Acoustic Applications Research Articles

Bayesian design of broadband multilayered microperforated panel absorbers.

In some noise control and architectural acoustics applications, nonfibrous, hygienic materials are desirable or even strictly required. In meeting such restrictive requirements, microperforated panel (MPP) sound absorbers represent a potential solution. Yet, they typically possess limited absorption bandwidth. Combining multiple MPPs into a multilayer system may broaden the absorption frequency ranges while maintaining high absorption. When increasing the overall absorption bandwidth, each additional MPP layer also increases the complexity of the design process because the design parameters are correspondingly increased by four per each additional layer. This paper applies a Bayesian inferential framework to the design of multilayer MPP absorbers with a parsimonious structural configuration, which penalizes the overlayered configurations. This Bayesian framework demonstrates that the practical design of multilayer MPP absorbers may be accomplished with two levels of model-based inference: model selection and parameter estimation. The design process proceeds inversely from a design target to design parameters, including the required number of MPP layers and their corresponding MPP parameters. This paper discusses the Bayesian design formulation, unified implementation of two levels of Bayesian inference, and experimental validation of a Bayesian design for a multilayered MPP absorber, which is able to meet the design target arising from practice.

Ultra-Low-Noise MIMO Distributed Acoustic Sensor Using Few-Mode Optical Fibers

Distributed optical fiber acoustic sensing technology (DAS) based on Rayleigh backscattering (RBS) is experiencing a rapid development because of the unique capability of measuring acoustic waves along long-distance optical fiber with high spatial resolution, that has broad prospects of applications, including geophysical prospecting, seismology, pipeline security, and train tracking. Despite the numerous applications, DAS currently suffers from high noise level and insufficient signal-to-noise ratio (SNR) due to inherent low RBS coefficient (&#x223C; &#x2212;70 dB&#x002F;m) in fiber, and cannot meet the application requirements of weak signal detection. Here, an ultra-low-noise MIMO DAS system using few-mode fibers (FMF) is proposed. FMF is characterized by higher non-linear effect threshold and larger capture fraction of RBS light, and through MIMO technology, the system can realize higher diversity scale and obtain more SNR gain. In addition, &#x2018;frequency label&#x2019; method is proposed to address the signal aliasing problem in transmission modes. In preliminary experiments, a 4&#x00D7;4 MIMO &#x03A6;-OTDR system is realized, where the minimum noise floor is &#x2212;88 dB rad²&#x002F;Hz with corresponding strain resolution of 0.15 <inline-formula><tex-math notation="LaTeX">$p\varepsilon /\sqrt {Hz} $</tex-math></inline-formula>. These results pave the way for advanced acoustic applications of DAS, such as acoustic emission and marine acoustics.

Influences of Various Parameters on Sound Absorption Properties of Vetiver Grass Fiber-based Developed Composite Material

Recently, the trend of natural fibers based eco-friendly materials utilization in the field of acoustic application has been growing rapidly in place of traditional synthetic materials to counter environmental issues, due to their cheap processing cost and other several advantages. In this work, sound absorption and thermal insulation properties of the vetiver grass (Chrysopogon zizanioides) based material have been investigated. Efforts have been carried out in developing porous vetiver grass fibers based composite material. The developed samples tested for the sound absorption coefficient (alpha) over a wide range of frequencies (100 Hz – 4000 Hz) by the reverberation chamber method as per IS 8225-1987/ISO 354- 2003/ASTM 423-909-19 and noise reduction coefficient (NRC) also been calculated. The experimental outcome proved that vetiver grass-based manufactured material has comparable sound absorption to already developed traditional synthetic materials. Further, two different bulk densities, thickness and fibre lengths-based samples were developed and their sound absorption acoustic performances were evaluated to see the influences of these parameters on sound absorption characteristics. Apart from these, some required physical properties as per application requirements were also discussed. However, in this study major focus has been done on acoustical properties.

Soundscape Evaluation of a Heritage Event in an Open Environment: The Water Tribunal of the Plain of Valencia (Spain)

The acoustic evaluation of indoor environments is common in the application of virtual acoustics. In addition, in the study of cultural heritage buildings, it is a useful tool, but it is not so common when describing the acoustic environment in intangible cultural heritage events and even in outdoor environments. In this paper, the acoustic environment of the Water Tribunal of the Plain of Valencia (Spain) is studied. It is analyzed from a soundscape perspective, characterizing the sound source and evaluating it within relation to the environment and evaluating its subjective response. With the research carried out, it has been obtained, on the one hand, a complete study of the acoustics of the environment of the Water Tribunal and, on the other, an enhancement of the Valencian tangible and intangible heritage.

