Transmission Loss Characteristics Research Articles

Experimental Evaluation of UWB Transmission Waveform with Body-Shadowing in an Indoor Environment

Wireless radio transmission performance in a realistic environment is a significant issue for designing and evaluating in short-range transmission technologies. Human body-shadowing is a significant propagation effect in an indoor wireless communication network. This paper presents the measurement model of impulse radio transmission with human body-shadowing in an indoor environment with IEEE 802.15.4 multipath impulse parameters. The impulse radio transfer function measurement model for the human body impulse radio transfer function with frequency band cover from 3 GHz to 11 GHz. The optimum system evaluation of impulse radio transmission is due to the human body and antennas. The characteristics of impulse radio transmission loss are using decay factor, log-normal standard, clusters, and ray arrival rate. The contributions of this research can be evaluating the human body impulse radio transfer function. And the design of the wireless radio system with the body shadowing effects and ambient environments.

ACTIVE NOISE CANCELATION IN AUTOMATIVE MUFFLER

In Day to day life our environment is getting more and more polluted and it is affected by noisier. Our people also adapted with this harsh environment so we need a new type of absorption material which is adaptive with this environment and which can be used in our vehicles to reduce the amount of noise produce by it. One of the type of abortive material is silicon carbide foam and sound absorption material. For reducing the amount of noise emitted by the exhaust of an internal combustion engine. This noise is reduced as the transmission loss (TL) when the muffler increases. Various types of components are present in the mufflers like foam, sound absorption materials, silicon carbide filter etc., which can reduce the noise. This paper explains about TL characteristics and also different methods.

Synchronized acoustic and atmospheric measurement system for characterization of atmospheric sound propagation

Abstract The aim of the paper is to describe a portable, modular, and scaleable system for measuring concurrent acoustic transmission loss and atmospheric characteristics. This system has been developed specifically to inform an effort to improve the ability to implement high fidelity numerical predictions of acoustic transmission loss, particularly in acoustically complex outdoor ranges, such as those that occur in coastal areas. Such a system has broad possible applicability in many outdoor atmospheric acoustic monitoring scenarios.

Vibro-acoustic modelling and analysis of segmented aluminum fuselage of transport aircraft with blankets

Vibroacoustic phenomenon is of prime importance in aviation industry as it is the driving cause for the annoyance to the passengers inside the aircraft. The great deal of effort has been put into studying the method of reducing high frequency noise inside the cabin of aircraft and the same has been achieved to acceptable level. In present work, vibroacoustic modeling and analysis of segmented aluminum fuselage with blankets made up of porous material was carried out. The surface model of segmented aluminum fuselage created using CATIA V5 R11 and meshing carried by HYPERMESH 10 followed by analysis in ABAQUS 6.10. The sound transmission loss analysis from exterior to interior cabin of segmented fuselage was carried out using finite element analysis for vibroacoustic phenomenon and it is compared with fuselage skin embedded with blanket. The sound transmission loss characteristics of various foams as blankets were studied and simulated of varius foams such as melamine, polyester, polyurethane and plastic foams. The results revealed that reduction of sound transmission loss in noise achieved at maximum excitation frequency of 159 Hz inside the fuselage cabin. The overall noise reduction inside the fuselage cabin for Melamine, polyester, polyurethane and plastic foams achieved to 10 dB, 11.5 dB, 8 dB and 14 dB respectively.

