Search Results (57)

Balancing ventilation and broadband sound insulation remains a significant challenge in noise control engineering, particularly when simultaneous airflow and broadband noise reduction are required. Conventional porous absorbers and membrane-type metamaterials remain fundamentally constrained by ventilation-blocking configurations or narrow operational bandwidths. This study presents a ventilated composite metamaterial unit (VCMU) co-integrating optimized labyrinth channels and the Helmholtz resonators within a single-plane architecture. This design achieves exceptional ventilation efficiency through a central flow channel while maintaining sub-λ/30 thickness (λ/31 at 860 Hz). Coupled transfer matrix modeling and finite-element simulations reveal that Fano–Helmholtz resonance mechanisms synergistically generate broadband transmission loss (STL) spanning 860–1634 Hz, with six STL peaks in the 860 and 1634 Hz bands (mean 18.4 dB). Experimental validation via impedance tube testing confirmed excellent agreement with theoretical and simulation results. The geometric scalability allows customizable acoustic bandgaps through parametric control. This work provides a promising solution for integrated ventilation and noise reduction, with potential applications in building ventilation systems, industrial pipelines, and other noise-sensitive environments. Full article

Based on the three-parameter approximate JCAL analytical model (hereinafter referred to as the three-parameter model), this study conducted an in-depth analysis of the effects of porosity, median pore size, and pore size standard deviation on the acoustic performance of porous materials and developed a composite porous material composed of glass fibers and zeolite particles. Experimental results indicate that the pore size distribution significantly affects the acoustic performance of fibrous porous sound-absorbing materials. Specifically, smaller pores lead to better sound absorption at mid–low frequencies, with the optimal sound absorption performance observed when the median pore size is between 60 and 80 μm. Increasing the material density and decreasing the fiber diameter help reduce the internal pore size, thereby improving the material’s sound absorption performance. Additionally, the appropriate addition of zeolite can further optimize the internal pore size and effective sound-absorbing interface, thus enhancing the material’s sound absorption performance. When the material density is 120 kg/m³ and the zeolite substitution rate is around 10%, the material exhibits the best acoustic performance, with a noise reduction coefficient (NRC) reaching 0.65, which is a 10.17% increase compared to the material without zeolite. Comparing the simulation data from the three-parameter model with the actual measurement data shows that the model has excellent predictive performance for the sound absorption coefficient (SAC) of single-fiber porous materials (with an error of approximately 5%). However, for composite porous materials, due to the complex changes in interfaces, there is a certain prediction error (with the maximum error reaching 12.81%), indicating that the model needs further optimization and correction when applied to composite materials. Full article

Pumice forms when a volcanic explosion ejects highly pressurized, superheated rock, rapidly cooling and depressurizing, resulting in a porous structure. In countries with high volcanic activity, pumice stone is a low-cost natural material that is lightweight, non-toxic, eco-friendly, durable, and heat-resistant. Among other applications, pumice has been used as an aggregate to produce lightweight concrete or cementitious material to produce blended cement or geopolymer. Since pumice stone is highly porous, it could be used as a naturally occurring multiscale porous sound-absorbing material, which may add interesting properties for absorbing sound energy. Normally, a double-porosity granular material presents higher sound absorption at low frequencies than a solid-grain material with the same mesoscopic characteristics at a reduced weight. This study uses theoretical and experimental approaches to investigate the sound absorption characteristics of granular pumice samples. The tests were conducted on crushed pumice stones in granular form. The study suggests that pumice stones can be used as a novel material for sound absorption in room acoustics and noise control applications. Full article

