Incident Acoustic Pressure Research Articles

A Comparative Study on Acoustic Parameters of Porous Absorber of polyamide, polyester and polyurethane

The analysis and simulation of porous absorbers using COMSOL Multiphysics software is a powerful tool for predicting the acoustic performance of these materials. Porous absorbers are widely used in various industries, including automotive, aerospace, and architectural acoustics. The study aims to provide a better understanding of the acoustic properties of porous absorbers, and the simulation results could be used for optimizing the design of porous absorbers for specific applications. The main objective of this research is to investigate the effect of various parameters on the acoustic performance of porous absorbers, Sound pressure level, scattered acoustic pressure, Incident acoustic pressure, Point pressure, Normal Impedance, Absorption Coefficient. The absorber made from polyamide, Polyester and polyurethane are selected for the studies. The better absorbing results are obtained from the absorber made from polyurethane. The COMSOL software is used to simulate the acoustic behavior of porous absorbers, and the results are compared with experimental measurements to validate the accuracy of the simulation. Keywords: porous absorber, analysis and simulation, acoustic properties, comsol software.

Modeling of MEMS Transducers with Perforated Moving Electrodes.

Microfabricated electroacoustic transducers with perforated moving plates used as microphones or acoustic sources have appeared in the literature in recent years. However, optimization of the parameters of such transducers for use in the audio frequency range requires high-precision theoretical modeling. The main objective of the paper is to provide such an analytical model of a miniature transducer with a moving electrode in the form of a perforated plate (rigid elastically supported or elastic clamped at all boundaries) loaded by an air gap surrounded by a small cavity. The formulation for the acoustic pressure field inside the air gap enables expression of the coupling of this field to the displacement field of the moving plate and to the incident acoustic pressure through the holes in the plate. The damping effects of the thermal and viscous boundary layers originating inside the air gap, the cavity, and the holes in the moving plate are also taken into account. The analytical results, namely, the acoustic pressure sensitivity of the transducer used as a microphone, are presented and compared to the numerical (FEM) results.

Direction of arrival estimation of an acoustic wave using a single structural vibration sensor

The modal vibrational response of a flexible panel to an incident acoustic pressure wave is dependent on the direction of arrival (DOA) of the wave. This work presents a proof of concept whereby vibration measurements of flat panels made by structural sensors were used to infer the DOA of an incident acoustic wave. In the experiments reported here, rectangular panels with various material damping factors were excited in an anechoic space by acoustic waves incident at angles between −90° and ＋90° in the horizontal plane. Mel-frequency cepstral coefficients (MFCCs) were computed from the recorded panel responses and used to train a deep neural network (DNN) to estimate the DOA. Experimental results show that under controlled conditions, the DOA of incident acoustic waves containing broadband noise may be estimated to within ±5° with a reliability of 99.8% utilizing recordings from a single structural sensor. For acoustic waves containing less spectrally uniform human speech signals, a DNN trained using data from a single sensor correctly estimated DOA to within ±5° with a reliability of 86.5% and to within ±10° with a reliability of 96% within the experimental conditions. The scope of this work is to suggest that a panel’s modal response may contain sufficient information to enable DOA estimation with as few as one sensor. As such, a proof of concept is presented in place of a final engineering solution, along with a discussion of experimental limitations and future improvements.

Correlation Between Portal Vein Pressure and Subharmonic Scattering Signals From SonoVue Microbubbles in Canines.

The current gold standard for the clinical diagnosis of portal hypertension (PH) is an invasive and indirect estimation of portal vein pressure (PVP). Therefore, the need for a non-invasive PVP measurement method is urgent. Subharmonic scattering of ultrasound contrast agent (UCA) microbubbles is under investigation in clinical research as a pressure indicator. However, the driving acoustic pressure must be optimized to improve the ambient pressure sensitivity of the subharmonic amplitude for different UCAs. In this study, for the first time, we obtained the relationship between the PVP and the amplitude of the subharmonic signal scattered from SonoVue microbubbles by using two canines to build the PH model. The results revealed a desirable linear correlation between the subharmonic amplitude and PVP (<20 mmHg) at the incident acoustic pressure of 453 kPa (r=-0.910, p < 0.005; sensitivity: -2.003 dB/mmHg); this was one order of magnitude higher in sensitivity than that of the in vitro case with a detectable pressure variation of approximately 1 mmHg. This indicates the feasibility of using UCA microbubbles to accurately measure low ambient pressures in vivo and further exhibits the potential of the method for non-invasive pressure estimation in clinical applications.

