Micro-perforated Panel Research Articles

Transmission Loss Analysis of Simple Expansion Tube with Micro – perforated Cylindrical Panel

This study presents a development of simple expansion tube attach with micro-perforated cylindrical panel (MPCP) to improve the acoustic performance. A simulation based boundary element method (BEM) was carried out using PLM Simcenter 3D. The model was constructed in three dimensional in CAD NX Nastran 12 application and then meshing into small elements. The acoustic properties and boundary condition were defined for the simulation purpose. The model was then fabricated by 3D printer material and verified with the transmission loss measurement utilized the two-load method. In comparison, the transmission loss of simple expansion tube with and without MPCP show a good agreement of BEM analysis and experimental result. The addition of the MPCP inside the expansion tube improved the transmission loss by 2-10 dB in wider frequency band compared to the simple expansion tube. Finally, the air cavity depth of the expansion tube is varied to study it effect. Its showed that, the larger air cavity depth caused the transmission loss peak shift to a lower frequency range.

A Parametric Study of the Acoustic Performance of Resonant Absorbers Made of Micro-perforated Membranes and Perforated Panels

Sound absorbing surfaces are being increasingly requested for the acoustical treatment of spaces, like offices and restaurants, where high aesthetic standards are requested. In these cases, perforated and micro-perforated panels may represent the ideal solution in terms of low maintenance, durability, and mechanical resistance. In addition, such a solution might be conveniently realized while using optically transparent panels, which might offer extra value, as they could ensure visual contact, while remaining neutral in terms of design. The paper first investigates the reliability of prediction models by comparison with measured data. Subsequently, while taking advantage of a parametric optimization algorithm, it is shown how to design an absorber covering three octave bands, from 500 Hz to 2 kHz, with an average sound absorption coefficient of about 0.8.

Investigation of the acoustic properties of corrugated micro-perforated panel backed by a rigid wall

Extensive studies have been carried out on the acoustic performance of a micro-perforated panel (MPP) absorber which typically consists of a flat MPP fitted in front of a rigid backing wall. The present study concerns its acoustic properties when the conventionally flat perforated panel is replaced with a corrugated one that finds many applications in architecture. A three-dimensional finite element model is used to simulate the acoustic performance of a such corrugated MPP absorber at normal incidence, oblique incidence and diffuse field. Results show that the absorption performance of corrugated MPPA can be very different from conventional flat MPPA when the acoustic wave length is smaller than the corrugation depth. At low frequencies, the corrugated MPP performs similarly as a flat one of the same bulk perforation ratio. The absorption levels of the corrugated MPPA are considerably enhanced at the dips of absorption curves, which is favorable for reverberation control or broadband random noise reduction in large spaces and buildings. Further modal analysis shows that multiple modes of the corrugated configuration are excited at the peak and dip frequencies, and the acoustic response by the non-resonating modes give rise to the performance improvement. Absorption coefficients are also measured experimentally using an impedance tube. The measured normal incidence absorption coefficients compare well with the numerical predictions, which validates the numerical model and, in part, the numerical findings.

3D Printing of Polymeric Multi-Layer Micro-Perforated Panels for Tunable Wideband Sound Absorption.

The increasing concern about noise pollution has accelerated the development of acoustic absorption and damping devices. However, conventional subtractive manufacturing can only fabricate absorption devices with simple geometric shapes that are unable to achieve high absorption coefficients in wide frequency ranges. In this paper, novel multi-layer micro-perforated panels (MPPs) with tunable wideband absorption are designed and fabricated by 3D printing or additive manufacturing. Selective laser sintering (SLS), which is an advanced powder-based 3D printing technique, is newly introduced for MPP manufacturing with polyamide 12 as the feedstock. The acoustic performances of the MPPs are investigated by theoretical, numerical, and experimental methods. The results reveal that the absorption frequency bandwidths of the structures are wider than those of conventional single-layer MPPs, while the absorption coefficients remain comparable or even higher. The frequency ranges can be tuned by varying the air gap distances and the inter-layer distances. Furthermore, an optimization method is introduced for structural designs of MPPs with the most effective sound absorption performances in the target frequency ranges. This study reveals the potential of 3D printing to fabricate acoustic devices with effective tunable sound absorption behaviors and provides an optimization method for future structural design of the wideband sound absorption devices.

