Optical design of a Butterfly lens for a street light based on a double-cluster LED

We construct a precise optical model of the cluster LED and propose a design of a peanut form lens to achieve an optical utilization factor of 45% and uniformity of 1/2.7. Then we propose a new design of so-called Butterfly lens with unequal tilt design aimed to serve a double-cluster LED but with a tightened size. The optical utilization factor of the Butterfly lens is about 43.8%, the uniformity is around 1/2.7, and an averaged illuminance of 14 lx, which could meet almost all types requested by IESNA. The design of the Butterfly lens is proven workable for a double-cluster LED.     

Correlation of scanning thermal microscopy and near-field cathodoluminescence analyses on a blue GaN light emitting device

A scanning near-field thermal microscope and a scanning electron microscope/scanning near-field optical microscope hybrid system for near-field cathodoluminescence investigations were used to characterize blue GaN LEDs. Optoelectronic, electronic and thermal device properties are determinable with highest resolution. These results provide an interesting perspective with respect to failure analyses and reliability of the devices.     

Numerical simulation of the properties of solar cells based on GaPNAs/Si heterostructures and GaN nanowires

Using methods of numerical simulation, the modes of operation are considered and structures are determined for solar cells of combined dimension based on a planar GaPNAs/Si heterostructure and an array of GaN nanowires. It is shown that the array of GaN nanowires features antireflective properties at a level no lower than 2.5% under illumination with the AM1.5D solar spectrum. The efficiency of solar cells is affected to the greatest extent by the lifetimes of minority charge carriers and the thickness of photoactive layers. It is demonstrated that the efficiency of two-junction solar cells composed of GaPNAs alloy layers and an array of GaN nanowires on a Si substrate can be as high as 32% for AM1.5D.     

背照式AIGaN/GaN基光电探测器的结构设计及性能模拟

基于扩散漂移方程,对背照式日盲紫外AlxGa1-xN异质结p-i-n光电二极管和可见盲GaN同质结吸收区和倍增区分离的雪崩光电二极管(SAM-APD)进行了建模,模拟分析了这两种探测器的光电响应特性和电学参数,结果与实测数据和文献报道数据一致性较好.计算时还考虑了材料制备和器件工艺的实际情况,分析了有关参数对器件性能的...     

Comparison of a simulation and an exact method for reliability evaluation of large networks using a personal computer

An analysis of the relative merits and demerits of a simulation and an exact method for system reliability evaluation is presented. The comparison is performed using computer programs developed on a personal computer. The networks used in the analysis are randomly generated. Although computer implementations of some system reliability evaluation methods are available in the reliability literature, the programs are not portable. Most of the programs were developed either on a mainframe or a mini computer in different software environments. Due to the recent developments in computer technology, extremely fast personal computers are available. The emphasis of this paper is on the use of a standard personal computer, such as the IBM-PC or a compatible, in order to develop and compare computerized algorithms.     

Optical properties of blue light-emitting diodes in the InGaN/GaN system at high current densities

The current-voltage and brightness-voltage characteristics and the electroluminescence spectra of blue InGaN/GaN-based light-emitting diodes are studied to clarify the cause of the decrease in the emission efficiency at high current densities and high temperatures. It is found that the linear increase in the emission intensity with increasing injection current changes into a sublinear increase, resulting in a decrease in efficiency as the observed photon energy shifts from the mobility edge. The emission intensity decreases with increasing temperature when the photon energy approaches the mobility edge; this results in the reduction in efficiency on overheating. With increasing temperature, the peak of the electroluminescence spectrum shifts to lower photon energies because of the narrowing of the band gap. The results are interpreted taking into account the fact that the density-of-states tails in InGaN are filled not only via trapping of free charge carriers, but also via tunneling transitions into the tail states. The decrease in the emission efficiency at high currents is attributed to the suppression of tunneling injection and the enhancement of losses via the nonradiative recombination channel “under” the quantum well.     

