基于均匀圆阵的信号二维方向角和多普勒频率的盲估计

针对均匀圆形阵列 ,在时空旋转因子的基础上 ,推导出四阶累积量矩阵 ,采用波达方向矩阵法 ,实现了信号的方位角、俯仰角和多普勒频率的同时估计。此估计算法利用所有阵元信息估计信号波达方向 ,提高了方向估计精度 ,解决了“频率兼并”问题 ,使有效应用范围扩大。利用了四阶累积量的盲高斯性 ,有效地抑制了高斯白或有色噪声的影响 ,仿真结果表明了此算法的有效性     

基于空间平滑处理的稳健宽带高分辨方位估计算法

实际系统中阵列误差导致的模型失配问题一直是高分辨方位估计技术走向实用化的一个瓶颈。相对于窄带信号,宽带信号阵列模型误差更加复杂和多样,通过建立宽带阵列信号误差模型,得出了基于空间平滑的稳健的宽带高分辨算法是一种抑制阵列误差的有效方法的结论,这种基于空间平滑的宽带高分辨算法,通过空间平滑后对各频率处不同子阵的互谱密度矩阵求和,一定程度上减弱了阵列误差的影响,具有较高的稳健性。本文结合消声水池试验,分析并验证了其效果。     

ESPRIT方法在矢量水听器多目标方位估计中的应用

利用矢量水听器的特点，将ESPRIT方法应用于矢量水听器的方位估计算法中。该算法用单矢量水听器，在无需知道信号先验信息的条件下，可以实现对多个不相关单色信号的入射角估计，并且不受频率方位模糊问题的影响。与声压传感器组成的阵列相比，在相当的阵列尺寸和计算复杂度的条件下，可大大提高估计性能。     

压缩对称嵌套阵列和稀疏信号重构的近场目标方位估计

针对现有近场源估计算法中近场源数量受限于阵元数的问题,提出了一种基于稀疏对称嵌套阵列和稀疏信号重构的近场欠定波达方向估计方法。首先利用四阶累积量,将二维空间参数估计问题转化为一维参数估计问题,同时得到差分阵列;为了进一步提高估计分辨率与减少估计误差,对虚拟阵列的接收信号在空间域进行稀疏表示;最后通过L1范数最小二乘法得到目标源的波达方向。相较于现有算法,该方法可以估计更多的目标源,并且有更低的均方误差与更高的分辨率。实验仿真验证了算法的有效性与优越性。     

声矢量阵列的求根MUSIC算法及其性能分析

在传统声压传感器阵列的求根MUSIC算法的基础上,提出了基于矢量传感器阵列的求根MUSIC算法及其修正形式,通过接收阵列信号的空间谱,选择合适的引导方位,可实现声源的波达方向(DOA)估计.理论推导和仿真实验表明,采用均匀矢量传感器线性阵列的求根MUSIC算法在低信噪比、小快拍数情况下的估计性能要优于传统声压传感器阵列的求根MUSIC算法,同时该算法的计算量远远小于矢量传感器列的MUSIC算法.     

基于多重信号分类算法的复合材料冲击定位

为了提高复合材料结构冲击定位的精度和实时性,将阵列信号处理技术引入到结构健康监测领域,提出了利用小波变换和多重信号分类算法实现复合材料结构冲击定位的新方法:通过小波变换提取冲击响应信号某一窄带频率成分,运用多重信号分类(MUSIC)算法实现冲击源到达方向的估计;根据Lamb波传播特性,用小波变换求出某一中心频率下的对称模式和反对称模式的Lamb波到达同一传感器的时间差,结合对称模式和反对称模式Lamb的速度差就可以估计出冲击源到达传感器的距离,实现冲击定位。对玻璃纤维/环氧树脂复合材料层合板和碳纤维/双马树脂基复合材料层合板2种试件的实验均表明该方法能快速、精确地识别出冲击源位置。     