Coefficients of End Correction Depending on Geometric Properties of Micro-perforated Panel

The purpose of this paper is to calculate an accurate sound absorption coefficient for a micro-perforated panel absorber (MPPA). When the sound absorption coefficient is calculated, there is a difference between the measurement and the calculation. In the calculation, a resistive end correction coefficient (β) of 2 or 4 and a reactive end correction coefficient (δ) of 0.85 are generally applied. However, using an impedance tube test, we confirm that end correction coefficients change depending on the specification of the micro-perforated panel. The resistive end correction coefficient is in the range of 2–4 and increases when the hole diameter and the porosity decrease and the panel thickness increases. The reactive end correction coefficient is less than 0.85 and increases when the hole diameter and the panel thickness increase and the porosity decreases. Based on our experimental results, we derive new coefficient formulas expressed by the hole diameter (d), the hole spacing (b), the porosity (p) and the panel thickness (t). To verify the proposed formulas, the sound absorption coefficient calculation is compared with the measurement, which confirms that the absorption coefficient is affected by the ratio between the air mass inside the hole and the added air mass outside the hole. The relation between the two masses can be confirmed by the ratio of the panel thickness (t) to the hole diameter (d). In a single-layer MPPA, when t/d is greater than or equal to about 2, the absorption peak level of calculations, no matter what β is applied, is similar to the measurement. On the other hand, when t/d is less than about 2, the calculation is greatly affected by β. The sound absorption coefficients for both single- and double-layer MPPAs are compared according to the proposed formulas and coefficients of other researchers. The calculation of the proposed formulas among calculations is in good agreement with the measurement.

Absorption Coefficient of a Double-Layer Inhomogeneous Micro-perforated Panel Backed with Multiple Cavity Depths

Double-layer micro-perforated panels (MPPs) have been studied extensively as sound absorption systems to increase the absorption performance of single-layer MPPs. However, existing proposed models indicate that there is still room for improvement regarding the frequency bands of absorption for the double-layer MPP. This study presents a double-layer MPP formed with two single MPPs with inhomogeneous perforation backed by multiple cavities of varying depths. The theoretical formulation is developed using the electrical equivalent circuit method to calculate the absorption coefficient under a normal incident sound. The simulation results show that the proposed model can produce absorption coefficient with wider absorption bandwidth compared with the conventional double- and even triple-layer MPPs. The bandwidth can be increased to higher frequency by decreasing the cavity depth behind a sub-MPP with small hole diameter and a high perforation ratio, and to lower frequency by increasing the cavity depth behind a sub-MPP with large hole diameter and a small perforation ratio. The experimental data, measured by impedance tube, are in good agreement with the predicted results.

Exploration and optimization on the usage of micro-perforated panels as trim panels in commercial aircrafts

Micro-perforated panels (MPPs), as an alternative to porous materials for sound absorption, have been commonly used in electronic industries and aircraft engines but are barely used in aircraft cabins. The effect of MPPs on the sound insulation and absorption properties of aircraft cabin panels has been investigated in this article. Theoretical modeling has been conducted on an aircraft cabin panel structure with a trim panel replaced by an MPP trim panel, using the transfer matrix method and the classic MPP theory. It is indicated by the theoretical results that, although the sound transmission loss (STL) of the cabin panel with an MPP trim panel is lower than that with an un-perforated panel, the MPP trim panel can significantly enhance the sound absorption coefficient of the entire cabin panel structure. Based on the well-developed MPP theory, the sound absorption coefficient of an aircraft cabin panel with an MPP trim panel can be improved by optimizing the MPP's parameters at a specific frequency. Taking an engine frequency 273 Hz as an example, the optimization can increase the sound absorption coefficient to 1 by using the doublelayered MPPs. When the thermal acoustic insulation blanket is considered, although the STL of the proposed structure with double-layered MPP trim panels in a diffuse field is lower than those without MPP trim panels, the sound absorption in the cabin is significantly enhanced due to the double-layer MPP trim panel at the specific engine frequency and across all frequencies. The STL of the structure with double-layered MPP trim panels and TAIB can be higher than 40 dB from 880 Hz in a diffuse field, which implies its effectiveness as sound insulation structure in aviation industry. MPP trim panels provide a new idea for the design of aircraft cabin panels and areworthy of further research

