An acoustic Maxwell's fish-eye lens based on gradient-index metamaterials

We have proposed a two-dimensional acoustic Maxwell’s fish-eye lens by using the gradient-index metamaterials with space-coiling units. By adjusting the structural parameters of the units, the refractive index can be gradually varied, which is key role to design the acoustic fish-eye lens. As predicted by ray trajectories on a virtual sphere, the proposed lens has the capability to focus the acoustic wave irradiated from a point source at the surface of the lens on the diametrically opposite side of the lens. The broadband and low loss performance is further demonstrated for the lens. The proposed acoustic fish-eye lens is expected to have the potential applications in directional acoustic coupler or coherent ultrasonic imaging.

Near-field multiple super-resolution imaging from Mikaelian lens to generalized Maxwell's fish-eye lens

Super-resolution imaging is vital for optical applications, such as high capacity information transmission, real-time bio-molecular imaging, and nanolithography. In recent years, technologies and methods of super-resolution imaging have attracted much attention. Different kinds of novel lenses, from the superlens to the super-oscillatory lens, have been designed and fabricated to break through the diffraction limit. However, the effect of the super-resolution imaging in these lenses is not satisfactory due to intrinsic loss, aberration, large sidebands, and so on. Moreover, these lenses also cannot realize multiple super-resolution imaging. In this research, we introduce the solid immersion mechanism to Mikaelian lens(ML) for multiple super-resolution imaging. The effect is robust and valid for broadband frequencies. Based on conformal transformation optics as a bridge linking the solid immersion ML and generalized Maxwell's fish-eye lens(GMFEL), we also discovered the effect of multiple super-resolution imaging in the solid immersion GMFEL.

Fish-Eye Image Distortion Correction Based on Adaptive Partition Fitting

The acquisition of images with a fish-eye lens can cause serious image distortion because of the short focal length of the lens.As a result,it is difficult to use the obtained image information.To make use of the effective information in the image,these distorted imagesmust first be corrected into the perspective of projection images in accordance with the human eye’s observation abilities.To solve this problem,this study presents an adaptive classification fitting method for fish-eye image correction.The degree of distortion in the image is represented by the difference value of the distances fromthe distorted point and undistorted point to the center of the image.The target points selected in the image are classified by the difference value.In the areas classified by different distortion differences,different parameter curves were used for fitting and correction.The algorithm was verified through experiments.The results showed that this method has a substantial correction effect on fish-eye images taken by different fish-eye lenses.

Using UAVs for detection of trees from digital surface models

A difficult problem in forestry is tree inventory.In this study, a GoProHero attached to a small unmanned aerial vehicle was used to capture images of a small area covered by pinus pinea trees. Then, a digital surface model was generated with image matching. The elevation model representing the terrain surface, a ‘digital terrain model’,was extracted from the digital surface model using morphological filtering. Individual trees were extracted by analyzing elevation flow on the digital elevation model because the elevation reached the highest value on the tree peaks compared to the neighborhood elevation pixels. The quality of the results was assessed by comparison with reference data for correctness of the estimated number of trees. The tree heights were calculated and evaluated with ground truth dataset. The results showed 80% correctness and 90% completeness.

Moving Objects Detection Using Intersecting Cortical Model in Enhanced Fish-eye Image

A new method of the moving objects detection using the enhanced fish-eye lens and the intersecting cortical model （ICM） algorithm is proposed. The improved fish-eye lens is designed through controlling the entrance pupils of the lens. This lens has an ultra field of view about 183 degrees, and can image an ellipse picture on the 4 ： 3 rectangular CCD surface, which increases the CCD utilization and the image resolution. The ICM is a model based on pulse coupled neural network（PCNN） which is espeeially designed for image processing. It is derived from several visual cortex models and is basically the intersection of these models. The theoretical foundation of the ICM is given. An improved ICM algorithm in which some parameters are modified is used to detect moving objects specially. The experiment indicated that moving objects can be detected reliably and efficiently using ICM algorithm from the elliptical fish-eye image. It can be used in the field of traffic monitoring and other security domains.

A Beamforming Technique Using Rotman Lens Antenna for Wireless Relay Networks

Rotman lens,which is a radio frequency beam-former that consists of multiple input and multiple output beam ports,can be used in industrial,scientific,and medical applications as a beam steering device.The input ports collect the signals to be propagated through the lens cavity toward the output ports before being transmitted by the antenna arrays to the destination in order to enhance the error performance by optimizing the overall signal to noise ratio(SNR).In this article,a low-cost Rotman lens antenna is designed and deployed to enhance the overall performance of the conventional cooperative communication systems without needing any additional power,extra time or frequency slots.In the suggested system,the smart Rotman lens antennas generate a beam steering in the direction of the destination to maximize the received SNR at the destination by applying the proposed optimal beamforming technique.The suggested optimal beamforming technique enjoys high diversity,as well as,low encoding and decoding complexity.Furthermore,we proved the advantages of our suggested strategy through both theoretical results and simulations using Monte Carlo runs.The Monte Carlo simulations show that the suggested strategy enjoys better error performance compared to the current state-of-the-art distributed multiantenna strategies.In addition,the bit error rate(BER)curves drawn from the analytical results are closely matching to those drawn from our conducted Monte Carlo simulations.

