Impedance Tube Test Research Articles

Laboratory Evaluation of Mechanical Properties and Noise Absorption in Magnetite-Enhanced Concrete for Pavement Applications

This paper aims to evaluate the effects of incorporating magnetite as an aggregate in concrete mixtures and as a partial replacement for Portland cement in standard mortar mixtures, focusing on performance and mechanical properties. Noise pollution from cement concrete pavements has become a significant concern for residents, making it a priority to implement effective measures to reduce traffic noise pollution. The primary goal of this research is to explore the relationship between mixture design variables with magnetite aggregates as a partial replacement for Portland cement in concrete pavement and the mixture's acoustic performance. Samples with 0, 10, 20, 30, 40, and 50% replacement of aggregates with magnetite sand were prepared initially. Subsequently, Portland cement was replaced with 0, 1, 2, 3.5, 5, 7.5, 10, 15, and 20% magnetite concentrate powder in standard mortar. Routine tests, such as slump, density, and flow table, were conducted on fresh concrete and mortar. Additionally, compressive strength, flexural strength, water absorption, electrical resistance, and impedance tube tests were performed on the concrete and mortar mixes. The impedance tube measurements demonstrated an increase in the sound absorption coefficient for concrete incorporating magnetite compared to the reference concrete. Among the tested concrete samples, the one containing 50% magnetite as aggregate exhibited the highest sound absorption coefficient, reaching a maximum value of 0.1 within the frequency range of 315 to 400Hz. This value was 2.5 times higher than the maximum sound absorption coefficient of the reference concrete.

3D-printed multifunctional chiral metamaterial with invariant sound absorption under large deformation and low-frequency vibration control

ABSTRACT Acoustic metamaterials provide a distinctive route for reducing low-frequency noise and vibration; however, most are characterised by their singular functionality, e.g. sound absorption or vibration suppression. We present a 3D-printed multifunctional chiral metamaterial (MCM) with double helix structures inspired by cochlea and DNA for excellent acoustic, mechanical, vibration isolation and mitigation properties. By employing impedance matching, nearly perfect sound absorption can be obtained and kept invariably in the low-frequency range under strain from +25% to −25%, as confirmed by the standard impedance tube tests. The double helix structure provides versatile mechanical properties, including compressibility, stretchability, and recoverability. Excellent vibration isolation ability from 94 Hz and strong elastic wave attenuation performance between 199 and 254 Hz based on bandgap strategy are demonstrated by isolation and mitigation vibration tests and simulations. This 3D printed structure presents a promising solution for multipath noise control, setting a paradigm for biologically inspired multifunctional materials.

Improvement of Mechanical and Acoustic Characteristics of Halloysite Nanotube-Reinforced Polyurethane Elastomer Composites and Their Applications.

Polyurethane incorporated with nanofillers such as carbon nanotubes, basalt fibers, and clay nanoparticles has presented remarkable potential for improving the performance of the polymeric composites. In this study, the halloysite nanofiller-reinforced polyurethane elastomer composites were prepared via the semi-prepolymer method. The impact of different halloysites (halloysite nanotubes and halloysite nanoplates) in polyurethane composites was investigated. Scanning electron microscopy, X-ray diffraction, infrared spectroscopy, electronic universal tensile testing, and acoustic impedance tube testing were employed to characterize the morphology, composition, phase separation, mechanical properties, and sound insulation of the samples. The composite fabricated with 0.5 wt% of halloysite nanotubes introduced during quasi-prepolymer preparation exhibited the highest tensile strength (22.92 ± 0.84 MPa) and elongation at break (576.67 ± 17.99%) among all the prepared samples. Also, the incorporation of 2 wt% halloysite nanotubes into the polyurethane matrix resulted in the most significant overall improvements, particularly in terms of tensile strength (~44%), elongation at break (~40%), and sound insulation (~25%) within the low-frequency range of 50 to 1600 Hz. The attainment of these impressive mechanical and acoustic characteristics could be attributed to the unique lumen structure of the halloysite nanotubes, good dispersion of the halloysites in the polyurethane, and the interfacial bonding between the matrix and halloysite fillers.

