基于相位映射的三维主动视觉标定

通过在结构光发射单元和成像单元间施加几何约束条件,建立统一的坐标系.利用条纹投影和相位映射技术,构造了将编码相位图映射为物体的三维空间坐标的数学模型,进而获得深度图像空间坐标的计算值,然后将其与物体空间的三维标定数据基准进行比较,建立目标函数为误差平方和最小的非线性优化方程.两步法迭代求解这个优化方程,最终获得三维系统的结构参数.实验结果证明了本文提出的三维成像系统标定理论和方法的有效性.     

三维线性相位的递归数字滤波

本文讨论了如何获得三维线性相位的递归数字滤波器和相应的三维数字信息处理的应用。提出了二十种线性相位的三维递归数字滤波模式和对应的1280种不同的线性相位的递归数字滤波器转移函数的表达式。以其中的串联型结构为主要线索,进行了详细论述。本文给出的这些三维滤波系统具有简单方便,效率高,性能好的优点。缺点是:在进行时实处理时,需要一定的时延。     

分布式圆阵空间宽带声源定位方法

为提高空间声源定位精度、减少计算量、提高噪声鲁棒性,提出了一种高精度的分布式圆阵空间声源定位方法。该方法首先将声信号通过聚焦矩阵转换成窄带信号,再利用空间谱及其相位信息的群延迟函数乘积消除无关伪峰,得到高精度声源波达方向估计。然后借助于区域质心在三维坐标系的各投影面分别建立粗略信号源区域。最后结合联合可控响应功率相位,进行区域收缩,得到粗略收缩区域,并将互功率谱最大点作为声源定位估计。该方法利用群延迟函数提高了空间谱信息利用率,得到高精度波达方向估计,增强了初始区域的可靠性;区域质心收缩和可控响应功率相位联合应用,可快速锁定声源位置,降低搜索的复杂度。另外分布式阵列的大孔径、对子阵位置变化不敏感的特性增强了该方法对噪声的鲁棒性。仿真实验验证了该算法能实现高精度声源定位。      

分离物体三维测量的彩色结构光编码新方法

提出了一种结合颜色、格雷码和正弦光栅的编码新方法,用于测量空间分离物体的三维面形。该彩色格雷码正弦条纹图案表现为用颜色信息编码的正弦条纹图案,利用此条纹图案来记录物体的三维面形数据。首先投射一幅彩色格雷码正弦条纹来调制被测物体的三维信息,摄像机拍得物体表面的变形条纹图,然后应用傅里叶变换方法获取截断相位,根据编码特征进行解码来指导截断相位的展开,获得展开相位,进而恢复出物体的三维面形。该方法编码稳定,解码方法可靠,只需要拍摄一幅图,就可以较好地重建空间分离物体的三维面形。空间分离物体的实验结果以及与基于调制度排序的截断相位二维空间展开结果的对比,均证明了该方法的正确性和可行性。     

基于相位信息的图像特征定位

图像特征可以用一个基于Gabor小波变换的复向量来表示.图像的相位是空间位置的函数,根据这一原理,利用相位信息可以实现图像特征的定位.分析了图像信号相位信息的空间特性,以人脸图像为例,研究了相位信息在图像特征定位中的应用.     

基于空间调制器的透镜设计与成像研究

为了研究利用空间光调制器制作的菲涅尔透镜的特性,基于标量衍射理论推导了透镜的相位分布函数,建立了菲涅尔透镜的模型;并通过实验测量了空间光调制器的相位—灰度特性曲线,得到了相位与灰度的函数关系.制作了焦距为100 mm和150 mm的菲涅尔透镜相位灰度图.通过实验研究了该菲涅尔透镜成放大实像和缩小实像的成像规律;结果表明...     

抗反辐射导弹雷达诱饵合成场技术的研究

设置诱骗源是抗反辐射导弹的关键技术之一。现就抗反辐射导弹雷达诱饵合成场强度和相位做了探讨,给出了在两个辐射源情况下的空间合成场强度和相位的计算公式。     

雷达目标多维特性分析与应用

实际目标的雷达特性是多维空间中的函数,但雷达观测只能获得多维特性在低维空间中的切片或投影,深入分析有限的雷达观测数据蕴含的目标特性信息,对提升目标检测识别性能有重要意义.从三维散射率分布函数出发,推导了不同维度雷达图像与散射率分布函数积分投影的傅里叶变换对关系,并通过分析该关系所隐含的近似条件,指出实际目标散射特性的复杂性,得出了多维空间中形式化的散射模型.基于散射中心和雷达图像从不同的角度对多维散射模型的低维映射进行分析,给出了若干目标特性分析实例,包括棱形结构的相位逆转现象、多次散射的极化相位关系、空间目标腔体结构的色散现象、柔性结构的图像散焦效应等.形式化多维散射模型和低维映射研究方法为分析复杂目标的雷达散射特性提供了参考.     