The acoustic product development process, crucial for effective noise control, emphasises efficient testing and validation of materials for sound absorption in the R&D phase. Balancing cost-effectiveness, speed, and sustainability, the focus is on minimising excess materials. While strides have been made in reducing sample sizes for estimating random-incident absorption, challenges persist, particularly in establishing validity thresholds for smaller samples with increasing thickness, susceptible to potential overestimation due to edge effects. This study delves into analysing the absorption coefficients of widely used acoustic absorber types—polyester, fibreglass, and open-cell foam—in a full-scale reverberation chamber at Ventac, Blessington, and Wicklow. Demonstrating significant absorption above 500 Hz, these porous absorbers exhibit diminished effectiveness at lower frequencies. The strategic combination of these absorbers with different facings enhances their theoretical broadband absorption characteristics in practical applications. Moreover, the study assesses the validity threshold for reduced sample sizes, employing statistical analysis against ISO 354:2003 standard control samples of the absorber types. Analysis of Variance (ANOVA) on material groups underscores the significant influence of frequency components and sample sizes on the absorption coefficient. The determined validity threshold for 12.8 sqm ISO 354 standard control size is 7.7 sqm for the 25 mm open-cell foam. Similarly, the validity threshold of the 12 sqm ISO 354 standard control size is 9.6 sqm for the 20 mm 800 gsm polyester, 7.2 sqm for the 25 mm fibreglass, and the vinyl black on 25 mm fibreglass. Full article

Cellulose-based materials are now commonly used, including in the field of acoustic comfort. Often presented as a less environmentally impactful alternative to traditional acoustic absorbents (such as melamine, glass wool, etc.), these cellulose-based materials are more frequently derived from recycling, undergoing, in most cases, a technical process that allows these cellulose fibers to be obtained, thus inheriting the acoustic properties of the latter, with limited or even non-existent control. This paper proposes a manufacturing process that allows for the production of cellulose foam with precise control over its porosity, pore size, and interconnections. In addition to exhibiting good sound absorption properties, this process also enables the fabrication of gradient-porous structures and other hybrid materials, which can result in remarkable sound absorption properties. Full article

Noise is a concern in industries like aviation. Existing acoustic materials have limitations in terms of effective broadband sound attenuation and operating conditions. This work addresses these limitations by designing and developing a noise mitigation system using lightweight graded micro-porous material made from Cenospheres and high-char binder. However, Cenospheres are nearly spherical with rough surfaces, so determining the flow properties of sound propagation is challenging, and direct measurements are expensive. We developed a multivariable-fit inverse method to estimate these properties using an experimental absorption coefficient, validated first with smooth-surface glass beads and then applied to micro-porous material. The determined flow properties were used in a predictive acoustic analysis and validated experimentally. It was demonstrated that a microstructurally graded material is needed to optimize both sound absorption and transmission loss. A graded material system designed for turbofan engine acoustic liners (50 mm thick) met the target broadband sound absorption coefficient of ≥0.50 and transmission loss of ≥20 dB above 500 Hz. The study also highlights that larger particles in thicker layers enhance sound absorption, while a graded micro-structure improves overall acoustic performance. This research offers a novel approach for designing a lightweight acoustic material for aviation, marking a breakthrough in passive noise mitigation technology. Full article

This study investigates the development of biomimetic sound-absorbing components through laser sintering technology, drawing inspiration from wood’s natural porous structure. Using a pine wood powder/phenolic resin composite, various specimens were fabricated with different structural configurations (solid, fully porous, and varying straight-pore ratios) and cavity thicknesses. Sound absorption performance was evaluated using the impedance tube transfer function method. The effect of different composite structures, placement orientations, and cavity thicknesses on sound absorption performance was evaluated. The results demonstrate that solid laser-sintered samples exhibit inherent sound absorption properties due to microscopic pores, with absorption coefficients exceeding 0.234. The biomimetic wood-like structure, featuring multi-scale porosity at both microscopic and mesoscopic levels, shows enhanced broadband sound absorption, particularly in mid-high frequencies, with characteristic double-peak absorption curves. The study reveals that absorption performance can be optimized by adjusting structural parameters and thickness, enabling targeted frequency-specific sound absorption. This research establishes the feasibility of creating multi-frequency sound-absorbing materials using laser-sintered biomimetic wood structures, providing a foundation for future applications and development in acoustic engineering. Full article

