Multifrequency hologram matrix and its application to a two-dimensional imaging

The concept of a multifrequency hologram matrix is introduced and applied to a two-dimensional imaging system using a linear antenna array. The image processing is based on the coherent focusing of multifrequency beams synthesized from hologram matrices of several different frequencies. The imaging system is studied by means of a computer simulation and is shown to have a good range resolution.     

Normal mode theory for acoustic waves and its application to the interdigital transducer

A normal mode expansion for the analysis of acoustic-wave problems is given. The expansion is based on orthogonality relations between the modes of an acoustic wave, and makes it possible to relate the perturbation and propagation constant of a particular mode to the properties of the modes of the unperturbed system, and of the perturbation. The use of the general expansions is then demonstrated by using it to determine a variational expression of an interdigital transducer. The results obtained are very similar to those of Smith, and demonstrate the connection between the crossed-field and series formulations for the transducer impedance.     

低损耗太赫兹波导及其成像应用

高性能的太赫兹功能器件在太赫兹波的产生、传输及探测上都有着重要意义.报道了一种Kagome型低损耗太赫兹波导及其成像应用.首先根据反谐振波导理论设计了0. 1 THz处低损耗的太赫兹波导,其理论损耗低至0. 012 cm~(-1).然后使用3D打印技术制备波导实物,实验测得其损耗为0. 015 3 cm-1,波导末端光束发散角为6±0. 5°.最后基于该波导搭建了可重构太赫兹成像装置,分别实现了对隐藏刀片、矿石的反射和透射成像,在地下远距离勘探领域具有潜在的应用前景.     

Perfect sequence excitation of the NLMS algorithm and its application to acoustic echo control

Adaptive echo cancellers are currently being studied for applications such as audio teleconference systems or hands-free telephone sets with high speech quality. The purpose of the echo control is to eliminate the acoustic feedback from the loudspeaker to the microphone. One problem of echo cancellers using e.g. the normalized least mean square algorithm(nlms) for the adaptation of the coefficients is that the convergence properties degrade with colored signal input such as speech signals [8, 9, 17]. One approach to accelerate the convergence speed is to introduce linear prediction filters in order to decorrelate the speech signal [1, 2, 12, 15, 20]. This paper presents a new approach, named the excited lms algorithm orelms algorithm, which prewhitens the input signal applying perfect sequences. Coincidently, the proposed algorithm can be interpreted as a combination of the conventionalnlms algorithm and a system identification approach using m-sequences or related sequences.     

Underwater acoustic imaging

Underwater acoustic imaging systems are useful in providing underwater observation and inspection capabilities whenever optical systems cannot. Underwater acoustic imaging is a part of the larger field of acoustic imaging, and as such, has its own peculiarities and attributes as compared with the rest of the acoustic imaging field. In this report, the general characteristics of underwater acoustic imaging are presented. Three basic techniques of acoustic imaging that are appropriate for underwater imaging are discussed (focused, beamformed, and holographic) and examples of each of them are described. Then the limitations and promise for the future in underwater acoustic imaging are explored.     

软X射线激光全息术及其计算机模拟仿真

软Ｘ射线激光全息术采用短波长Ｘ射线激光光源，从而可获得空间分辨率很高的三维全息图，但目前它还存在许多问题。用计算机来模拟仿真提供了一种有力手段。本文采用方块、英文字母、汉字等作样品，对无透镜傅利叶变换软Ｘ射线激光全息术作了模拟仿真，其结果和可见光全息实验及理论都相符合。     

电声显微成像和应用

扫描电声显微镜(SEAM)是融现代电子光学技术、电声技术、压电传感技术、弱信号检测和脉冲图像处理以及计算机技术为一体的一种新型无损分析和显微成像工具。其成像机理是基于材料的微观热弹性能或者电学性能的变化，获取目前其他手段无法得到的信息。它可以原位(in situ)同时观察试样的二次电子像和电声像(SEAM)，兼有声学显微术非破坏性内部成像和电子显微术高分辨率快速成像的特点。本文重点阐述扫描电声显微镜的工作原理、结构和组成、电声显微成像的特点，以及电声成像的基本理论和影响分辨率的主要因素。并显示了扫描电声显微镜在观察功能晶体和陶瓷的电畴结构、金属材料的应力分布、半导体材料的缺陷和位错、MEMS器件的内部信息以及超导陶瓷的相变特性等方面的实际应用。为了和电声成像的实验结果进行比较，本文也介绍了在扫描探针显微镜基础上建立起来的扫描探针声学成像技术在电光陶瓷上的实际应用。     