Optimization and analysis of the acoustic and resistance performance of the plenum chamber via sample entropy and large eddy simulation

The noise of the plenum chamber plays an important role in the acoustic performance evaluation of ventilation and air condition (VAC) systems. The large eddy simulation (LES) model and Ffowcs Williams & Hawkings (FW–H) equation were used to obtain the transient flow and aerodynamic noise, respectively, and a continuous and uniform impedance boundary condition was introduced to calculate the transmission loss (TL) of the perforated board plenum chamber. The aerodynamic noise, TL, resistance and velocity uniformity distribution characteristics of the plenum chamber were predicted by numerical simulation. A full-scale test bed was built to verify the flow field prediction results, and the acoustic prediction results were verified by analog experiments. In addition, based on the sample entropy theory, the pressure fluctuation on the inner surface of the plenum chamber was evaluated. The results show that the perforated board changes the vortex structure in the plenum chamber and reduces the local resistance and the pressure fluctuation on the inner surface wall, and the local resistance coefficient can be reduced by up to 34%. However, the coefficient of velocity uniformity in the plenum chamber decreases by 4%. Furthermore, the perforated board can significantly reduce the TL and peak sound pressure level (SPL) of the plenum chamber. At the receiving point, the overall SPL can be reduced by up to 2.5 dB.

Sound absorption and transmission loss characteristics of 3D printed bio-degradable material with graded spherical perforations

The influence of spherical bubble perforations and their grading on acoustic characteristics of a 3D printed bio-degradable material is investigated. Samples with spherical bubble perforations of different sizes are distributed either uniformly or graded across the specimen thickness. A sample having typical cylindrical perforations is also analyzed for comparative analysis. Sound absorption (SA) and sound transmission loss (STL) characteristics are estimated by the impedance tube method. The results reveal that the SA of all functionally graded (FG) perforations is higher at low frequencies. The SA and bandwidth are higher for a specimen with uniform, lower diameter bubbles at higher frequencies. The STL of FG perforations is highest among the specimens, and the difference increases significantly with frequency. The numerical and experimental results match a high degree of accuracy. FG perforations exhibited superior performance for both SA and STL. The proposed graded spherical porosity can be effectively utilized in soundproofing applications across building and transportation sectors.

Biomimetic Metamaterial Design Simulation and Evaluation for Building Acoustics by Impedance Measurements

Abstract This study investigates the potentials of acoustic metamaterial (AMM) applications in room and building acoustics by means of impedance tube experiments. With their extreme properties in either sound absorption or transmission loss, AMMs can perform better than traditional acoustic materials in buildings. Importantly, they are also more sustainable and hygienic than fibrous and porous materials. Depending on the matrix material used, AMMs can vary in transparency and color. Considering both their acoustic and aesthetic values, this study develops different types of metamaterial for possible uses as a partition wall, a surface layer, or a design element. The proposed metamaterials are primarily based on the exploration of ratios and forms from nature—the golden ratio, web-labyrinthine structures, genetic and neural systems such as deoxyribonucleic acid (DNA) molecules, and the synapse structures in the brain—reproduced on a subwavelength scale. These abstractions are then combined with the 3-D space coiling and 3-D labyrinth approaches of AMM design. Modules of the proposed AMMs are manufactured in a 3-D printer and tested in an impedance tube to estimate their normal incidence sound absorption coefficients and transmission loss characteristics. Based on the results obtained, the modules with the higher performances are used in the design of partition walls of varying heights. Two real-case architecture studios are simulated with and without the proposed AMM interventions over field test–tuned acoustical models of the studios to assess the effectiveness of such an approach in a possible acoustical design problem.

Influence of Boundary Conditions on the Accuracy of Pulsation Dampers Characteristics in Analytical Models

A pressure pulsation phenomenon in positive displacement machinery and resulting from that noise and vibration problems are well-known and still unsolved issues. The article concerns modeling pressure pulsation dampers used for fluid machinery, in particular in gas systems. The currently used mathematical models based on the plane wave theory are verified in the special laboratory conditions with no flow and no wave reflections at the system outlet. The use of a compressor as an excitation source significantly influences the characteristics of a damper installed in a system. In this study, a measurement of common type dampers transmission loss characteristics with the use of pressure transducers is proposed. The article discusses the influence of boundary conditions in analytical models based on the plane wave theory on the accuracy of dampers characteristics. Basing on the measurements results some improvements in the analytical model are proposed.

