2020
2020
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Record 169 of
Title:Electromagnetic Performance of the Novel Hybrid-Pole Permanent Magnet Machines for High Peak Torque Density
Author(s):Liu, Yu-Xi(1); Cao, Ji-Wei(2); Gao, Qin-He(1); Liu, Zhi-Hao(1); Lu, Ya-Chao(3); Sun, Zhi-Yin(2)Source: IEEE Access Volume: 8 Issue: DOI: 10.1109/ACCESS.2020.3043432 Published: 2020Abstract:This paper proposes two novel hybrid rotors permanent magnet (PM) machines for the high torque density in short duration condition operation. In order to enhance the torque performance, the flux concentrated structure of spoke-type PM is employed to increase the air-gap flux density. Meanwhile, the non-magnetic connector of the rotor is employed to eliminate the magnetic flux leakage. The rotors of the conventional machines and the proposed machines are optimized by the finite element analysis (FEA). Furthermore, based on the comparisons of electromagnetic performances for the optimized machines, including the open-circuit flux density, torque, PM eddy current loss, overload capability, the characteristics of the proposed machines are analyzed. The results indicate that the proposed machine can improve the torque at rated and overload operation with growth rate 14.3% and 13.1%, respectively. Finally, a 12-slots/10-pole PM machine is prototyped and FEA is to be validated. ? 2013 IEEE.Accession Number: 20205209684136 -
Record 170 of
Title:Design of a double-telecentric optical system based on machine vision
Author(s):Wu, Tiantian(1,2); Ma, Xiaolong(1)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 11568 Issue: DOI: 10.1117/12.2579903 Published: 2020Abstract:With the development of industrial production, machine vision is playing a more and more important role in measurements and judgments. For the machine vision system, double-telecentric optical system can be used for visual inspection and measurement with good imaging effect and imaging accuracy. This paper mainly introduces a low telecentricity and low-distortion double-telecentric optical system. The designed system consists of only 5 lenses, which will reduce production costs. The object field of view is 50mm, the working wavelength is visible light, the total length of the system is 274mm, the working distance is 110mm, the maximum distortion is less than 0.025%, the object side telecentricity is better than 2.6×10-6 milliradians, and the image side telecentricity is better than 7.6×10-4 milliradians. The MTF is greater than 0.3 at the Nyquist frequency 91 lp/mm for the full field of view. The MTF curve of the optical system is close to the diffraction limit, which indicates the optical system has good imaging quality in space. The optimizing process and tolerance analysis of the optical system are showed in this paper. The results indicate that the double-telecentric optical system can be used in the production and inspection of parts in the industry. ? 2020 SPIE. All rights reserved.Accession Number: 20204909580550 -
Record 171 of
Title:Design of a zoom projection optical system for high resolution projector
Author(s):Qin, Guang(1,2); Fan, Xuewu(2); Ma, Zixuan(1,2); Zhang, Gengyao(1,2)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 11565 Issue: DOI: 10.1117/12.2579880 Published: 2020Abstract:With the rapidly development of optoelectronic technology and computer technology, the projection display technology has also been unprecedentedly developed. In this paper, a zoom projection objective lens is designed based on Digital Light Processing (DLP) projection display technology, the 0.47in DMD chip of Texas Instruments is selected in this paper, its resolution is 1920×1080 and its micromirror pitch is 5.4 μm. The optical system uses a 100% offset transmissive projection structure. The working wavelength of the whole zoom projection lens is visible light, and 14 lenses including protective glass are used for the projection lens, each lens in the designed system is spherical, the total length of the system is 220mm, the aperture of the optical system is about 58mm, focal length of the zoom projection lens ranges from 25mm to 32 mm, viewing angle ranges from 41 degree to 51degree, and F number is 1.7, the distortion of the designed system is less than 3%, the projected image plane relative illumination of the zoom projection lens above 90%, the telecentricity of the system is less than 1 degree. The MTF value is close to 0.3 at the Nyquist frequency 93 lp/mm for the full field of view, the designed system meet the requirements of projection. In order to meet the current processing level, the radius of curvature tolerance, the spacing tolerance, the eccentricity tolerance and the tilt tolerance are analyzed. The results show that the zoom projection lens is easy to process and produce. ? 2020 SPIE. All rights reserved.Accession Number: 20204909588159 -
Record 172 of
Title:Multispectral curved compound eye camera
