Sound Transmission Characteristics Research Articles

The two-cavity method for characterizing acoustical materials-an interlaboratory study

The study focuses on understanding the sound absorption and transmission characteristics of porous acoustical materials, which are determined by two key parameters independent of material thickness: characteristic impedance and propagation constant. These parameters can be characterized by testing a porous sample concept in a normal incidence impedance tube using either the two-thickness or the two-cavity method. In the two-thickness method, two samples of varying thicknesses are required. In contrast, the two-cavity method requires testing one sample at two air cavity depths. This method is particularly advantageous for materials that are costly or challenging to fabricate. This interlaboratory study evaluates the variability of characteristic properties determined using the two-cavity method. Porous acoustical materials were additively manufactured and tested in the Liner Technology Facility at NASA Langley Research Center and the Mechanics, Acoustics and Dynamics Lab (MADLab) at Michigan Technological University. The characteristic properties, derived from various cavity depth combinations, were used to predict the sound absorption curves of the sample with a rigid backing. These predictions were then compared with actual experimental absorption curves. The findings indicate that both the combinations of cavity depths and the sample's static airflow resistivity significantly influence the accuracy of the deduced properties.

Sound transmission loss analysis of novel sandwich plate with star-shaped auxetic cellular cores

A star-shaped auxetic cellular metamaterial with a negative Poisson’s ratio (NPR) was employed in this study to model lightweight sandwich panels, and an analysis of its sound transmission characteristics was conducted. Utilizing the first-order shear deformation theory (FSDT) and the Hamiltonian principle, the free vibration equation for the sandwich plate is derived. Subsequently, leveraging the fluid-structure coupling condition and incorporating the Navier method, the sound transmission loss (STL) is analytically described. The efficacy of the proposed method is validated through numerical analysis and an acoustic insulation experiment using an impedance tube. Based on the theoretical modeling, it is calculated that the sound insulation effect of the star-shaped cellular core exceeds that of the traditional reentrant cellular with NPR. A systematic analysis is subsequently conducted to explore the impact of star-shaped cellular structure parameters on the STL of the sandwich panel. It can be obtained that the increase in core layer thickness leads to a reduction in the first-order resonance frequency of the sandwich panel, but concurrently diminishing its sound insulation performance. The change of the connecting rib length exerts a more considerable influence on the structure’s STL compared to the side rib length. While as the cell wall thickness reduces from 2.0 to 1.0 mm, the average STL of the sandwich plate across the analysis band decreases by 8.43%, from 46.3 to 42.7 dB.

Improvement of broadband low-frequency sound insulation of sandwich plates with negative Poisson's ratio butterfly-shaped auxetic cellular

The novel cellular cores auxetic metamaterials with negative Poisson's ratio (NPR) exhibit unique mechanical deformation characteristics compared to conventional cellular cores, which can be further exploited in modeling lightweight sandwich structures. The butterfly-shaped auxetic cellular is not only an improvement upon the traditional re-entrant auxetic cellular with NPR, but also a kind of bionic design, which possesses higher stiffness and thus offers greater potential for sound insulation. Based on this, the present article explores a study of the sound transmission characteristics exhibited by sandwich plates with butterfly-shaped auxetic cellular core layers. Firstly, the motion equation is derived based on the first-order shear deformation theory and Hamilton's principle, which is further solved analytically based on fluid-structure coupling conditions and combined with Navier method. Then, the sound transmission loss (STL) is analytically described. The correctness of the theoretical model is verified by comparing the theoretical solution with the calculation results of the commercial software COMSOL and the experimental results of impedance tube sound insulation tests. Based on the theoretical model, it is calculated that the sound insulation effect of butterfly-shaped auxetic cellular core is better than that of traditional re-entrant cellular with NPR. An analysis is subsequently conducted to explore the impact of key parameters on the STL of the butterfly-shaped cellular sandwich plates.

