Showing papers on "Power density published in 2002"
TL;DR: In this article, the authors discuss the recent work at the Pacific Northwest National Laboratory (PNNL) in support of the design and development of low-cost modular solid oxide fuel cells using lower temperature, anode-supported SOFCs.
737 citations
TL;DR: In this article, the performance of a direct methanol fuel cell (DMFC) is analyzed as a function of three parameters, namely temperature, fuel flow rate and concentration.
358 citations
TL;DR: The application of high power pulses with peak voltage of -2 kV and peak power density of 3 kWcm-2 to magnetron plasma sources is a new development in sputtering technology as discussed by the authors.
290 citations
02 Jun 2002
TL;DR: Very high power densities have been shown for both SiC MESFET and GaN HEMT devices as discussed by the authors, along with good efficiency and linearity, provide an excellent base for future military and commercial power amplifier applications.
Abstract: Very high power densities have been shown for both SiC MESFET and GaN HEMT devices. Both of these active devices benefit from the high breakdown voltages afforded by their wide-bandgap semiconductor properties. The GaN device also benefits from current densities as high as 1 A/mm. This high power density, along with good efficiency and linearity, provide an excellent base for future military and commercial power amplifier applications. High power densities are possible using narrow band power-matching networks. Although the gain-bandwidth limitation is exacerbated due to the high-impedance load lines required, high power design is possible even over multi-octave bandwidths.
86 citations
07 Nov 2002
TL;DR: SiC SIT technology offers many military system advantages including lower cost, lower weight, higher power and high temperature of operation and higher efficiency transmitters with minimal cooling requirements and SiC RF MESFET's and circuits are candidates for use in efficient linear transmitters for commercial and military communications.
Abstract: Two SiC transistors that are investigated for microwave power applications are the 4H-SiC static induction transistor (SIT) and the 4H-SiC metal-semiconductor field-effect transistor (MESFET). Ultrahigh frequency 4H-SiC SITs have demonstrated record-breaking pulsed power per package (900 W) with excellent associated power-added efficiency (PAE) of 78%. S band 4H-SiC MESFETs have shown a record power-density of 5.6 W/mm and 36% PAE, as well as 80 W continuous-wave (CW) power (1.6 W/mm), with an associated PAE of 38%. X-band MESFET power density of 4.3 W/mm was obtained for exploratory CW devices. These performance gains are afforded by the advantageous material properties of silicon carbide. SiC SIT technology offers many military system advantages including lower cost, lower weight, higher power and high temperature of operation and higher efficiency transmitters with minimal cooling requirements. SiC RF MESFET's and circuits are candidates for use in efficient linear transmitters for commercial and military communications.
81 citations
TL;DR: In this paper, the effect of maximizing power density on the performance of the cycle efficiency is discussed. And the results obtained from this work can be helpful in the thermodynamic modeling and in evaluation of Miller engines over Atkinson and Joule-Brayton engines.
80 citations
TL;DR: In this article, polyaniline (PANI) has been potentiodynamically deposited on stainless steel substrate and characterized in a gel polymer electrolyte (GPE), which facilitates a voltage limit of the capacitor to 1 V instead of 0.75 V in aqueous electrolytes.
Abstract: Studies on redox supercapacitors employing electronically conducting polymers are of great importance for hybrid power sources and pulse power applications. In the present study, polyaniline (PANI) has been potentiodynamically deposited on stainless steel substrate and characterized in a gel polymer electrolyte (GPE). Use of the GPE facilitates a voltage limit of the capacitor to 1 V, instead of 0.75 V in aqueous electrolytes. From charge-discharge studies of the solid-state PANI capacitors, a specific capacitance of 250 F g(-1) has been obtained at a specific power of 7.5 kW kg(-1) of PANI. The values of specific capacitance and specific power are considerably higher than those reported in the literature. High energy and high power characteristics of the PANI are presented. (C) 2002 The Electrochemical Society.
78 citations
TL;DR: In this article, the effect of methanol pretreatment on the performance of a direct formic acid fuel cell (DFAFC) was investigated and it was shown that conditioning of the cell in methanols results in a substantial increase in current.