Effect of temperature on sound transmission loss of laminated composite plate

In this investigation, by an analytical approach, the influence of several key parameters, especially the temperature on the sound isolation capacity of the symmetrically finite orthotropic laminated composite plate is studied. The plate is modeled with classic thin-plate theory and is assumed to be simply supported on all four sides. The incident acoustic pressure is modeled as a harmonic plane wave impinging on the plate at an arbitrary angle. The sound transmission loss is calculated from the ratio of incident to transmitted acoustic powers

Vibroacoustic behavior of a rectangular composite plate in thermal environment

This paper is a study of the vibroacoustic behavior of orthotropic laminated composite rectangular plate under a sound wave excitation in thermal environments. An improved analytical procedure has been developed that allows for an efficient solution of the finite composite plate sound transmission problem. A symmetrically orthotropic laminated composite plate is considered. The plate is modeled with classic thin-plate theory and is assumed to be clamped on all four sides. The incident acoustic pressure is modeled as a harmonic plane wave impinging on the plate at an arbitrary angle. The sound transmission loss is calculated from the ratio of incident to transmitted acoustic powers.

Phononic-Crystal-Based Particle Sieving in Continuous Flow: Numerical Simulations.

Sieving specific particles from mixed samples is of great value in fields such as biochemistry and additive manufacturing. In this study, a particle sieving method for microfluidics was proposed based on a phononic crystal plate (PCP), the mechanism of which originates from the competition between the trapping effect of the resonant PCP-induced acoustic radiation force (ARF), disturbance effect of acoustic streaming (AS), and flushing effect of the continuous inlet flow on particles suspended in microfluidic channels. Specifically, particles with different sizes could be separated under inlet flow conditions owing to ARF and AS drag forces as functions of the particle diameter, incident acoustic pressure, and driving frequency. Furthermore, a comprehensive numerical analysis was performed to investigate the impacts of ARF, AS, and inlet flow conditions on the particle motion and sieving efficiency, and to explore proper operating parameters, including the acoustic pressure and inlet flow velocity. It was found that, for each inlet flow velocity, there was an optimal acoustic pressure allowing us to achieve the maximum sieving efficiency, but the sieving efficiency at a low flow velocity was not as good as that at a high flow velocity. Although a PCP with a high resonant frequency could weaken the AS, thereby suiting the sieving of small particles (<5 μm), a low channel height corresponding to a high frequency limits the throughput. Therefore, it is necessary to design a PCP with a suitable resonant frequency based on the size of the particles to be sieved. This investigation can provide guidance for the design of massive acoustic sorting mi-crofluidic devices based on phononic crystals or acoustic metamaterials under continuous flow.

Metasurface zero-impedance matching mechanism for aerodynamic noise reduction

In order to control the low-mid frequency aerodynamic noises, the zero-impedance matching mechanism of a stepped multi-neck Helmholtz resonator (SMNHR) metasurface on a 1/4 scale Ahmed upper surface is revealed through simulation and experiment. First, this stepped multi-layer neck widens the resonance peak bandwidth compared to the single neck of Helmholtz resonator (HR) due to the decreased acoustic mass and almost unchanged surface acoustic resistance under free inducement without fluid flow. Then, under incident fluid flow, the stepped neck improves the interaction between the cavity and main flow, and thus reduces the surface acoustic impedance. Moreover, the formation of larger pressure difference at the SMNHR interface results in greater shear force, which generates stronger vortexes and bigger ellipse vortex areas inside the neck causing rapidly increased flow velocity and further decreased impedance. Furthermore, increasing the absorption area ratio of SMNHR could make the impedance much smaller as well as less affected by the increasing main-flow velocity, i.e., it is easier to achieve zero impedance even under higher main-flow velocity. When the incident acoustic pressure at the interface are counteracted by the scattered acoustic pressure, the zero-impedance matching is achieved and the near-wall acoustic pressure could be minimized. Finally, a subwavelength SMNHR metasurface composed of four parallel cells with a larger broadband is designed and verified by the wind tunnel test, in which an average sound pressure level (SPL) reduction of 3.59 dB (A) within 1320 Hz−5350 Hz under a main-flow velocity of 50 m/s is realized. The zero-impedance matching mechanism with the metasurface design presented could have potential applications for controlling aerodynamic noises, especially in the low-frequency broadband aspects.

