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- 2019
- polycrystalline ferrite-garnet
- magnetoplasmonic crystals
- magnetooptical effects
- deposition
- ion-beam methods
- sputtering
- plasmon resonance
- Physics
- Moscow Technological University
- Moscow State University
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All-fiberized top-hat beam shaper by mode content control and multimode interference suppression
摘要： A new method of all-fiberized top-hat beam shaper based on controlling mode content and suppressing multimode interference is proposed both numerically and experimentally. The sample is fabricated by fusion splicing a predetermined tapered multimode fiber to a nearly single mode fiber. A 2D simulation model to calculate the mode content weight with different taper ratio and taper shape is established, and the output intensity profile in multimode fiber is investigated. Based on the simulation results, we fabricated an all-fiberized beam shaper, achieving a top-hat beam at a taper ratio of 0.51 with parabolic taper shape. The flatness factor of the top-hat beam is measured to be about 0.6. Theoretical results show a good agreement with the experiment results.
关键词： optical fiber devices,beam shaper,Fiber optics,laser beams
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE 10th Sensor Array and Multichannel Signal Processing Workshop (SAM) - Sheffield (2018.7.8-2018.7.11)] 2018 IEEE 10th Sensor Array and Multichannel Signal Processing Workshop (SAM) - An Adaptive Sequential Competition Test for Beam Selection in Massive MIMO Systems
摘要： To solve the problem of beam selection or capturing the highest possible signal power, we propose a sequential test that can adapt to the SNR operating point and speed up the selection procedure in terms of the number of required observations in comparison to a perfectly tuned fixed length test assuming genie knowledge. The speed up gets higher for lower SNR and becomes of particular interest in massive Multiple Input Multiple Output (MIMO) systems using beamforming, where the number of candidate beams is large and exhaustive search can cause intolerable delay due to limited channel coherence time.
关键词： Generalized Likelihood Ratio Test,Millimeter wave,Sequential Test,Beam Selection,Massive MIMO
更新于2025-09-23 15:22:29
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60-GHz 2-D Scanning Multibeam Cavity Backed Patch Array fed by Compact SIW Beam-Forming Network for 5G Applications
摘要： This paper presents a 2x2 multibeam array employing a novel wideband linearly polarized cavity-backed patch antenna for fifth generation (5G) wireless communication technology. The antenna array comprises four layers stacked on top of one another. The proposed antenna element is composed of three substrate layers and excited using a substrate integrated waveguide (SIW) aperture-coupled feed. The antenna element exhibits -10-dB impedance bandwidth of 36.2% from 53 to 76.4 GHz with very flat gain and excellent radiation characteristics. A prototype is fabricated and tested. The compact 2-D scanning multibeam 2x2 antenna array is demonstrated at 60-GHz, where the proposed antenna element is utilized as a radiating element. By employing a novel compact beam forming network (BFN) in the design, the proposed array achieves a size reduction of better than 28% compared to an array fed with conventional BFN, without degradation in the array performance. A wide bandwidth larger than 27 % for |S11|<-10 dB and a peak gain of 12.4 dBi is achieved. The array shows a good symmetrical radiation pattern in the two perpendicular planes. Verified by prototype measurements, the proposed antenna element and multibeam array with features of a compact structure, low cost, wide bandwidth and superior radiation performance, would be practically attractive for 5G applications.
关键词： fifth generation (5G),linear polarization,60 GHz,SIW,beam-forming network,multibeam antenna
更新于2025-09-23 15:22:29
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Effect of short-circuit stress on the degradation of the SiO2 dielectric in SiC power MOSFETs
摘要： This paper presents the impact of a short-circuit event on the gate reliability in planar SiC MOSFETs, which becomes more critical with increased junction temperature and higher bias voltages. The electrical waveforms indicate that a gate degradation mechanism takes place, showing a large gate leakage current that increases as the gate degrades more and more. A failure analysis has been performed on the degraded SiC MOSFET and then compared to the structure of a new device to identify possible defects/abnormalities. A Focused-Ion Beam cut is performed showing a number of differences in comparison to the new device: (i) cracks between the poly-silicon gate and aluminium source, (ii) metal particles near the source contact, and (iii) alterations in the top surface of the aluminium source. The defects have been correlated with the increase in gate-leakage current and drain-leakage current.
