Showing papers on "Power density published in 1998"

Intermediate Temperature Solid Oxide Fuel Cells Using a New LaGaO3 Based Oxide Ion Conductor I. Doped as a New Cathode Material

Abstract: ‐based perovskite oxides doped with Sr and Mg exhibit high ionic conductivity over a wide range of oxygen partial pressure. In this study, the stability of ‐based oxide was investigated. The ‐based oxide was found to be very stable in reducing, oxidizing, and atmospheres. Solid oxide fuel cells (SOFCs) using ‐based perovskite‐type oxide as the electrolyte were studied for use in intermediate‐temperature SOFCs. The power‐generation characteristics of cells were strongly affected by the electrodes. Both Ni and (Ln:rare earth) were suitable for use as anode and cathode, respectively. Rare‐earth cations in the Ln site of the Co‐based perovskite cathode also had a significant effect on the power‐generation characteristics. In particular, a high power density could be attained in the temperature range 973–1273 K by using a doped for the cathode. Among the examined alkaline earth cations, Sr‐doped exhibits the smallest cathodic overpotential resulting in the highest power density. The electrical conductivity of increased with increasing Sr doped into the Sm site and attained a maximum at . The cathodic overpotential and internal resistance of the cell exhibited almost the opposite dependence on the amount of doped Sr. Consequently, the power density of the cell was a maximum when was used as the cathode. For this cell, the maximum power density was as high as 0.58 W/cm2 at 1073 K, even though a 0.5 mm thick electrolyte was used. This study revealed that a ‐based oxide for electrolyte and a ‐based oxide for the cathode are promising components for SOFCs operating at intermediate temperature.

Optical Studies of Individual InAs Quantum Dots in GaAs: Few-Particle Effects

Abstract: Optical emission from individual strained indium arsenide (InAs) islands buried in gallium arsenide (GaAs) was studied. At low excitation power density, the spectra from these quantum dots consist of a single line. At higher excitation power density, additional emission lines appeared at both higher and lower energies, separated from the main line by about 1 millielectron volt. At even higher excitation power density, this set of lines was replaced by a broad emission peaking below the original line. The splittings were an order of magnitude smaller than the lowest single-electron or single-hole excited state energies, indicating that the fine structure results from few-particle interactions in the dot. Calculations of few-particle effects give splittings of the observed magnitude.

Method of polishing CVD diamond films by oxygen plasma

Abstract: According to a first aspect of the present invention a method for polishing the surface of a diamond film with a low power density plasma in a reactor comprising the steps of disposing O2 gas and a fluorinated gas such as SF6, CF4, NF3, and C2F6 in the reactor, providing power to the reactor so that the power density in the reactor is between about 1.0 watts/cm2 and about 1.1 watts/cm2 for a first duration, and maintaining temperature in the reactor at between about 200° to about 400°. According to a second aspect of the present invention a method for polishing the surface of a diamond film with a high power density plasma in a reactor comprising the steps of disposing of a sputter gas such as Ar, O?2? or N2 in the reactor, providing power to the reactor so that the power density in the reactor is between about 3.0 watts/cm?2? and about 7.5 watts/cm2 for a first duration, and performing a sputter etch, disposing O?2? gas and a fluorinated gas such as SF6, CF4, NF3 and C2F6 in the reactor, and providing power to the reactor so that the power density in the reactor is between about 1.5 watts/cm?2? and about 3.0 watts/cm2 for a second duration.

`Triggerless' triggering of vacuum arcs

Abstract: Vacuum arcs can be initiated without external means of power enhancement at the cathode surface (by using a high-voltage trigger, laser triggering, and so on). Arc initiation by simply applying the relatively low voltage of the arc power supply is possible if the cathode-anode-separating insulator is coated with a conducting layer and the current at the layer-cathode interface is concentrated at one or a few contact points. The local power density at these contact points can exceed which is sufficient for plasma production and thus arc initiation. This `triggerless' principle has been tested successfully with a large number of cathode materials. One extended test was performed with titanium and more than pulsed vacuum arc initiations have been obtained.

