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Distribution of carriers in gradient-doping transmission-mode GaAs photocathodes grown by molecular beam epitaxy

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Chinese Physics B 2009年第10期18卷 4541-4546页

作者：张益军常本康杨智牛军邹继军 Institute of electronic Engineering and Optoelectronic technology Nanjing University of Science and Technology

The gradient-doping structure is first applied to prepare the transmission-mode GaAs photocathode and the integral sensitivity of the sealed image tube achieves 1420μA/lm. This paper studies the inner carrier concentration distribution of the gradient-doping transmission-mode GaAs photocathode after molecular beam epitaxy （MBE） growth using the electrochemical capacitance-voltage profiling. The results show that an ideal gradient-doping structure can be obtained by using MBE growth. The total band-bending energy in the gradient-doping GaAs active-layer with doping concentration ranging from 1×10^19 cm-3 to 1×1018 cm-3 is calculated to be 46.3 meV, which helps to improve the photoexcited electrons movement toward surface for the thin epilayer. In addition,by analysis of the band offsets, it is found that the worse carrier concentration discrepancy between GaAs and GaA1As causes a lower back interface electron potential barrier which decreases the amount of high-energy photoelectrons and affects the short-wave response.

关键词： GaAs photocathode gradient doping molecular beam epitaxy carrier concentrationdistribution

High-resolution digital beamforming of UWB signals based on Carathéodory representation for delay compensation and array extrapolation

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Journal of Systems Engineering and electronics 2018年第5期29卷 918-926页

作者： DU Qiang SONG Yaoliang JI Chenhe AHMAD Zeeshan School of electronic and Optical Engineering Nanjing University of Science and TechnologyNanjing 210094China

To realize high-resolution digital beamforming(DBF)of ultra-wideband(UWB) signals, we propose a DBF method based on Carath ′eodory representation for delay compensation and array extrapolation. Delay compensation by Carath ′eodory representation could achieve high interpolation accuracy while using the single channel sampling technique. Array extrapolation by Carath ′eodory representation reformulates and extends each snapshot, consequently extends the aperture of the original uniform linear array(ULA) by several times and provides a better realtime performance than the existing aperture extrapolation utilizing vector extrapolation based on the two dimensional autoregressive(2-D AR) model. The UWB linear frequency modulated(LFM) signal is used for simulation analysis. Simulation results demonstrate that the proposed method is featured by a much higher spatial resolution than traditional DBF methods and lower sidelobes than using Lagrange fractional filters.

关键词： beamforming ultra-wideband(UWB) array extrapolation Carathéodory representation fractional delay

A collision Arbitration Protocol Based on Specific Selection Function

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Chinese Journal of electronics 2017年第4期26卷 864-870页

作者： SU Jian REN Yuqing YANG Ying HAN Yu WEN Guangjun nanjing University of Information Science and technology University of electronic Science and technology of China nanjing University of Science and technology Chengdu University of technology

Fast and effective identifications of a large number of items are required in many Radio-frequency identification(RFID) applications. Simultaneous responses from multiple tags are corrupted by collisions and thus result in low identification efficiency. To address the problem of low identification efficiency, many existing tag anticollision algorithms try to schedule the identification process to avoid collisions. A novel anti-collision scheme based on specific selection function is presented, in which tags pick a slot according to a selection function instead of being randomly assigned to slots within a frame. If collision occurs, the reader sends the custom command SETBM according to the collision information. When probed by the SETBM, the tags apply the selection function to its partial ID and send the mapped result to the reader. According to the mapped result, the reader assigns the time slot to the tags. All tags collided in the same slot will be identified by the tree traversal scheme. compared to the most of existing anti-collision algorithms, simulation results show that our proposed algorithm can achieve better performance in terms of identification efficiency, time efficiency, and energy consumption.

关键词： RFID Anti-collision Time efficiency En ergy consumption

An effective array beamforming scheme based on branch-and-bound algorithm

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Journal of Systems Engineering and electronics 2023年第6期34卷 1483-1489页

作者： YE Xiaodong LI Li WANG Hao TAO Shifei School of electronic and Optical Engineering Nanjing University of Science and TechnologyNanjing 210094China

In this paper, we propose an effective full array and sparse array adaptive beamforming scheme that can be applied for multiple desired signals based on the branch-and-bound algorithm. Adaptive beamforming for the multiple desired signals is realized by the improved Capon method. At the same time,the sidelobe constraint is added to reduce the sidelobe level. To reduce the pointing errors of multiple desired signals, the array response phase of the desired signal is firstly optimized by using auxilary variables while keeping the response amplitude unchanged. The whole design is formulated as a convex optimization problem solved by the branch-and-bound algorithm. In addition,the beamformer weight vector is penalized with the modified reweighted l_(1)-norm to achieve sparsity. Theoretical analysis and simulation results show that the proposed algorithm has lower sidelobe level, higher SINR, and less pointing error than the stateof-the-art methods in the case of a single expected signal and multiple desired signals.

关键词： multiple desired signal auxiliary variable branchand-bound algorithm reweighted-norm.

Equivalent Method of Solving Quantum Efficiency of Reflection-Mode Exponential Doping GaAs Photocathode

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Chinese Physics Letters 2009年第10期26卷 99-101页

作者：牛军杨智常本康 Institute of electronic Engineering and Optoelectronic technology Nanjing University of Science and Technology Nanjing 210094 Department of electronic and Electric Engineering Nanyang Institute of Technology Nanyang 473004

The mathematical expression of the electron diffusion and drift length LDE of exponential doping photocathode is deduced. In the quantum efficiency equation of the reflection-mode uniform doping cathode, substituting LDE for LD, the equivalent quantum efficiency equation of the reflection-mode exponential doping cathode is obtained. By using the equivalent equation, theoretical simulation and experimental analysis shows that the equivalent index formula and formula-doped cathode quantum efficiency results in line. The equivalent equation avoids complicated calculation, thereby simplifies the process of solving the quantum efficiency of exponential doping photocathode.

