Transmission Loss Performance Research Articles

Sound transmission loss and energy absorbing performance of stiffened doubly-curved shells with corrugated-honeycomb hybrid cores

Compared to traditional lightweight corrugation and cellular cores, the novel cellular cores auxetic metamaterials with negative and zero Poisson's ratios possess distinctive mechanical deformation traits, making them suitable for modeling lightweight sandwich structures. Therefore, the concept of combining auxetic metamaterial cellular with folded corrugation is proposed to construct a new type of corrugated honeycomb hybrid cores for studying the sound insulation and energy absorption characteristics of the stiffened sandwich doubly-curved shells, wherein the honeycomb core possesses a full range of Poisson's ratio characteristic and is composed of cellular cores exhibiting positive, negative, and zero Poisson's ratios (PPR, NPR, and ZPR). The Hamilton's principle is hired to derive the governing equations and considers fluid-structure coupling by applying normal velocities continuity conditions at the fluid-structure interface, which is further analytically solved using Navier's techniques, and the sound transmission loss (STL) is described analytically. The accuracy of these results is validated through comparisons with both experimental measurements conducted in an impedance tube and simulated outcomes generated by the COMSOL commercial software. The properties of stiffened sandwich doubly-curved shells with corrugated honeycomb hybrid cores are meticulously evaluated and compared, and the results show that the hybrid cellular core type significantly impacts the STL, wherein the average STL of the corrugation ZPR cellular hybrid cores stands at 42.06 dB within the broad low-frequency range of 380–2422 Hz, which has increased by 9.11% and 8.31% compared to the values of the corrugation NPR and traditional PPR cellular hybrid cores, the specific energy absorption (SEA) of the corrugation ZPR cellular hybrid cores is 13.06 kJ/m3, which has increased by 16.19% and 18.08% compared with the corrugation NPR and PPR cellular hybrid cores, respectively, indicating that the corrugation ZPR cellular hybrid cores have better sound insulation and energy absorption characteristics than the corrugation NPR and PPR cellular hybrid cores.

Sound transmission loss and energy absorbing performance of stiffened doubly-curved shells with corrugated-honeycomb hybrid cores

Compared to traditional lightweight corrugation and cellular cores, the novel cellular cores auxetic metamaterials with negative and zero Poisson's ratios possess distinctive mechanical deformation traits, making them suitable for modeling lightweight sandwich structures. Therefore, the concept of combining auxetic metamaterial cellular with folded corrugation is proposed to construct a new type of corrugated honeycomb hybrid cores for studying the sound insulation and energy absorption characteristics of the stiffened sandwich doubly-curved shells, wherein the honeycomb core possesses a full range of Poisson's ratio characteristic and is composed of cellular cores exhibiting positive, negative, and zero Poisson's ratios (PPR, NPR, and ZPR). The Hamilton's principle is hired to derive the governing equations and considers fluid-structure coupling by applying normal velocities continuity conditions at the fluid-structure interface, which is further analytically solved using Navier’s techniques, and the sound transmission loss (STL) is described analytically. The accuracy of these results is validated through comparisons with both experimental measurements conducted in an impedance tube and simulated outcomes generated by the COMSOL commercial software. The properties of stiffened sandwich doubly-curved shells with corrugated honeycomb hybrid cores are meticulously evaluated and compared, and the results show that the hybrid cellular core type significantly impacts the STL, wherein the average STL of the corrugation ZPR cellular hybrid cores stands at 42.06dB within the broad low-frequency range of 380-2422 Hz, which has increased by 9.11% and 8.31% compared to the values of the corrugation NPR and traditional PPR cellular hybrid cores, the specific energy absorption (SEA) of the corrugation ZPR cellular hybrid cores is 13.06 kJ/m3, which has increased by 16.19% and 18.08% compared with the corrugation NPR and PPR cellular hybrid cores, respectively, indicating that the corrugation ZPR cellular hybrid cores have better sound insulation and energy absorption characteristics than the corrugation NPR and PPR cellular hybrid cores.

