Micro-perforated Panel Research Articles

Elasticity and modal effects on the optimal performance of micro-perforated multi-layered absorbers

Multi-layered wall-treatments with thin lightweight micro-perforated panels offer a potential solution to achieve broadband noise absorption while complying with mass saving and compactness. This study examines how vibrational effects, often neglected, may impede the wideband acoustical performance of such partitions, made up of a distribution of either periodic or graded micro-perforated membranes or panels. The impedance translation method and a scattering matrix analysis have been implemented. It is found that the elasticity behavior of thin micro-perforated membranes has a beneficial effect on the acoustical efficiency of the partitions. The contributions of the individual acoustical resonances tend to merge if the elasticity effects are accounted for. If the partition is optimized, near-constant high absorption and low transmission values are obtained over a wide frequency range. A more robust design involves partitions made up of micro-perforated panels. It was observed that the first volumetric volumetric mode of the panels modifies the absorption properties of the partition. It cross-couples with the acoustical resonances and redistributes their spectral locations. This structural resonance sets an upper frequency bound, below which the partition achieves a high broadband performance. It should be accounted for when setting the frequency limits of the total dissipation to be optimized.

Improving acoustic absorption modeling of additively manufactured microperforated panels through kriging-based approaches

Microperforated panels (MPPs) have emerged as good acoustic absorbers, with the Maa model being commonly utilized for predicting their acoustic absorption and impedance. However, discrepancies arise when applying this model to MPPs fabricated through additive manufacturing. Additive manufacturing offers design flexibility, but it challenges traditional acoustic models by not achieving ideal geometric characteristics. For instance, non-circular perforations resulting from the additive manufacturing, deviate from the perfect circular shape assumed in the Maa model. This non-ideal geometry poses challenges in predicting MPP acoustic absorption, particularly at lower frequencies and in wideband scenarios. Microscopic examinations reveal microporosity within panel solids, adding complexities not usually accounted for by models assuming a solid structure around perforations. This study investigates the observed disparity between Maa model predictions and experimental results due to manufacturing defects, microporosity within the MPPs and panel vibration. We address these challenges by introducing Kriging, a spatial interpolation technique, to refine the absorption model. The Kriging model demonstrates remarkable agreement with experimental data, offering a more accurate representation of the acoustic performance of additively manufactured MPPs. The proposed methodology not only contributes to advancing the understanding of acoustic absorption in MPPs but is also promising for optimizing their performance in real-world applications.

A study on a micro perforated panel applied luggage board design for road noise reduction

The automotive industry is on the age of rapid transformation from internal combustion engine vehicles to electric vehicles powered by motors. The main source of noise in conventional internal combustion engine vehicles is the engine, while electric vehicles are mainly affected by road and wind noise. A road noise in the medium and low frequency bands, caused by friction between tires and road surfaces, can be improved by increasing the thickness and weight of the insulation material. Still, this countermeasure causes other challenges that related to driving efficiency decrease because of limitations space and weight. As a new method to reduce road noise, therefore, the study introduces the luggage board which applied the micro-perforated panel system. This system utilizes a resonance-type sound absorbing material with excellent sound absorption characteristics at specific frequencies so that a tire pattern noise within the 800-1,000 Hz could be reduced. Because the thickness of the luggage board is partially limited, the study set a number of variations such as changing the porosity, perforated diameter in the perforated panel system. As a result, the study confirmed 2% improvement A.I. (Articulation Index) in the interior with installation of the designed luggage board on the vehicle.

Investigation on enhancement of noise reduction of partially open windows and balconies through mock-up test

Application of Acoustic Windows and Acoustic Balconies is a recent trend in Hong Kong to mitigate road traffic noise impact. In severe situations, enhancement is needed for the mitigation measures to provide additional improvement in acoustic performance. The performances of several common enhancements including micro-perforated absorber panels, perforated absorption panels, and balcony sidewalls are investigated through 1:1 mock-up test. The mock-up test aimed to mimic the actual situation, by referencing the spatial relationship between line sources and receivers. International standards are followed in the mock-up test, including ISO 16283-3: 2016 for microphone setting-out and BS EN 1793-3 for normalized traffic noise spectrum. Based on the mock-up test results, the research revealed that the enhancements' performance changes with line source orientation and suggested the optimum usage of enhancements.