关键词： Focused-Ion Beam,Short circuit,Gate-oxide breakdown,Gate oxide,Degradation,Defects,Reliability,SiC MOSFET,Failure analysis,SEM
更新于2025-09-23 15:22:29
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Directionality properties of the nGEM detector of the CNESM diagnostic system for SPIDER
摘要： The ITER project requires additional heating by two neutral beam injectors, each accelerating up to 1 MV a 40 A beam of negative deuterium ions for one hour. Such requirements have never been reached, so it was decided to build in Padova a facility (PRIMA) that hosts two experimental devices: SPIDER, a 100 kV negative H/D RF beam source, and MITICA, a full-scale injector for the ITER NBI. SPIDER has begun operation in 2018, while MITICA is expected to start after 2020. In both devices the accelerated deuterium beam impinges on an actively cooled beam dump used to stop the deuterons. Detection of fusion neutrons produced between beam–deuterons and dump-embedded deuterons will be used as a means to resolve the horizontal beam intensity profile. A neutron detection system called Close-contact Neutron Emission Surface Mapping (CNESM) is installed right behind the SPIDER beam dump, with the aim to provide the neutron emission map of the beam dump surface. The core of this diagnostic system is an nGEM (neutron-Gas Electron Multiplier) detector which will be able to reconstruct the fast neutron beam profile with an efficiency of about 10?4. A crucial point in order to correctly reconstruct the profile of the deposited D? power is the directionality discrimination capability of the detector. This paper reports on the results of the characterization of the nGEM directionality capabilities, performed at the Frascati Neutron Generator (FNG) using 2.5 MeV neutrons, before installation of the detector inside the SPIDER vacuum vessel.
关键词： Neutral beam injector,Directionality,Neutron imaging,GEM detectors,Deuterium map
更新于2025-09-23 15:22:29
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[IEEE 2017 IEEE Workshop on Recent Advances in Photonics (WRAP) - Hyderabad (2017.12.18-2017.12.19)] 2017 IEEE Workshop on Recent Advances in Photonics (WRAP) - Differential Pressure Sensor Using Integrated Optical MEMS and Double Ring Resonator
摘要： In this work, we designed and simulated a differential pressure sensor using a double ring resonator with radius 5μm and 4μm placed on the fixed of a cantilever beam with dimensions 100μm x 30μm x 5μm. The stress induced on the cantilever changes the refractive index in the waveguide which results in the shift of the resonant wavelength. A sensitivity of 15.544pm/kPa is achieved. The sensor is operated at wavelength equal to 1.55μm and can be used for aircraft, medicine and automobile.
关键词： Cantilever beam,Opto-mechanical effect,Differential pressure sensor,Double ring resonator
更新于2025-09-23 15:22:29
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Bias Impact Analysis and Calibration of Uav-Based Mobile Lidar System
摘要： Over the past few years, developments in mobile mapping technology, specifically Unmanned Aerial Vehicles (UAVs), have made accurate 3D mapping more feasible, thus emerging as an economical and practical mobile mapping platform. LiDAR-based UAV mapping systems are gaining widespread recognition as an efficient and cost-effective technique for rapid collection of 3D geospatial data. To derive point clouds with high positional accuracy, estimation of mounting parameters relating the laser scanners to the onboard GNSS/INS unit is the foremost and necessary step. In this paper, we first devise an optimal flight and target configuration by conducting a rigorous theoretical analysis of the potential impact of bias in mounting parameters of a LiDAR unit on the resultant point cloud. Then, we propose a LiDAR system calibration strategy that can directly estimate the mounting parameters for spinning multi-beam laser scanners onboard a UAV through an outdoor calibration procedure.