The acoustic performance of sound barrier absorption materials utilized in substations is subject to variations due to factors such as sandstorms, corrosion, and rainfall. In this study, a model of the absorbing material was developed based on the Delany–Bazley model using COMSOL simulation software, version 5.6. The influence of porosity and material thickness on the absorption coefficient was analyzed, and the patterns of change were summarized. The results indicated that porosity significantly affected the entire analysis frequency range, while material thickness had a more pronounced impact in the low-frequency range. Building upon these findings, a blended fiber absorption material was formulated through research efforts. Experimental results demonstrated that the aluminum fiber diameter measured 30 microns, while the aramid fiber diameter was 12 microns; additionally, their mass ratio was established at 3:1. The material thickness was determined to be 10 cm with a face density of 2500 g/m², resulting in optimal absorption performance. Durability tests revealed that this material could sustain effective acoustic performance across various complex environments. Finally, simulations and analyses regarding noise reduction effects were conducted within actual application scenarios; it was found that the noise reduction capability of the blended fiber sound barrier absorption material exceeded that of glass wool by 4.78 dB. Full article

Thin sound-absorbing materials are particularly desired in space-constrained applications, such as in the automotive industry. In this study, we theoretically analyzed the structure of relatively thin glass wool or polyester wool laminated with a nonpermeable polyethylene membrane and a permeable nonwoven fabric sheet. We also measured and compared the sound-absorption coefficients of these samples between experimental and theoretical values. The sound-absorption coefficient was derived using the transfer matrix method. The Rayleigh model was applied to describe the acoustic behavior of glass wool and nonwoven sheet, while the Miki model was used for polyester wool. Mathematical formulas were employed to model an air layer without damping and a vibrating membrane. These acoustic components were integrated into a transfer matrix framework to calculate the sound-absorption coefficient. The sound-absorption coefficients of glass wool and polyester wool were progressively enhanced by sequentially adding suitable nonwoven fabric and PE membranes. A sample approximately 10 mm thick, featuring permeable and nonpermeable membranes as outer layers of porous sound-absorbing material, achieved a sound-absorption coefficient equivalent to that of a sample occupying 20 mm thickness (10 mm of porous sound-absorbing material with a 10 mm back air layer). Full article

A new type of porous sound-absorbing sound barrier was developed with quartz sand and self-developed polysiloxane resin. The forming process of the material was studied. The test specimens of the porous sound-absorbing sound barrier were prepared with different mesh numbers of quartz sand and different proportions of resin, and the void properties, compressive strength, durability, and acoustic performance were investigated. Based on the mix design results, it is suggested that 20-mesh quartz sand and a 10:1 mass ratio of quartz sand are used to prepare the porous sound-absorbing sound barrier. The durability study showed that the porous sound-absorbing sound-barrier material had good salt and alkali resistance, poor acid resistance, good water stability, and freeze–thaw stability. The laboratory acoustic test and practical engineering application results showed that the porous sound-absorbing sound barrier had excellent acoustic performance and good noise-reduction effects. Full article

Porous sound absorption ceramic is one of the most promising materials for effectively eliminating noise pollution. However, its high production cost and low mechanical strength limit its practical applications. In this work, low-cost and in situ mullite whisker-reinforced porous sound-absorbing ceramics were prepared using recyclable construction waste and Al₂O₃ powder as the main raw materials, and AlF₃ and CeO₂ as the additives, respectively. The effects of CeO₂ content, AlF₃ content, and sintering temperature on the microstructure and properties of the porous ceramics were systematically investigated. The results showed that a small amount of CeO₂ significantly promoted the growth of elongated mullite crystals in the resultant porous ceramics, decreased the growth temperature of the mullite whiskers, and significantly increased the biaxial flexural strength. When 2 wt.% CeO₂ and 12 wt.% AlF₃ were added to the system, mullite whiskers were successfully obtained at a sintering temperature of 1300 °C for 1 h, which exhibited excellent properties, including an open porosity of 56.4 ± 0.6%, an average pore size of 1.32–2.54 μm, a biaxial flexural strength of 23.7 ± 0.9 MPa, and a sound absorption coefficient of >0.8 at 800–4000 Hz. Full article