Vibro-acoustic coupling analysis of dynamic performance of the double panel system with mechanical links

The theoretical prediction model for the dynamic performance of a double panel system that takes into account the effect of mechanical links is developed in this paper. The double panel system is established considering both the vibro-acoustic coupling and the effect of the mechanical links between two flexible panels. Firstly, the modal characteristics of the double panel system are analyzed and compared with the results calculated by the finite element method. The accuracy and efficiency of the proposed model have been validated. Subsequently, the forced response of the double panel system under different external excitations is studied. It is shown that the mechanical link resulted in less response level of the double panel system in in low frequency range due to the structural path in the energy transmission of the double panel system. Finally, the effect of the mechanical link parameters on the dynamic performance of the double panel system is discussed. The results reveal that the stiffness coefficients, location distributions, and number of mechanical links can significantly influence the dynamic behavior of the double panel system. Therefore, the theoretical model can be used in optimization techniques to improve the sound transmission characteristics of the double panel system.

A novel arc-type auxetic cellular doubly-curved shells with negative Poisson's ratio for broadband low-frequency sound insulation

The novel cellular cores auxetic metamaterials with negative Poisson's ratio (NPR) have unique mechanical deformation characteristics compared to conventional cellular cores, which can be further applied to modeling lightweight sandwich structures. The Arc-type cellular core is based on the traditional re-entrant cellular core and incorporates a bending configuration, facilitating a smooth transition of the cell elements. Based on that, the sound transmission characteristics of sandwich doubly-curved shells with NPR arc-type auxetic cellular core layer is studied in this article. The Hamilton's principle is applied 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 method, and the sound transmission loss (STL) is described analytically. The correctness of the proposed formula is verified by comparing the theoretical solution with the calculation results of the commercial software COMSOL and the experimental results of impedance tube sound insulation. Based on the theoretical model, it is calculated that the average STL of the arc-type cellular is 6.61% higher than that of the traditional re-entrant cellular within the broad low-frequency range of 100–2448Hz. Then the effect of key parameters on the STL of sandwich structure is systematically analyzed, and the results show that the first frequency of the sandwich shell decreases with the increase of the rib thickness, but increases with the increase of the arc radius. Notably, a smaller arc radius and a larger rib thickness exhibit superior sound insulation properties across a broad frequency range. In addition, when the core layer thickness increases from 0.007m to 0.009m, the average STL of sandwich structures is reduced by 7.38% in a broad low-frequency range of 100–2448Hz.

Broadband low-frequency sound insulation of stiffened sandwich PFGM doubly-curved shells with positive, negative and zero Poisson's ratio cellular cores

Compared to the conventional cellular cores, the cellular cores auxetic metamaterials with negative and zero Poisson's ratios have unique mechanical deformation characteristics, which can be further applied to modeling lightweight sandwich structures. Based on that, the sound transmission characteristics of a novel stiffened sandwich porous functionally graded materials (PFGM) doubly-curved shells with full Poisson's ratio characteristic range cellular cores are investigated in this study. The adjustment of material properties of PFGM face sheets in the thickness direction is achieved through power law based on component volume fraction, and the core layer consists of cellular cores with positive, negative, and zero Poisson's ratios (PPR, NPR, and ZPR). Two common types of stiffened sandwich shell types, namely, the shell with PFGM face sheets and metal-rich cellular cores (type-A), and the ceramic-rich cellular cores (type-B), are discussed, and the Hamilton's principle is used to derive the governing equations. By applying normal velocities continuity conditions at the fluid-structure interface to consider fluid-structure coupling, which is further analytically solved using Navier's technology, and the average sound transmission loss (STL) with broadband low-frequency is described. The effectiveness of the established theoretical model is confirmed by comparing it with previously published results, experimental and simulated results obtained by impedance tube and COMSOL commercial software. A systematic comparison is conducted on the performance of stiffened sandwich PFGM doubly-curved shells with full Poisson's ratio characteristic range cellular cores, and the results show superior performance in the sound insulation for the sandwich shell with ZPR cellular cores, considerably at a broad low-frequency range of 220–2040 Hz, in comparison with the sandwich shell with NPR cellular cores and conventional PPR cellular cores types. This work's findings can serve as a benchmark for future studies and help to design and create engineering sandwich structures with improved sound insulation properties.

