薄壳目标的多基地声散射特性研究

文章对水中薄壳目标的多基地声散射特性进行了理论仿真与试验测量研究。首先采用有限元耦合边界元和基尔霍夫(Kirchhoff)近似积分两种不同的数值计算方法对内部充气球冠圆柱壳的多基地声散射特性进行建模仿真,然后通过目标在消声水池的散射声场试验测量验证仿真结果的有效性。采用相同的数值计算方法对Benchmark模型的多基地散射声场进行仿真计算,分析多基地(全向)声散射特性及散射机理。结果表明,水中目标多基地散射的回波强度与回波结构与多基地分置角相关,且回波亮点的主瓣宽度也随多基地分置角变化而变化;Benchmark模型的艇体和指挥舱之间存在强烈的干涉作用,使多基地(全向)散射声场的竖状条纹发生倾斜。研究为水下目标的多基地探测提供理论支持。     

玻璃微珠颗粒系中超声散射的数值和实验研究

利用超声在球形颗粒中的单散射理论模型, 分析了散射系数计算收敛问题, 玻璃微珠颗粒的散射声压分布和消声系数随物性参数和颗粒尺寸参数的变化关系, 进而研究了不同粒度分布颗粒群中声衰减谱的特性. 由变声程脉冲回波法测量了3种不同粒度分布玻璃微珠声散射衰减谱, 与理论计算进行了对比, 二者较好地吻合. 结果表明, 具有合适物性参数的弹性颗粒声散射模型可用于声散射衰减谱准确预测, 采用宽频超声衰减谱有利于对颗粒系进行粒度分布分析.     

ZnS∶Mn~(2+)薄膜电致发光器件中电子散射过程的研究

研究了薄膜电致发光器件中的电子散射过程,计算了ＺｎＳ∶Ｍｎ２＋中声学声子、极化光学声子、电离杂质及谷间散射的几率随电子能量的变化关系,对各种散射过程进行了比较,发现极化光学声子散射及谷间散射较为重要,杂质散射的重要性取决于浓度的大小。同时研究了它们在不同能谷中的行为。进而研究了温度对散射过程的影响。     

基于AR倒谱法研究人体脾组织微结构的变化

本文利用AR倒谱法对人体正常脾和脾增生组织的回波信号进行了分析,对软组织中散射元的平均间距进行了估计,结果表明：两种脾组织散射元的平均间距明显不同;AR倒谱能有效的反映软组织的微观结构特征,说明AR倒谱是软组织超声散射信号分析与软组织散射元平均间距定征的一种有效方法。     

ZnS：Mn^2＋薄膜电致发光器件中电子散射过程的研究

研究了薄膜电致发光器件中的电子散射过程，计算了ＺｎＳ：Ｍｎ＾２＋中声学声子，极化光学声子，电离杂质及谷间散射的几率随电子能量的变化关系，对各种散射这程了比较，发现极化光学声子散射及谷间散射较为重要，杂质散射的重要性取决于浓度的大小。同时研究了它们在不同能谷中的行为，进而研究了温度对散射过程的影响。     

血管网光声成像的机器学习抗散射仿真研究

乳腺癌已成为全球女性发病率最高的肿瘤疾病,微血管成像对乳腺癌的治疗方案和预后有重要意义。光声层析成像术(Photoacoustic Tomography, PAT)可有效对乳腺癌内微血管网进行成像,但肿瘤组织内部的异质微结构和钙化点的散射对成像质量影响较大。针对该问题,文章基于U-Net的卷积神经网络对不同颗粒散射条件下软组织中血管网图像散斑开展仿真研究。仿真结果表明,该神经网络可以学习光声散斑图像和成像目标之间的映射关系,提取出隐藏在噪声中的血管光声信号,并重建出轮廓清晰、背景清晰的高质量血管图像,表明U-Net网络可以从高度模糊的散射图像中提取出有效的光声信息,实现目标图像的高清重建,在乳腺癌的诊断成像中具有广阔的应用前景。     

浅海目标特性的动态模拟

基与亮点模型[1],本文推导了浅海多途环境中目标声散射回波传递函数的表达式,给出潜艇近场声散射回波随着海况、声源的相对速度、距离、方位角变化的动态模型.     

