the acoustic energy is dissipated in the form of heat with viscoelastic material. Helmholtz resonator can fill in the defect of the poor absorption effect between the Micro-perforated plate (MPP) and the mechanical impedance plate (MIP). The acoustic impedance of the proposed sound absorber is investigated by using acoustic electric analogy method and impedance transfer method. The influence of the tube’s length of Helmholtz resonator and the number of Helmholtz resonator on the sound absorption is studied. The corresponding results are in agreement with the theoretical calculation and prove that the composite structure has the characteristics of improving the low frequency sound absorption property.

Acoustic properties of micro-perforated panel absorber having arbitrary cross-sectional perforations

Abstract Micro-perforated panel absorber is used in many noise control applications as a next-generation absorbing material. Perforation shapes of micro-perforated panel studied are usually circular in the past. However, in practice, the perforations are often non-circular or irregular shape due to manufacturing techniques. Sound absorption coefficient and absorption bandwidth of the micro-perforated panel absorber may be further improved, when the perforations in shape are changed. In view of the existing exact solutions of sound propagation in tubes, the simple formulas of specific acoustic impedances of the tubes for triangle and square cross-sectional perforations are derived. Mass reactance end correction of the micro-perforated panel is obtained based on the sound radiation of a shaped piston. The specific acoustic impedance ratio of the micro-perforated panel absorber is calculated and analyzed, which can predict its sound absorption bandwidth. Finally, for closed perforations, the influences of the perforations in shape (including triangle, circle, square and irregular circle) on sound absorption of the MPP absorber are discussed in collaboration with FE simulations.

3D プリンタを用いた微小多孔板の吸音性能に関する研究

Micro-perforated panel (MPP) absorber achieves good sound absorbing performance by reducing the scale of perforation to submillimeter. We have introduced a resin 3D printer in order to manufacture the absorber with small scale perforation. Since resin MPP absorber has less rigidity than metal one it has extra absorption peaks due to the panel elastic vibration. By referring to the past worthwhile researches, we introduce a theoretical acoustic impedance model that accounts vibration of circular plate then we evaluate this model by comparing the experimental results. We also evaluate the sound absorbing performance by changing the geometries of perforation.

Numerical analyses of the sound absorption of cylindrical microperforated panel space absorbers with cores.

Microperforated panels (MPPs) are next-generation absorption materials because they can provide wideband sound absorption without fibrous materials and can be composed of diverse materials to meet global environmental demands. The fundamental absorbing mechanism is Helmholtz-resonance absorption due to perforations and an air cavity. MPPs are typically backed by rigid flat walls, but to reduce the restrictions on the MPP absorber properties, one of the authors has proposed MPP space sound absorbers without backing structures, including three-dimensional cylindrical microperforated panel space absorbers (CMSAs). Advantages of MPPs without backing structures are design flexibility and ease of use. Besides, the absorption characteristics of a CMSA with a core, which has a rigid cylindrical core inside the CMSA, have been experimentally tested, but a method to predict the absorption characteristics is necessary to design CMSAs with cores. Herein the two-dimensional combined Helmholtz integral formulation method is employed, and its prediction accuracy is evaluated by comparing the measured and predicted absorption characteristics of a CMSA with a core. Furthermore, a parametric study with regard to the core size is carried out to investigate the transition of the absorbing mechanism.

A Compound Micro-perforated Panel Sound Absorber with Partitioned Cavities of Different Depths

The micro-perforated panel (MPP) sound absorber is becoming a good replacement of conventional porous absorbers in building noise control. The MPP absorber is fiber-free and avoids potential harms such as powdered fibers and damage to the person's health. This paper presents a new compound MPP sound absorber architecture with excellent sound absorption performance both on higher sound absorption coefficient and broader absorption band compared with single MPP absorber. The absorber consists of an array of parallel-arranged MPP sub-absorbers with different depths, where different local resonances are apparent and dominate. In this paper, firstly, an analytical method is proposed to look into the mechanism of the absorber architecture design and this method is validated through simulations based on a finite element procedure. Secondly, the acoustic properties from different MPP absorber dimension sets are investigated through simulations with the proposed theoretical method. Results show that the presented MPP absorber can have normal incidence sound absorption coefficients higher than 0.5 over the frequencies from 370Hz to 2520Hz, with maximum value of 0.9. This indicates that the proposed MPP absorber provides a good alternative for indoor sound absorption applications in commercial and industrial buildings.