An efficient frequency-domain prediction method for aeroacoustic radiation and scattering using equivalent sources

An efficient radiation and scattering prediction method is proposed in the frequency domain based on the convective Ffowcs Williams–Hawkings (FW–H) equation and the convective equivalent-source method (ESM). In this work, the convective FW–H equation and its spatial derivatives are adopted to develop ESM-I and ESM-S for predicting incident acoustic pressure and acoustic pressure gradient, respectively. The equivalent sources strength of ESM-I and ESM-S are determined by matching the pressure and pressure gradient boundary conditions on the integral surface of FW–H equation. The pressure gradient from ESM-S constructs a hard-wall boundary on a solid surface for the prediction of scattered pressure. Since then the total acoustic pressure can be efficiently evaluated from the incident and scattered components. An energy-based singular value decomposition method is adopted to filter the small singular values that probably lead to solution instability. Convective Green functions are suggested, which allow the final prediction methodology to be suitable for situations in different dimensions with the inclusion of moving-medium effects. Available analytical solutions for point sources as well as a monopole scattered by a cylinder, a sphere and a plane are used to examine the parameter sensitivity and accuracy of the proposed methodology.

Subharmonic Scattering of SonoVue Microbubbles Within 10-40-mmHg Overpressures In Vitro.

Ultrasound contrast agent microbubbles are considered promising sensors to measure portal vein pressure noninvasively. In this study, we investigated the subharmonic scattering power and optimal incident acoustic pressure of SonoVue microbubbles (concentration: [Formula: see text]/mL 0.9% NaCl solution) in the ambient pressure range of 10-40 mmHg with 10-mmHg increments at a temperature of 25 °C. The results demonstrated that the subharmonic response of the SonoVue microbubbles existed in three stages: the first growth stage (40-300 kPa), saturation (300-400 kPa), and the second growth stage (400-540 kPa). In the first growth stage, the subharmonic amplitude increased with ambient pressure. However, while the ambient pressure increased, the subharmonic amplitude decreased in the second growth stage. The best correlation of the subharmonic amplitudes with the ambient pressures was obtained at a high incident acoustic pressure of 520 kPa (sensitivity: 0.15 dB/mmHg, r2 = 0.99 , and root-mean-square error = 0.49 mmHg), which indicated that the subharmonic signals in the second growth stage might be suitable for estimating low ambient pressures. The results presented in our study may pave the way for portal vein pressure estimation using SonoVue microbubbles as sensors in clinical applications.

Precise micro-particle and bubble manipulation by tunable ultrasonic bottle beams

This paper reports a method to generate tunable bottle beams using an ultrasonic lens, by which the bottle position can be precisely adjusted with the change of the acoustic frequency. Therefore, the position of a single particle or bubble in liquid can be manipulated without using phased array which is costly and huge with complex circuits. Furthermore, we introduced this method to multiple bubble manipulation using acoustic holography. The bottle properties against frequency are theoretically and experimentally analyzed. It is shown that the bottle position depends almost linearly on the operating frequency, which provides a basis for the precise manipulation of bubbles and particles. In addition, the relationship between the acoustic radiation force and the drag force under different incident acoustic pressures is considered, establishing a limit on the moving velocity of the trapped particles. The ultrasonic field observation is further demonstrated by Schlieren imaging system. The proposed method has potential biomedical applications, such as more flexible cell manipulation and targeted drug delivery in vivo, as well as potential applications in the study of chemical reactions between micro objects.

Experimental demonstration of enhanced acoustic energy harvesting with a subwavelength metamaterial plate

In this work, we propose an acoustic energy harvesting metamaterial consisting of an array of silicone rubber pillars and a PZT patch deposited on an ultrathin aluminum plate with several holes based on locally resonant mechanism. The resonance is formed by removing four pillars, drilling a few of holes and attaching the PZT patch on the aluminum plate. The strain energy originating from an incident acoustic wave is centralized in the resonant region, and the PZT patch is used to convert the elastic strain energy into electrical power. Numerical analysis and experimental results show that the proposed millimeter-scale harvester with holes obviously improves the effect of acoustic energy harvesting while performing at the subwavelength scale for sonic low-frequency environment (less than 1150 Hz). In addition, the experimental results demonstrate that the maximum output voltage and power of the proposed acoustic energy harvesting system with 16 holes of 2 mm radius are 3 and 10 times higher than those without holes at the resonant mode for 2 Pa of incident acoustic pressure. Both the number and size of holes have a significant effect on the performance of acoustic energy harvesting. The advantages of the proposed structure are easy-to-machine and full of practicality, and it can be used in broad applications for low-frequency acoustic energy harvesting.

