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arXiv 2017年

作者： Miller, Kevin J. Hallman, Kent A. Haglund, Richard F. Weiss, Sharon M. Interdisciplinary Graduate Program in Materials Science Vanderbilt University NashvilleTN37235 United States Department of Physics and Astronomy Vanderbilt University NashvilleTN37235 United States Department of Electrical Engineering and Computer Science Vanderbilt University NashvilleTN37235 United States

Phase-change materials (PCMs) have emerged as promising active elements in silicon (Si) photonic systems. In this work, we design, fabricate, and characterize a hybrid Si-PCM optical modulator. By integrating vanadium dioxide (a PCM) within a Si photonic waveguide, in a non-resonant geometry, we demonstrate ~ 10 dB broadband modulation with a PCM length of 500 nm. Copyright © 2017, The Authors. All rights reserved.

关键词： Phase change materials

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Synthesis and Structural Characterizations of Cu_2ZnSnS_4 Thin Films

Synthesis and Structural Characterizations of Cu_2ZnSnS_4 Th...

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IEEE Photovoltaic Specialists Conference

作者： Liyuan Zhang Xin Zhang Sreejith Karthikeyan Stephen A. Campbell Department of Electrical and Computer Engineering University of Minnesota 200 Union Street SE Minneapolis MN 55455 USA Department of Chemical Engineering and Materials Science University of Minnesota 421 Washington Avenue SE Minneapolis MN 55455 USA

ISBN: (纸本)9781479933006

We investigate the synthesis of kesterite Cu_2ZnSnS_4 (CZTS) thin films using thermal evaporation from copper, zinc and tin pellets and post-annealing in sulfur atmosphere at 600 ℃. X-ray diffraction and Raman scattering results show that the films produced from a Cu/Sn/Cu/Zn precursor at 600℃ for 4 hours are kesterite phase CZTS with traces of ZnS. Grain sizes of 1 um or above are obtained from SEM images. We explored the effect of the sulfurization temperature, sulfurization time and metal precursor evaporation sequence on the CZTS structure and film morphology. The beneficial effect of impurity diffusion in grain growth has also been observed in this work.

关键词： absorbing materials CZTS film morphology sulfurization

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Asymmetric Metal-Dielectric Metacylinders and Their Potential Applications From engineering Scattering Patterns to Spatial Optical Signal Processing

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Physical Review Applied 2021年第3期15卷 034010-034010页

作者： Ali Momeni Mahdi Safari Ali Abdolali Nazir P. Kherani Romain Fleury Laboratory of Wave Engineering Swiss Federal Institute of Technology in Lausanne (EPFL) Lausanne CH-1015 Switzerland Department of Electrical and Computer Engineering University of Toronto 10 King’s College Road Toronto M5S 3G4 Canada Applied Electromagnetic Laboratory School of Electrical Engineering Iran University of Science and Technology Narmak Tehran Iran Department of Materials Science and Engineering University of Toronto 140 College Street Toronto Ontario M5S 3E4 Canada

We propose a bianisotropic hybrid metal-dielectric structure comprising dielectric and metallic cylindrical wedges wherein the composite metacylinder enables advanced control of electric, magnetic, and magnetoelectric resonances. We establish a theoretical framework in which the electromagnetic response of this meta-atom is described through the electric and magnetic multipole moments. The complete dynamic polarizability tensor, expressed in a compact form, is derived as a function of the Mie-scattering coefficients. Further, the constitutive parameters—determined analytically—illustrate the tunability of the structure’s frequency and strength of resonances in light of its high degree of geometric freedom. Flexibility in the design makes the proposed metacylinder a viable candidate for various applications in the microscopic (single meta-atom) and macroscopic (metasurface) levels. We show that the highly versatile bianisotropic meta-atom is amenable to being designed for the desired electromagnetic response, such as electric dipole-free and zero or near-zero (backward and forward) scattering at the microscopic level. In addition, we show that the azimuthal asymmetry gives rise to normal polarizability components, which are vital elements in synthesizing asymmetric optical transfer function at the macroscopic level. We conduct a precise inspection, from the microscopic to the macroscopic level, of the metasurface synthesis for emphasizing on the role of normal polarizability components for spatial optical signal processing. It is shown that this simple two-dimensional asymmetric meta-atom can perform first-order differentiation and edge detection at normal illumination. The results reported herein contribute toward improving the physical understanding of wave interaction with artificial materials composed of asymmetric elongated metal-dielectric inclusions and open the potential of its application in spatial signal and image processing.

