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A diode-end-pumped, passively Q-switched, Nd:YAG laser with a monolayer graphene as saturable absober simultaneously emitting at 1319 and 1338 nm was demonstrated for the first time. The maximum output power, the minimum pulse duration and the highest repetition rate were 586 mW, 317 ns, and 102 kHz, respectively. The corresponding peak power was about 18.1 W. Key words: passively Q-switched, dual wavelength, monolayer graphene, diode-end-pumped, Nd:YAG. Nous presentons pour la premiere fois un laser Nd: YAG a commutation Qpassive et pompe par diode en extremite, avec une monocouche de graphene comme absorbant saturable, qui emet simultanement a 1319 et 1338 nm. La puissance maximale de sortie est 586 mW, la duree minimale de l'impulsion est de 317 ns et le plus haut taux de repetition est de 102 kHz. Le pic de puissance correspondant est de 18.1 W. [Traduit par la Redaction] Mots-cles: commutation Q passive, a double longueur d'onde, graphene monocouche, laser Nd: YAG, pompe par diode en extremite. PACS Nos.: 42.60.Gd, 42.60.Jf, 42.60.Lh., 1. Introduction Diode pumped solid-state lasers emitting at 1.3 µm spectral range have attracted a lot of interest owing to their applications in medicine, surgery, and communications. For 1.3 µm [...]

An ultra HPLC--diode array detector (UHPLC--DAD) method was developed and validated for rapid determination of cholesteryl-hexahydrophthaloyl-5-fluorouracil (CH5F) conjugate in standard drug, lipid nanoemulsion and dissolution samples. The chromatographic identification of this conjugate was achieved on Hypersil GOLD 50 x 2.1 mm reversed phase C18 column having a 1.9 pm packing as a stationary phase using methanol-water (80 : 20, v/v) as a mobile phase, at a flow rate of 0.4 mL/min with DAD detection at 276 nm. The proposed UHPLC--DAD method is linear in the concentration range of 1-50 µg/mL with correlation coefficient of 0.998. The proposed method is precise, accurate, robust, sensitive and specific for analysis of the conjugate. High assay value (98.7%) of CH5F conjugate in lipid nanoemulsion was obtained by the proposed method. Forced degradation studies indicated that conjugate was sufficiently stable under oxidative stress conditions degraded under acid, base and thermal stress conditions. The proposed UHPLC-DAD method successfully and resolved drug conjugate peak in the presence of its degradation products which established stability and indicating property of the method. Results of the present study indicated that the proposed UHPLC--DAD method can be successfully used for routine determination of CH5F conjugate in standard drug and pharmaceutical formulations. Keywords: UHPLC--DAD, cholesteryl-hexahydrophthaloyl-5-fluorouracil, lipid nanoemulsion, dissolution DOI: 10.1134/S1061934815050056, 5-Fluorouracil (5-FU) is a very common anticancer drug belonging to antimetabolite class that is recommended clinically for the management and treatment of various kinds of tumors like colorectal, breast and [...]

We present a compact wavelength stabilized diode laser system at 671 nm on a micro-optical bench as a light source for shifted excitation Raman difference spectroscopy (SERDS). The laser system consists of two broad-area gain media in separate laser cavities using two reflection Bragg gratings with slightly different center wavelengths. A spectral width below 100 pm and a constant wavelength shift of 0.57 [+ or -] 0.06nm is obtained up to output powers of 250mW. The suitability of this light source for SERDS is demonstrated using Raman spectra of ethanol with increasing concentrations of Cresyl Violet as the fluorescent contaminant. OCIS codes: 140.2020, 140.4780, 230.3990, 300.6260, 300.6450.

This paper considers the transient performance and stability of a recurrent discrete Fourier transform (DFT) based control method for a series active filter integrated with a 12-pulse diode rectifier. The control method targets specific harmonics and/or the negative sequence fundamental component of the supply current, and is intended for use with nonsinusoidal/unbalanced supply voltages. The proposed control method is based on DFTs instead of the dq-method, and a simple approach is used to account for small frequency variations found in practical power systems. Index Terms--Active filters, digital control, discrete Fourier transforms (DFTs).

In the previous literature, the introduction of the virtual-space-vector (VV) concept for the three-level, three-leg neutral-point-clamped converter has led to the definition of pulsewidth modulation (PWM) strategies, guaranteeing a dc-link capacitor voltage balance in every switching cycle under any type of load, with the only requirement being that the addition of the three phase currents equals zero. This paper presents the definition of the VVs for the general case of an n-level converter, suggests guidelines for designing VV PWM strategies, and provides the expressions of the leg duty-ratio waveforms corresponding to this family of PWMs for an easy implementation. Modulations defined upon these vectors enable the use of diode-clamped topologies with passive front-ends. The performance of these converters operated with the proposed PWMs is compared to the performance of alternative designs through analysis, simulation, and experiments. Index Terms--Capacitor voltage balance, diode-clamped, multilevel, pulsewidth modulation (PWM), virtual vector.

