On-Line Particle Size Analysis Using Ultrasonic Velocity Spectrometry

A new method is described for the determination of particle size distribution of slurries based on ultrasonic velocity spectrometry combined with gamma-ray transmission. This method shares the advantages of ultrasonic attenuation spectroscopy of being capable of analyzing highly concentrated samples without dilution. However the ultrasonic velocity method is better suited to fine particles of diameter from about 0.1 to 30 μm, a greater volume of slurry is analysed and therefore sampling errors are reduced, and precise theoretical models are readily available to permit the accurate determination of size distribution by inversion of ultrasonic velocity measurements. The method can also be used to accurately determine particle size cut points by linear correlation. Using either inversion or correlation methods, the accuracy of particle size information from ultrasonic velocity spectroscopy is significantly enhanced by the independent measurement of solids loading by gamma-ray transmission. In addition, larger sizes can be measured by combining the ultrasonic velocity method with ultrasonic attenuation measurements. The method has been tested in the laboratory on a wide variety of mineral and paint slurries. The method determined the size distribution of single component silica and alumina samples in water in agreement with laser diffraction measurements and the method successfully distinguished well and poorly dispersed TiO₂ suspensions. For composite samples the method discriminated separate TiO₂ and CaCO₃, components and determined their proportions to within 0.25% volume. In addition the method, in combination with ultrasonic attenuation measurements, determined the size fractions of iron ore slurries below 10 and 30 μm to within 1.3% and 1.0% relative respectively, when compared with laser diffraction measurement of particle size. The CSIRO is presently designing an industrial gauge which will be manufactured and installed in an industrial slurry stream in 1997.     

Study of low concentrated ionic ferrrofluid stability in magnetic field by ultrasound spectroscopy

Ultrasound spectroscopy has been used to investigate the effect of magnetic field on particle (cluster) size distribution in ionic ferrofluid. The method applied is non-destructive, fast and sensitive to structural changes of a suspension as it is based on measurements of ultrasonic attenuation. Changes in the ultrasound attenuation induced by an external magnetic field have been measured for different frequencies of the acoustic wave. According to the Harker-Temple theory, the aggregation process has been analysed on the basis of the cluster size distribution determined for different magnetic field intensities.     

Particle Size Distribution Analysis of Industrial Colloidal Slurries using ultrasonic spectroscopy

Several solid-liquid suspensions containing submicron particles at moderate to high concentrations (5 to 50 volume percent) are encountered in industrial slurry processing. Measurements of ultrasonic attenuation spectra are used in a newly developed AcoustoPhor particle analysis system to get particle size distributions of such colloidal suspensions. This paper deals with the performance evaluation of the AcoustoPhor system. The automated ultrasonic spectrometer component of the AcoustoPhor system was tested using a reference silicone liquid for its accuracy and precision. The particle size distribution (PSD) estimation capabilities were evaluated using a set of well-dispersed slurries covering a wide range of particle concentrations. Sensitivity to process variations was evaluated in field tests at a pigment manufacturing plant. The AcoustoPhor system appears to be capable of providing reliable PSD data for inorganic pigment slurries with particle diameters ranging from 0.01 to 100 micrometers at particle concentrations as high as 50 volume percent.     

Ultrasonic Spectrometry for Particle Size Analysis in Dense Submicron Suspensions

Ultrasonic spectrometry was applied to the particle size analysis of disperse systems. The investigations were made for acoustic conditions called the long-wavelength regime (LWR). In the LWR the acoustic behaviour is governed by dissipative effects rather than by scattering. Two principal theoretical approaches to ultrasonic spectrometry — scattering theory and coupled phase models — are introduced. A model based on a newly developed coupled phase model and the scattering theory (ECAH theory) is implemented in the ultrasonic spectrometer Acousto Phor. Experiments were carried out for several suspensions with a high density contrast. It could be demonstrated that the model successfully describes acoustic attenuation and that the inversion algorithm finds particle size distributions comparable to those given by other measurement techniques. With regard to the particle size, a lower and an upper limit for the applicability were determined, which include three decades. As a further result, the model was validated at concentrations up to 10 vol.%. The model is considered to be open to development to cover even higher concentrations.     

