Average Absorption Coefficient Research Articles

Rectangular extended neck Helmholtz resonant acoustic structure for low frequency broadband sound absorption

Abstract The Helmholtz resonant structure with a rectangular extended neck is designed in this work to solve the low-frequency broadband sound absorption problem. Theoretical and finite element absorption models have been established and are used for low-frequency acoustic design. What makes it interesting is that all parameters of the rectangular extended neck Helmholtz resonator can be adjusted to shift the working frequency. Four coupling structures with different neck depths, neck opening areas, cavity cross-sectional areas, and cavity depths are respectively designed. Each of these structures exhibits multiple sound absorption coefficient peaks to enhance the low-frequency absorption capacity. The effectiveness of the coupling structure is further analyzed by examining the broadband acoustic absorption mechanism based on the particle vibration velocity distribution. It is found that cells with different acoustic impedance contribute differently to the sound absorption, and cells with longer necks provide better noise reduction at low frequencies. The experiment is verified in the impedance tube, and the result shows that the coupling structure with 9 cells and a cavity depth of only 4cm achieves an average sound absorption coefficient above 0.8 at 210-340 Hz, thus verifying the accuracy of the theoretical model. Overall, the Helmholtz resonant cavity acoustic structure with a rectangular extended neck proposed in this study has a simple structure with low-frequency broadband acoustic absorption performance, providing a new approach for designing low-frequency broadband acoustic structures.

Enhancing light absorption of deep ultraviolet photodiodes through intelligent algorithm-guided design of resonant nano-optical structures

Abstract The surface of the deep ultraviolet (DUV) photodiodes requires an enhanced light absorption to improve wall-plug efficiency. The resonant Mie scatterer has a high optical mode density with a high refractive index all-dielectric resonant structure, which causes strong light coupling and improves forward scattering, providing a new perspective for efficient light absorption on the surface of the DUV photodiodes. In this work, a method is proposed for the design of nano-optical structures that is capable of supporting forward light scattering across the resonant bandwidth. This is achieved by utilizing intelligent algorithms in conjunction with Maxwell’s equations. The results show that the average light absorption coefficient of the optimized optical structure is improved to more than 96% with angle-independent and polarization-independent characteristics. Based on intelligent algorithms, a reverse design approach can be employed to maximize this effect, thereby offering novel avenues for enhancing the wall-plug efficiency of the DUV photodiodes.

Sound absorption performance and mechanism of aluminum foam with double-layer structures of conventional and porous cell walls

Open-cell aluminum foam exhibits sound absorption valleys in the 2500-4000 Hz range, reducing its sound absorption performance in the 800–6300 Hz range. This paper prepared a novel aluminum foam with a double-layer structure using the infiltration casting method, and its pore structure, sound absorption performance, acoustic model, and sound absorption mechanism are investigated. The double-layer structure consists of a conventional pore (CP) layer with a single pore size of 250 μm or 600 μm and a porous cell wall (PCW) layer with double pore diameters of 250 μm and 600 μm. As the thickness ratio between the CP and PCW layers decreases, the acoustic absorption valley value of the double-layer structure increases when combined with a small-pore CP layer. In contrast, it decreases slightly when combined with a large-pores CP layer. The double-layer structure reaches a sound absorption valley value and average sound absorption coefficient of 0.912 and 0.902, respectively. The double-layer structure's sound absorption valley value is better than that of a homogeneous structure, improving sound absorption performance. A Lu modified model is established to characterize the sound absorption of the double-layer structure, which closely matches the experimental results. The modified model further analyzed the vital geometrical parameters affecting the absorption valleys. Acoustic impedance analysis shows the enhanced sound absorption valleys are due to: 1) Gradient acoustic impedance reduces sound reflections at the air-structure interfaces and increases secondary reflection at the interfaces in the structure; 2) The series–parallel configuration increased the resonance peak bandwidth, while the dual-sized resonance cavities regulated the resonance peak frequency.