This paper proposes a method of modeling and simulation of photovoltaic arrays. The main objective is to find the parameters of the nonlinear I-V equation by adjusting the curve at three points: open circuit, maximum power, and short circuit. Given these three points, which are provided by all commercial array datasheets, the method finds the best I--V equation for the single-diode photovoltaic (PV) model including the effect of the series and parallel resistances, and warranties that the maximum power of the model matches with the maximum power of the real array. With the parameters of the adjusted I--V equation, one can build a PV circuit model with any circuit simulator by using basic math blocks. The modeling method and the proposed circuit model are useful for power electronics designers who need a simple, fast, accurate, and easy-to-use modeling method for using in simulations of PV systems. In the first pages, the reader will find a tutorial on PV devices and will understand the parameters that compose the single-diode PV model. The modeling method is then introduced and presented in details. The model is validated with experimental data of commercial PV arrays. Index Terms--Array, circuit, equivalent, model, modeling, photovoltaic (PV), simulation.

A diode end-pumped doubly Q-switched YV[O.sub.4]/Nd:YV[O.sub.4] laser has been realized for the first time to our knowledge by using both an electro-optic (EO) modulator and a [Cr.sup.4+]:YAG saturable absorber. A 3.8 ns pulse width is generated by this laser under a pump power of 15W at 2kHz, which is obviously compressed in comparison with that of 8.8 ns from a single actively EO Q-switched laser. Under the same conditions, peak power values of 174.7 and 93 kW are also obtained. A coupled equation is given to theoretically analyze the experimental data. The experimental and theoretical results show that the doubly Q-switched laser has the advantages of a shorter pulse width and higher pulse peak power in contrast with a singly Q-switched laser. OCIS codes: 230.2090, 140.3580, 140.3430, 140.3540.

Unidirectional electric current flow, such as that round in a diode, is essential for modern electronics. It usually occurs at asymmetric interfaces such as p-n junctions or metal/semiconductor interfaces with Schottky barriers. We report on a diode effect associated with the direction of bulk electric polarization in BiFe[O.sub.3]: a ferroelectric with a small optical gap edge of ~2.2 electron volts. We found that bulk electric conduction in ferroelectric monodomain BiFe[O.sub.3] crystals is highly nonlinear and unidirectional. This diode effect switches its direction when the electric polarization is flipped by an external voltage. A substantial visible-light photovoltaic effect is observed in BiFe[O.sub.3] diode structures. These results should improve understanding of charge conduction mechanisms in leaky ferroelectrics and advance the design of switchable devices combining ferroelectric, electronic, and optical functionalities.

The Cygnus radiographic machine is a relatively compact low-energy (< 3 MV) X-ray source with some extremely desirable features for radiographic applications. These features include small spot size, which is critical for high-spatial resolution, and high dose in a low-energy range. The X-ray source is based on bremsstrahlung production in a small-diameter (~0.75 mm) tungsten rod by a high-current (~60 kA) electron beam converging at the tip of the rod. For quantitative analysis of radiographic data, it is essential to determine the bremsstrahlung spectrum accurately. We have used the radiographic chain model to self-consistently model the diode with a 2-D particle-in-cell (PIC) code (Merlin) linked to an electron-photon Monte Carlo code to obtain the spectrum under three different situations: a steady-state spectrum using a voltage pulse of 2.25 MV, a time-integrated spectrum using a time-dependent experimental voltage pulse, and the spectrum resuiting from inclusion of reflexing electrons around the anode rod in our PIC simulation. Detailed electron dynamics were obtained. We conclude that the time-integrated bremsstrahlung spectrum is significantly softer than that of the steady state. Including the effects of reflexing electrons using a Monte Carlo transport method in Merlin produced a spectrum in better agreement with experimental data. Index Terms--Cygnus, diode, flash radiography, simulation.

The paper is concerned with the analysis of 2-D scattering of an electromagnetic (EM) pulse by a perfectly conducting wedge moving with a relativistic velocity in a free space. The incident signal is described by a Dirac delta function. Analytical solution to this scattering problem is found, and its physical interpretation is given. The field representation, valid for all scatterer velocities, is then simplified to the case of moderate and low velocities, appropriate for practical applications. Index Terms--Diffraction, Dirac delta, electromagnetic pulse, moving wedge.