Design and evaluation of an acoustic liner applied to a UAV ducted rotor in hover

Unmanned aerial vehicles (UAVs) are currently being used for reconnaissance missions, tactical surveillance, and infrastructure inspection. These missions and operations could be performed near inhabited areas, possibly leading to noise complaints. For most UAVs, the rotor blades are the dominant source of noise. While some UAV concepts are equipped with rotor ducts for aerodynamic and safety reasons, few studies focus on the acoustic benefit of rotor ducts with integrated acoustic liners, similar to implementations on turbofan aircraft. The liner concept used in this study, called a Long Elastic Open Neck Acoustic Resonator (LEONAR), achieves good low frequency performance in a limited available space. The LEONAR concept extends the holes of the facesheet perforations into the resonator cavities with hollow tubes. As a result, the columns of air in the facesheet holes are prolongated without increasing facesheet thickness, thereby shifting the resonant frequencies of the liner lower. The objectives of this paper are to describe the simulation of noise radiated from a rotor in a duct with a LEONAR liner, the design of a liner integrated along the duct inner surface to mitigate radiated noise between 1000-5000 Hz, and impedance tube tests of liner samples to validate the predicted impedances.

Acoustical characterization and modelling of the effects of eco-friendly flame retardant treatments on hemp fiber stacks

Vegetal wools are a bio-based insulator which building applications are limited due to their flammability. To overcome this problem while respecting their bio-based nature, it seems relevant to identify and apply an environmentally friendly fireproof treatment. However, the impact of this treatment on the acoustic performance of the vegetal wools is not examined in the literature. The objective of this work is to evaluate the efficacy of two phosphorus-based fireproof treatment methods i.e., impregnation and pulverization, and their impact on the acoustic properties of hemp fiber stacks. To assess the efficacy of the fireproof treatment, the amount of phosphorus grafted and the thermal degradation of the hemp fibers were evaluated through inductive coupled plasma (ICP) and thermogravimetric analysis (TGA), respectively. On the acoustic side, the impedance tube test results showed that the treatment can negatively impact the acoustic performance of hemp fiber samples, by the reduction of the sound absorption coefficient. To better understand the effects of treatments on the porous structure characteristics of the samples, parameters such as porosity, resistivity, tortuosity, etc. are determined and the acoustic absorption of the stacks is simulated using the JCAL modelling method.

Revisiting the sound absorption mechanisms of a finite flexible perforated panel absorber using a numerical approach.

This study investigates the sound absorption mechanisms of a finite flexible perforated panel absorber. Different from existing work where the mechanisms were often investigated by comparing the sound absorption coefficient curves of different absorber configurations, a numerical approach, called virtual impedance tube (VIT) technique, is developed and used for the analysis. One advantage of this technique is the vast dataset generated can be used to investigate the sound absorption mechanisms from an energy standpoint. The developed VIT technique is first validated using the impedance tube test, where a proportion-integration-differentiation control algorithm is developed to maintain the incident sound at a desired sound pressure level. Then, the sound absorption mechanisms at three absorption peaks, i.e., hole-cavity controlled, panel-cavity controlled, and panel controlled, are investigated and the dominant energy dissipation mechanism at different sound pressure levels (SPLs) is revealed. Finally, an impedance model that takes account of the panel vibration and is applicable to various SPLs is proposed and validated.

3D Cementitious composites printing with pretreated recycled crumb rubber: mechanical and acoustic insulation properties

ABSTRACT Cementitious materials incorporating recycled crumb rubber have become a common sustainable resolution in diverse building environments to achieve various functions in terms of lightweight, ductility, as well as energy absorption. This study explored the 3D printed rubberised cementitious composites (3DPRC) in two aspects: examining the effects of crumb rubber pretreatment conditions on compressive properties; conducting experimental and numerical analysis on the acoustic dissipation characteristics of 3DPRC. Fine crumb rubber granules (3-5 mm) replaced 10%, 20%, and 30% of river sand in the composites. Uniaxial compression tests indicated that the compressive strength of 3DPRC decreased with the increase of crumb rubber content and introduced anisotropic behaviour. Impedance tube tests were conducted to evaluate the sound absorption and insulation capabilities of 3DPRC. An optimal Noise Reduction Coefficient (NRC) of 0.35 was achieved with 30% crumb rubber. The sound insulation properties depend strongly on the mass density and porosity of the 3DPRC. Additionally, it is proved that the volume of built-in air gap has positive effects on both sound absorption and insulation properties. The results from Finite Element Method (FEM) numerical simulations correlated well with experimental data, proving the efficiency of the simulation and validating the experimental results.

