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。     

基于相关函数包络峰细化的高精度超声测距法

建立了超声测距时延估计模型,由于窄带超声回波参考信号与接收信号的相关函数在极值点附近具有慢衰减高频振荡特性,所以有必要将搜索直接相关函数的极值点转化为搜索相关函数包络的极值点.针对相关峰常规插值方法在多倍插值的情况下存在计算复杂、时延估计精度不高等缺点,结合超声回波信号的窄带带通特性和相关峰细化(Fine Interpolation of Correlation Peak)原理,提出了直接提取相关函数包络及包络峰细化方法,并分析了其计算复杂度.仿真与实验研究表明,该方法能大大提高相关函数包络峰值分辨率,适用于类超声回波信号的带通信号精细时延估计问题.     

基于WVD-Radon变换的宽带延展目标回波参数提取

分析了宽带延展目标的时延一时间伸缩效应及其导致的回波信号在时域和频率域的特性；针对LFM信号的时频分布特点，利用WVD和Radon联合变换技术，提取LFM信号在时一频域分布上的特性参数，提出了一种宽带延展目标回波参数提取方法，得到了目标的时延一时间伸缩分布．仿真结果表明，该方法是可行的．     

基于ADS半物理平台的声表面波标签测试

提出了一种基于ADS半物理平台的声表面波标签测试方法。采用矢量网络分析仪实际测试声表面波标签实物的S参数,在ADS软件中构建标签的物理抽象模型,并虚拟构建标签激励信号,利用ADS瞬态仿真功能获得标签回波信号,再采用MATLAB对回波进行数字正交解调,从而客观准确地测量标签各反射栅的时延、相位。最后通过搭建的半物理平台对声表面波标签进行了测试,表明了ADS半物理平台的有效性。     

复合材料超声检测中的回波时延估计方法

在用超声脉冲回波法检测金属-非金属粘接结构的质量以及测量非金属层厚度时,需要提取出各界面回波间的延迟时间作为特征值.当非金属层较薄时,各回波信号间会产生严重混叠,难以准确获得时延估值.提出了一种多界面粘接结构的高分辨率时延估计方法,综合利用了维纳滤波解卷积技术和最大熵谱估计方法,从混叠信号中得到精确的时延估值,很好地解决了特征值提取困难的问题,并用模拟信号和实验信号验证了该方法.     

宽带声学多普勒流速剖面仪球面散射回波模型研究

宽带声学多普勒流速剖面仪通过处理水下体积回波信号进行流速估计,回波模型的准确度决定了理论仿真的正确性。针对回波的散射特性,通过分析水层回波信号的时空关系,提出一种球面散射水层回波模型,并利用坐标旋转方法推导出该水层回波解析式。相比其他方法,该模型解析式充分体现了散射体模型形状对回波的作用,更加接近实际情况。对该模型下回波信号进行频谱和自相关特性分析,采用复相关算法估算流速。通过与实测数据进行对比,结果证明了该回波信号模型与解析式的正确性。     

矢量水听器阵时频MUSIC算法研究

时频MUSIC算法利用信号的时频分布构造空间时频分布矩阵,并用该矩阵代替传统的相关矩阵进行DOA估计,可以有效抑制噪声和干扰,提高算法的稳健性。时频子空间算法突破了传统子空间算法中阵元数对估计信号个数的限制,时频点包含了信号的时频空三维信息,通过时频点的选择可直接确定信号的频率从而确定阵列流型矩阵。对于宽带信号,在进行方位估计时避免了频域搜索,减少了运算量。将时频MUSIC算法应用于二维矢量水听器垂直线阵中,充分利用矢量水听器的标、矢量信息和信号的时、频信息进行宽带信号的二维波达方位估计。仿真研究验证了算法的有效性。     

振速轴向不一致下矢量传感器阵列方位估计方法EI北大核心CSCD

针对振速轴向不一致时矢量传感器阵列的方位估计精度不高问题,提出了一种两步加权交替迭代自适应方法(two-step weighted alternating iterative approach,TWAIA)。在矢量传感器阵列稀疏信号模型中引入轴向角度偏差参数,并把重构的干扰加噪声协方差矩阵作为加权项,基于加权协方差矩阵拟合和加权最小二乘分别构建了关于稀疏信号功率和轴向偏差矩阵的代价函数。首先固定轴向偏差矩阵,采用正则化加权稀疏协方差矩阵拟合方法估计稀疏信号功率;然后固定稀疏信号功率,采用正则化加权最小二乘估计轴向偏差矩阵,并根据轴向偏差在矩阵中的分布特性,重构期望的轴向偏差矩阵,以此交替的方式迭代更新稀疏信号功率和轴向偏差矩阵,直到被估计的稀疏信号功率相较于前一次的迭代值不再变化为止。最终通过对估计的稀疏信号功率谱峰搜索即可实现声源的波达方向估计。仿真结果表明,相较于现有方位估计方法,提出的TWAIA提高了振速轴向不一致时矢量传感器阵列的方位估计精度。     

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...     