High-power microwave 0.25-μm gate doped-channel GaN/AlGaN heterostructure field effect transistor

Abstract: We report on the high-power performance of the 0.25-/spl mu/m gate Doped-Channel GaN/AlGaN Heterostructure Field Effect Transistors (DC-HFETs). At a drain bias voltage of 18 V and drain bias current of 46 mA, these 100-/spl mu/m wide devices exhibit high gain at 8.4 GHz with a power density reaching 1.73 W/mm. The devices also display high gain at moderate power over a wide range of frequencies. This high gain at high frequency is a result of an optimal doping level in the AlGaN layer that gives rise to a high sheet charge density while maintaining a high-channel electron mobility. These results demonstrate the excellent microwave power capability of the GaN/AlGaN based heterostructure field effect transistors.

A method and apparatus for magnetically enhanced sputtering

Abstract: In magnetically enhanced sputtering, pulses are applied having a very high instantaneous power, of the order of at least 0.1 kW-1 MW. In such sputtering regions (23) exist in which electrons are trapped by the magnetic field generated by magnets (17) cooperating with the electric field between the anode being part of the wall (5) enclosing the chamber in which sputtering is performed and the cathode which at the same time is the target (9), from which material is to be sputtered. An ionization of the gas in the chamber will then for lower applied power occur preferably in those regions (23) causing a non-uniform erosion of the target (9). For very high power in the pulses or power density in the pulses the gas in said regions and in regions adjacent thereto will enter another state of fully ionization, which considered in energy terms is located above the unwanted state of an electric arc which is formed for a lower supplied power. The region (27) in which this another state exists will be more homogeneous and have a wider extension than the ionized regions (23) produced for a lower supplied power. This results in a more uniform erosion of the target (9) and a more uniform coating of the substrate (13). The high power pulses can also be used in sputtering ion pumps, allowing them to start pumping from moderately low pressures, e.g. in the range of 10-1-10-2 torr.

Preferential Vaporization during Laser Ablation Inductively Coupled Plasma Atomic Emission Spectroscopy

Abstract: The Zn-to-Cu ratio in brass was measured by laser ablation inductively coupled plasma atomic emission spectroscopy. The influence of laser beam properties (pulse width, wavelength, and power density) on fractional laser ablation was investigated. The behavior of the Zn/Cu ratio vs. laser power density shows that there are different mechanisms influencing ps and ns laser ablation. With the use of a 30 ns pulse duration from an excimer laser, thermal vaporization appears to be the dominant process in the low-power density region. The Zn/Cu ratio approaches stoichiometry at higher power density, but the ablated mass still remains Zn rich. With a 35 ps pulse Nd:YAG laser, a nonthermal mechanism appears to govern the laser ablation process. When a 3 ns Nd:YAG laser is used, both thermal and nonthermal processes exist. For both 3 ns and 30 ps Nd:YAG lasers, stoichiometric ablation can be achieved at higher power densities.

High power density solid oxide fuel cell having a graded anode

Abstract: The present invention concerns a high power density solid oxide fuel cell having a cathode, electrolyte and graded porous anode. The graded porosity of the anode allows easy transport of fuel gases thereby minimizing concentration polarization. Power densities of about 1.8 W/cm2 at 800° C. and about 0.8 W/cm2 at about 650° C. have been achieved with graded porous anodes as thick as 0.75 mm. These fuel cells having a graded porous anode are more durable and mechanically reliable than those found in the art.