Sound transmission characteristics of X-shape inertial amplification acoustic metamaterial

This paper presents a new type of acoustic metamaterial plate periodically attaching X-shape inertial amplification (XIA) mechanisms to realize the low-frequency bandgaps and efficient sound insulation. Different from the conventional approaches relying on the mass law to reduce noise, XIA mechanisms mitigate the vibration, as well as the sound radiation, of the host structures by amplifying the inertia of the added small mass. The theoretical model of the XIA plate for computing the sound transmission loss (STL) and the band structure is verified numerically and experimentally. The results show that the XIA mechanism can open up transverse wave bandgaps in the band structure starting at a low frequency. The bandgap-induced attenuation of flexural vibrations significantly improves the STL performance of the host plate. However, the XIA mechanisms cause the early coincidence at the same time, showing an intersection of the real dispersion curve and the acoustic trace wave number curve in the band structure and a sharp valley in the STL curve. Parametric studies reveal that the amplification angle θ has the largest influence on the performance metric net STL gain G40dB. Moreover, increasing the amplification angle θ, the amplification ratio ξ, and reducing the amplification span d, can realize the STL peaks shifting towards low frequency. Finally, to expand application scenarios of XIA plates for sound insulation, two enhancement strategies of the multi-stage approach and the multi-mechanism approach are investigated.

Multi-Order Asymmetric Acoustic Metamaterials with Broad Bandgaps at Subwavelength Scales.

Noise manipulation at the subwavelength scale remains a challenging problem. To obtain better broadband sound isolation within the subwavelength range, a class of asymmetric acoustic metamaterials (AAMs) based on rotation is proposed, and this class of AAMs can further improve subwavelength sound isolation performance by introducing multi-orders. The influences of changing the alternate propagation length of the coiled channel and the square cavity in the unit cell on the band frequency distribution and the omnidirectional band structure were investigated. The effective parameters are calculated with the S-parameter retrieval method, and the generation and change mechanisms of the bandgaps were elucidated. The calculation of sound transmission characteristics showed that, in the asymmetric mode, the overall sound isolation performance of the structure was greatly improved, and the relative bandwidth expanded as the alternate propagation length of the coiled channel and square cavity increased. The omnidirectional bandgaps from the first-order to the third-order AAMs occupied 63.6%, 75.96%, and 76.84% of the subwavelength range, respectively. In particular, the first bandgap moves to the low frequency and becomes wider. Both the experimental results and numerical analyses consistently showed that disrupting structural symmetry enhances acoustic metamaterials for superior broadband sound isolation, inspiring broader applications for asymmetry in this field.

Low frequency noise control using coupled loudspeaker and negative impedance circuit

It remains a technical challenge for low-frequency duct noise control devices to combine compact and broadband features at same time. A semi-active noise control approach is introduced to solve this problem. The device consists of a main pipe and two loudspeakers connected by a circuit containing a negative impedance network. Due to the effect of the negative impedance circuit, the virtual bypass is composed of the coupled loudspeaker and the circuit has sound transmission characteristics close to a physical duct in a certain frequency range. The effect of the negative impedance network and circuit on the performance of the silencer is studied by using the transfer matrix method. Through the design of the circuit, the sound transmission process of the virtual bypass can be realized. If the proper circuit network and parameters are selected, the virtual bypass HQ tube can achieve compact broadband noise control at low frequencies. A semi-active noise control device has 10dB noise reduction in the range of 100-300Hz.

Acoustic wave propagation through eco-friendly porous panels at normal incidence

Human and non-human subjects are exposed to micro plastics through drink, food, and air. Micro-plastics propagating through atmosphere are breathable particles during inhalation and exhalation leading to deposition of them in the deep lung via the alveoli of the lungs. Teabags are made of plastics that are not recyclable and biodegradable. Therefore, we intend to remove used teabags from the natural environment by repurposing them to make sound attenuating panels for building and architectural industries, contributing in this way to a sustainable circular economy. The panels were designed and developed from consumed teabags as porous material by filling a frame to investigate acoustics wave propagation through them at normal incidence. Experimental testing was carried out on circular teabag panels in an impedance tube using a transfer function method to determine their sound absorption coefficient and transmission loss. Furthermore, the impedance gun method was used to determine the absorption properties of square panels. Results show that 75 mm thick circular panels give an absorption coefficient higher than 0.8 between 400 and 1600 Hz. Up-to 9.8 dB sound transmission loss of circular panels is obtained at higher frequencies. Absorption coefficients for square teabag panels are very good despite a coincidence-dip seen at 800 Hz. The satisfactory sound absorption and sound transmission characteristics of acoustic panels made of consumed tea bags can make this recycled material a cost-effective solution in the production of sustainable acoustic treatment in indoor spaces. The results suggest that recycling of consumed teabag as the panel could be applied as alternative sound absorbing materials.