Meta-structure based on coupled resonators for low-frequency broadband sound absorption

This work investigates and explains the behavior of an acoustic meta-structure based on different coupled Helmholtz resonators (HR). The analytical formulation of the Maa model is used to represent both the acoustic impedance and the sound absorption mechanism of the absorber. The structures are numerically modeled using finite element method and validated experimentally in an impedance tube considering sound waves of normal incidence. The absorber samples were manufactured in ABS (acrylonitrile butadiene styrene) polymer material with the additive manufacturing technique by extrusion of material. The results of the impedance tube, numerical and theoretical tests showed agreement and the sound absorber showed a sub-wavelength scale with perfect sound absorption ( 0.97) and broadband of 292 Hz in the low frequency region (200 - 600 Hz). We deduced that the excellent experimental result obtained is due to the high resolution used in the sample manufacturing (± 0.1 mm) which minimized manufacture errors. Finally, the influences of the main parameters of the HR panel (width and depth of the micro-slit) on the sound absorption coefficient of the absorber were also analyzed.

Design and construction of the Texas Christian University impedance tube

The two-microphone impedance tube test method is a well-established and widely used technique for determining the acoustic absorption coefficient and impedance ratio of materials. This method uses two closely spaced microphones to simultaneously measure the incident and reflected sound waves. A two-microphone impedance tube measurement system made of 6061-T6 Aluminum with a diameter of 3 inches, a 0.5 inch wall thickness, and microphones spaced 2.7 inches apart has been constructed for undergraduate research at Texas Christian University (TCU). These geometrical values suggest a usable frequency range of 50 Hz to 2637.77 Hz as referenced in ASTM Standard E1050-19. Validation of the system was achieved by taking measurements on Owen Corning Type 705 pressed fiberglass board with a 1-inch thickness and comparing them to absorption data provided by the manufacturer. Additional validation measurements were taken without a test sample in place. All validation tests suggest that the TCU impedance tube is an accurate measurement system.

Prediction of the sound pressure response in an enclosed cavity with sound absorbent walls using the CMA and AMA methods

The sound pressure response in an enclosed cavity with sound absorbent walls is predicted using the classical modal analysis (CMA) method and the asymptotic modal analysis (AMA) method. The sound absorbing material is represented as an equivalent fluid with frequency dependent bulk material properties. The equivalent fluid properties can be obtained from either impedance tube test data or based on micro-scale Biot material properties. In the low frequency range, the CMA method is implemented to include the frequency dependent material properties. In the medium and high frequency ranges, when modal density is high, the frequency dependence effects become cumbersome using CMA. The AMA method has been developed as an asymptotic extension of the CMA method for the mid- and high-frequency ranges and is extended here to incorporate the frequency dependence of an equivalent fluid properties of the sound absorbing materials. An enclosed rectangular box subjected to loudspeaker excitation is used to evaluate the effect of absorption materials using the CMA method for the low-frequency range and the AMA method for the mid- and high-frequency ranges. Test data have also been obtained for comparisons of the CMA method in the low frequency range. Using these procedures, the CMA and AMA methods can be applied to represent absorbent materials over a wide frequency range for enclosure architectural design.

