Auditory perception of objects by blind persons, using a bioacoustic high resolution air sonar

A high-resolution octave band air sonar for spatial sensing and object imaging by blind persons is described. The system has wide-angle overlapping peripheral fields of view with a narrow central field superposed. It is noninvasively coupled to the auditory system for neural processing and spatial imaging. Blind persons learn to comprehend the auditory cortical multiple-object image that is created. The real-time synchronous relationship between hearing a change in the sensor sounds and the sensed motor actions causing the change seems to aid the learning process. Computer based testing of the sensor system is described so as to relate the physical system performance with the time-varying human auditory perception. This is so that the basic psychometric experiments studying the sensor bio-acoustic spatial resolution, resulting from the superposition of two wide-angle peripheral fields with one central narrow field, may be better understood. These tests confirm that the auditory ability of subjects to resolve close objects using the combined fields is significantly improved relative to using the peripheral fields alone. These measurements are supported by blind children learning to use the sensor system.     

Dolphin (Tursiops truncatus) echoic angular discrimination: effects of object separation and complexity

A bottlenose dolphin was tested on its ability to echoically discriminate horizontal angular differences between arrays of vertically oriented air-filled PVC rods. The blindfolded dolphin was required to station in a submerged hoop 2 radial m from the stimuli and indicate if an array with two rods (S+) was to the right or the left of a single rod (S-). The angular separation between the two rods (thetaw) was held constant within each experiment while the angle between the S+ and the S-stimuli (thetab) varied to produce angular differences (deltatheta= thetab-thetaw) ranging from 0.25 to 4 degrees. In experiment I, thetaw was maintained at 2 degrees and in experiment II, thetaw was maintained at 4 degrees. Resulting 75% correct thresholds (method of constant stimuli) were 1.5 and 0.7 degrees, respectively. The two main findings of this study are: (1) decreasing the number of targets does not aid in localization, and (2) increasing the space between the rods enhances localization. Taken as a whole, the experiments suggest dolphins have a well-developed ability to resolve spatial information through sonar.     

Improvement of optical resolution in far-field imaging by optical multiplication

Based on the idea of the complex filters suggested by Toraldo di Francia in 1952, super-resolved imaging has been achieved by using interferometric image multiplication. The question of whether super-resolution implies a limited field of view is discussed, and an analytical criterion to decide this question is obtained. Three different imaging configurations are investigated, all of which gave a spatial resolution exceeding that corresponding to the full open aperture of the optical system. A resolution limit 55% of the Rayleigh limit was achieved for incoherently illuminated objects. One price that must be paid for the super-resolution is inefficient use of the light source. A second price is a limitation to the usable field of view.     

高分辨率制冷型中波广角红外成像系统的光学设计

设计了一个F数为2,工作波段为3.7～4.8μm,全视场2ω=111.2°的高分辨率制冷型中波广角红外成像光学系统。该系统采用二次成像构型,通过Si、Ge、ZnSe三种材料六片式对称布局,利用折/衍混合器件及非球面,实现了光学被动消热差设计,使系统在-55℃至+80℃的宽温范围内,在空间频率为33lp/mm处的光学传递函数(MTF)均大于0.4,系统在15μm的像素尺寸内,能量集中度大于70%;采用f-θ设计,使成像系统对不同视场具有相同的角分辨率;通过引入光阑像差和控制像方视场角,使像面具有较好的均匀性,边缘视场最低相对照度为中心视场的90.9%,且具有近100%的冷光阑效率,同时,系统具有较好的冷反射抑制效果,该光学系统适用于像素为15μm,分辨率为640pixel×512pixel的中波制冷探测器。     

Autostereoscopic three-dimensional display with high dense views and the narrow structure pitch

An auto-stereoscopic three-dimensional （3D） display method with the narrow structure pitch and high dense viewpoints is presented. Normally, the number of views is proportional to the structure pitch of the lenticular lens array. Increasing the density of views will decrease the spatial display resolution. Here a lenticular lens array with one pitch covering 5.333 subpiexels and a novel subpixel arrangement method are designed, and a 32 view 3D display is demonstrated. Compared with the traditional 6-view 3D display, the angular resolution and the displayed depth of field are significantly improved.     

Backscattering response from periodic spatial patterns in random media

Abstract

In wave-based remote sensing or radio-location of distant objects in a random medium, a high-frequency electromagnetic wave is scattered by object discontinuities, and portions of the scattered radiation can traverse the same random inhomogeneities as the initial incident field. The statistical dependence of the forward–backward travelling events results in an anomaly in the backscattered intensity pattern that carries information about the scattering object. The quality of this information depends on the ability to resolve the fine-structure elements. In this work we investigate the resolving properties of periodic spatial objects by using the random propagators of the stochastic geometrical theory of diffraction.     