Effective medium modelling of real-world multi-modal metamaterial panels achieving broadband vibroacoustic attenuation

Locally resonant metamaterials can achieve unprecedented vibroacoustic performance by subwavelength distributions of small mechanical resonators on a host structure. Substantial broadband vibroacoustic attenuation can be achieved by multi-modal metamaterial panels, which exploit multiple translational and rotational resonator modes to manipulate the overall bending wave propagation. However, the multi-modal metamaterial concept has been studied only for idealized conditions, such as infinite panel extent and uniformly distributed resonators, limiting practical applicability. Efficient methodologies are still needed to study the behaviour of multi-modal metamaterial panels in real-world scenarios. In this work, this challenge is tackled by developing generalized effective medium models, i.e., homogenized material representations through equivalent macro-scale properties, tailored for finite-sized multi-modal metamaterial panels. For the special but important case of simply supported rectangular panels with uniformly distributed resonators, a dedicated analytical effective medium model is developed. For arbitrary boundary conditions and resonator distributions, effective medium finite elements are formulated. The diffuse sound transmission loss (STL) performance is efficiently predicted through Deterministic - Statistical Energy Analysis (Det-SEA), by coupling the effective medium model of the finite-sized metamaterial panel with a diffuse model of the surrounding sound fields. The proposed prediction approaches are validated against detailed FEM modelling, demonstrating that significant computational reductions are achieved while preserving accuracy. Results showcase that multi-modal metamaterial panels maintain broadband vibracoustic attenuation also when subjected to boundary effects and under partial metamaterial treatment.

Numerical investigation on acoustic damping characteristics of dual Helmholtz resonators in presence of a grazing flow

In this study, the acoustic damping performances of the dual Helmholtz resonators were numerically evaluated using a 3D model. The grazing flow passes tangentially through the resonator neck, with a Mach number range of 0 ≤ Ma ≤ 0.1. The numerical model operates by solving the linearized Navier–Stokes equations. The current model is validated through a comparison with experimental data. The model is then utilized to explore the effects of the dual Helmholtz resonators on acoustic transmission loss performance in the presence of a grazing flow. Three key parameters are examined: 1) different implementation configurations of the dual Helmholtz resonators (including Models (b), (c), and (d)), 2) the mean temperature of the grazing flow, and 3) the axial distance between the dual Helmholtz resonators. For comparison, the acoustic damping performance of these dual Helmholtz resonators is compared to the single Helmholtz resonator case (Model (a)). The maximum transmission loss of Model (c) is significantly higher, recording values of 91%, 89.4%, and 92.5% than those observed for Model (a) at Ma = 0, Ma = 0.05, and Ma = 0.1, respectively. It is observed that the dual Helmholtz resonators dramatically increase the transmission loss. Model (c) is demonstrated to be associated with the most significant damping on the acoustic plane waves in comparison with that of Model (a). Additionally, the maximum transmission loss of Model (c) is 23.23 dB, 30.32 dB, and 34.58 dB at mean temperatures of 300 K, 600 K, and 900 K, respectively. Therefore, increasing the mean temperature is shown to be beneficial to enhance transmission losses in the presence of the grazing flow. Furthermore, under Ma = 0.1, the resonant frequency of Model (c) is 127 Hz, 152 Hz, and 172 Hz, corresponding to mean temperatures of 300 K, 600 K, and 900 K. It can be concluded that increasing the temperature has the effect of broadening the resonant frequency, especially at a high grazing flow Mach number. However, increasing the mean temperature results in a reduction of transmission loss in the absence of the grazing flow. In the case of Model (c), a 32 cm axial distance results in a 5.6% larger transmission loss at Ma = 0 and a 26.4% larger loss at Ma = 0.1 compared to a 16 cm axial distance. This indicates that increasing the axial distance between the dual Helmholtz resonators improves transmission loss.