3–1-type PZT-based porous ceramic and composites with highly oriented pore structure for acoustic applications

3–1-type PZT-based porous ceramic and composites with highly oriented pore structure for acoustic applications

An Overview of Direction-of-Arrival Estimation Methods Using Adaptive Directional Time-Frequency Distributions

Direction of arrival (DOA) is one of the essential topics in array signal processing that has many applications in communications, smart antennas, seismology, acoustics, radars, and many more. As the applications of DOA estimation are broadened, the challenges in implementing a DOA algorithm arise. Different environments require different modifications to the existing methods. This paper reviews the DOA algorithms in the literature. It evaluates and compares the performance of the three well known algorithms, including MUSIC, ESPRIT, and Eigenvalue Decomposition (EVD), with and without using adaptive directional time–frequency distributions (ADTFD) at the preprocessing stage. We simulated a case with four sources and three receivers. The sources were well separated. Signals were received at each sensor with an SNR value of −5 dB, 0 dB, 5 dB, and 10 dB. The angles of the sources were 15, 30, 45, and 60 degrees. The simulation results show that the ADTFD algorithm significantly improved the performance of MUSIC, while it did not provide similar results for the ESPRIT and EVD methods. As expected, the computation time of the algorithms was increased by implementing the ADTFD algorithm as a preprocessing step.

Tunable asymmetric acoustic transmission device based on acoustic grating and sonic crystal with point defect

A numerical demonstration is given of the feasibility of a newly designed tunable asymmetric acoustic transmission device, for which the acoustic transmission coefficients for perpendicularly incident left- and right-running waves are different at a particular single frequency within a forbidden zone. The proposed device consists of a hybrid, sonic-crystal-based resonant structure with horizontal periodicity and a one-dimensional periodic rectangular acoustic grating with vertical periodicity. The former structure exhibits a wide bandgap through which only waves with particular combinations of their frequency and propagation direction can tunnel. The direction dependence of the acoustic transmission is based on the geometrical asymmetry of the placement of the grating, and on the narrowband correspondence between the diffraction angle of the grating and the allowed transmission direction through the sonic-crystal-based structure. Angular and spectral tuning are possible by changing the grating and/or the sonic crystal periodicity. The device has potential applications in underwater acoustics for asymmetric transmission systems and secure communication systems.

Material Selection Process for Acoustic and Vibration Applications Using the Example of a Plate Resonator.

In this work, a new method for selecting suitable materials is presented. This method has a high potential for a variety of engineering applications, such as the design of sound-absorbing and vibration-loaded structures, where a large number of different requirements have to be met. The method is based on the derivation of functional dependencies of selected material parameters. These dependencies can be used in parameter studies to consider parameter combinations that lie in the range of real existing and targeted material groups. This allows the parameter space to be reduced, the calculation to be accelerated, and suitable materials to be (pre-)selected for the respective application, which contributes to a more target-oriented design. The method is applied to the example of a plate resonator. For this purpose, a semi-analytical model is implemented to calculate the transmission loss as well as the reflected and dissipated sound power of plate silencers, taking into account the influence of flow velocity and fluid temperature on the performance of plate silencers.

Modeling musician diffraction for artificially excited clarinet directivity measurements

Directivity measurements of musical instruments have many applications in musical, audio, and architectural acoustics. Typical measurement methods include artificially excited instruments and instruments played by live musicians. While recent advances in directivity measurement techniques enable higher resolutions for played instruments, the results are still limited in bandwidth and repeatability compared with directivity results from artificially excited instruments. However, artificially excited instruments typically neglect musician diffraction and absorption. This work compares possible approaches for representing musician diffraction in artificially excited clarinet measurements to improve their directivity results for room simulations or auralizations.

Development of Polymer-Ceramic-Metal Graded Acoustic Matching Layers via Cold Sintering.