Determination of optical properties of single crystal diamond substrates grown via welding-assisted microwave plasma enhanced chemical vapour deposition

Lab grown single crystal diamonds (SCDs) offer unrivalled hardness, a wide range of optical transparency, and supremely high thermal conductivity reliable materials to be a part of devices run at high frequency, temperature, and power. Effective synthesis techniques are essential in enhancing the potential applications of high-quality SCDs. This study aims to decrease the thermal contact resistance between diamond seeds and the molybdenum holder by utilizing welding material. Quality of grown diamond substrates (plates) were assessed by analysing optical properties through Raman, UV-Vis, and FT-IR spectroscopic methods. The findings revealed that the grown single-crystal diamonds have excellent transmittance (>70%) and absorption at 270 nm. Calculations also showed an average absorption coefficient of 1.1 cm−1, indicating the high quality of the grown SCDs with nitrogen impurities below 10 ppm. The absorption observed in the FTIR spectra, ranging from 1600 cm−1 to 2700 cm−1 with a peak at 2354.13 cm−1, is referred to as the “two phonon region,” which is a distinctive feature of the diamond phase.

Spectrum-driven acoustic metasurface for broadband noise control

To address the issue of broadband noise with tonal characteristics in indoor environments, a spectrum-driven acoustic metasurface (SAM) is proposed in this study. By combining the concept of coiled-up space with the synergetic effect between cascaded Helmholtz resonators, SAM with compact size can achieve targeted absorption of broadband noise with arbitrary tonal characteristics. Furthermore, an inverse design method based on genetic algorithms is proposed to regulate the sound absorption performance of SAM and its effectiveness is demonstrated through a case study on controlling transformer noise. Experimental results show that with a subwavelength thickness, SAM can efficiently absorb both the low-frequency noise of the transformer and the broadband noise of the cooling fans. The average sound absorption coefficient within the frequency range of 500–1000 Hz is 0.8, and reaches up to 0.85 at 100 Hz. This study provides theoretical guidance for targeted regulation of broadband noise with multiple low-frequency tonal components.

Simultaneously enhanced the sound absorption coefficient and dimensional stability of Carboxymethyl cellulose/clay aerogel by impregnating polyurethane

Carboxymethyl cellulose (CMC) aerogel could be used in the manufacture of highly efficient sound-absorbing materials because of its low density and sustainability. However, owing to its low mechanical strength and brittleness, preparing porous sound absorption materials with excellent sound absorption performance has always been a challenging problem. Herein, carboxymethyl cellulose/organic exfoliation of montmorillonite/thermoplastic polyurethane (CMC/OMMT/TPU) composite aerogels were successfully obtained via a simple impregnation and freeze-drying process. The effect of TPU and OMMT on the sound absorption properties of cellulose aerogels was detailedly discussed. The results revealed that the CMC/OMMT/TPU composite aerogel had hierarchically porous structures, and the sound absorption performance was significantly improved. The average sound absorption coefficient of CMC/OMMT/TPU composite aerogel could reach as high as 0.807 (500–6500 Hz). The main reason for this improvement is caused by the multiple scattering of sound waves on the arranged porous surface, as well as the viscous damping of the air inside the structure between the TPU, CMC and OMMT. Furthermore, the dimensional stability of the prepared aerogel is also greatly enhanced after using TPU. This work provides a new approach for the development of aerogel with stable morphology and sound absorption performance, which would be widely used in construction and military fields.