Author(s):Yu, Xiaodan(1,2); Liu, Chenyang(2,3); Zhang, Yuanjie(1,2); Xu, Huangrong(1,2); Wang, Yuanyuan(1,3); Yu, Weixing(1,2)Source: Optics Express Volume: 28 Issue: 7 DOI: 10.1364/OE.385368 Published: March 30, 2020Abstract:In this work, we propose a new type of multispectral imaging system, named multispectral curved compound eye camera (MCCEC). The so called MCCEC consists of three subsystems, a curved micro-lens array integrated with selected narrow-band optical filters, an optical transformation subsystem, and the data processing unit with an image sensor. The novel MCCEC system can achieve multi-spectral imaging at an ultra-large field of view (FOV), and obtain information of multiple spectrum segments at real time. Moreover, the system has the advantages of small size, light weight, and high sensitivity in comparison with conventional multispectral cameras. In current work, we mainly focus on the optical design of the MCCEC based on the overlap of FOV between the neighboring clusters of ommatidia to achieve the multispectral imaging at an ultra-large FOV. The optical layout of the curved micro-lens array, narrow-band filter array and the optical relay system for image plane transformation are carefully designed and optimized. The whole size of the optical system is 93 mm × 42 mm × 42 mm. The simulation results show that a maximum FOV of about 120° can be achieved for seven-waveband multispectral imaging with center wavelengths of 480 nm, 550 nm, 591 nm, 676 nm, 704 nm, 740 nm, and 767 nm. The new designed MCCEC has a great potential as an airborne or satellite-born payload for real time remote sensing and thus paves a new way for the design of compact and light-weight spectral-imaging cameras with an ultra large FOV. ? 2020 Optical Society of America.Accession Number: 20201508395064 -
Record 173 of
Title:Shaping attosecond pulses by controlling the minima in high-order harmonic generation through alignment of CO2 molecules
Author(s):Jin, Cheng(1,2); Wang, Su-Ju(3); Zhao, Xi(3); Zhao, Song-Feng(4); Lin, C.D.(3)Source: Physical Review A Volume: 101 Issue: 1 DOI: 10.1103/PhysRevA.101.013429 Published: January 23, 2020Abstract:We report a simple method for generating shaped attosecond pulses by using a CO2 molecule. Unlike most other molecules, owing to its unique energy and angle dependence and the presence of deep minima in the photoionization transition dipole moment, the shape of harmonic spectra, especially the position and depth of minima, can be readily controlled by tuning the degree of alignment. The sensitive alignment dependence of the minima is due to the coherent interference of a laser-induced dipole from each molecule when CO2 molecules are moderately aligned, but not when they are well aligned or when they are isotropically distributed. Such a sensitivity offers a simple way of controlling the spectral amplitude and phase of the generated harmonics and thus shaping the generated attosecond pulses, for example, producing structured attosecond pulses by splitting a single burst into two. We illustrate how such pulses are generated and how to characterize them. This method offers a simple way to shape attosecond pulses at the generation step. It can be easily implemented experimentally to generate attosecond pulses with strong phase variations for unique applications. ? 2020 American Physical Society.Accession Number: 20200608120239 -
Record 174 of
Title:High current density photocathode for CW terahertz photoconductive vacuum devices
Author(s):Dai, Jun(1); Ruan, Cunjun(1); Xu, Xiangyan(2); Liu, Hulin(2); Ding, Yikun(1)Source: Vacuum Volume: 180 Issue: DOI: 10.1016/j.vacuum.2020.109587 Published: October 2020Abstract:For vacuum electronics-related terahertz (THz) sources, robust, quick-response, and tunable continuous emission electron emitters are still challenging. In this paper, a continuous emission high current density Na2KSb(Cs) photocathode is developed and verified experimentally. The photocathode emission enhancement is achieved through optimization of film thickness, adjustment of the cesium activation, and dynamic optimization of the quantum efficiency during the synthesis process. The detailed evaporation procedures to perform the photocathode growth is investigated and reported. To maintain a higher current density, performances of photocathode evaporated on borosilicate glass and sapphire are tested respectively and analyzed comparatively. The results show that remarkable continuous current density can be achieved at 30 mA/cm2 on glass substrates, and 3 A/cm2 on sapphire substrates respectively. We found that the thermal conductivity of the substrates has a significant impact on high current density operations. The optimal emission current density has reached a promising value for future excitation of continuous wave (CW) THz wave radiation based on the photoconductive vacuum devices. These results also offer an opportunity to approach the generation and temporal shaping of planar array electron beams for THz vacuum tubes. ? 2020Accession Number: 20203008961591 -
Record 175 of
Title:System design of an optical interferometer based on compressive sensing: An update