70 citations
01 Jan 2002
TL;DR: In this article, two radial inflow combustor designs were examined; a single-zone arrangement and a primary and dilution-zone configuration, both of which were micro-machined from silicon using DRIE and aligned fusion wafer bonding.
Abstract: As part of an effort to develop a micro-scale gas turbine engine for power generation and micro-propulsion applications, this paper presents the design, fabrication, experimental testing, and modeling of the combustion system. Two radial inflow combustor designs were examined; a single-zone arrangement and a primary and dilution-zone configuration. Both combustors were micro-machined from silicon using Deep Reactive Ion Etching (DRIE) and aligned fusion wafer bonding. Hydrogen-air and hydrocarbon-air combustion was stabilized in both devices, each with chamber volumes of 191 mm3 . Exit gas temperatures as high as 1800 K and power densities in excess of 1100 MW/m3 were achieved. For the same equivalence ratio and overall efficiency, the dual-zone combustor reached power densities nearly double that of the single-zone design. Because diagnostics in micro-scale devices are often highly intrusive, numerical simulations were used to gain insight into the fluid and combustion physics. Unlike large-scale combustors, the performance of the micro-combustors was found to be more severely limited by heat transfer and chemical kinetics constraints. Important design trades are identified and recommendations for micro-combustor design are presented.Copyright © 2002 by ASME
68 citations
Patent•
09 Dec 2002TL;DR: In this article, the authors proposed a very low emission hybrid electric vehicle incorporating an integrated propulsion system which includes a fuel cell, a metal hydride hydrogen storage unit, an electric motor, high specific power, high energy density nickel-metal hyddride (NiMH) batteries, and preferably a regenerative braking system.
Abstract: A very low emission hybrid electric vehicle incorporating an integrated propulsion system which includes a fuel cell, a metal hydride hydrogen storage unit, an electric motor, high specific power, high energy density nickel-metal hydride (NiMH) batteries, and preferably a regenerative braking system. The nickel-metal hydride battery module preferably has a peak power density in relation to energy density as defined by: P>1,375−15E, where P is greater than 600 Watts/kilogram, where P is the peak power density as measured in Watts/kilogram and E is the energy density as measured in Watt-hours/kilogram.
67 citations
TL;DR: In this article, the electrical performances of the fabricated microtransformers were analyzed and compared with predictions obtained from models based on an analytical approach, and an efficiency of 40% for a power density of 1.2 W/cm/sup 2/ was measured.
Abstract: This paper presents the electrical performances of the fabricated microtransformers. Measurements for open-circuit and short-circuit impedance up to a frequency of 100 MHz are presented. The measured results are compared with predictions obtained from models based on an analytical approach. The use of a microtransformer in a 2-MHz dc-dc converter is reported. An efficiency of 40% for a power density of 1.2 W/cm/sup 2/ was measured.
TL;DR: In this article, the power density, defined as the ratio of power output to maximum specific volume in the cycle, is taken as the objective for performance analysis of an endoreversible closed Brayton cycle coupled to variable temperature heat reservoirs in the viewpoint of finite time thermodynamics or entropy generation minimization.
TL;DR: In this article, extreme ultraviolet (EUV) spectroscopy was performed on microwave discharges of helium with 2% hydrogen, where lines were identified as hydrogen transitions to electronic energy levels below the ground state corresponding to fractional quantum numbers.
TL;DR: In this article, the neutral gas temperature in a CF4 planar inductive discharge was measured with space and time resolution using laser-induced fluorescence of the CF radical with analysis of the rotationally resolved excitation spectra.
Abstract: The neutral gas temperature in a CF4 planar inductive discharge was measured with space and time resolution using laser-induced fluorescence of the CF radical with analysis of the rotationally resolved excitation spectra. Strong temperature gradients are observed and temperatures as high as 900 K are reached at the reactor center at 50 mTorr with a power density of 0.15 W/cm3. The temperature at the reactor center increases with both gas pressure and power, but is independent of the gas flow rate. A simple model based on the global thermal energy balance is proposed to explain these results. The fraction of the injected rf power consumed in gas heating varies from 4.4% to 42% under our conditions (5–50 mTorr, 250 W rf power). Axial temperature profiles were measured in the steady state and in the time afterglow. The typical temperature relaxation times are several hundreds of microseconds. A numerical two-dimensional, time-dependent thermal model is in good agreement with the results.
