Impedance Tube System Research Articles

Development of acoustic impedance tube system using 3D printing and finite element analysis

This study aims to demonstrate and provide a practical guide on correctly designing, fabricating, and verifying the acoustic impedance tube system. Many parts required to build this tube system were uniquely designed and 3D printed, such as the driver case, specimen holder, microphone holder, etc. In addition, this acoustic tube is designed to meet three functions: standard sound absorption measurement, in-situ measurement, and microphone mismatch measurement. Various types of specimens are tested to verify the accuracy of the measurement and how it compares to the poroelastic theoretical models and FEM models. To estimate the poroelastic parameters, measurement and FEM models were used to run the optimization process. The validation study shows good agreement in all three cases: measurement, the poroelastic model, and the FEM model.

An acoustic impedance design method for tubular structures with broadband sound insulations and efficient air ventilation

In this research, we proposed an acoustic impedance-based design method to increase the soundproofing bandwidths and maintain efficient air ventilation for tubular structures consisting of hollow air-flowing channels. This research has great potential to provide design guidelines based on an acoustic impedance model and even/odd mode analysis for hollow-tube ventilated devices containing resonance and antiresonances. We introduced a thin ventilated structure with a subwavelength thickness of 0.107 λ where λ corresponds to the lowest frequency within the filtering bandwidth, a 19.4 % cross-section open for air passage, and a 10 dB fractional bandwidth of 110.2 % (i.e., 90 % sound energy is blocked), which is broader than that of a conventional Fano-like structure of 44.7 %. To experimentally verify the proposed approach, two prototypes, including lateral-coupled and longitudinal-coupled devices, were designed, fabricated with 3D printing, and experimentally characterized via a commercial-available impedance tube system. The simulations matched the measurements and demonstrated the 10 dB fractional bandwidth of 65 % and 91.5 % and ventilation efficiencies of 21.4 % and 33.4 %, respectively. The main contribution of this work is that the proposed approach can be adopted for lateral or longitudinal coupled ventilated structures with broadband sound insulations and lower the effects of resonance-induced sound transmissions. Besides, the proposed acoustic-impedance model can significantly save the required tremendous computational resources and time compared to FEM simulations. Moreover, the proposed lateral and longitudinal ventilated structures are expected to benefit broadband sound filtering and noise reduction for thin panel or tubular silencers

Effect of geometrical parameters and additional mass on the acoustic and vibration control of the bilayer resonant metamaterials

Due to the advantages of lightweight, small size, high stiffness, and adjustable parameters, plate metamaterials have shown great practical application value in the field of acoustic vibration control in engineering. For low-frequency vibration and noise control, an annular slotted bilayer plate metamaterial is designed, which can realize sound insulation and vibration reduction at 100–150 Hz (low-frequency range). By changing the geometric parameters of the annular slotted bilayer plate, the structural parameters of the additional mass, the material parameters, and its distribution position, the acting frequency band is reduced and the band gap of sound insulation and vibration reduction is widened. The integral metamaterial panels of circular and square PA12 were fabricated by 3D printing technology, and then, the acoustic and vibration characteristics were tested in the ZK1030 impedance tube system and Polytec full-field scanning laser vibration measurement system, respectively. The results show that the structure has the best performance by varying the resonant ring thickness of the lattice structure, controlling the wave incidence angle to 0°, and pointing force excitation in the X direction. However, when the mass of the additional mass block is certain, the distribution position of the mass block has less effect. The experimental result was reasonably consistent with the simulation analysis result. This work can provide a reference for the design of bilayer plate acoustic metamaterials with low-frequency broadband acoustic insulation and low-damping vibration based on periodic structures in engineering.

Improvement of natural fiber's properties and evaluation of its applicability as eco-friendly materials in noise pollution control.