基于高亮度LED散热基板导热系数的检测方法

导热系数在化工、建筑、科研生产中有着广泛的应用。目前国内外关于导热系数的检测方法很多,相关的标准也不少。检测样本不同,对检测方法的适用领域、测量范围和精度的要求也不同。在检测时,选择合适的检测方法至关重要。通过对比分析国内外各种导热系数的检测方法,引入一种适合印制电路板行业高亮度LED散热基板导热系数的新检测方法。通过试验验证,确定其在高亮度LED散热基板的导热系数检测方面的适用性。     

Optical properties of photodetectors based on single GaN nanowires with a transparent graphene contact

We report the fabrication and optical and electrical characterization of photodetectors for the UV spectral range based on single p–n junction nanowires with a transparent contact of a new type. The contact is based on CVD-grown (chemical-vapor deposition) graphene. The active region of the nitride nanowires contains a set of 30 radial In_0.18Ga_0.82N/GaN quantum wells. The structure is grown by metal-organic vaporphase epitaxy. The photodetectors are fabricated using electron-beam lithography. The current–voltage characteristics exhibit a rectifying behavior. The spectral sensitivity of the photodetector is recorded starting from 3 eV and extending far in the UV range. The maximal photoresponse is observed at a wavelength of 367 nm (sensitivity 1.9 mA/W). The response switching time of the photodetector is less than 0.1 s.     

基于补偿法的均匀照明自由曲面LED反光杯设计

根据面向理想光源的设计原理,提出了基于能量补偿和坐标迭代的自由曲面母线求解方法。在二维坐标系中建立系统模型,由反光杯反射光对直射投射光进行补偿,将反光杯右上边缘的光线反射到目标面左边缘,且随着光线下移反射光线逼近目标中心。根据Snell定律,以上边缘点为初始点,逐一迭代得母线上各点坐标,旋转或拉伸生成所求反光杯。在Tracepro软件中的模拟结果表明对圆形或正方形目标照度均匀性均优于85%,且系统能量利用率仅由LED出光角度和反光杯反射系数决定,该结构可使LED光源用于大范围照明。     

Optimization of the parameters of HEMT GaN/AlN/AlGaN heterostructures for microwave transistors using numerical simulation

The numerical simulation, and theoretical and experimental optimization of field-effect microwave high-electron-mobility transistors (HEMTs) based on GaN/AlN/AlGaN heterostructures are performed. The results of the study showed that the optimal thicknesses and compositions of the heterostructure layers, allowing high microwave power implementation, are in relatively narrow ranges. It is shown that numerical simulation can be efficiently applied to the development of microwave HEMTs, taking into account basic physical phenomena and features of actual device structures.     

Measurement method for output port reflectance of an erbium-doped fiber amplifier

A novel method to measure output port reflectance of an erbium-doped fiber amplifier (EDFA) was demonstrated. This technique was verified through simulating a "black box" EDFA with a reflector prior to the input port of a nonisolated EDFA.     

Analytical modeling and ATLAS simulation for a homojunction LED in the mid-infrared spectral region

A generic analytical model and the ATLAS simulation of a homojunction light emitting diode（LED） based on p＋-InAs0.91Sb0.09/n0-InAs0.91Sb0.09/n＋-InAs0.91Sb0.09 materials grown on lattice matched p＋-GaSb substrate are presented.This LED is suitable for use as source in the optical absorption gas spectroscopy in the mid-infrared spectral region at 300 K.The various electro-optical properties of the homojunction LED are evaluated using analytical techniques and ATLAS device simulation software.The current-voltage characteristics of the structure are computed analytically and simulated,and the results are found to be in good agreement.The output power of the homojunction LED is estimated as a function of bias current under high carrier injection and compared with the reported experimental results.     

Origin of the radiative emission in blue-green light emitting diodes based on GaN/InGaN heterostructures

Phase separation effects induced by spinodal decomposition taking place in cubic In_xGa_1−xN epitaxial layers were investigated by means of resonant Raman scattering (RRS) and X-ray diffractometry (XRD) experiments. The alloy epilayers were grown by radio-frequency plasma-assisted molecular beam epitaxy on GaAs (001) substrates. Ab initio theoretical calculation of the alloy phase diagram predicts the formation of In-rich phases in the layers which is confirmed by the RRS and XRD experiments. Photoluminescence observed at room temperature and 30 K from the layers shows light emission in the blue-green region of the spectrum. RRS experiments demonstrated that the observed emission is directly linked to the In-rich separated phases (quantum dots) in the alloy. The results support the model that the origin of light emission in nitride-based light emitting diodes and laser diodes is related to quantum confinement effects taking place in quantum dots formed in the InGaN layers, active media of the devices.     

Thermal investigation of LED array with multiple packages based on the superposition method

In this paper, the superposition method is used to investigate the complete temperature field of a light-emitting diode (LED) packaging substrate, based on the results of transient temperature rise measurements and the thermal resistance coupling matrix. The feasibility of use of the superposition method in an LED array with multiple packages has been proved first by temperature comparisons with the simultaneous operation of an array (5×5) of 25 high power LEDs mounted on a metal core printed circuit board (MCPCB). Compared with existing approaches, the superposition method will measure the internal temperature of chip directly, accurately and nondestructively. According to the relatively accurate and reliable self-heating and coupling temperature rise data, optimization scheme of LED lamp with multiple packages is proposed. The results show that increasing the heat source separation distance and improving the thermal conductivity of thermal interface materials will reduce the temperature rise and thermal non-uniformity.     

