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In-situ Measurements and Thermo-mechanical Simulation of Ti-6Al-4V Laser Solid Forming Processes
摘要： Residual stresses and distortions are two technical obstacles for popularizing the Additive Manufacturing (AM) technology. The evolution of the stresses in AM components during the thermal cycles of the metal depositing process is not yet clear, and more accurate in-situ measurements are necessary to calibrate and validate the numerical tools developed for its simulation. In this work a fully coupled thermo-mechanical analysis to simulate the Laser Solid Forming (LSF) process is carried out. At the same time, an exhaustive experimental campaign is launched to measure the temperature evolution at different locations, as well as the distortions and both the stress and strain fields. The thermal and mechanical responses of single-wall coupons under different process parameters are recorded and compared with the numerical models. Good agreement between the numerical results and the experimental measurements is obtained. Sensitivity analysis demonstrates that the AM process is significantly affected by the laser power and the feeding rate, while poorly influenced by the scanning speed.
关键词： Numerical simulation,Laser Solid Forming (LSF),Thermo-mechanical analysis,Additive manufacturing (AM),In-situ measurements of residual stresses
更新于2025-11-28 14:24:20
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Cu nanoclusters in ion exchanged soda-lime glass: Study of SPR and nonlinear optical behavior for photonics
摘要： Nanomaterials with large optical nonlinearities have received considerable attention in the field of modern science and nanotechnology. In this paper, we have studied nonlinear optical and surface plasmon resonance properties and behavior of Cu nanoclusters formed in ion exchanged soda-lime glass. The soda-lime glasses were successfully doped with Cu nanoclusters in the ion-exchange process. The size of the clusters estimated from the optical absorption spectroscopy results closely matched with those obtained from the transmission electron microscopy data. The results revealed that spherical shaped Cu nanoclusters were homogeneously distributed in the glass matrix and the size of the Cu nanoclusters varied from 4 to 10 nm. The structure and chemical state were further analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. The nonlinear optical behavior of the materials was analyzed using femtosecond Z-scan technique. The nonlinear refraction index (n2), nonlinear absorption coefficient (β) and the third-order nonlinear optical susceptibility (χ(3)) were estimated to be -1.72 × 10?17 m2/W, 9.96 × 10?11 m/W, and 0.56 × 10?11 esu, respectively, which shows possible application in the field of photonics.
关键词： Surface plasmon resonance,Z-scan technique,Metal forming and shaping,Structural,Nanoparticles
更新于2025-11-20 15:33:11
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Effect of laser forming on mechanical properties of multiple-phase steels by using a thermal–microstructure–mechanical model
摘要： Based on a forming temperature-controlled mixed strain-hardening law, a temperature-controlled thermal–microstructure–mechanical model was developed to predict the deformation in ferrite–martensite dual-phase steel before and after complex laser forming. Phase transformation in dual phase steel was predicted by coupling a kinetic transformation model with the developed model during laser forming. The corresponding algorithm of the constitutive model was used in three-dimensional finite element method to simulate the material deformation and mechanical properties during the laser forming. The simulated results agree well with the experimental results. Laser forming influences the mechanical properties of the material significantly, leads to bending deformation of the scanned sample and induces a ferrite-to-martensite transformation. The influence of scanning line number on the tensile strength and bending deformation of the scanned specimen was investigated. The tensile strength and bending angle are related positively to the number of scanning lines on the sample.
关键词： Stress-strain curve,Phase transformation,Thermal–microstructure–mechanical model,Sheet metal,Laser forming
更新于2025-09-23 15:23:52
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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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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
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mmWave CMOS Power Amplifiers for 5G Cellular Communication
摘要： This article covers the basics of millimeter-wave PA design in CMOS technology for integrated phased arrays, targeting the upcoming 5G new radio (NR) cellular communication standard. Key PA figures of merit, as well as application of beam-forming phased arrays to combine power over-the-air, are briefly reviewed. Then, starting from practical handset form factor constraints and system-level drivers, CMOS-specific technological and design-related challenges are conceptually illustrated using a simple single-transistor PA. A survey of the state-of-the-art is presented to give examples of the challenges and illustrate the PA techniques used to tackle them in linear 28-GHz CMOS PAs for 5G NR.
