宽带声学多普勒流速剖面仪回波信号模型分析

宽带声学多普勒流速剖面仪（Broadband Acoustic Doppler Current Profile,BBADCP）通过接收海洋体积混响信号进行频偏估计,体积散射模型的准确性决定了理论仿真的正确性。针对BBADCP的信号模型特点,建立了散射体单元散射叠加效应的海洋体积回波时空特性及散射模型,推导了叠加噪声后散射回波的具体表达式。通过散射回波的离散化,把各参数（幅度、频率、调制）分离开来,单独考虑各参数对测速精度的影响。利用复协方差算法对水流流速进行估计,分析了信噪比、水流流速、紊流效应等因素对BBADCP流速估计的影响,验证了体积散射模型的正确性。     

一种用于水声运动目标成像的空间散射模型

水声成像过程中为了分析所接收的运动目标回波、理解接收信号的形成机理,提出了一种用于该情况的空间散射模型,并利用此模型仿真了"T"型阵成像声呐接收的回波信号。对信号的分析说明了空间散射模型的正确性。以空间散射模型为基础,利用傅里叶变换波束形成算法对不同条件下的球体目标进行了水声成像,并分析了成像性能。性能分析说明了水声目标大小、距离等因素对成像的影响情况,还特别强调了在运动情况下目标的成像情况。以上工作完成了对"T"型阵水声成像过程的模拟,为成像过程回波信号研究和成像声呐研制提供了理论基础和仿真手段。     

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。     

基于空气耦合超声导波法对开闭器水层厚度的研究

针对传统接触式超声检测高压电线杆开闭器水层厚度存在漏电风险问题,提出使用非接触式空气耦合超声导波技术对开闭器中水层厚度进行测量。对开闭器水中导波传播过程进行仿真并计算水层厚度;搭建开闭器实验室平台,控制水层厚度,改变换能器之间距离,对回波信号进行分析并计算水层厚度;控制换能器之间距离,改变水层厚度,对回波信号进行分析并计算水层厚度。通过仿真与实验使用几何声学对水层厚度进行计算得出关系式,将仿真与实验两者结果进行对比,有高度一致性,验证空气耦合超声导波法对开闭器中水层厚度测量的可行性与准确性。该方法可为测量开闭器中水层厚度提供新思路。     

基于分布式时延矢量联合估计的血流检测算法

依据超声血流散射回波信号的产生机理,引入更精确的分布式回波阵列模型来代替传统的点目标模型.基于散射子的运动效应对序列脉冲串激励信号的检测回波之间产生的附加时延效应,定义函数形式已知的分布式时延矢量,该矢量含有两个未知参数:中心速度和分布参数,利用其与回波阵列协方差矩阵的噪声子空间的正交特性,进行二维参数的联合搜索.搜索...     

利用声相关流速剖面仪观测深水散射层

讨论了利用声相关流速剖面仪进行深水散射层观测的可行性。结合声相关流速剖面仪垂直发射编码调制信号、多阵元接收的特点以及测量流剖面三维速度的优势,提出利用回波强度和垂向速度两种方法对深水散射层进行观测。在23kHz声相关流速剖面仪工程样机海试数据的基础上,利用这两种观测方法对DSL进行了观测。观测结果表明：利用声相关流速剖面仪可以直观地观测深水散射层的分布及运动规律,这两种观测方法是实际可行的。     

脉冲激光成像探测系统回波信号仿真

研究激光脉冲回波信号特性并建立其数学模型,是应用回波信号处理技术处理回波,生成目标三维激光仿真图像的基础.首先建立了激光器发射脉冲信号能量在时间和空间上的分布模型,然后依据成像目标的激光图像仿真模板,采用累加激光脚印各采样区发射脉冲信号与对应目标散射面单位冲激响应卷积值的方法,生成了探测器接收回波仿真信号,最后分析了影响回波信号仿真精度的因素.通过对激光脚印采样区个数的合理设置实现了激光脉冲回波波形的精确仿真.     

