Reverberant Field Research Articles

Interlaboratory comparison of ISO 354 sound absorption coefficient measurements for four sound absorbing materials

Sound absorption coefficients are among the most important acoustic parameters of building materials. The coefficients are measured in reverberation chambers using the ISO354 measurement procedure. The complex reverberant sound field that builds up in such facilities is closely related to the concept of the diffuse sound field and is difficult to characterize experimentally. Due to the limited quantitative assessment of the sound field, there is no general agreement in the scientific community on how to improve the method of measuring sound absorption coefficients, although significant differences have been reported between the results of different laboratories. To address part of this challenge, we investigate how specific the variations between laboratory results are for a particular material. In our investigation, we evaluated four different sound absorbing materials in five independent acoustics laboratories. Four of the reverberation chambers used suspended diffusers, while the complex shape of one chamber was designed to achieve a diffuse sound field. The results show that the interlaboratory deviations are not very specific to the material tested, while general differences between the facilities can be observed. Furthermore, the meticulous geometric design of the chambers can be seen as an alternative to the use of suspended diffusers.

Simulated analysis and experimental validation of sound field distribution regularity for a large-scale non-anechoic harbor pool

The large-scale underwater space, such as large water pool or large-scale harbor pool can provide a good experimental environment for the measurement of the underwater radiated noise of vessel. However, it's not as simple as measuring the sound power of a small machine in the air, the measurement and evaluation of the low frequency mechanical noise and radiated sound power of vessel requires a specific reverberation environment in the large-scale underwater space. Therefore, in this paper, the reverberant sound field characteristics of large-scale underwater space are simulated and calculated by finite element analysis, and experimental measurements are carried out in the large-scale harbor pool. It was found the cut-off frequency of large-scale underwater space depends on the depth of the water pool, and the lower limit frequency depends on the volume of the water pool. The dock door does not reduce the spatial average sound pressure in the reverberation sound field, the floating box platform does not effect on the cut-off frequency but has an effect on the sound energy of the reverberant sound field. It is possible to select the appropriate underwater experimental environment for the measurement and evaluation of different mechanical noise sources. The sound pressure level obtained by calculating the sound source at different locations in the reverberation area is basically the same, and in a 16 × 22 hydrophone arrays, more than 160 array elements are selected, each between 0.25 m and 1 m, a stable sound pressure level can be obtained through spatial averaging. Through experimental measurement verification in the large-scale harbor pool, low-frequency sound sources are emitted from 6 different positions, three hydrophone arrays data are collected, and the measured sound pressure level error is within 1.4 dB. These conclusions are conducive to the actual measurement and evaluation of noise sources of vessel.

Whole embryo biomechanics with reverberant optical coherence elastography

Many morphogenesis processes during embryo development are fundamentally biomechanical processes, and disruption of these events can lead to debilitating congenital abnormalities. Imaging the biomechanical properties of embryos could provide insight into developmental disorders and could open new therapy avenues. However, current methods are invasive and are incapable of producing viscoelasticity maps of live samples in 3D. To overcome these limitations, we propose the use of reverberant shear wave fields in combination with optical coherence tomography (OCT) for high-resolution elastography at different developmental stages of murine embryos. A 1 kHz quasi-harmonic stimulation was applied to induce the diffuse shear field, which leveraged the heterogeneous microstructure and boundaries of the different tissue segments in the embryos. With this approach, we show how the shear wave speed (i.e., stiffness) of the spine, heart, and mid-brain increased as the embryo developed from embryonic day (E) 9.5 to E 11.5 at five separate stages. This noncontact technique is a promising method for imaging the biomechanical properties of different embryo structures during development with important applications for understanding developmental diseases and exploring treatments.

