Wave Sound Field Research Articles

Numerical Study of the Movement of Fine Particle in Sound Wave Field

Inhalable particulate matter, especially PM2.5 is one of the main pollutants in China and it's harmful to both human health and atmosphere. Since the removal efficiency of traditional dust removal devices such as ESP for PM2.5 is very low, pretreatment becomes necessary before the dust gets into the dust remover. Acoustic agglomeration is one of the pretreatment technologies which uses sound wave with high intensity to make fine particles get agglomerate and grow up, and improves the efficiency of traditional dust removal devices for PM2.5. In sound wave field, fine particles are carried by the medium which in this paper is air, and vibrate with different amplitude because of different particle sizes, thus relative movement appears and then particles have more chances to collide and get agglomerate. In this paper, the movement of particles with different sizes in travelling wave sound field and standing wave sound field were calculated, including the velocity, displacement, amplitude and so on. The situation that Re<1 was considered and Viscous force in Stokes region was chose as the main forces here. Studying the movement of fine particle in sound field with different conditions has great meaning in learning the mechanisms of acoustic agglomeration.

In-situ measurement of sound absorbing properties using plane-wave sound field reproduced by virtual loudspeaker array

A new method of measuring the acoustic properties of sound absorbing material in situ under reproduced plane wave sound field is proposed. This method employs a single loudspeaker to synthesize a virtual array of loudspeakers which reproduce the plane wave sound field in front of the material surface, and applies the standard transfer function method to measure acoustic impedance and absorption coefficient. Simulation shows that this method can accurately measure absorption coefficient in the frequency range of 100–1.6 k Hz. This method is also applied to measure the absorption coefficient and acoustic impedance of two test samples in a semi-anechoic chamber, and compared with two other existing in-situ measurement methods. The proposed method demonstrates higher accuracy in measuring both acoustic impedance and absorption coefficient for the strongly-absorbing material sample in the frequency range of 175–1.6 k Hz and for the weakly-absorbing material sample in the frequency range of 250–1.6 k Hz. Experimental results and theoretical analysis also show that insufficient signal-to-noise ratio and unwanted reflected waves contribute to the insufficient accuracy of this method below 175 Hz.

Motion of a rigid prolate spheroid in a sound wave field.

The motions of a rigid and unconstrained prolate spheroid subjected to plane sound waves are computed using preliminary analytic derivation and numerical approach. The acoustically induced motions are found comprising torsional motion as well as translational motion in the case of acoustic oblique incidence and present great relevance to the sound wavelength, body geometry, and density. The relationship between the motions and acoustic particle velocity is obtained through finite element simulation in terms of sound wavelengths much longer than the overall size of the prolate spheroid. The results are relevant to the design of inertial acoustic particle velocity sensors based on prolate spheroids.

Large-amplitude acoustic streaming

AbstractA mechanism is proposed for the generation of large-amplitude acoustically-driven streaming flows in which time-mean flow speeds are comparable to the instantaneous speed of fluid particles in a high-frequency sound-wave field. Motivated by streaming observed in high-intensity discharge (HID) lamps, two-dimensional flow of a density-stratified ideal gas in a channel geometry is analysed in the asymptotic limit of high-frequency acoustic-wave forcing. Predictions of streaming flow magnitudes based on classical arguments invoking Reynolds stress divergences originating in viscous boundary layers are orders of magnitude too small to account for the observed mean flows. Moreover, classical ‘Rayleigh streaming’ theory cannot account for the direction of the cellular mean flows often observed in HID lamps. In contrast, the mechanism proposed here, which invokes fluctuating baroclinic torques away from viscous boundary layers and thus is largely independent of viscous effects, can account both for the magnitude and the orientation of the observed streaming flows.

Characterization of directional microphones in an arbitrary sound field

An acoustic characterization method for directional microphones is presented that does not require an anechoic chamber to provide a controlled plane wave sound field. Measurements of a directional microphone under test are performed in a nearly arbitrary sound field for several angles of sound incidence, and the corresponding sound pressure and pressure gradients in the vicinity of the test microphone are measured using an automated probe microphone scanning system. From these measurements, the total acoustic frequency response of the directional microphone can be decomposed into its sensitivities to sound pressure and pressure gradient using a least squares estimation technique. These component responses can then be combined to predict the directional response of the microphone to a plane wave sound field. This technique is demonstrated on a commercially available pressure gradient microphone, and also on a combination sound pressure-pressure gradient microphone. Comparisons with the plane wave responses measured in an anechoic environment show that the method gives accurate results down to 100 Hz.