A fixed-beam frequency-tunable coplanar stripline (CPS) antenna array using the phase reversal technique and varactor diodes tuning is presented. The antenna array is composed of plurality of half-wavelength CPS sections interconnected by phase reversing crossovers. These crossovers have two functions: they serve as the radiators (small dipoles) of the array and also provide their own required in-phase excitations for broadside radiation. Two rnicrostrip-to-CPS transitions for excitation of the balanced input/output antenna array are implemented and compared. A six-element array is demonstrated theoretically and experimentally, with 9.3 dBi of gain for bidirectional radiation and 12.5 dBi of gain for unidirectional radiation using a back reflector. Moreover, shunt varactor diodes are incorporated along the CPS structure to achieve frequency tuning through a bias voltage control while broadside radiation patterns remain fixed. The return loss and the radiation patterns at several frequencies are presented, and up to 50% tuning range is obtained. The proposed antenna array is simple and uniplanar with small lateral size, high radiation efficiency and high directivity. In addition, it uses a very simple biasing circuit with high DC-RF isolation. Its balanced input/output makes it suitable for RF system integration and active integrated antenna design. Index Terms--Antenna array, coplanar stripline (CPS), phase reversal, tunability.

Single- and dual-polarized slot-ring antennas with wideband tuning using varactor diodes have been demonstrated. The single-polarized antenna tunes from 0.95 to 1.8 GHz with better than -13 dB return loss. Both polarizations of the dual-polarized antenna tune from 0.93 to 1.6 GHz independently with better than--10 dB return loss and > 20 dB port-to-port isolation over most of the tuning range. The capacitance of the varactor diodes varies from 0.45 to 2.5 pF, and the antennas are printed on 70 x 70 x 0.787 [mm.sup.3] substrates with [[member of].sub.r] = 2.2. The dual-polarized slot-ring antenna can either be made both frequency-and polarization-agile simultaneously, or can operate at two independent frequencies on two orthogonal polarizations. To our knowledge, this is the first dual-polarized tunable antenna with independent control of both polarizations over a 1.7:1 frequency range. Index Terms--Annular slot antennas, dual-polarized antennas, reconfigurable antennas, slot antennas, slot-ring antennas, tunable antennas.

Simplified space vector modulation (SVM) techniques for multilevel converters are being developed to improve factors such as the computational cost, number of commutations, and voltage distortion. The feedforward SVM presented in this paper takes into account the actual dc capacitor voltage unbalance of the multilevel power converter. The resulting technique is a low-cost generalized feedforward 3-D SVM method and is particularized for three-phase multilevel diode-clamped converters. This new modulation technique can be applied to topologies where the gamma component may not be zero. The computational cost of the proposed method is similar to those of comparable methods, and it is independent of the number of levels of the power converter. Experimental results using a three-level diode-clamped converter are presented to validate the proposed modulation technique. Index Terms--Modulation, multilevel systems, voltage control.

We have constructed a variable spectral-width, wavelength-tunable light source using a non-fiber-coupled broadband superluminescent diode device with an optical feedback mechanism. As lasing occurs, a strong output light which is linearly polarized and monochromatic is obtained. The spectral width varies with the injection current and the optical feedback ratio. By incorporating a dispersing prism into the feedback branch, a wavelength-tunable, external-cavity-feedback laser source is achieved. The result is a convenient, inexpensive apparatus suitable for experiments in undergraduate optics courses.

This paper addresses a transformerless mediumvoltage adjustable-speed motor drive consisting of two five-level diode-clamped PWM converters connected back-to-back. It is followed by designing, constructing, and testing a 200-V downscaled model to verify the validity and effectiveness of the medium-voltage motor drive. This downscaled model has four split dc capacitors equipped with a voltage-balancing circuit using two bidirectional buck-boost choppers. The two five-level converters are based on sinusoidal pulsewidth modulation with a carrier frequency of 3 kHz. The motor tested in this paper is a three-phase four-pole induction motor rated at 200 V, 5.5 kW, and 60 Hz. Experimental waveforms show that the four split dc-capacitor voltages are well balanced in any operating conditions and that the total harmonic distortion values of the input line current and the output motor current are 3.9% and 3.5%, respectively. Index Terms--Medium-voltage drives, multilevel inverters, neutral-point-clamped converters, voltage balancing.

Several pulsewidth modulation (PWM) strategies have been proposed for the three-level three-phase diode-clamped dc-ac converter. Among them, the nearest-three virtual-space-vector PWM guarantees the dc-link capacitor voltage balance under any operating condition, provided that the addition of the three phase currents equals zero. This paper extends this modulation concept to the four level converter. The new virtual vectors are presented and a simple modulation solution is defined. Conventional nearest-three space vector PWM cannot comprehensively achieve balanced and stable dc-link voltages. The proposed modulation solution enables the practical use of the four-level converter since it guarantees the dc-link capacitor voltage balance for any operating condition and load, provided that the addition of the three phase currents equals zero. Simulation and experimental results prove the goodness of the presented approach. Index Terms--Capacitor voltage balance, diode-clamped, multilevel, pulsewidth modulation (PWM), virtual vector.