Non-negative intensity for planar structures under stochastic excitation

Identification of regions on a vibrating structure which radiate energy to the far field is critical in many areas of engineering. Non-negative intensity is a means to visualize contributions of local surface regions to sound power from vibrating structures. Whilst the non-negative intensity has been used for structures under deterministic excitation due to structural forces or harmonic incident acoustic pressure excitation, it has not been considered for analyzing a structure under stochastic excitation. This work analytically formulates non-negative intensity in the wavenumber domain to investigate the surface areas on a vibrating planar structure that are contributing to the radiated sound power in the far field. The non-negative intensity is derived in terms of the cross spectrum density function of the stochastic field and the sensitivity functions of either the acoustic pressure or normal fluid particle velocity. The proposed formulation can be used for both infinite planar structure and finite plate in an infinite baffle. To demonstrate the technique, a simply supported baffled panel excited by a turbulent boundary layer as well as an acoustic diffuse field is considered and those regions contributing to the radiated sound power are identified. It is demonstrated that the non-negative intensity distribution is dependent on the stochastic excitation. It is also found that for a panel under stochastic excitation the more the non-negative intensity distribution is concentrated within the panel surface, the more efficient the panel radiates sound to the far field.

Effect of Incident Acoustic Pressure Amplitude on the Transmission Loss of Helmholtz Resonators

Acoustic transmission loss is a common parameter utilized throughout several studies to evaluate the acoustic characteristics of a given test element. Transmission loss has been frequently referred to as a source independent parameter. However, this work presents evidence that the incident acoustic pressure amplitude does, in fact, have an effect on the measured transmission loss for some passive damping devices. The transmission loss was experimentally measured utilizing the two-source location method and the specimens tested include an expansion chamber, a quarter wave resonator, a Herschel–Quincke tube and various Helmholtz resonators. When varying the power supplied to the acoustic source, it was noted that all the devices exhibited nearly constant values of transmission loss, with the exception of the Helmholtz resonators. The Helmholtz resonators had a significant variance of transmission loss with respect to the acoustic source power. This decrease in performance is caused by the “jet-flow” phenomenon occurring at the Helmholtz resonator neck, which results in increased acoustic losses. The present work illustrates that the assumption of source independence, which is often made when using transmission loss to evaluate damping devices, must be taken with caution, as this assumption is case dependent and may be crucial when scaling experimental studies to an industrial setting.

The use of an acoustic quiet zone as an active acoustic cloaking system

The use of active control to acoustically cloak an object has been demonstrated previously, and is effective if the scattered component of the pressure field can be measured and directly minimised. In practice, this is non-trivial as a pressure sensor in the sound-field will detect the superposition of the incident and scattered pressures. An alternative approach is presented here which uses the control sources to generate a zone of quiet around the scattering object, with a constraint on their exterior radiation. This reduces the incident acoustic pressure on the object and thus the acoustic scattering. In this case, real-time measurements of scattered pressure or detailed geometrical knowledge of the scattering object are not required. The performance of the proposed acoustic cloaking strategy is assessed using simulated data of a rigid spherical scattering object, using a practical arrangement of control sources and error sensors. The same arrangement of sources and sensors is also used to directly minimise the scattered sound field

Considerations for Choosing Sensitive Element Size for Needle and Fiber-Optic Hydrophones-Part II: Experimental Validation of Spatial Averaging Model.

Acoustic pressure can be measured with a hydrophone. Hydrophone measurements can underestimate incident acoustic pressure due to spatial averaging effects across the hydrophone sensitive element. The spatial averaging filter for a nonlinear focused beam is a low-pass filter that decreases monotonically from 1 to 0 as frequency increases from 0 to infinity. Experiments were performed to test an analytic model for the spatial averaging filter. Nonlinear pressure tone bursts were generated by three source transducers with driving frequencies ranging from 2.5 to 6 MHz, diameters ranging from 19 to 64 mm, and focal lengths ranging from 38 to 89 mm. The nonlinear pressure fields were measured using four needle hydrophones with nominal geometrical sensitive element diameters of 200, 400, 600, and [Formula: see text]. The average root-mean-square difference between theoretical and experimental spatial averaging filters was 5.8% ± 2.6%.

