Sound Pressure Distribution Research Articles

Research on creation and evolution of artificial diffuse sound field

In a closed space, it is difficult to create a diffuse sound field by using a single source in the reverberation tank. In this paper, a methodology for construction of diffuse sound field using multiple source excitation is proposed. Proposed methodology is based on space processing technique for a single source sound field and also involves reciprocity of sound field transfer function. Firstly, the analytical method of acoustic excitation reverberation field is studied and subsequently the sound pressure equation for excitation reverberation sound field in case of multi sound is obtained. In addition, the numerical method to observe the influence of sound source distribution upon uniformity of sound field is studied by the acoustic analysis software ACTRAN. Finally, diffuse sound field in a glass tank of 1.5 m × 0.9 m × 0.6 m dimensions, is constructed by using 30 emission transducers of the same type. In the end, the diffuse sound field is scanned using scanning array and is then evaluated by measuring the standard difference of the space distribution of sound field. The results show that the standard deviation of the sound pressure distribution in the diffused sound field in comparison with 30 transmitting transducers simultaneously within the reverberation control area is not greater than 3.9 dB under the narrow band condition. Hence, it clearly illustrates that construction of diffused sound field by this method is definitely a viable option.

Fragmentation of cavitation bubble in ultrasound field under small pressure amplitude.

In the present study, dynamic behavior and fragmentation mechanism of acoustic cavitation bubbles are investigated under relatively small pressure amplitudes of ultrasonic wave through a three-dimensional compressive multiphase flow simulation and experimental observations. It is found that the oscillating bubble takes a non-spherical shape soon after occurring the Rayleigh collapse following the sound pressure distribution around the bubble. Then, the amplitude of non-spherical deformation is enhanced during small high-frequent oscillations after the Rayleigh collapse due to the fluid inertial effect. Finally, the oscillating bubble is fragmented into two smaller ones with the Laplace pressure gradient becoming the final trigger of bubble fragmentation. Besides, the results reveal that the temperature of bubble surface is varied when the non-spherical bubble deformation is large, while during spherical bubble oscillations the surface temperature remains almost unchanged.

A new method for researching the acoustic field of a gas ultrasonic flowmeter based on a Gaussian beam

Ultrasonic flowmeters are widely used in natural gas measurement. In order to achieve high accuracy, it is crucial to research the acoustic field. Therefore, a new method, which has the advantages of ray acoustics and wave acoustics, is proposed based on a Gaussian beam, through which the ultrasonic propagation trajectory, propagation time and sound pressure distribution can be analyzed. In order to apply a Gaussian beam in a gas ultrasonic flowmeter, flow information is added into its equation regarding three aspects: sound speed, angular frequency and sound pressure phase. In this paper, the feasibility of the improved Gaussian beam method has been verified by simulation and experiments. Firstly, under different uniform flow velocities, errors between the new method and COMSOL simulation are less than 1%. Secondly, compared with static experiments, when 125 kHz ultrasonic transducers are used, the errors between them are within ±6%. When a microphone is used to measure the sound pressure of a 36.2 kHz transducer, errors between them are within ±1.4%. Finally, sound pressure under different flow velocities has been verified through a dynamic experiment. The sound pressure and experimental voltage show the same trend of change. Verification shows that the improved Gaussian beam method can be used for acoustic field research in gas ultrasonic flowmeters.

Sound pressure distribution within human ear canals: II. Reverse mechanical stimulation.

This work is part of a study of the interactions of ear canal (EC) sound with tympanic membrane (TM) surface displacements. In human temporal bones, the ossicles were stimulated mechanically "in reverse" to mimic otoacoustic emissions (OAEs), and the sound field within the ear canal was sampled with 0.5-2 mm spacing near the TM surface and at more distal locations within the EC, including along the longitudinal EC axis. Sound fields were measured with the EC open or occluded. The reverse-driven sound field near the TM had larger and more irregular spatial variations below 10 kHz than with forward sound stimulation, consistent with a significant contribution of nonuniform sound modes. These variations generally did not propagate more than ∼4 mm laterally from the TM. Longitudinal sound field variations with the EC open or blocked were consistent with standing-wave patterns in tubes with open or closed ends. Relative contributions of the nonuniform components to the total sound pressure near the TM were largest at EC natural frequencies where the longitudinal component was small. Transverse variations in EC sound pressure can be reduced by reducing longitudinal EC sound pressure variations, e.g., via reducing reflections from occluding earplugs.