Multidiode broadband microwave signal modulators based on 4H-SiC p-i-n diodes were fabricated and fully characterized for the first time. The diodes used for the modulator fabrication exhibited a blocking voltage of 1100 V, a 100-mA differential resistance of 1-3 [ohm], a punch-through voltage (100 V) capacitance below 0.5 pF, and a carrier effective lifetime of 15 ns. The three-diode modulators are characterized by a transmission loss of 1-2 dB and isolation of 27-34 dB in the 2-7-GHz frequency range, while their switching speed is as low as 30 ns. Two-diode modulators were specially designed for high-temperature operation. These modulators are characterized by a transmission loss of 1.1-2.6 dB and isolation of 33-44.5 dB in the 2-7-GHz frequency range at temperatures up to 300[degrees] C. Index Terms--Insertion loss, isolation, microwave modulators, p-i-n diode, silicon carbide, switches.

The paper presents the design of a source injection parallel coupled (SIPC) quadrature voltage controlled oscillator (QVCO), realized in a complementary architecture, which is usually preferred in low-power applications as it exploits [approximately equal to] 50% bias current reduction with double efficiency compared to the structure with single coupled, when operating in the current-limited regime. A stacked spiral inductor exhibiting a Q factor of 5.8, with pMOS based depletion mode varactor of 32% in tuning range, corresponding to 3.2-3.6GHz of tuning frequency, is implemented in 0.18[micro]m CMOS technology. The phase noise of the SIPC QVCO architecture simulated at 1MHz of offset frequency is indicated to be-114.3dBc/Hz, while dissipating 11.0mW of core circuit power. Key words: Phase noise, pMOS varactor, Quadrature voltage controlled oscillator (QVCO), Source injection parallel coupled VCO (SIPC-QVCO), Stacked spiral inductor, INTRODUCTION Increasing demand for higher capacity in the growing LAN (WLAN) market has led to the introduction of a new generation of WLAN standards using more spectrally efficient modulation techniques. [...]

The design of electrically steerable traveling wave microstrip antenna arrays is presented. Varactor diode based phase shifters implemented on the same metallic layer as the patch elements are used to provide a variable progressive phase shift in the array. Two antennas for the 5.8 GHz ISM band, manufactured as single layer printed designs on a standard PTFE soft substrate, are demonstrated. A ten-element beam-tilting vertical array using transmission type phase shifters is realized, yielding between 11.8 to 13.9 dBi gain for the 0[degrees] to 11[degrees] beam tilt tuning range. Using wide phase tuning range reflection type phase shifters a five-element horizontally scanning array with -32[degrees] to 32[degrees] steering range and 10.9-11.3 dBi gain has been realized. Index Terms--Microstrip antennas, microwave phase shifters, phased arrays, traveling wave antennas.

The analysis and systematic design procedure for multiconductor coupled-line Marchand baluns are presented in this paper. A simple two-conductor coupled-line model is used to analyze the Marchand balun and simplify the analysis significantly. Two monolithic balanced frequency doublers with miniature Marchand baluns are implemented to verify the design procedure. Both the chips achieve the smallest chip sizes at their operating frequencies with comparable performance. Index Terms--Balun, diode, frequency doubler, Marchand balun, monolithic microwave integrated circuit (MMIC).

A diode-pumped injection-seeded Nd:YAG laser system with an average output power of 38 W is described. The laser operates at 300 Hz with pulse energies up to 130 mJ. The temporal pulse shape is nominally flat in time and the pulse width is user selectable from 350 to 600 ps. In addition, the spatial profile of the beam is near top hat with contrast OCIS codes: 140.0140, 140.3280, 140.3480, 140.3530, 140.3580.

A new digital-to-analog converter (DAC) structure employing Schottky diode samplers has been developed for very high-speed operation. Instead of switching used for conventional DACs, sampling of a digital bit stream is employed to retrieve the analog signals based on sampling theory. The sampled signals are added using an R-2R resistive ladder network. The samplers are designed to provide impedance matching for reflected signals. The DAC was fabricated as a hybrid circuit, and it achieved 1 Gs/s. Due to its transmission-line architecture, our design is scalable for use at much higher frequencies, as well as higher resolutions. Index Terms--Digital-analog conversion, digtial-to-analog converter (DAC), sampler, Schottky diode.