弹性球壳声散射对矢量水听器测向影响研究

以平面波在弹性球壳上声散射理论为基础,建立了弹性球壳近场声散射对矢量水听器目标定向性能影响计算模型,分析了入射声波信号频率、入射角度以及矢量水听器安装位置对目标定向的影响。计算和理论分析结果表明．弹性球壳声散射对矢量水听器测向性能的影响与壳体散射特性和水听器安装位置密切相关,在低频和高频段测向误差相对比较小,而在中频段则测向误差比较大,可通过选择工作频段,或者采用声学处理,降低壳体声散射强度,减小对矢量水听器测向性能的影响。研究结果为矢量水听器工程应用奠定了理论基础。     

半空间内二维圆柱声散射理论解析解

采用理论解析方法研究半空间内二维非紧致圆柱的声散射。齐次Helmholtz方程的解在柱坐标系内用自由空间格林函数的级数展开式表示。基于镜像源方法,利用刚性半空间边界反射圆柱散射声波来解决半空间边界和圆柱之间的多重散射。结合等效源原理,处理半空间边界质量型阻抗特性和刚度型阻抗特性对声传播的影响,推导单位强度简谐单极子点声源产生声场的理论表达式。总声场可以表示为四个分量的总和:入射声场、反射波以及圆柱和镜像圆柱的散射声场。采用边界积分方法对声散射进行计算,以验证理论公式的正确性。点声源模型的理论解析值与边界积分方法数值解在研究的波数和观察点角度范围内一致。     

双基地海底散射建模与仿真分析

海底的声散射是产生浅海混响的主要原因之一。采用小斜率近似方法研究了粗糙液-液分界面的海底散射问题,通过一个统一的方法实现微扰近似和Kirchhoff近似的无缝衔接且不受表面高度均方根条件限制。类比APL-UW模型,利用最低阶小斜率近似求解粗糙海底界面散射截面,并结合Jackson等人的海底沉积层体积散射截面表达式,建立了一个计算双基地海底散射强度的＂小斜率-体积＂模型。针对几种典型的海底类型进行了数值仿真与性能分析,并将数值预报结果与APL-UW模型进行了对比。结果表明,小斜率-体积模型在整个角度范围内较为准确,并且与APL-UW模型的预报结果吻合程度较高,两者散射强度差值小于2 dB。     

On the validity of the anomalous diffraction approximation in light-scattering studies of soft biomedical tissues

In simulations of light propagation in soft biomedical tissues, the tissue is generally modeled as a turbid medium. In one such model, suspended scatterers are assumed to be homogeneous spheres of size following a fractal size distribution law. In this paper, we examine, within the framework of this model, the accuracy of a well-known approximation known as the anomalous diffraction approximation. The deployment of this approximation allows the tissue scattering coefficient to be expressed in a closed analytic form. It is demonstrated that use of the anomalous diffraction approximation yields reasonably good results for the tissue scattering coefficient, the phase function and the asymmetry parameter. It is also shown that the experimentally observed wavelength dependence of the scattering coefficient follows analytically from the formulas obtained using this approximation. The results are important from the point of view of constructing more realistic tissue models which may include non-spherical scatterers.     

The impact of various imaging parameters on ultrasonic displacementand velocity estimates

The accuracy of displacement and velocity data in ultrasonic motion detection systems depends on a combination of ultrasonic imaging parameters. These include magnitude and direction of target motion, target region dimensions, scattering media, ultrasonic frequency of interrogation, digital sampling frequency, and signal type (envelope detected or RF). Because the impact of scattering media in particular has heretofore received little or no attention, we provide experimental results and computer analysis to evaluate the influence of different scattering media on the accuracy of ultrasonic displacement and velocity estimates using porcine liver, porcine muscle, and woolen sea sponge samples. Our experimental results show that for identical target dimensions and displacements, the accuracy of ultrasonic displacement and velocity estimates in porcine muscle samples are substantially higher than in porcine liver samples. Analysis of experimentally derived autocovariance curves for each tissue type indicates that the improvement in accuracy for muscle samples is not, in fact, due to differences in the speckle characteristics for each tissue type. The improvement is attributed to the presence of well-defined and resolvable image structures from muscle and the lack of such resolvable structures in porcine liver tissue. We provide a summary of the factors impacting ultrasonic displacement and velocity measurements, and discuss why and how a combination of one or more imaging parameters affects these measurements     

A compound scattering pdf for the ultrasonic echo envelope and its relationship to K and Nakagami distributions

A compound probability density function (pdf) is presented to describe the envelope of the backscattered echo from tissue. This pdf allows local and global variation in scattering cross sections in tissue. The ultrasonic backscattering cross sections are assumed to be gamma distributed. The gamma distribution also is used to model the randomness in the average cross sections. This gamma-gamma model results in the compound scattering pdf for the envelope. The relationship of this compound pdf to the Rayleigh, K, and Nakagami distributions is explored through an analysis of the signal-to-noise ratio of the envelopes and random number simulations. The three parameter compound pdf appears to be flexible enough to represent envelope statistics giving rise to Rayleigh, K, and Nakagami distributions.     