A family of three phase, polymer-ceramic-metal (Poly-cer-met) electrically conducting composites was developed via cold sintering for acoustic matching application in medical ultrasound transducers. A range of acoustic impedance ( Z ) between MRayl with low attenuation (<3.5 dB/mm, measured at 10 MHz) was achieved in composites of zinc oxide, silver, and in thermoplastic polymers like Ultem polyetherimide (PEI) or polytetrafluoroethylene (PTFE) at sintering pressure less than 50 MPa and temperature of 150 °C. Densities exceeding 95% were achieved, with resistivities less than 1 Ω -cm. The acoustic velocity was homogeneous across the part (variations <5%). The acoustic velocities exceeded 2500 m/s for Z above 12 MRayl. The experimentally measured acoustic impedance of ZnO/Ag/PEI composites was observed to be in close agreement with the theoretical logarithmic model developed for different volume fractions of individual phases at the percolation limit for Ag. Thus, the acoustic properties of this family of matching layers (MLs) can be predicted to a good approximation before experimental realization. Additionally, a non-conducting low Z (5 MRayl MRayl) with acoustic velocities exceeding 2000 m/s was achieved using hydrozincite as the ceramic component. Scaling of the composites to 2'' diameter was demonstrated. A -6 dB bandwidth greater than 85% was measured for a three ML ultrasound transducer, fabricated using a single cold sintered layer ( Z = 19 MRayl) and two other commercial layers in the stack. Finally, a co-cold sintered graded prototype consisting of three tape-casted formulations corresponding to Z = 5 , 9, and 19 MRayl, while still retaining the correct distributions of the components was demonstrated.

Quantifying and transferring environmental uncertainties in underwater acoustic modeling

Uncertainties in environmental inputs represent a major source of uncertainty in underwater acoustic model outputs and applications thereof (e.g., transmission-loss estimation, source localization). Seabed geoacoustic parameters are often estimated by the inversion of ocean acoustic data. Hence, rigorous quantification of geoacoustic inversion uncertainties and the transfer of these uncertainties to modeling applications are of key importance. Uncertainty estimation in geoacoustic inversion is naturally accommodated in a Bayesian formulation, which combines data and prior information to form the posterior probability density (PPD) of seabed parameters. Important components of this approach include quantitative model selection for seabed parameterizations consistent with the information content of the data; an appropriate model for residual data errors that specifies the likelihood function; and nonlinear estimation of the PPD, which is normally carried out using Markov-chain Monte Carlo (MCMC) methods. MCMC characterizes the PPD using a large ensemble of dependent random samples of the geoacoustic parameters, which can be computationally demanding. However, these uncertainties can be transferred efficiently to subsequent propagation-modeling applications using a much-smaller, randomly chosen (independent) subset from the ensemble. The approach is illustrated using simulations and inversion of ship noise recorded on a horizontal array of hydrophones at the New England Mud Patch.

Partial field visualization using an advanced circular aperture, continuous-scan acoustic array

ATA Engineering, Inc. designed, fabricated, and tested a novel circular aperture acoustic array for continuous-scan beamforming and acoustical holography applications. The array comprises an outer perimeter of stationary reference sensors coupled to a multi-arm inner rotating array that samples the entire aperture plane. The unique architecture allows the user to perform both fixed-receiver and continuous-scan beamforming with a single array with the latter method also enabling high-spatial-resolution partial field visualization. The presentation will show results from far- and near-field partial field visualizations over the rotating array circular aperture taken at different orientations. The presentation will also describe the use of the array to measure and model isolated sources, and experimentally verify their boundary element method-predicted sound fields in the presence of a scattering body.

Analysis of turbulence and scattering effects on detecting elevated sources with a microphone array

Sound waves propagating in urban environments are affected by turbulence, scattering from numerous structures, and atmospheric refraction. These effects can be incorporated into beamforming algorithms but at the cost of increased processing time and algorithm complexity. An analysis of incorporating refraction effects into the beamformers for a simplified scenario is performed on detection algorithms based on four generalized beamforming algorithms. Simulated results for beamforming algorithms implemented with no model mismatch error are compared to results for classical beamforming algorithms implemented with model mismatch errors generated by atmospheric refraction. Their relative performance is evaluated using the area under the receiver operating characteristic curve statistic calculated with Monte Carlo simulations. The results processed with data that include effects from turbulence and rough surface scattering show that there is no significant improvement in detection performance obtained by including refraction effects into the beamforming algorithms over a wide range of frequencies. The results indicate that complex beamforming algorithms are not required for many urban acoustic applications.