Broadband low-frequency sound insulation of a metamaterial plate with inertial amplification

The recent development of Inertia Amplification (IA) acoustic metamaterial (AMM) opens a new venue for insulating low-frequency sound waves. This differs from conventional approaches that rely excessively on the structural density of the insulator and, therefore, lead to prohibitively heavy structures. The IA-AMM acquires a large effective density and a broad flexural bandgap by amplifying the inertia of many small mass elements periodically distributed in its unit cells, thus holding great promise as an effective yet lightweight solution for low-frequency sound insulation. This paper explores this possibility through numerical and experimental investigations. A semi-analytical model of an IA-AMM plate is developed by combining analytical equations characterizing the kinematics of an IA mechanism and FEM equations governing the vibration of the host plate. Based on this model, sound transmission characteristics of the plate under various sound incidences are analyzed with different amplification angles. By comparing with a locally resonant AMM plate, we found that the IA-AMM plate's sound transmission losses (STLs) are significantly and systematically improved over a wide frequency range of 116–544 Hz. To understand the underlying physics, the band diagram of the IA-AMM plate is calculated, which indicates the formation of a flexural bandgap covering the frequencies of the improved STL. The velocity contour of the plate at the center frequency of this bandgap also reveals much-suppressed vibration velocity amplitudes and a dipole-like sound radiation directivity, further explaining the observed enhancement of the sound insulation ability. Numerically predicted improvement of sound insulation is finally confirmed by experiments.

Study on sound transmission characteristics and positioning strategy of gas insulated transmission line shell

Gas insulated transmission line (GIL) is widely used for large-capacity power transmission in complex environment, and has the characteristics of long distance and totally enclosed structure. When the insulation fault occurs inside GIL, its metal shell structure makes it more difficult to monitor through optical, electrical and other physical quantities. Considering the rapidity and accuracy of positioning, the propagation of sound waves along the GIL sheath is a commonly used method in GIL on-site PD testing and running state online monitoring for fault positioning. This paper establishes a high-pressure GIL acoustic propagation simulation model based on pipe acoustics theory, analyzes the frequency dispersion and mode distribution of acoustic waves along the GIL shell, determines an appropriate fault location strategy based on the propagation velocity and attenuation of the selected acoustic wave mode, and carries out experiments to verify it. The results of the research show that the low order bending wave F(1,1) propagated along the GIL shell has good positioning characteristics, and the propagation velocity conforms to the dispersion curve distribution. By taking into account the attenuation and delay of the acoustic wave passing through epoxy insulators or expansion joints in the fault localization strategy, the localization accuracy can be improved by 60%. And this positioning strategy was verified to be effective in the GIL insulation fault localization test conducted in the field.

Experimental Study on Downhole Acoustic Wave Propagation Characteristics in Curved Drill String

Aiming at the problem of the unclear sound wave attenuation in the signal transmission of the load-bearing drill string, an experimental device for the sound wave propagation characteristics in the curved drill string was set up. The influence of the drill string structure and acoustic excitation parameters on the sound propagation characteristics in the drill string under different loads is different. The results show that the curvature of the drill string has an influence on the propagation of the sound wave in the drill string, and its rule is related to the curvature of the drill string and the frequency of the sound wave. The pulse repetition rate, excitation voltage, and pulse width only affect the passband amplitude, and the effect is significantly greater than the curvature of the drill string. The main influencing factor of its sound transmission characteristics is the degree of drill string curvature. The low-frequency signal should be preferentially selected as the carrier of downhole information transmission after considering the influence of drill string bending on acoustic transmission.