Sound Absorption Analysis of Micro Perforated Panel with Ladder Change Type Cross Section

A kind of variable cross section micro perforated panel (MPP) with ladder micro porous is introduced in this paper. Based on the double layers MPP theory and neglected the effect of cavity between two layers of MPP, sound absorption model of MPP with ladder micro porous is established. Numerical simulations are carried out to predict the sound absorption of MPP with ladder micro porous. The predicted results show good agreement with measurements. Through analyzing the weight to the sound-absorbing of orifice size, this study also points out that the smaller orifices play the major role in the sound absorption.

A finite-element formulation for room acoustics simulation with microperforated panel sound absorbing structures: Verification with electro-acoustical equivalent circuit theory and wave theory

A simple frequency-domain finite-element method (FD–FEM) for sound field analyses inside rooms installed with microperforated panel (MPP) sound absorbing structures is described here. This method can also analyze sound absorbing structures composed of MPPs and permeable membranes (PM) simply by changing the only material parameters of MPP into those of PM. As the first stage of the study, the validity of the present FD–FEM is tested through the numerical experiments based on the impedance tube method for measuring the absorption characteristics at normal incidence. In the numerical experiments, we calculated the absorption characteristics of a single MPP absorber, a double-leaf MPP space absorber and a space absorber composed of MPP and PM by using the FD–FEM in two-dimensions, and the computed absorption characteristics are compared with those calculated by an electro-acoustical equivalent circuit theory or a wave theory based on Helmholtz–Kirchhoff boundary integral equation. The results showed that the presented FD–FEM can analyze the absorption characteristics at normal incidence of the MPP sound absorbing structures accurately with the simplicity of the formulation.

Room acoustics simulation with single-leaf microperforated panel absorber using two-dimensional finite-element method

Room acoustics simulation with single-leaf microperforated panel absorber using two-dimensional finite-element method

A note on the fabrication methods of flexible ultra micro-perforated panels

Micro-perforated panel (MPP) absorber has been studied and developed for decades and is becoming more and more popular in an environment protective society. Although the traditional MPPs are rigid, the research results in recent years have indicated that flexible MPPs with ultra-micro perforations of diameter less than 100μm (ultra-MPPs) may have great potential to become a wideband sound absorber in high frequency range. However, it is a great challenge for both traditional mechanical methods and micro-fabrication technology to fabricate so small holes directly on flexible materials, which greatly limits the development of flexible ultra-MPPs. Therefore a new technical solution is strongly desired. To meet this demand, a new process, based on mold manufacturing technology and casting technology, is developed, and the key and specific process steps are presented in this paper.

Bayesian sampling for practical design of multilayer microperforated panel absorbers

Bayesian sampling is applied to produce practical designs for microperforated panel acoustic absorbers. Microperforated panels have the capability to produce acoustic absorbers with very high absorption coefficients, without the use of porous materials. However, the absorption produced by a single panel is limited to a narrow frequency range, particularly at high absorption coefficient values. To provide broadband absorption, multiple microperforated panel layers may be combined into a multilayer absorber. To design such an absorber, the necessary number of layers must be determined and four design parameters must be specified for each layer. Using Bayesian model selection and parameter estimation, this work presents a practical method for designing multilayer microperforated panel absorbers. Particular attention is paid to aspects of the underlying sampling method that enable automatic handling of design constraints such as limitations of the manufacturing process and availability of raw materials.

Oblique incidence sound absorption of parallel arrangement of multiple micro-perforated panel absorbers in a periodic pattern

The sound absorption performance of a micro-perforated panel (MPP) absorber array at oblique incidence and in diffuse field is investigated both numerically and experimentally. The basic module of the MPP absorber array consists of four parallel-arranged MPP absorbers with different cavity depths, and the whole MPP absorber array is created by arranging the basic modules in a periodically repeating pattern. Results show that the influence of incidence angle mainly lies in two aspects. First, the parallel absorption mechanism breaks down at lower frequencies at oblique incidence than at normal incidence due to the non-compactness of the resonating MPP absorber, which becomes non-compact if the time delay of incident wave across it is comparable to or larger than π/2. Second, the equivalent acoustic impedance of the MPP varies with respect to incidence angle which in turn changes the sound absorption performance of the MPP absorber array. Influence of the azimuthal angle is insignificant. Because of mutual influence among the member MPP absorbers, the normal incidence sound absorption of the MPP absorber array can be noticeably different from that of the basic module tested in impedance tube. The measured sound absorption coefficients of a prototype specimen in reverberation room compare well with the numerical predictions. The extra sound absorption due to diffraction of sound at the free edges of test specimen is the most efficient around 500Hz.