The use of green and eco-natural fibers due to availability, biodegradability, reasonable cost, and non-toxic effects are known as potential acoustic materials in research. Nevertheless, in this area, the use of chemical treatment in natural fibers as an effective strategy to improve the overall properties and acoustic performance is faced with limitations. So that the current paper aims to investigate the effect of alkali treatment on the mechanical and acoustical properties of jute fibers and evaluation of its applicability in noise pollution control. To determine the effect of alkali treatment on the sound absorption behavior of jute fibers, a sufficient amount of both types of fibers (raw and treated) were used to the fabrication of acoustic samples with thicknesses of 30, 40 and 50mm at a density of 200kg/m3. The acoustic evaluation was measured by the Impedance tube system according to transfer function method using by the standard ISO 10534-2. The morphological and tensile properties of fibers were evaluated by the Scanning Electron Microscopy (SEM) and tensile test (ASTM C1557-14 standard). Moreover, Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) were used to study and compare the chemical properties of raw and treated fibers. The result showed that the mean tensile strength and crystallinity index (CI) of treated fibers comparing with raw fibers increased by 61.66% and 3.26% respectively. The use of Alkali treatment helped to improve sound absorption performance of jute fibers with different thicknesses. Furthermore, noise reduction rate (NRC) in treated acoustic samples compared to untreated with a thickness of 50mm increased from 0.66 to 0.69. Finally, the alkali treatment has enhanced the properties of jute fibers and confirmed the applicability of these fibers in acoustic absorption. The online version contains supplementary material available at 10.1007/s40201-022-00799-x.

Sustainable Sound Absorber from Nonwoven Fabric of Natural Biduri Fibers (Calotropis gigantea) with Polyester Binder

ABSTRACT In recent years, the research on sound-absorbing material has been directed to sustainable materials such as kenaf fiber and coconut coir fiber. Herein, this study offers the acoustic absorption performance of a novel natural fiber that is biduri fiber (Calotropis gigantea). Biduri fiber is a cellulose fiber that has a low density and a hollow structure along the fiber; hence, it has potential for sound absorption. Biduri fibers were thermally bonded with polyester fibers into nonwoven fabric. The sound absorption coefficient was measured using an impedance tube system, according to International Organization for Standardization (ISO) 10534-2:1998. The nonwoven fabric effectively absorbed high-frequency sound (2000–5000 Hz). The absorption coefficient reached 0.95 at 1600 Hz for nonwoven fabric with 95 wt.% of biduri fibers, a density of 25.9 kg m−3, and a thickness of 15–21 mm, which was better than glass wool and several natural fibers. Nonwoven fabrics with a thickness of 15–21 mm and ≥80 wt.% of biduri fibers met Indonesian National Standard 8443:2017 for high- and low-frequency sound silencers. Using the approximate relationship of the absorption coefficient between normal and random incidence sound, it was found that those nonwoven fabrics were categorized as class B sound-absorbing material according to ISO 11654:1997.

Comparison of Experimental and Empirical Approaches for Determination of Sound Absorption Properties of Bagasse and Cornhusk Fibers

ABSTRACT The significant physical, economic and environmental properties of some agricultural wastes have made them viable alternatives for the conventional sound-absorbing materials. Therefore, it is necessary to identify these types of agricultural wastes and investigate the acoustic behavior and applicability of mathematical predictive models for sound absorption of the samples fabricated from such wastes. In this regard, this study was conducted to investigate the sound absorption coefficient (SAC) values of the samples made from sugarcane and corn husk wastes using experimental and empirical methods. The morphological examination of sugarcane and corn husk fibers was performed by Field emission scanning electron microscopy (FESEM). Having prepared the fibers, several cylindrical samples with a constant density (150 kg/m3) and different thicknesses (20, 30 and 40 mm) were fabricated. The SAC values, porosity and airflow resistivity of these samples were then measured using ISO 10534–2 (impedance tube system), SEM and ASTM C522–03, respectively. The Delany-Bazley (DB) analytical model and the reversed Delany-Bazley model with Nelder-Mead Simplex (DB-NMS) were also used to predict the SAC values. Based on the acoustic performance of the fabricated samples, the SAC values for the thickness of 40 mm and frequency of 500 Hz were, respectively, 0.42 and 0.54 for sugarcane and corn. Increasing the thickness of the samples and creating an air gap behind them were found to be the acceptable approaches for improving the sound absorption. It was found that the DB-NMS model would appropriately follow the experimental results. The purposeful application of agricultural waste and analytical acoustic models because of their outstanding benefits and an effective approach will encourage the usability of natural materials (as eco-friendly, cheap and efficient acoustic products) in indoor and outdoor commercial applications.