High sound pressure level sound absorption in acoustic resonant metamaterials: adapting a mass-spring model for nonlinear effects

In aerospace, conventional materials as micro-perforated panels backed by cavities are used to absorb sound at high sound pressure levels. These solutions are not optimal at low frequencies compared to resonant acoustic metamaterials, which present an acoustic absorption peak with a wavelength-to-thickness ratio greater than conventional materials, i.e., a ratio>>5. Acoustic resonant metamaterials are mainly studied at low sound pressure levels (<100dB). However, they are sensitive to increasing the amplitude of acoustic excitation. The studied metamaterial is composed of a compact array of thin single-perforation panels spaced by thin cylindrical air cavities. In a previous study, a mass-spring model was developed for low sound pressure levels. The perforations are modeled by equivalent masses, whereas cavities by equivalent springs. In the perforations, high values of the acoustic velocity lead to an increase in the acoustic resistance of the material. This effect is considered by the Forchheimer parameter in the mass-spring model. To determine this parameter and to study how it is impacted by the metamaterial geometry, the computational fluid dynamic method is used. The mass-spring model is adapted with a nonlinear term. The adapted model agrees well with simulations by finite element method at sound pressure levels up to 140dB.

Random incidence absorption characteristics and parameterized design of micro-perforated panel absorbers with parallel-arranged backing cavities at different depths

Micro-perforated panel absorbers (MPAs) are recognized as efficient and environmentally friendly materials for sound absorption, prompting significant research efforts to expand their frequency ranges. This study investigates the acoustic performance of MPAs with parallel-arranged backing cavities at different depths (PCD) under random incidence conditions. Initially, an analytical model is proposed to predict the acoustic performance of PCD-MPA. The model exhibits significant consistency with finite element simulations and experimental measurements, validating its reliability in calculating absorption coefficients within the primary frequency band of concern (500~4000 Hz) in architectural acoustics applications. Subsequently, a thorough discussion of the key parameters, including the depth sequence and perforation parameters, which influence the random incidence absorption characteristics of PCD-MPA is presented based on the proposed model. These discussions lead to the development of an enhanced parameterized design method aimed at improving the absorption performance of PCD-MPA, enabling precise modulation of parameter combinations to meet specific application requirements and design nearly perfect absorbers.

The acoustic properties of FDM printed wood/PLA-based composites

The acoustic properties of the Fused Deposition Modelling (FDM) printed PLA wood composite was investigated. Initially tensile and flexural of wood PLA composite was studied with respect to varying layer thickness (0.15 mm, 0.20 mm, and 0.30 mm), infill density (30%, 60%, and 90%), and pattern (Layer, Triangle, and Hexagon). The outcomes demonstrated that the specimen produced with a hexagonal pattern, 90 % infill density, and 0.2 mm layer thickness had the highest tensile (16 MPa) and flexural strength (16 MPa). Utilizing this optimized parameter, micro-perforated panels were printed and acoustic properties were studied. Five specimens with a 3 mm thickness, various perforation diameters (5 mm, 4 mm, and 3 mm), and architecturally tapered perforations were fabricated. Using the impedance tube approach, the sound transmission loss and sound absorption coefficients were measured. The findings indicate that, in comparison to all the printed specimens, tapered type perforation with an exterior diameter of 5 mm and an internal diameter of 4.7 mm showed highest sound absorption coefficient of 0.60 Hz. A viscous loss is obtained by its convergent hole diameter reduction, which results in sound attenuations and is easily absorbed in the micro-perforated panel. Similar to this, the specimen printed with smaller perforation diameters (3 mm) had a high sound transmission loss of 79 dB. The small diameter of the perforations prevented the passage of sound waves. The current study is anticipated to lay the groundwork for extensive future research on these classes of materials, potentially serving as a catalyst for advancements in FDM based polymeric materials research and development.

A novel acoustic micro-perforated panel (MPP) based on sugarcane fibers and bagasse

Natural materials are becoming a reliable alternative to traditional artificial materials used in sound absorption insulation. The present study was conducted to investigate the acoustic insulation of micro-perforated panel (MPP) based on sugarcane fibers and bagasse as an available and environmentally friendly material. The absorption properties of single- and double-leaf natural micro-perforated panels (MPP) made of bagasse and also nonnatural MPPs made of Plexiglass were measured using an impedance tube based on ISO 10534–2. Then the effect of bagasse and sugarcane fibers composite on the air gap of MPP was investigated. The results showed the peak sound absorption of the bagasse composite is in the range of 1000 to 2000 Hz, and the sugarcane fiber composite has a higher sound absorption coefficient than the bagasse composite. Also, natural MPPs have a higher absorption coefficient than nonnatural MPPs at all frequencies, and as the panel thickness increases, the peak absorption coefficient shifts to lower frequencies. The peak sound absorption coefficient of double-leaf MPPs made of bagasse is 76%, in the range of 160 to 200 Hz. Using sugarcane fiber composite in the air gap of single- and double-leaf natural MPPs causes the absorption peak to shift to frequencies below 100 Hz. According to the results, natural MPPs have a high sound absorption coefficient at low frequencies. These panels can control sounds with much lower frequencies, especially in a double layer and along with cane fiber composite in their air gap.

