Building a metamaterial slab with gosper curve

Sound attenuation in triple panel using locally resonant sonic crystal and porous material

The present study investigates the impact of sound transmission loss of vertical noise barriers for high-speed railways on insertion loss at various speed grades and heights. The findings reveal an initial increase in insertion loss followed by a plateau as sound transmission loss improves. A threshold value exists for weighted sound transmission loss, beyond which the insertion loss remains relatively constant. This threshold referred to as the minimum weighted sound transmission loss decreases with increasing train speeds and increases with higher noise barrier heights. The variation in insertion loss was calculated for noise barriers at heights of 2m and 3m under different sound transmission loss conditions, using measured sound source data corresponding to train speeds of 150km/h, 200km/h, 250km/h, 300km/h, and 350km/h. By polynomial fitting, at a train speed of 400 km/h, the minimum weighted sound transmission loss for 2m and 3m high noise barriers are determined to be 20dB and 21dB respectively.

Acoustic panels are widely used for sound insulation in various applications. Sound transmission loss (STL) through the panel is due to a change in acoustic impedance as sound travels from one medium to another. In double panels, STL further increases due to multiple reflections in air cavity. Recently the sonic crystal (SC) has emerged as an interesting research topic which provides sound attenuation in specific frequency bands. The present paper aims at combining the property of a SC with the acoustic panel for enhancing the STL through the double panel. Initially, an analytical method is developed to obtain the STL through the double panel. Further finite element (FE) simulations are performed using acoustic structure interaction to obtain the STL through the double panel which is in good agreement with the analytical predictions. The SC, along with the double panel, is analyzed using the FE method for the combined effect of both sound attenuators. Further, glass wool is considered as a filler material between the double panel as well as between the double panel and the SC assembly. It is found that the combined structure of the double panel and the SC with glass wool as filler gives the best STL for all different cases for the same external dimensions.

The present study focuses on a silencer built within the thick portion of a door edge and reports on the results of evaluating silencers by determining sound transmission loss via theoretical analysis and experiments on three types of silencers. The theoretical analysis involved determining the calculated values of sound transmission loss obtained using the transfer matrix method. The change in cross-sectional shape was analyzed by elemental division of the transfer matrix. Using the above, simulations were performed with respect to the optimum shape of the silencer. These theoretical analyses were then compared with the measurement results. Furthermore, the study includes the results of an experiment that attempted to restrain the dip in sound transmission loss by adding a non-woven fabric to the opening of the silencer. In a side branch silencer with an increasing shape wherein the longitudinal cross-section is a linear or an exponential function, the peak of the transmission loss was shifted to the lower frequency side when compared with that in the case of a rectangular side branch silencer. Furthermore, in comparisons between the two, the sound attenuation peak frequency was lower in the case of the exponential shape. The resonance of the side branch was suppressed by adding a non-woven fabric to the opening of the side branch silencer. As a result, the peak and dip of sound attenuation were alleviated, and the sound attenuation characteristics could be adjusted.

Simplified method for calculating airborne sound transmission through composite barriers

Small perforations in corrugated sandwich panel significantly enhance low frequency sound absorption and transmission loss

The authors present numerical results for a systematic parametric study of the effect of honeycomb core geometry on the sound transmission and vibration properties of in-plane loaded honeycomb core sandwich panels using structural acoustic finite element analysis (FEA). Honeycomb cellular structures offer many distinct advantages over homogenous materials because their effective material properties depend on both their constituent material properties and their geometric cell configuration. From these structures, a wide range of targeted effective material properties can be achieved thus supporting forward design-by-tailoring honeycomb cellular structures for specific applications. One area that has not been fully explored is the set of acoustic properties of honeycomb and understanding of how designers can effectively tune designs in different frequency ranges. One such example is the insulation of target sound frequencies to prevent sound transmission through a panel. This work explored the effect of geometry of in-plane honeycomb cores in sandwich panels on the acoustic properties the panel. The two acoustic responses of interest are the general level of sound transmission loss (STL) of the panel and the location of the resonance frequencies that exhibit high levels of sound transmission, or low sound pressure transmission loss. Constant mass honeycomb core models were studied with internal cell angles ranging in increments from −45 deg to +45 deg. Effective honeycomb moduli based on static analysis of honeycomb unit cells are calculated and correlated to the shift in resonance frequencies for the different geometries, with all panels having the same total mass. This helps explain the direction of resonance frequency shift found in the panel natural frequency solutions. Results show an interesting trend of the first resonance frequencies in relation to effective structural properties. Honeycomb geometries with smaller core internal cell angles, under constant mass constraints, shifted natural frequencies lower, and had more resonances in the 1–1000 Hz range, but exhibited a higher sound pressure transmission loss between resonant frequencies.