In recent years, the electrical load demand in automobiles has been increasing steadily due to the usage of several subsystems to improve engine performance, passenger comfort, and safety. The current production Lundell alternator is not able to meet the future growing power demand due to its inherent design limitations. Therefore, an efficient, high-power generation system is needed to meet the growing electric power demand in automobiles. The recent trend to adopt the 42-V power system in automobiles allows one to add more subsystems in an efficient way. In this paper, a three-phase 42-V 4-kW induction-machine-based automotive power generation scheme is proposed to meet the future electrical power demand in automobiles. This scheme uses a low-cost diode bridge rectifier directly connected to the induction machine to transfer active power to the battery and the load. The excitation to the machine is supplied by means of a low-power pulsewidth-modulation (PWM) inverter to control the output voltage of the generator connected to the diode bridge rectifier. This paper presents a new control methodology to regulate the output voltage of an induction generator directly connected to a diode bridge rectifier by controlling the auxiliary PWM inverter. The simulated performance results of a 4-kW 42-V induction generator scheme at various speeds and loads are presented. Index Terms--Automotive power generation, diode bridge rectifier, 42-V system, induction machine, pulsewidth-modulation (PWM) inverter, reactive power control, voltage control.

The monolithic integration of tunneling diodes (TDs) with other semiconductor devices such as high electron-mobility transistors (HEMTs) or HBTs, creates novel quantum functional nonlinear devices and circuits with unique properties: the negative differential resistance and the extremely low dc power consumption. In this paper, we present a family of InP-HEMT-TD-based voltage-controlled oscillators operating in the 4-6-GHz band suitable for wireless applications, along with an effective analytical treatment of the stability issues. Prototypes having different circuit topologies of HEMT-TD devices have been designed and fabricated. The circuits generated an output power in the range of -11 to -18 dBm when operated at a bias current of 1.75 mA at 500 mV. Phase noise characteristics and tuning capability of the circuit configuration have been experimentally determined. The maximum tuning range of 150 MHz and the maximum single sideband-to-carrier ratio of -97 dBc/Hz at 200 kHz have been achieved. Index Terms--Microwave voltage-controlled oscillator (VC), monolithic microwave integrated circuit (IC), quantum-well device.

The 4H-SiC JBS diode offers nearly zero reverse-recovery charge. The use of the SiC JBS diode in hard switching applications eliminates the reverse recovery and the associated transistor turn-on current, as indicated by the experimental results.

Three-phase uncontrolled rectifiers with capacitive filters are highly sensitive to line voltage unbalance, drawing significantly unbalanced line current even under slightly unbalanced voltage condition. This paper presents an analysis of this 'unbalance amplification effect' for an ideal rectifier circuit without ac- and dc-side inductors. A novel way of modeling the voltage unbalance is established by introducing a deviation voltage superimposed on balanced three-phase line voltages, which allows simplified analysis of the rectifier operation. With proper approximations, closed-form expressions for symmetrical components of the fundamental line current and correspondingly the current unbalance factor are derived in terms of the voltage unbalance factor, filter reactance, and load current. The equivalent rms value of the third harmonic current is also derived. The analysis clearly shows high sensitivity of the current unbalance to the voltage unbalance, and provides a basic guideline for rectifier circuit design. The validity of the analysis is confirmed by simulation. Index Terms--Diode rectifier, harmonics, power quality, unbalance, unbalance factor, uncontrolled rectifier.

This paper concerns neutron detection below 500-keV energies. The paper studies numerically simulated responses from thermalized neutrons. These neutrons are induced by monoenergetic dose equivalent neutron beams ranging between 14 MeV and 1 eV. Results are first discussed against several moderating stack efficiencies. The discussion analyzes the lowest standard deviation relative to the mean thermalized flux calculated over several incident neutron energy bands of which upper values decrease from 14 MeV to 100 keV. The simulated responses show near 50% response accuracy if monitoring neutrons in the range 1 eV to 100 keV with a small 1.5-cm radius 5-cm thick polyethylene cylinder. Adding neutron converter foils, the efficiency is then calculated against secondary photon detection. An overlap between fast neutron detection efficiencies and those at lower energies is found to be possible, so that similar diodes can be used for both recoil protons and radiative photon detection. Index Terms--Epithermal, neutron, numerical simulation, personal dosimetry, room temperature diode, silicon, thermal.