Optimization and Modeling of Sound-Absorption Properties of Natural Fibers for Acoustical Application

ABSTRACT Kenaf fibers have long been utilized because of their remarkable properties, such as availability, durability, and strength. Recently, they have also been used as sound-absorbing composites for noise control purposes. This paper investigates the possibility of improving the tensile strength of kenaf fibers through optimizing the alkaline treatment process. It also considers the effects of such optimization on the acoustic absorption coefficients of the samples fabricated from these treated kenaf fibers as well as the applicability of the numerical model to predict the acoustic absorption. Having employed the response surface methodology (RSM) to optimize the alkaline treatment process and achieve optimal conditions for the kenaf fibers, the scanning electron microscopy (SEM) and tensile test were used to study and compare the morphological and tensile properties of raw fibers (nonoptimal) and the fibers treated in optimal conditions. Several cylindrical samples with constant thickness and density (30 mm and 200 kg/m3) were then made of fibers treated in optimal conditions. The sound absorption coefficient, porosity, and airflow resistivity of these samples were measured based using ISO 10534–2 (impedance tube system), SEM and ASTM C423-09A, respectively. The results demonstrated that the tensile strength of optimally treated fibers increased by 182.39%. The acoustic absorption coefficients of the samples fabricated from these fibers were also higher at all frequencies (low-, mid-, and high-frequency range) compared with samples made of untreated fibers in a way that the Sound Absorption Average value of the former increased by 17.97%. Moreover, it was found that inverted Dunn and Davern model via Nelder-Mead simplex method well follows the sound absorption pattern from the experimental results in the overall frequency range. The use of multifaceted improvement approaches for natural materials such as kenaf fibers increases the usability of these materials as sustainable and eco-friendly alternatives in the engineering process of manufacturing sound-absorbing materials.

Mechanical, DMA and Sound Acoustic behaviour of Flax woven fabric reinforced Epoxy composites

In this current investigation, alkali and Trimethoxymethylsilane treated custom made (irregular type) basket woven fabric at different weight percentages (0, 25, 35 and 45 wt.% and named as Pure epoxy, 25 FE, 35 FE, and 45 FE respectively) were reinforced with epoxy resin to develop flax/epoxy composites and tested for mechanical, dynamic mechanical, and sound absorption properties as per ASTM standards. Mechanical results revealed that, amongst the composites, 45 FE showed highest tensile strength, flexural strength, Impact strength and Shore D hardness of 91.07 MPa, 109.5 MPa, 295.65 J m−1, and 85.23 respectively, whereas ILSS property did not shows much appreciable progress even at high fiber loadings. Dynamic mechanical analysis (DMA) tests were conducted for five different frequencies (0.5, 1, 2, 5, and 10 Hz) at varying temperature and properties such as storage modulus (E′), loss modulus (E″), and damping (tanδ curve) were evaluated. DMA properties of the composites have found to be improved after reinforced with the treated flax fabric. Effectiveness coefficient (C) confirms that 45FE composites exhibited better strong fiber-matrix interface and shows good agreement with cole-cole plot analysis. Sound absorption performance of the composites were determined in terms of sound absorption coefficient (SAC) using Impedance tube system for the frequency range 0–6400 Hz. Results indicated that flax-epoxy composites exhibit better sound absorption properties at medium and higher frequency levels. SEM analysis was carried out to understand the cause of failure in mechanically fractured composites. Moreover, morphologies of the fibers were also studied by XRD technique.

Morphological, acoustical, mechanical and thermal properties of sustainable green Yucca (Y. gloriosa) fibers: an exploratory investigation.

