Showing papers on "Power density published in 1997"

High power electrochemical capacitors based on carbon nanotube electrodes

Abstract: Carbon nanotube sheet electrodes have been prepared from catalytically grown carbon nanotubes of high purity and narrow diameter distribution, centered around 80 A. Our study shows that the electrodes are free-standing mats of entangled nanotubes with an open porous structure almost impossible to obtain with activated carbon or carbon fiber. These properties are highly desirable for high power and long cycle life electrochemical capacitors. Specific capacitances of 102 and 49 F/g were measured at 1 and 100 Hz, respectively, on a single cell device with 38 wt % H2SO4 as the electrolyte. The same cell had a power density of >8000 W/kg.

Shock waves from a water-confined laser-generated plasma

Abstract: Generation of a high amplitude shock wave by laser plasma in a water confinement regime has been investigated for an incident 25–30 ns/40 J/λ=1.064 μm pulsed laser beam. Experimental measurements of temporal and spatial profiles of induced shock waves for this regime of laser shock processing of materials were performed using a velocimetry interferometer system for any reflector system. Above a 10 GW/cm2 laser intensity threshold, a saturation of the peak pressure is shown to occur while the pressure pulse duration is reduced by parasitic plasma occurring in the confining water. The observation of the interaction zone with a fast camera system shows that this breakdown plasma, which mainly occurs at the very surface of the water rather than within the water volume, limits the efficiency of the process. This plasma absorbs the incident laser energy, and the power density reaching the target gradually decreases with increasing power densities while the shock-wave duration is correspondingly reduced. Both pr...

Erbium-doped phosphate glass waveguide on silicon with 4.1 dB/cm gain at 1.535 µm

Abstract: Erbium-doped multicomponent phosphate glass waveguides were deposited by rf sputtering techniques. The Er concentration was 5.3×1020 cm−3. By pumping the waveguide at 980 nm with a power of ∼21 mW, a net optical gain of 4.1 dB at 1.535 μm was achieved. This high gain per unit length at low pump power could be achieved because the Er–Er cooperative upconversion interactions in this heavily Er-doped phosphate glass are very weak [the upconversion coefficient is (2.0±0.5)×10−18 cm3/s], presumably due to the homogeneous distribution of Er in the glass and due to the high optical mode confinement in the waveguide which leads to high pump power density at low pump power.

Reduced-Temperature Solid Oxide Fuel Cell Based on YSZ Thin-Film Electrolyte

Abstract: A planar thin-film solid oxide fuel cell has been fabricated with an inexpensive, scalable, technique involving colloidal deposition of yttria-stabilized zirconia (YSZ) films on porous NiO-YSZ substrates, yielding solid oxide fuel cells capable of exceptional power density at operating temperatures of 700 to 800°C. The thickness of the YSZ film deposited onto the porous substrate is approximately 10 Rim after sintering, and is well bonded to the NiO/YSZ substrate. Ni-YSZ/YSZ/LSM cells built with this technique have exhibited theoretical open-circuit potentials (OCPs), high current densities, and exceptionally good power densities of over 1900 mW/cm 2 at 800°C. Electrochemical characterization of the cells indicates negligible losses across the Ni-YSZ/YSZ interface and minor polarization of the fuel electrode. Thinfilm cells have been tested for long periods of time (over 700 h) and have been thermally cycled from 650 to 800°C while demonstrating excellent stability over time.

Rechargeable lithium batteries

Abstract: The market for lithium batteries is undergoing a rapid expansion as new applications demand higher densities of energy and power storage. Simple theoretical estimates show that lithium and lithium ion cells can reach specific energies of 880 and 500 W h kg–1 respectively. With an electrolyte conductivity above 3 × 10–4 S cm–1 and thickness below 0.01 cm, a power density of 300 W dm–3 can be obtained without excessive energy losses. Diffusion in porous or polymer composite electrodes is enhanced by an interpenetrating electrolyte provided the electrode particles are small. Batteries using transition metal oxide positive electrodes and carbon negative electrodes are expected to give practical specific energies up to 180 W. h kg–1 including packaging and other essential additional materials in the near future.

Poly(3,4‐ethylenedioxythiophene) as Electrode Material in Electrochemical Capacitors

Abstract: We have investigated the conjugated polymer poly(3,4-ethylenedioxythiophene) as electrode material in electrochemical supercapacitor. The conjugated polymer is prepared by chemical polymerization in the form of thin films on nonconducting plastic substrates. One film is electrochemically reduced to the neutral state, while the other is kept in the as-prepared, doped state. The films are thin immersed in a liquid organic electrolyte. In the charged state the supercapacitor cell voltage is 0.8 V and the energy density is measured to 1 to 4 Wh/kg of active electrode material, depending on the current density used during discharge. The power density (delivered energy/discharge time) also depends on the current density and at the highest current densities investigated (1 mA/cm 2 ) it reaches 2.5 kW/kg of active electrode material.