Low-frequency broadband absorbers based on coupling micro-perforated panel and space-curling chamber

<p indent=0mm>Conventional acoustic absorbers, which are made of porous and fibrous materials, usually have a structural thickness comparable to the working wavelength, which inevitably hinders their applications in low frequency range. A micro-perforated panel with a backward cavity has high efficient absorption in low frequency region, yet still processes a bulky size comparable to the resonant wavelength. In the past two decades, metamaterials and metasurfaces, which possess the functionalities cannot be achieved by the natural materials, such as deep-subwavelength thickness, negative mass density or bulk modulus, negative refraction, etc., have got continuous attention and hence rapidly developed. Using the compact structures, such as membrane-type acoustic metamaterials, curling-up space structures, Helmholtz resonators with embedded apertures, to realize perfect absorption in low frequency has broadened the horizon of the acoustic absorption and provided a novel way for noise control. However, because of the dispersive nature of resonance, the aforementioned perfect absorbers cannot achieve broadband high absorption, which unavoidably confines their application. It is known that a micro-perforated panel features a broadband characteristic, while curling-up space structures have the capacity in absorbing the low frequency waves. Therefore, we come up with the idea of utilizing the micro-perforated panel and curling-up chamber to realize the high absorption in low and broad frequency region. In this work, we propose a hybrid absorber. By introducing the concept of curling chambers and coupling them to micro-perforated panels, the proposed acoustic absorber possesses remarkable properties such as deep-subwavelength thickness, broad absorption band and high absorption efficiency. Theoretical analyses, numerical simulations and experiments are carried out to reveal the underlying physical mechanism of the acoustic absorbers, whose results showed excellent agreements with each other. First, we theoretically analyze the absorption performance of each component consisting of a micro-perforated panel and a curling chamber. Then, we conduct the numerical validation and operate the experiment to verify the theoretical model. Through numerical optimizations, we finally design the two components achieving perfect absorption at lower <sc>(282 Hz)</sc> and higher <sc>(429 Hz)</sc> frequencies, respectively. Using the coupled mode theory, we present an absorber coupling the low- and high-frequency components. The hybrid absorber possesses the ability that the absorption coefficient is larger than 0.5 in the frequency range from 232 to <sc>533 Hz,</sc> and larger than 0.8 from 262 to <sc>469 Hz,</sc> while its structural thickness is only 10 cm (<italic>λ</italic>/12,<italic> λ</italic> is the working wavelength corresponding to the lower resonant frequency). To understand the underlying physical mechanism, we use the commercial software COMSOL MULTIPHYSICS to show the interaction (i.e., coupling) between the two components. As shown by the simulated results, at the resonant frequency of each component <sc>(282</sc> or 429 Hz), when planar wave impinges normally on the whole absorber surface, only the corresponding component has sound energy exchange with the outside. However, at the frequency between the two resonant frequencies, both of them switch sound energy with the outside, which demonstrates the coupling effect. In this way, the hybrid absorber can realize the broadband high absorption in low frequency range. Compared to traditional bulky structures, the proposed absorber possesses the ability such as easy to fabrication, deep subwavelength and broadband high absorption, and hence may be widely used in noise control engineering.

