Multiple Diodes Research Articles

The growth response of leaf lettuce at different stages to multiple wavelength-band light-emitting diode lighting

This study investigated the effects of a combination of light-emitting diodes (LEDs) that emit different bands of short wavelengths on the growth response of leaf lettuce (Lactuca sativa var. crispa) at the seedling stage (1–14d old) and vegetative stage (15–28d old). The wavebands included red (R; range: 623–673nm), light red (Lr; range: 599–644nm), blue (B; range: 427–478nm), light-blue (Lb; range: 435–489nm), cyan (C; range: 466–532nm), green (G; range: 494–564nm), and ultraviolet-A (UV-A; range: 383–426nm). In the light treatments, a photon flux of 300±12 (standard deviation [SD]) μmolm−2s−1 was provided for 18hd−1 at the seedling and vegetative stages with such LED light formulas (combinations) including LrLb (61.5% and 38.5%, respectively), RCB (42.8%, 30.0%, and 27.2%, respectively), LrLbG (49.0%, 36.1%, and 14.9%), and RBUV-A (52.9%, 37.0%, and 10.1%), with each fraction denoting the percentage of total photon flux. The air temperature, relative humidity, and CO2 levels for all treatments were maintained at 22±2°C, 64±8%, and 570±75ppm, respectively. The data obtained revealed the variability of light formula effects on lettuce plant physiological indices (including the number of leaves, leaf length, leaf area, dry mass, fresh mass, chlorophyll-a (chl-a) content, and nitrate content). Provision of RBUV-A and RCB LED irradiation during the vegetative stage could increase the shoot fresh mass of leaf lettuce. In addition, providing different LED light formulas to lettuce plants at the seedling and vegetative stages resulted in tremendous differences in nitrate contents, especially with the use of two light formulas with and without reversal of lighting sequence. Finally, the adoption of LrLbG or LrLb LED irradiation during different growth stages resulted in the lowest physiological indices of lettuce plants.

A compact low cost “master–slave” double crystal monochromator for x-ray cameras calibration of the Laser MégaJoule Facility

The Alternative Energies and Atomic Energy Commission (CEA-CESTA, France) built a specific double crystal monochromator (DCM) to perform calibration of x-ray cameras (CCD, streak and gated cameras) by means of a multiple anode diode type x-ray source for the MégaJoule Laser Facility. This DCM, based on pantograph geometry, was specifically modeled to respond to relevant engineering constraints and requirements. The major benefits are mechanical drive of the second crystal on the first one, through a single drive motor, as well as compactness of the entire device. Designed for flat beryl or Ge crystals, this DCM covers the 0.9–10keV range of our High Energy X-ray Source. In this paper we present the mechanical design of the DCM, its features quantitatively measured and its calibration to finally provide monochromatized spectra displaying spectral purities better than 98%.

Comparison of ultraviolet light emitting diodes with traditional UV for greywater disinfection

The current technological status of ultraviolet light emitting diodes (UV-LEDs) has reached a point where small-scale ultraviolet (UV) water disinfection applications, that is, for greywater reuse appear increasingly promising. This study compares the germicidal and economical aspects of UV-LEDs with traditional UV. Pure cultures and environmental greywater samples were exposed to different radiation doses from both UV sources with the germicidal effect comparative at equivalent doses. The impact of particle size on disinfection efficiency was investigated in two greywater fractions of varying mean particle size. Disinfection efficiency was found to be dependent on particle size with larger particles reducing microbial inactivation for both UV sources. Post-UV blending to detach particle-associated coliforms resulted in higher bacterial counts for both UV sources although to a lesser extent for UV-LEDs suggesting that it might be less affected by the presence of particles than traditional UV sources, possibly due to the UV radiation being emitted by multiple diodes at different angles compared to the traditional UV collimated beam setup. Nevertheless, removal of particles prior to UV disinfection is necessary to meet strict water reuse standards. Although UV-LEDs are currently prohibitively expensive, improvements in performance indicators might make this technology economically competitive within the next few years.