Stable relativistic/charge-displacement channels in ultrahigh power density (≈1021 W/cm3) plasmas

Abstract: Robust stability is a chief characteristic of relativistic/charge-displacement self-channeling. Theoretical analysis of the dynamics of this stability (i) reveals a leading role for the eigenmodes in the development of stable channels, (ii) suggests a technique using a simple longitudinal gradient in the electron density to extend the zone of stability into the high electron density/high power density regime, (iii) indicates that a situation approaching unconditional stability can be achieved, (iv) demonstrates the efficacy of the stable dynamics in trapping severely perturbed beams in single uniform channels, and (v) predicts that ≈104 critical powers can be trapped in a single stable channel. The scaling of the maximum power density with the propagating wavelength λ is shown to be proportional to λ−4 for a given propagating power and a fixed ratio of the electron plasma density to the critical plasma density. An estimate of the maximum power density that can be achieved in these channels with a power of ≈2 TW at a UV (248 nm) wavelength gives a value of ≈1021 W/cm3 with a corresponding atomic specific magnitude of ≈60 W/atom. The characteristic intensity propagating in the channel under these conditions exceeds 1021 W/cm2.

A high-power and high-efficiency monolithic power amplifier at 28 GHz for LMDS applications

Abstract: A high-power and high-efficiency monolithic power amplifier operating from 27.5 to 29.5 GHz is presented for local multipoint distribution service. Using 0.15-/spl mu/m InGaAs/AlGaAs/GaAs pseudomorphic high electron-mobility transistor devices, the two-stage power amplifier on 4-mil GaAs substrate demonstrated greater than 16-dB small-signal gain, 32-dBm (1.6 W) power with 35% power-added efficiency. The amplifier attained peak output power of 33.9 dBm (2.4 W) and peak power-added efficiency of 37%. At the peak power level, the amplifier exhibited power densities in excess of 640 mW/mm, which is the highest output power density attained by Ka-band monolithic power amplifiers. At lower drain voltage, the amplifier attained 43% power-added efficiency with 30-dBm output power.

Optical and electrical properties of R.F. magnetron sputtered ZnO:Al thin films

Abstract: Optical and electrical properties of Al-doped ZnO films, deposited by R.F. magnetron sputtering, have been investigated as a function of preparation conditions in an attempt to develop transparent films with low electrical resistivity. The electrical resistivity as well as the Hall mobility of sputtered films depend on the R.F. power density and thickness of the films when it is less than about 300 nm. The free carrier concentration is almost independent on the film thickness and the R.F. power. The optical transmission of the films in the visible range does not depend on the thickness as well as on the R.F. power and is about 90% from the substrate transmission there. In the near-infrared, where the absorption is due to free carriers, the transmission depends strongly on the film thickness and on the preparation conditions.

Electron gun and collector design for 94-GHz gyro-amplifiers

Abstract: This paper presents the electrical design of a magnetron injection gun and collector for high peak and average power TE/sub 01/ W-band gyro-amplifiers. The magnetron injection gun design employs an optimized double-anode geometry and a cathode angle of 500 to achieve superior beam optics that are relatively insensitive to electrode misalignments and field errors. A transverse relative velocity spread of 1.6% at a velocity ratio of 1.5 is obtained in simulations for a 6-A 65-kV beam. Cathode edge emission was modeled, found to produce a major effect on velocity spread, and will be eliminated by nonemissive cylinders affixed to the cathode. The collector, which also serves as the output waveguide, is designed to minimize the required collector length while avoiding excessive power loading on the collector surface. An average power density of less than 640 W/cm/sup 2/ on a 3.25-cm-diameter collector is achieved for 91-kW average beam power. Both the gun and collector are currently under construction.

6.1 W continuous wave front-facet power from Al-free active-region (λ=805 nm) diode lasers

Abstract: Al-free active-region diode lasers grown by low-pressure, metal-organic chemical vapor deposition and emitting at λ=805 nm have been optimized for high continuous wave output power. The 1-mm-long devices consisting of an InGaAsP/In0.5Ga0.5P/In0.5(Ga0.5Al0.5)0.5P laser structure have a threshold-current density, Jth, of 310 A/cm2 and relatively high values for the characteristic temperatures of the threshold current, T0 (135 K), and differential quantum efficiency, T1 (900 K). Lasers with 10%/90% coatings and a 100-μm-wide stripe provide a maximum cw output power of 6.1 W at a heatsink temperature of 10 °C. The devices fail due to catastrophic optical mirror damage (COMD), where the internal power density, PCOMD, is 17.4 MW/cm2; that is, twice that for conventionally facet-coated, 810 nm emitting, AlGaAs active-region diode lasers.