关键词： electronics and devices Optics quantum optics and lasers condensed matter: structural mechanical & thermal

Signal recovery method based on co-prime array

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Journal of Systems Engineering and electronics 2017年第2期28卷 224-234页

作者： Shuang Qiu Weixing Sheng Xiaofeng Ma Yubing Han Renli Zhang School of electronic and Optical Engineering Nanjing University of Science and TechnologyNanjing 210094China

A signal waveform recovery method based on the co-prime array is investigated to extract the waveform of the desired signal from spatial interferences in narrowband scenarios. The direction of arrivals (DOAs) of the desired signal and interference signals are estimated with the compressive sensing approach based on angle grids, and the signal power together with the noise power are estimated. Thereafter, a modified steepest descent (SD) method is derived to recover the waveform of the desired signal and interferences utilizing the estimated power and directions. The recovered waveform of the desired signal is the output of the proposed method. The situation in which the signals are not on the predefined angle grids is also considered. The DOAs estimated via the predefined angle grids are corrected based on the maximum likelihood (ML) angle estimation. compared to the existing beamforming methods on co-prime array, the proposed method can obtain the waveform of the desired signal. Simulation results demonstrate that the proposed method can achieve good performance in signal waveform recovery and output signal to noise ratio. © 2017 Beijing Institute of Aerospace Information.

关键词： compressed sensing Maximum likelihood Maximum likelihood estimation Recovery Signal reconstruction Signal to noise ratio

Non-coherent sequence detection scheme for satellite-based automatic identification system

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Journal of Systems Engineering and electronics 2017年第3期28卷 442-448页

作者： Haosu Zhou Jianxin Wang School of electronic and Optical Engineering Nanjing University of Science and TechnologyNanjing 210094China

The satellite-based automatic identification system (AIS) receiver has to encounter the frequency offset caused by the Doppler effect and the oscillator instability. This paper proposes a non-coherent sequence detection scheme for the satellite-based AIS signal transmitted over the white Gaussian noise channel. Based on the maximum likelihood estimation and a Viterbi decoder, the proposed scheme is capable of tolerating a frequency offset up to 5% of the symbol rate. The complexity of the proposed scheme is reduced by the state-complexity reduction, which is based on per-survivor processing. Simulation results prove that the proposed non-coherent sequence detection scheme has high robustness to frequency offset compared to the relative scheme when messages collision exists.

关键词： non-coherent sequence detection scheme satellite based automatic identification system frequency offset messages collision Viterbi decoder

Optical Pulling Force in Non-Paraxial Bessel Tractor Beam Generated with Polarization-Insensitive Metasurface

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Chinese Physics Letters 2023年第5期40卷 25-32页

作者：沈哲黄昕宇 School of electronic and Optical Engineering Nanjing University of Science and TechnologyNanjing 210094China

Tractor beams,able to produce optical pulling forces(OPFs)on particles,are attracting increasing ***,non-paraxial Bessel tractor beams are generated using polarization-insensitive *** are found to exert on dielectric particles with specific radii at the axes of the *** strengths of the OPFs depend on the radii of the particles,which provides the possibility of sorting particles with different *** the OPFs,the radius ranges of particles vary with the polarization states or topological charges of the incident *** change of polarizations can provide a switch between the pulling and pushing forces,which offers a new way to realize dynamic manipulation of *** change of topological charges leads to disjoint radii ranges for the OPFs exerting on particles,which provides the possibility of selective optical ***,we study the behaviors of particles in the tractor *** simulation results reveal that linearly or circularly polarized tractor beams can pull particles a sufficient distance towards the light source,which verifies the feasibility of separating particles.

关键词： attracting separating forces

Improved electron capture capability of field-assisted exponential-doping GaN nanowire array photocathode

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Journal of Materials Science & technology 2020年第7期42卷 54-62页

作者： Lei Liu Feifei Lu Sihao Xia Yu Diao Jian Tian Department of Optoelectronic technology School of Electronic and Optical EngineeringNanjing University of Science and TechnologyNanjing 210094China

The exponential-doping GaN nanowire arrays(GaN NWAs)photocathode has a"light-trapping effect",and the built-in electric field can promote the concentration of the photogene rated carrier center to the top surface of the ***,in the preparation ofactual NWAs photocathodes,the problem that photons emitted from the sides of the nanowires cannot be effectively collected has been *** proposed field-assisted exponential-doping GaN NWAs can bend the motion trajectory of the emitted electrons toward the collecting *** this study,the quantum efficiency(QE)and collection efficiency(CE)of the external field-assisted exponential-doping GaN NWAs photocathode are derived based on the two-dimensional carrier diffusion equation and the initial energy and angular distribution,*** a field-assisted exponential-doping GaN NWAs with a width d=200 nm and a height H=400 nm,the optimal structural parameters are obtained:the incident angleθ=50°and the nanowire spacing is L=335.6 *** this basis,the field intensity of 0.5 V/μm can maximize the CE of the *** the results show that the field-assisted approach does contribute to the collection of emitted electrons,which can provide theoretical guidance for high-performance electron sources based on exponential-doping GaN NWAs *** field-assisted exponential-doping GaN NWAs cathode is expected to be verified by the experimental results in the future.

关键词： Exponential-doping GaN nanowire array Photocathode Field-assisted Quantum efficiency Electrons collection