Experimental assessment and numerical simulations of marine fouling effect on underwater sound absorption coatings

Underwater sound absorption coatings capable of absorbing sound energy is essential to conceal underwater vehicles. While the accumulation of marine fouling on surfaces of ship hulls, platforms, and submarines can significantly alter their acoustic properties. Currently, the precise impact that different stages of marine fouling have on underwater sound absorption coatings remains unclear. In this study, a novel lab assessment method was developed to investigate the acoustic effect of marine fouling on the underwater sound absorption coatings. Four distinct stages of marine fouling were artificial fabricated and characterized, including conditioning film, microfouling, medium macrofouling, and heavy macrofouling. These effects are quantified through comprehensive tests conducted in a water-filled impedance tube. It is found that the first two stages of marine fouling have a negligible impact on the underwater sound absorption performance within the low frequency range of 500 Hz and 2000 Hz. While a limited impact is observed in the frequency range of 2000 Hz–5000 Hz, where the sound absorption coefficient remains approximately 0.6. Conversely, in the third and fourth stages of fouling, the average sound absorption coefficient drops from 0.8 to 0.2. Further, a new acoustic finite element method (FEM) model of hard fouling was developed to predict the acoustic effect, and the numerical results show the same trend with the experimental results. These findings emphasize the importance of considering antifouling strategies during the design of underwater sound absorption coatings, with a particular focus on targeting hard fouling organisms as the primary objective.

Hierarchical-porous acoustic metamaterials: A synergic approach to enhance broadband sound absorption

A novel design for hierarchical-porous acoustic metamaterials (HPAM) is proposed to enhance the functionality of Helmholtz-type resonators and porous materials, achieving continuous and efficient broadband sound absorption. This method can potentially eliminate absorption valley and improve the coupling strength through a synergistic energy dissipation mechanism and hybrid impedance matching behavior. Excellent sound-absorbing capability of the elaborately crafted HPAM was demonstrated analytically, numerically, and experimentally. Specifically, the results revealed an impressive average absorption coefficient of 0.77, with 73 % of the α points exceeding 0.8 across the entire test frequency range. Furthermore, the sound absorption of HPAM can be further optimized to attain ultra-broadband properties by modifying the hierarchical configuration and composite design of the porous materials. The physical mechanism is revealed through the integration of the hierarchical scaling effect and the energy-trapped mode. Numerical simulations revealed the emergence of three distinct absorption peaks at frequencies of 0.76, 1.4, and 3.6 kHz, respectively, and the effective absorption spectrum exceeded 3.4 kHz. Overall, the proposed design highlights the role of hierarchical structures and porous materials in synthesizing superior sound-absorbing properties that fullyelucidate the relationship between structure and performance,and provide an avenue for potential noise-control applications.

Wet Chemical Synthesis of Ultrathin γ-Ga2O3 Quantum Wires Enabling Far-UVC Photodetection with Ultrahigh Selectivity and Sensitivity.

As compared to solar-blind ultraviolet (UV) photodetectors (PDs), far-UVC PDs not only show some irreplaceable advantages but also are more challenging to be developed. To solve this challenge, we report herein a soft template-assisted solvothermal route to synthesize ultrathin γ-Ga2O3 quantum wires (UQWs) with diameters down to 1-2 nm. These UQWs all exhibit a cluster-like absorption feature with a strong peak located between 190 and 230 nm and an edge below 250 nm, allowing highly selective absorption to far-UVC light. Notably, their normalized absorption coefficients were experimentally and theoretically confirmed to increase obviously with decreasing their diameters. Self-powered photoelectrochemical-type PDs based on Ga2O3 QWs of 1.7 nm diameter were therefore fabricated, exhibiting an excellent far-UVC detection performance with an unprecedented ultrahigh spectral selectivity (R210 nm/R250 nm = 452). As a proof of concept, this paper offers a new idea for developing ultrawide bandgap semiconductor materials and devices by leveraging a strong quantum confinement effect.