Improving transmission loss performance of aluminum extrusion in railway vehicles using lightweight material

This study developed a method for improving the transmission loss performance of aluminum extrusion by reinforcing the inner space of the extruded material with a lightweight material, such as acrylic plastic. First, the dynamic characteristics of the aluminum extrusion were analyzed, and the characteristics of noise transmission were evaluated through an acoustic mode analysis of the air layer for the inner space of the extruded material. Furthermore, to improve the transmission loss performance of the aluminum extrusion, methods were developed for increasing the vibration stiffness and altering the acoustic mode of the inner space. Additionally, a simulation analysis of the vibration mode and a response analysis based on the excitation of sound were performed to validate the proposed model; the effectiveness of the model for noise and vibration reduction was compared with that of the existing model. This analysis was conducted using models wherein the acrylic plastic was partially and totally inserted into the interior space of aluminum extrusion. The results indicated that the noise performance of the short reinforcement model with the partially inserted acrylic plastic was improved by 3 dB and that of the long reinforcement model with the totally inserted acrylic plastic was degraded by > 4 dB compared with the existing aluminum panel.

Predicting trends in the sound transmission loss performance of steel-framed wall partitions using yield strength

Mechanical properties of beams and panels are commonly used for calculating structural loads and deformation under stress and strain. Stress and strain analysis for steel beams may result in the determination of yield strength, a commonly reported steel framing property in the steel industry. This characteristic of steel framing is rarely, however, linked to trends in sound transmission loss (STL). This paper provides an analytical basis for linking the yield strength of steel framing to the STL of vertical double-leaf partitions with a focus on acoustic impedance of the beam. Experimental data are shown that validates this analytical basis. These results may be used as evidence for including the reporting of the yield strength in standardized test reports.

The integration of metamaterials into building elements

The building industry continues to rely on homogeneous materials for acoustic insulation despite the progress of research into acoustic metamaterials. With the inevitable densification of housing, the severity of noise pollution within residential living environments is escalating. While the insulation of high-frequency audible sound through building elements is often relatively good between 1 and 5 kHz, the overall acoustic transmission loss performance is often significantly limited by two specific frequency regions. The mass air mass resonance band, and the coincidence band. We present the results of an investigation into the use of metastructures and metasurfaces to improve transmission loss in these frequency regions with a focus on scalable implementation. These metastructures are metamaterial systems constructed from impedance change elements, surface variations and vibroacoustic resonant elements. The performance of selected systems from this research are presented. Experimental and modeling results are in good qualitative agreement and promising diffuse-field testing results indicate significant attenuation within the targeted band regions. The merits of each technique are analysed, and results indicate which methods are most effective at either mitigating or shifting the regions of poor transmission loss outside of the most important part of the audible frequency region.

Examination of acoustic properties of polymer-coated nonwoven textile samples

In this study, different types of polymeric layers were coated in different weights (g/m2) on nonwoven fabrics by extrusion process and then, sound absorption and transmission loss properties of each sample were examined. Nonwoven fabrics were produced from polyester (PET) fiber, formed by the carding process and bonded by the needle punching process. These samples were tested between 50-6000 Hz frequency range to reveal the effect of polymer layer type and weight coated on nonwoven fabrics on the sound absorption and transmission loss performance at the low, medium, and high-frequency values. Polymer layers were coated with the weight of 400 gsm and 800 gsm. Nonwoven fabric samples coated with polyethylene or polypropylene layers and nonwoven fabric samples without polymeric coating were tested by using an impedance tube and compared in terms of sound absorption and transmission loss performance. In the test system, two sides of the samples were tested separately. It was seen that the sound absorption performance of the samples changed in case the sound wave was first incident to the polymeric layer or nonwoven layer.

Revealing the Sound Transmission Loss Capacities of Sandwich Metamaterials with Re-Entrant Negative Poisson's Ratio Configuration.

Due to the influence of mass law, traditional lightweight sandwich structures have struggled to surpass solid structures in sound insulation performance. To this end, we propose an acoustic metamaterial structure with a sandwich configuration based on the re-entrant negative Poisson's ratio (NPR) structure and systematically investigate its sound transmission loss (STL) performance under incident plane wave conditions. We used the acoustic impedance tube method to experimentally study the sound insulation performance of the re-entrant NPR sandwich structure under free boundary conditions, and then established an acoustic analysis simulation model based on COMSOL Multiphysics software, which verified that the results obtained by the experiment and the numerical simulation were in good agreement. The results show that the sandwich structure exhibits excellent sound transmission loss performance in the studied frequency range (250-4000 Hz), and the overall sound insulation performance exceeds the curve of the mass theorem, basically achieving more than 20 dB when the sandwich thickness is 2 cm. Finally, we conduct parametric studies to establish a correlation between the geometric design of NPR sandwich structures and their sound transmission loss performance. The research shows that the changes of the length of the ribs, the distance from the ribs to the center of the unit, and the length of the upper wall and the lower wall have a significant impact on the sound insulation performance of the re-entrant NPR sandwich structure, while the change of the wall thickness basically will not affect the sound insulation performance of the sandwich structure. This research can provide practical ideas for the engineering application of noise suppression designs of lightweight structures.