表征超声衰减谱粒度的改进和声搜索算法

针对超声衰减谱法颗粒粒径测量,提出一种改进和声搜索算法,在和声搜索算法迭代达到200次时,加入拟牛顿算法,调节和声搜索算法全局和局部搜索能力,提高算法的收敛精度.对服从3种典型粒径分布函数颗粒系进行数值模拟,改进算法反演得出罗辛-拉姆勒(Rosin-Rammler)分布参数值相对误差小于8％,正态分布参数值相对误差小于...     

Investigation of the influence of humidity on the ultrasonic agglomeration of submicron particles in diesel exhausts

Removing very fine particles in the 0.01-1 micro m range generated in diesel combustion is important for air pollution abatement because of the impact such particles have on the environment. By forming larger particles, acoustic agglomeration of submicron particles is presented as a promising process for enhancing the efficiency of the current filtration systems for particle removal. Nevertheless, some authors have pointed out that acoustic agglomeration is much more efficient for larger particles than for smaller particles. This paper studies the effect of humidity on the acoustic agglomeration of diesel exhausts particles in the nanometer size range at 21 kHz. For the agglomeration tests, the experimental facility basically consists of a pilot scale plant with a diesel engine, an ultrasonic agglomeration chamber a dilution system, a nozzle atomizer, and an aerosol sampling and measuring station. The effect of the ultrasonic treatment, generated by a linear array of four high-power stepped-plate transducers on fumes at flow rates of 900 Nm(3)/h, was a small reduction in the number concentration of particles at the outlet of the chamber. However, the presence of humidity raised the agglomeration rate by decreasing the number particle concentration by up to 56%. A numerical study of the agglomeration process as a linear combination of the orthokinetic and hydrodynamic agglomeration coefficients resulting from mutual radiation pressure also found that acoustic agglomeration was enhanced by humidity. Both results confirm the benefit of using high-power ultrasound together with humidity to enhance the agglomeration of particles much smaller than 1 micro m.     

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。     

High frequency attenuation measurements of lipid encapsulated contrast agents

A number of recent studies have indicated the potential of ultrasound contrast agent imaging at high ultrasound frequencies. However, the acoustic properties of microbubbles at frequencies above 10 MHz remain poorly understood at present. In this study we characterize the high frequency attenuation properties of (1) BR14, (2) BR14 that has been mechanically filtered (1 and 2 microm pore sizes) to exclude larger bubbles, and (3) the micron to submicron agent BG2423. A narrowband pulse-echo substitution method is employed with a series of four transducers covering the frequency range from 2 to 50 MHz. For BR14, attenuation decreases rapidly from 2 to 10 MHz and then more gradually from 10 to 50 MHz. For 2 microm filtration, the attenuation peaks between 10 and 15 MHz. For 1 microm filtration, attenuation continues to rise until 50 MHz. The agent BG2423 exhibits a diffuse attenuation peak in the range of 15-25 MHz and remains high until 50 MHz. These results demonstrate a strong influence of bubble size on high frequency attenuation curves, with bubble diameters of 1-2 microm and below having more pronounced acoustic activity at frequencies above 10 MHz.     

Ultrasonic Measurement of Sub-Micron Particles

Based on technology described in a Du Pont patent for an offline system, we have developed a prototype in-line ultrasonic cell for measuring particle size distribution. We have used this cell to verify the Allegra-Hawley model of ultrasonic attenuation in dilute (< 5 % vol) slurries of sub-micron ceramic particles, and we are developing a model that can cope with the multiple scattering effects occuring at higher concentrations. In this paper we present the results of attenuation measurements for ultrasound (2–50 MHz) in slurries with concentrations ranging from 0.5 010 to 38 010 (vol). The attenuation is proportional to slurry concentration up to 5 010 (vol) and is predicted by single scattering models. Above approximately 100% concentration, the attenuation is actually lower than expected. For the dilute slurries we find excellent agreement between our measurements and the Allegra-Hawley calculations, and the effects of the particle size distribution are evident in the ultrasonic attenuation spectrum. These ultrasonic data can be inverted to determine the particle size and concentration in aqueous slurries of sub-micron particles.     