Multifunctional hybrid plate lattice structure with high energy absorption and excellent sound absorption

Lattice structures are featured by their extraordinary mechanical performances in specific stiffness, specific strength, energy absorption, and sound absorption, etc. The recent trend of multifunctionality in engineering applications has raised new requirements for the integration of their mechanical and acoustic properties. In this paper, a multifunctional hybrid plate lattice structure denoted as SBHP is proposed by hybridizing the traditional body-centered cubic plate (BCCP) and simple cubic plate (SCP) lattice structures, and its acoustic and energy absorption properties are investigated by theoretical modeling, simulation analysis and experimental verification. The effects of hole diameters and plate thicknesses on the sound absorption performance are investigated by impedance matching and system damping state analysis. The results show that the average sound absorption coefficient of SBHP-1 is increased by 24% and 62%, and the normalized half-absorption bandwidth is enlarged by 45% and 89% than those of BCCP and SCP, respectively. Heterogeneous lattice structures constructed by using the synergistic mechanism of strong and weak coupling have a more outstanding broadband sound absorption effect. This work provides an effective approach for the design of multifunctional lightweight structures with excellent broadband sound absorption and high energy absorption.

Study on sound absorption valley and acoustic absorption performance of small-pore aluminum foam composited with 304 stainless steel fibers

Open-cell aluminum foam exhibits a sound absorption valley (SAV) in the 2500–4000 Hz frequency range, reducing its acoustic absorption in the range of 1000–6300 Hz. A small-pore aluminum foam composited with 304 stainless steel fibers (SP-SS304F aluminum foam) with a porosity of 82 % was fabricated via infiltration casting, and its pore structure, acoustic absorption performance, and mechanism were investigated. The pore structure of SP-SS304F aluminum foam consisted of 223–676 μm main pores, 125–373 μm cell wall pores, and 30–60 μm 304 stainless steel fibers. The fibers existed completely embedded in the cell walls, partially or completely embedded in the cell cavities. As the pore diameter decreases, the SAV value increases and then decreases. With increasing fiber content, the SAV value showed a similar trend. The increased SAV value benefits the enhancement of the average sound absorption coefficient (SAC). The SP-SS304F foam aluminum reaches an optimal SAC value of 0.899. Its static resistivity value is 24,345 Pa.s/m2. Finite element simulations reveal the reasons for the improved acoustic absorption performance of SP-SS304F aluminum foam: First, the small-diameter and pore-embedded fibers improve the acoustic impedance matching, reducing sound reflections at the SAV frequency. Second, the reduced pore diameters and partially or completely pore-embedded fibers increase the pore surface areas, intensifying the acoustic absorption by pore structure.

Acoustic and thermal properties of panels made of fruit stones waste with coconut fibre

Using natural porous and fibrous materials for acoustic and thermal conditioning in the construction sector is a solution to achieve a comfort level in buildings. The novelty of this research work lies in employing agricultural and agro-industry waste to solve noise and thermal insulation problems. This study was conducted to investigate a multilayered panel made of fruit stones and coconut fibre from agro-industry waste. Acoustic absorption, and acoustic and thermal transmission, tests were run on four different fruit stone types, olive, cherry, apricot and peach, plus a coconut fibre layer. Although they are not structural elements, bending tests were run to ensure panels’ structural integrity. Acoustic tests complied with the recommendations of Standards ISO 10534–2 and ASTM E 2611–09, based on the standing wave tube to obtain the acoustic absorption coefficient and sound transmission loss, respectively. Standard EN 12667 was considered for the thermal test to determine the thermal conductivity coefficient based on the hot plate method. The results show an average sound absorption coefficient above 0.5 and sound insulation over 25 dB within certain frequency ranges. The cherry panels had absorption values of around 0.7 and apricots had sound insulation values of up to 30 dB. Samples’ thermal transmittance coefficient values were between 3.0 and 3.4 (W/m2K), which indicate panels’ ability to provide thermal insulation. The cherry and olive panels obtained the lowest thermal conductivity (around 0.14 W/mK). The backing effect of the coconut fibre layer improves all the panels’ acoustic absorption and thermal properties.

