An Experimental Approach for Detection of the Acoustic Radiation Induced Static Component in Solids

We propose an experimental approach to directly detect the acoustic radiation induced static component(SC)of primary longitudinal(L) wave propagation in solids using an ultrasonic pitch-catch technique,where a lowfrequency ultrasonic transducer is used to detect the SC generated by the co-propagating primary L-wave tone burst that is excited by a high-frequency ultrasonic transducer.Essentially,the experimental approach proposed uses a dynamic method to detect the SC generated.The basic requirement is that the central frequency of the low-frequency ultrasonic transducer needs to be near the center of the main lobe frequency range of the time-domain envelope of the primary L-wave tone burst.Under this condition,the main lobe of the frequency spectrum of the SC pulse generated adequately overlaps with that of the low-frequency ultrasonic transducer.This will enable the generated SC pulse to be directly detected by the low-frequency ultrasonic transducer.The performed experimental examination validates the feasibility and effectiveness of the proposed approach for direct detection of the acoustic radiation induced SC generated by L-wave propagation in solids.     

复杂流场的超声-激光测量原理研究

本文从复杂流场—旋涡场参量的超声—激光测试方法的需要出发,论述了超声波产生的声相位光栅对激光产生的偏转效应.并研制了适用于产生空气超声相位光栅的大功率高频超声换能器、位移灵敏接收器、数字相位差测定仪等设备,采用了超声发射的匹配技术等,从而获得了明显的空气超声-激光偏转效应,并且测定了两光束的偏转时间差.本文的结果为利用超声-激光的空气声光偏转效应测量空气旋涡流场参量提供了实验依据.     

Coherent Brillouin spectroscopy in a strongly scattering liquid by picosecond ultrasonics

In a modification of a picosecond ultrasonic technique, a short acoustic pulse is launched into a liquid sample by a laser pulse absorbed in a semitransparent transducer film and is detected via coherent Brillouin scattering of a time-delayed probe pulse. With both excitation and probing performed from the transducer side, the arrangement is suitable for in vivo study of biological tissues. The signal is collected from a micrometer-thick layer next to the transducer and is not affected by the diffuse scattering of probe light deeper in the sample. The setup, utilizing a 33 nm thick single crystal SrRuO(3) transducer film, is tested on a full fat milk sample, with 11 GHz acoustic frequency recorded.     

Controlled cell aggregation in a pulsed acoustic field

Cell aggregation in ultrasonic resonators can be obtained in a few seconds. Hundreds even thousands of cells can be levitated in suspension and generate 2D or 3D aggregates. Nevertheless, the aggregation rate and the 2D or 3D configurations of the resultant aggregates are very difficult to control. This work reports on a novel way of generating and controlling particle and cell aggregates using pulsed ultrasound. This technique specifically explores (in addition to the ultrasound wave, frequency and amplitude) the time of ultrasound application, i.e. the number of pulses as well as the pulse repetition frequency. We demonstrate that with pulsed ultrasound, particles and/or cells levitate in suspension, as with continuous ultrasound, and the aggregation rate can be modified in a controlled manner. By carefully tuning the number of pulses and the repetition frequency, the 3-D and 2-D configurations of the aggregates can be selectively generated. In addition, pulsed ultrasound limits transducer heating, thus allowing for higher acoustic energies than those currently employed with continuous ultrasound.     

Acoustic energy output of a transducer unit

The acoustic energy output of a magnetostrictive transducer unit has been observed by the calorimetric method. The object was to observe the energy output of the unit from low to high ultrasonic intensities under identical conditions of transducer frequency and acoustic load. The design and construction of the calorimeter and its mode of operation are discussed in some detail.     