盲波束形成算法及其C语言实现

阵列信号处理作为信号处理的一个重要分支，在通信，雷达，声呐，地震勘探，射电天文等领域获得了广泛应用和迅速发展。波束形成技术是阵列信号处理中的一个主要问题，它使阵列方向图的主瓣指向所需的方向，盲波束形成算法，可以在不知道阵列流形，信号和干扰方位的情况下，仅根据各个阵元的观测数据，恢复出信号．本文主要讨论应用VC 语言实现和比较了几种基于累积量的盲波束形成算法的性能。     

高分辨阵列测向的最小二乘自校正算法

本文提出一种高分辨阵列测向的最小二乘自校正算法。在模型失配的情况下,可同时对信号的到达方向及未知的模型误差参数进行估计。该算法适用于存在相干信号源及低信噪比,短数据的情况。为简单起见,本文仅考虑阵元的增益及相位误差参数。     

一种新型的OFDM智能天线

根据自适应天线阵列理论，结合给定的参考波束的误差，引入虚拟干扰的概念，对目标波束图形状进行调整，提出一种新的可以应用于任意类型天线阵列的波束综舍算法．应用提出的新算法，在主辩和旁瓣位置都可以对波束进行有效的调节．最终获得阵列的最优权矢量，能够最小化目标波束图与参考波束图间的差异．理论分析与仿真结果表明，与现有的同类算法相比，该算法能更有效地获得与参考波束基本相符的波束．应用于OFDM智能天线系统时，对不同子载波频率上信号进行单独处理，利用该算法进行波束综合，能够在整个有效频段，使所有子载波上获得基本一致的阵列输出．     

高分辨方位估计方法的稳健性研究

基于特征分解理论的子空间类高分辨方位估计方法是目前阵列信号处理领域的研究重点。与波束形成法相比，子空间类法的特点为估计精度高和分辨能力强。但是这类高分辨方法对阵列模型失配十分敏感，存在阵列误差时其估计性能明显下降。文章通过仿真和实验深入研究了MUSIC、Johnson和Mini-Norm等子空间类高分辨方位估计方法的稳健性问题，分析了一定信噪比条件下阵列误差对上述三种方法估计结果的影响程度。研究结果表明，MUSIC法和Johnson法的估计性能相当，而Mini—Norm法的稳健性明显高于MUSIC法和Johnson法，分辨能力和估计精度较好，具有良好的工程应用前景。     

Superimposed noninterfering probes to extend the capabilities of phase Doppler anemometry

We propose using multiple superimposed noninterfering probes (SNIPs) of the same wavelength but different beam angles to extend the capabilities of phase Doppler anemometry. When a particle is moving in a SNIP the Doppler signals that are produced exhibit multiple Doppler frequencies and phase shifts. The resolution of the measurements of particle size (i.e., by fringe spacing and Doppler frequency) increases with beam angle. Then, with the solution proposed, even with only two detectors several measurements of size can be obtained for the same particle with increasing resolution if we consider higher frequencies in the signal. Several optical solutions to produce SNIPs as well as a signal-processing algorithm to treat the multiple-frequency Doppler signals are proposed. Experimental validations of the sizing of spherical and cylindrical particles demonstrate the applicability of this technique for particle measurement. We believe that this new technique can be of great interest when high resolution of size, velocity, and even refractive index is required.     