超声Lamb波在缺陷处的二维散射特性研究

利用散射系数周向分布图研究了超声Lamb波在缺陷处的二维散射特性。建立了超声Lamb波与缺陷交互作用的有限元仿真模型,采用双元激励法产生单一S0模态入射信号,利用吸收边界消除边界回波的影响,采集缺陷所有方向上的散射信号并产生散射系数周向分布图。此模型的计算结果与实验结果一致,证明了模型的正确性。研究了S0模态与通孔和通透裂纹两种缺陷的交互作用,并测量了S0模态以零度角入射缺陷时的周向散射系数分布图,利用其图形特征可以进行缺陷种类识别。分析了散射场中多模态信号的能量分布,指出检测中若激励单一模态,而接收多模态信号,可以防止漏检,更有效地检测缺陷。     

一种低失真度多普勒测速仪回波模型的构建和分析研究

为了支撑研究并评估多普勒测速仪（Doppler Velocity Log,DVL）信号处理算法的性能,需模拟海底回波信号,故需构建失真度低的海底回波模型。文章提出了扇环形海底回波模型,在此基础上,构建了一种基于散射理论的海底回波优化模型。将此优化模型和传统模型进行了对比分析,结果表明,优化模型较传统模型,与真实海底回波之间的包络特性误差更小,宽带回波的包络特性误差降低了20%以上,验证了所构建的回波模型的有效性和优越性。     

声表面波温度传感器抗干扰技术研究

目的设计一种声表面波(SAW)温度传感器抗干扰技术,以提高温度测量的稳定性。方法分析SAW谐振器(SAWR)回波特性,建立SAWR回波信号熵能量模型,发现SAWR回波信号的衰减过程与熵能量的上升过程对应。当回波信号达到噪声水平时,熵能量的单调上升过程消失。为了抑制正弦干扰设计一种改进型自相关算法,利用该算法对信号进行去噪的同时使谐振器回波信号的衰减特性和正弦干扰的等幅特性得到保持。结果根据模拟仿真结果设置了SAWR回波信号的检测阈值(V_(thre)=1),并对该阈值进行了蒙特卡罗仿真实验。仿真结果表明,当信号信噪比大于4dB时,SAWR回波信号的检测率达到86%,而正弦干扰误检率小于0.5%。最后应用该算法对实际的正弦信号和SAWR回波信号进行了检测,得到的误检率接近于0。结论实验结果显示,所设计的算法可以用作声表面波温度传感器的抗干扰技术。     

仿生皮肤等效材料超声波测试方法的研究

为评定汽车安全碰撞实验模拟人的皮肤肌肉等效复合材料的力学特性,提出仿生皮肤等效材料的超声检测方法。通过测试仿生皮肤等效材料对超声波声速、衰减、散射和吸收率的变化,建立仿生皮肤等效材料力学性质与超声回波信号频率之间的关系模型,对仿生皮肤等效材料的弹性模量、组织特性、粘弹性和松弛模量进行等效性的分析与评定。对3种不同密度的仿生皮肤等效材料的声速、弹性模量和声衰减等参数进行了测算,结果表明:该测试方法正确可行,测试数据为仿生皮肤等效材料的设计合成、制备提供力学参数依据,对仿生材料的力学等效性能评定有着重要的参考价值。     

相关测速声呐模型参数矩阵化求解方法

相关测速声呐的基本原理是“波形不变性”。该原理指出：发射具有一定时间间隔的信号，接收回波相关性最大的两个基元之间的间距与载体移动速度成正比。相关测速算法首先通过回波数据构建数据相关矩阵，然后利用速度估计算法将理论相关模型和回波数据构建的相关矩阵进行拟合得到最优参数信息，进而解算出载体速度信息。文章以简化最优参数求解流程为目标，提出了基于矩阵推导的参数拟合运算方法。该方法通过将底混响时空相关函数模型中的目标参量进行分离，进而将函数转变为矩阵形式，随后通过矩阵QR分解等手段，根据局部最小二乘法推导目标参数的求解公式，并直接求解出目标参数的解析解。仿真和湖上试验数据验证了该方法可以作为一种速度解算方法的可行性，并且具有运算复杂度低的优点。     

浅海单模入射声场目标回波特性研究

浅海环境中,目标回波受到入射和散射双向过程的信道多途影响,具有复杂的多途结构。基于相控垂直阵的单模发射技术能激发出指定的单个简正波声场,可以降低海底混响干扰,简化目标回波多途结构,为主动探测提供了一种有效手段。在信道中点声源目标回波模型基础上,采用简正波本征函数加权研究了单模声场入射下球形目标散射问题,建立了浅海单模入射声场目标回波预报模型,并利用模型对刚性球回波进行了数值计算。结果表明:总声源级相同条件下,单模发射声场与传统的点声源发射声场相比具有一定的阵发射增益,目标回波具有较高的声压级;单模入射能够消除单程多途的影响,回波结构相对简单,有利于目标的探测和识别。     

Flow velocity profile via time-domain correlation: error analysis and computer simulation