The objective of this study was to evaluate the acoustical, morphological, mechanical and thermal properties of fibers extracted from the leaves of Yucca (Y. gloriosa) shrub. Several tests were performed on either untreated or alkali-treated (5% NaOH) fibers. The chemical analysis of the fibers was performed to determine their lignin, cellulose, hemicellulose, wax and moisture content. Fourier transform infrared (FTIR) and thermogravimetric analysis were respectively employed to chemically and thermally analyze the fibers. The microscopic examination was also carried out using scanning electron microscope (SEM). INSTRON universal testing machine and an impedance tube system were employed for measuring the tensile properties of the fibers and the sound absorption coefficient values of the samples fabricated from the same fibers, respectively. The results from the experiments revealed that the fibers have low density (1.32g/cm3) and higher cellulose content (66.36wt.%,). The mechanical characterization of these fibers also confirmed they are similar to the other lignocellulose fibers used for the reinforcement of polymer matrix composites. The tensile strength test conducted on Yucca fibres showed that mechanical properties of alkali treated fibers are superior to the untreated fibers. The thermal analysis also demonstrated that the alkali treated fibres can thermally withstand temperatures of up to 364°C which confirms the fact that the thermal stability of fibers was improved by alkali treatment. Fibers extracted from the leaves of Yucca demonstrated fair amounts of mechanical and thermal resistance and strength. The samples fabricated from Yucca fibers demonstrated fair levels of sound absorption coefficients particularly at higher frequency ranges which are typical to the other natural fibers. The possible use of Yucca fibers as either a reinforcing agent for composites or a sound absorbing medium is highly promising.

Experimental and mathematical survey of sound absorption performance of date palm fibers

The present study examines the acoustic behavior sample composites made of date palm natural fibers and polyvinyl alcohol. It also provides the comparison between the sound absorption coefficients obtained from the experimental tests and the ones predicted by the mathematical models. An impedance tube system was used to measure the normal sound absorption coefficient of the samples. Using the differential equation algorithm, the predicted sound absorption coefficient for the Johnson-Champoux-Allard model was also calculated. The sound absorption properties of samples increased significantly by increasing the frequency, and increasing the thickness of materials with constant density. Comparison of the data from the experimental tests and mathematical model showed that increasing the thickness of samples will make the predicted and tested values of acoustic absorption coefficient significantly comparable. Date palm fibers have a good potential for dissipating the energy of sound waves particularly when an air gap is introduced behind the sample and can be used as a new source for the fabrication of natural fiber reinforced composites.

Preparation and Sound Insulation Performance of Superfine Metal Powder/Nitrile-Butadiene Rubber-Polyvinyl Chloride Microcellular Foaming Material

Lightweight sound insulation materials have received much attention. In this study, a series of superfine metal powder (SFM)/nitrile-butadiene rubber (NBR)-polyvinyl chloride (PVC) microcellular foaming materials were prepared with NBR-PVC as matrix and SFM as modifiers by employing the method of molding foaming. Analysis on the morphology of cross section, pore size, and pore distribution possessed by SFM/NBR-PVC was conducted by scanning electron microscopy (SEM), as well as the image processing software of Image-Pro. Then detailed discussion on the effect of SFM with different mass fractions in the matrix on the foaming quality was provided. In the meanwhile, the performance of sound insulation was tested by four-channel impedance tube system. The results show significant improvement for foaming quality and sound insulation performance of NBR-PVC microcellular foaming material through the addition of SFM. In comparison with the pure NBR-PVC materials, the microcellular foaming material exhibits the best performance of foaming quality and sound insulation when the SFM content in matrix is 30 wt%. It is shown that the average pore diameter and the foaming capacity decrease by 60% and 31%, respectively, while the surface density increases by 131%. In the meantime, the sound insulation index of SFM/NBR-PVC microcellular material increases by 7.2 dB to 30.5 dB, which conforms to the requirements of new lightweight sound insulation materials in modern time. Finally, the mechanism of the optimization conducted for sound insulation performance after the addition of SMF is explained.

Sound Absorption Characterization of Natural Materials and Sandwich Structure Composites

Natural fiber and wood are environmentally friendly materials with multiscale microstructures. The sound absorption performance of flax fiber and its reinforced composite, as well as balsa wood, were evaluated using the two-microphone transfer function technique with an impedance tube system. The microstructures of natural materials were studied through scanning electrical microscope in order to reveal their complex acoustical dissipation mechanisms. The sound absorption coefficients of flax fiber fabric were predicted using a double-porosity model, which showed relatively accurate results. The integrated natural materials sandwich structure was found to provide a superior sound absorption performance compared to the synthetic-materials-based sandwich structure composite due to the contribution of their multiscale structures to sound wave attenuation and energy dissipation. It was concluded that the natural-materials-based sandwich structure has the potential of being used as a sound absorption structure, especially at high frequency.