Frequency encoding of resonant mass sensors for chemical vapor detection

Chemical vapors can be detected by a resonant mass sensor array with selective absorption coatings implementing a frequency encoding method. The sensor array consists of sensor elements with different frequencies for their identifications in the frequency response obtained with a pulse Fourier transform detection scheme. Zero-loading resonance frequencies are chosen so that frequency shift due to absorption is bounded within a predefined region so that there is no overlap of peaks and all peaks can be assigned to the correct elements at any operation conditions. Mechanical oscillations of all or selected numbers of the sensor elements are excited by application of an excitation signal. Free oscillation decay signals from all or selectively excited sensor elements are detected and digitized. The free oscillation decay signal is subjected to a spectral analysis routine converting into a frequency spectrum, in which frequency shifts due to absorption of chemical vapors can be obtained. The implementation of the frequency encoding method with pulse Fourier transform detection to resonant mass sensors allows simultaneous multisensor detection, fast data acquisition speed, high signal-to-noise ratio by coaddition of raw data, flexible excitation, reduced complexity of electronic hardware, application of advanced data/spectral analysis algorithms, and realization of many other advantages by the introduction of the pulse Fourier transform method. A practical chemical vapor sensing system is demonstrated experimentally by use of nine frequency-encoded and polymer-coated sensors.     

声学多普勒测速仪标校技术研究

为了提高声学多普勒测速仪输出速度的准确度,安装过程中测速基阵与载体之间的偏差角不可忽略,安装偏差角包括航向偏角,横摇角及纵摇角三类。介绍了一种三维空间上的多普勒标定技术,通过高精度的GPS导航仪以及多普勒测速仪对海底测速,利用速度比值差校准航偏角。通过纵向剖面的几何关系,从航偏角出发进而获得纵摇角和横摇角的大小,完成了三维方向上多普勒测速仪的校准,使多普勒测速仪坐标系与载体坐标系能够进行精确转换,从而提高了声学多普勒测速仪输出速度的准确度。外场试验较好地证明了该方法的有效性,分析结论看出在二维平面上,造成误差的原因主要在于安装偏角的航向偏角,而在三维空间上,尤其垂向速度,误差主要由纵摇角和横摇角产生。该方法可以快速地对三维安装偏角进行校准,运算量小,并且在对海水测速后续研究中可以形成一套体系。     

High-Accuracy Analog Measurements via Interpolated FFT

By use of an interpolated fast-Fourier-transform (FFT) algorithms are developed for multiparameter measurements upon periodic signals. Eight pertinent measurements, such as fundamental frequency, phase, and amplitude, are made with enhanced accuracy compared to existing algorithms, including tapered-window-FFT algorithms. For the more general case of nonharmonic multitone signals also the method is shown to yield exact amplitudes and phases if the tone frequencies are known beforehand. These measurements are useful in a variety of applications ranging from analog testing of printed-circuit boards to measurement of Doppler signals in radar detection.     

聚焦矩阵在水中宽带目标被动跟踪中的应用

针对水中机动宽带目标,对于设计好的均匀线列阵,采用空间重采样方法计算基阵的恒定束宽阵元权系数,进而利用该阵元权系数产生聚焦矩阵,通过聚焦矩阵将不同频带的子带信号映射到同一参考频率上,然后将所有频率成分的信号功率谱密度矩阵作平均,并结合MUSIC(Multiple Signal Classification)算法,估计出目标的方位信息,从而实现水中宽带目标的被动跟踪。采用该方法进行仿真试验分析,结果表明在小孔径基阵上可实现宽带单目标的稳定测向被动跟踪,且对多目标具有一定的角被动分辨效果。     

Doppler angle estimation using AR modeling

The transit time spectrum broadening effect has long been explored for Doppler angle estimation. Given acoustic beam geometry, the Doppler angle can be derived based on the mean Doppler frequency and the Doppler bandwidth. Spectral estimators based on the fast Fourier transform (FFT) are typically used. One problem with this approach is that a long data acquisition time is required to achieve adequate spectral resolution, with typically 32-128 flow samples being needed. This makes the method unsuitable for real-time two-dimensional Doppler imaging. This paper proposes using an autoregressive (AR) model to obtain the Doppler spectrum using a small number (e.g., eight) of flow samples. The flow samples are properly selected, then extrapolated to ensure adequate spectral resolution. Because only a small number of samples are used, the data acquisition time is significantly reduced and real-time, two-dimensional Doppler angle estimation becomes feasible. The approach was evaluated using both simulated and experimental data. Flows with various degrees of velocity gradient were simulated, with the Doppler angle ranging from 20° to 75°. The results indicate that the AR method generally provided accurate Doppler bandwidth estimates. In addition, the AR method outperformed the FFT method at smaller Doppler angles. The experimental data for Doppler angles, ranging from 33° to 72°, showed that the AR method using only eight flow samples had an average estimation error of 3.6°, which compares favorably to the average error of 4.7° for the FFT method using 64 flow samples. Because accurate estimates can be obtained using a small number of flow samples, it is concluded that real-time, two-dimensional estimation of the Doppler angle over a wide range of angles is possible using the AR method     