Flat-panel detectors using amorphous silicon p-i-n diodes have been developed for chest and therapeutic portal imaging. In radiation therapy, an imaging device is exposed to a high radiation dose. The radiation damage affects the leakage current of diode and may decrease the whole system performance. In this research, we have investigated the radiation damage to the leakage current of a-Si: H diode made by plasma-enhanced chemical vapor deposition (PECVD) and ion-shower doping method, and studied the effect of a copper plate generally used in portal imaging to increase the efficiency of detector. We measured the transient current of diodes between radiation exposures, and obtained the leakage current of diodes as a function of absorbed dose. The two diodes show similar behavior when used with a copper plate. Leakage current shows linear dependence on the absorbed dose, and threshold dose was observed when a copper plate was placed on the top. Ion-shower diode shows higher rate of current increase, which is considered to originate from the intrinsic junction properties. Index Terms--Amorphous silicon diode, ion-shower doping, leakage current, radiation damage.

Modulation strategies for multilevel inverters have typically focused on synthesizing a desired set of three phase sinusoidal voltage waveforms using a fixed number of dc voltage levels. This results in the average current injection and hence the net power drawn from the multiple dc bus terminals to be unmatched and time varying. Subsequently, the dc-bus voltages are unregulated, requiring corrective control action to incorporated. In this paper, the principle of reciprocity transposition in introduced as a means for modeling the dc-bus current injection simultaneously as the modulation strategy is formulated. Furthermore, a new sinusoidal pulsewidth-modulation strategy that features constant and controllable current injection at the dc-bus terminals while maintaining output voltage waveform quality is introduced. The proposed strategy is general enough to be applied to converters with an even number of levels and an odd number of levels. Analytical results comparing the performance of the proposed modulator with a conventional multiple carrier modulator are presented for example multilevel converters with four and five levels. Computer simulation results verifying the analytical results are presented for a four-level converter. Index Terms--Multilevel systems, power conversion, pulsewidth modulation.

The converter topologies identified as diode-clamped multilevel (DCM) or, equivalently, as multipoint clamped (MPC), are rarely used in industrial applications, owing to some serious drawbacks involving mainly the stacked bank of capacitors that constitutes their multilevel dc link. The balance of the capacitor voltages is not possible in all operating conditions when the MPC converter possesses a passive front end. On the other hand, in ac/dc/ac power conversion, the back-to-back connection of a multilevel rectifier with a multilevel inverter allows the balance of the dc-link capacitor voltages and, at the same time, it offers the power-factor-correction capability at the mains ac input. An effective balancing strategy suitable for MPC conversion systems with any number of dc-link capacitors is presented here. The strategy has been carefully studied to optimize the converter efficiency. The simulation results related to a high-power conversion system (up to 10 MW) characterized by four intermediate dc-link capacitors are shown. Index Terms--High-power drives, medium-voltage drives, multipoint-clamped converters, multilevel converters, pulsewidth modulation.

Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate dc sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed. Index Terms--Medium-voltage drives, multilevel converter, multilevel inverter, power converters.

The Multi-angle Imaging SpectroRadiometer (MISR) consists of nine cameras pointing from nadir to an extreme of 70.5[degrees] in the view angle. It is a pushbroom imager with four spectral bands per camera. Instrument specifications call for each camera to be calibrated to an absolute uncertainty of 3 % and to within 1% relative to the other cameras. To accomplish this, the MISR instrument utilizes an on-board calibrator (OBC) to provide updates to the instrument gain coefficients on a bimonthly basis (i.e., once every two months). Spectralon diffuse panels are used in the OBC to provide a uniform target for the nine MISR cameras to view. The radiometric scale of the OBC is established through the use of photodiodes. The stability of the MISR OBC system and its in-flight calibration are discussed in this paper. Index Terms--Calibration, photodiodes, radiometry.

We describe a stacked detector made of thin cadmium telluride (CdTe) diode detectors. By using a thin CdTe device, we can overcome the charge loss problem due to the small mobility and short lifetime of holes in CdTe or cadmium zinc telluride (CdZnTe) detectors. However, a CdTe detector with a thickness of more than 5 mm is needed for adequate detection efficiency for gamma-rays of several hundred keV. Good energy resolution and good peak detection efficiency are difficult to obtain using such a thick CdTe detector. The stacked detector enabled us to realize a detector with both high-energy resolution and good efficiencies for gamma rays up to several hundred keV. In order to verify this concept, we constructed a prototype made of ten layers of a 0.5-mm-thick CdTe diode detectors with a surface area of 21.5 mm x 21.5 mm. With this, we have achieved 5.3-keV and 7.9-keV energy resolution [full width at half maximum (FWHM)] at 356 keV and 662 keV, respectively, at the temperature of -20 [degrees]C. Index Terms--Cadmium telluride (CdTe), CdTe diode detector, cadmium zinc telluride (CdZnTe), stacked detector.