Effects of multiwall carbon nanotube addition on the corrosion resistance and underwater acoustic absorption properties of polyurethane coatings

In this study, the effect of multiwall carbon nanotube (CNT) addition on the anticorrosion and underwater acoustic absorption properties of polyurethane (PU) coatings was studied. The corrosion and mechanical properties of various coatings were characterized through electrochemical impedance spectroscopy, polarization curve measurement, salt spray tests, pull-off tests, and dynamic mechanical analysis. Underwater acoustic absorption properties were evaluated using an underwater acoustic impedance tube system comprising two hydrophones, a sound and vibration data acquisition module, a power amplifier, and a speaker. The results indicated that the corrosion resistance and adhesion strength of the PU coating was enhanced by adding 0.4 wt% CNTs. When additional CNTs were added (1 wt%), however, the corrosion rate of the coating increased. Measurement of the underwater sound absorption coefficient revealed that the underwater acoustic absorption properties of the PU + CNT composite coatings increased as the CNT content increased to 1 wt%.

Experimental measurements of acoustical properties of snow and inverse characterization of its geometrical parameters

Snow is a sound absorbing porous sintered material composed of solid matrix of ice skeleton with air (+water vapour) saturated pores. Investigation of snow acoustic properties is useful to understand the interaction between snow structure and sound waves, which can be further used to devise non-destructive way for exploring physical (non-acoustic) properties of snow. The present paper discusses the experimental measurements of various acoustical properties of snow such as acoustic absorption coefficient, surface impedance and transmission losses across different snow samples, followed by inverse characterization of different geometrical parameters of snow. The snow samples were extracted from a natural snowpack and transported to a nearby controlled environmental facility at Patsio, located in the Great Himalayan range of India. An impedance tube system (ITS), working in the frequency range 63–6300Hz, was used for acoustic measurements of these snow samples. The acoustic behaviour of snow was observed strongly dependent upon the incident acoustic frequency; for frequencies smaller than 1kHz, the average acoustic absorption coefficient was found below than 0.4, however, for the frequencies more than 1kHz it was found to be 0.85. The average acoustic transmission loss was observed from 1.45dBcm−1 to 3.77dBcm−1 for the entire frequency range. The real and imaginary components of normalized surface impedance of snow samples varied from 0.02 to 7.77 and −6.05 to 5.69, respectively. Further, the measured acoustic properties of snow were used for inverse characterization of non-acoustic geometrical parameters such as porosity, flow resistivity, tortuosity, viscous and thermal characteristic lengths using the equivalent fluid model proposed by Johnson, Champoux and Allard (JCA). Acoustically derived porosity and flow resistivity were also compared with experimentally measured values and good agreement was observed between them.

Experimental Determination of Acoustic Losses in an Acoustic Resonator Using Impedance Tube Technique

In order to increase the potential applications of thermoacoustic engine, coiling the resonator tube is another idea to miniaturise the engine. Resonator is an essential component used to sustain the driving acoustic waves. Coiling of resonator will definitely improve the engine footprint but it may introduce losses that are not encountered by the straight resonator. A straight resonator tube is the easiest design and will have small energy losses, but it requires large space. The proposed work in coiling the resonator will certainly create more energy losses than the previous designs but the magnitude of these losses are unknown. In this paper, an impedance tube system was built to measure the sound energy losses of coiled tubes of different configurations and comparing the results with the losses in a straight tube. The impedance tube system designed for the testing consists of an upstream tube, the test section and a downstream tube. A similar investigation was also conducted for different number of sharp turns of the tubes. The two-load method was used to analyse the results by using the four-microphone impedance tube methodology. The results showed significant differences between the four configurations and the outcomes were found to be very useful in the future when designing miniature thermoacoustic engine. Nomenclature