面向结构光三维测量的相位展开技术综述(特邀)

结构光三维形貌测量方法越来越多地应用于逆向工程、航空航天、生物医学、文物保护等领域。相位展开作为结构光三维测量中的一个关键环节对测量精度、速度和可靠性起着决定性作用。文中综述了相位展开技术的基本原理、国内外研究现状、各类方法的优缺点和未来发展方向。首先根据相位展开计算方法不同，将现有的用于结构光三维形貌测量技术的相位展开技术分为以下四类进行详细的介绍：时间相位展开技术、空间相位展开技术、基于深度学习的相位展开技术和其他相位展开技术；然后详细比较了各种技术的优缺点；最后总结了相位展开技术的特点并展望了该技术的未来研究方向。基于文中综述的内容，研究者们可用于了解各类相位展开技术的原理与进展，进而根据不同方法的特点对比结合应用需求和测量条件选择最有效的相位展开技术，实现三维形貌的精确测量。     

JPEG2000对PMP图像压缩效果的定量研究

探讨了新一代静态图像压缩标准JPEG2000在三维面形测量中的应用.针对三维面形测量中的相位测量轮廓术,在减少图像存储空间,同时又不明显降低图像应用质量的前提下,采用了JPEG2000有损压缩技术对光栅投影图进行压缩.对相移法中得到的变形光栅图进行不同压缩比的压缩,比较了压缩后重构图像展开的相位与未经压缩的原图展开的相位之间的误差.通过定量计算压缩前后相位函数间的最大误差和均方根误差,分析了在相同压缩比的条件下,三维面形复杂程度与三维重建误差的关系.文中还比较了不同相移次数的光栅投影图的压缩对相位误差的影响.本文的研究结果对在相位测量轮廓术中合理的选择JPEG2000图像压缩比具有参考价值.     

A finite-element-boundary integral formulation for scattering bythree-dimensional cavity-backed apertures

A novel numerical technique is proposed for the electromagnetic characterization of the scattering by a three-dimensional cavity-backed aperture in an infinite ground plane. The technique combines the finite element and boundary integral methods to formulate a system of equations for the solution of the aperture fields and those inside the cavity. Specifically, the finite element method is used to formulate the fields in the cavity region, and the boundary integral approach is used in conjunction with the equivalence principle to represent the fields above the ground plane. Unlike traditional approaches, the proposed technique does not require a knowledge of the cavity's Green's function and is, therefore, applicable to arbitrary shape depressions and material fillings. Furthermore, the proposed formulation leads to a system having a partly full and partly sparse as well as symmetric and banded matrix which can be solved efficiently using special algorithms     

On the aperture and pattern space factors for rectangular and circular apertures

A consequence of a recently discovered edge condition for planar apertures is that all planar aperture distributions are separable physically into a product of an edge factor and an aperture space factor, analogous to the way in which the radiation pattern separates into a product of an element factor and a pattern space factor. An exact relationship between these aperture and pattern space factors for physically realizable vector fields is derived here for rectangular and for circular apertures. For rectangular apertures it leads to a two-dimensional set of doubly orthogonal functions that are characteristic of the aperture geometry. Characteristic functions for circular apertures, however, are shown to exist only if the vector fields are circularly symmetric, although for scalar fields they exist for completely arbitrary aperture distributions with arbitrary edge taper. For rectangular apertures the characteristic functions consist of products of spheroidal functions and for circular apertures they are obtained from a generalization of the spheroidal functions. Some of the properties of these generalized spheroidal functions are developed here.     

Electromagnetic scattering by and transmission through athree-dimensional slot in a thick conducting plane

A hybrid numerical technique for a characterization of the scattering and transmission properties of a three-dimensional slot in a thick conducting plane is presented. The technique combines the finite element and boundary integral methods to formulate a system for the solution of the aperture fields and by virtue of the finite element method, it is applicable to inhomogeneously filled slots of arbitrary shape. The numerical implementation is described for the edge-based expansion functions associated with rectangular brick elements, and examples are presented demonstrating the validity, versatility, and capability of the technique. These also provide some understanding of the slots scattering and transmission properties as a function of its geometry and material filling     

Discretized Gabor-based beam algorithm for time-harmonic radiation from two-dimensional truncated planar aperture distributions .II. Asymptotics and numerical tests

For pt.I see ibid., vol.50, no.12, p.1751-59 (2002). In this second part of the two-part sequence dealing with Gabor-based Gaussian beam (GB) representations for the excitation of time-harmonic three-dimensional (3-D) vector electromagnetic fields excited by two-dimensional (2-D) arbitrarily polarized truncated planar aperture distributions (set in a discretized [configuration (space)]-[spectrum (wavenumber)] phase space), we employ high-frequency asymptotic approximations to reduce the formal solutions developed in part I to efficient algorithms for implementation. The resulting explicit expressions for the 3-D GB propagators are applied to the species of narrow-waisted GBs, which possess ray-like features without the failures of ray fields in ray-optical transition regions. The potential utility of such GBs in the synthesis of wave interactions with complex environments has been discussed previously. The narrow-waisted GB algorithms for the aperture and radiated near-to-far zone fields are calibrated for robustness, accuracy and efficiency by comparison with numerically generated reference solutions in a series of tests involving coordinate-separable rectangular aperture distributions with cosine amplitude tapers.     