Mathematical modeling of melting during laser materials processing

Abstract: Melting is encountered in almost all laser materials processing. This article deals with a one-dimensional heat conduction problem to investigate the melting rate during laser materials processing. The problem is solved approximately to obtain a correlation among melt depth, power density, and laser irradiation time. Based on this correlation, the dynamics of melting, a relationship between the melt depth and power density and an average melting velocity are expressed by simple analytic formulas. These expressions are further simplified for high power densities (I⩾109 W/m2). The times to reach the melting and boiling temperatures at the surface of the workpiece are also calculated.

Method and system for dynamically power budgeting with device specific characterization of power consumption using device driver programs

Abstract: A computer system that provides device specific power characterizations for power control and budgeting functions is disclosed. The device driver programs of the computer system or a power characterizer of the system determines device specific power characterizations for corresponding devices under device specific controlled conditions. The device specific power characterizations are stored in persistent storage for subsequent use by power control and budgeting functions.

Electric vehicle power supply

Abstract: To obtain an electric vehicle power supply 10 having a high output power density and regenerative power density, and which is compact and lightweight wherein a first battery 12 whose regenerative power density increases with decrease of the SOC and a second battery 14 whose output power density increases with increase of the SOC are used as an electrical storage device, and control is performed so that the SOC of the first battery 12 is maintained low while the SOC of the second battery 14 is maintained high. The regenerative power density of the first battery 12 is therefore high, the regeneration current from the motor 32 is mainly stored by the first battery 12, and the force used to drive the motor 32 is mainly output by the second battery 14 which has a high output power density.

Stimulated emission from optically pumped GaN quantum dots

Abstract: Stimulated emission was observed from optically pumped GaN quantum dots in an AlxGa1−xN separate confinement heterostructure fabricated on 6H-SiC(0001) substrate by metal organic chemical vapor deposition. Nanostructural GaN quantum dots, with an average size of ∼10 nm width, ∼1–2 nm height, and density of ∼1011 cm−2, were self-assembled on the AlxGa1−xN cladding layer surface. The stimulated emission peak was observed at ∼3.48 eV, which is ∼50 meV lower than that of spontaneous emission. The excitation power dependence on the emission intensity clearly indicates threshold pump power density of 0.75 MW/cm2 for the onset of stimulated emission.

SiC for Microwave Power Transistors

Abstract: The advantages of SiC for high power, microwave devices are discussed. The design considerations, fabrication, and experimental results are described for SiC MESFETs and SITs. The highest reported f max for a 0.5 μm MESFET using semi-insulating 4H-SiC is 42 GHz. These devices also showed a small signal gain of 5.1 dB at 20 GHz. Other 4H-SiC MESFETs have shown a power density of 3.3 W/mm at 850 MHz. The largest SiC power transistor reported is a 450 W SIT measured at 600 MHz. The power output density of this SIT is 2.5 times higher than that of comparable silicon devices. SITs have been designed to operate as high as 3.0 GHz, with a 3 cm periphery part delivering 38 W of output power.

High density, optically corrected, micro-channel cooled, v-groove monolithic laser diode array

Abstract: An optically corrected, micro-channel cooled, high density laser diode array achieves stacking pitches to 33 bars/cm by mounting laser diodes into V-shaped grooves. This design will deliver>4kW/cm2 of directional pulsed laser power. This optically corrected, micro-channel cooled, high density laser is usable in all solid state laser systems which require efficient, directional, narrow bandwidth, high optical power density pump sources.

Analysis and evaluation of the transverse flux circumferential current machine

Abstract: With the evolution of novel high power density machines, it becomes important to compare the power potential of such machines with vastly different topologies having a variety of different waveforms of back EMF and current. The approach of this paper is based on general-purpose sizing and power density equations, which will permit a comparison of the main dimensions and power of such machines. In this paper, the comparison method of machine power densities is extended to include the transverse flux circumferential current type permanent magnet (TFCCPM) machine, and furthermore to compare the power production capability between the TFCCPM machine and the well-known squirrel cage induction machine.

Repetition rate dependence of gray-tracking in KTiOPO4 during second-harmonic generation at 532 nm

Abstract: The aim of this work is to study gray tracking during type II second-harmonic-generation 1064→532 nm in halide flux grown KTiOPO4 crystals. The repetition rate of the laser varies from 1 to 20 kHz. We experimentally demonstrate that the gray-tracking threshold, expressed by the harmonic peak power density, is a decreasing exponential function of the Q-switch frequency. The corresponding 532 nm average power density, however, remains constant.