Optimal Acoustic Attenuation of Weakly Compressible Media Permeated with Air Bubbles

Based on fuzzy logic （FL） and genetic algorithm （GA）, we present an optimization method to obtain the optimal acoustic attenuation of a longitudinal acoustic wave propagating in a weakly compressible medium permeated with air bubbles. In the optimization, the parameters of the size distribution of bubbles in the medium are optimized for providing uniformly high acoustic attenuation in the frequency band of interest. Compared with other traditional optimization methods, the unique advantage of the present method is that it can locate the global optimum quickly and effectively in need of knowing the mathematical model precisely. As illustrated by a numerical simulation, the method is effective and essential in enhancing the acoustic attenuation of such a medium in an optimal manner. The bubbly medium with optimized structural parameters can effectively attenuate longitudinal waves at intermediate frequencies with an acoustic attenuation approximating a constant value of lO（dB/cm）. Such bubbly media with optimal acoustic attenuations may be applied to design acoustic absorbent by controlling broader attenuation band and higher efficiency.     

A theoretical study of the feasibility of acoustical tweezers: ray acoustics approach

The optical tweezer has been found to have many biomedical applications in trapping macromolecules and cells. For the trapping mechanism, there has to be a sharp spatial change in axial optical intensity and the particle size must be much greater than the wavelength. Similar phenomenon may exist in acoustics. This work was undertaken to demonstrate theoretically that it is possible to acoustically trap particles near the focal point where most of the acoustic energy is concentrated if certain conditions are met. Acoustic force exerted on a fluid particle in ultrasonic fields is analyzed in a ray acoustics regime where the wavelength of acoustic beam is much smaller than the size of the particle. In order to apply the acoustical tweezer to manipulating macromolecules and cells whose size is in the order of a few microns or less, a prerequisite is that the ultrasound wavelength has to be much smaller than a few microns. In this paper, the analysis is therefore based on the field pattern produced by a strongly focused 100 MHz ultrasonic transducer with Gaussian intensity distribution. For the realization of acoustic trapping, negative axial radiation force has to be generated to pull a particle towards a focus. The fat particle considered for acoustic trapping in this paper has an acoustic impedance of 1.4 MRayls. The magnitude of the acoustic axial radiation force that has been calculated as the size of the fat particle is varied from 8lambda to 14lambda. In addition, both Fresnel coefficients at various positions are also calculated to assess the interaction of reflection and refraction and their relative contribution to the effect of the acoustical tweezer. The simulation results show that the feasibility of the acoustical tweezer depends on both the degree of acoustic impedance mismatch and the degree of focusing relative to the particle size.     

Intercomparison of Inversion Algorithms for Particle‐Sizing Using Mie Scattering

The applicability of different inversion algorithms to retrieve a size distribution of particles in air from light scattering is examined. The investigation is focused on an optical measurement setup with an elliptical mirror as the main optical element. In order to evaluate the capabilities of the individual inversion methods, light scattering by spherical particles is simulated in the size ranges of 0.1 – 10 μm and 0.05 – 1 μm. The distribution of the particle diameters is modeled with three different parametric functions, i.e., RRSB, logarithmic‐normal and a more specific distribution from an ultrasonic nebulizer. Different kinds of noise, e.g., additive and/or multiplicative, are applied in different levels to the simulated scattering measurement to include real physical measurement conditions. The convergence properties of the scattering simulation are investigated with respect to the number of size classes, and thus, information concerning the size resolution required to simulate a measurement for a given particle size distribution is obtained. Further parameters of interest are the minimum angular resolution of the measurements, the number of size classes of the retrieved particle size distribution and the measured polarization of the scattered light.     