Mapping Defect Density in MBE Grown <inline-formula> <tex-math notation="TeX">${\rm In}_{0.53}{\rm Ga}_{0.47}{\rm As}$ </tex-math></inline-formula> Epitaxial Layers on Si Substrate Using Esaki Diode Valley Characteristics

Growing good quality III-V epitaxial layers on Si substrate is of utmost importance to produce next generation high-performance devices in a cost effective way. In this paper, using physical analysis and electrical measurements of Esaki diodes, fabricated using molecular beam epitaxy grown In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As layers on Si substrate, we show that the valley current density is strongly correlated with the underlying epi defect density. Such a strong correlation indicates that the valley characteristics can be used to monitor the epi quality. A model is proposed to explain the experimental observations and is validated using multiple temperature diode I-V data. An excess defect density is introduced within the device using electrical and mechanical stress, both of which are found to have a direct impact on the valley current with a negligible change in the peak current characteristics, qualitatively supporting the model predictions.

Beam Shaping of Multiple Laser Diodes Using a Kinoform

Kinoform is a kind of computer-generated holograms which only has phase modulation. It has high utilization efficiency of illuminating light because a kinoform does not have amplitude modulation. Because of the above advantage of high utilization efficiency, kinoform is desirable as beam shaping element. This study is a location of the basic study to design the kinoform which can shape the laser beams of multiple laser diodes. We inspected the influence for beam shaping of multiple laser diodes without phase difference and discuss the dependence of shaped beam intensity on a ratio of Gaussian radius and range of laser light, the number of laser diodes and the sampling points of the desired shaped beam intensity.

Rectifier Design Using Distributed Greinacher Voltage Multiplier for High Frequency Wireless Power Transmission

This paper discusses the design of a high frequency Greinacher voltage multiplier as rectifier; it has a greater conversion efficiency and higher output direct current (DC) voltage at high power compared to a simple halfwave rectifier. Multiple diodes in the Greinacher voltage multiplier with distributed circuits consume excited power to the rectifier equally, thereby increasing the overall power capacity of the rectifier system. The proposed rectifiers are a Greinacher voltage doubler and a Greinacher voltage quadrupler, which consist of only diodes and distributed circuits for high frequency applications. For each rectifier, the RF-to-DC conversion efficiency and output DC voltage for each input power and load resistance are analyzed for the maximum conversion efficiency. The input power with maximum conversion efficiency of the designed Greinacher voltage doubler and quadrupler is 3 and 7 dB higher, respectively;than that of the halfwave rectifier.

Enhanced Internal Quantum Efficiency and Light Extraction Efficiency of Light-emitting Diodes with Air-gap Photonic Crystal Structure Formed by Tungsten Nano-mask

We demonstrate the blue InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) with an embedded air-gap photonic crystal (PC) which was fabricated by the lateral epitaxial overgrowth of GaN layer on the tungsten (W) nano-masks. The periodic air-gap PC was formed by the chemical reaction of hydrogen with GaN on the W nano-mask. The optical output power of LEDs with an air-gap PC was increased by 26% compared to LEDs without an air-gap PC. The enhanced optical output power was attributed to the improvement in internal quantum efficiency and light extraction efficiency by the air-gap PC embedded in GaN layer.

Note: Coupling of multiple laser diodes into a multi-mode fiber

Diode lasers are coupled to a multi-mode fiber (with 100-400 μm core) using a reflector in the form of a regular pyramid. The optimization of the optical setup allows to couple 60%-90% of light into the fiber. The demonstrator achieves 3.5 W in the 100/125 μm fiber with 8 violet (405 nm) diodes, 5.5 W in the 100/125 μm fiber with 8 blue (445 nm) diodes, and 3.3 W in the 200/250 μm fiber with red (638 nm) diodes. The device can work with lasers emitting at many different wavelengths, including green (532 nm) frequency-doubled lasers. Our work was motivated by potential medical applications of these laser sources.