Flute-model acoustic metamaterials with simultaneously negative bulk modulus and mass density

We experimentally constructed a three-dimensional flute-model meta-molecule structure acoustic metamaterial (AM) from a periodic array of perforated hollow steel tubes (PHSTs) and investigated its transmission and reflection behaviors in an impedance tube system. The AM exhibited a peak and dip, and an inverse phase, thus exhibiting the local resonance of the PHSTs. Based on the homogeneous media theory, the effective bulk modulus and mass density of the AM were calculated to be simultaneously negative; the refractive index was also negative. PHST AM slab focusing experiments showed that the medium with a resonant structure exhibited a distinct metamaterial property.

Experimental Investigations on the Effects of Coiling and Bends on the Sound Energy Losses through a Resonator Tube

In order to miniaturize the thermoacoustic engine, thereby to increase their potential applications, coiling the resonator tube is one of the solutions to make it smaller in size (rather than scaling the engine). Whether in a standing wave or travelling wave engine, a resonator is necessary to sustain the driving acoustic waves. However, the curvature of the tube may introduce losses that are not encountered by the normal straight resonator. A straight resonator tube is the easiest design and will have small losses, but it requires large space. However, there are only few studies regarding the effect of resonator coiling. This work investigates the effect of the coiling of the tubes and the bends effects on the efficiency of the sound energy transmission through the tube experimentally. This work consists of the design of an impedance tube system to measure the sound energy losses of coiled tubes of different configurations and comparing the results with the losses in a straight tube. A similar investigation is also conducted for different number of sharp turns of the tubes (u-shaped bend and 90° bend tube). The impedance tube system designed for the testing consists of an upstream tube, the test section and a downstream tube. The two load method was used to analyze the results by using the four-microphone impedance tube methodology. The results showed significant differences between the four configurations and the outcomes were found to be very useful in the future when designing thermoacoustic looped engine.

Tunable acoustic metamaterial with negative modulus

A tunable negative modulus metamaterial is presented, and it is achieved by adjusting the medium density and an effective volume of a split hollow sphere (SHS). This work comprises experimental and numerical studies. The effects of water/air component and the steel ball on the transmission properties were investigated in the impedance tube system. The experimental results show that the transmission dip has a significant blue-shift with increasing water content, whereas the steel ball has a relatively small influence on the resonant frequency. The simulated results by the finite-element method (FEM) are in agreement with the experimental results. Based on medium parameters among the SHS, acoustic metamaterial (AM) with negative modulus can easily be designed in the expected frequency domain, and it provides a convenient route to tune AMs.

Two-dimensional acoustic metamaterial with negative modulus

We designed a two-dimensional acoustic metamaterial with periodical array of split hollow sphere (SHS) and investigated its transmission behaviors in the impedance tube system. The results showed that the acoustic metamaterial exhibited a transmission dip and inverse phase close to 5 kHz, which indicated the local resonance of SHS. Based on the homogeneous-media theory, the effective modulus of the acoustic metamaterial was calculated to be negative. The finite element method and resonant model simulation results also confirmed the local resonance and negative response in acoustic metamaterial, which agreed well with experiment results. This metamaterial is able to achieve the double negative acoustic metamaterial conveniently by arraying acoustic “atoms” with negative mass density in the matrix.

The effect of high-amplitude sound on the attenuation of perforated tube silencers

A time-domain computational approach is applied to investigate the behavior of perforated tube silencers at high sound levels. The one-dimensional computational technique employs a lumped parameter model for the perforate flows. The lumped parameter perforate model is based on time-invariant approximations for the equivalent length l(eq) and resistance R, consistent with the use of a nonlinear perforate impedance. Empirical expressions for l(eq) and R are developed experimentally using nondimensional scaling parameters. The model is applied to geometries representative of automotive resonators and multiple-duct mufflers. Conditions are simplified from those in an actual automotive system by considering single-frequency excitation and zero mean flow. Simulations with linear perforate behavior are compared to experimental data obtained with an extended impedance tube system. Simulations with nonlinear perforate behavior for one concentric tube resonator are compared to published experimental data.