Sound absorption properties of the metamaterial curved microperforated panel

This paper proposes a metamaterial that utilizes resonators to enhance the sound absorption capacity of the curved microperforated panel (CMPP), and reliable theoretical analyses and experimental verification are comprehensively given. A metamaterial curved microperforated panel (MCMPP) absorber is formed by attaching local resonators on the CMPP. The displacements of the midplane of the curved panel are expanded into the improved Fourier series based on Spectral-Geometry Method (SGM), and the vibration equations of the MCMPP are derived by the Rayleigh-Ritz method. The sound absorption characteristics of the MCMPP are solved by the effective medium method and the acoustic-electric analogy method. Both a structure-acoustic coupling simulation model and an impedance tube test system are established to validate the accuracy of the present theoretical model. The essential parametric analyses are carried out in conjunction with mode splitting and acoustic-vibrational coupling, and the results show that the local resonance absorption peak within 1000 Hz increases from 1 to 5 with the absorption coefficients greater than 0.8 at these peaks under the installation options of the periodic gradient array and multiple resonances, realizing the effective absorption in multiple frequency bands. This paper provides theoretical support and experimental protocols for the design and application of the metamaterial curved microperforated panel.

Acoustic transmission loss in Hilbert fractal metamaterials

Acoustic metamaterials are increasingly being considered as a viable technology for sound insulation. Fractal patterns constitute a potentially groundbreaking architecture for acoustic metamaterials. We describe in this work the behaviour of the transmission loss of Hilbert fractal metamaterials used for sound control purposes. The transmission loss of 3D printed metamaterials with Hilbert fractal patterns related to configurations from the zeroth to the fourth order is investigated here using impedance tube tests and Finite Element models. We evaluate, in particular, the impact of the equivalent porosity and the relative size of the cavity of the fractal pattern versus the overall dimensions of the metamaterial unit. We also provide an analytical formulation that relates the acoustic cavity resonances in the fractal patterns and the frequencies associated with the maxima of the transmission losses, providing opportunities to tune the sound insulation properties through control of the fractal architecture.

Determining mechanical and acoustical behaviors of all-recycled PP sandwich structures with bi-directional sinusoidal corrugated core

By recycling the waste polymer material and using it in weight reduction studies of electric vehicles, a double-sided gain is achieved against environmental pollution. Sandwich structures with prismatic cores obtained by recycling waste polymers can be used in structural applications of light and heavy commercial vehicles and public transportation vehicles that carry cargo and passengers. These sandwich vehicle parts could help to increase the max. range and load-carrying capacity of electric vehicles. In this study, sandwich plates with prismatic egg-box cores were produced with waste Polypropylene. Since the materials are collected from different waste sources, the physical properties (additive ratio, secondary substance determination, density) of the recycled material were measured. Thereafter, hardness, quasi-static flatwise and edgewise compression, and 3-point bending tests were done to determine the mechanical properties of the structure. After that, dynamic compression and 3-point bending tests were performed to determine the strength and impact energy absorption capacity of the structure in collision situations. Finally, impedance tube tests were carried out for the acoustic characterization, which is one of the important parameters affecting interior cabin comfort, and Sound Transmission Loss (STL) and Sound Absorption Coefficient (SAC) values of the structure were determined.

Effect of Variation in Pineapple Leaf Fiber Composition with Polyurethane Matrix in Composite Panels on Acoustic Properties and Porosity

Noise can cause medical, psychological, and environmental disturbances. One of the efforts to reduce noise is by using acoustic materials. Acoustic materials can be made using natural fiber composites. This study uses pineapple leaf fiber as fiber and polyurethane as a matrix that will be formed into a sound-absorbing composite panel. This study aims are to determine the effect of variations in the composition of pineapple fiber-reinforced composites with polyurethane matrix on acoustic properties and porosity, determine the effect of frequency on acoustic properties, and determine the relationship between porosity and acoustic properties. The method used in this research uses a characterization tool in the form of a one-microphone impedance tube and porosity test equipment. Composite panels are made by varying the composition of pineapple leaf fibers with polyurethane matrix with the ratio of pineapple leaf fiber composition to polyurethane matrix, namely 50%: 50%, 60%: 40%, 70%: 30%, 80%: 20% and 90%: 10%. Based on the research, it was found that the more the amount of pineapple leaf fiber composition is used, the absorption coefficient, sound transmission loss, and prostitution will increase while the reflection coefficient decreases. The higher the frequency used, the absorption coefficient and sound transmission loss will increase while the reflection coefficient decreases for all frequencies. The relationship between porosity and acoustic properties is that the higher the porosity, the absorption coefficient and sound transmission loss will increase while the reflection coefficient decreases