Sound transmission characteristics of a plate backed by an irregular cavity

The study of the coupling cavity provides an effective theoretical reference for the acoustic design. However, most of the previous studies are based on idealized models and there is little research on the sound radiation power about the irregular shapes. The work in this paper achieves the generalization of the model and explores the impact of irregular back cavities on the sound radiation of the plate structures. The influence on the results of the sound insulation performance testing of the plate is also investigated when irregular cavities involved. The displacement of the plate and the sound pressure inside the cavities are expressed as multidimensional Fourier series with additional terms, which will contribute to maintaining the continuity of pressure and velocity at the boundaries. The sound field of the irregular cavity is considered as a unit cubic one in a new coordinate system by coordinate transformation method. The arbitrary boundary of the cavities is realized by adding the energy terms of impedance into the Lagrange equation. The Hamilton’s principle is employed to realize the complete coupling between the plate and the sound fields on both sides. The sound radiation power of the plate can be obtained by using the Rayleigh integral. By using Fast Cosine Transform, the quadruple integrals of the radiation power are simplified to improve accuracy and efficiency of the calculation. Numerical results from the analytical approach are compared with those given by Finite Element Analysis (FEM) to guarantee the rightness and validity of the models. Moreover, experimental results are also given to discuss the reasons of the bias between theory and practice.

Experimental investigation on the enhancement of plenum window noise reduction using solid scatterers.

The sound transmission across plenum windows installed with rigid non-resonant cylindrical scatterer arrays was investigated in detail using scale-down model measurements carried out inside a fully anechoic chamber. The arrays have manifested to some extent the acoustical behaviors of virtual sonic crystals. The maximum cross section blockage ratio was 0.6. The effects of plenum window gap, array configuration, and scatterer diameter on the sound transmission characteristics were also examined. Results indicate that the window cavity longitudinal modes and the gap modes control the sound transmission characteristics at low frequencies. The upper bound of this frequency range increases with decreasing gap width. Within this frequency range, the scatterers have negligible effect on the sound transmission. At higher frequencies, the array configurations with scatterer(s) attached to the window walls result in stronger sound reduction. There are relatively higher sound transmission loss improvements around the frequencies where a full bandgap is observed. There are wide bandgaps in various lattice directions, and the present results suggest that they play a role in the broadband improvement of sound reduction.

Numerical analysis of the effects of canal wall‐up and canal wall‐down mastoidectomy on the sound transmission characteristics of human ears

Purpose The aim of this work was to study the effect of canal wall-up (CWU) and canal wall-down (CWD) and mastoid obliteration in conjunction with CWD (CWD-MO) mastoidectomy on the sound transmission characteristics of the human ear. Methods Three mastoidectomy surgical methods, CWU, CWD and CWD-MO, were simulated on the freshly dissected cadaver heads. Then, the finite element (FE) models corresponding to these surgical methods were established by micro-computed tomography (Micro-CT) and reverse engineering technology, and the accuracy of the models was verified. Finally, the FE Models were used to analyze the effects of different surgical methods on the sound transmission characteristics of the human ear. Results For CWU, since the integrity of the outer wall of the ear canal is ensured, the sound pressure (SP) gain of the ear canal and the stapes footplate displacement (FPD) gain after this operation are close to normal values. For CWD, due to severe damage to the outer wall of the ear canal, a negative gain of the ear canal SP occurs in the high-frequency range, and the resonance frequency is significantly reduced. For CWD-MO, the frequency range of SP negative gain in the ear canal is reduced due to the addition of fillers in the ear canal to reduce the degree of damage, and the resonance frequency is increased compared to CWD. Conclusions The impact of three types of mastoidectomy, including CWU, CWD, and CWD-MO, on the sound transmission characteristics of the human ear after surgery is relatively small.