Non-isoplanatic lens aberration correction in dark-field digital holographic microscopy for semiconductor metrology

In the semiconductor industry,the demand for more precise and accurate overlay metrology tools has increased because of the continued shrinking of feature sizes in integrated circuits.To achieve the required sub-nanometre precision,the current technology for overlay metrology has become complex and is reaching its limits.Herein,we present a dark-field digital holographic microscope using a simple two-element imaging lens with a high numerical aperture capable of imaging from the visible to near-infrared regions.This combination of high resolution and wavelength coverage was achieved by combining a simple imaging lens with a fast and accurate correction of non-isoplanatic aberrations.We present experimental results for overlay targets that demonstrate the capability of our computational aberration correction in the visible and near-infrared wavelength regimes.This wide-ranged-wavelength imaging system can advance semiconductor metrology.

单反相机在仿古建筑精细建模中的应用

普通单反相机、手持相机等非量测相机用于近景摄影测量辅助精细建模时,由于仿古建筑细节纹理具有高度相似性,获取的影像又缺少高精度定位测姿系统(POS)信息,在空中三角测量运算时,会匹配出大量错误连接点,以至于不能顺利重建三维模型,针对这一问题,本文提出一种单反相机用于大型仿古建筑精细建模的方法,采用先分区后融合的空中三角测量方法,避免出现错误连接点,通过试验证明该方法能有效避免出现错误连接点,融合建模的纹理精度和位置精度均能满足地理实体生产和实景三维的要求。

人工智能口腔实景图像识别技术用于龋齿筛查的效能研究

目的基于人工智能(AI)图像识别技术,评估智能手机(Sp)和数字化单反相机(DSLR)两种设备采集的口内实景照片用于龋齿筛查的效能研究。方法建设“益生牙kid”AI龋齿筛查云平台,通过AI图像识别深度学习算法不断迭代学习口腔临床医生筛查龋齿的方法,并用混合矩阵验证其识别效果。使用Sp及DSLR两种设备,同时采集27位受试者口内照片。每位受试者按照采集标准,Sp和DSLR分别获取3张、5张不同牙位照片,两组照片提取上传至龋齿筛查云平台,分别获得359、480个牙位龋齿筛查结果。受试者同时接受口腔医师使用WHO龋齿分级评判标准进行临床龋齿筛查。采用敏感度、特异度及曲线下面积(AUC)等作为AI龋齿图像识别效果的评价指标。结果混淆矩阵结果显示低风险早期龋和高风险成洞龋识别准确度高达90%以上,而中风险釉质轻度缺损龋齿识别准确度仅为32%。口腔医师采用WHO龋齿评判标准与AI筛查龋齿结果比较,Sp拍摄的口内照片诊断龋齿敏感度、特异度及AUC值分别为75.6%、85.8%及0.849;DSLR拍摄的口内照片诊断龋齿敏感度、特异度及AUC值分别为80.0%、86.2%及0.859。结论AI口腔实景图像识别龋齿筛查技术与临床医生龋齿诊断结果接近。Sp拍摄龋齿照片更便捷高效,与临床DSLR相比筛查正确率接近,实际推广应用价值更高。