一种低声速沉积层海底参数声学反演方法

软泥底环境下沉积层参数的声学反演是国际水声领域的一个研究热点.浅海中,当高声速基底和海水之间存在一层低声速(小于海水声速)的沉积层时,小掠射角情况下不同频率声传播损失会出现周期性增大现象.基于此现象,提出一种适用于低声速沉积层的海底参数声学反演方法.首先,推导给出小掠射角情况下传播损失周期增大的频率间隔与沉积层声速、厚度及近海底海水声速之间的解析表达式;其次,利用一次黄海实验中软泥底环境下的宽带声传播信号,提取了小掠射角下传播损失增大的频率周期;再次,把该解析表达式作为约束条件,结合Hamilton密度与声速的经验公式,采用匹配场处理反演给出沉积层的声速、密度、厚度及基底的声速、密度;然后,利用声传播损失数据反演得到泥底环境下不同频率的声衰减系数,通过拟合发现泥底声衰减系数随频率近似呈线性关系;最后,给出了双层海底模型和半无限大海底模型等效性的讨论.反演结果为低声速沉积层海底声传播规律研究与应用提供了海底声学参数.     

Measurement of the acoustic properties of a nerve-muscle preparation as a function of physiologic state

Nerve-muscle preparations of Sprague Dawley rats were exposed to low dosage ultrasound. The objectives were to measure the velocity of propagation and attenuation of ultrasonic energy in both the relaxed and contracted states. A tension-measuring system and associated ultrasonic instrumentation were designed to measure the tension developed in stimulated muscle and its corresponding acoustic parameters, ie the attenuation coefficient, (db cm^-1) and the velocity of propagation, c (ms^-1). Each test was performed at ultrasonic frequencies 3.1, 5.35, and 7.68 MHz and with the preparation maintained at 23 ± 0.5° C. Attenuation of ultrasonic energy was observed to increase by 10 ± 0.5% in the active state from its value in the relaxed state. The relation between the attenuation and the acoustic frequency was found to be approximately linear over the frequency range tested. The velocity of propagation in the active state did not change appreciably from its value in the relaxed state and was observed to be independent of the acoustic frequency in the range used.     

Ultrasonic characterization of heavy metal TeO2–WO3–PbO glasses below room temperature

The longitudinal ultrasonic attenuation measurements have been made using pulse echo method at fundamental frequencies of 2, 4, 6 and 8 MHz in 20WO₃–(80−x) TeO₂–xPbO ternary tellurite glasses (x=10, 12.5, 15, 17.5 and 20 mol%) in the temperature range 160–280 K. The results showed the presence of a broad peak which shifts to higher temperature with increasing frequency. The ultrasonic attenuation peaks suggest that the experimental behavior is controlled by thermally activated structural relaxations. The internal friction, acoustic activation energy, deformation potential, relaxation strength, number of loss centers and density of state have been calculated both as a function of temperature and PbO content. The acoustic activation energy was found to decrease from 0.156 to 0.135 eV with the increase of PbO content. The results showed that both the number of loss centers and their activation energy decrease with the atomic ring size. An increase in the density of state is observed with addition of PbO content at the same frequency in the whole range of temperature which is associated with structural units formed when PbO is added.     

Geoacoustic Inversion Based on a Vector Hydrophone Array

We propose a geoacoustic inversion scheme employing a vector hydrophone array based on the fact that vector hydrophone can provide more acoustic field information than traditional pressure hydrophones. Firstly, the transmission loss of particle velocities is discussed. Secondly, the sediment sound speed is acquired by a matchedfield processing （MFP） procedure, which is the optimization in combination of the pressure field and vertical particle velocity field. Finally, the bottom attenuation is estimated from the transmission loss difference between the vertical particle velocity and the pressure. The inversion method based on the vector hydrophone array mainly has two advantages： One is that the MFP method based on vector field can decrease the uncertain estimation of the sediment sound speed. The other is that the objective function based on the transmission loss difference has good sensitivity to the sediment attenuation and the inverted sediment attenuation is independent of source level. The validity of the inverted parameters is examined by comparison of the numerical results with the experimental data.     