Determination of acoustic impedances of multi matching layers for narrowband ultrasonic airborne transducers at frequencies <2.5 MHz - Application of a genetic algorithm

The effective ultrasonic energy radiation into the air of piezoelectric transducers requires using multilayer matching systems with accurately selected acoustic impedances and the thickness of particular layers. One major problem of ultrasonic transducers, radiating acoustic energy into air, is to find the proper acoustic impedances of one or more matching layers. This work aims at developing an original solution to the acoustic impedance mismatch between transducer and air. If the acoustic impedance defences between transducer and air be more, then finding best matching layer(s) is harder. Therefore we consider PZT (lead zirconate titanate piezo electric) transducer and air that has huge acoustic impedance deference. The vibration source energy (PZT), which is used to generate the incident wave, consumes a part of the mechanical energy and converts it to an electrical one in theoretical calculation. After calculating matching layers, we consider the energy source as layer to design a transducer. However, this part of the mechanical energy will be neglected during the mathematical work. This approximation is correct only if the transducer is open-circuit. Since the possibilities of choosing material with required acoustic impedance are limited (the counted values cannot always be realized and applied in practice) it is necessary to correct the differences between theoretical values and the possibilities of practical application of given acoustic impedances. Such a correction can be done by manipulating other parameters of matching layers (e.g. by changing their thickness). The efficiency of the energy transmission from the piezoceramic transducer through different layers with different thickness and different attenuation enabling a compensation of non-ideal real values by changing their thickness was computer analyzed (base on genetic algorithm). Firstly, three theoretical solutions were investigated. Namely, Chebyshev, Desilets and Souquet theories. However, the obtained acoustic impedances do not necessarily correspond to a nowadays available material. Consequently, the values of the acoustic impedances are switched to the nearest values in a large material database. The switched values of the acoustic impedances do not generally give efficient transmission coefficients. Therefore, we proposed, in a second step, the use of a genetic algorithm (GA) to select the best acoustic impedances for matching layers from the material database for a narrow band ultrasonic transducer that work at frequency below the 2.5 MHz by considering attenuation. However this bank is rich, the results get better. So the accuracy of the propose method increase by using a lot of materials with exact data for acoustic impedance and their attenuation, especially in high frequency. This yields highly more efficient transmission coefficient. In fact by using increasing number of layer we can increase our chance to find the best sets of materials with valuable both in acoustic impedance and low attenuation. Precisely, the transmission coefficient is almost equal to unity for the all studied cases. Finally the effect of thickness on transmission coefficient is investigated for different layers. The results showed that the transmission coefficient for air media is a function of thickness and sensitive to it even for small variation in thickness. In fact, the sensitivity increases when the differences of acoustic impedances to be high (difference between PZT and air).     

Modeling and experimental validation of hydrodynamics in an ultrasonic batch reactor

Simulation of hydrodynamics in ultrasonic batch reactor containing immobilized enzymes as catalyst is done. A transducer with variable power and constant frequency (24 kHz) is taken as source of ultrasound (US). Simulation comprises two steps. In first step, acoustic pressure field is simulated and in second step effect of this field on particle trajectories is simulated. Simulation results are compared with experimentally determined particle trajectories using PIV Lab (particle image velocimetry). Effect of varying ultrasonic power, positioning and number of ultrasonic sources on particle trajectories is studied. It is observed that catalyst particles tend to orientate according to pattern of acoustic pressure field. An increase in ultrasonic power increases particle velocity and also brings more particles into motion. Simulation results are found to be in agreement with experimentally determined data.     

一种基于互易原理的超声功率新测量方法

本文从换能器的互易原理出发，利用平面波自易校准法获得换能器的自由场发送电流响应．根据平面活塞型换能器的衍射规律，推导出发射声功率的表达式．由此计算互易换能器在给定驱动电流（或电压）作用下的辐射超声功率．基于上述原理，使用自易校准装置测量了互易换能器的声功率一频率曲线．估计的测量不确定优于±20％．     

复频聚焦超声换能器水中焦区商场特性的研究

本文对新研制的一种复频聚焦超声换能器的辐射声场进行了实验研究,测定了辐射压在轴向上的分布曲线,进而确定了焦区位置,这与理论所得结果符合较好,测定了辐射声压在焦平面上的分布曲线,并对焦区声场进行了定位,最后对换能器在水中焦区辐射声的频谱进行了研究,不仅观测到了两个源波,而且还观测到了和频波,差频波以及倍频波,证实了声散射声效应的存在。     