High Temperature Effect on Absorption Coefficient of M-MPPs and Sandwich Structures Coupled with MPPs

This paper addresses the effect of high temperature on absorption performance of sandwich material coupled with microperforated panels (MPPs) in multiple configurations using a finite element model (FEM) over a frequency range from 10 to 3000 Hz. The structure is backed with a rigid wall which can either be Aluminium or Al-Alloy used in aeronautic or automobile. The wave propagation in porous media is addressed using Johnson Champoux Allard model (JCA). The FEM model developed using COMSOL Multiphysics software makes it possible to predict the acoustic absorption coefficient in multilayer microperforated panels (M-MPPs) and sandwich structure. It is shown that, when structures made by MPPs or sandwich materials are submitted to high temperature, the absorption performance of the structure is strongly modified in terms of amplitude and width of the bandgap. For application in sever environment (noise reduction in engines aircrafts), Temperature is one of the parameters that will most influence the absorption performance of the structure. However, for application in the temperature domain smaller than 50?C (automotive applications for example), the effect of temperature is not significant on absorption performance of the structure.

Some considerations on the use of space sound absorbers with next-generation materials reflecting COVID situations in Japan: additional sound absorption for post-pandemic challenges in indoor acoustic environments

In this study, we first point out the possible acoustic problems associated with the post-pandemic operation of built environments. In particular, we focus on the problem of acoustic deficiency due to the lack of absorption. This deficiency, which is likely to be encountered in most enclosed spaces in a range of establishments, is due to the reduced number of audience members or users of the space as a result of social distancing. As one of the promising solutions to this problem, we introduce a sound absorption technique using three-dimensional (3D) space sound absorbers developed through our recent research projects. Significantly, the type of sound absorber proposed herein is made of materials that are especially suited to hygiene considerations. The materials are microperforated panels (MPPs) and permeable membranes (PMs), both of which are easily washable and sanitised. Furthermore, we point out that 3D-MPP or PM space absorbers possess the additional value of aesthetic designability.

Study on sound insulation performance of the periodic arrangement expansion chambers structure with built-in micro-perforated panel

The periodic arrangement expansion chambers structure with built-in micro-perforated panel (MPP) is proposed. The transmission loss (TL) of expansion chambers before and after the introduction of MPP is analyzed by transfer matrix method and finite element method. In the low frequency range, the TL curves obtained by the transfer matrix method and finite element method are consistent. Both show that the first pass frequency of the structure disappears and the sound insulation bandwidth of the structure widens obviously after the introduction of MPP. The influences of the parameters of the periodic expansion chambers structure on the TL are numerically analyzed. By making hole on the inserted MPP, ventilation cooling function is realized. The result shows that the overall sound insulation effect is still satisfying after making appropriate hole. Additionally, expansion chambers and double MPP with hole insertion structure has been constructed. The result shows that the second pass frequency of expansion chambers structure also disappears. Therefore, the sound insulation performance of the expansion chambers structure is further improved by adding double-layer MPP. The sound insulation performance of the periodic expansion chambers structure with ventilation capability is tested by laboratory experiments. Excellent sound insulation ability is confirmed.

Wideband sound absorption of a double-layer microperforated panel with inhomogeneous perforation

Micro-perforated panel (MPP) absorber is increasingly gaining popularity as an alternative sound absorber in buildings compared to the well-known synthetic porous materials. A single MPP has a typical feature of a Helmholtz resonator with a high amplitude of absorption but a narrow absorption frequency bandwidth. To improve the bandwidth, a single MPP can be cascaded with another single MPP to form a double-layer MPP. This paper proposes the introduction of inhomogeneous perforation in the double-layer MPP system (DL-iMPP) to enhance the absorption bandwidth of a double-layer MPP. Mathematical models are proposed using the equivalent electrical circuit model and are validated with experiments with good agreement. It is revealed that the DL-iMPP produces a wider half-absorption bandwidth compared to the conventional homogeneous double-layer MPP. The absorption bandwidth to higher frequencies can be effectively controlled by reducing the air cavity between the iMPPs and to the lower frequencies by increasing the back cavity depth at the second layer.