Sound wave excitation of spin current

The kinetics of conduction electrons interacting with the field of sound waves in a constant magnetic field is studied. Macroscopic balance equations for macroscopic spin components are derived to describe nonlinear acoustic resonance regime. It is shown that such an interaction may give rise to a spin current.

1J2-6 Analysis and Observation of Sound Wave Field from Finite Aperture Piezoelectric Transducer : Fact-finding of Misfit between Conventional Analysis and Experiment Observation(Measurement Techniques, Imaging, Nondestructive Evaluation 2)

1J2-6 Analysis and Observation of Sound Wave Field from Finite Aperture Piezoelectric Transducer : Fact-finding of Misfit between Conventional Analysis and Experiment Observation(Measurement Techniques, Imaging, Nondestructive Evaluation 2)

Complex intensity in circular ducts containing an obstruction

Sound intensity may be defined as a complex quantity in which the real part of the intensity is related to the magnitude of the local mean energy flow, and the imaginary part to the local oscillatory transport of energy. By treating intensity as a complex quantity it is possible to visualise energy flow in a different way and this has the potential to aid in the interpretation of, say, sound fields scattered by objects. Accordingly, the sound field scattered by an object placed in a semi-infinite circular duct is examined here. Experimental measurements of complex intensity are obtained in three (orthogonal) directions using a Microflown intensity probe, and measurements are compared to predictions obtained using a finite element based theoretical model. Comparisons between prediction and measurement are undertaken for both plane wave and multi-modal sound fields and here it is noted that when at least one higher order mode propagates it becomes more difficult to obtain good agreement between prediction and experiment for the complex intensity.

Non-Invasive Method of Obtaining a Pre-Determined Acoustic Wave Field in an Essentially Uniform Medium Which is Concealed by a Bone Barrier, Imaging Method and Device for Carrying out Said Methods

A non-invasive method of obtaining a target soundwave field in the brain by means of an array of transducers positioned outside the skull, the method comprising a training stage during which, on the basis of a three-dimensional image giving the porosity of the skull at all points, digital simulation is used to determine individual sound signals to be emitted by the transducers in order to obtain the target soundwave field in the brain. After the training stage, the array of transducers is used to locate the position of the array of transducers relative to the skull by echography and to ensure that the array of transducers is accurately positioned.

Sound Field Characteristics in Air Gaps of Noncontact Ultrasonic Motor Driven by Two Flexural Standing Wave Vibration Disks

The sound field characteristics in the air gaps of the noncontact ultrasonic motor driven by two flexural standing wave vibration disks were analyzed by finite element method (FEM). Standing wave sound fields with an opposite phase were generated in the two air gaps by a single driving stator. Traveling wave sound fields in the two air gaps are formed as the superposition of the standing wave sound fields generated by two stators whose temporal phases and spatial positions are different from each other. The traveling direction of the calculated sound fields coincided with the rotating direction of the rotor observed in the experiments. The intensity of the sound field generated in the air gap by the single driving stator was measured by detecting the voltage induced in another stator. A gap distance wider than 0.5 mm is required for a high revolution speed because the sound field generated in the gap on the opposite side of the rotor is weak in an air gap narrower than 0.3 mm.