Ultrasonic particle concentration in a line-driven cylindrical tube

Acoustic particle manipulation has many potential uses in flow cytometry and microfluidic array applications. Currently, most ultrasonic particle positioning devices utilize a quasi-one-dimensional geometry to set up the positioning field. A transducer fit with a quarter-wave matching layer, locally drives a cavity of width one-half wavelength. Particles within the cavity experience a time-averaged drift force that transports them to a nodal position. Present research investigates an acoustic particle-positioning device where the acoustic excitation is generated by the entire structure, as opposed to a localized transducer. The lowest-order structural modes of a long cylindrical glass tube driven by a piezoceramic with a line contact are tuned, via material properties and aspect ratio, to match resonant modes of the fluid-filled cavity. The cylindrical geometry eliminates the need for accurate alignment of a transducer/reflector system, in contrast to the case of planar or confocal fields. Experiments show that the lower energy density in the cavity, brought about through excitation of the whole cylindrical tube, results in reduced cavitation, convection, and thermal gradients. The effects of excitation and material parameters on concentration quality are theoretically evaluated, using two-dimensional elastodynamic equations describing the fluid-filled cylindrical shell with a line excitation.     

Particle sizing using passive ultrasonic measurement of particle–wall impact vibrations

In continuously stirred reactor vessels the non-invasive recovery of the particle size could be used to monitor the reaction process. Experimental and numerical investigations have shown empirically that the frequency of the peak vibration response arising from the particle–wall impact is inversely proportional to the particle size. The passive monitoring of these impact vibrations using an ultrasonic transducer has the potential therefore of non-invasively recovering the particle size. However, the vessel geometry, fluid loading, variable impact position and velocity, stirrer and transducer effects, and noise levels make this problem very complex. There are a large number of system parameters and this makes empirical derivations of cause and effects extremely difficult. The first objective of this paper is to derive an analytical expression for the vibrations arising from a spherical particle impacting a circular plate. Using a series expansion in terms of the plate loss parameter, an expression for the frequency of the peak pressure in terms of the system parameters is derived. In particular, its explicit dependency on the impacting particle size and the impact velocity is found. The inverse problem of recovering the particle size from the experimental data is then investigated. A set of experiments are described where the impact vibrations are recorded using an ultrasonic transducer attached to the rear of a thin plate. The results show that it is possible to recover the particle size using this approach. Data from a second set of experiments, involving multi-particle impacts with a vessel wall in a continuously stirred reactor, are then used. The inverse problem of recovering the particle size from the vibration spectrum was then investigated with encouraging results.     

Modeling of a high frequency ultrasonic transducer using periodic structures

Solidly mounted integrated transducers with a Bragg cell inserted between the piezoelectric film and the substrate are investigated for high frequency ultrasonic applications. A numerically stable recursive one dimensional transmission/reflection model was used to analyze the behavior of the periodic structure. This theoretical analysis includes the study of the influence of the acoustic properties of the constitutive layer, the effect of the number of cells and their arrangement. A 35 MHz integrated transducer consisting in a PZT ceramic laid down on a Au/PZT Bragg cell deposited on a porous substrate was fabricated and characterized. Both theoretical and experimental results highlight the interest of using a periodic structure for high frequency ultrasonic 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.     

Analysis and identification for the electromagnetic ultrasonic interfacial echoes using instantaneous spectrum and artificial neural network

The proper frequency is experimentally chosen to be the operation frequency of the electromagnetic acoustic transducer. The instantaneous amplitude, phase and frequency of the detected ultrasonic echoes from a multilayer adhesive sample of steel and rubber materials are calculated and composed to form three-dimensional instantaneous spectrum which is successful to distinguish the testing signals from different adhesive states qualitatively. Then, average instantaneous parameters in sensitive time window are picked up and used as the input eigenvectors for the BP artificial neural network. Identified results in both training and testing volumes demonstrate that the detected electromagnetic ultrasonic interracial echoes can be identified and classified automatically with the correctness ratio larger than 95%.     