Influences of parameters of film on acoustical absorption performance of copper film-copper fiber composite structure

Fiber porous materials excel at sound absorption, but their effectiveness suffers at thin thicknesses. This study proposed a novel copper film-copper fiber porous material (FFM) structure to overcome this limitation. We designed a composite material with improved sound absorption, by coating a thin copper film onto an existing copper fiber matrix. This innovative approach enables effective sound absorption when the sample thickness is small. Our analysis revealed that FFM structures are better than the individual copper film and fiber porous material regarding sound absorption, particularly near their resonance frequency. Notably, a 2 mm-thick FFM structure boasts an average sound absorption coefficient of 0.35, a remarkable fourfold increase compared to the individual copper fiber matrix (0.08). The further investigation explores the influence of copper film thickness and bond area percentage on acoustic performance. We successfully validate our simulation model against experimental data, enabling us to calculate energy consumption ratios for various design parameters. This provides research ideas for optimizing FFM structures for specific noise reduction applications.

Study on Sound Absorption Properties of Polyvinyl Chloride (PVC) Film Multicavity Structure Materials

Since the development of industry, sound absorption and noise reduction have gradually become an urgent problem to be solved. Lightweight polymer film materials are very effective in response to sound waves, and sound waves can easily cause vibration of the film, which can convert sound energy into vibration and film friction to achieve sound absorption. The application conditions of the film material are very harsh, that is, a support body is required to fix the film and the film needs to be tensioned. The film is very thin and easy to damage. The idea of this research is to transform the film into a bubble structure and use a large number of film bubbles to form a cavity structure material. As a unit of the sound absorption structure, bubbles can avoid damage to the film. In this paper, commercial polyvinyl chloride film bubble materials are used to prepare two kinds of film multicavity structure materials, and the sound absorption performance of this film multicavity structure material is studied. The research results show that this film multicavity structure material has very excellent broadband sound absorption performance, which changes the narrow band sound absorption properties of the usual film single cavity. The average sound absorption coefficient can reach 0.84 in frequency range from 500 Hz to 6400 Hz. This structural material has a single peak sound absorption curve at the middle and low frequency bands, which is the characteristic of resonance sound absorption. And at the middle and high frequency bands, it exhibits the characteristics of broadband sound absorption. The film multicavity structure material has both cavity sound absorption and broadband sound absorption characteristics.

Preparation and Modification of Flexible Polyurethane Foam for Effective Flame Resistance and Sound Absorption

Polyurethane foam as an important sound absorption material is limited by the poor flame resistances in building field, but the modifications of flame resistances tend to have adverse effects on the sound absorption performance. Herein, dibutyltin dilaurate and triethylenediamine are used simultaneously as catalysts, and four new types of flame retardant polyether polyols (FPMPO) are synthesized and combined with modified expanded graphite (PEG) to prepare the flame resistance flexible polyurethane foam (FFPUF) by one-step method. The results show that the combination of the two catalysts can control the cell structure of FFPUF availably for sound absorption. The FPMPO have little negative influence on the cell morphology and the sound absorption performance of FFPUF, but the increase of flame resistances is finite due to the limited amount of FPMPO. In order to improve the flame retardant properties further, the FPMPO and the PEG are combined in the modification. Benefitting by the effective control structure and the modification with composite flame retardant, the FFPUF shows excellent sound absorption and flame retardant properties. The LOI value of FFPUF is 33.4 and the vertical burning level reaches V-0, and the average sound absorption coefficient maintains 0.68 in the 800-6300 Hz range.

The Effects of Sound Absorption of Stage House on the Acoustics of Auditorium in an Opera House

The coupling effects between the stage house and the auditorium in opera houses make the sound field very complex. In the present study, the effects of stage absorption on the primary monaural objective room acoustic parameters in the seating area of an opera house in China were investigated by means of computer simulation and scaled model measurement. In computer simulations, the absorption coefficient of the ceiling and walls of the stage house was changed across several steps, and then a series of experiments were conducted in a 1:20 scaled hall with and without curtains and wall absorption on the stage to verify the simulation results. It was found that stage absorption has a significant influence on early decay time (EDT), reverberation time (RT) and clarity (C80) in the seating area, while the effect on sound strength (G) is much smaller. The values of EDT and RT decrease with an increase in sound absorption on the stage, while C80 displays an opposite trend. In addition, when the average absorption coefficient of the stage walls and ceiling is over 0.5, the variations in these four parameters due to the increase in stage absorption can be constrained within an acceptable range.