In this paper, we propose a louver with a simple structure and a high aperture ratio. A louver element with a sound attenuating structure composed of layered two flat rectangular tubes, each of which is wedge-shaped with thickness decreasing toward the closed end, was constructed and experimentally and theoretically analyzed. Samples having more basic structures were also constructed and compared. In the theoretical analysis, the sound attenuation characteristics of a louver element were clarified considering sound attenuation in the clearance between two planes, as is typically observed in the flat rectangular tubes furnished in the louver element. To consider the sound attenuation due to the viscosity of the air in the rectangular tube, the propagation constant and characteristic acoustic impedance were derived using the Navier-Stokes equations, etc. Further, the sound transmission loss was calculated by the transfer matrix method. The tendency of the theoretical values in consideration of the attenuation of sound wave roughly agreed with the experimental values. Note that the attenuation of sound wave is evident in a thin or wedge-shaped tube and has to be considered in the theoretical analysis. The number of flat rectangular tubes was doubled without increasing the thickness of a louver element. The structure is useful as a louver slat because sound attenuation is achieved in a wide frequency range while maintaining a high aperture ratio.

Vibro-acoustic response and sound transmission loss characteristics of truss core sandwich panel filled with foam

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.

Experimental study to measure the sound transmission loss of natural fibers at tonal excitations

Origami-based acoustic metamaterial for tunable and broadband sound attenuation

The characteristics of sound transmission loss of V-type noise barriers for reduction of wind load under the influence of multiple parameters is numerically investigated in this work. The results show that sound-absorbing materials and the heights of ventilation channels are the most important factors affecting sound insulation property of V-type noise barriers. The increase of the airflow resistivity of sound-absorbing materials will increase sound transmission loss in the high frequency band of noise barriers. When the airflow resistivity is increased from 1000Pa*s/m2 to 15000 Pa*s/m2, weighted sound transmission loss is increased by 7dB. The weighted sound transmission loss is inversely proportional to the height of ventilation channels. The height of ventilation channels is reduced from 51mm to 6mm, and the weighted sound transmission loss is increased by 5.7dB.

Sound transmission loss and bending properties of sandwich structures based on triply periodic minimal surfaces

This study focuses on the discussion of the correlation of acoustic and dynamic characteristics of hybrid panels, namely Micro-perforated Panel (MPP) and Honeycomb (HC) structures. Acoustic characteristics in experimental studies are obtained by the sound absorption coefficient and Sound Transmission Loss. Meanwhile, the dynamic characteristics are obtained by the mode and frequency response analysis of numerical simulation methods. The results of these two characteristics serve as a benchmark for the development of experimental data studies/analysis. The purpose of this study is to obtain dynamic characteristics using mode and frequency response analysis through the finite element method. The development of this experimental study/analysis data is to overcome the drawbacks of experimental testing. The weakness obtained from experimental studies is that the stages are complicated and require a very large amount of money. The method in this study was carried out by numerical simulation using the finite element method using the Ansys 2019 R3 program. The results of this study obtained dynamic characteristics from the development of experimental study analysis methods using numerical simulations through the finite element method. Numerical simulation on the hybrid panel provides efficiency at the experimental testing stage. The results of the mode and frequency response analysis obtained by numerical simulation methods have similarities in the frequency range of high and low frequency values of sound absorption coefficient and soundtransmission loss.