Author(s):Liu, Gang(1); Liu, Gang(2); Wen, Desheng(1); Song, Zongxi(1); Jiang, Tuochi(1); Jiang, Tuochi(2)Source: Optics Express Volume: 28 Issue: 13 DOI: 10.1364/OE.394130 Published: June 22, 2020Abstract:In a recent article, the authors developed a new optical interferometric telescope architecture based on compressive sensing theory (CS-CPCIT)(Liu et al., MNRAS, 478, 2065, 2018). A new optical interferometric telescope, also known as the Segmented Planar Imaging Detector for Electro-optical Reconnaissance (SPIDER)(Duncan et al., AMOS Conf., 27, 2015), provides a significant reduction in the weight, size and power consumption compared with traditional optical interferometry. The new CS-CPCIT system has a more concise structure and a better spatial frequency sampling capability compared to those of SPIDER. In this paper, we propose an update to CS-CPCIT, which changes the relationship between the number of spatial frequencies sampled and the number of lenslets from linear to quadratic while maintaining a concise structure. Other attractive properties of the update to CS-CPCIT include a high sampling efficiency and a greatly improved maximum number of spatial frequencies that can be sampled. ? 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.Accession Number: 20202808910689 -
Record 176 of
Title:Several ways to realize multi-band common aperture optical imaging system(Invited)
Author(s):Deng, Jian(1); Qu, Rui(2); Huang, Jianbing(1)Source: Hongwai yu Jiguang Gongcheng/Infrared and Laser Engineering Volume: 49 Issue: 6 DOI: 10.3788/IRLA20201017 Published: June 25, 2020Abstract:By using differential method, the inter-band chromatic aberration and intra-band chromatic aberration conditions in optical system were introduced, and the extended complex chromatic aberration theory was established. By comparing the refractive vs chromatic coefficients of each band and the whole band, the material was matched and iteratively optimized to correct all kinds of aberrations. Several ways of realizing the multi-band common aperture (MCA) optical system were discussed, including the medium-wave (MW)/near-infrared (NIR) secondary imaging system with transmission structure, which was introduced into the respective detectors by the dichroic beam splitter in convergent optical path; the MW/long-wave (LW) infrared secondary imaging system with transmission structure, which adopted the co-focal surface design of the co-optical road; and the AN/AAQ- 33 "Sniper XR " pod 's main optical system, which adopted MW/NIR co-aperture transmission fore telescope system; the AN/ASQ-228 ATFLIR pod 's main optical system, which adopted the MCA off-axis three-mirror anastigmatic (TMA) fore telescope system; the AN/AAS-52 MTS-B pod's main optical system, which adopted the MCA coaxial bias field of view (FOV) TMA fore telescope system; the EKV's main optical system, which adopted the MCA coaxial four mirror secondary imaging system. And correspondingly, some coaxial mirror-lens fore telescope systems were introduced, and the last, some typical missile borne MCA imaging optical structures were introduced. ? 2020, Editorial Board of Journal of Infrared and Laser Engineering. All right reserved.Accession Number: 20203109004353 -
Record 177 of
Title:Spin momentum-dependent orbital motion
Author(s):Yan, Shaohui(1); Li, Manman(1); Liang, Yansheng(2); Cai, Yanan(1); Yao, Baoli(1)Source: New Journal of Physics Volume: 22 Issue: 5 DOI: 10.1088/1367-2630/ab7edd Published: May 2020Abstract:We present a theoretic analysis on (azimuthal) spin momentum-dependent orbital motion experienced by particles in a circularly-polarized annular focused field. Unlike vortex phase-relevant (azimuthal) orbital momentum flow whose direction is specified by the sign of topological charge, the direction of (azimuthal) spin momentum flow is determined by the product of the field's polarization ellipticity and radial derivative of field intensity. For an annular focused field with a definite polarization ellipticity, the intensity's radial derivative has opposite signs on two sides of the central ring (intensity maximum), causing the spin momentum flow to reverse its direction when crossing the central ring. When placed in such a spin momentum flow, a probe particle is expected to response to this flow configuration by changing the direction of orbital motion as it traversing from one side to the other. The reversal of the particle's orbital motion is a clear sign that spin momentum flow can affect particles' orbital motion alone even without orbital momentum flow. More interestingly, for dielectric particles the spin momentum-dependent orbital motion tends to be 'negative', i.e., in the opposite direction of the spin momentum flow. This arises mainly because of spin-orbit interaction during the scattering process. For the purpose of experimental observation, we suggest the introduction of an auxiliary radially-polarized illumination to adjust the particle's radial equilibrium position, for the radial gradient force of the circularly-polarized annular focused field tends to constrain the particle at the ring of intensity maximum. ? 2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.Accession Number: 20202308785912 -