Light absorption properties and source contributions of black and brown carbon in Guangxi, southern China

Black carbon (BC) and brown carbon aerosols (BrC) are primary light-absorbing carbonaceous aerosols that significantly influence the global and regional radiation balance, as well as air quality. Guangxi Zhuang Autonomous Region, as a primarily agricultural province of China and neighbouring Southeast Asia, is subjected to both local emissions and pollution transport from Southeast Asian biomass burning. To investigate the light absorption properties and source contributions of BC and BrC in this region, observations from a 7-wavelength Aethalometer are employed to estimate the light absorption properties of BC and BrC over the period from March to December 2020 in Nanning, China. This study focuses on analysing the absorption contributions of BC and BrC to the total absorption of carbonaceous aerosols, identifying their emission sources, and exploring the impact of long-range transport of biomass burning (BB) from Southeast Asia on BC and BrC based on backward trajectory and weighted concentration-weighted trajectories (WCWT) model. Our results show that the absorption Ångström exponent (AAE) of light-absorbing carbonaceous aerosols varies from 0.54 to 2.08, reflecting the presence of different absorbing aerosol sources with specific optical properties. The average absorption coefficients of BC and BrC at 370 nm, denoted as babs,BC(370) and babs,BrC(370), are 42.25 Mm−1 and 9.63 Mm−1, respectively, with the highest value observed in winter. The average absorption of BrC contributes 19% to the total absorption from light-absorbing carbonaceous aerosols, and this contribution decreases for high babs,BrC(370) values, with the highest value in summer at 20%. For the BC source apportionment using a site-specific AAE, fossil fuel combustion (FF) contributes 57%, with its highest proportion in summer (62%). Meanwhile, biomass burning (BB) accounts for 43%, with the greatest contribution in winter (58%). These results highlight the considerable role of BB in Guangxi. In terms of the BrC sources, secondary BrC (BrCsec) is responsible for 32% of the total light absorption of BrC at 370 nm, and is particularly characterized by a much higher level of 35% at night, meaning the dominant role of BrCsec in Nanning. The relative contribution of babs,BrC,sec(370) increases with a higher contribution of babs,BrC(370) to aerosol absorption. Compared with the BrCsec, primary BrC values are higher in spring and winter, due to the increased emissions from biomass burning. Based on the analysis of backward trajectory and WCWT, the increase in BC and BrC during March and April is mainly influenced by the long-range transport of BB from Southeast Asian countries, e.g., Laos and Thailand. Overall, the contributions of BB and FF emissions to BC are comparable in Guangxi, while BrC mainly formed from primary sources is significantly impacted by both local emissions and the long-range transport of BB. Studying the optical characteristics and emission sources in this region can promote the understanding of the radiative effect of light-absorbing carbonaceous aerosols under the joint contributions from biomass burning and industrial emissions.

Structural characteristics properties of sugarcane bagasse and its sound absorption as composites