Angular Integral Autocorrelation for Speed Estimation in Shear-Wave Elastography

The utilization of a reverberant shear-wave field in shear-wave elastography has emerged as a promising technique for achieving robust shear-wave speed (SWS) estimation. However, many types of estimators cannot accurately measure SWS within such a complicated 3D wave field. This study introduces an advanced autocorrelation estimator based on angular integration known as the angular integral autocorrelation (AIA) approach to address this issue. The AIA approach incorporates all the autocorrelation data from various angles during measurements, resulting in enhanced robustness to both noise and imperfect distributions in SWS estimation. The effectiveness of the AIA estimator for SWS estimation is first validated using a k-Wave simulation of a stiff branching tube in a uniform background. Furthermore, the AIA estimator is applied to ultrasound elastography experiments, magnetic resonance imaging (MRI) experiments, and optical coherence tomography (OCT) studies across a range of different excitation frequencies on tissues and phantoms, including in vivo scans. The results verify the capacity of the AIA approach to enhance the accuracy of SWS estimation and the signal-to-noise ratio (SNR), even within an imperfect reverberant shear-wave field. Compared to simple autocorrelation approaches, the AIA approach can also successfully visualize and define lesions while significantly improving the estimated SWS and SNR in homogeneous background materials and providing improved elastic contrast between structures within the scans. These findings demonstrate the robustness and effectiveness of the AIA approach across a wide range of applications, including ultrasound elastography, magnetic resonance elastography (MRE), and optical coherence elastography (OCE), for accurately identifying the elastic properties of biological tissues in diverse excitation scenarios.

Key comparison CCAUV.W-K2: features of hydrophone calibration

The results of key comparison are the most convincing and objective indicator of confirmation of the correctness and accuracy of the newly developed measurement method. The results of comparison and measurement methods applied at the second key comparison of national standards of the unit of sound pressure in water CCAUV.W-K2, organized by the Consultative Committee for Acoustics, Ultrasound and Vibration of the International Committee for Weights and Measures, are described. A feature of the comparison is that the calibration range has been expanded into the low frequency region by two octaves compared to the first key comparison CCAUV.W-K1. The results of the CCAUV.W-K2 comparison were considered successful. Important scientific results of participation in the comparison were confirmation of: the correctness of the hydrophone free-field calibration methods developed at VNIIFTRI (at ultra-low frequencies for a sound-reflecting water tank and in the noise reverberant sound field of the water tank), the equivalence of the calibration results when radiating signals of various types: chirp, noise and ton-burst. In the process of performing control calibrations, the pilot laboratory discovered violations of the stability of the reference hydrophone of comparison. When comparing the results obtained by participants, there was an increase in the discrepancy between the results in the frequency range 60–100 kHz, which is considered the least problematic.

Mathematical model channel in the middle of the room systems 5G and 6G

For point-to-point connections in 5G systems, the E-band [1] has already been standardized, which means that the next generation of 6G will also use it. The E-band is located in the frequency range from 60 to 90 GHz. The use of the E-band allows radio systems to approach data transmission over optical fiber in terms of connection speed [1]. An increase in the frequency of the operating range automatically leads to a decrease in the coverage area of one transmitter. The size of cells in 5G and 6G systems is already micro-cells and pico-cells, which sometimes provides coverage only in a certain building. Most of the models used to calculate radio routes located inside buildings are based on the formula describing the propagation of radio waves in free space. However, the presence of walls, floors, furniture, people and other objects significantly affects the nature of radio wave propagation. The variety of conditions leads to the necessity of using some empirical models based on numerous experiments to investigate the conditions of radio wave propagation indoors. In this work, it is proposed to take two models as a basis - an experimental one [3] and an analytical one taking into account the reverberation field [2]. The combination of the analytical and experimental model allows you to estimate both the line-of-sight channel and the channel without line-of-sight; take into account the individual features of the premises, significantly reducing the error characteristic of experimental models; Due to the use of the indicator of the degree of losses on the route according to the experimental model, it is possible to more accurately take into account the nature of the premises. Thus, it is possible to combine the advantages and reduce the disadvantages of two modeling approaches.

Static and dynamic diffuse wave inspection of delaminations in carbon fiber reinforced composites