Scansys、Pentacam、CASIA和Arcscan测量近视眼ICL植入术后拱高比较

目的评估国产三维眼前节分析系统Scansys、Pentacam三维眼前节全景分析仪、频域眼前节光学相干断层扫描仪(CASIA SS-1000)和新型超高频数字超声扫描系统(Arcscan Insight100)测量近视眼有晶状体眼后房型人工晶状体(ICL)植入术后中央拱高的差异及一致性。方法采用诊断试验研究方法,纳入2019年6—12月于河南省人民医院眼科行ICL V4c植入术的近视患者56例56眼,术后同时应用Scansys、Pentacam、CASIA和Arcsan测量中央拱高。比较4种仪器拱高测量值的差异;4种仪器拱高测量值的相关性采用Pearson相关性分析,一致性比较采用Bland-Altman法分析。结果Scansys、Pentacam、CASIA和Arcscan拱高测量值分别为(481.8±191.6)、(476.4±190.6)、(619.3±207.5)和(534.0±221.2)μm,总体比较差异有统计学意义(F=143.301,P<0.001),其中Scansys和Pentacam拱高测量值明显低于CASIA和Arcscan,Arcscan拱高测量值低于CASIA,差异均有统计学意义(均P<0.001)。Arcscan-CASIA、Arcscan-Pentacam、Arcscan-Scansys、CASIA-Pentacam、CASIA-Scansys、Pentacam-Scansys拱高测量值均呈强正相关(r=0.982、0.933、0.931、0.942、0.941、0.989,均P<0.001)。Scansys、Pentacam、CASIA和Arcscan拱高测量值组内相关系数分别为0.985、0.975、0.998、0.992;CASIA和Arcscan、CASIA和Scansys、CASIA和Pantacam、Arcscan和Scansys、Arcscan和Pantacam拱高测量值差值95%一致性界限分别为-170~0、0~280、0~280、-110~210、-100~220μm,差值的绝对值最大值超出临床的可接受范围,一致性欠佳;Scansys和Pentacam拱高测量值差值95%一致性界限为-60~50μm,一致性良好。结论4种仪器测量近视眼ICL V4c植入术后拱高重复性均良好,其中,Scansys和Pentacam的拱高测量值偏小,两者一致性良好,结果可以互相替代;而CASIA拱高测量值最大,其次为Arcscan,彼此差异较大,测量结果不能相互替代,在临床工作中应结合实际情况综合分析。

Bi-prism-based single-lens three dimensional digital image correlation system with a long working distance: Methodology and application in extreme high temperature deformation test

As a novel three dimensional digital image correlation （3D DIC） method, the bi-prism-based single lens （BSL） 3D DIC method has been proposed and developed in recent years. Making use ofa bi-prism, this method is able to perform a 3D DIC measurement using only a single camera. Thus, the integration level of a BSL 3D DIC system could be much higher than that of the double-camera 3D DIC system. In this paper, using a small-angle bi-prism and a camera with a longer focal length, a special BSL 3D DIC system with a long working distance is designed for measurements in extreme environments. The principle of the system is first studied, and practical methods are then proposed for the system set-up and the determination of system parameters. Then, feasibility of the measurement system is verified by out-of-plane rigid-body translation tests. Finally, the BSL 3D DIC system is proven to be capable of combining with a high-temperature testing instrument to perform deformation tests in a high-temperature environment of up to 1500℃.

Square Maxwell’s fish-eye lens for near-field broadband achromatic super-resolution imaging

Broadband super-resolution imaging is important in the optical field.To achieve super-resolution imaging,various lenses from a superlens to a solid immersion lens have been designed and fabricated in recent years.However,the imaging is unsatisfactory due to low work efficiency and narrow band.In this work,we propose a solid immersion square Maxwell's fish-eye lens,which realizes broadband(7-16 GHz)achromatic super-resolution imaging with full width at half-maximum around 0.2λ based on transformation optics at microwave frequencies.In addition,a super-resolution information transmission channel is also designed to realize long-distance multi-source super-resolution information transmission based on the super-resolution lens.With the development of 3D printing technology,the solid immersion Maxwell's fish-eye lens is expected to be fabricated in the high-frequency band.

数码单反相机焦平面光电转换函数的测量及分析

为了在光学实验中合理应用数字成像设备,需要获取并处理其物理输入量与数字输出量之间的关系。基于ISO 14524:2009标准,对数码单反相机Canon EOS 500D的焦平面光电转换函数进行了实验测量及数据分析。通过比较不同尺寸像素区域及不同图片格式对测量结果的影响,发现焦平面光电转换函数的测量偏差随像素区域尺寸的减小而增大,而RAW和JPEG两种文件格式的数字输出值与焦平面曝光量的关系分别为线性和非线性。当单反相机用作光分布记录测量的仪器时,采用直接反应传感器接收的辐照度信息的RAW格式作为输出数据,可以获得较大的动态范围,理论上可以避免相机非线性变换等后续处理带来的影响,经过必要的校正可以更精确地表示场景信息。

中继透镜分辨率在像素编码曝光成像中对图像重构质量的影响分析

像素编码曝光成像技术是一种先进的高速成像技术,其利用数字微镜器件(digital micromirror device,DMD)对相机每个像素的曝光进行编码,将多帧图像信息融入到单帧编码图像中,然后再利用解码算法进行图像重构,将低帧频相机的图像采集速率提升数倍,实现低帧频相机的高速成像.在该技术中,DMD的像素与相机像素之间的精确匹配是实现编码曝光成像的前提,因此,相关研究人员主要关注于如何实现像素的精确匹配.然而,两者之间中继成像系统的分辨率作为编码曝光成像的另一重要影响因素,却鲜有人研究和分析.为此,本文从理论上分析了中继成像系统的分辨率对解码图像重建效果的影响,并结合模拟和实际成像实验对理论分析进行验证.在此基础上,搭建了像素编码曝光成像系统,提出了一种基于条纹相位的成像系统点扩散函数估计方法,并将Richard-Lucy反卷积算法引入到编码图像的重构过程中,有效改善编码曝光成像的质量,对于像素编码曝光成像技术的发展具有重要的意义.