Noise pollution is one of the serious environmental pollutions. In recent years, the preparation of sound absorption composites using natural fibers as reinforcement material has attracted much attention. Sugarcane bagasse is a by-product of sugarcane. In order to improve the utilization rate of sugarcane bagasse, enrich and expand the application field of its renewable resources, sugarcane bagasse as a reinforcement material, and polycaprolactone as a matrix material are used to prepare sugarcane bagasse/polycaprolactone sound absorption composites by hot press molding technology to analyze the sound absorption performance. The sound absorption mechanism of the sugarcane bagasse sound absorption composites is revealed. First, the structural characteristics of sugarcane bagasse were characterized, and the relationship between its structure and sound absorption performance was analyzed. Second, the effects of sugarcane bagasse length, mass fraction, hot pressing pressure, hot pressing time, and hot pressing temperature on the sound absorption performance were investigated by one-factor analysis. The results show that when the length of sugarcane bagasse was 1.0 mm, the mass fraction was 35%, the hot pressing pressure was 12 MPa, the hot pressing time was 20 min, and the hot pressing temperature was 130°C, the average sound absorption coefficient was 0.38, the noise reduction coefficient was 0.31, and the maximal sound absorption coefficient was 0.80. This study provides an experimental and theoretical basis for the research and development of sound absorption composites made of sugarcane bagasse, and provides a new solution for the recycling of sugarcane bagasse.

Constructing graphene-based aerogel with bi-continuous interpenetrating networks as a multi-functional microwave absorber

The design of three-dimensional networks in graphene-based aerogels is an effective strategy for fabricating a lightweight microwave absorber with strong absorption and broad effective bandwidth. Herein, a multi-functional aerogel with bi-continuous interpenetrating networks comprised of reduced graphene oxide (RGO) and cellulose nanofiber (CNF) was developed via an “ice-dissolving” (freezing and solvent exchange) and subsequent annealing strategy. Different from the conventional step-by-step construction of two independent networks, the bi-continuous interpenetrating networks were simultaneously built in a one-step freezing process. Notably, the network structure of the aerogel can be tuned by adjusting the concentration of CNF (CCNF) during the freezing stage. When the CCNF increased from 2 to 8 wt%, the network structure transitioned from a single three-dimensional RGO skeleton to ordered bi-continuous interpenetrating networks, and then to a disordered CNF/RGO mixed network. The mutual contributions from the RGO skeleton and CNF network endowed the aerogel (14.96 mg cm−3) with improved conduct loss and optimized characteristic impedance, leading to an excellent microwave absorption capacity. Consequently, the aerogel achieved a maximum reflection loss of −68.3 dB and an effective bandwidth of 6.9 GHz, respectively. Moreover, the unique network structure also enabled the sample to have superior noise absorbing performance (normalized absorption coefficient of 0.894 in 250–6300 Hz) and good structural stability. This strategy provides a facile avenue for constructing multi-functional aerogels with bi-continuous interpenetrating networks for both microwave absorption and noise absorption applications.

Laser additive manufacturing of hierarchical multifunctional chiral metamaterial with distinguished damage-resistance and low-frequency broadband sound-absorption capabilities

Traditional materials or advanced artificially engineered metamaterials are incapable of effectively addressing the simultaneous challenges of impact energy hazards and low-frequency noise. There is an urgent need for multifunctional materials that can address this multi-physics field coupling problem. Herein, a hierarchical multifunctional chiral metamaterial (HMCM) is proposed for damage-resistance and low-frequency broadband sound-absorption capabilities fabricated by means of laser powder bed fusion technology. Cavity resonators with internally extended tubes with hierarchical chiral configuration were selected as primary units. The damage-resistance performance of the HMCM was investigated systematically through experimental, numerical, and theoretical methods. Crashworthiness design and optimization on the multifunctional chiral metamaterial were implemented to explore the effect of geometrical parameters including distance ratio and wall thickness distribution on crushing resistance. It was determined that specific configurations in these parameters significantly enhance mechanism for dissipating energy of the HMCM. Furthermore, the designed metamaterial has been experimentally, numerically, and theoretically proven to possess quasi-perfect broadband sound absorption in the target range of 425 Hz to 553 Hz with an average sound absorption coefficient exceeding 0.9. Overall, this work not only offers a promising solution for designing multifunctional metamaterials but also highlights the potential of additive manufacturing techniques in the development of such sophisticated materials.