This paper aims to realize a self-reference delamination inspection in CFRPs with diffuse ultrasonic waves. The static experiments are first conducted on samples with a machined defect of 0.5 mm in height which simulates an opening state delamination. The diffusivity decreases with delamination diameter (pristine, 6 mm, 12 mm) at a constant depth and increases with delamination depth (0.25 mm, 0.75 mm) at a given diameter. However, no clear pattern can be found for the dissipation coefficient because of the intrinsic absorption and manufacturing uncertainties. Both coefficients are insensitive to the delamination height under loading. In contrast, the corresponding maximum cross-correlation coefficient from coda wave interferometry shows a variation of 2.4–7 % in different samples. A sharp transition can be found due to the clapping effect when the delamination is fully closed. After then, the static loading is replaced by acoustic stressing pulse from PZT in a closed delamination sample. The low frequency pulse induced reverberation field is sampled by a high frequency diffuse wave semi-synchronously, which mimics a cyclic and low amplitude loading during service. All the dynamic cross-correlation coefficient curves present an ascending trend during voltage ramp-up due to the viscoelastic effect, no matter in the intact zone or delamination zone. When the voltage threshold of 250 V is reached, the clapping effect can be triggered. A descending trend has been found not only when the excitation is right above but also near the delamination. This can be applied as an indicator of the delamination existence regionally without scanning. Such nonlinear measurement system can be expanded to passive imaging and other deficiency inspection in CFRPs with less demanding facilities.

A nested generalized sidelobe canceller for source counting, localization, and signal separation in reverberant fields

This paper proposes a nested generalized sidelobe canceller (NGSC) for typical array signal processing tasks, including source counting, localization, and signal separation. Multiple blocking matrices are arranged in a nested structure to successively eliminate dominant sources until the remaining signal is predominantly incoherent noise. The microphone signals are dereverberated using a multichannel weighted prediction error algorithm. In source counting, the number of sound sources is determined by tracking the average power of the blocked signal. In source localization, the direction-of-arrival (DOA) is estimated via cosine similarity in conjunction with the golden section search. In signal separation, the estimated DOA enables speech separation in a linearly constrained minimum variance beamformer with postfiltering (LCMV-PF). Monte Carlo simulations are performed to compare the proposed NGSC approach with four baselines, minimum description length, second order statistic of the eigenvalue, multistage Wiener filtering, and multiple signal classification. The results show that NGSC achieves at least 28.80% higher source counting accuracy with a 1.04° lower root mean square degree error than the baselines. The signal-to-distortion ratio achieved by LCMV-PF is 1.52 dB higher than that achieved by the linearly constrained minimum power beamformer and the multichannel Wiener filter.

Reverberant Sound Field Analysis of a Rectangular Room by Modal Synthesis Method

It is well known that the reverberation time within an enclosed space is dominated by its boundary surface absorption. The absorption can then be interpreted as averaged damping ratio of acoustical modes or a loss factor. The damping ratio can be determined during steady state excitation or during the transient decay or reverberation process. In this paper, acoustical reverberant field is considered as a synthesis of independent acoustical modes with their corresponding damping ratios. Each damping ratio is calculated from the absorption coefficient of the enclosed space considering the wavenumber vector. It is suggested that the consideration for the wave travelling direction in determining the modal decay rate give better results for a simple rectangular room.

Investigating vibration-based methods of measuring impact noise insulation to improve reproducibility at low frequencies

Standard impact noise insulation testing is based on measuring the average sound level in a reverberant field in order to estimate the incident and/or radiated sound power. While this method is straightforward, the variation under reproducibility conditions is significant, and a significant portion of the uncertainty is due to the complications of measuring the sound field in the receiving space. This variation is largest at low frequencies, where the effects of spatial variation and modes in the receiving room are well documented. Measuring the vibration on the surfaces of an assembly, or measuring the vibration propagation through an assembly, may provide another measure of the impact insulation of the assembly that is not affected by the sources of uncertainty associated with measuring the sound field in a room. This paper reports on the results of preliminary investigations on floor assemblies in situ while excited by impact sources and the comparison with conventional receiving room sound pressure measurements.

Lightweight modular construction of school classrooms, reverberation time prediction versus field testing

Lightweight modular schools are in the early phases of being designed and constructed throughout NSW as part of Schools Infrastructure “Modern Methods of Construction (MMC).” This method proposes the use of CLT (Cross Laminated Timber) panels, timber floor and wall cassettes, and/or hybrid systems. Schools Infrastructure NSW has developed, along with PKA Acoustic Consulting’s acoustic input, the “Kit of Parts” catalogue which utilises predetermined set of components that can easily be assembled and constructed. The classroom layout is therefore defined and can be incorporated into the acoustic predictive model. Additionally, the absorption characteristics of lightweight constructions differ to conventional construction and therefore should be considered. This presentation discusses the significance of construction type and fitout finishes, by comparing predicted reverb times of modular lightweight classrooms with in-situ absorptive testing at various cold shell, warm shell, and completed fitout stages of a school classroom and open learning space.