Analysis on sound absorption in Sonic Black Holes

Exploration of Acoustic black holes (ABHs) for sound wave manipulation is referred to as Sonic black holes (SBHs). Different from the ideal SBH structure with continuously varied wave propagation boundary formed by putting extensive number of rings inside, the wave trapping and energy dissipation mechanism of practically realized SBH structure with discrete varied wave propagation boundary formed by quite limited number of rings inside are still not clear. To fill the gap, finite element simulations are performed to assess the sound absorption performance of a practical discrete SBH structure and explore the sound absorption mechanism behind. The validity of the FEM results is demonstrated through comparisons with experimental data obtained through impedance tube tests. Analyses reveal that the physical mechanism underpinning the sound absorption of practically realized SBH device is attributed to the combined effects of the ABH-induced wave speed changes, energy trapping and the spatially graded local resonances of series cavities formed by the space between two adjacent rings. While shedding light on the underlying sound attenuation mechanism, studies provide guidelines for further investigations on SBH structures.

The sound insulation performance of light wood frame construction floor structure based on phononic crystal theory

The development of timber structures worldwide is rapid and promising. Acoustic insulation is an important metric to measure the quality of occupants' living conditions. Therefore, to effectively improve the harm caused by low-frequency noise of the wood structure floors that people are concerned about, this paper combines the structural characteristics of the light wood frame construction floor with the phononic crystal structure with excellent sound insulation performance and carries out the impedance tube test through the simulation calculation results of COMSOL software. Impedance tube tests and field test studies were also carried out on a two-story light wood frame construction floor in Nanjing, China, to obtain a phononic crystal structure building cover with good sound insulation performance … The conclusion of the study shows that: the G8-40 phononic crystals structure obtained by COMSOL simulation matches with its impedance tube test results, and the effectiveness of its sound insulation performance has been verified by the airborne sound insulation field test; the phononic crystals structure floor has excellent sound insulation performance in the low-frequency band, which can significantly improve the user's living comfort needs and has good engineering application value.

Enhancing Air Traffic Management and Reducing Noise Impact: A Novel Approach Integrating Băneasa Airport with Otopeni RO Airport

Over the years, Bucharest’s Henri Coandă International Airport has registered a constant and high increase in air traffic, in terms of both passengers and aircraft movements. This paper presents a traffic diversion solution for the Otopeni RO airport, which aims to alleviate air traffic congestion by redirecting a proportion of the planes to the nearby airport at Băneasa. The primary challenge faced by diversion to Băneasa Airport is the proximity of residential areas to the runway at distances of less than 300 m, resulting in significant noise pollution issues. At Otopeni Airport, the main operators use aircraft equipped with CFM 56 turbo engines; therefore, this study begins with an evaluation of the noise directivity of a CFM aircraft engine via measurement. The data thus collected enabled the identification of the dominant frequencies in the acoustic spectrum of the engine noise. A resonant screen solution has been proposed as a solution for Băneasa Airport, emphasizing the importance of implementing solutions to address the noise pollution faced by those living near Băneasa Airport, due to its proximity to the residential area. Various configurations of perforated metal sheets with different perforation patterns were compared to the test performance of solid sheets to optimize noise absorption. Using the impedance tube tests to achieve the highest absorption coefficient, it was determined that the optimal distance between the perforated metal sheets and the resonant screen was 30 mm. Based on the CFM 56 turbo engine noise directivity and the impedance tube tests, a multitude of numerical simulations were conducted using the IMMI software (IMMI 2011). The simulations were performed for two scenarios with and without an acoustic barrier, accounting for the typical configuration of two engines on an aircraft. The results indicate a reduction of 15 dBA with the implementation of a 4-m-high acoustic barrier, in the case of a CFM 56 engine operating at full throttle while the aircraft is on the ground. Through numerical simulations, the optimized resonant screen demonstrated its potential to significantly reduce noise levels, thereby enhancing the overall acoustic environment and quality of life for the communities surrounding Băneasa Airport. The identified findings could serve as a basis for further research and the implementation of innovative solutions to manage air traffic and reduce the impact of aircraft noise in surrounding areas.