Solid-state devices have had a major impact on the development of microwave and millimeter-wave systems. Starting with development work dating back to the 1940s, a variety of two- and three-terminal device structures have been proposed, fabricated, and found their way into commercial and military applications. These devices have resulted in the realization of numerous systems that would not otherwise be possible. The device development effort has been closely linked to advances in semiconductor materials growth and processing technology. Many of the advanced device concepts can only be implemented with the advent of advanced materials growth technology, such as molecular-beam epitaxy, and fine-line lithography techniques, such as electron-beam lithography. Advanced materials technology has also provided the ability to fabricate heterostructures that permit the advantages of multiple material layers to be optimized for device applications. High-performance diodes and transistors are now available for use from UHF into the millimeter-wave spectrum, approaching terahertz frequencies. The development, operating principles, and state-of-the-art of various diode and transistor structures are reviewed. Index Terms--Active device, diode, electron beam, heterostructure, lithography, MBE, microwave, molecular-beam epitaxy, semiconductor, solid-state device, transistor.

The rod-pinch diode is a cylindrical pinched-beam diode that provides an intense pulsed small-diameter bremsstrahlung source for radiography. For this work, the diode consists of a 1- to 6.4-mm-diameter anode rod that extends through the hole of an annular cathode. After exiting the cathode, wider anodes taper down to a 1 mm diameter. All of the anode rods then have a 1-mm-diameter tungsten tip that is usually tapered to a point. Rod-pinch diodes with anode rods of different materials, lengths, and diameters were powered by the Gamble H generator at peak voltages of 1.0 to 1.8 MV and peak currents of 30 to 60 kA. The radiation was characterized with temporally and spatially resolved X-ray diagnostics. Pinhole-camera images and time-resolved pin-diode measurements indicate that the radiation is emitted primarily from the vicinity of the rod tip. The dose measured with thermoluminescent detectors through a plexiglass transmission window ranges from 0.6 to 2.8 R at 1 m from the rod tip and the dose/charge scales faster than linearly with the diode voltage. The full-width at half-maximum (FWHM) of the radiation pulse is 30 to 50 ns. The size of the radiation source is determined by measuring its edge spread function. The source diameter, defined here as the FWHM of the derivative of the edge spread function, decreases from 2 mm for a 6.4-mm-diameter rod to 1 mm or less for a 1-mm-diameter rod. Analysis suggests that the central portion of the radiation distribution at the source can be approximated by a uniformly radiating circular disc. Index Terms--Critical current, electron beam diode, pinching, pulsed power, radiography, space-charge-limited current.

Byline: Yuji Aburakawa (1), Hiroyuki Ohtsuka (1) Keywords: subcarrier optical transmission; superluminescent diode; intensity noise; predistorter; superimposed subcarrier modulation; optical reflection Abstract: It is important to consider optical reflectionconditions when designing fiber-oriented wirelessaccess systems around subcarrier optical transmissionsince the noise characteristic can be significantlydegraded by optical reflection, especially if narrowspectral width devices are used. The superluminescentdiode (SLD) offers stable noise and 3rd-orderintermodulation distortion (IM3) characteristics thatfollow the ideal cubic law, even under multipleoptical reflection. The SLD-predistorter combinationis proposed as a way to overcome the SLD's narrowdynamic range. It is experimentally found that thepredistorter reduces IM3 by 8 dB. The receiversensitivity of a practical system that uses theSLD-predistorter combination is discussed from theviewpoint of overall design. A superimposedsubcarrier modulation (SSM) technique is also proposedin order to reduce the reflection noise. Weexperimentally confirm that the SSM technique reducesthe noise degradation and provides stable opticaltransmission. An SSM design methodology is presentedthat takes both noise and linearity into account. TheSLD-predistorter and the SSM scheme make it possibleto realize stable transmission performance and widerdynamic range in the presence of optical reflection. Author Affiliation: (1) NTT Wireless Systems Laboratories, 1-1, Hikarino-oka, Yokosuka, Kanagawa, 239-0847, Japan Article History: Registration Date: 27/09/2004

Many new chaotic systems with algebraically simple representations are described. These systems involve a single third-order autonomous ordinary differential equation (jerk equation) with various nonlinearities. Piecewise linear functions are emphasized to permit easy electronic implementation with diodes and operational amplifiers. Several new simple and robust chaotic electrical circuits are described and evaluated.

We propose a novel self-mixing laser diode speckle velocimeter based on autocorrelation. The self-mixing laser diode launches and receives reflected light from a moving surface that has a random reflection profile. Some portion of the scattered light backcouples into the laser cavity and causes random intensity variations in the form of speckle signals. These speckle signals obtained from a self-mixing laser diode are processed by use of autocorrelation. The linear relation between the velocity and the reciprocal of the correlation time of the speckle intensity fluctuations allows us to determine the velocity easily if proper calibration is performed. The range of the investigated velocity is 20-450 mm/s. For an aluminum target that moves at a velocity of 350 mm/s, the measurement error is less than 2%.