TL;DR: In this paper, the specific absorption rate (SAR) inside a layered model of the human skin between 3-100 GHz was investigated numerically by the finite-difference time-domain method for a frequency of 77 GHz.
Abstract: This investigation is divided into three parts. First, the W-band dielectric properties of different biological tissues are determined. Then, the electromagnetic field in the human eye and skin is simulated for plane-wave exposure. An analytical method is used to investigate the specific absorption rate (SAR) inside a layered model of the human skin between 3-100 GHz. Furthermore, the SAR inside a detailed model of the human eye is investigated numerically by the finite-difference time-domain method for a frequency of 77 GHz. Maximum local SAR values of 27.2 W/kg in skin tissue and 45.1 W/kg in eye tissue are found for 77 GHz and an incident power density of 1 mW/cm/sup 2/. In the third part of the investigation, the temperature changes of superficial tissue caused by millimeter-wave irradiation are measured by a thermal infrared imaging system. The exposure setup is based on a horn antenna with a Gunn oscillator operating at 15.8-dBm output power. The measurements showed a maximum temperature increase of 0.7/spl deg/C for a power density of 10 mW/cm/sup 2/ and less than 0.1/spl deg/C for 1 mW/cm/sup 2/, both in human skin (in vivo), as well as in porcine eye (in vitro). The comparison of the temperature measurements with a thermal bio-heat-transfer simulation of a layered skin model showed a good agreement.
TL;DR: In this paper, a new combined power cycle model (Dual+Joule-Brayton) has been introduced and optimized based on the obtained results for MPD analysis of the dual cycle.
TL;DR: In this paper, Cation-doped CeO2 electrolyte has been evaluated in single-cell and short-stack tests in solid oxide fuel cell environments and applications, along with conductivity measurements, indicate that an ionic transference number of ∼0.75 can be expected at 800°C.
Abstract: Cation-doped CeO2 electrolyte has been evaluated in single-cell and short-stack tests in solid oxide fuel cell environments and applications. These results, along with conductivity measurements, indicate that an ionic transference number of ∼0.75 can be expected at 800°C. Single cells have shown a power density >350 mW/cm2. Multicell stacks have demonstrated a peak performance of >100 mW/cm2 at 700°C using metallic separators.
TL;DR: In this paper, the authors present state-of-the-art performance for an RF-power LDMOS transistor with a dual-layer RESURF of the drift region, which allows for a sub-spl mu/m channel length and high breakdown voltage of 110 V.
Abstract: In this letter, we present state-of-the-art performance, in terms of output power density, for an RF-power LDMOS transistor. The novel device structure has a dual-layer RESURF of the drift region, which allows for a sub-/spl mu/m channel length and a high breakdown voltage of 110 V. The output power density is more than 2 W/mm at 1 GHz and a V/sub DS/=70 V, with a stable gain of 23 dB at V/sub DS/=50 V. At 3.2 GHz the power density is over 1 W/mm at V/sub DS/=50 V and 0.6 W/mm at V/sub DS/=28 V. These results are to our knowledge the best ever for silicon power MOSFETs.
25 Feb 2002
TL;DR: In this article, the authors investigated the key factors determining the performance of supercapacitors using single-walled carbon nanotube (SWNT) electrodes and found that most of the surface area of the SWNT electrode contributed to the theoretically estimated specific capacitance.
Abstract: We have investigated the key factors determining the performance of supercapacitors using singlewalled carbon nanotube (SWNT) electrodes. Several parameters of compositions of the binder, annealing temperature, type of current collectors, charging time and discharging current density are optimized for the best performance of the energy density and power density. We find a maximum specific capacitance of 180 F/g and a measured power density of 20 kW/kg at the energy density of 7 Wh/kg in a solution of 7.5 N KOH. The specific surface area and the specific capacitance increase with increasing annealing temperatures of the sample. It was found that most of the BET surface area of the SWNT electrode contributed to the theoretically estimated specific capacitance. Minimization of the contact resistance is independent of the specific capacitance but directly related to the maximum of the power density.