The Physical and Sound Absorption Property of Lightweight Rigid Polyurethane Composite Reinforced Bamboo Fiber for Roof Applications

Rigid polyurethane (RPU) foams as roof insulation have become increasingly popular in Southeast Asian countries and have been extensively used for absorbing sound and reducing noise because of their good sound damping, viscoelasticity, and low density. In this study, the RPU foam composite reinforced bamboo fiber was investigated by physical characterization by SEM, TGA, and FTIR, and the sound absorption was measured by the Impedance Tube Test. The morphology result of the RPU foam composite indicates the size of the diameter pore influenced the sound absorption by adding bamboo fiber as a filler. The thermal degradation of the presence of lignin in the bamboo fiber at the temperature range of 400 °C to 500 °C and the total weight loss is 76 % at 429 °C temperature. FTIR spectrum shows that the peak at 2890 to 2935 cm-1 are indicated –CH stretching vibrations and characteristics for bamboo fiber can be used in polymer composites. The sound absorption of RPU 25 foam composite reinforced bamboo fiber was found 0.74 absorbance at a frequency of 1250 Hz. RPU foam reinforced bamboo fiber as a filler has the highest transmission loss RPU 35 is 21 dB at a frequency range of 1600 Hz. The findings indicate by increasing the content of bamboo fiber as filler, the diameter of the open pore of RPU 25 and RPU 35 foam composite had the potential for sound absorption to absorb at low frequency to achieve greater sound absorption for roof insulation.

Laboratory evaluation on performance of Polyurethane Porous Elastic Mixture

Poroelastic road surface (PERS)has high rubber particle content and air void, and its noise reduction performance is excellent. However, the performance of Polyurethane Porous Elastic Mixture (PUPEM) prepared with different contents of rubber particles and different types of polyurethane (PU) are rarely studied. This study aims to evaluate the comprehensive and functional performance of PUPEM and to analyze the influence of rubber particle content and PU type on PUPEM. PUPEM was prepared using different types of PU and different rubber particle content. The high-temperature performance, low-temperature bending performance, water stability performance, and skid resistance performance of PUPEM were evaluated by rutting test, low-temperature bending test, freeze–thaw splitting test, immersion Cantabro loss test, pendulum friction coefficient tester and sand patch method. The effects of air void content, rubber particle content, and thickness on the noise reduction performance of PUPEM were also studied by impedance tube test and dynamic modulus test. The results indicate that the PUPEM has excellent high-temperature performance, favorable low-temperature bending performance and skid resistance, and its water stability can meet the specification requirements. PUPEM also has favorable sound absorption and noise reduction performance through voids and noise reduction performance through elastic damping. In addition, the maximum sound absorption coefficient of PUPEM corresponds to a frequency that is influenced by the thickness. In order to balance the road performance and noise reduction of PUPEM mixture, it is recommended that the rubber particle content is 10%, and the polyurethane PU-Ⅰ with larger isocyanate index is used.

Study on sound insulation performance of sonic black hole with micro-perforated plates

According to the traditional law of mass, the insulation of low-frequency sound usually requires thick, high-density materials. However, lightweight metamaterials containing acoustic structures can also achieve high acoustic transmission losses. In this study, we present a sonic black hole (SBH) device coupled with micro-perforated plates (MPPs) and intraluminal column structure to achieve high sound insulation performance with light weight. The finite element model (FEM) is developed to analyze the acoustic energy distribution and dissipation inside the SBH device to evaluate its sound transmission loss (STL), and the accuracy of the analytical model is verified by impedance tube testing. The analysis results show that the SBH device has excellent sound insulation performance in the broadband and low frequency mainly due to the energy dissipation caused by the MPPs and column structure, and wavelength compression, energy focusing caused by the SBH effect. Finally, the sound insulation capacity of SBH can be further improved by improving the structure, such as increasing the complexity of acoustic medium flow and adding the number of layers of MPPs. The numerical model and the calculation results of this paper provide a new way of thinking for the design and optimization of SBH sound insulation structures.