Richtmyer–Meshkov instability: theory of linear and nonlinear evolution

A theoretical framework to study linear and nonlinear Richtmyer-Meshkov instability (RMI) is presented. This instability typically develops when an incident shock crosses a corrugated material interface separating two fluids with different thermodynamic properties. Because the contact surface is rippled, the transmitted and reflected wavefronts are also corrugated, and some circulation is generated at the material boundary. The velocity circulation is progressively modified by the sound wave field radiated by the wavefronts, and ripple growth at the contact surface reaches a constant asymptotic normal velocity when the shocks/rarefactions are distant enough. The instability growth is driven by two effects: an initial deposition of velocity circulation at the material interface by the corrugated shock fronts and its subsequent variation in time due to the sonic field of pressure perturbations radiated by the deformed shocks. First, an exact analytical model to determine the asymptotic linear growth rate is presented and its dependence on the governing parameters is briefly discussed. Instabilities referred to as RM-like, driven by localized non-uniform vorticity, also exist; they are either initially deposited or supplied by external sources. Ablative RMI and its stabilization mechanisms are discussed as an example. When the ripple amplitude increases and becomes comparable to the perturbation wavelength, the instability enters the nonlinear phase and the perturbation velocity starts to decrease. An analytical model to describe this second stage of instability evolution is presented within the limit of incompressible and irrotational fluids, based on the dynamics of the contact surface circulation. RMI in solids and liquids is also presented via molecular dynamics simulations for planar and cylindrical geometries, where we show the generation of vorticity even in viscid materials.

Fundamental constraints on the performance of broadband ultrasonic matching structures and absorbers

Recent fundamental results concerning the ultimate performance of electromagnetic absorbers were adapted and extrapolated to the field of sound waves. It was possible to deduce some appropriate figures of merit indicating whether a particular structure was close to the best possible matching properties. These figures of merit had simple expressions and were easy to compute in practical cases. Numerical examples illustrated that conventional state-of-the-art matching structures had an overall efficiency of approximately 50% of the fundamental limit. However, if the bandwidth at -6 dB was retained as a benchmark, the achieved bandwidth would be, at most, 12% of the fundamental limit associated with the same mass for the matching structure. Consequently, both encouragement for future improvements and accurate estimates of the surface mass required to obtain certain desired broadband properties could be provided. The results presented here can be used to investigate the broadband sound absorption and to benchmark passive and active noise control systems.

Two-dimensional numerical simulations for the time-averaged acoustic forces acting on a rigid particle of arbitrary shape in a standing wave.

The time-averaged acoustic force can be applied to many practical fields such as contactless particle manipulation in biomedicine. It is necessary to accurately predict the mean forces on suspended obstacles to design ultrasonic particle manipulators. Although there have been many analytical solutions on this topic, it is difficult to determine the acoustic forces on obstacles under more complex system conditions such as proximity to the chamber wall, complex viscous function, acoustic streaming, and complicated particle shapes. Therefore, the numerical modeling may become a powerful tool. In this paper, the time-averaged forces, which act on rigid 2-D particles with different shapes in ideal and viscous fluids exerted by a standing sound wave field, are computed by solving the Navier-Stokes equations directly using the finite volume method (FVM) technique. The cylinder results agree well with Haydock’s theoretical prediction and his lattice Boltzmann simulations. Then, the force and torque acting on a needle shaped particle in a standing wave are calculated and discussed in detail. Furthermore, the viscous effects of the host medium are also investigated. Our program with the FVM algorithm proves to be quite suitable for calculating the acoustic forces in standing waves.

Acoustic radiation force on coated cylinders in plane progressive waves

The purpose of this paper is to present the theory of the static acoustic radiation force on layered cylinders. The frequency dependence of the acoustic radiation force function Y p (which is the radiation force per unit energy density and unit cross-sectional surface) for coated cylinders suspended in an incident plane wave sound field is analyzed, in relation to the thickness of the outer covering layer and the surrounding fluid. Explicit numerical calculations are presented for layered lossless cylinders immersed in water. The fluid-loading effect on the radiation force function curves is also analyzed by considering a high-density fluid surrounding the cylinders. These results show how absorption and the exterior fluid surrounding the cylinders affect the acoustic radiation force. It is shown here that the theory developed is much broader in scope compared to other existing theories.

The Effect of Thermal Barriers on Sound Wave Propagation

Sound propagation through regions of non-uniform temperature distribution in a gas is studied numerically. The main objective of this study is to determine the impact of temperature gradients on the sound wave parameters and to evaluate the effectiveness of using regions of hot gas as sound barrier. Such regions of hot gas (low acoustic impedance) can be generated by remotely depositing energy into a selected volume of gas, for example, by means of electrical discharge. Sound attenuation through the hot gas region is studied systematically for a range of sound wave and thermal field parameters by solving the two-dimensional unsteady compressible Euler's equations along with the ideal gas state equation using a finite volume scheme. Particular attention is given to the practical case when sound wavelength is comparable to the thickness of the thermal barrier. The present two-dimensional model indicates that considerable sound attenuation can be achieved at large incidence angles and a critical angle for total internal reflection is possible.