Optical properties of nanopillar AlGaN/GaN MQWs for ultraviolet light-emitting diodes.

Nanopillar AlGaN/GaN multiple quantum wells ultraviolet light-emitting diodes (LEDs) were fabricated by nanosphere lithography and dry-etching. The optical properties of the nanopillar LEDs were characterized by both temperature-dependent and time-resolved photoluminescence measurements. Compared to an as-grown sample, the nanopillar sample has a PL emission peak blue-shift of 7 meV, a 42% enhanced internal quantum efficiency at room temperature and a reduced radiative recombination lifetime from 870 picosecond to 621 picosecond at 7K. These results are directly from the suppressed quantum confined stark effect that is due to the strain relaxation in the nanopillar MQWs, further revealed by micro-Raman measurement. Additionally, finite-difference time domain simulation also proves better light extraction efficiency in the nanopillar LEDs.

Illusion induced overlapped optics

The traditional transformation-based cloak seems like it can only hide objects by bending the incident electromagnetic waves around the hidden region. In this paper, we prove that invisible cloaks can be applied to realize the overlapped optics. No matter how many in-phase point sources are located in the hidden region, all of them can overlap each other (this can be considered as illusion effect), leading to the perfect optical interference effect. In addition, a singular parameter-independent cloak is also designed to obtain quasi-overlapped optics. Even more amazing of overlapped optics is that if N identical separated in-phase point sources covered with the illusion media, the total power outside the transformation region is N2I0 (not NI0) (I0 is the power of just one point source, and N is the number point sources), which seems violating the law of conservation of energy. A theoretical model based on interference effect is proposed to interpret the total power of these two kinds of overlapped optics effects. Our investigation may have wide applications in high power coherent laser beams, and multiple laser diodes, and so on.

Improved Time-Reversal-Based Beamforming Using a Self-Biasing Switch

In this letter, a self-biasing switch is proposed to reduce the artifacts associated with time-reversal-based beamforming. This device consists of multiple diodes placed in series on a 50- Ω microstrip. At low incident voltages, this device behaves like a high-pass filter, rejecting low-power transients over a broad bandwidth. Once the activation voltage of these diodes is exceeded, the capacitive elements of this filter are shorted, allowing energy to pass with significantly less attenuation. By preferentially attenuating low-power transients, this device can suppress the temporal artifacts associated with the time reversal process. An experimental demonstration of this device is performed using a reverberant cavity as a passive delay line network. Measured outputs from this cavity are used as inputs to a simulated array of Vivaldi antennas to demonstrate the proposed improvement in beamforming.

Degradation behaviors of InGaN/GaN-based multiple quantum wells blue light-emitting diodes by chip size

This paper analyses the degradation of the optical, electrical, and thermal characteristics of InGaN/GaN-based light-emitting diodes (LEDs) with different chip sizes. Their optical, electrical, and thermal characteristics were periodicity-monitored during the test. The small chip showed an increase in ideality factor and high series resistance. This led to the degradation of the electrical characteristic, and hence to high thermal resistance, finally resulting in low light output power. In the large chip, the high operating current made the junction temperature high. This, together with the thermal degradation on the LED surface and metal pad, led to a decrease in light output power. In the middle chip, the optical and electrical degradation ratio was lower than that in the other samples and, therefore, the light output power decreased to a lesser degree.

Enhancing the performance of green GaN-based light-emitting diodes with graded superlattice AlGaN/GaN inserting layer

Green InGaN/GaN multiple quantum wells light-emitting diodes with graded superlattice (GSL) AlGaN/GaN inserting layer are investigated numerically and experimentally. Our simulation results indicate that GSL inserting layer can decrease the effective barrier height of holes by 57 meV, which makes holes more easily inject into the quantum wells. The piezoelectric polarization field near the last barrier is suppressed effectively by introducing of the GSL inserting layer. As a result, the efficiency droop radio is improved from 35.8% to 19.4% at current density of 100 A/cm−2.