Transmission Loss Performance Analysis of Acoustic Coatings under Hydrostatic Pressure Considering Cavity Pressure

Transmission Loss Performance Analysis of Acoustic Coatings under Hydrostatic Pressure Considering Cavity Pressure

Vibroacoustic topology optimization for sound transmission minimization through sandwich structures

Recently, metamaterials, sandwich panels, and a combination of both have shown potential for creating lightweight, load-bearing structures with good noise and vibration suppression properties. However, designing these structures is difficult due to the complex vibroacoustic innate physics and the need to balance conflicting requirements. Structural optimization methods can help address this multi-functional, multi-physical design challenge. While much research has been conducted on optimizing the materials and sizes of plates and sandwich cores, the systematic topological design of fully coupled vibroacoustic cores has not yet been explored. To address this gap, this work presents a topology optimization framework for the vibroacoustic design of sandwich structure cores, with the goal of minimizing sound transmission while constraining volume and structural stiffness. The framework is used to conduct a systematic design analysis, focusing on the dynamic behavior of the optimized structures. The versatility of the methodology is demonstrated by analyzing different targeted frequency ranges, different angles of incidence and the trade-off between the acoustic and structural performance. The resulting designs are lightweight, load-bearing, and achieve high sound transmission loss performance, exceeding the mass law by 15–40 dB in targeted frequency ranges of 500Hz in the interval between 1000Hz and 3000Hz.

Magnetic field and thermal environment effects on sound transmission loss of double-walled cracked piezoelectric cylindrical nanoshells

Based on a non-local strain gradient theory (NSGT), this article analytically studies the sound transmission loss (STL) performance of a special type of double-walled partially cracked piezoelectric nanoshell structures of cylindrical shape undergoing initial electric potential and longitudinal magnetic field. The structure, which includes a specific number of axial and circumferential surface cracks, is struck by a plane wave in a thermal setting. Such cracks have minimal size compared to the nano-shell structure as a whole, minimizing the effects of curvature for this problem. The first-order shear deformation theory (FSDT) is utilized to explain the displacement components, and Hamilton’s concept is applied to obtain the coupled vibroacoustic equations that are used to generate the governing equations of the system for the two crack types, giving us an idea of the resulting structural stiffness in the presence of cracks using coefficients of crack compliance that are derived from the line spring model (LSM). The mechanical and acoustic properties are then checked to see their effect on the system response followed by a series of validation case studies. This evaluation also allows one to optimize a similar structure by selecting appropriate external parameters such as electric voltage, magnetic field intensity, different crack types, nonlocal and strain gradient parameters, variations of temperature, and incident angle of sound waves.

Sound insulation performance of curved sandwich structure combined with acoustic metamaterials

Sandwich structures are widely used in various fields. Curved sandwich structures have attracted the attention of researchers owing to their superior stiffness and strength. With the application of the structures in engineering, it is required that the structures can not only meet the needs of mechanical loads but also can cope with thermal, acoustic, optical, and electrical loads. Sound insulation is one of the most common problems in the fields of aerospace, transportation, and architecture, so it is imperative to research new structures with good mechanical and acoustic properties. In this paper, a composite structure which is coupled with curve shell sandwich structure and acoustic metamaterials is proposed to obtain good mechanical and acoustic properties. Based on the harmonic expansion method and principle of virtual work, the theoretical model is established and the sound transmission loss (STL) performance is studied. Then, the effects of the geometry of the structure and material parameters on the STL of the structure are discussed.