关键词： Electric polarization Imaging & optical processing Metamaterials Mie scattering Polarization of light Dielectrics Metals Light scattering

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Performance Analysis and Optimization for Jammer-Aided Multi-Antenna UAV Covert Communication

arXiv

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arXiv 2022年

作者： Du, Hongyang Niyato, Dusit Xie, Yuan-Ai Cheng, Yanyu Kang, Jiawen Kim, Dong In The School of Computer Science and Engineering Energy Research Institute @ NTU Interdisciplinary Graduate Program Nanyang Technological University Singapore The School of Computer Science and Engineering Nanyang Technological University Singapore The Institute of Electrical Engineering Yanshan University Qinhuangdao066004 China Alibaba-NTU Singapore Joint Research Institute Nanyang Technological University Singapore639798 Singapore The Department of Electrical and Computer Engineering Sungkyunkwan University Suwon16419 Korea Republic of

Unmanned aerial vehicles (UAVs) have attracted a lot of research attention because of their high mobility and low cost in serving as temporary aerial base stations (BSs) and providing high data rates for next-generation communication networks. To protect user privacy while avoiding detection by a warden, we investigate a jammer-aided UAV covert communication system, which aims to maximize the user's covert rate with optimized transmit and jamming power. The UAV is equipped with multi-antennas to serve multi-users simultaneously and enhance the Quality of Service. By considering the general composite fading and shadowing channel models, we derive the exact probability density (PDF) and cumulative distribution functions (CDF) of the signal-to-interference-plus-noise ratio (SINR). The obtained PDF and CDF are used to derive the closed-form expressions for detection error probability and covert rate. Furthermore, the covert rate maximization problem is formulated as a Nash bargaining game, and the Nash bargaining solution (NBS) is introduced to investigate the negotiation among users. To solve the NBS, we propose two algorithms, i.e., particle swarm optimization-based and joint two-stage power allocation algorithms, to achieve covertness and high data rates under the warden's optimal detection threshold. All formulated problems are proven to be convex, and the complexity is analyzed. The numerical results are presented to verify the theoretical performance analysis and show the effectiveness and success of achieving the covert communication of our algorithms. © 2022, CC BY.

关键词： Unmanned aerial vehicles (UAV)

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Accelerating Wireless Federated Learning via Nesterov's Momentum and Distributed Principle Component Analysis

arXiv

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arXiv 2023年

作者： Dong, Yanjie Wang, Luya Chi, Yuanfang Wang, Jia Zhang, Haijun Yu, Fei Richard Leung, Victor C.M. Hu, Xiping The Faculty of Engineering Shenzhen MSU-BIT University Shenzhen China The College of Computer Science and Software Engineering Shenzhen University Shenzhen China Beijing Advanced Innovation Center for Materials Genome Engineering Beijing Engineering and Technology Research Center for Convergence Networks and Ubiquitous Services Institute of Artificial Intelligence University of Science and Technology Beijing Beijing China The Department of Systems and Computer Engineering Carleton University Ottawa Canada The Department of Electrical and Computer Engineering The University of British Columbia Vancouver Canada

A wireless federated learning system is investigated by allowing a server and workers to exchange uncoded information via orthogonal wireless channels. Since the workers frequently upload local gradients to the server via bandwidth-limited channels, the uplink transmission from the workers to the server becomes a communication bottleneck. Therefore, a one-shot distributed principle component analysis (PCA) is leveraged to reduce the dimension of uploaded gradients such that the communication bottleneck is relieved. A PCA-based wireless federated learning (PCA-WFL) algorithm and its accelerated version (i.e., PCA-AWFL) are proposed based on the low-dimensional gradients and the Nesterov's momentum. For the non-convex loss functions, a finite-time analysis is performed to quantify the impacts of system hyper-parameters on the convergence of the PCA-WFL and PCA-AWFL algorithms. The PCA-AWFL algorithm is theoretically certified to converge faster than the PCA-WFL algorithm. Besides, the convergence rates of PCA-WFL and PCA-AWFL algorithms quantitatively reveal the linear speedup with respect to the number of workers over the vanilla gradient descent algorithm. Numerical results are used to demonstrate the improved convergence rates of the proposed PCA-WFL and PCA-AWFL algorithms over the benchmarks. © 2023, CC BY.

关键词： Momentum

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Broadband angular momentum cascade via a multifocal graphene vortex generator

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Chinese Optics Letters 2022年第10期20卷 91-95页

作者： Zhongwei Jin Guiyuan Cao Hongtao Wang Han Lin Baohua Jia Cheng-Wei Qiu College of Optical and Electronic Technology China Jiliang UniversityHangzhou 310018China Department of Electrical and Computer Engineering National University of SingaporeSingapore 117583Singapore Centre of Translational Atomaterials(CTAM) Faculty of ScienceEngineering and TechnologySwinburne University of TechnologyHawthornVIC 3122Australia School of Science RMIT UniversityMelbourneVIC 3000Australia The Australian Research Council(ARC)Industrial Transformation Training Centre in Surface Engineering for Advanced Materials(SEAM) Swinburne University of TechnologyHawthornVIC 3122Australia

Light beams carrying orbital angular momentum(OAM)have inspired various advanced applications,and such abundant practical applications in turn demand complex generation and manipulation of optical ***,we propose a multifocal graphene vortex generator,which can produce broadband angular momentum cascade containing continuous integer non-diffracting vortex *** device naturally embodies a continuous spiral slit vortex generator and a zone plate,which enables the generation of high-quality continuous vortex modes with deep depths of ***,the generated vortex modes can be simultaneously tuned through incident wavelength and position of the focal *** elegant structure of the device largely improves the design efficiency and can be fabricated by laser nanofabrication in a single ***,the outstanding property of graphene may enable new possibilities in enormous practical applications,even in some harsh environments,such as aerospace.