Electromechanical equivalent circuit of the radially polarized cylindrical piezoelectric transducer in coupled vibration.

Electromechanical equivalent circuit of the radially polarized cylindrical piezoelectric transducer in coupled vibration is obtained. The equivalent elasticity method is used to analyze the coupled vibration. It is an approximate analytical method, ignoring the shear and torsion stresses and strains, dividing the coupled vibration into the extensional radial and longitudinal vibrations. A mechanical coupling coefficient is introduced to connect these two equivalent vibrations. According to the electromechanical equivalent circuit, the resonance frequency equations as functions of the frequency and the mechanical coupling coefficient are acquired. The sound pressure level and far field sound pressure distribution for the transducer in water are simulated. It is demonstrated that the radiation range of the cylindrical transducer is larger than that of the ring-type transducer. Several prototypes of the transducer are fabricated; the radial and longitudinal resonance frequencies are measured. The experimental resonance frequencies are in good agreement with the analytical results. The acquisition of the electromechanical equivalent circuit contributes to analyzing the electromechanical characteristics of the radial polarized cylindrical transducer.

Acoustic characteristics of standing waves in ultrasound-assisted laser–metal inert gas hybrid welding

We propose an ultrasound-assisted laser–metal inert gas hybrid welding process, where acoustic effects are introduced by applying ultrasonic vibration in the axial direction of the arc. We studied the acoustic characteristics in the space between the acoustic radiating and reflecting surfaces. Based on a simplified two-dimensional model, we used the finite-element method to study the influence of the height and inclination of the radiating surface on the acoustic characteristics. The simulated sound pressure distribution was highly sensitive to the height and inclination of the radiating surface. The sound pressure decreased as the height of the radiating surface increased from a maximum value at the resonance height, and decreased as the inclination of radiating surface increased. Experimental results of the detachment of a water droplet from a needle were consistent with the simulation results. We simulated the distribution of the standing-wave field under different radiating concave-sphere surfaces to evaluate the acoustic focusing effects. Both experimental and simulation results for ultrasonic standing-wave levitation of plastic beads revealed the concave-sphere shape to be optimal.

Low frequency band gaps of Helmholtz resonator coupled with membrane

<sec> In this paper, a phononic crystal is designed using a Helmholtz resonator with a membrane wall, in which the coupled vibration of air and membrane is utilized. The structure of the Helmholtz resonator is a two-dimensional structure. On the basis of the square Helmholtz resonator, a " W”-type outlet is used as a cavity outlet to increase the air quality involved in resonance, and the cavity wall is replaced with a membrane with distribution mass to increase the number of resonance units. </sec><sec> The finite element method is used to calculate the band gaps and transmission loss of sound below 1700 Hz. The results show that the starting frequency of the first band gap of the structure is further reduced. At the same time, it is lower than the starting frequency of ordinary Helmholtz structure and the natural frequency of membrane under the same conditions. Then, a new peak of transmission loss is obtained, and its value is greater than the original structure’s. And although the width of the first band gap is reduced, some new band gaps appear in the low-frequency range, so that the total band gap width is improved. </sec><sec> By analyzing the vibration mode of the membrane and sound pressure distribution, it is found that the sum of the sound pressures of the outer cavity is zero at the starting frequencies of the band gaps, and the sound pressure of the inner and outer cavity are respectively positive and negative at the cut-off frequency. With the increase of frequency, the vibration mode of the membrane gradually turns from low-order to high-order, but no anti-symmetric-type mode participation is found at the starting and cut-off frequency. </sec><sec> The components of the structure can be made equivalent to corresponding ones, respectively, i.e. air in the outlet is equivalent to uniform flexible rod, and the air in the inner and outer cavity are equivalent to a spring. So that the structure can be equivalent to a series system consisting of a rod, a spring and a membrane at starting frequency of the band gap, and a loop system consisting of a rod, two springs and a membrane at cut-off frequency. Thus, by the transfer matrix method and the Rayleigh-Ritz method considering the influence of tension and elastic modulus, it is possible to calculate the range of band gap which is extremely close to the result from the finite element method. Through the analysis of the formulas, it can be found that the new band gap is caused by the new vibration mode produced by the membrane or the air in the cavity outlet, and the lower starting frequency of the first band gap is due to the reduction of the equivalent extent of the system by the membrane. </sec><sec> By adjusting the relevant parameters of the membrane and the cavity outlet respectively, it can be found that the band gaps of the structure correspond to the modes of different orders of the air in the cavity outlet and the membrane. In other words, the change of the natural frequency of a certain mode of air in the outlet or membrane only has a greater influence on the corresponding band gap but has less influence on other band gaps, also, the trends of change are the same, and the change values are very close to each other. But, changing the volume of the inner cavity and the outer cavity has a great influence on all the band gaps. Therefore, it is possible to adjust some band gaps through this method. </sec>