非侵入式超声波浆料浓度测量技术研究*

设计了一种基于非侵入式超声波透射衰减法的浆料浓度测量系统,根据超声传播衰减原理,建立超声衰减值与浆料浓度之间的关系。实验中采用生物显微镜和激光粒度仪对颗粒标称粒径进行验证,采用中心频率为200 kHz的超声波换能器,利用一发一收模式对超声波在有机玻璃管内的浆料进行非侵入式测量并分析透射波信号,对体积百分浓度小于25%、不同粒径的石英砂浆料进行测量,通过拟合方法获得浆料温度、体积百分浓度与声衰减对应的关系,并据此构造浓度求解方程,通过现场实时在线测量并与取样结果进行对比验证方程的准确性,结果显示,本方法可有效测量浆料浓度。     

Experimental study of underwater transmission characteristics of high-frequency 30 MHz polyurea ultrasonic transducer

In this paper, we present the transmission characteristics of a polyurea ultrasonic transducer operating in water. In this study, we used a polyurea transducer with fundamental resonance at approximately 30 MHz. Firstly, acoustic pressure radiated from the transducer was measured using a hydrophone, which has a diameter of 0.2 mm. The transmission characteristics such as relative bandwidth, pulse width, and acoustic sensitivity were calculated from the experimental results. The results of the experiment showed a relative bandwidth of 50% and a pulse width of 0.061 μs. The acoustic sensitivity was 0.60 kPa/V with good linearity, where the correlation coefficient R in the fitting calculation was 0.996. A maximum pressure of 13.1 kPa was observed when the transducer was excited at a zero-to-peak voltage of 21 V. Moreover, we experimentally verified the results. The results of the pulse/echo experiment showed that the estimated diameters of the copper wires were 458 and 726 μm, where the differences between the actual and measured values were 15% and 4%, respectively. Acoustic streaming was also observed so that a particle velocity map was estimated by particle image velocimetry (PIV). The sound pressure calculated from the particle velocity obtained by PIV showed good agreement with the acoustic pressure measured using the hydrophone, where the differences between the calculated and measured values were 12–19%.     

Measurements of acoustic properties of aqueous dextran solutions in the VHF/UHF range

The acoustic properties of aqueous solutions of dextran are characterized in the frequency range of 70-400 MHz by the bio-ultrasonic spectroscopy system using an ultrasonic transmission comparison method. The attenuation, velocity, impedance, and density of aqueous dextran solutions, for six molecular weights in the range of 10,400-2,000,000 Da in the concentration range 520% by weight, are reported. All four parameters increase with increasing concentration. As the molecular weight increases, the attenuation coefficient increases and the velocity decreases. The precise frequency and molecular weight dependences of the acoustic properties of the solutions are readily determined by the system.     

Boundary element simulation of backscattering properties for red blood with high frequency ultrasonic transducers

High frequency ultrasonic imaging (e.g. >30 MHz) from blood is difficult due to its tenuous backscattered pressure and the interference from adjacent tissues as well. To increase the sensitivity focused transducer has to be used, thus raising the complexity of interpreting the received signals. A numerical simulation of the ultrasonic scattering property from erythrocyte and rouleaux based on boundary element method was performed with experimental results based on a modified substitution method. The results (proportional relationship between backscattered pressure and frequency and the frequency limit for Rayleigh scattering) closely coincide with experimental data for erythrocyte. Rouleaux model results also show the dependence of degree of red cell aggregation on backscattering properties. The boundary element method serves as a good means to calculate the acoustic scattering from blood cells under arbitrary incident waves.     

Oscillating bubble concentration and its size distribution using acoustic emission spectra

New method has been proposed for the estimation of size and number density distribution of oscillating bubbles in a sonochemical reactor using acoustic emission spectra measurements. Bubble size distribution has been determined using Minnaert's equation [M. Minnaert, On musical air bubbles and sound of running water, Philanthr. Mag. 16 (1933) 235], i.e., size of oscillating bubble is inversely related to the frequency of its volume oscillations. Decomposition of the pressure signal measured by the hydrophone in frequency domain of FFT spectrum and then inverse FFT reconstruction of the signal at each frequency level has been carried out to get the information about each of the bubble/cavity oscillation event. The number mean radius of the bubble size is calculated to be in the range of 50-80mum and it was not found to vary much with the spatial distribution of acoustic field strength of the ultrasound processor used in the work. However, the number density of the oscillating bubbles and the nature of the distribution were found to vary in different horizontal planes away from the driving transducer surface in the ultrasonic bath. A separate set of experiments on erosion assessment studies were carried out using a thin aluminium foil, revealing a phenomena of active region of oscillating bubbles at antinodal points of the stationary waves, identical to the information provided by the acoustic emission spectra at the same location in the ultrasonic bath.