Control of sound transmission into a hybrid double-wall sandwich cylindrical shell

A 3D analytical model is formulated for diffuse sound field transmission control through a smart hybrid double concentric sandwich circular cylindrical shell structure in presence of external and internal air gap mean flows. The multi-input multi-output sliding mode control is applied to enhance the sound transmission loss characteristics via direct control action of a uniform force piezoelectric actuator layer along with semi-active variation of the stiffness/damping characteristics of the electrorheological fluid core layer incorporated in a non-collocated configuration within the external or internal shell structure. Extensive numerical simulations examine the uncontrolled/controlled diffuse field sound transmission loss spectrums in a broad frequency range for single-wall and hybrid double-wall sandwich shells at selected external and air gap Mach numbers. The proposed smart hybrid active/semi-active double-wall configuration is demonstrated to provide satisfactory overall acoustic insulation control performance with much lower operative energy requirements. Limiting cases are considered, and validity of the formulation is verified against the available data.

Nonlinear vibro-acoustic behavior of cylindrical shell under primary resonances

Nonlinear vibro-acoustic behavior of cylindrical shell excited by an oblique incident plane sound wave under primary resonances is analytically examined in this paper. Donnell’s nonlinear shallow shell theory is used to model the cylindrical shell. Coupled nonlinear differential equations of the system are analytically derived using Galerkin’s approach. The Multiple Scales Method is hence, employed to solve the corresponding nonlinear equations. Then, the effects of crucial design parameters including incident sound wave amplitude, damping ratio and thickness of the shell on the characteristics of the sound transmission loss are studied for different resonance cases. In addition, the effect of detuning parameter on the bifurcation and behavior of the limit cycle under primary resonance is examined. The results show that the detuning parameter is a bifurcation parameter and Neimark–Sacker, flip, and period-3 bifurcations occur when this parameter is varied. Also, according to the results, by getting away from the resonance frequencies, excitation level incorporates no significant effect on the transmission loss of the shell.

Acoustic behaviour of 3D printed bio-degradable micro-perforated panels with varying perforation cross-sections

Influence of perforations having arbitrarily varying cross-sections on the acoustic behaviour of 3D printed bio-degradable panels made of Poly Lactic Acid (PLA) is presented. Circular perforations having six different types of cross-sectional variations namely convergent-divergent (CD), divergent-convergent (DC), convergent (C), divergent (D) with two different perforation diameters are realized using Fused Filament Fabrication (FFF) based 3D printing. Sound absorption and transmission loss characteristics of these perforated panels are estimated through impedance tube technique. Results revealed that sound absorption of perforated panels with varying cross-section is better than uniform cross-sectional perforation for the given frequency range. Among, the different cross-sectional variations explored, comparable and lower transmission losses are exhibited by DC and D perforation pattern with respect to constant diameter 1 mm panel. The sound transmission results of all other five specimens were significantly higher than constant diameter 8 mm panel and observed to be increasing with frequency. Geometrical perforation variations are noted to be a very crucial factor in designing soundproof panels as presented in this work. The experimental results are compared with the numerical results and found to be in good agreement. Such numerical analysis paves the guidelines for designing optimum perforation geometries prior to the on-field testing of the functional prototypes.

Acoustic analysis of functionally graded porous graphene reinforced nanocomposite plates based on a simple quasi-3D HSDT

The sound radiation and sound transmission loss (STL) characteristics of functionally graded porous graphene reinforced nanocomposite plates (FG-PGRC) are investigated based on a simple quasi-3D high order shear deformation theory (HSDT) considering bending, shear and thickness stretching effects. The Gaussian Random Field scheme theory and Halpin-Tsai micromechanical model are used to estimate the material properties of FG-PGRC plates. The governing equations are derived based on Hamilton's principle. The sound radiation and sound transmission loss of FG-PGRC plates are obtained via modal theory and Rayleigh integral method. The effects of GPL and porosity distribution patterns, weight fraction of GPLs, porosity coefficient, thickness to width ratio, damping, temperature and incidence angle on acoustic properties of FG-PGRC plates are analyzed. Results indicate that the acoustic characteristics of FG-PGRC plates are significantly influenced by above parameters. Proper design of relevant parameters can improve the acoustic characteristics of FG-PGRC plates.