Low cost acoustic transducer calibration system

An acoustic calibration system was developed primarily for underwater acoustic transducers, although applicable for a variety of acoustic applications. Historically, such systems have been large, highly customized, and very expensive. With the advent of compact cost-effective digital PC-based oscilloscopes and data acquisitions systems (e.g., devices from TiePie, Cleverscope, and Digilent), a development that began as a senior capstone-design project has recently been demonstrated. Our system is based on the TiePie Digital Oscilloscope, a PC based signal generation and acquisition systems, a power amplifier, optional preamplifier and stepper motor with controller for radiation patterns. More specifically, the receive sensor signals are acquired with a TiePie Handyscope HS6 DIFF (1000MS/s, USB 3.0 oscilloscope, with four differential analogue channels) and the transmit signal (signal generation, transmit voltage and current acquisition) utilizes a TiePie HS5-540XM 5 (500 MHz, 1-channel generator, 2-channel acquisition) measuring system. The calibration and data display is controlled with MATLAB and controlled through a graphical user interface (GUI). Examples of Transmit Pressure Response per Volt (TR/V or TVR), Free Field Voltage Sensitivity (FFVS), and Beam Pattern measurements will be provided. [Work supported by BTech Acoustics LLC.]

THE INFLUENCE OF PROCESS PARAMETERS ON THE PROPERTIES OF GLASS FOAM PRODUCED FROM INDUSTRIAL WASTE GLASS USING SiC AS THE FOAMING AGENT

Glass foams having a low bulk density, 0.22-0.36 g.cm-3 were produced using waste glass as the raw material and SiC as the foaming agent.. The produced glass foam has very high insulation performance with a very low thermal conductivity of 0.045-0.065 W.m-1.K-1, making it suitable for thermal and acoustic applications. Despite its highly porous structure, it exhibits a very high compressive strength between 0.08-6.99 MPa and a good dimensional stability. The environmentally friendly glass foam produced in this study has a potential as a structural and insulation material in construction applications. Nano-sized foaming agents enhances the efficiency of the reaction in the manufacturing process. The properties such as volume change, weight loss, microstructure, the mineralogical structure, the sintered bulk density, and the porosity of the prepared samples were measured and analyzed. The characterization of the thermal and the mechanical properties of the samples was performed by testing their compressive strength, and thermal conductivity.

Low-Frequency Low-Reflection Bidirectional Sound Insulation Tunnel with Ultrathin Lossy Metasurfaces

We report both numerical and experimental constructions of a tunnel structure with low-frequency low-reflection bidirectional sound insulation (BSI). The designed tunnel was constructed from a pair of lossy acoustic metasurfaces (AMs), which consists of six ultrathin coiled unit cells, attached on both sides. Based on the generalized Snell′s law and phase modulations for both AMs, the tunnel with the low-frequency BSI was constructed based on sound reflections and acoustic blind areas created by the AMs. The obtained transmittances were almost the same for sound incidences from both sides and were lower than −10 dB in the range 337–356 Hz. The simulated and measured results agreed well with each other. Additionally, we show that the low-reflection characteristic of the tunnel can be obtained simultaneously by thermoviscous energy loss in coiled channels of the unit cells. Finally, an interesting application of the designed tunnel in an open-window structure with low-frequency low-reflection BSI is further simulated in detail. The proposed tunnel based on the ultrathin lossy AMs has the advantages of ultrathin thickness (about λ/35), low-frequency low-reflection BSI, and high-performance ventilation, which may have potential applications in architectural acoustics and noise control.

Enhancement of convergence efficiency for airborne ultrasonic self-bending beam with phase-modulating reflector

Acoustic self-bending beams for airborne ultrasound are highly expected to expand the capabilities of existing acoustic applications. Our previous study has implemented amplitude control based on the Airy function to achieve an ultrasonic self-bending beam in air. However, the amplitude control lacks sound pressure convergence into the main lobe. To improve the convergence, we propose using a reflector to achieve phase modulation. In this study, we used the Airy function and developed the reflector that incorporates different heights to control spatial phase distribution. Using the proposed reflector demonstrated a self-bending beam for an airborne ultrasound experimentally. In addition, compared to the amplitude modulation, the phase modulation using the proposed reflector improved convergence efficiency of sound pressure level by more than 6 dB at distances of 0.7 m and 1.0 m from the emitter.