Impact of sound attenuation on ultrasound-driven yield improvements during olive oil extraction

High frequency ultrasound can enhance olive oil extractability industrially. However, the ultrasound attenuation phenomena and their implications on extractability, are not well understood. This work aims at evaluating the ultrasound attenuation effects on the oil extraction efficiency, while providing deeper insights into the physics behind the ultrasound extraction in a heterogeneous medium. Olives were collected and processed both in Italy and Uruguay during their respective harvest seasons. Sound pressure distribution was characterized in a high frequency ultrasound reactor, carrying 3 kg of water or paste, by using an indirect contact hydrophone device at 0.4 MHz or 2 MHz. A through-transmission ultrasonic technique was applied to determine attenuation profiles and coefficients in paste at the central frequency of each transducer, with various paste to water ratios and reactor sizes. Other ultrasound improvements on extractability were evaluated including reduction of malaxation time (10, 30 min), sonication time (2.5, 5 min) and power level (174, 280 W) without water addition and in a reactor with a 14.5 cm transducer to wall distance. However, no sound pressure levels in paste were detectable beyond 9 cm from the transducer at both frequencies. Among the various effects evaluated, an emission frequency of 0.4 MHz better improved extractability compared to 2 MHz. The attenuation profiles corroborated these findings with attenuation coefficients of 3.9 and 5.3 dB/cm measured near the respective frequencies. Improvements in oil extractability due to increasing sonication time and power level were significant (p < 0.05) also when sonicating beyond 14.5 cm and without water addition. Oil extractability improvements were observed even when sound pressure was undetectable beyond 9 cm from the transducer, suggesting that the standing wave oil trapping effect is not the governing mechanism for separation in high attenuation media for large scale systems.

Characteristics of sound pressure in the tire cavity arising from acoustic cavity resonance excited by road roughness

Under the conditions of the low-noise powertrain design and the small road roughness, the noise in car cabin from the tire cavity resonance is often remarkable. The analysis on the sound pressure inside the tire cavity arising from cavity resonance is the key work for understanding the transferring characteristics and performing the subsequent noise control. In this paper, the finite element model of a tire coupling with acoustic medium in the tire cavity is constructed and verified by tests. In order to simulate tire cavity resonance excited by road roughness, the excitation is researched firstly. There are two main excitation of tire cavity resonance: effective road roughness and the effects of tire’s rolling. The effective road roughness obtained from the road roughness power spectrum density and vehicle vibration model is taken into consideration. On this basis, the sound pressure distributions in tire cavity excited by road roughness are simulated. Also the influences of inflation pressure as well as tire load on the sound pressure distribution are studied. These works may lay a foundation for attenuating the noise inside car cabin from tire acoustic resonance.