Analytical model of vibro-acoustic coupling between the membrane loaded with concentrated masses and the acoustic cavity

In this paper, sound radiation and sound transmission characteristics of a membrane-cavity system loaded with concentrated masses are analyzed. The Fourier cosine series function with additional terms is used as the mode function of membrane to model the single membrane structure, which is suitable for arbitrary boundary conditions. The concentrated masses are regarded as the concentrated mass points without considering their sizes, and the coupling structure of membrane and mass blocks is constructed. The structure-sound field fully coupled model is also constructed by using the energy principle and Rayleigh–Ritz method. Several numerical examples computed by finite element method are used for verification. The influence of the added mass blocks on the membrane modes and acoustic properties of the coupling system is discussed, including membrane parameters, mass block arrangement, quantity and mass, etc. Also, the mass blocks are dispersed for analysis. Results show that dispersing the mass can significantly increase the frequency of the coupling mode between the membrane and concentrated masses and better suppress the vibration. But increasing dispersion points does not further enhance vibration suppression. Instead, it expands the area where the membrane vibrates violently.

Free vibration and sound transmission properties of beetle elytron plate: structural parametric analysis

Honeycomb plate (HP), which is a high-strength and lightweight structure, has good vibration characteristics, while beetle elytron plate (BEP) has better mechanical properties. To promote the engineering application of BEPs, the vibration and sound transmission characteristics of aluminium BEPs were investigated in this paper with HP as the comparison object. This paper investigated the effects of the number of trabeculae, the ratio of length and width, skin thickness, core height and core thickness on the first 4 frequencies using finite element method. The results show that (1) the vibration characteristic of BEP is optimal when the number of trabeculae is 6, and its 3rd and 4th modes show mixed mode, i.e., torsion-bending or bending-torsion mode. (2) The frequencies of BEPs are generally lower than those of HPs. Compared with HPs, the ratio of length and width and core thickness have a smaller influence on the mode shapes of BEPs, and the core height has a smaller influence on BEPs’ frequencies. When the skin thickness is small, increasing the thickness can effectively change the natural frequencies of BEPs and HPs. (3) Considering the common frequencies of four applications (aircrafts, unmanned aerial vehicles, high-speed trains and automobiles) of sandwich plates, the effects of the abovementioned parameters including the ratio of length and width, skin thickness, core height and core thickness are analysed. (4) Combined with the theoretical calculation formula, the effect of the above structural parameters on the sound transmission characteristic is explored using the index of sound transmission loss, and targeted recommendations are given. This paper progresses the application in engineering.

Sound transmission loss of a sandwich functionally graded cylindrical shell integrated with magneto-electro-elastic patches

Magneto-electro-elastic materials offers the inherent capability of energy transformation from one type to another, hence making them suitable for improving the vibroacoustic behavior of the structures. The current article is an analytical investigation into the sound transmission characteristics of a smart functionally graded cylindrical shell equipped with magneto-electro-elastic patches while a steady fluid flow exists outside of the cylinder. The complete set of equations of motion are derived after accounting for all components of displacement according to the first-order shear deformation theory. The utilized patches are controlled via an electric field, indicating the smart nature of the structure. The Power-law model is adopted to calculate the effective mechanical properties of the functionally graded core layer. After defining proper boundary conditions, the vibroacoustic equations are obtained with the aid of Hamilton's principle. A comprehensive validation study is also conducted to show the reliability of the developed formulation. In addition, by examining the effect of a large number of electric, magnetic, flow Mach number, geometric and acoustic parameters, recommendations are made to effectively optimize similar structures that benefit from such materials. One of the important findings of this study is that applying electric and magnetic fields in the low frequency band improves the sound transmission loss. Therefore, the magneto-electro-elastic patches can be used in active structural acoustic control approaches as actuators.

Sound transmission loss of double-walled sandwich cross-ply layered magneto-electro-elastic plates under thermal environment

This study offers a comprehensive investigation into the parameters affecting the sound transmission characteristics of a double-walled sandwich magneto-electro-elastic cross-ply layered plate resting on viscoelastic medium in thermal environment. To this end, the walls of this sandwich structure are modeled based on the assumptions of the first-order shear deformation theory. The governing equations are derived via a coupled set of equations targeting vibration and acoustic aspects of the problem after the application of Hamilton’s principle. The obtained equations are then solved by the implementation of double Fourier series and the second velocity potential, giving an accurate estimation of sound transmission loss under initial magnetic and electric potentials, variations of temperature, ply angle, acoustic cavity depth, incident angle of sound waves, and viscoelastic parameters.