Analysis of electromagnetic radiation from a video output amplifierinside a monitor by using FDTD method

The finite-difference time-domain (FDTD) method is used to analyze the electromagnetic compatibility and interference (EMC and EMI) problems due to the electromagnetic radiation from a video output amplifier located inside a computer monitor. The multiple grid technique is implemented in the FDTD method to improve the computational efficiency. The video output amplifier is modeled by a rectangular iron container with an equivalent dipole antenna located at the center of one opened wall facing the cathode-ray-tube (CRT). The coupled electric fields inside and outside the monitor are calculated. It is found that higher values of coupled electric fields occur near the monitor screen. It is also found that the coupled electric fields outside the CRT region drop sharply in amplitude. Simulation results of coupled electric fields at a distance of 3 m from the monitor screen also comply with the FCC regulations. Calculation results also agree with the experimental data for coupled electric fields outside the monitor screen at a measured distance of 3 m     

基于FDTD的结构耦合对超声传播影响的仿真研究

基于提高小尺寸复杂结构零件的超声检测的精确性的目的,采用时域有限差分法,分别建立了带有一个和3个圆形空腔的铝板模型,研究了不同铝板宽度下结构耦合对超声传播的影响。研究结果表明,对于两种结构的铝板,当宽度小于8个波长（20 mm）时,超声通过空腔的透射功率明显增大,其最高相对变化分别为10.5倍和6倍左右。这说明当铝板宽度与波长可比拟时,空腔与铝板之间有明显的耦合效应,且空腔的增加削弱了这种耦合效应,使得铝板宽度变化对超声传播的影响减弱。     

A method for measuring the frequency response of photodetector modules using twice-modulated light

In this paper, a novel method is proposed for measuring the frequency response of a photodetector (PD) and its associated amplifier, which is called a PD module in this paper, by using light whose intensity is modulated twice. A distinctive feature of the twice-modulated light is that it contains two frequency components that essentially have equal intensities. A measurement system was constructed consisting of an He-Ne laser source and two acoustooptic modulators to verify the method. This study shows the resolution to a problem caused by the use of acoustooptic modulators (AOMs). This method can be readily used for determining the frequency responses of a PD module in the frequency range of up to tens of megaHertz.     

Design of a matching network for an HF antenna using the realfrequency method

The real frequency method (RFM) is used to design a matching network for an electrically short loaded dipole. The RFM is demonstrated to be superior to other analytical and numerical techniques in the sense that it yields the maximum flat transducer power gain possible, and that it does not require any analytical modeling of the load impedance to be matched. For this reason, the RFM is found to be well suited for matching distributed systems such as antennas     

A switching control strategy based on output regulation subspaces for the control of induction motors using a three-level inverter

In this work we present the design of a new switching control strategy for a three-level converter aimed to improve the performance of a direct torque control (DTC) for induction machines, special attention is given to the reduction of torque ripple. As in classical DTC, the proposed technique is aimed to directly regulate the outputs: torque and flux amplitude. We show that classical DTC can be considered as a particular case of the proposed control strategy. The proposed criterion to design the switching control sequence is based on a quadratic criterion of the output errors plus a prediction in one-step ahead, and an interesting partition of the input state space generated by the output regulation subspaces (ORS) to facilitate the selection of the control vector for reducing the computational load. As a result, a control vector is selected without the requirement of an auxiliary space vector or any other modulation technique. Simulations results using the proposed control technique confirm the validity of this approach.     

Numerical simulation of annular phased arrays for anatomicallybased models using the FDTD method

Annular phase arrays (APAs) of aperture and dipole antennas used for hyperthermia are simulated in three dimensions by using the finite-difference time-domain (FDTD) method. A 17363 cell, 1.31 cm resolution, anatomically based model of the human torso surrounded by a bolus of deionized water is used for calculations of specific absorption rates (SARs). Test runs on the calculation of fields in the water-filled interaction space and with homogeneous circular- and elliptical-cylinder phantoms correlate well with the experimental data in the literature, lending support to the accuracy of the FDTD method for near-field exposure conditions. Results are given for APAs using different sizes of aperture and dipole antennas and for a subannular array to obtain higher SARs in the liver. It is concluded that, because of its flexibility, the proposed procedure may be useful for a variety of realistic radiofrequency applicators for hyperthermia and other biomedical applications