A convected frequency-domain equivalent source approach for aeroacoustic scattering prediction of sources in a moving medium

In this paper, a convected frequency-domain approach for acoustic scattering prediction is suggested, for sources and scattering surfaces in a uniform constant flow. Frequency-domain moving-medium formulations are used for prediction of the incident acoustic pressure and acoustic pressure gradient. The latter is required for evaluation of the hardwall boundary condition in a moving medium and allows a convected definition of the equivalent sources. The scattering approach is validated by the analytical case of scattering of a pulsating monopole source by a rigid sphere. The applicability of the methodology to moving-medium problems is demonstrated for rotating and pulsating monopole point sources in a uniform flow, located near an infinite flat scattering surface. The suggested approach allows frequency-domain scattering predictions for sources in a uniform constant flow of any subsonic velocity, enabling direct inclusion of convection effects on incident and scattered acoustics. The hardwall boundary condition is thus evaluated directly in a moving medium. The need for a Lorentz transform is obviated, overcoming the complexity it introduces and the limitations it imposes.

Efficient Method to Predict Rotor Noise Scattered by an Axisymmetric Body

This paper presents an efficient method for predicting noise radiated from rotating sources and scattered by an axisymmetric body, in which a frequency-domain numerical method and a null-field method are employed to compute the acoustic radiation and scattering phenomena, respectively. The novelty of the present research is that an advanced method is proposed to locate fictitious interior observers inside the scattering surface, contributing to that the incident acoustic pressure received by the fictitious interior observers can be efficiently computed. Numerical cases show that the developed method ensures high computational accuracy and significantly improves the computational efficiency compared with existing methods, showing an appealing application potential in efficiently predicting rotor noise scattered by the shaft and casing. Parametric studies are carried out to investigate the effects of the hub–tip ratio and the rotating frequency on a rotor noise scattered by a hub.

Inactivation of Planktonic Escherichia coli by Focused 2-MHz Ultrasound

This study was motivated by the desire to develop a non-invasive means to treat abscesses, and represents the first steps toward that goal. Non-thermal, high-intensity focused ultrasound (HIFU) was used to inactivate Escherichia coli (∼1 × 109 cells/mL) in suspension. Cells were treated in 96-well culture plate wells using 1.95-MHz ultrasound and incident focal acoustic pressures as high as 16 MPa peak positive and 9.9 MPa peak negative (free field measurements). The surviving fraction was assessed by coliform culture and the alamarBlue assay. No biologically significant heating was associated with ultrasound exposure. Bacterial inactivation kinetics were well described by a half-life model, with a half-time of 1.2 min. At the highest exposure levels, a 2log inactivation was typically achieved within 10 min. The free field-equivalent peak negative acoustic pressure threshold for inactivation was ∼7 MPa. At the highest acoustic pressures used, inactivation efficacy was insensitive to reciprocal changes in pulse length and pulse repetition frequency at constant duty factor. Although treated volumes were very small, proof of principle was provided by these experiments.

Prediction of sound transmission through, and radiation from, panels using a wave and finite element method.

This paper describes the extension of a wave and finite element (WFE) method to the prediction of noise transmission through, and radiation from, infinite panels. The WFE method starts with a conventional finite element model of a small segment of the panel. For a given frequency, the mass and stiffness matrices of the segment are used to form the structural dynamic stiffness matrix. The acoustic responses of the fluids surrounding the structure are modelled analytically. The dynamic stiffness matrix of the segment is post-processed using periodic structure theory, and coupled with those of the fluids. The total dynamic stiffness matrix is used to obtain the response of the medium to an incident acoustic pressure. Excitation of the structure by oblique plane waves and a diffuse sound field are considered. The response to structural excitation and the consequent radiation are determined. Since the size of the WFE model is small, computational times are small. Various example applications are presented to illustrate the approach, including a thin isotropic panel, an antisymmetric, cross-ply sandwich panel and a symmetric panel with an orthotropic core.