KBA-X射线显微镜空间分辨力模拟和Au网格实验测量

 通过光线追踪模拟在SGⅡ激光装置上利用第9路激光入射到Cu背光靶面产生X射线,通过Au网格背光照相,利用KBA显微镜对此网格成像,获得了清晰的网格图像。通过对实验网格数据的分析发现:在掠射角减小的方向,空间分辨力随视场的变化比掠射角增大的方向变化小,与光线追踪模拟比较,二者均表明KBA的视场是非对称的,从实验图像数据得出,视场的不对称相对于中心位置约为30%。     

Spatial perception and adaptive sonar behavior

Bat echolocation is a dynamic behavior that allows for real-time adaptations in the timing and spectro-temporal design of sonar signals in response to a particular task and environment. To enable detailed, quantitative analyses of adaptive sonar behavior, echolocation call design was investigated in big brown bats, trained to rest on a stationary platform and track a tethered mealworm that approached from a starting distance of about 170 cm in the presence of a stationary sonar distracter. The distracter was presented at different angular offsets and distances from the bat. The results of this study show that the distance and the angular offset of the distracter influence sonar vocalization parameters of the big brown bat, Eptesicus fuscus. Specifically, the bat adjusted its call duration to the closer of two objects, distracter or insect target, and the magnitude of the adjustment depended on the angular offset of the distracter. In contrast, the bat consistently adjusted its call rate to the distance of the insect, even when this target was positioned behind the distracter. The results hold implications for understanding spatial information processing and perception by echolocation.     

Large-aperture double-focus laser collimator for PAT performance testing of inter-satellite laser communication terminal

A laser collimator is necessary for testing and verification of the pointing, acquisition and tracking (PAT) performance of inter-satellite laser communication terminals on the ground. The laser collimator must have a large clear aperture to fit the PAT performance testing system. The PAT subsystem has a large field of view for the acquisition and a high angular accuracy for the fine tracking. To resolve the conflict between large field of view and fine angular resolution, a large-aperture double-focus laser collimator is proposed and its optical design and mechanical structure are described. The collimator mainly consists of a primary lens, a reflector, a beam-splitting plate, a secondary lens, two compensating lenses, two imaging sensors and a laser. The primary lens directly forms the long focal length arm of the collimator. The combination of the primary lens and the secondary lens form the short focal length arm of the collimator. The collimator has an angular resolution <0.75 μrad and a 10 mrad field of view. For the collimator, the incident beam is focused on the two imaging sensors by its two arms, and the beam emitted from the laser is collimated and transmitted. The collimator is combined with an optical scanner and a fine beam deflector to test and verify the PAT performance of the inter-satellite laser communication terminal in a full physical manner.     

拖曳线列阵声呐平台噪声的空域矩阵滤波抑制技术

针对拖曳线列阵声呐平台噪声构成近场强干扰影响声呐弱目标探测的问题,利用近场平台噪声的多途传播特性,将匹配场定位技术和平面波目标方位估计技术结合,使用平台噪声到达接收阵的拷贝向量以及平面波方向向量共同设计平台噪声零响应约束空域矩阵滤波器,实现了平台噪声抑制.推导得出滤波器设计最优化问题的最优解,利用广义奇异值分解简化最优解表达式,并给出滤波器对平面波方向向量整体响应误差以及对平台噪声拷贝向量响应。利用平台噪声拷贝向量与远场平面波方向向量相关性,解释了平台噪声构成强干扰的原因,以及滤波后存在探测盲区的原因。由仿真可知,空域矩阵滤波处理可获得更小的探测盲区,同时获得盲区外更高的探测能力.      

宽视场长波红外光学系统设计

介绍了宽视场长波红外(LWIR)光学系统技术指标。离轴三反射镜消像散(TMA)型光学系统光谱覆盖范围宽,可提供一个空间分辨率高、观测范围大的无遮挡视场,能够在F数相对较小的光学系统中实现接近衍射极限的光学性能。TMA型光学系统能满足推扫式LWIR扫描仪所要求光学系统大观测视场、高光学效率等指标,可作为预先研究星载遥感仪的光学结构。     

眼模型下的投影式头盔物镜设计及视空间评价

进一步完善了投影式头盔系统的视空间评价方法,应用接近实际情况的眼模型来模拟人眼对头盔物镜系统进行评价。由视空间的评价结果出发,从眼模型的成像效果反过来进一步指导头盔系统的设计工作。设计结果显示,轴上视场和大视场的调制传递函数特性良好,在轴上视场可以达到1′的人眼最小分辨角,在大视场可以达到微显示器单个像素确定的视锐度,表明此系统在视空间的分辨力满足实际使用需要。系统最大畸变小于5%,色差不会对人眼分辨产生影响。     

Measurement of spatial resolution of the micro-CT system

The performance test is an important and necessary work for the micro-CT (computed tomography) system. The focal spot size of the micro focus X-ray tube is measured. The method of measuring the spatial resolution of micro-CT is introduced. A line-pair resolution of 28.2 lp/mm at the 10% modulation transfer function (MTF) level can be achieved with 14.7 μm spot size, 12.3 μm voxel size and a 25 mm field of view. In addition, a tungsten wire with the diameter of 5 μm can be detected by the system.     