Strain sensing in underwater acoustics with a hybrid π-shifted FBG and different interrogation methods

Although Piezo-Electric Transducers (PZT) hydrophones are widely accepted and technologically mature in the field of Acoustic Emissions (AE) strain sensing underwater, optical fiber-based sensors are gaining more attraction due to their multiplexing capability, small size, high resolution, high sensitivity and immunity to Electromagnetic Interference (EMI). In this paper, we propose a hybrid Fiber Bragg Grating (FBG) system based on combining two apodized FBGs (AFBGs); named Nuttall and Cos8, separated by a pi-phase shift to apply it for underwater strain sensing. This combination results in optimum performance in terms of the reflection properties including high peak reflectivity, narrow Full Width at Half Maximum (FWHM), remarkable side lobes suppression, high roll-off rate, good Ripple Factor (RF) and high Detection Accuracy (DA) as well. In addition, an excellent multiplexing capability, high temperature and strain sensitivities and a stable operation over increased temperatures, strain and pressure levels (up to 250 °C, 1000 µstrain and 100 MPa) are achieved. Moreover, mechanical analysis and comparisons revealed that the Polymer Optical Fiber (POF) recorded the highest sensitivity among other fiber types and their coatings with a value of 1.43 pm/µstrain, making it applicable in the strain sensing in underwater acoustics. Furthermore, in this work, a detailed comparative study is performed between several types of interrogators targeting an optimum interrogator for the strain sensing application in underwater acoustics. The obtained results reveal that the linear edge absorption filter detection method achieves better results among the other types. But, unfortunately, when talking about the multiplexing capability, it shows a remarkable failure. Whereas, the Mach–Zehnder. Interferometry (MZI) comes in the second place with higher resolution range (103–104) with tunable sensitivity, fast measurement speed, good long-term stability, high multiplexing capability and medium cost. Accordingly, it could be applicable in the application understudy.

Topology optimization of soft compressible phononic laminates for widening the mechanically tunable band gaps

Active tuning of frequency bandgaps has received significant attention in the recent past. To this end, soft compressible phononic composites have indicated great promise owing to their capability to undergo large reversible deformations and deformation dependent constitutive properties. In this investigation, we present an optimization framework for arriving at the optimum topology of a two-phase soft compressible phononic composite for maximizing the frequency gap between the first four consecutive frequency bands of longitudinal wave propagation. The laminate is subjected simultaneously to an equal biaxial pre-stretch in the plane perpendicular to the direction of wave propagation and a prestress in the direction of wave propagation. The nonlinear hyperelastic neo-Hookean material model is employed for characterizing the constitutive behavior of the soft compressible laminate phases. The finite element method with Bloch–Floquet theory is employed for finding the band-structure of the infinitely periodic soft laminate. A gradient-based method of moving asymptotes is used to solve the underlying topology optimization problem. In particular, we present the optimum unit cell designs for two separate problems involving maximization of the absolute width of the band gap and that of the relative width of the band gap when compared to that in the un-deformed laminate. Test cases are presented to highlight the effects of the levels of biaxial prestretch and the longitudinal prestress. Our results indicate that a compressional longitudinal prestress and a lateral prestretch have a favorable impact on widening of the frequency band-gaps. The numerical framework and the inferences reported here can find their potential use in the optimal design of soft compressible composites used in acoustic applications.

Immersed boundary methods in wave-based virtual acoustics.

Volumetric wave-based simulation methods for room and virtual acoustics, such as the finite difference time domain method, are computationally intensive; for large volumes, operation over a regular grid is desirable for the sake of efficiency. In coping with realistic irregular geometries (such as enclosures or scattering objects), form-fitting meshing can disturb grid regularity and introduce new difficulties in terms of maintaining numerical stability. An alternative is the immersed boundary method, allowing for the representation of an irregular boundary over a regular grid through additional forcing terms in the dynamical system. While heavily used in fluid-structure interaction problems, such methods have seen less application in virtual acoustics. In this article, a simplified form of the immersed boundary method tailored to virtual acoustics is presented. Under appropriate passivity-preserving discretisation techniques, simple numerical stability conditions can be proved, and in particular, impedance boundaries may be incorporated easily without any risk of numerical instability. In addition, the method retains a largely explicit character with a small linear system solution required over the immersed boundary surface. Numerical results in two and three dimensions, illustrating various interior and exterior problem scenarios, are presented.