Board-mountable power supply module

Abstract: A power supply module package suitable for both high packaged power density and cost effective manufacture. In an exemplary embodiment, the power supply module includes: (1) at least one printed circuit board containing conductors for interconnecting components of the power supply, (2) a thermally conductive baseplate or case operable for transferring heat generated inside the module to the outside environment, wherein the external package dimensions are of a sufficiently small size to allow the user the greatest flexibility in the design of the overall circuit assembly, (3) at least one power magnetic device operable for providing electrical isolation between the input and the output of the power module, and (4) a set of electrical leads to facilitate communication and power flow between the module and circuitry being powered. The present invention provides a highly compact, thermally conductive package for a power supply module (perhaps a DC/DC converter) that is cost effective, readily manufacturable, durable, and easily mounted to a circuit card, allowing the power module to, for example, form a portion of a distributed power architecture.

Observation of Laser Oscillation from CaGa 2S 4:Eu 2+

Abstract: The first observation of laser oscillation from a single crystal of CaGa2S4:Eu2+ (1 at%) is described in this report. A liquid nitrogen cooled thin platelet (0.8 mm thick), whose one flat surface was coated with aluminum to increase the reflectivity, was excited from the other uncoated side with a pulsed dye laser beam having a photon energy of around 2.48 eV. When the input power density exceeded a threshold value of ~10 MW/cm2, a directional beam having a sharp spectral line at around 2.19 eV emerged from the sample. This laser was found to have interesting wavelength tunability extending to ~200 A, possibly related to the broad gain spectrum of Eu2+ emission in this material.

Pulsed intense electron beams generated in transient hollow cathode discharges: fundamentals and applications

Abstract: For the commercial application of pulsed power, material processing with intense pulsed particle beams is a very interesting subject. Recently, high-voltage (1-70 kV), low-pressure (1-100 Pa) transient hollow-cathode discharges turned out to be sources for pulsed intense electron beam generation suitable for this application. The remarkable parameters of these electron beams-beam currents of 50-1000 A (10-30% of the maximum discharge current) with a high energy component (mean energy of about 0.25-0.75 of maximum applied voltage) of 20-70% of the maximum beam current, power density up to 10 W/cm/sup 2/, beam diameters of 0.1-3 mm, beam charge efficiency of 3-5%-captured the attention not only of the scientific community in the last decade. The electron beam is emitted during the early phases of the discharge, and only weak dependence of the high energetic peak of the beam current was found on the external capacity, which determine the development of the later high-current phases. However, the beam parameters depend on the breakdown voltage, gas pressure, and discharge geometry (including self-capacity). In this paper, the characteristics of the pulsed intense electron beams generated in two configurations-multigap pseudosparks and preionization-controlled open-ended hollow-cathode transient discharges (PCOHC)-are described. Such electron beams already were used successfully in a variety of pulsed power applications in material processing, deposition of superconducting (YBaCuO) and diamond-like thin films, microlithography, electron sources for accelerators, and intense point-like X-ray sources, and some preliminary experiments revealed new potential applications such as pumping of short-wavelength laser active media. These pulsed electron beams could be used further in any kind of pulsed power applications that require high-power density, small or high electron energy, and small-beam diameters.

Laser-cladding process: a study using stationary and scanning CO2 laser beams

Abstract: In a precise and controlled laser-cladding process, the effect of power density and beam-interaction time play a vital role. We study this process in both stationary and scanning beam modes with the laser cladding of stellite 6 on mild steel, Cr–Ni base materials, and we demonstrate their effects on the evolution of coarse, fine and very fine cladding microstructure. The effect of the various parameters such as input power, beam-interaction time, scanning frequency and the traverse speed are considered. The possible applications in the rapid prototyping industries are well illustrated.

Improved internal combustion engine and working cycle

Abstract: The invention is concerned with a method of deriving mechanical work from a combustion gas in internal combustion engines and reciprocating internal combustion engines (100) for carrying out the method. In its preferred embodiments, the method includes the steps of (i) producing an air charge, (ii) controlling the temperature, density and pressure of the air charge, (iii) transferring the air charge to a power cylinder (7) of the engine such that an air charge having a weight and density selected from a range of weight and density levels ranging from below atmospheric weight and density to heavier-than-atmospheric weight and density is introduced into the power cylinder, and (iv) then compressing the air charge at a lower-than-normal compression ration, (v) causing a predetermined quantity of charge-air and fuel to produce a combustible mixture, (vi) causing the mixture to be ignited within the power cylinder, and (vii) allowing the combustion gas to expand against a piston operable in the power cylinders with the expansion ratio of the power cylinders being substantially greater than the compression ratio of the power cylinders of the engine.