Noncontact Transportation of Planar Object in an Ultrasound Waveguide.

This paper investigates acoustic levitation and noncontact transportation techniques for use with planar objects. An acoustic levitation system was developed which consists of a 1-mm-thick and 400-mm-long bending plate along with two bolt-clamped Langevin-type transducers (BLTs) that have stepped horns. A plane reflector was installed parallel to the vibrating plate to generate an ultrasound standing wave between the reflector and the plate. The sound pressure distribution in the ultrasound waveguide was calculated via finite-element analysis to investigate the effects of levitation of a planar object in the standing-wave field. A 1-mm-thick polystyrene plate was levitated along the nodal line of the acoustic standing wave in the waveguide. By controlling the driving phase difference between the two BLTs, the position at which flexural vibration occurs on the vibrating plate could be shifted along the length direction, and the trapped planar object could be moved by 9 mm along the same direction when the phase difference was varied from 0° to 360°.

Sound field reconstruction using multipole equivalent source model with un-fixed source locations.

The equivalent source methods (ESM) that have been developed to this point can generally be classified into two categories: one in which a relatively large number of lower order sources are fixed at various locations, and one in which a series of higher order sources are fixed at one location. The present work started with a model in the latter category, but the individual sources were then allowed to move separately to locations which were determined by using a nonlinear optimization procedure based on the measured sound field data. To test this approach, experiments were conducted using a small loudspeaker cabinet; measurements were made using an array of microphones on all sides of the loudspeaker. It was found that by allowing the source components to move, the sound field representation in both the near and far fields was improved, particularly at high frequencies, compared to the model with fixed source locations. By comparison with results obtained from boundary element calculations based on laser vibrometer measurements of the loudspeaker's diaphragm and tweeter velocities, it was found that the proposed ESM can also be used to accurately predict the sound pressure distribution on the source surface.

Development and evaluation of ultrasound-facilitated drug delivery device

We developed a new ultrasound-facilitated delivery (UFD) device with a drug infusion sapphire needle enabling real-time magnetic resonance imaging (MRI) observation and an ultrasound piezoelectric transducer (drive frequency: 260 kHz) with an effective structure for increasing drug diffusion. The sapphire needle (outside diameter: 0.6 mm, inside diameter: 0.3 mm, length: 150 mm) was grown by a micro-pulling-down method. The transducer is composed of two-stacked layers of lead zirconate titanate (PZT) on a brass base. The sound pressure distribution of the developed UFD device in water was measured with a miniature probe hydrophone, showing good agreement with the value simulated by the finite element method (FEM) analysis. The developed UFD device demonstrated high efficiency and reliability of drug diffusion, exhibiting an 8.5% increase in the volume of drug diffusion with 80% higher reproducibility and 66% lower driving voltage than the previous device. Consequently, the operating temperature of the new UFD device was decreased from 60 °C to room temperature.

Simulation research on effect of magnetic nanoparticles on physical process of magneto–acoustic tomography with magnetic induction**Project supported by the National Natural Science Foundation of China (Grant Nos. 51507171,and 61427806).

Magneto–acoustic tomography with magnetic induction (MAT-MI) is a multiphysics coupled imaging technique that is combined with electrical impedance tomography and ultrasound imaging. In order to study the influence of adding magnetic nanoparticles as a contrast agent for MAT-MI on its physical process, firstly, we analyze and compare the electromagnetic and acoustical properties of MAT-MI theoretically before and after adding magnetic nanoparticles, and then construct a two-dimensional (2D) planar model. Under the guidance of space-time separation theory, we determine the reasonable simulation conditions and solve the electromagnetic field and sound field physical processes in the two modes by using the finite element method. The magnetic flux density, sound pressure distribution, and related one-dimensional (1D), 2D, and three-dimensional(3D) images are obtained. Finally, we make a qualitative and quantitative analysis based on the theoretical and simulation results. The research results show that the peak time of the time item separated from the sound source has a corresponding relationship with the peak time of the sound pressure signal. At this moment, MAMPT-MI produces larger sound pressure signals, and the sound pressure distribution of the MAMPT-MI is more uniform, which facilitates the detection and completion of sound source reconstruction. The research results may lay the foundation for the MAT-MI of magnetically responsive nanoparticle in subsequent experiments and even clinical applications.