A sandwich anechoic coating embedded with a micro-perforated panel in high-viscosity condition for underwater sound absorption

The interest of this article lies in the underwater application of micro-perforated panel (MPP). In this paper, a new type of sound absorption structure based on MPP and viscoelastic substrate for underwater usage is proposed. The MPP in the condition of high-viscosity castor oil generates absorption peak in low-frequency bandwidth, and the rubber substrate of appropriate thickness achieves good absorption performance in medium–high frequency. The sound absorption formula for the new structure is derived from the transfer matrix method based on wave propagation equation, the equation for elastomer vibration, Maa’s equation for MPP and continuity conditions for sound waves. The proposed model is tested in a hydroacoustic impedance tube filled with water, which shows good agreement with theoretical results. The absorption coefficient (α) is clearly improved within the frequency above 1 kHz ~ 15 kHz due to MPP. It can be seen that such structures can enhance the absorption dominantly in the low-frequency range, broaden the absorption bandwidth, and have the potential to be utilized as an underwater anechoic coating.

Flexible micro-perforated panels prepared by CNC machining

With the advantages of light weight, thin thickness and environment friendly, the micro-perforated panel (MPP) has been widely studied for noise reduction. Maa’s model pointed out that the MPP could obtain higher sound absorption over broader frequency band when the perforations were reduced to less than 100 μm. However, it is challenging to manufacture MPPs with the aperture of approximate 100 μm, thus its potential application has been restricted. In this study, we used a computer numerical control (CNC) milling machine to process MPP. Four different kinds of raw materials including paperboard, polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polycarbonate (PC) were taken to prepare micro-perforated panels (MPPs). It has been indicated that MPPs with good sound absorption properties were successfully prepared by this facile method.

A Sandwich Coating Containing Micro-perforated Panel for Underwater Sound Absorption

This paper focuses on the underwater application of Micro-perforated panel (MPP) for broadband sound absorption. In this paper, MPP-rubber coating (MPPRC), a novel sandwich anechoic coating embedded with MPP in high-viscosity condition, is proposed. The acoustic impedance for MPP is derived from Maa’s equation and vibration modal modification, while the acoustic propagation property of the viscoelastic rubber layer is obtained by the wave propagation equation. The theoretical calculation for the absorbency of the composite structure is conduced based on electro-acoustic analogy method and transfer matrix approach. The sound absorption validation is carried on in a hydroacoustic impedance tube filled with water, and the experimental results match with the theoretical model. Compared with the equal-thickness rubber, the MPPRC performances better at a lower frequency of 1.6 kHz ∼15 kHz due to MPP, which shows the potential to be utilized as an underwater anechoic coating.

Natural Ventilation Performance Simulation and Analysis of New Type Sound Insulation Window

To evaluate the ventilation performance of new type sound insulation window, a window model with streamline-structure micro-perforated panel absorber (MPA) was simulated based on computational fluid dynamics (CFD). Finite element model of the insulation window was built to analyze the flow field in muffler channel, velocity in vent and pressure loss of the channel. To contrast with the simulation model, an insulation window artifact was produced and tested in ventilation quantity detection. The results show that the dominant pressure loss is local hydraulic loss that comes from MPA structure. The total pressure loss increased by 4.3 Pa under 0.5 m/s inlet wind velocity. The difference of pressure loss between simulation and actual test is 6.3%. CFD simulation is an effective and low-cost method to evaluate the ventilation performance with visual results. The results provide valuable reference for optimal design of insulation window.