Vibro-acoustic characteristics of viscoelastic sandwich panel: effect of inherent damping

This paper presents the effect of the inherent material damping of aluminium facings and fibre reinforced polymer (FRP) core composite sandwich panel on vibro-acoustics and sound transmission loss characteristics. The modal strain energy method is used to calculate the modal damping ratio at each mode. To determine the forced vibration response, the harmonic analysis is carried out. From the kinematic continuity of velocity of the structure and the acoustic particle velocity at the surface, the sound power level is calculated. From the results, it is revealed that 19.89 dB of overall sound power level is reduced by including the modal damping ratio in the finite element modeling. Further, it is noticed that by replacing the aluminium plate to aluminium face sheet with an FRP core sandwich panel, the overall sound power level of 11.76 dB and 10.78 dB is reduced based on the same volume and weight analysis respectively.

Banana fibre-based structures for acoustic insulation and absorption

In this article, acoustic properties of fibrous structures made of banana fibres have been studied. Impedance tube method was used for the testing of acoustic barrier properties. An attempt to counter low-frequency noise as well as enhancing transmission loss characteristics of fibrous structures was carried out. The effect of different parameters and arrangement of structures with respect to sound source on sound absorption as well as sound insulation of these structures has been reported. A unique structure has been developed with varying compactness throughout its thickness, and it was observed that the areal density of samples, compactness of structure and arrangement of structures can be utilised to customise its sound barrier and absorption behaviour. Maximum noise reduction coefficient of 0.78 and transmission loss up to 23 dB was observed for samples with gradient in compactness. Acoustic performance of the structure developed as a part of this research is at par or better than acoustic materials reported in literature and other commercial products.

Sound transmission through truncated conical shells

A theoretical model is presented to investigate the sound transmission through a thin-walled truncated circular conical shell excited by an oblique incident plane sound wave, which impinges on the outer surface of the shell. Love’s theory is used to implement the governing equations of the shell motion, and a convergent power series solution is applied to obtain the exact dynamic response of the shell. In order to calculate the acoustic pressure loadings acting on the shell surfaces, the shell is divided into several narrow segments which can be considered to be locally cylindrical. At first, the model predictions are compared with their experimental and analytical counterparts reported in the literature. Then, the effects of crucial design parameters including different boundary conditions at the ends of the shell, cone angle, incident sound wave angle, length, radius, thickness and material properties of the shell, and the material properties of the fluid media are studied on the characteristics of the sound transmission loss. The proposed model can provide an effective tool in the acoustic design stage of the truncated circular conical shells.

Study on the Analyses of Transmission Loss and Phase Characteristics for High-Speed Differential Transmission Lines with the Copper Surface Roughness Parameter

Study on the Analyses of Transmission Loss and Phase Characteristics for High-Speed Differential Transmission Lines with the Copper Surface Roughness Parameter

Sound transmission loss behavior of sandwich panel with different truss cores under external mean airflow

This paper presents an analytical study on the sound transmission loss characteristics of sandwich plate with different truss cores under external mean airflow. Three types of truss cores are considered, which include pyramidal core, tetrahedral core and 3D-kagome core. The sandwich plate is immersed in a mean airflow of velocity tangential to the acoustically deformed boundary and it is impinged by a plane sound wave in the incident acoustic field. By applying velocity continuity condition at fluid–structure interfaces, the coupling of fluid–structure interaction is described analytically. The validity and feasibility of the proposed theoretical model are verified by comparisons with numerical simulation results calculated by commercial finite element software (LMS Virtual.Lab). Based on the developed theoretical model, the influences of the truss core radius and height, different truss core types, external mean flow and material combination types on sound transmission loss are subsequently presented.