Sound transmission loss of meta-acoustic barriers with anomalous effective-mass

Meta-acoustic barriers (MABs) that are inspired by acoustic metamaterials (AM) offer opportunities to defy mass law-driven sound transmission loss (TL) performance that is characteristic of conventional acoustic barriers. In this analytical parametric study, the TL behavior of MABs that incorporate various local oscillator configurations are analyzed using an effective-mass modeling approach. Resonant, damped and inertant local oscillator configurations and combinations thereof that result in negative and complex effective-mass for the meta-acoustic barrier are considered. The influence of the local configuration’s orientation, oblique incidence and the presence of multiple oscillator types are examined using nondimensionalized metrics and compared to the performance of static mass and volume-equivalent limp mass and double wall barriers. It is shown that due to their anomalous effective-mass, such barriers display tunable TL bandwidths exceeding that of mass-equivalent conventional barriers indicating new device implications. The effective-mass modeling approach can easily be adapted to account for the presence of different dynamic features within various types of inclusions considered and is thus an efficient tool to evaluate meta-acoustic barrier designs. Inasmuch as these meta-acoustic barrier structures can be realized using recent advances in additive and hybrid manufacturing techniques, opportunities exist to create lightweight barriers for tonal and broadband acoustic applications.

Sound transmission loss of an automotive floor panel section with cross members

Analyzing sound transmission loss (STL) of vehicle body panels is essential in assessing the noise transmitted into a vehicle. For a long time, floor panels have been assumed to follow the mass law performance with the effects of some cross members being ignored. In this paper, a typical automotive floor panel section with cross members is designed to understand how the sound transmission loss performance is affected by cross members. A hybrid analysis method was employed, in which the structure surface together with the 1-D acoustic space inside the cross members are represented by the boundary element modeling and finite element modeling respectively. Through various iterations, it has been shown that the cross member could affect panel STL significantly due to some lower order modes of the panel that are induced by the cross members and resonated acoustic modes inside 1-D acoustic spaces. Results are verified by in-situ STL measurements on a real vehicle. Finally, a sensitivity analysis was conducted based on the selected model to understand the contribution of each design variable to STL performance.

Sound Insulation Properties of Malaysian Biomass Waste Fibre UF Composites

Natural fibrehas a good capacity as acoustic insulation materials because of its characteristics, and therefore it is widely used in many applications. This research aims to explore biomass waste from the palm oil mill and coconut production as insulation materials. Fibre wastes used for this study included the empty fruit bunch (EFB), mesocarp fibre (MF) and coconut coir fibre (CF), which were treated using sodium hydroxide (NaOH) to eliminate excess oil and fibre surface impurities. The effect of the treatment was also considered to observe the effect towards the sound transmission loss (STL) performance of natural fibre. Three varying concentrations of NaOH (1%, 2% and 3%) were used to treat the fibre. The STL of EFB, MF and CF were measured using the impedance tube method with four microphones at frequencies from 160 Hz to 5,000 Hz. Pretreatment on EFB, MF and CF showed a decrement on the fibre diameter and changes on the fibre surface morphologies after examining using the scanning electron microscopy (SEM) analysis. The results showed that EFB, MF and CF treated fibre had higher STL performances than untreated fibre. The STL performances were increased by increasing the tested frequency from 160 Hz to 5,000 Hz. Changes in fibre morphology following the fibre pretreatment affected the STL performances of EFB, MF and CF. Additionally, treated MF using 2% of NaOH concentrations obtained the highest STL amongst all the test samples.