The coherent sound field separation method combining compressive sensing

When multiple coherent sound sources are distributed on the same side of the holographic surface, the conventional method must use known information such as sound source distribution and geometry. In view of this situation, a method of coherent sound field separation combined with compressive sensing is proposed. The method is based on the plane equivalent source near-field acoustic holography method and the orthogonal matching pursuit algorithm of compressive sensing technology. Get the distribution of the virtual sound source on the plane, and then the virtual sound sources are grouped and selected. Finally, the distribution of sound pressure in the near-field plane after separation of the sound field is calculated using the conduction matrix. The method does not require other prior knowledge. The simulation results show that this method can be used as an effective complementary method for coherent sound field separation based on single-sided measurement.

Prediction of combustion noise of an enclosed flame by simultaneous identification of noise source and flame dynamics

Large-Eddy Simulation (LES) is combined with advanced System Identification (SI) to simultaneously infer models for the source of combustion noise and the dynamic response to velocity fluctuations of a turbulent premixed flame. A Box-Jenkins model structure allows SI of both the noise source and the flame dynamics from time series data generated with single LES. The models that result from this ‘black-box’ SI approach are purely data-driven and do not rely on estimates of characteristic flow or flame parameters, such as turbulence intensity or flame length. In confined combustion systems the spectral distribution of combustion noise is strongly modulated by the cavity acoustics and the flame dynamics. By incorporating the identified models into a network model for the combustor acoustics, a linear Reduced Order Model (ROM) is built to predict the spectral distribution of sound pressure within the combustor for two different outlet reflection conditions. The identified flame transfer function as well as the ROM-based predictions of the pressure spectra in the combustor are compared with satisfactory qualitative and quantitative agreement against measurements. An interpretation of the pressure spectra based on eigenmode analysis elucidates the interplay between combustion noise generation, flame dynamics and cavity resonances.

Microwave induced thermoacoustic tomography based on probabilistic reconstruction

The performance of the existing reconstruction algorithms based on compressive sensing (CS) in microwave induced thermoacoustic tomography (MITAT) is influenced by the positions of detectors. Besides, some a priori information, such as target distribution or the correlation among thermoacoustic signals, has not been taken into account. In this letter, a probabilistic reconstruction algorithm in MITAT based on sparse Bayesian learning is proposed. Different from norm-based point estimation algorithms in CS, the sound pressure distribution which needs to be estimated is provided by probability distributions in the probabilistic reconstruction algorithm and an image is reconstructed based on the posterior density. Compared with the widely used norm-based point estimation algorithms (GPSR, Lasso) whose solution is not always the sparsest, the sparse Bayesian learning framework is globally convergent which can produce the sparsest solution at the posterior mean. Therefore, the robustness of the probabilistic reconstruction is better than that of norm-based point estimation algorithms. In addition, the estimations of the initial pressure distributions can be more accurately provided if the correlation of thermoacoustic signals can be considered, especially under the condition of low signal to noise ratio (SNR). Simulations and experiments on real breast tumors demonstrate that the proposed algorithm improves the robustness of reconstruction and show better performance at low SNRs.

Diagnosis and analysis of abnormal noise in the pure electric vehicle’s air condition compressor at idle

A pure electric vehicle may produce an abnormal ‘clicking noise’ when idling, especially as start-up, which can be a serious problem in terms of product performance. In this paper: (1) professional evaluators carry out subjective evaluations and the abnormal noise-generation mechanism and its transfer path are analysed; (2) the mode shape and sound pressure distribution are both simulated using the finite element method; (3) the AC compressor’s sound source is identified and located in the main frequency domain using the acoustic array and image formation method, so vibration and interior vehicle noise measurements from the compressor are carried out; and (4) based on the established causes of the abnormal noise, three effective approaches – structure reinforcement, manufacturing process improvement and start-up control optimization – are presented to help prevent abnormal noises from the AC compressor.