Influence of sample surface condition on chemical analysis using laser ablation inductively coupled plasma atomic emission spectroscopy

Abstract: The influence of sample surface condition on chemical analysis was investigated when using laser ablation sampling with inductively coupled plasma atomic emission spectroscopy (ICP-AES). The ablated mass quantity and composition were found to be significantly different from original vs. pre-ablated surfaces. The ablated mass quantity from original surfaces was much greater than that from pre-ablated surfaces, and the ablation rate (mass per unit area and time) was constant or independent of power density below 0.3 GW/cm2. For pre-ablated surfaces, the mass ablation rate follows exponential behavior in the same power density region. The measured composition of the ablated mass was found to be dependent on the surface condition and laser power density, for both original and pre-ablated surfaces. Understanding the influence of laser energy and surface conditions on mass ablation is essential for accurate and precise chemical analysis.

Hybrid energy storage system

Abstract: An energy storage system including a first power conversion device and a second power conversion device for providing energy to loads upon interruption of a main power source. A first power conversion device is connected in parallel to a first load, receives energy from an energy storage device and provides power to the first load. A second power conversion device is connected in series with a second load, receives energy from the energy storage device and provides power to the second load. The first and second power conversion devices are rated so that power consumption by the power conversion devices is reduced.

Stimulated emission at 34 K from an optically pumped cubic GaN/AlGaN heterostructure grown by metalorganic vapor-phase epitaxy

Abstract: A cubic GaN/AlGaN heterostructure has been grown on a GaAs (100) substrate by metalorganic vapor-phase epitaxy under low V/III ratio conditions, which resulted in a flat GaN layer. Stimulated emission was observed at 387 nm from the cleaved edge of an optically pumped cubic GaN/AlGaN heterostructure at 34 K. The threshold power density was 2.4 MW/cm2.

Motor vehicle serial hybrid drive for I.C. engine operated only at or near full load

Abstract: A serial hybrid drive has an internal combustion engine, a generator coupled mechanically to the internal combustion engine, an energy store coupled electrically to the generator, and at least one electric drive motor electrically connected to the generator and the energy store. The internal combustion engine/generator unit is operated along an operating characteristic whose power corresponds to the temporally smoothed power requirement of the electric drive motor, and the internal combustion engine is always operated at or near full load. In such case, the energy store has an energy storage capacity of at most a few kilowatt hours and a high power density, and compensates for the short-term power differences between the instantaneous power requirement of the electric drive motor and the power output by the internal combustion engine/generator unit and corresponding to the temporally smoothed power requirement of the electric drive motor.

Two-Dimensional Spatial Distribution of the Time-Integrated Emission from Laser-Produced Plasmas in Air at Atmospheric Pressure

Abstract: Emission from Nd:YAG laser-produced plasmas generated in air at atmospheric pressure has been studied with spatial resolution. With the use of a charge-coupled device (CCD), two-dimensional spatial distributions of the time-integrated line emission from plasmas of metallic (copper and stainless steel) and ceramic (alumina) samples were measured for laser power densities in the range 80-900 GW/cm2. Geometrical parameters (distance of the maximum, width in two directions) and the total space- and time-integrated emission were obtained as a function of power density. At the range 100-700 GW/cm2, the formation of a plasma in air for the metallic samples was shown to be responsible for a decrease in the total intensity of lines emitted from the sample plasma, accompanied by effects in the spatial profiles along the laser direction. Beyond 700 GW/cm2, a sharp increase of the line intensities was observed, related to the absence of the shielding air plasma.

Evolution of subkilometer scale ionospheric irregularities generated by high-power HF waves

Abstract: Electron density irregularities in the F region excited by the European incoherent scatter (EISCAT) high-power high-frequency (HF) facility in Ramfjordmoen, Norway, have been studied in detail by observing scintillations of 250-MHz satellite signals traversing the HF beam Spaced antenna measurements were performed to determine the temporal structure of scintillation and the drift of the irregularities Studies of scintillation spectra indicate that even though the onset occurs nearly simultaneously for all irregularity scale sizes, the electron density irregularities with wavelengths in the range of 50–15 m attain their saturation amplitudes within tens of seconds, whereas longer scale-size irregularities with wavelengths exceeding 100 m saturate in the timescale of minutes The threshold power density requirement for the generation of irregularities of different scales has also been studied by the variation of the heater power It is found that for large-scale (>100 m) irregularities the threshold power density varies inversely as the irregularity wavelength with a power law index of 4 as predicted by the theories of self-focusing instability