Enhancing low frequency sound absorption of micro-perforated panel absorbers by using mechanical impedance plates

Micro-perforated panel (MPP) absorbers have been widely used for noise control because of their environmental friendliness and attractive appearance. The fundamental absorbing mechanism of a conventional MPP absorber is cavity resonance absorption. Micro-perforated panel absorbers backed with mechanical impedance plates (MIP) are proposed to enhance the performance of low-frequency sound absorption, where conventional MPP absorbers cannot provide sufficient absorption in the case that the backed cavity is limited. Low-frequency sound waves penetrate the micro-perforated panel and are incident on the impedance plates, which will be effectively stimulated to vibrate when the frequency of the incident sound wave is close to resonance frequency of the plate. Due to the viscous material at the boundary, the mechanical impedance provides viscous damping, thereby enabling improved sound attenuation. The acoustic impedance of the proposed sound absorber is investigated using the transfer matrix method. The results of theoretical calculation are in good agreement with the experimental results. The composite structure combines the sound absorption mechanisms of cavity resonance and mechanical resonance. Low-frequency absorption is effectively enhanced without the need to increase the total thickness of the structure.

Sound absorption of a flexible micro-perforated panel absorber based on PVDF piezoelectric film

Micro-perforated panel (MPP) has been widely used in the noise control field. However, the performance at low frequencies is relatively poor due to the restricted space limitations in actual applications. Hence in this paper a flexible micro-perforated panel absorber (PVDF-MPPA) based on Polyvinylidene fluoride (PVDF) piezoelectric film is proposed, which is composed of a perforated aluminum-electrode PVDF piezoelectric film and a small air cavity. Its sound absorption at low frequency can be improved by employing panel vibration effect and shunting the electrodes of piezoelectric film with some electrical impedance. The corresponding structure of the PVDF-MPPA was designed and fabricated. Experiments were performed under different shunting cases such as open circuit, short circuit, and resonant circuit in an impedance tube with the testing frequency range from 100Hz to 1600Hz. The results demonstrated that the PVDF-MPPA with shunt circuits had a wider absorption bandwidth compared with a rigid MPP absorber with the same structural parameters. When compared with the open circuit and short circuit cases, the PVDF-MPPA with resonant circuit definitely has a better low frequency absorption performance if the shunting parameters have been carefully tuned. By using shunt-damping technology, the PVDF-MPPA has a potential to be widely used as an efficient sound absorber in practical situations because of its simple structure and good absorption performance at low frequencies.

Numerical study of the acoustic properties of micro-perforated panels with tapered hole

Micro-perforated panel (MPP) absorbers, well known as a basis for the next generation of sound absorbing materials, are now being widely used in noise control engineering. In order to design the structural parameters of MPP absorbers according to the actual demand, a straightforward method to predict the absorption performance of such absorbers is needed. However, traditional predicting methods, such as equivalent electric-acoustic circuit method, the transfer matrix method, modal analysis method and so on, are based on analytical solution. The use of these methods not only requires development and application of special techniques, but also is not suitable for MPPs with irregular-shaped holes, such as tapered holes which can be used to improve the sound absorption performance of a thick MPP absorber. In order to overcome the problem, a numerical procedure based on finite element method (FEM) is developed to obtain the specific acoustic impedance of an MPP. Using this method, the acoustic performance of MPPs with tapered holes as well as the effect of various parameters on their normal incidence absorption performance is numerically investigated and the findings are useful to guide the structural design.

Analysis of Sound Absorption Properties of Three-Leaf Microperforated Panel Absorbers without a Rigid Backing

Microperforated panel (MPP) absorbers have been developed rapidly and used in many fields in recent years. First, based on the Maa’s theory, the theoretical development of MPP is reviewed in this paper. Furthermore, structure design and processing technology of MPP are introduced. Finally, the further development of MPP is discussed. Based on the MPP theory and electro-acoustical equivalent circuit principle, sound absorption properties of three-leaf microperforated panel (TMPP) absorbers without a rigid backing are studied to broaden the sound absorption bandwidth of MPP structure. Simulation results show that TMPP absorbers without a rigid backing have two resonance peaks and the energy dissipated coefficient remains constant in the low frequency range. The resonance frequency moves toward low frequency region with the increasing of the distance, thickness and pore diameter of MPP and moves toward high frequency region with the increasing of the perforation when other parameters keep invariant. The energy dissipated coefficient more than 0.5 over 8 octaves by choosing proper parameters. In conclusion, TMPP absorbers without a rigid backing have good sound absorption properties in a wide frequency range.