High power density electric drive for an hybrid electric vehicle

Abstract: This paper describes the electric drive system for an experimental hybrid electric vehicle 'Freedom'. The drive system is based on 4, PWM-VSI fed in-wheel PM brushless motors, using a novel PWM control strategy and a digital current phase angle control scheme that does not require a high resolution absolute position sensor. Each wheel of the vehicle is fitted with a 12-pole, 3-/spl phi/, PM motor with surface mounted Magnaquench magnets and an integral speed reducer packaged within the hollow rotor. Each PM motor is rated at 9 kW continuous (@3560 rpm) and 29 kW peak. The PM brushless motors had a trapezoidal EMF and were supplied with 120/spl deg/ quasi-square wave currents from the IGBT inverters operating at 18 kHz PWM frequency. The paper focuses on the development of the PWM-VSI inverters, the PWM strategy and the microcontroller system that implements the phase angle control scheme. Test results were provided on the performance of the electric drive. A new control strategy is outlined for controlling the braking torque when the battery is fully charged or when the motor speed exceeds the no-load speed. Two types of high power density inverter packages were developed for the Freedom vehicle. The Phase I system utilized forced air cooling to provide 32 kW peak power per inverter (@160 A pk) and Phase II system utilized direct liquid cooling to provide 45 kW peak power per inverter (@300 A pk). The liquid cooled system achieved an improvement of 2.5 times power density by weight and 4 times the power density by volume over the air cooled system.

An intermediate temperature solid oxide fuel cell utilizing superior oxide ion conducting electrolyte, doubly doped LaGaO3 perovskite

Abstract: LaGaO3-based perovskite oxide doped with Sr and Mg exhibits high ionic conduction over a wide oxygen partial pressure. In this study, the stability of the LaGaO3 based oxide was investigated. It became clear that LaGaO3 based oxide is very stable for reduction and oxidation. SOFCs utilizing LaGaO3-based perovskite type oxide for electrolyte were further studied for the decreased temperature solid oxide fuel cells. The power generation characteristics of cells were strongly affected by the electrode, both anode and cathode. It became clear that Ni and LnCoO3 (Ln: rare earth) are suitable for anode and cathode, respectively. Rare earth cations in the Ln-site of Co-based perovskite cathode also have a great effect on the power generation characteristics. In particular, high power density could be attained in the temperature range from 973 to 1273 K by using doped SmCoO3 for the cathode. The electrical conductivity of SmCoO3 increases with increasing Sr amount doped for the Sm site and attained the maximum at Sm0.5Sr0.5CoO3. The cathodic overpotential and the internal cell resistance exhibit almost opposite dependence on the amount of doped Sr. Consequently, the power density of the cell reaches a maximum when Sm0.5Sr0.5CoO3 is used for cathode. On this cell, the maximum power density is as high as 0.58 W/cm2 at 1073 K, although a 0.5 mm thick electrolyte is used. Therefore, this study reveals that the LaGaO3 based oxide for electrolyte and the SmCoO3 based oxide for cathode are promising for solid oxide fuel cells at intermediate temperature.

Laser glazing of plasma-sprayed zirconia coatings

Abstract: A CO2 laser with cylindrical focal lens has been used to glaze the surface layer of plasma-sprayed ZrO2-20wt% Y2O3/MCrAlY coatings. Both a continuous-wave laser and a pulsed laser were used in this study. Different parameter settings for power, travel speed, and pulse frequency were used, and their effects on the melting width, melting depth, coupling efficiency, microstructure, surface roughness, and process defects have been evaluated. Results show that the melting width of the glazed track was slightly smaller than the diameter of the raw beam. The melting depth increased with increasing energy density for both a continuous-wave laser and a pulsed laser. The coupling efficiency as about 40 to 65% for a continuous-wave laser, which increased with increasing laser travel speed, but decreased with an increase in energy density. The power density has no significant effect on coupling efficiency. Defects, such as bubbles or depressions, occur easily with a continuous wave laser. A high-quality glazed layer is successfully produced using a pulsed laser. The surface roughness of the plasma-sprayed ceramic coatings was significantly improved by laser glazing. Surface roughness decreased slightly as the pulse frequency increased for the glazed surface. Based on this study, proper processing parameters have been suggested.