单像素成像及其在三维重建中的应用

不同于数码相机使用光电探测器阵列来获取图像,单像素成像通过使用一系列掩膜图案对场景进行采样,并将这些掩膜图案中的信息与单像素探测器测量得到的相应光强做关联计算以重建图像。虽然在传统可见光成像领域,单像素成像性能远不如数码相机,但许多研究成果表明,其在复合波长、太赫兹、X射线以及三维成像等一些非常规应用中具有一定优势。介绍了单像素成像技术的发展历程,用数学模型对其成像原理进行了解释,并分析了影响其性能的要点。此外,文中还对三维单像素成像技术的研究工作及其潜在的应用前景进行了总结和展望。     

A new application of acoustic micro imaging: screening MCM-C multilayer defects

Acoustic Micro Imaging (AMI) has been successfully applied for detecting soldering and underfill failures when analyzing surface mounted devices (SMD), ball-grid array (BGA) and flip-chip mounting, as well as to find internal defects, discontinuities, delaminations, and leakages in plastic packaged ICs. This paper highlights new possibilities of AMI in analyzing multilayer defects in thick-film structures. Studying a model system of multilayer thick film, it has been found that C-mode Scanning Acoustic Microscopy (C-SAM) technique seems to be a good candidate for differentiating not only the location surface defects, subsurface bubbles but also short circuit locations, nondestructively. Low Temperature Cofired Ceramic Multichip Module (MCM-C LTCC) interconnection substrates and thick-film multilayer structures are generally built up from relatively high-glass-content dielectric and conductive materials, causing one of the most important problems of the technology. In the recent failure analysis investigations, it has been demonstrated that not only rude blistering effect or pinholes can cause short circuit failures leading to decreased yields, but ionic migration and dendritic growth through the melted glass electrolyte can also occur. Short circuit locations remain generally undetected in conventional morphology studies of the surface performed with optical and scanning electron microscopy. Thus, they can only be analyzed by destructive methods, after polishing or cross-section preparation, even then the right position can be located only with difficulties. A special method has been developed by analyzing optical and acoustic multilevel picture for revealing the short circuit locations nondestructively. Performing conventional destructive investigation followed by scanning electron microscopy (SEM) and electron microprobe analysis proved the latter finding. This may be a relevant contribution for future multilayer failure analysis processes.     

Extension of Bojarski’s identity and its application to the imaging simulated

On the bases of physical optics and Born approximation, Bojarski’s identity is extended strictly to the generally scattering scheme. The results are compared with that obtained by S. R. Raz (1976) and related problems are discussed. Computer simulation demonstrates the improvement in the imaging just as shown in theoretical analysis. Subject supported by the National Natural Science Foundation of China.     

短波红外成像技术及其军事应用

短波红外可以提供可见光、微光夜视、中波、长波红外所不能提供的信息。实现短波红外成像,填补微光夜视和中波红外成像之间的光谱空缺,实现在三个大气红外透射窗口的“无缝隙探测”,对在红外波段全面获取目标的信息具有重要意义,可应用于夜视、侦察与监视、遥感、遥感系统、红外成像制导、光电对抗等领域。     

Signal processing in acoustic imaging

A review of signal processing methods which can be used to improve the effectiveness of systems designed for acoustic imaging and bearing estimation is presented. Topics covered include a) signal processing for increased resolution, b) the processing of stochastic acoustic signals, c) image processing, enhancement, and pattern recognition. The discussion of resolution processing includes lateral resolution improvement by both superresolution techniques and aperture synthesis, and improvement of both range and Doppler resolution. The stochastic signal-processing section addresses adaptive processing, as well as methods of imaging in the case of incoherent, noisy signals.     