Experimental study on sound absorbing property of spatial absorber of non-woven fabric with micro-perforated plate-like structure

Microperforated panel (MPP) absorbers have been widely used in noise reduction and are regarded as a promising alternative to the traditional porous materials. However, the flat panel-like shape restricts their practical use in actual rooms or buildings. To overcome these limitations, three-dimensional MPP spatial sound absorbers have been proposed. MPP are mostly metal materials with high cost. It is relatively easy to make cylinders or cubes, and difficult to make other complex structures. In view of this, a kind of non-woven material which can replace micro-perforated board is proposed in this paper. This kind of non-woven material has the characteristics of low cost, flexibility, convenient moulding and good sound absorption performance. The impedance tube experiments has been employed to study the normal incidence sound absorption coefficient for the non-woven fabric materials. The experimental results show that the sound absorption properties of non-woven fabrics are similar to those of ultra-micro MPP. Three kinds of spatial sound absorbers have been made by non-woven materials. They are the hollow cylindrical, fan-shaped, and honeycomb-like spatial sound absorbers, respectively. The measurement of reverberation chamber results show that the sound absorption capacity of the honeycomb-like spatial sound absorber is better than the hollow cylindrical and fan-shaped spatial sound absorbers. Adding non-woven cylindrical boundary layer can further improve the sound absorption performance of the fan-shaped and honeycomb-like space absorber.

Sound absorption of face-centered cubic sandwich structure with micro-perforations

This paper presents a novel ultra-lightweight micro-perforated sandwich structure with face-centered cubic (FCC) core as a sound absorber, which encompasses excellent mechanical features as well as acoustic properties. The structure, which consists of air cavities and small perforations on both the top panel and the corrugated plates, is considered as a combination of multi-layered micro-perforated panel absorbers (MPPAs). A theoretical model that makes use of an equivalent electrical circuit (EEC) approach is established. Validation of the model with experimental results and numerical simulations shows good agreement. The dependence of the acoustic absorption on features of the perforations and of the FCC structure is discussed. Based on the observations, an optimized structure is proposed by using simulated annealing method to yield good acoustic absorption property in the low frequency range.

Acoustic performance of countersunk micro-perforated panel in multilayer porous material

This study investigates the acoustic performance of a countersunk micro-perforated panel, along with two distinct porous materials used in a multilayer porous absorber configuration. Additive manufacturing is applied to create sub-millimeter perforation with different hole spacings on polymer micro-perforated panels. Experiments are conducted in an impedance tube, in which the effects of the perforation ratio, air gap, and varying porous layer configurations on the sound absorption capabilities are investigated. For validation, considering the converging hole profile in the micro-perforated panel, an integration method with end correction is used to calculate the tapered section impedance, and the traditional Maa theory is used for the uniform hole. The theoretical impedance of the multilayer absorber is calculated using the transfer matrix method and subsequently compared to the experimental results. The results demonstrate that the countersunk hole micro-perforated panel exhibits a significant improvement in sound absorption, and the introduction of porous materials extends the sound absorption bandwidth. Furthermore, the results indicate that the sound absorption capability depends on the porous material placement in the multilayer absorber configuration.

Parameter Optimization for Composite Structures of Microperforated Panel and Porous Metal for Optimal Sound Absorption Performance

The composite structure of a microperforated panel and porous metal is a promising sound absorber for industrial noise reduction, sound absorption performance of which can be improved through parameter optimization. A theoretical model is constructed for the composite structure of a microperforated panel and porous metal based on Maa’s theory and the Johnson–Champoux–Allard model. When the limited total thickness is 30 mm, 50 mm, and 100 mm respectively, dimensional optimization of structural parameters of the proposed composite structure is conducted for the optimal average sound absorption coefficient in the frequency range (2000 Hz, 6000 Hz) through a cuckoo search algorithm. Simulation models of the composite structures with optimal structural parameters are constructed based on the finite element method. Validations of the optimal composite structures are conducted based on the standing wave tube method. Comparative analysis of the theoretical data, simulation data, and experimental data validates feasibility and effectiveness of the parameter optimization. The optimal sandwich structure with an actual total thickness of 36.8 mm can obtain the average sound absorption coefficient of 97.65% in the frequency range (2000 Hz, 6000 Hz), which is favorable to promote practical application of the composite structures in the fields of sound absorption and noise reduction.