The article discusses using a diode laser to probe the gain spectrum of a chemical oxygen-iodine laser. Topics include absorption spectrum, gain linewidth, and cavity temperature.

A MOSFET, connected as a diode with gate and drain short circuited and biased in saturation mode, is proposed as a substitute for the high-value feedback resistor to provide dc feedback and signal reset in integrated charge amplifiers with BJT input transistors. This paper describes the MOSFET design rules to set the desired value of the discharge time constant, to minimize its noise contribution, and to operate it in a low voltage circuit. The behavior of the MOSFET as an almost fixed value resistor is evidenced by the single time-constant discharge of the signal at the output of a prototype preamplifier for fast ( Index Terms - Integrated circuit design, MOSFET circuit, noise.

The characteristics of a fabricated micro mirror were determined using an optical measurement-system. The system consisted of a helium-neon laser, a p-i-n lateral-effect photodiode, and other fundamental optical elements. For testing, we used a micro mirror array (1 x 4) in which each mirror was composed of a mirror plate, two torsional flexure hinges, two address electrodes, and two support posts. A mirror plate was designed to a size of 100 x 110 x 1.5 [[[micro]meter].sup.3] and the hinge size was 20 [[micro]meter] long, 5 [[micro]meter] wide, and 0.5 [[micro]meter] thick. The micro mirror array was fabricated using micromachining technology and a lithography-galvanoformung-abformung-like process using nickel electroplating. The variation in the mirror's deflection angle with applied voltage was measured as a static characteristic. The downward threshold voltage of the 0.5-[[micro]meter] thick hinge was 48 V. The step response time, as a dynamic characteristic, was 21.8 [[micro]seconds] when a 64-V step voltage higher than the downward threshold voltage was applied to an address electrode. The lifetime of the fabricated micro mirror was tested for both unidirectional and bidirectional operation. Index Terms - Lifetime, micro mirror array, optical measurement system, p-i-n lateral-effect photodiode.

Visible-light-emitting diodes of three different colors have been used to detect an absorbing compound (potassium permanganate) in trace quantities in aqueous solution. Photothermal absorption in a closed cell caused deflection of a water meniscus held at a small pinhole. The displacement was monitored with optical-fiber interferometry. The technique was limited by LED emission intensities and environmental acoustic noise, giving minimum detectable absorption coefficients of 2 x [10.sup.-4] [cm.sup.-1] at 478 and 658 nm and 3 x [10.sup.-4] [cm.sup.-1] at 524 nm. The magnitude and form of meniscus deflection signals were shown to be in good agreement with theory.

Silicon carbide bipolar diodes were fabricated by nitrogen implantation, annealed at 1100 degrees C, passivated with a deposited oxide and characterized. The quality of the junction was analyzed using capacitance and current voltage measurements. Three peaks were observed using admittance spectroscopy, with two corresponding to nitrogen and aluminium shallow levels. The third peak was studied in depth using deep level transient spectroscopy.

A new three-phase high-quality boost rectifier system is introduced in this paper. The single switch and input-diode bridge in this rectifier operate with zero-current switching (ZCS) while the dc-side diode operates with zero-voltage switching (ZVS). The semiconductor stresses are constant and independent of load-current variations. A multiresonant scheme is used to achieve this property. Line-current waveforms of low-harmonic content are obtained naturally by these rectifiers. Simulation and experimental results are supplied to confirm the validity of the proposed concept. Index Terms - High power factor, low-harmonic rectifer, ZCS resonant rectifier.

We report on the fabrication and characterization of a microstrip x-ray detector with a very high dynamic range based on GaAs diodes. The detector material was grown by Liquid Phase Epitaxie (LPE) and showed a typical n-type background doping of 2 x [10.sup.13][cm.sup.-3]. The thickness of the epitaxial layer was between 75 and 200 [[micro]meter]. At 27 V bias the thickness of the active layer was 45 [[micro]meter]. The detector consists of 48 strips with a pitch of 50 [[micro]meter] and a strip length of 3 mm. No cross talk between the diodes was observed. Measurements using a micro focus x-ray tube showed a mean quantum efficiency of the detector for the energy range between 35 and 100 keV of 9.5 %. The maximum contrast was a factor of 400 between the signal in areas that were not shaded with lead and areas that were shaded with 5 mm lead. The maximum counting rate without amplifier saturation was 4.5 x [10.sup.5] per second, which gives a dynamic range of 4.5 x [10.sup.5] above 25 keV. The high dynamic range of this kind of x-ray detectors makes them very interesting for non destructive material testing.