Effects of absorption placement on sound field of a rectangular room: A statistical approach

Room resonances create dramatic fluctuations in the distribution of sound pressure throughout the listening region of a room. Previous studies indicate that the addition of sound absorbing material decreases room resonances and shifts its modal characteristics. The present study proposes an approach which qualifies the effects that the additional absorption in a listening room may have on the sound fields and the frequency responses. Finite element analysis was employed for modelling the low-frequency responses of a room. The study analyses frequency responses at various listening positions involving different amounts and different placement of sound absorbents on room surfaces by observing standard deviation for linearity across a chosen frequency range. Two-dimensional sound field plots at listening height were also used to examine the spatial changes of room resonances caused by the additional absorption. The present study applied a modified statistical approach to evaluate both the sound field and the frequency responses of a room. The results were then applied to re-evaluate the effects of the absorbers location on the listening region through the proposed approach.

Simultaneous identification of transfer functions and combustion noise of a turbulent flame

The Large Eddy Simulation/System Identification (LES/SI) approach allows to deduce a flame transfer function (FTF) from LES of turbulent reacting flow: Time series of fluctuations of reference velocity and global heat release rate resulting from broad-band excitation of a simulated turbulent flame are post-processed via SI techniques to derive a low order model of the flame dynamics, from which the FTF is readily deduced. The current work investigates an extension of the established LES/SI approach: In addition to estimation of the FTF, a low order model for the combustion noise source is deduced from the same time series data. By incorporating such a noise model into a linear thermoacoustic model, it is possible to predict the overall level as well as the spectral distribution of sound pressure in confined combustion systems that do not exhibit self-excited thermoacoustic instability. A variety of model structures for estimation of a noise model are tested in the present study. The suitability and quality of these model structures are compared against each other, their sensitivity regarding certain time series properties is studied. The influence of time series length, signal-to-noise ratio as well as acoustic reflection coefficient of the boundary conditions on the identification are examined. It is shown that the Box-Jenkins model structure is superior to simpler approaches for the simultaneous identification of models that describe the FTF as well as the combustion noise source. Subsequent to the question of the most adequate model structure, the choice of optimal model order is addressed, as in particular the optimal parametrization of the noise model is not obvious. Akaike's Information Criterion and a model residual analysis are applied to draw qualitative and quantitative conclusions on the most suitable model order. All investigations are based on a surrogate data model, which allows a Monte Carlo study across a large parameter space with modest computationally effort. The conducted study constitutes a solid basis for the application of advanced SI techniques to actual LES data.

Study on the Influence of Acoustically Inhomogeneous Characteristics on Magneto-acoustic-electrical Tomography

Magneto-acoustic-electrical tomography (MAET) is a method of non-invasive conductivity imaging, with three couplings of magnetic field, acoustic field and electric field. It is suitable for the conductivity imaging of low-conductivity fluid or approximate fluid medium. MAET will have a broad application prospect in the field of bio-impedance imaging. Acoustic and electrical characteristics of biological tissue are important factors in magneto-acoustic-electrical tomography, it is essential to evaluate the effect of acoustic inhomogeneity on the sound pressure distribution and the electrical signal. In this paper, a numerical analysis of the positive problem of magneto-acoustic -electrical tomography of eight groups of human tissues with different density and sound velocity, such as blood and cerebrospinal fluid, is carried out. Firstly, establishing a two-dimensional plane model of pure fluid and applying ultrasonic excitation. Secondly, combining with the current continuity theorem and getting the target body potential distribution. Finally, the voltage signal can be calculated. The simulation results show that compared to the acoustic parameter value usually used in the approximate calculation, the voltage signal error of the muscle tissue is the largest of the seven groups of parameters under the same condition. The results of the study laid the foundation for the study of the influence of the acoustically inhomogeneous model of human tissue on the magneto–acoustic -electrical tomography.