Research on the design and noise reduction performance of periodic noise barriers based on nested structure

The rapid development of highway transportation has led to a gradual deterioration of the sound environment along highways. The theory of periodic structures provides a new approach for the design of traffic noise barriers. However, the lack of practical numerical models and on-site experimental validation has hindered the widespread application of periodic structure sound barriers. This study investigates the noise reduction performance of nested structure periodic sound barriers. Results from semi-anechoic chamber tests demonstrate excellent wave attenuation at the air gap of the barrier, achieving a peak noise reduction of 16 dB without the addition of any sound-absorbing materials or treatment measures, particularly at local peaks in the highway noise spectrum. To enhance the noise reduction performance of nested structure periodic sound barriers, three optimization measures were explored: filling sound-absorbing materials inside the scattering elements, adding micro-perforated panels, and their combined effects. The results indicate that both porous sound-absorbing materials and micro-perforated panels can improve noise reduction effectiveness, especially outside the air gap. In the optimization design of nested structure periodic sound barriers, adding porous sound-absorbing materials inside the micro-perforated panels effectively enhances noise reduction within the air gap. Considering the abundance of abandoned w-beam guardrails in highway projects, which also meet the requirements of scattering elements, this study proposes the use of abandoned w-beam guardrails as scattering elements. This approach aligns with principles of cost-effectiveness and environmental sustainability, and it provides design guidance to promote the application of nested structure periodic sound barriers in traffic noise control.

Electrical-Modulated Flexible Acoustic Metamaterial: Enhancing Low-Frequency Absorption via an Ionic Electroactive Polymer.

The growing concern over low-frequency noise pollution resulting from global industrialization has posed substantial challenges in noise attenuation. However, conventional acoustic metamaterials, with fixed geometries, offer limited flexibility in the frequency range adjustment once constructed. This research unveiled the promising potential of ionic electroactive polymers, particularly ionic polymer-metal composites (IPMCs), as a superior candidate to design tunable acoustic metamaterial due to its bidirectional energy conversion capabilities. The previously perceived limitations of the IPMC, including slow reaction and high energy expenditure, owning to its inherent sluggish intermediary ionic mass transport process, were astutely leveraged to expedite the attenuation of low-frequency sound energy. Both our experimental and simulation results elucidated that the IPMC can generate voltage potentials in response to acoustic pressure at frequencies significantly higher than those previously established. In addition, the peak absorption frequency can be effectively shifted by up to 45.7% with the application of a 4 V voltage. By further integration with a microperforated panel (MPP) structure, the developed metamaterial absorbers can achieve complete sound absorption, which was continuously tunable under minimal voltage stimulation across a wide frequency spectrum. In addition, a microslit structure IPMC metamaterial absorber was designed to realize modulation of the perforation rate, and the absorption peak can be shifted by up to 79.2%. These findings signify a pioneering application of ionic intelligent materials and may pave the way for further innovations of tunable low-frequency acoustic structures, ultimately advancing the pragmatic deployment of both soft intelligent materials and acoustic metamaterials.

Acoustic measurement of super-small-particle-filtering stainless steel wire cloths

The super-small-particle-filtering stainless steel (SSPFSS) wire cloth can serve as a front cover on resonators in mufflers, offering a broader noise reduction bandwidth compared to the resonators themselves. Like micro-perforated panels (MPPs), the SSPFSS wire cloth provides flexibility in resonator design and manufacturing. In this study, we conduct measurements of the transfer impedance of SSPFSS cloths and sound absorption coefficients of absorbers covered by SSPFSS cloths. For comparison purposes, we also calculate the sound absorption coefficient of foam and various absorbers covered by MPPs, traditional perforated panels, and fabric using referenced empirical equations.