An ultrasonic human-blood-flow velocity profile measurement method using time-domain correlation of consecutive echo pairs has been developed. The time shift between a pair of range gated echoes is estimated by searching for the shift that results in the maximum correlation. The time shift indicates the distance a group of scatterers has moved, from which flow velocity is estimated. The basis for the computer simulations and error analyses of the scheme includes a band-passed white Gaussian noise signal model for an echo from a scattering medium, the estimate of flow velocity from both a single scatterer and multiple scatterers, and a derived precision estimation. The error analysis via computer simulation includes an evaluation of errors associated with the correlation method. For a uniform flow velocity profile, beamwidth modulation represents the greatest error source. However, for a nonuniform flow velocity profile, the jitter caused by a small flow velocity gradient can exceed the other error sources. A detailed computer simulation evaluated the interdependencies of window length, beam width, vessel diameter, and viewing angle on the estimation of flow velocity.     

浅海波导远程信混比预报模型

浅海主动探测时,海底混响是目标回波的主要背景干扰,信混比影响主动声纳的性能.混响和目标回波都属于海洋中的散射问题,利用简正波方法,结合平面波散射函数建立了浅海远程信混比预报模型,实现了不同环境参数下信混比的量化分析.仿真比较了不同信号形式、频率以及不同海底底质下的刚性球信混比曲线,从理论上分析了回波随距离的振荡现象.结果表明：用无指向性的声源探测目标时,信混比较低,探测较为困难;宽带信号照射下目标回波更加平稳;简正波之间的干涉导致回波随距离发生振荡,频率越高,干涉结构越复杂;在硬海底环境中信混比相对较小且目标回波振荡剧烈.     

Statistical characterization of diffuse scattering in ultrasound images

The marginal statistics for the diffused ultrasound speckle echo has been postulated as exhibiting circularly symmetric Gaussian behavior similar to the laser speckle for monochromatic illumination under the assumption of a large number of unresolvable scatterers per resolution cell. This is known in the literature as the Rayleigh scattering condition. This paper presents a formal statistical test, the Kolmogorov-Smirnov nonparametric goodness of fit statistical test, to test the hypothesis that the unresolvable part (diffuse part) of the backscatter echo follows a Rayleigh scattering condition, and obtain numerical values for the scatterer concentration required for the Rayleigh condition to be valid. In addition, it presents a formal statistical test, the Kolmogorov-Smirnov nonparametric homogeneity statistical test, to compare two regions of interest with different scattering concentrations without prior knowledge of the nature of the scattering conditions (Rayleigh or non-Rayleigh scattering). Unlike all previous parametric testing methods that treat the A-scan or B-scan echo as a random sample, the authors' method presents formal tests based on the colored nature of the diffuse backscattered echo which is a more realistic model of the diffuse scattering component. The tests are demonstrated on simulations of RF scans with different scatterer concentrations per resolution cell as well as on phantom data which mimic tissue.     

Non-Rayleigh statistics of ultrasonic backscattered signals

The statistics of the envelope of the backscattered signal from tissues have been known to vary from the well-known Rayleigh model. The K-distribution is used to model this non-Rayleigh behavior, since the generalized K-distribution encompasses a wide range of distributions like Rayleigh, Lognormal, and Rician. Computer simulations were conducted using a simple one-dimensional discrete scattering model to investigate the properties of the echo envelope. Significant departures from Rayleigh statistics were seen as the scattering cross sections of the scatterers became random. The validity of this model was also tested using data from tissue mimicking phantoms. Results indicate that the density function of the envelope can be modeled by the K-distribution and the parameters of the K-distribution can provide information on the nature of the scattering region in terms of the number as well as the scattering cross sections of the scatterers.     

A thin film phantom for blood flow simulation and Doppler test

The thin film phantom is a new type of ultrasound resolution test object. It consists of a thin planar substrate that is acoustically matched to the surrounding media. Precisely located scatterers on the surface of the substrate generate echo signals. The patterning of scatterers on the substrate allows echogenicity to be controlled as a function of position, which enables the production of a test object with highly reproducible and controllable scattering characteristics. We show that by vibrating the substrate in a suitable manner, an echo signal may be generated that simulates bidirectional flow. We demonstrate that a vibration of low amplitude at frequency f₀ produces a Doppler spectral signal at f₀ and -f₀, within the limits of aliasing. Furthermore, by driving the film with a bandlimited noise signal, we illustrate how a velocity distribution may be simulated. A time-varying flow velocity may be simulated by varying the noise bandwidth with time. Finally, using this technique, we demonstrate a system that simulates an arterial flow pattern, including its characteristic velocity distribution in forward and reverse directions simultaneously