Gaussian mode analysis of Cassegrain antenna efficiency

Gaussian mode analysis is a convenient way to characterize long focal length systems, such as the Cassegrain antenna at the secondary focus. We use multimode Gaussian optics to derive several interesting results concerning the aperture efficiencies of Cassegrain antennas fed by corrugated conical horns. The highest efficiency is obtained when the antenna is illuminated by a wide-band, wide-angle horn which has its phase center at the secondary focus, or equivalently by a narrow-band diffraction limited horn with its phase-center located at a confocal tertiary focus. In both cases this corresponds to placing the horn aperture at a position where the incoming fields are frequency-independent and have limited spatial extent. We generalize these results to show that a true image of the aperture distribution can always be formed on the spherical cap in the aperture of any arbitrary scalar horn, by using a single refocusing tertiary lens or mirror. Since both the incoming fields and the horn aperture fields on this surface are frequency independent, it follows that the aperture efficiency is also independent of frequency with either of these arrangements. We suggest that devices for shaping the aperture illumination, such as shaped lenses or dual shaped subreflector systems, should, in general, be installed near an image of the telescope aperture distribution.     

The physical optics fields of an aperture on a perfectly conducting screen in terms of line integrals

The physical optics fields due to an aperture on a perfectly conducting screen are expressed in terms of line integrals over the boundary of the aperture. These line-integral representations have the same properties as the ones in terms of surface integrals over the aperture; in particular, they admit arbitrary, source distributions, and are continuous everywhere in the source-free half-space, including the geometric optics shadow boundary.     

Discretized Gabor-based beam algorithm for time-harmonic radiation from two-dimensional truncated planar aperture distributions .I. Formulation and solution

In this first part of a two-paper sequence, we develop a Gabor-based Gaussian beam (GB) method for the representation of three-dimensional (3-D) time-harmonic vector electromagnetic fields excited by two-dimensional (2-D) truncated arbitrarily polarized planar aperture field distributions. The biorthogonal Gabor basis is tied to a lattice in the discretized four-dimensional (4-D) [configuration (space)]-[spectrum (wavenumber)] phase space which spans the 2-D aperture plane. This study generalizes previous investigations of the simpler corresponding procedure for 2-D fields excited by one-dimensional (1-D) apertures. By subsequent specialization, in the 1-D aperture case, to narrow-waisted 2-D ray-like GBs, we have shown that tracking such beams through interactions with complex environments and recombining them to synthesize the total 2-D field produces robust, efficient and accurate algorithms that are useful for a variety of forward and inverse scattering scenarios. Extension to the time domain via narrow-waisted pulsed GBs has likewise been considered. These potential applications have motivated the extension here to general 3-D EM fields excited by time-harmonic 2-D truncated apertures. The presentation relates each step in the analytic development to a corresponding step in the 1-D aperture case, thereby highlighting the complications (in the parameterizing phase space) associated with the 2-D aperture problem. The outcome is the formal exact solution of the problem under consideration.     

Hybrid finite element-modal analysis of jet engine inlet scattering

With the goal of characterizing jet engine inlets, a hybrid finite element-modal formulation is presented for the analysis of cavities with complex terminations. The finite element method (FEM) is used to find the generalized scattering matrix for an N-port representation of the complex termination. Where N is the number of traveling modes in the cavity. The cavity is assumed to be circular at the termination (engine) but the remainder of the cavity can be of arbitrary cross section. The scattered fields are obtained by tracing the fields back out of the cavity via a high frequency or modal technique with the generalized scattering matrix used in determining the fields at an aperture near the irregular cavity termination. “Proof of concept” results are presented and several issues relating to the implementation of the FEM are addressed. Among these, a new artificial absorber is developed for terminating the FEM mesh and the suitability of edge or node based elements is examined     

Electromagnetic scattering from three-dimensional cavities via aconnection scheme

The electromagnetic scattering from arbitrary three-dimensional cavities is presented. To alleviate computational constraints for three-dimensional problems, a connection scheme is developed based on microwave network theory. This scheme allows the cavity to be divided into sections and each section to be analyzed independently of the rest of the cavity. Each section of the cavity is represented by a generalized admittance matrix which if formulated via a boundary-integral equation approach. Using the concept of input and load admittance, the aperture admittance matrix of the cavity can be derived by cascading the admittance matrices of individual sections. Once the cavity aperture admittance matrix is obtained, the aperture electric field and the backscattered field are found by the standard generalized network formulation. Numerical results are compared against modal solutions of regularly shaped cavities with good agreement. This connection scheme leads to a reduction in computational resources, especially for cavities with one dimension much larger than the other two     

导电平面上三维任意腔体的散射分析

本文利用边界积分法及连接算法分析导电平面上的三维腔体散射。在引入广义导纳矩阵后,可将腔体分为几段,分别用积分方程法计算每段的广义导纳矩阵。然后利用连接算法得到整个腔体的口径导纳矩阵。最后由广义网络原理求解腔体的口径等效磁流及后向散射场。本文方法极大地缓解了计算机内存对腔体尺寸的限制,提高了分析效率,可作为一种机辅设计算法。