Low-Level Laser Therapy and Vibration Therapy for the Treatment of Localized Adiposity and Fibrous Cellulite

IntroductionIn recent years, there has been an upsurge in the application of low-level laser therapy in various medical diseases. Additionally, vibration therapy is a new and effective measure to prevent muscular atrophy and osteoporosis, along with some general health-related beneficial effects of exercise on skeletal muscles such as improvement of endothelial function and an increased enzyme capacity of energy metabolism. The aim of this study was to evaluate the application of a 635 nm and 0.040 W exit power per multiple diode laser in combination with vibration therapy for the application of non-invasive reduction of circumference in patients with localized adiposity and cellulite.MethodsThe study enrolled men and women (N = 33) aged 18–64 years with localized adiposity or fibrous cellulite. The evaluation parameters were: photographic evaluation, perimetric evaluation, blood tests, ecographic evaluation, histological evaluation, and subjective and objective tests.ResultsThe results produced were statistically analyzed and resulted in a significant reduction of fat thickness when compared to the measurement prior to the treatment (P < 0.0001). Moreover, subjective and objective tests, as well as ecographic and histological evaluations, confirmed the reduction of fat thickness.ConclusionIn this study we have demonstrated the safety and efficacy of the combination between low-level laser therapy and vibration therapy for the resolution of localized adiposity and fibrous cellulite.

Measurement of normalized spectral responsivity of digital imaging devices by using a LED-based tunable uniform source

We present an instrumentation solution for measurement of normalized spectral responsivity of digital imaging sensors and cameras. The instrument consists of multiple light-emitting diodes (LEDs), a single-grating monochromator, and a small-size integrating sphere. Wavelength tuning is achieved by a proper selection of LED in accordance with the monochromator setting in a range from 380 to 900 nm. High spectral purity with a bandwidth of 5 nm is realized without using double gratings and order-sorting filters. Experimental characteristics and calibration of the instrument are described with the related error and uncertainty sources. The performance is demonstrated by measuring a monochrome charge-coupled device and a trichromatic complementary metal-oxide-semiconductor device. The measurement uncertainty is evaluated to be less than 1% (k=2) except several wavelengths with low LED power.

Device characteristics and thermal analysis of AlGaInP-based red monolithic light-emitting diode arrays

We investigated the device characteristics of AlGaInP/GaInP multiple quantum wells monolithic light-emitting diode (LED) arrays operating at λ ∼ 630 nm, together with experimental and theoretical thermal analysis. The optical and electrical properties were experimentally measured. The junction temperature of a single LED with 300 × 300 µm2 was experimentally determined by the electroluminescence emission peak shift method, which led to a thermal resistance of ∼47 K W−1. As the number of LEDs in arrays was increased, the optical power output (Popt) was also increased. For 1 × 4 and 2 × 2 LED arrays, the Popt was about 15 mW at 300 mA and it was maximized to ∼23 mW at 670 mA. From the measured light–current–voltage data, the detailed theoretical calculations on the thermal properties were carried out by a three-dimensional steady-state heat dissipation model using the measured heat source densities. The internal temperature profiles were obtained for different separation distances, array sizes and injection currents. The internal temperature was largely increased with the increase in array size and the decrease in the separation distance.