关键词： multi-beam laser scanners,UAV,GNSS/INS,mounting parameters,LiDAR
更新于2025-09-23 15:22:29
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A Slow-Wave Structure Optimization with Variable Helix Section Length in STWT Based on CI-NMCSO Algorithm
摘要： A novel slow-wave structure optimization method on Chaos-improved Normal mutation cat swarm optimization (CI-NMCSO) algorithm is proposed. Under the variable helix section length in STWT, the CI-NMCSO combined with 1D CHRISTINE code is used to calculate the best set of pitch distribution and section length with the objective function of electron beam efficiency improvement. Quantum particle swarm optimization (QPSO) and Cauchy mutated cat swarm optimization (CMCSO) algorithms are applied to make performance comparison. Experimental results show that the beam efficiency has been increased by CI-NMCSO from rated value 30% to 45.3%, and the values using CMCSO and QPSO are 41.8% and 36.5%, respectively, the convergence speed of CI-NMCSO is the fastest, only 16 iterations, while CMCSO and QPSO take 19 and 23 iterations, so the performance of CI-NMCSO is better than CMCSO and QPSO on both optimization precision and calculation speed in terms of slow-wave structure optimization, and is also superior to that with equal section length when the helix section length is variable.
关键词： space traveling-wave tube,electron beam efficiency,chaotic transformation,Slow-wave structure,normal mutation cat swarm optimization
更新于2025-09-23 15:22:29
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Beam-Doppler Unitary ESPRIT for Multitarget DOA Estimation
摘要： High-resolution direction of arrival (DOA) estimation is a critical issue for mainbeam multitarget tracking in ground-based or airborne early warning radar system. A beam-Doppler unitary ESPRIT (BD-UESPRIT) algorithm is proposed to deal with this problem. Firstly, multiple snapshots without spatial aperture loss are obtained by using the technique of time-smoothing. Then the conjugate centrosymmetric discrete Fourier transform (DFT) matrix is used to transform the extracted data into beam-Doppler domain. Finally, the rotational invariance property of the space-time beam is exploited to estimate DOA of the target. The DOA estimation accuracy is improved greatly because the proposed algorithm takes full advantage of temporal information of the signal. Furthermore, the computational complexity of the presented algorithm is reduced dramatically, because the degree of freedom after beam transformation is very small and most of the operations are implemented in real-number domain. Numerical examples are given to verify the effectiveness of the proposed algorithm.
关键词： computational complexity,DOA estimation,time-smoothing,ESPRIT,beam-Doppler domain
更新于2025-09-23 15:22:29
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Self Optimization Beam-Forming Null Control Based SINR Improvement
摘要： In this paper, a self optimization beamforming null control (SOBNC) scheme is proposed. There is a need of maintaining signal to interference plus noise ratio (SINR) threshold to control modulation and coding schemes (MCS) in recent technologies like Wi-Fi, Long Term Evolution (LTE) and Long Term Evolution Advanced (LTE-A). Selection of MCS depends on the SINR threshold that allows maintaining key performance index (KPI) like block error rate (BLER), bit error rate (BER) and throughput at certain level. The SOBNC is used to control the antenna pattern for SINR estimation and improve the SINR performance of the wireless communication systems. The nulling comes with a price; if wider nulls are introduced, i.e. more number of nulls are used, the 3 dB beam-width and peak side lobe level (SLL) in antenna pattern changes critically. This paper proposes a method which automatically controls the number of nulls in the antenna pattern as per the changing environment based on adaptive-network based fuzzy interference system (ANFIS) to maintain output SINR level higher or equal to the required threshold. Finally, simulation results show a performance superiority of the proposed SOBNC compared with minimum mean square error (MMSE) based adaptive nulling control algorithm and conventional fixed null scheme.
关键词： self optimization beamforming null control,adaptive neural fuzzy inference system (ANFIS),SINR improvement,digital beam-forming (DBF)
更新于2025-09-23 15:22:29