基于超声波测量技术的颗粒尺寸分布模型的研究

提出了一种利用单颗粒背向散射信号来进行粒径分布估算的超声波测量技术,系统阐述了其 理论基础及基本工作原理。被测颗粒的散射信号幅度与它在探测区中的位置、颗粒尺寸和形状有关。 通过理论分析,建立了一个可用于描述散射信号幅度概率分布与颗粒系尺寸分布之间关系的数学模 型,对该模型的反演计算便可得到颗粒系的尺寸分布信息。为了避免求解过程中的病态系数矩阵问 题,将模型求解转化成了易于解决的最优化问题。仿真实例结果验证了该技术的可行性。     

基于超声衰减谱的纳米颗粒粒度分布测量研究

利用变声程方式测量纳米颗粒悬浮液的超声衰减谱,以McClements模型和BLBL模型为理论基础,采用最优正则化(ORT)算法,反演得到纳米颗粒的粒度分布。运用该方法,对体积浓度1%的纳米二氧化钛-水悬浊液进行测量,与透射电镜(TEM)图像以及离心沉降纳米粒度分析仪检测结果对比,测量结果吻合较好,表明了利用超声衰减谱方法测量纳米颗粒粒度分布的可行性与可靠性。      

多分散Au-Ag合金纳米球的光谱消光法反演

贵金属纳米颗粒具有局域表面等离子体共振特性而引起了广泛的关注,其中Au-Ag合金纳米颗粒具有良好的结构稳定性、光热性能以及潜在的抗癌功效而得到普遍研究。在众多应用中的特性与其粒径和浓度密切相关,然而目前常用的电子显微镜观察法和动态光散射法不能同时获得粒径和浓度信息,因此采取有效手段测量颗粒粒径和浓度信息至关重要。基于光谱消光法,利用非负的Tikhonov正则化方法解决反演问题,并根据Mie理论计算消光矩阵。针对噪声问题,采取两种情况研究多分散Au-Ag合金纳米球粒径分布与浓度的反演问题。未添加噪声情况下,颗粒系Ⅰ的反演相对误差小于颗粒系Ⅱ,在波长范围300～500 nm之间的反演相对误差最小,对应平均粒径、粒径标准差和颗粒数浓度的反演相对误差分别为0%,-0.03%和0%。添加随机噪声情况下,将0.5%和1.0%的随机噪声添加进颗粒系Ⅰ中的消光谱,经过数据比较发现在波长范围200～600 nm之间的反演相对误差最小。当添加0.5%的随机噪声时,粒径分布、粒径标准差和颗粒数浓度的变化范围分别为79.76～80.15 nm, 5.60～6.61 nm和0.995 8×1010～1.005 9×1010个·cm-3;当添加1.0%的随机噪声时,粒径分布、粒径标准差和颗粒数浓度的变化范围分别为78.87～80.27 nm, 5.36～9.00 nm和0.992 4×1010～1.027 7×1010个·cm-3。反演结果随着随机噪声的增大,变化范围也明显增大即反演相对误差增大,并且每次添加相同随机噪声后的反演结果不同。为了减少随机噪声导致的不稳定性,对100次反演结果进行平均得到平均粒径、粒径标准差和颗粒数浓度。当随机噪声从0.5%增大至1.0%时,其反演结果的相对误差均增大,但是反演得到的粒径分布、粒径标准差和颗粒数浓度相对误差均小于6%,这说明通过反演算法得到的反演结果具有较好的稳定性。研究表明,光谱消光法为反演多分散Au-Ag合金纳米球粒径分布与浓度提供了一种简单、快速的表征手段,也对研究非球形纳米颗粒有启示作用。     

超声衰减和速度谱测量亚微米乳液的粒径

研究了超声衰减谱法和相速度测量高浓度多分散脂肪两相乳浊液的粒径分布问题.在理论分析基础上,实验测量了多个浓度(2%～20%)脂肪乳试样在2～13 MHz频带下超声衰减和相速度谱,结合反演算法由实验数据计算出乳浊液颗粒的粒径分布,并讨论了相速度法的意义和特点.将原始浓度(20%)下测得粒径分布与消光法在稀释条件下相同试样测量结果作对比,二者比较吻合,表明超声谱法可在无稀释的高浓度条件下作乳浊液粒径分布的表征.