Effects of Chamber Perforations, Inlet and Outlet Pipe Diameter Variations on Transmission Loss Characteristics of a Muffler Using Comsol Multiphysics

Confronted with noise disturbance during transmission of vehicle exhaust air, several mufflers have been designed to control the noise and improve the transmission characteristics. In order to optimize the noise control and attenuation quality, the internal geometry, inlet and outlet pipe diameters of a designed muffler were varied and the performance evaluated using finite element method (FEM). Furthermore, 2mm diameter equal circular perforations were introduced in the resonator chamber to verify the effect on the transmission loss characteristics. The results show that the performance of the muffler with inlet pipe diameter variation is significantly better (68dB) than the standard muffler (55dB) in controlling and reducing acoustic wave propagation within the same frequency range of (200~580Hz). The performance improved further to 70 dB by the introduction of circular perforations in resonator chamber. However, with the variation in the outlet diameter increase the performance of the muffler was 55dB but within a higher frequency range of 220~680Hz which is not reliable for acoustic wave propagation control. The average transmission loss performance of the designed mufflers were 48.62, 47.77, 39.01 and 37.77dB for the resonator chamber perforation, inlet pipe diameter increase, outlet pipe diameter increase and standard muffler respectively. Therefore, the designed muffler with resonator chamber perforations is the best for optimal acoustic wave control.

Effects of Microcavity Local Resonators on the Bandgap Characteristics of a Two-Dimensional Phononic Crystal Structure

The emergence of acoustic metamaterials generated a lot of attention in the study of low-frequency vibration, noise control and reduction in engineering applications. As a result, the elastic wave bandgap characteristics of a two-dimensional microcavity local resonator structure for two soft rubber materials was investigated using finite element methods (FEM). The transmission spectrum of the displacement eigenmodes of the bandgap edges relating to the lowest bandgap was calculated. The results showed that the phononic crystal structure without a microcavity local resonator plate has bandgap characteristics of elastic wave propagation in the high-frequency range between 2200~2400Hz. However, with the introduction of microcavity resonator plates in the phononic crystal structure low-frequency bandgaps are obtained in the region of 0~198Hz and 0~200Hz respectively. The low-frequency bandgaps appeared as a result of the microcavity local resonator plate which increased the path length through which the wave is transmitted. The phononic crystal microcavity local resonator plate structure has varying transmission loss characteristics of -65dB, -85dB, -100dB and -150dB in the low-frequency range depending on the number of local resonator plates introduced into the cell structure and density of the cell structure. The study provided a good demonstration of wave propagation in artificially engineered materials with critical emphasis on the effects of local resonators in a microcavity structure.

Effects of rough surface on sound propagation in shallow water**Project supported by the National Natural Science Foundation of China (Grant Nos. 11434012, 11874061, and 41561144006).

Underwater acoustic applications depend critically on the prediction of sound propagation, which can be significantly affected by a rough surface, especially in shallow water. This paper aims to investigate how randomly fluctuating surface influences transmission loss (TL) in shallow water. The one-dimension wind-wave spectrum, Monterey–Miami parabolic equation (MMPE) model, Monte Carlo method, and parallel computing technology are combined to investigate the effects of different sea states on sound propagation. It is shown that TL distribution properties are related to the wind speed, frequency, range, and sound speed profile. In a homogenous waveguide, with wind speed increasing, the TLs are greater and more dispersive. For a negative thermocline waveguide, when the source is above the thermocline and the receiver is below that, the effects of the rough surface are the same and more significant. When the source and receiver are both below the thermocline, the TL distributions are nearly the same for different wind speeds. The mechanism of the different TL distribution properties in the thermocline environment is explained by using ray theory. In conclusion, the statistical characteristics of TL are affected by the relative roughness of the surface, the interaction strength of the sound field with the surface, and the changes of propagating angle due to refraction.