Multifocal acoustic radiation force-based reverberant optical coherence elastography for evaluation of ocular globe biomechanical properties.

Quantifying the biomechanical properties of the whole eye globe can provide a comprehensive understanding of the interactions among interconnected ocular components during dynamic physiological processes. By doing so, clinicians and researchers can gain valuable insights into the mechanisms underlying ocular diseases, such as glaucoma, and design interventions tailored to each patient's unique needs. The aim of this study was to evaluate the feasibility and effectiveness of a multifocal acoustic radiation force (ARF) based reverberant optical coherence elastography (RevOCE) technique for quantifying shear wave speeds in different ocular components simultaneously. We implemented a multifocal ARF technique to generate reverberant shear wave fields, which were then detected using phase-sensitive optical coherence tomography. A 3D-printed acoustic lens array was employed to manipulate a collimated ARF beam generated by an ultrasound transducer, producing multiple focused ARF beams on mouse eye globes ex vivo. RevOCE measurements were conducted using an excitation pulse train consisting of 10 cycles at 3kHz, followed by data processing to produce a volumetric map of the shear wave speed. The results show that the system can successfully generate reverberant shear wave fields in the eye globe, allowing for simultaneous estimation of shear wave speeds in various ocular components, including cornea, iris, lens, sclera, and retina. A comparative analysis revealed notable differences in wave speeds between different parts of the eye, for example, between the apical region of the cornea and the pupillary zone of the iris (). Moreover, the study also revealed regional variations in the biomechanical properties of ocular components as evidenced by greater wave speeds near the apex of the cornea compared to its periphery. The study demonstrated the effectiveness of RevOCE based on a non-invasive multifocal ARF for assessing the biomechanical properties of the whole eyeball. The findings indicate the potential to provide a comprehensive understanding of the mechanical behavior of the whole eye, which could lead to improved diagnosis and treatment of ocular diseases.

Enhancing plane-wave emission with a combination device based on acoustic metamaterial

Generating high sound-intensity plane waves typically requires transducer arrays with complex synchronizing systems and high-output amplifiers. This work proposes a simple combination device to convert fan-shaped waves into elevated sound-pressure plane waves. The proposed device primarily relies on phase reconstruction of near-zero index metamaterials and the superposition of reflected waves in the reverberation field. The compact device, which is easy to manufacture, consists of a short waveguide equipped with two types of converters. One of the converters makes use of inverted cone's sound-guiding properties to convert fan-shaped waves into cylindrical waves over a broad frequency band. The other converter is comprised of rigid cylinders with triangular lattice arrays, effectively acting as the near-zero index metamaterial to transform cylindrical waves into plane waves. Both the simulated and experimental results show that the emitted plane waves can be linearly amplified by increasing the number of point sources that are separated by integer multiples of the wavelength in the vertical cavity. This study presents a straightforward and efficient approach to generate plane waves with a low-cost array assembly design, thereby enabling the widespread use of acoustic testing and underwater detection.

A modal expansion method for simulating reverberant sound fields generated by a directional source in a rectangular enclosure

The prediction of reverberant sound fields generated by a directional source is of great interest because practical sound sources are not omnidirectional, especially at high frequencies. For an arbitrary directional source described by cylindrical and spherical harmonics, this paper developed a modal expansion method for calculating the reverberant sound field generated by such a source in both two-dimensional and three-dimensional rectangular enclosures with finite impedance walls. The key is to express the modal source density using the cylindrical or spherical harmonic expansion coefficients of the directional source. A method based on the fast Fourier transform is proposed to enable the fast computation of the summation of enclosure modes when walls are lightly damped or rigid. This makes it possible to obtain accurate reverberant sound fields even in a large room and/or at high frequencies with a relatively low computational load. Numerical results with several typical directional sources are presented. The efficiency and the accuracy of the proposed method are validated by the comparison to the results obtained using the finite element method.

Reverberant optical coherence elastography using multifocal acoustic radiation force.

In this study, we introduce a multifocal acoustic radiation force source that combines an ultrasound transducer and a 3D-printed acoustic lens for application in reverberant optical coherence elastography (Rev-OCE). An array of plano-concave acoustic lenses, each with an 11.8 mm aperture diameter, were used to spatially distribute the acoustic energy generated by a 1 MHz planar ultrasound transducer, producing multiple focal spots on a target plane. These focal spots generate reverberant shear wave fields detected by the optical coherence tomography (OCT) system. The effectiveness of the multifocal Rev-OCE system in probing mechanical properties with high resolution is demonstrated in layered gelatin phantoms.