Record 178 of
Title:Topology optimization design of large aperture mirror for the vt system of svom
Author(s):Lin, Feng(1,2); Wang, Wei(1); Zhang, Jian(1); Fan, Xuewu(1); Xu, Wenjing(1,2)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 11570 Issue: DOI: 10.1117/12.2580256 Published: 2020Abstract:This article, which is based on the topology optimization theory, considered the lightweight design of large aperture reflectors. Firstly, the material selection is based on the low temperature environment and the low temperature infrared optical mechanical structure design principles. Then, by using the minimum deformation of the mirror surface as the objective function, mirror volume and rigid body displacement as design restraints, and imposing manufacturing constraints, a conceptual design of the mirror back with manufacturability was accomplished. Finally, by using the finite element analysis method to compare the performance of the topologically optimized mirror and the primal mirror, it shows that the topologically optimized mirror met the design requirements in terms of lightening effect and structural rigidity, and the surface figure met the requirements under the influence of gravity, which emphasizes the feasibility and practicality of topology optimization in the large aperture mirror' design. ? 2020 SPIE. All rights reserved.Accession Number: 20204909580486 -
Record 179 of
Title:A novel approach for space debris recognition based on the full information vectors of star points
Author(s):Du, Yun(1,2,3); Wen, Desheng(1); Liu, Guizhong(2); Qiu, Shi(1); Yao, Dalei(1,2,3); Yi, Hongwei(1); Liu, Meiying(1,3)Source: Journal of Visual Communication and Image Representation Volume: 71 Issue: DOI: 10.1016/j.jvcir.2019.102716 Published: August 2020Abstract:The recognition and detection of space debris has become one of significant research fields recently. Compared with natural images, effective information are very few contained in star images. In the past years, the gray values of star points and the continuity of sequential star images are utilized by numerous algorithms to carry out the recognition and detection through fusion of consecutive star images, which have been achieved good performance. However, with the rapid increase of star image data, those algorithms seem to be inadequate in recognition ability. In this paper, we propose one novel approach based on the full information vectors of star points to recognize moving targets with the machine learning method which is never utilized in space debris recognition field. Besides gray values, we further deeply excavate the characteristics of each star point in a single frame by the equal probability density curve of Gaussian distribution. The elliptical pattern characteristic vectors of star points can be input into the machine learning method for classification of static stars and moving targets in a single frame. Finally, trajectories of moving targets can be determined within 3 frames by the full information vectors. Therefore, traditional processing methods are abandoned and the proposed brand new approach redefines the recognition technical route of space debris. The experimental results demonstrate that moving targets can be successfully recognized in a single frame and the coverage rate of moving targets can reach 100%. Compared with other traditional methods, the proposed approach has better performance and more robustness. ? 2019 Elsevier Inc.Accession Number: 20202708903349 -
Record 180 of
Title:Highly accurate 3D reconstruction based on a precise and robust binocular camera calibration method
Author(s):Hu, Guoliang(1,2); Zhou, Zuofeng(1); Cao, Jianzhong(1); Huang, Huimin(1,2)Source: IET Image Processing Volume: 14 Issue: 14 DOI: 10.1049/iet-ipr.2019.1525 Published: December 1, 2020Abstract:The precision of the camera calibration is one of the key factors that affect attitude measurement accuracy in many computer vision tasks. This study proposes a new calibration approach for binocular cameras. Firstly, based on singular value decomposition, the best transformation matrix to the essential matrix is approximated as the initial guess, which is solved in using the Frobenius norm. Secondly, the initial guess is refined through maximum likelihood estimation. A new calculating expression is derived for computing the relative position matrix of the binocular cameras. The Levenberg-Marquardt algorithm is then implemented to refine the initial guess. Large sets of synthesised and real point correspondences were tested to demonstrate the validity of the proposed method. Extensive experiments demonstrated that the proposed method outperforms the state-of-the-art methods. The error rate of the proposed method was 0.5% for the length test and about 1% for the angle test at a range of 1 m. This method can advance three-dimensional (3D) computer vision one additional step from laboratory environments to real-world use. ? The Institution of Engineering and Technology 2020.Accession Number: 20210109729241