고전압 IGBT SPICE 시뮬레이션을 위한 모델 연구

본 논문에서는 SPICE 시뮬레이션을 위한 고전압 insulated gate bipolar transistor(IGBT)의 개선된 모델을 제안하였다. IGBT를 부속 소자인 MOSFET과 BJT의 조합으로 구성하고, 각 소자의 각종 파라미터 값을 조절하여 기본적인 전류-전압 특성과 온도변화에 따른 출력특성의 변화 등을 재현하였다. 그리고 비선형적인 리버스 트랜스퍼 커패시턴스 등의 기생 커패시턴스의 전압에 따른 변화를 높은 정확도로 재현하기 위해, 복수의 접합 다이오드, 이상적인 전압 및 전류 증폭기, 전압제어 저항, 저항과 커패시터 수동소자 등을 추가하였다. 본 회로모델을 1200V급의 트렌치 게이트 IGBT의 모델링에 이용하였으며, 실측자료와 비교하여 통해 모델의 정확도를 검증하였다. In this paper, we proposed a SPICE model of high-voltage insulated gate bipolar transistor(IGBT). The proposed model consists of two sub-devices, a MOSFET and a BJT. Basic I-V characteristics and their temperature dependency were realized by adjusting various parameters of the MOSFET and the BJT. To model nonlinear parasitic capacitances such as a reverse-transfer capacitance, multiple junction diodes, ideal voltage and current amplifiers, a voltage-controlled resistor, and passive devices were added in the model. The accuracy of the proposed model was verified by comparing the simulation results with the experimental results of a 1200V trench gate IGBT.

Thermal uniformity of packaging multiple light-emitting diodes embedded in aluminum-core printed circuit boards

The gallium nitride (GaN) based white light emitting diode (LED) luminaire system presents a pathway to enhance efficacy, functionality, and the possibility to cut down pollution from traditional lamps. Much effort has been done to improve its performance/price ratio to penetrate the market, including designing and optimizing the LED package structure. Multichips embedded on the aluminum core printed circuit boards (Al-PCB) architecture is one of the features of the LED package method, along with low thermal resistance, low price, and easier development compared with luminaire systems. However, the thermal resistance of the packaged LED varies with the stochastic parameters of the LED packing process, thus posing challenges in packing cost and reliability. In the present paper, the thermal uniformity of packaging the LED array embedded on Al-PCB technology is explored using the Bayesian probability theory. The stochastic thermal characteristics of Al-PCB are investigated by an active infrared imager, and its thermal time constant matrix-based probability is suggested to estimate uniformity. A package design procedure, involving multi-physical finite element simulation, Al-PCB infrared checking, and probability estimation, is proposed. Finally, a 12 LED array for MR-16 lamp is demonstrated. The results show that the thermal uniformity of Al-PCB plays a significant role in packaging multiple LED embedded on Al-PCB, which can be physically indicated by the thermal time constant matrix-based probability. The suggested package procedure sheds light on solving the cost-related thermal uniformity of the LED array. In addition, a proposal to further reduce cost by replacing Au wire with Ag bonding wire is not deemed to be possible based on scanning electron microscopy structure analysis.

Efficiency and droop improvement in green InGaN/GaN light-emitting diodes on GaN nanorods template with SiO2 nanomasks

This study presents the green InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) grown on a GaN nanorods template with SiO2 nanomasks by metal–organic chemical vapor deposition. By nanoscale epitaxial lateral overgrowth, microscale air voids were formed between nanorods and the threading dislocations were efficiently suppressed. The electroluminescence measurement reveals that the LEDs on nanorods template with SiO2 nanomasks suffer less quantum-confined Stark effect and exhibit higher light output power and lower efficiency droop at a high injection current as compared with conventional LEDs.

Improved Light Extraction of GaN-Based Blue Light-Emitting Diodes with ZnO Nanorods on Transparent Ni/Al-Doped ZnO Current Spreading Layer

We reported the light-extraction properties of InGaN/GaN multiple quantum wells blue light-emitting diodes (LEDs) with ZnO nanorod arrays (NRAs) on Ni/Al-doped ZnO (AZO) films as a current spreading layer (CSL). The Ni/AZO bilayer exhibited a high optical transmittance of ∼80% at λ∼460 nm. The electrical property of AZO films was improved by inserting a thin Ni layer, which leads to the better current–voltage characteristics of LEDs. The ZnO nanorods can be easily grown on the AZO surface of Ni/AZO CBL as the same materials by a simple wet chemical growth. For 450 ×450 µm2 LED with Ni/AZO CSL, the incorporation of ZnO NRAs into the AZO surface improved the light output power by ∼14% at 100 mA without causing any electrical degradation compared to the conventional LED without ZnO NRAs.