Potential of wood fiber/polylactic acid composite microperforated panel for sound absorption application in indoor environment

This study introduces a novel approach using wood fiber/PLA composite microperforated panel (WFCMPP) for indoor sound absorption purposes. WFCMPP, comprising rubber tree chip-derived fibers and a polylactic acid (PLA) matrix, with the dimensions of the rubber tree chip-derived fibers ranging from 0.5 to 1 mm, demonstrated promising sound absorption coefficients comparable to other natural fiber composite microperforated panels. The maximum sound absorption coefficient was recorded at 0.989 with a resonance frequency of 1416 Hz when the wood fiber composition was 30 %. The study also investigates the impact of wood fiber composition on sound absorption, revealing a linear relationship between fiber content and both porosity and sound absorption. The peak sound absorption coefficient of WFCMPP remained almost identical at different air gap thicknesses, showcasing the versatility and effectiveness of the samples. Additionally, the performance remained robust even with variations in air gap size. Scanning electron microscope analysis confirms the irregular porous structure and complexity contributing to enhanced sound absorption. WFCMPP presents a sustainable and effective alternative for acoustic applications, combining sound absorption performance with environmental considerations.

Assessing acoustic performance of building material: A finite element model for 3D printed multilayer micro-perforated panels with compressed earth blocks

This study deals with 3D printing multilayered micro-perforated panels (M-MPPs) coupled with buildings materials as compressed earth block for noise reduction applications. The sound absorption coefficient α is utilized as a metric to assess the sound insulation capabilities across a frequency range spanning from 10 to 3000 Hz, then evaluated and validated by numerical and experimental methods. The FEM model developed makes it possible to predict the acoustic absorption of M-MPPs by tuning the frequency range and varying optimized acoustics parameters, considering hole-hole interaction and taking into account visco-thermal effects that are present in compressed earth blocks. It is shown that the shape of perforations and material properties including the porosity rate, arrangement in the design of multilayer micro-perforated structures are identified to play a significant role in the sound performance of the entire structure. In addition, the application of MPP coupled with compressed earth blocks improve the sound absorption capacity of the composite structure. The developed FEM leads to accurate prediction of performance, efficient optimization, and cost effectiveness. Finally, the present study reveals the importance of M-MPPs combined with compressed earth blocks (CEBs) as viable noise reduction materials, particularly relevant for engineering applications and development initiatives in emerging economies.

A tunable high-order micro-perforated panel metamaterial with low-frequency broadband acoustic absorption

We proposed a tunable high-order micro-perforated panel metamaterial for broadband absorption, in which the energy dissipation modes is reconstructed by the cavity partition plates. Owing to the more degrees of freedom in impedance design, the metamaterial not only obtains multiple perfect absorption peaks with broader bandwidth, but also allows for flexible frequency regulations. By coupling 12 high-order cells, the metamaterial finally achieves a smooth spectrum with 94% average absorption across the range of 300–3200 Hz, which is verified by the simulation and experiment. This metamaterial could have great applications in noise control engineering owing to the extraordinary performance.

Acoustic measurement of super-small-particle-filtering stainless steel wire cloths

The super-small-particle-filtering stainless steel (SSPFSS) wire cloth can serve as a front cover on resonators in mufflers, offering a broader noise reduction bandwidth compared to the resonators themselves. Like micro perforated panels (MPP), the SSPFSS wire cloth provides flexibility in resonator design and manufacturing. In this study, we conduct measurements of the transfer impedance of SSPFSS cloths and sound absorption coefficients of absorbers covered by SSPFSS cloths. For comparison purposes, we also calculate the sound absorption coefficient of foam and various absorbers covered by MPP, traditional perforated panels, and fabric using referenced empirical equations.

Application of Microperforated Panel Parallel Baffle Silencers in Ducts

Microperforated panel (MPP) baffle sound absorbers are analogous to glass fiber parallel baffles frequently used in building air moving equipment or large exhaust systems. The MPP baffles in this study consists of two microperforated panels with honeycomb sandwiched between them. The MPP baffles are tested by positioning them in a duct and measuring the insertion loss where insertion loss is defined as the difference in outlet sound power without and with the baffled treatment. It is demonstrated that the insertion loss of the MPP baffle treatments is superior to single MPP sheets positioned in the duct and the honeycomb by itself. A finite element model of the MPP baffle is also developed and results correlate acceptably with the measured results.

Sound Absorption Performance of Ultralight Honeycomb Sandwich Panels Filled with "Network" Fibers-Juncus effusus.

This study investigates lightweight and efficient candidates for sound absorption to address the growing demand for sustainable and eco-friendly materials in noise attenuation. Juncus effusus (JE) is a natural fiber known for its unique three-dimensional network, providing a viable and sustainable filler for enhanced sound absorption in honeycomb panels. Microperforated-panel (MPP) honeycomb absorbers incorporating JE fillers were fabricated and designed, focusing on optimizing the absorber designs by varying JE filler densities, geometrical arrangements, and MPP parameters. At optimal filling densities, the MPP-type honeycomb structures filled with JE fibers achieved high noise reduction coefficients (NRC) of 0.5 and 0.7 at 20 mm and 50 mm thicknesses, respectively. Using an analytical model and an artificial neural network (ANN) model, the sound absorption characteristics of these absorbers were successfully predicted. This study demonstrates the potential of JE fibers in improving noise mitigation strategies across different industries, offering more sustainable and efficient solutions for construction and transportation.