TL;DR: In this article, a new method of a carbon nanotube purity estimation has been developed on the basis of Raman spectroscopy, where the spectra of carbon soot containing different amounts of nanotubes were registered under heating from a probing laser beam with a step-by-step increased power density.
Abstract: A new method of a carbon nanotube purity estimation has been developed on the basis of Raman spectroscopy. The spectra of carbon soot containing different amounts of nanotubes were registered under heating from a probing laser beam with a step-by-step increased power density. The material temperature in the laser spot was estimated from a position of the tangential Raman mode demonstrating a linear thermal shift (-0.012 cm-1/K) from the position 1592 cm-1 (at room temperature). The rate of the material temperature rise versus the laser power density (determining the slope of a corresponding graph) appeared to correlate strongly with the nanotube content in the soot. The influence of the experimental conditions on the slope value has been excluded via a simultaneous measurement of a reference sample with a high nanotube content (95 vol. %). After the calibration (done by a comparison of the Raman and the transmission electron microscopy data for the nanotube percentage in the same samples) the Raman-based method is able to provide a quantitative purity estimation for any nanotube-containing material.
TL;DR: An overview of SiC static induction transistor (SIT) development is presented in this paper, where basic conduction mechanisms are introduced and discussed, including ohmic, exponential, and space charge limited conduction (SCLC) mechanisms.
Abstract: An overview of silicon carbide (SiC) static induction transistor (SIT) development is presented. Basic conduction mechanisms are introduced and discussed, including ohmic, exponential, and space charge limited conduction (SCLC) mechanisms. Additionally, the impact of velocity saturation and temperature effects on SCLC are reviewed. The small signal model, breakdown voltage, power density, and different gate structures are also discussed, before a final review of published SiC SIT results. Published S-band (3–4 GHz) results include 9.5 dB of gain and output power of 120 W, and L-band (1.3 GHz) results include 400 W output power, 7.7 dB of gain, and power density of 16.7 W/cm.
TL;DR: In this article, the radiative transfer in a system at local thermodynamic equilibrium is investigated on the basis of the solution of the (geometrical optics) transfer equation, accounting for the non-local nature of radiative process due to both reabsorption of the emitted radiation and reflectivity of the walls of the system.
Abstract: The radiative transfer in a system at local thermodynamic equilibrium is investigated on the basis of the solution of the (geometrical optics) transfer equation, accounting for the non-local nature of the radiative process due to both re-absorption of the emitted radiation and reflectivity of the walls of the system. The specific case of the electron cyclotron (EC) radiation in a cylindrical fusion plasma with specularly reflecting walls for which an analytical solution can be derived, is addressed and, in particular, the radial profile of the net power density radiated is evaluated by making use of an improved expression for the EC absorption coefficient. A detailed numerical analysis, carried out by varying both the wall reflection coefficient and the radial profile of the plasma temperature, reveals that a reversal of the net power density profile can occur on the plasma outboard for sufficiently high wall reflectivity. From a comparison with bremsstrahlung radiation profiles it is apparent that a local treatment of EC power emission is needed for sufficiently hot plasmas as expected, e.g. in the so-called advanced regimes of DT tokamak reactors. Furthermore, an exact approach is used to check the accuracy of approximate EC net power density profiles as calculated with the CYTRAN code showing that the latter provides a globally reasonable approximation. Evaluating the total EC radiated power from the exact local approach shows that its scaling with the reflection coefficient is very well described by a scaling following from a recently established global model for the EC radiation, which improves the well-known Trubnikov scaling. The results obtained are discussed in view of their possible relevance to affecting the plasma temperature profile.
Patent•
23 Sep 2002TL;DR: In this paper, a very low emission hybrid electric vehicle incorporating an integrated propulsion system which includes a hydrogen powered internal combustion engine, a metal hydride hydrogen storage unit, an electric motor, high specific power, high energy density nickel-metal hyddride (NiMH) batteries, and preferably a regenerative braking system is presented.