Assessing the acoustic impedance of indoor wall surfaces through a phase array sensor

Reliable data on the acoustic absorption behavior of building materials are crucial for predicting and, therefore, designing desired acoustic conditions in the built environment. The existing methods, such as impedance tube and reverberation room, might not always be feasible due to their ownrespective limitations such as angle of incidence, large materials samples, and reproducibility issues. In this light, this study is concerned with incorporating a method based on a phased array sensor to predict the random acoustic impedances of an indoor wall surface. Considering multipath propagation in a reverberant field, it focuses on accurately designing the array shape and the sensor number. As a case study for validation, it uses parallel arranged micro-perforated panels (MPP) placed as a wall finishing material in a 10.2m × 5.47m × 3.6m sized room. Comparisons between theoretical and predicted results through the implemented method show a fair agreement. The material was also previously assessed in the impedance tube for its normal absorption coefficient. Further comparisons between results obtained through geometrical acoustics software and impedance tube are also discussed for their discrepancies regarding the proposed method.

Model based spectral feature analysis in reverberant acoustic fields

The spectral features of a reverberant acoustic field that can lead to improved source localization methods are investigated. Of particular interest are identification of deterministic and probabilistic features that characterize the environment and models of the acoustic transfer function that generate such features. For example, models that predict Schroeder’s invariant standard deviation in the pressure response at source-receiver distances where the direct sound approaches the reverberant field energy are proposed. Models examined include non-stationary Gaussian processes for the acoustic reverberant components and all-pass parametric models of the acoustic impulse response.

Quantitative biomechanics using reverberant optical coherence elastography

In this presentation, I will introduce and discuss recent developments in our effort for quantitative biomechanics of tissues and organs using a multifocal acoustic radiation force source (that combines an ultrasound transducer and a 3D-printed acoustic lens) in reverberant optical coherence elastography (Rev-OCE). An array of plano-concave acoustic lenses, each with an 11.8 mm aperture diameter, were used to spatially distribute the acoustic energy generated by a 1 MHz planar ultrasound transducer, producing multiple focal spots on a target plane. These focal spots generate reverberant shear wave fields detected by the Optical Coherence Tomography (OCT) system. The effectiveness of the multifocal Rev-OCE system in probing mechanical properties with high resolution is demonstrated in layered gelatin phantoms, tissues ex vivo, and whole mouse embryos in vivo.

Bayesian selection of plane-wave decomposition models.

Plane-wave decompositions, whereby a measured sound field is described as a superposition of plane waves, are central to many applications in acoustics and audio engineering. This letter applies a Bayesian probabilistic inference framework to the plane wave decomposition problem and examines the Deviance Information Criterion (DIC) for selecting the optimum number of waves in the decomposition. The framework learns the model directly from the data and, as such, adapts to the wavefield under study. The DIC is applied to data measured in two reverberant sound fields (highly-reverberant and lightly-damped) to determine the simplest models providing the preferred fit to the data.

An improved deconvolution beamforming algorithm for acoustic imaging of low signal-to-noise ratio sound sources in reverberant field

Most of the existing acoustic imaging studies in reverberant field ignore the influence of signal-to-noise ratio. As a result, commonly used beamforming algorithms in reverberant backgrounds have poor imaging accuracy for low signal-to-noise ratio sound sources. In response to that problem, an improved adaptive beamforming algorithm called SC-DAMAS is put forward in this paper. The algorithm replaces the free-field Green's function with the impulse response function, making the algorithm more suitable for acoustic imaging of low signal-to-noise ratio in a reverberant environment. Besides, the comparative simulation results with the conventional beamforming method and orthogonal matching pursuit algorithm-based DAMAS, as well as sound source acoustic imaging experiments are carried out to analyze its effectiveness. It is indicated that, in the reverberation field, the SC-DAMAS has no obvious sidelobes and achieves higher positioning accuracy for acoustic imaging of low signal-to-noise ratio sound source than the abovementioned counterparts, and its imaging test result is consistent with the actual situation, which verifies the effectiveness of the algorithm.