Development of a low-frequency broadband sound absorber based on a micro-perforated panel coupled with the Helmholtz resonator system

In the field of vibration and noise reduction, micro-perforated panel (MPP) structures and Helmholtz resonators (HR) play crucial roles as common sound-absorbing elements. However, independently applied MPP and HR structures cannot provide sufficiently wide absorption bandwidths at low frequencies. To achieve low-frequency broadband sound absorption, this study proposes a novel low-frequency broadband sound absorption structure (EMH) based on MPP and HR with a thickness of 40 mm to achieve a subwavelength, efficient, and compact design. We establish theoretical models of MPP and HR coupled systems, systematically analyze the sound absorption performance of same-element and different-element coupled structures, and employ the particle swarm optimization (PSO) algorithm to obtain structural parameters for efficient coupled sound absorption. Furthermore, we compare the sound absorption performance of three optimized coupled structures (MPP-coupled (SM), HR-coupled (SH), and MPP and HR-coupled) from the perspective of the theoretical calculation of the sound absorption coefficient and finite element analysis of the sound absorption mechanism. Finally, samples fabricated using 3D printing technology are tested in an impedance tube. The results demonstrate that efficient coupled sound absorption of MPP and HR can be achieved through parameter optimization. SH and SM exhibit nearly perfect sound absorption in the frequency ranges of 323–495 Hz and 615–1600 Hz, respectively, whereas the effective absorption bandwidth of EMH can reach 1225 Hz in the range of 200–1600 Hz. EMH shows superior low-frequency broadband sound absorption performance with a lightweight and simple structure, which holds the potential for application in low-frequency noise control.

Optimization and Comparative Analysis of micro-perforated panel sound absorbers: A study on structures and performance enhancement

In this study, three MPP (micro-perforated panels) absorber configurations (simple, series, parallel) were investigated via the response surface method (RSM) to broaden the absorption bandwidth. The study focused on the average normal sound absorption coefficient (SAC) in the range of 125–3000 Hz via an impedance tube. The impedance tube results were finally compared with the Finite Element Method (FEM) and Equivalent Circuit Method (ECM) simulations. Samples Fabrication involves 3D printing, with optimized configurations exhibiting expanded absorption bandwidths. The average absorption coefficient was 1.5 times higher in series MPPs and 1.2 times higher in single and parallel MPPs compared to the non-optimal state. In the optimal state, the series and parallel structures outperform the single design, and among the studied factors the hole diameter significantly influenced sound absorption more than others. The alignment of coefficients from various methods with RSM predictions was noteworthy. The results obtained from the FEM and ECM methods align perfectly, This study underscores RSM’s effectiveness, demonstrating optimization benefits and coherence between numerical, theoretical, and experimental models in evaluating MPP absorbers.

Acoustic properties of a micro-perforated muffler with parallel-arranged cavities of different depths

Low-frequency noise generated by ventilation systems propagates into indoor environment through ducts. In this study, a novel micro-perforated panel (MPP) muffler, with the absence of porous material in cavities, backed radially with parallel-arranged cavities of different depths (PCD) is proposed. Based on the two-load method, numerical simulations and experiments are conducted to evaluate sound transmission loss (TL) and sound wave radiating coefficients (SWRC) of the PCD-MPP muffler. Influences of muffler parameters on TL and SWRC are then discussed by numerical simulation. A wideband compound PCD-MPP muffler with high performance is finally proposed. Results show that the numerical model provides accurate prediction on acoustic properties of the PCD-MPP muffler by comparing with the results by experiments. Numerical results demonstrate that, the coupling effect of absorption resonance occurred by cavities of different depths contributes to the wideband silencing performance. TL, absorptance and reflectance improve when enhancing the length of the muffler, while TL and absorptance move to lower frequencies with the increase of cavity depth. In addition, TL of the compound PCD-MPP muffler is higher than 20 dB within the frequency range of 700–1600 Hz, with a maximum TL of 42.5 dB. The present work also highlights the higher TL and absorptance than other types of MPP mufflers, and silencing performance can be customized by adjusting the perforation parameters and cavity depths, which may provide a valuable reference in ventilation noise reduction with the absence of porous material.