Fast method for measuring power density distribution of non-circular and irregular electron beams

Abstract: A fast method for measuring the power density distribution of electron beams has been developed. The method employs a refractory metal disc containing regularly spaced radial slits and a Faraday cup to measure electron beam profiles as the beam is oscillated in a circular pattern over the disc. This beam profiling method can be used for real time focusing along a given beam sweep orientation by monitoring one of the beam profiles. When the focus setting is satisfactory, all of the beam profiles can then be stored for computed tomography (CT) reconstruction. The CT reconstruction renders an image of the powder density distribution and provides beam statistics as a permanent file for process control records. The process (taking ∼1 min to perform in its entirety using a conventional PC) was used to investigate the influence of focus setting on the power density distribution of 5 mA electron beams operating at accelerating voltages of 80 and 140 kv. Results of these tests show the effects of beam asti...

Tracking metallic objects by information incorporated therein

Abstract: The subject of the invention is method and device system for entering and retrieving information in the surface layer of objects made of solid matters. The information is entered with a (concentrated) beam directed to the surface and having a power density selected to induce permanent change at least in the surface layer of the material's structure in a way that the power density of the beam is smaller that the power density of the beam causing visible deformation, but bigger than that of the beam that causes (within the order of magnitude of the beam's diameter) inhomogeneities commensurable with the structural inhomogeneities generally present in the material. The invention can be used for all materials, the structure or internal stress of which can be modified with high energy density surface treatment (at the location of the treatment) (specially with the local laser treatment of ferromagnetic material).

Cascaded second-harmonic and sum-frequency generation of a CO2 laser by use of a single quasi-phase-matched GaAs crystal.

Abstract: Cascaded second-harmonic and sum-frequency generation were used to obtain the third harmonic of a CO(2) laser in a single quasi-phase-matched GaAs crystal. Both continuous-wave and pulsed regimes with a single-pass configuration were studied. The continuous case confirmed the good capability of the GaAs stack to bear high average power density. In the pulsed regime a 0.66% peak power conversion efficiency was achieved for the third harmonic when the laser was pumping at 8.2 MW/cm(2) , in fair agreement with theoretical predictions.

Process for fabricating SOI substrate with high-efficiency recovery from damage due to ion implantation

Abstract: First, oxygen ions of a high concentration are implanted into a silicon substrate 1, by which a high-concentration oxygen implanted layer 3 is formed. Subsequently, a heat treatment for about 4 hours at 1350° C. is carried out in an atmosphere of Ar with a 0.5% concentration oxygen for the formation of a buried oxide layer 5. Next, pulse laser annealing is performed for melting and recrystallization of the surface silicon layer. Pulsed laser beam is radiated at an energy density of 1200 mJ/cm2 or more. The pulsed laser beam is able to melt the semiconductor surface in several 10's nsec by virtue of its extremely large power density in irradiation of 107 W/cm2. By iterating this pulse laser annealing, the surface silicon layer iterates to melt and recrystallize, activating the activities of crystal defects, by which damage recovery based on crystal seeds is accomplished.

High power RF operation of AlGaN/GaN HEMTs grown on insulating silicon carbide substrates

Abstract: Excellent RF performance is reported for AlGaN HEMTs fabricated on electrically insulating SiC substrates. The transistors have an fmax = 42 GHz, and an ft = 15 GHz. At 10 GHz, 320 µm wide transistors had a total power of 900 mW with a gain of 6.5 dB, which corresponds to a power density of 2.8 W/mm.