关键词： optical vortex multifocus broadband wavelength tunability graphene

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3×2 integrated microphotonic switches

3×2 integrated microphotonic switches

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Asia-pacific Optical Communications 2004

作者： Soo Jin Chua Eugene A. Fitzgerald Bharat Chaudhari Center for Optoelectronics Department of Electrical and Computer Engineering National University of Singapore Singapore 119260 Singapore Department of Materials Science and Engineering Massachusetts Institute of Technology Massachusetts 02139 USA International Institute of Information Technology Pune 411027 India

A microphotonic switch with three input waveguides and two output waveguides and integrated with an optical power splitter has been proposed. It is fabricated on the multimode interference principle i

关键词： Microphotonic switch,optoelectronic device,optical waveguide,integrated optics,optical power splitter,multimode interference,silicon-germanium,semiconductor materials.

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Design and Realization of Low Cost Discrete PSD Controller for Power Electronics Applications

Design and Realization of Low Cost Discrete PSD Controller f...

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International Conference on computer engineering and Applications (ICCEA)

作者： Ondrej Krejcar Michal Tutsch Robert Frischer Ivo Spicka Department of Measurement and Control Faculty of Electrical Engineering and Computer Science VSB-Technical University of Ostrava Ostrava Czech Republic Department of Automation and Computing in Metallurgy Faculty of Metallurgy and Materials Engineering Technical University of Ostrava Ostrava Czech Republic

ISBN: (纸本)9781424460793;9780769539829

Most systems are controlling by common PID controllers. These PID controllers are available in variety possibilities. They are divided by types of controlling systems, by speed of action interference, by complexity, by robustness etc. Most of industrial controllers are very expensive and except of some basic setting they are not offering any other way, how to involve into controlling process. On the other side, developing new analog controller to control simple systems is not reasonable in financial or time issue. That's why we decided to build simple, discrete controller and implement its algorithm into single chip eight bit microcontroller (MCU). This discrete controller - PSD - is characteristic its simplicity and variability. It can control plenty of less complicated systems by a mere change of its characteristic parameters. Thanks to modern approach is possible to create a full-featured controller including power action element on an area equal to 7cm 2 .

关键词： Costs Power electronics Control systems Three-term control Interference Robust control electrical equipment industry Industrial control Process control Microcontrollers

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High efficiency deep-UV emission at 219 nm from ultrathin MBE GaN/AlN quantum heterostructures

arXiv

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arXiv 2017年

作者： Islam, S.M. Protasenko, Vladimir Lee, Kevin Rouvimov, Sergei Verma, Jai Xing, Huili Jena, Debdeep Department of Electrical & Computer Engineering Cornell University NY14853 United States Notre Dame Integrated Imaging Facility University of Notre Dame IN46556 United States Department of Electrical Engineering University of Notre Dame IN46556 United States Department of Materials Science and Engineering Cornell University NY14853 United States

Deep ultraviolet (UV) optical emission below 250 nm (~5 eV) in semiconductors is traditionally obtained from high aluminum containing AlGaN alloy quantum wells. It is shown here that high-quality epitaxial ultrathin binary GaN quantum disks embedded in an AlN matrix can produce efficient optical emission in the 219-235 nm (~5.7 to 5.3 eV) spectral range, far above the bulk bandgap (3.4 eV) of GaN. The quantum confinement energy in these heterostructures is larger than the bandgaps of traditional semiconductors, made possible by the large band offsets. These MBE-grown extreme quantum-confinement GaN/AlN heterostructures exhibit internal quantum efficiency as high as 40% at wavelengths as short as 219 nm. These observations, together with the ability to engineer the interband optical matrix elements to control the direction of photon emission in such new binary quantum disk active regions offers unique advantages over alloy AlGaN quantum well counterparts for the realization of deep-UV light-emitting diodes and lasers. Copyright © 2017, The Authors. All rights reserved.

关键词： III-V semiconductors

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Purcell-enhanced X-ray Imaging in Ultra-thin Scintillators

Purcell-enhanced X-ray Imaging in Ultra-thin Scintillators

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Conference on Lasers and Electro-Optics (CLEO)

作者： Roman Schuetz Yaniv Kurman Neta Lahav Avner Shultzman Charles Roques-Carmes Alon Lifshits Segev Zaken Rotem Strassberg Orr Be’Er Yehonadav Bekenstein Ido Kaminer Department of Electrical and Computer Engineering Technion - Israel Institute of Technology Haifa Israel Department of Materials Science and Engineering Technion - Israel Institute of Technology Haifa Israel Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge MA USA

We demonstrate improved X-ray imaging using nanophotonic scintillators. Our scintillators rely on Purcell enhancement for brighter and faster emission. Applying this concept in radiology and nuclear medicine could ena... 详细信息

ISBN: (纸本)9781957171258

关键词： Positron emission tomography Purcell effect Spatial frequency Spontaneous emission X ray imaging X rays

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