Special relativity corrections for space-based lidars

The theory of special relativity is used to analyze some of the physical phenomena associated with space-based coherent Doppler lidars aimed at Earth and the atmosphere. Two important cases of diffuse scattering and retroreflection by lidar targets are treated. For the case of diffuse scattering, we show that for a coaligned transmitter and receiver on the moving satellite, there is no angle between transmitted and returned radiation. However, the ray that enters the receiver does not correspond to a retroreflected ray by the target. For the retroreflection case there is misalignment between the transmitted ray and the received ray. In addition, the Doppler shift in the frequency and the amount of tip for the receiver aperture when needed are calculated. The error in estimating wind because of the Doppler shift in the frequency due to special relativity effects is examined. The results are then applied to a proposed space-based pulsed coherent Doppler lidar at NASA's Marshall Space Flight Center for wind and aerosol backscatter measurements. The lidar uses an orbiting spacecraft with a pulsed laser source and measures the Doppler shift between the transmitted and the received frequencies to determine the atmospheric wind velocities. We show that the special relativity effects are small for the proposed system.     

含裂纹故障的齿轮系统动力学特性研究及其故障特征分析

考虑齿轮的时变啮合刚度、传动误差和轴承支撑刚度的影响,建立含齿根裂纹故障的齿轮系统多自由度力学模型,基于动力学方法对其故障机理进行研究。通过材料力学的方法计算齿轮在正常和含裂纹两种情况下的啮合刚度,对比两种刚度曲线的变化趋势,便于进行精确的动力学特性分析;对建立的模型求解系统的动态响应,结果表明当齿根存在裂纹时,其时域波形中会出现周期性的冲击现象,频谱中在啮合频率的基频及其倍频等地方形成一系列等间隔的边频谱线,其间隔大小等于故障齿轮的转频;这些边频成分幅值较低,能量分散且分布不均匀,在不同频带的幅值大小存在差异。针对上述特点,通过正交小波包方法对信号的频带进行分解,应用倒频谱分析各子频带信号的边频成分;结果表明,该方法能够有效的提高信号的信噪比,有助于识别和提取信号中由裂纹故障引起的边频成分。     

Estimating the blood velocity vector using aperture domain data

Most conventional blood flow estimation methods measure only the axial component of the blood velocity vector. In this study, we developed a new method for two-dimensional (2-D) velocity vector estimation in which time shifts resulting from blood motion are calculated for the individual channels using aperture domain data. This allows the construction of a time-shift profile along the array direction as a function of channel index, which is approximated by a first-order polynomial whose zeroth-order and first-order terms can be used to determine the axial and lateral velocity components, respectively. The efficacy of the proposed method was verified by simulations and experiments in which the transducer array had 64 elements, an aperture size of 1.96 cm, and a center frequency of 5 MHz. The flow velocity ranged from 5 to 35 cm/s and the Doppler angle ranged from 0 degrees to 90 degrees. The experimental results show that the accuracy of axial velocity estimation is higher for the new method than for the autocorrelation-based conventional method when the signal-to-noise ratio is larger than 0 dB. The mean estimation error for the axial velocity component is 2.18% for the new method, compared to 4.51% for the conventional method. The mean estimation error for the lateral velocity component is 15%, which is comparable to existing methods.