The automotive industry is rapidly advancing toward the electrification of vehicles. Battery electric vehicles present unique challenges in heat and noise control due to the absence of an internal combustion engine. These challenges arise from the stringent operating temperature requirements of batteries and the distinct characteristics of their power sources, such as differences in rpm and mounting positions compared to traditional engines. To address these issues, porous sound-absorbing materials and porous insulation materials are commonly employed. Conversely, there is an increasing demand for materials that are both lightweight and compact yet capable of providing excellent sound absorption and thermal insulation. Although porous sound absorbers and insulators are similar, they differ in the microstructure required to achieve high performance, specifically in the size and connectivity of their fluid phases. This increases the challenge of integrating superior sound absorption and insulation properties within the same material. In this study, computational microstructure modeling was employed to develop a non-woven fabric composed of flattened ellipsoidal particles with nanoporosity. This innovative material demonstrates exceptional thermal insulation and sound absorption characteristics attributable to its nanoporosity and high tortuosity. Full article

This study focused on manufacturing efficient automobile sound-absorbing materials through alkaline treatment and dimple processing of recycled polyethylene terephthalate (rPET) nonwoven fabric. The rPET nonwoven fabric was produced with a sound-absorbing material through compression molding. It was improved through the development of porous sound-absorbing materials through alkaline treatment and resonant sound-absorbing materials through dimple processing. As a result of morphological analysis, alkaline treatment showed that pore size and air permeability increased according to temperature and concentration increase conditions. On the other hand, dimple processing caused a decrease in air permeability and a decrease in pores due to yarn fusion, and as the dimple diameter increased, the sound-absorbing coefficient increased in the 5000 Hz band. Finally, it was judged that effective sound absorption performance would be improved through a simple process through alkaline treatment and dimple processing, and thus there would be applicability in various industrial fields. Full article

Stains produced by bacteria or those found in blood and food byproducts accumulate in highly porous caries lesions. They can interfere with accurate diagnosis and the selective removal of carious tissue during cavity preparations. Short-wavelength infrared (SWIR) imaging studies have shown that stain molecules do not absorb light beyond 1200 nm. The objective of this study was to image affected and infected dentin atSWIR wavelengths. Sections of 3 mm thickness were cut from the extracted teeth with deep dentinal lesions. The sound (normal), affected (stained), and infected (demineralized) dentin on each section were examined with reflected light at wavelengths from 400 to 1700 nm, red and green fluorescence, and with optical coherence tomography (OCT). Microcomputed tomography (microCT) was used to measure the mineral density at each location investigated. Significant (p < 0.05) differences were observed in the reflected light intensity at 400–850 nm and for fluorescence between the sound, affected, and infected dentin. SWIR imaging did not show significant reductions in reflectivity for the affected and infected dentin. SWIR images may be valuable for monitoring the lateral spread of dentinal lesions on the occlusal surfaces of teeth. Full article

The automotive industry needs to improve energy efficiency rapidly to achieve carbon neutrality while creating a safe, secure, and comfortable driving environment for customers. Porous sound-absorbing materials and porous thermal insulators are typically used to satisfy these requirements despite limitations in mass and space. While these porous materials are similar, the microstructures they offer for high performance differ in the size and connectivity of their fluid phases, which enhances the difficulty of achieving excellent sound absorption and thermal insulation in the same material. In this study, a hydrophobic cellulose nanofiber–poly(methylsiloxane) xerogel composite was developed using computational microstructure modeling. This porous material has high porosity and excellent thermal insulation and sound absorption properties. Full article