706 改良近距離音響ホログラフィ法による平面音波の計測結果

I have proposed a converted Nearfield Acoustic Holography (NAH) method which lightens the workload of measurement at high frequency. In former researches, the theoretical background and the effectiveness of proposing method are explained, and are verified in numerical simulations and experimentations. In former research, the numerical simulations and experimentations are applied to the point sound source(s). However the NAH method is originally based on the plane wave theory. In this research, the experimentations are performed to the plane wave sound field created by vibrated plate. As a result, it is verified that the proposing method can reconstruct almost similar images compared with original NAH method, with lesser workload.

Theoretical calculation of the modulated acoustic radiation force on spheres and cylinders in a standing plane wave-field

The acoustic radiation force on objects is the result of nonlinear properties of wave propagation in continuous media. The acoustic radiation force is known to be static for a continuous wave and is used for many applications. This force can also be dynamic (oscillatory) if the incident sound wave-field is modulated (slow time-variations). The purpose of the present paper is to develop the theory for the dynamic radiation force on spheres and cylinders immersed in ideal fluids and placed in a plane standing wave-field. It is assumed that the amplitude-modulated field is produced by dual-frequency plane wave beams propagating along the same direction. Analytical solutions and equations for the dynamic components of the force are derived. Explicit numerical calculations are presented for elastic spheres and cylinders, and rigid and fluid spheres, as well as air bubbles in water. The equations provide analytical radiation force dependencies on the acoustic field and medium parameters. Results show a new dynamic effect in the radiation force functions’ curves that results in the splitting of the resonance peaks as long as the modulation frequency increases. It is shown that the radiation force has slow time variations and cannot be treated as a steady-state phenomenon.

Experimental Investigation of Deflection of High-Speed Water Current with Aerial Ultrasonic Waves

Inside a simulated standing wave sound field that was formed with high intensity aerial ultrasonic waves with a frequency of 20 kHz and a rigid plate, we passed a high-speed current of water with a diameter of approximately 0.6 mm and a speed of 5–30 m/s and deflected the current using primarily the force of the field's sound radiation pressure. Together with the acoustic radiation force, acoustic streaming, produced from convergent ultrasonic waves and moving in a direction away from the rigid plate, generated a force that acted on a small object placed inside the standing wave sound field. The water current was deflected almost proportionally to the magnitude of this compound force. The current's angle of deflection depended on the electric power supplied to the sound source that produced the convergent ultrasonic waves and on the speed of the current.

Improvement of Dispersibility of Nanosize Diamond by Sonochemical Reaction–Relationships among Acoustic Intensity, Disaggregation, and Surface Modification–

Aggregated nanosize diamond particles were disaggregated and had their surfaces modified by ultrasound exposure. A standing wave sound field was formed in a water tank using a Langevin-type transducer. Acoustic cavitation was generated in the water tank. Aggregated nanosize diamond particles with sizes of about 5 µm were disaggregated in particles with sizes of 40 nm by ultrasound exposure for 20 min. The magnitude of the zeta potential on nanosize diamond particles was increased by more than twice by ultrasound exposure. The sound field in the water tank was measured using a hydrophone. The average acoustic intensity was calculated from measured values of sound pressure. The zeta potential began to increase with increasing average acoustic intensity of more than 800 W/m2.

Acoustic instabilities at the transition from the radiation-dominated to the matter-dominated universe

The transition from acoustic noise in the radiation-dominated universe to the density structures in the matter dominated epoch is considered. The initial state is a stochastic field of sound waves moving in different directions. The construction of the initial state is compatible with the hyperbolic type of propagation equation for density perturbations, and parallel to the theory of stochastic background of gravitational waves. Instantaneous transition between the cosmological epochs is assumed, and Darmois-Israel joining conditions are applied to match solutions for sound waves with growing or decaying modes at the decoupling. As a result a substantial amplification of the low scale structures is obtained.