深水多波束测深系统海底回波信号快速仿真方法

针对传统深水多波束测深系统海底回波信号仿真方法计算量大和不适用于存在载体姿态的问题,提出一种深水多波束测深系统海底回波信号快速仿真方法。基于扩展散射体海底回波信号仿真模型,考虑载体姿态,通过预先计算海底散射点强度分布确定主要作用区域的散射点,并将这些散射点的强度作为回波信号幅值加权来得到回波信号。利用这一方法,在保持较小计算量的同时,可以得到包括载体姿态特征的仿真数据。此外,利用这种方法还可以进行相位不一致性等误差因素的仿真。     

宽带目标回波模型的物理解释及小波变换表示

在点目标回波模型基础上，通过对理想运动体目标的分析，引入了距离-速度联合分布密度和时延-时间伸缩联合分布密度函数的概念，详细推导了延展目标的宽带回波模型，解释了各密度函数和宽带扩展函数的物理意义及相互关系，最后给出了宽带回波模型的小波变换表示方法。     

Classification of ultrasonic B-mode images of breast masses using Nakagami distribution

The Nakagami distribution was proposed recently for modeling the echo from tissue. In vivo breast data collected from patients with lesions were studied using this Nakagami model. Chi-square tests showed that the Nakagami distribution is a better fit to the envelope than the Rayleigh distribution. Two parameters, m (effective number) and α (effective cross section), associated with the Nakagami distribution were used for the classification of breast masses. Data from 52 patients with breast masses/lesions were used in the studies. Receiver operating characteristics were calculated for the classification methods based on these two parameters. The results indicate that these parameters of the Nakagami distribution may be useful in classification of the breast abnormalities. The Nakagami distribution may be a reasonable means to characterize the backscattered echo from breast tissues toward a goal of an automated scheme for separating benign and malignant breast masses     

高速铣削22SiMn2TiB高强度钢的铣削力建模与试验研究

通过涂层硬质合金刀片对22SiMn2TiB高强度钢进行四因素四水平的正交铣削试验,采集切削力信号,对试验数据进行方差分析(ANOVA),得到了切削参数对铣削力影响的规律.通过多元线性回归建立了两个铣削力预测经验模型——二次模型和指数模型,并进行了模型的显著性分析,发现二次模型优于指数模型,指数模型对Fz的拟合效果差.     

EFP垂直侵彻靶后破片云描述模型

针对靶后破片是影响装甲保护能力和聚能装药毁伤的主要问题,基于EFP垂直侵彻的靶后破片,建立其初始靶后破片云的数学描述模型,并在此基础上采用有限元仿真软件AUTODYN-3D对EFP垂直侵彻钢靶形成靶后破片的过程进行数值模拟。数值模拟结果与靶场实验结果进行对比,结果表明:仿真的EFP成型参数、靶后破片空间分布状态和靶板开孔特征均与实验较为吻合。因此,证明该仿真模型和所得靶后破片云初始描述模型具有较高的可信度,可以为EFP对装甲目标的毁伤评估方面提供一定的参考。     

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.     

Measurement of radio channels using an elastic convolver and spreadspectrum modulation. II. Results

A spread spectrum measurement system using a surface acoustic wave convolver has been used to measure radio wave propagation in steel works at 1.75 GHz with an echo delay resolution of ≈20 ns. Due to the high metal content of the factory halls, path loss is found to be small and its exponent to range between 1.1 and 2.3 only. We observed a delay spread between 82 and 548 ns depending on the size of the steel mill, its construction and machinery. Characterizing the radio channel by a stochastic delay line model the echo amplitude probability distribution is found to fit a Rician or log-normal distribution rather than a Rayleigh distribution. The fit of the amplitude distributions is determined by a χ² hypothesis test. From the channel impulse response the coherence bandwidth is deduced to range between 2.4 and 27.4 MHz     

基于热-力耦合模型的纤维丝束带铺放残余应力的模拟及实验研究

采用有限元分析计算和实验测试2种方法,在热-力耦合载荷作用下,对纤维丝束带铺放成型时的残余应力进行了研究。首先,建立纤维丝束带铺放的热-力耦合模型,利用有限元分析研究了不同温度和压力参数条件下纤维丝束带铺放残余应力的模拟结果。其次,对结果进行分析比较得到各个因素对纤维丝束带铺放残余应力的基本影响规律;最后进行不同温度和压力等铺放参数对纤维丝束带铺放成型时残余应力影响的实验测试研究,以验证热-力耦合有限元模型计算结果的正确性。结果表明:2种方法得到的残余应力分布基本一致,只是残余应力的最大值之间存在着差别。      

Cumulative detection probabilities and range accuracy of a pulsed Geiger-mode avalanche photodiode laser ranging system

Cumulative pulses detection with appropriate cumulative pulses number and threshold has the ability to improve the detection performance of the pulsed laser ranging system with GM-APD. In this paper, based on Poisson statistics and multi-pulses cumulative process, the cumulative detection probabilities and their influence factors are investigated. With the normalized probability distribution of each time bin, the theoretical model of the range accuracy and precision is established, and the factors limiting the range accuracy and precision are discussed. The results show that the cumulative pulses detection can produce higher target detection probability and lower false alarm probability. However, for a heavy noise level and extremely weak echo intensity, the false alarm suppression performance of the cumulative pulses detection deteriorates quickly. The range accuracy and precision is another important parameter evaluating the detection performance, the echo intensity and pulse width are main influence factors on the range accuracy and precision, and higher range accuracy and precision is acquired with stronger echo intensity and narrower echo pulse width, for 5-ns echo pulse width, when the echo intensity is larger than 10, the range accuracy and precision lower than 7.5 cm can be achieved.