倾斜摄影测量技术在矿山大比例尺地形图测绘中应用

文章通过分析无人机倾斜摄影测量的作业流程,以及在矿山大比例尺地形图测绘中的关键技术。结合规范和实际大比例尺的测图要求,验证了无人机倾斜摄影测量技术的精度、可靠性和可行性。为矿山三维模型的建设和大比例尺矿山测图项目的提升提供了参考。

影像稳定系统发展和趋势解析

画面不稳定往往是在移动拍摄时,肩扛或手持设备使镜头不稳定导致的,而频繁晃动的画面会给观看者带来疲劳、烦躁及反感的情绪。在图片摄影和影视创作中,为了能获得更稳定的拍摄效果,拍摄者往往需要运用影像稳定系统。因此,众多设备厂商研制了3种类型,4种不同方式的稳定系统。其中,斯坦尼康和三轴云台稳定器属于物理稳定;镜头防抖、机身五轴防抖系统属于光学稳定;图像数字稳定系统属于电子稳定。这几类稳定系统各有特色,在众多的纪录片、影视剧中发挥着各自的特点,在未来的影视创作中,影像稳定系统将会发挥举足轻重的作用。

便携式显微镜/远视镜实时观察和记录系统的低成本组建

目的:为轻便型视屏神经外科配备便携式显微镜/远视镜实时观察和记录系统。方法:系统由显像设备、成像设备和支架组成。显像设备为Dell便携式计算机;成像设备包括DFK-21AU04 USB CCD摄像头、Computar MLH-10×macro镜头和COPL-40-W同轴光灯头复合体;支架为改造的MA241102便携式气动弹簧摇臂式支架。通过视屏观察(15 cm)深瓶中的干豆、切开的新鲜石榴及成年SD大鼠活体颈总动脉分叉部;在视屏图像引导下阻断成年SD大鼠大脑中动脉。结果:Qy/Fx-0810-Mi/Ma便携式实时观察和记录系统小巧轻便、廉价实用,能够从不同角度观察手术野,工作距离超过54 cm,视屏图像清晰、逼真、有立体感且与实际操作同步。结论:可低成本组建适合轻便型视屏神经外科的便携式显微镜/远视镜实时观察和记录系统。

大视场数字式太阳敏感器设计

提出了一种新型的大视场数字式太阳敏感器设计方法,其光学系统由全景环形光学镜头和滤光膜组成。该敏感器具有视场大、结构简单及功耗低的特点。从工作原理出发,建立了该敏感器模型,并利用搭建的实验平台,对敏感器进行精度标定。设计中,采用非线性最小均方最优解来确定模型中的参数。对测量误差进行分析,消除系统误差后,敏感器的测量精度由0.4°提高到0.02°。测试结果表明此太阳敏感器具有120°×180°的大视场和0.02°的测量精度,能很好满足视场要求较高的姿态确定系统。

并行共焦测量中的并行光源技术综述

并行共焦测量技术的核心是将单点共焦测量变成多点同时扫描测量,从而使共焦测量速度显著提高。本文介绍了共焦测量技术原理,综述了用于并行共焦的并行光源技术,分析了这些方法的优点和不足。结合作者近年来的研究成果,重点阐述了基于微透镜阵列和数字微镜器件(DMD)产生并行光源的新方法。分析和研究了DMD的空间光调制机理,最终建立了一种单光源双光路并行像散共焦测量系统。

无透镜片上显微成像技术:理论、发展与应用

同时实现大视场、高分辨率成像是光学显微技术发展至今不断追求的永恒目标。传统光学显微镜由于其光学设计原理限制,空间带宽积一般总是限制在百万像素量级,从而无法同时兼顾高分辨率与大视场。另一方面,复杂的光学系统也使显微镜变得日趋昂贵、笨重、复杂且难以维护,极大地限制了其推广和应用。无透镜片上显微成像技术是近年来发展出的一种新概念计算成像技术:其不利用成像透镜聚焦,而直接将所观测的样本紧贴于成像器件光敏面上方记录图像,并结合相应的图像恢复算法实现清晰物像的反演与重构。由于具有视野大、分辨率高、无需标记、成本低、便携性好和可实现三维(3D)成像等优点,无透镜片上显微镜有望拓展传统显微成像技术的疆界,成为一种新型的快捷、便携的就地检验(POCT)工具。文中从无透镜成像基本原理、实验系统、重构方法及其典型应用进行了综述。最后,讨论了无透镜显微成像现存的一些关键问题以及今后可能的发展方向。