High-power high-efficiency quasi-CW Sb-based mid-IR lasers using 1.9-/spl mu/m laser diode pumping

Abstract: Power efficiency is a critical issue for mid-infrared (mid-IR) semiconductor lasers. Previously, the highest power and efficiency 4-/spl mu/m laser was pumped with 0.98-/spl mu/m laser diode. This letter used 1.9-/spl mu/m diode pumping for better quantum defect ratio and heat flow geometry. A 3.7-/spl mu/m InAsSb-AlAsSb laser yielded a pump-power-limited 1.25-W single-ended output in 1-ms-long pulse with 6.5% net optical-to-optical efficiency, in contrast with a 0.67-W thermally limited output and 2.7% efficiency with 0.98-/spl mu/m diode pumping, at 70 K. The results are believed to represent the highest quasi-continuous-wave power from a single device, highest efficiency, and, scaled to the emitting aperture, highest power density for any 3-4-/spl mu/m semiconductor laser for 1-ms pulse and /spl ges/70 K.

Two-plane focusing of 30 keV undulator radiation.

Abstract: An imaging experiment using a two-plane focusing refractive lens made of aluminium and operated in the hard X-ray range is described. The lens is made of a series of 1 and 0.8 mm-diameter lenses drilled through a 2 mm aluminium plate. It is exposed to the white beam from an undulator with total power as high as 1.7 kW and normal-incidence power density of 100 W mm(-2). The measured r.m.s, size of the image is 0.12 x 0.06 mm at a photon energy of 30 keV. Theoretical estimates for the transmission, aperture and tolerance of alignment of such lenses are made. It is found that the aperture of the lens is dominated by photoelectric absorption (Compton scattering) in the low (high) energy range of the spectrum. Beryllium is the most promising material.

Power extraction investigations for a 10-kW-class supersonic COIL

Abstract: In a stable resonator configuration, the output power and the power density distribution of a chemical oxygen-iodine laser (COIL) were measured for various outcoupling geometries: Diaphragms with slit apertures of various size were introduced intracavity in front of the outcoupling mirror. The slit was placed at different positions along the flow axis. Furthermore, outcoupling mirrors of various reflectivity were used. For all experimental conditions the measured power density distribution at the outcoupling mirror reveals strong symmetry effects: The beam patterns are always symmetric to the resonator axis. The beam shape and the beam size are defined by the hardware aperture that is nearest to the resonator axis. As a function of the slit width, the laser output power saturates well before the aperture of the resonator is fully opened. Fifty percent of the maximum output power were achieved at a width of 6 mm only. Good agreement is found between the measured data and theoretical calculations, when taking into account the specific flow conditions. The data highlight the significance of deactivation processes and the strong iodine repumping mechanism within the cavity. For standard operating conditions a Rigrod type analysis reveals a small signal gain that is nearly constant throughout the cavity exceeding 1.3% cm-1. The outcoupling reflectivity for the maximum power output was found at a value of about 94%. These experimental data agree well with a simplified analytic model for gain saturation and power extraction as derived by G. D. Hager et al.

Control of consumed power of air conditioner

Abstract: PROBLEM TO BE SOLVED: To achieve the energy saving and the power saving by obtaining an amount of power consumption in a given period by measuring a total consumed electric power of a plurality of air conditioners and obtaining the stop time for stopping respective air conditioner depending on the amount of power consumption, in a method for controlling the consumed power of a plurality of air conditioners connected by a common electric power supply line. SOLUTION: To measure the consumed power making use of a real quantity (demand) meter installed by a power company, the uptake of pulses is started. Here, within a time limit of 30 minutes, the transition of electric energy (prediction electric power) is calculated with a sampling time of approximately 1 second and this prediction electric power and the set electric power are compared. In case the predicted electric power exceeds the set electric power, the present electric power reduction rate is elevated by 10% (one step), for example. When the predicted electric power falls within the set electric power due to such an elevation of the rate, a control signal is generated for elevating the electric power reduction rate by one step. However, in case the predicted electric power does not fall within the set electric power even when the electric power reduction rate is elevated to the limit, all stop signals are outputted. COPYRIGHT: (C)1999,JPO