Airborne synthetic aperture acoustic imaging

This paper presents a system model and inversion for airborne synthetic aperture acoustic (SAA) imaging. The system model accurately represents the intercation of the acoustic source and the target region at near range values. Moreover, the model incorporates the fact that the relative speed of the vehicle's (transmitter/receiver) with respect to the target region is comparable to the acoustic wave propagation speed. The inversion utilizes the principle of spectral decomposition of spherical phase functions to develop a wavefront reconstruction method from SAA data. Processing issues and selection of appropriate acoustic FM-CW sources are discussed. Results are provided that exhibit the superior accuracy of the proposed SAA system model and inversion over their synthetic aperture radar (SAR) counterpart in which the vehicle's speed is assumed to be much smaller than the wave propagation speed     

太赫兹成像雷达技术发展与制导应用探讨

太赫兹波是频段介于红外光和毫米波之间的电磁辐射,处于电子学向光学的过渡区域,兼顾了微波穿透特性和红外线成像分辨力高的特点,在雷达、宽带通信、安全探测和遥感侦察等军事领域具有巨大的潜在应用前景。本文介绍了太赫兹成像雷达的技术特点,结合导弹制导的应用要求和技术发展现状,重点分析了太赫兹成像雷达技术应用于制导的可行性,并对相关问题进行了初步探讨。     

随机混沌感知矩阵及其在成像雷达中的应用

根据压缩感知理论提出了一种适用于成像雷达的新算法,在成像目标分布满足稀疏性前提下,利用发射的随机混沌序列( SCS )形成卷积矩阵,然后通过随机行抽取构造随机感知矩阵( SC-SM)。给出了完整的算法实现框架,从理论上证明了SCS的随机性和统计独立性以及SCSM的有限等距性( Restricted Isometry Property,RIP)。仿真结果验证了算法的有效性,同时分析了影响算法性能的主要因素。与匹配滤波法相比,所提算法重构误差小,输出旁瓣低。 SCSM与其他随机矩阵具有相同的性能,然而,SCSM容易在硬件上实现,且更适用于要求保密性高和抗干扰能力强的场合。     

Holography and Medicine

Holography has emerged from the laboratory and is slowly becoming a useful tool in a variety of engineering and scientific areas. The potential exists for holography to serve as such a tool in medical and biological research. Holography can be used to form three-dimensional images. Three dimensionality is a consequence of the recording of phase information in the hologram. The presence of phase information in holographic images makes them extremely versatile and amenable to such a posteriori techniques as interferometry and dark-field imagery. Holography can also be used to analyze images, that is, to enhance image contrast and resolution, or to perform such functions as correlation analyses and pattern recognition. Moreover, the versatility of holography extends beyond the visible portion of the electromagnetic spectrum; holograms made with infrared, ultraviolet, microwave, or ultrasonic illumination, or ``synthetic' holograms made using a computer can be used to produce visible images or to analyze nonvisible images. The manner in which holography's potential can be used in biomedical applications is discussed.     

全息技术在扬声器选择中的应用

介绍了扬声器各部分的作用及对扬声器输出特性的影响,同时介绍了应用全息技术测试扬声器的方法,为扬声器的定量分析提出了新途径。     

基对称扩展信道极化算法及其在OFDM水声通信系统中的应用

针对水声通信系统中低密度校验(Low Density Parity Check,LDPC)码存在的译码复杂度高和译码错误平层问题,设计了基于极化码编码的水声通信系统,并针对水声信道的极化问题提出了新的基对称扩展极化权重(Polarization Weight,PW)信道极化法.该算法通过PW高阶基计算各个子信道的极化权...     

一种新NLMS自适应滤波算法及其在多路回波消除中的应用

提出一种NLMS改进算法并对其收敛性进行了证明。该算法计算复杂度低于Sankaran(1997)所提出的带有正交改正因子的归一化算法(NLMS-OCF)和仿射投影算法(APA),并具有易于实现等特点。仿真结果表明,以单路语音信号作输入时,新算法具有比NLMS-OCF算法更好的收敛速度和精度,而在收敛速度和精度相当的情况下,新算法比APA算法所占用的CPU时间少。将新算法扩展成两路算法后,扩展算法仍然保持了这些特点,与Sankaran(1999)两路NLMS-OCF及Benesty(1996)所提多路仿射算法(APA-MC)相比,新算法更适合于应用到多路回波消除等实时性要求高的场合。1