基于宽波束磁电偶极子天线的宽角扫描线性相控阵列

设计并加工了两款基于宽波束磁电偶极子天线单元的宽角扫描线性阵列.首先,通过加载磁偶极子的方法拓展了天线单元的3-dB波束宽度.然后,基于该宽波束天线单元设计了两款具有良好宽角扫描特性的一维阵列天线.实测结果表明,天线单元的E面方向图3-dB波束宽度在9GHz—12 GHz均大于107°,H面方向图3-dB波束宽度在7GHz—12 GHz均大于178°.E面阵列中心单元的有源驻波比在9GHz—13 GHz小于2,相对阻抗带宽为36.36%.H面阵列中心单元的有源驻波比在9.6GHz—12.6 GHz小于2.5,相对阻抗带宽为27.03%.E面阵列在9GHz—12 GHz可实现±70°的有效宽角扫描.H面阵列在9GHz—GHz可实现±90°的有效宽角扫描.与传统的扫描阵列相比,设计的阵列可实现有效宽带宽角扫描,在X波段相控阵雷达方面具有广阔的应用前景.     

Optical digital microscopy for cyto- and hematological studies in vitro

The dependence of the spatial resolution and field of view of an optical microscope equipped with a CCD camera on the objective magnification has been experimentally investigated. Measurement of these characteristics has shown that a spatial resolution of 20–25 px/μm at a field of view of about 110 μm is quite realistic; this resolution is acceptable for a detailed study of the processes occurring in cell. It is proposed to expand the dynamic range of digital camera by measuring and approximating its light characteristics with subsequent plotting of the corresponding calibration curve. The biological objects of study were human adipose tissue cells, as well as erythrocytes and their immune complexes in human blood; both objects have been investigated in vitro. Application of optical digital microscopy for solving specific problems of cytology and hematology can be useful in both biomedical studies in experiments with objects of nonbiological origin.     

Incoherent recovering of the spatial resolution in digital holography

We report on a technique to recover the spatial resolution of digitally recorded and reconstructed holograms of large objects. Due to the high-contrast speckle noise diminishes the spatial resolution in coherent imaging systems our proposal is based on the reduction of the contrast of it. This aim is achieved through the superposition on an intensity basis of digitally reconstructed holograms of the same static scene. We show a theoretical justification of the procedure and experimentally-obtained results of applying the technique with digitally reconstructed holograms of an object with very poor optical contrast.     

Design of a wide-angle, lightweight head-mounted display using free-form optics tiling

We present a concept of a wide-angle, lightweight, optical see-through head-mounted display (HMD) using free-form optics tiling. Free-form optics tiling can potentially address several critical problems in existing tiled HMD designs that use rotationally symmetric optics. The optical design of our tiled optical see-through HMD achieves a field of view (FOV) of 56° × 45° and an angular resolution of 3.2 arcmin with two display channels. We demonstrate a proof-of-concept prototype and present some of its manufacturing details. The FOV can be further enlarged by tiling more display channels together at their bottom and side surfaces.     

海洋环境噪声空间相关特性建模综述*

相对于大多数声纳,海洋环境噪声通常被视为背景干扰。水听器基阵的信噪比增益成为了基阵设计和性能估计的重要参数。从空间相关特性的角度看,当信号场已知时,阵增益可唯一由噪声场的空间相关特性来确定,这就是海洋环境噪声空间相关特性建模的动机。根据环境和声场之不同,文献中已给出几种不同的噪声场模型。为了阐明已有模型的特点及未来的研究方向,本文对噪声场空间相关特性建模做了简要综述。     

傅里叶望远镜外场实验性能改进和结果分析

为了实现对傅里叶望远镜成像系统更接近实际的仿真,改进了外场实验系统结构。采用反射式目标,利用准直扩束镜替代空间滤波器和准直透镜,使用大靶面电荷耦合器件作为监视器。在无大气和包含200m水平大气两种情况下,分别对2.5mm的4种不同空间频谱分布目标进行实验。实验选用9×9,17×17,33×33和65×65傅里叶分量分别进行重构。最高成像角分辨率为3.5″。结果表明含大气与无大气重构结果的Strehl比值相近,从而证明傅里叶望远镜成像系统能够克服下行链路低阶大气扰动的影响。