Revealing the sound insulation capacities of TPMS sandwich panels

Triply periodic minimal surface (TPMS) sandwich panels have superior characteristics, including lightweight and extraordinary mechanical properties, so that they are widely applied in diverse industrial and engineering applications. However, their sound suppression potential is far away understood. The present study investigates P- and G-type TPMS sandwich panels’ sound insulation performances with two different boundary conditions through a method combining theoretical, numerical, and experimental studies. First, we use Reissner's theory for sandwich panels to construct the vibration governing equation for the four-sided simply supported TPMS sandwich panel. By introducing sound pressure as double Fourier series into the vibro-acoustic governing equation, we derive the theoretical solution for the sound transmission loss (STL) performance. Second, we employ the sound impedance tube method to experimentally investigate the STL performance of TPMS sandwich panels with free boundary conditions. Then, we numerically study the TPMS sandwich panels’ suppression of sound capacity under both boundary conditions based on the direct acoustic vibration coupling theory. The results obtained by the theoretical, numerical and experimental methods are in good agreement and demonstrate that the TPMS sandwich panels’ relatively good sound suppression ability. Last, we conduct parametric studies to correlate the TPMS sandwich panel design to STL performance. Results show that the G-type TPMS sandwich panel is significantly superior to the P-type TPMS sandwich panel in terms of sound insulation capacity, which can achieve sound insulation of more than 20 dB at a broad frequency range, extending from 250 to 5000 Hz by an ultrathin thickness of about 2.4 cm, approximately 1/57λ for the lowest working frequency. Besides, the P-type TPMS sandwich panel's sound insulation capacity is more sensitive to the chief design parameters than the G-type one. Moreover, the constant (C) and the lattice constant (T) have the least and the most considerate influence on the STL property for both the P- and G-type TPMS sandwich panels. The research findings reported in this study can provide practical ideas for lightweight structures’ noise suppression design.

Ultralow loss hollow-core negative curvature fibers with nested elliptical antiresonance tubes.

Hollow-core negative curvature fibers can confine light within air core and have small nonlinearity and dispersion and high damage threshold, thereby attracting a great deal of interest in the field of hollow core fibers. However, reducing the loss of hollow-core negative curvature fibers is a serious problem. On this basis, three new types of fibers with different nested tube structures are proposed in the near-infrared spectral regions and compared in detail with a previously proposed hollow-core negative curvature fiber. We used finite-element method for numerical simulation studies of their transmission loss, bending loss, and single-mode performance, and then the transmission performance of various structural fibers is compared. We found that the nested elliptical antiresonant fiber 1 has better transmission performance than that of the three other types of fibers in the spectral range of 0.72-1.6 µm. Results show that the confinement loss of the LP01 mode is as low as 6.45×10-6 dB/km at λ = 1.06 µm. To the best of our knowledge, the record low level of confinement loss of hollow-core antiresonant fibers with nested tube structures was created. In addition, the nested elliptical antiresonant fiber 1 has better bending resistance, and its bending loss was below 2.99×10-2 dB/km at 5 cm bending radius.

Lightweight decorated membranes as an aesthetic solution for sound insulation panels

The need for energy-efficient vehicles and machines often drives performance design towards mass reduction, harming noise and vibration. Metamaterials are recently being studied as a possible solution to tackle this classical acoustic problem with reduced mass and promising attenuation, at least in narrow frequency bands. This work presents a solution based on variations of the so-called decorated membrane acoustic metamaterial (MAM) by assembling membranes of different shapes and sizes into a supercell. Tessellation concepts are used to ensure the geometric compatibility between each component and the periodicity of the supercell. Finite element models are derived to estimate unit cells’ sound transmission loss performance, experimentally validated on a transmission loss tube. Finally, full MAMs panels are conceived based on the validated models, showing an attenuation band formation around the membranes’ mass-dominated frequencies, thus realising a metamaterial that can outperform the mass law.

Parametric study of acoustic windows using a Green’s Function transfer matrix method

The Green’s function dependent transfer matrix method was applied to model sound transmission loss of a plenum window with a given configuration. The analytically calculated transmission loss reasonably followed that of the experimental data obtained from a previous study. The troughs in the calculated transmission loss spectra were found aligning well with the natural frequencies of the acoustic modes inside the plenum chamber. Vectorization of the calculations shows a 10-fold acceleration in computation, enabling desktop evaluation of transmission losses of plenum window systems with various configurations. Utilizing the analytical model, a parametric study of varying the three crucial design parameters, including the gap width, the overlapping length and the area ratio, between the outlet and inlet openings of the plenum window was conducted. The results demonstrated that increases in the latter two design parameters would improve the transmission loss performance of the plenum window at low frequencies, while increasing the gap width would compromise its transmission loss performance. Also, an increase in the overlapping length would widen the frequency range coverage with elevated transmission loss performance.