Quantitative modeling of the anisotropy of ultrasonic backscatterfrom canine myocardium

Reports extensions and new results of the First Time Domain Born approximation model used by Mottley and Miller (1982) to describe the anisotropy of ultrasonic backscatter measured in canine myocardium. The interaction of an ultrasonic plane wave impulse with a single cylindrical scatterer using time and frequency domain approaches is reviewed. Myocardial tissue is modeled as a suspension of aligned cylindrically shaped scatterers uniformly distributed in a homogeneous medium. The authors propose extensions to this model to deal with nonideal scatterer orientation, by introducing axial distribution functions and scatterer size distributions based on histology, modeled as a uniform distribution. The backscatter coefficient in the range 2.0-8.0 MHz is calculated. An algorithm to compute the average differential scattering cross section is presented. Ultrasonic elastic properties of myocardial tissue are discussed. Results of the anisotropy of the numerically computed backscatter parameters for model media having nominal mechanical and acoustic properties of canine myocardial tissue are presented and compared to available experimental data along with discussion of possible conclusions     

A general statistical model for ultrasonic backscattering from tissues

The backscattered ultrasonic echo from tissue can be described in terms of Rayleigh distribution or K distribution. Even though both generalized K distribution and homodyned K distribution can account for some of the scattering conditions that exist in tissues, the analytical complexity involved with these distributions is significant. A much simpler generalized model based on the Nakagami distribution is proposed here. This model can describe the statistics of the envelope of the backscattered echo from an ensemble of scatterers with varying number densities, varying cross sections, and the presence or absence of regularly spaced scatterers. Computer simulations and experiments on tissue-mimicking phantoms have been undertaken to test the validity of the model. Results clearly show the versatility of the Nakagami distribution and its parameter to model the backscattered envelope from tissues. It is suggested that Nakagami distribution may be a good model for use in tissue characterization because of its simple analytical nature and ability to encompass different scattering conditions.     

浓度对超声检测颗粒两相流的影响

讨论了颗粒两相流检测中常用的超声单散射模型和复散射模型 ,研究了浓度对超声检测颗粒两相流的影响。通过实验测得了超声在体积浓度为１ %～１０ %的ＴｉＯ２-水悬浊液中传播时的衰减系数。结果表明 ,悬浊液中的超声衰减系数随着浓度和频率的升高而增大。实验的结果和使用的超声散射模型的理论值在低浓度时吻合较好 ,而在高浓度时有所偏离。文中对这种偏差的原因进行了讨论。     

A possible method for retrieval of particle size distribution from its phase function in a fractal tissue model

In problems relating to light propagation in soft biomedical tissues, the tissue is generally modeled as a turbid medium. In one of the often used models, the suspended scatterers have been assumed to be of spherical shape following a fractal size distribution law. This paper studies the relationship between scattering phase function features of tissue and the fractal dimension within the framework of a fractal tissue model. It is demonstrated that witin the framework of this model the measurement of scattering phase function at two or three near-forward angles can be employed to infer fractal dimension of the model tissue. This method for tissue characterization therefore could be a potentially useful method for early detection of cancer of soft tissues.     

基于超声振动的显微切割技术

为了满足生物组织显微分离的需求,将超声振动引入微切割领域,开发了一套基于超声振动的显微切割系统.在对超声振动微切割理论研究基础上,结合生物组织切割的具体特点,完成了系统总体方案的设计,并对关键技术开展研究,研制了面向生物显微切割技术的执行模块与控制模块,实现了系统的集成.同时,利用该显微切割系统对新生小鼠大脑组织进行超声振动显微切割实验,取得了较理想的切割效果,充分验证了超声振动显微切割技术对生物组织操作的可行性和有效性.     

基于小波变换利用超声估计生物组织散射元平均间距

生物组织散射元平均间距是描述生物组织微观结构和生物组织和超声散射特性和重要参数,文中构建并物理仿真了生物组织散射元一维超声散射模型,用小波变换方法估计了仿一物组织散射元的平均间距。