关键词： beam-forming,efficiency,linearity,millimeter-wave,power amplifier,phased array,CMOS,5G
更新于2025-09-23 15:22:29
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[IEEE 2018 China International SAR Symposium (CISS) - Shanghai (2018.10.10-2018.10.12)] 2018 China International SAR Symposium (CISS) - An Automatically Steering Optical Beam-Forming Network for Phased Array Antenna Based on Dense Wavelength Division Multiplexing
摘要： It is proposed an automatically steering optical beam-forming network (OBFN), which is consisted of an optical fiber loop structure. The loop structure is composed by an optical switch, an optical fiber splitter, and an optical true time delay lines based on dense wavelength division multiplexing (DWDM). The channel number of the DWDM is matched with the number of the phased array antennas (PAA). The true time delay difference between two adjacent channels is set as a basic step. And the optical wave modulated by radio frequency (RF) signal can run into the loop and suffer increased delay with increased circles. Thus the PAA is steered automatically without additional controlling and programming. The performance of this design is analyzed with its maximal circle numbers and the splitting ratio of the optical splitter in theory. The concept-proof experiments with 8 optical channels for DWDM are carried out and the simulation of the PAA radiation pattern is given.
关键词： optical switch,optical beam-forming network,optical fiber loop,optical controlled phased array radar,wavelength division multiplexing
更新于2025-09-23 15:22:29
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COMPACT ROTMAN LENS STRUCTURE CONFIGURATIONS TO SUPPORT MILLIMETER WAVE DEVICES
摘要： The development of modern communication devices for the latest technologies such as 5G has brought the millimeter wave technology into the spotlight because it offers higher data rates and bandwidth. Since highly directional transmissions are necessary for communication in these frequencies due to high path loss and atmospheric absorption, the use of adaptive antennas is inevitable. Rotman lenses have long been used as analog beam forming networks to support linear array antennas for electronic scanning. Their broad bandwidth and planar structure make them ideal for a variety of applications. However, their overall dimensions can be prohibitive especially for large scan angles. In this paper, we propose a few compact configurations that reduce the overall dimensions of Rotman lens as much as 50% without degrading its performance.
关键词： compact configurations,Rotman lens,millimeter wave,beam forming networks,electronic scanning
更新于2025-09-23 15:21:21
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Effect of High Temperature Forming Gas Annealing on Electrical Properties of 4H-SiC Lateral MOSFETs with Lanthanum Silicate and ALD SiO<sub>2</sub> Gate Dielectric
摘要： We investigated the impact of an initial lanthanum oxide (La2O3) thickness and forming gas annealing (FGA) conditions on the MOSFET performance. The FGA has been shown to dramatically improve the threshold voltage (VT) stability of 4H-SiC MOSFETs. The FGA process leads to improve VT instability and high field effect mobility due to reduction of the interface states density as well as traps by passivating the dangling bonds and active traps in the Lanthanum Silicate dielectrics. By optimizing the La2O3 interfacial layer thickness and FGA condition, SiC MOSFETs with high threshold voltage and high mobility while maintaining minimal VT shift are realized.
关键词： Silicon carbide,Lanthanum Silicate,Atomic layer deposition,Forming Gas Annealing
更新于2025-09-23 15:21:21
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Effect of Post Oxide Annealing on the Electrical and Interface 4H-SiC/Al<sub>2</sub>O<sub>3</sub> MOS Capacitors
摘要： This paper reports on the effect of forming gas annealing on the C-V characteristics and stability of Al2O3/SiC MOS capacitors deposited by atomic layer deposition, (ALD). C-V and I-V measurements were performed to assess the quality of the Al2O3 layer and the Al2O3/SiC interface. In comparison to as-deposited sample, the post oxide annealing (POA) in forming gas at high temperatures has improved the stability of C-V characteristic and the properties at the interface of Al2O3/SiC capacitors. However, the oxide capacitance and oxide breakdown electric field degrade with increased annealing temperature. The results provide indications to improve the performance of Al2O3/SiC capacitors 4H-SiC devices by optimizing the annealing temperature.
关键词： forming gas,Al2O3,atomic layer deposition,interface state density,4H-SiC
更新于2025-09-23 15:21:21