Abstract: A very low emission hybrid electric vehicle incorporating an integrated propulsion system which includes a hydrogen powered internal combustion engine, a metal hydride hydrogen storage unit, an electric motor, high specific power, high energy density nickel-metal hydride (NiMH) batteries, and preferably a regenerative braking system. The nickel-metal hydride battery module preferably has a peak power density in relation to energy density as defined by: P > 1,420 - 16E, where P is greater than 600 Watts/kilogram, where P is the peak power density as measured in Watts/kilogram and E is the energy density as measured in Watt-hours/kilogram.
TL;DR: In this paper, the DC and microwave power performance of metal organic chemical vapour deposition-grown AlGaN/GaN HEMTs on SiC substrate was reported, which exhibited high maximum current density of 1.1 A/mm with high peak extrinsic transconductance of 234 mS/mm.
Abstract: The DC and microwave power performance of metal organic chemical vapour deposition-grown AlGaN/GaN HEMTs on SiC substrate is reported. The devices exhibited high maximum current density of 1.1 A/mm with high peak extrinsic transconductance of 234 mS/mm. At 26 GHz, the devices achieved continuous-wave (CW) power density of 5 W/mm with power-added-efficiency of 30.1%, which represents the highest output power density and associated power-added efficiency reported above 20 GHz.
TL;DR: In this article, the electron deposition in an Ar-Kr-F2 mixture, based on a solution of the electron Boltzmann equation, is presented, and the model is relevant to an electron-beam generated KrF* laser amplifier at atmospheric pressure.
Abstract: The electron deposition in an Ar–Kr–F2 mixture, based on a solution of the electron Boltzmann equation, is presented. The model is relevant to an electron-beam generated KrF* laser amplifier at atmospheric pressure. Sets of cross sections for Ar, Kr, and F2 have been compiled. Calculations have been performed to determine the electron energy distribution function, energy per electron–ion pair and the ionization and excitation rates. It is found that the inclusion of inner shell ionization and the subsequent Auger emission are essential for matching known results on both the energy per electron–ion pair Wei and the stopping power in pure Ar or Kr target gases. For the chosen Ar–Kr–F2 mixture, Wei is calculated to be 24.6 eV. The excitation-to-ionization ratio is calculated to be 0.38 for Ar and 0.54 for Kr at low input power density Pbeam (1 kW/cm3). Both ratios increase with Pbeam, particularly for Kr which attains 0.8 at 1 MW/cm3. The dependency on Pbeam and the excitation efficiency for Kr is significan...
TL;DR: In this paper, RF-plasma MBE has been used for the growth of undoped Al/sub 0.25/Ga/sub0.75/N/GaN HEMT structures on semi-insulating SiC substrate.
Abstract: RF-plasma MBE has been used for the growth of undoped Al/sub 0.25/Ga/sub 0.75/N/GaN HEMT structures on semi-insulating SiC substrates. Devices with a 1.5 /spl mu/m gate length have an f/sub T/ of 10 GHz and have demonstrated an output power density of 6.3 W/mm at 2 GHz. Details of the growth process and device results are presented.
TL;DR: In this paper, the design and modeling of a high power piezoelectric pulse generator is presented and discussed, which produces a transient voltage pulse when mechanically compressed and can be implemented in a computer model.
Abstract: The design and modeling of a high power piezoelectric pulse generator is presented and discussed. The piezoelectric element produces a transient voltage pulse when mechanically compressed. This investigation presents a theoretical description of the pulse generator as well as methods to implement it in a computer model. The computer model of the pulse generator can be separated in two functional parts-the mechanical model and the electrical model. The two models are linked by the electromechanical constants of the piezoelectric material. Additionally, this investigation presents techniques used to model the diagnostic system that measures the generator output. Finally, two experiments (i.e., piezoelectric projectile and bench test) have been performed on the piezoelectric pulse generator to compare the results with the computer model. The piezoelectric material used in this investigation is barium titanate. In the first experiment, the experimental results and the simulation results are not in good agreement due to the problem with the diagnostic system. Experimentally, the peak current, peak power, and power density are 58.2 A, 28.4 kW, and 517 kW/cm/sup 3/, respectively. The second experiment gives the results that are very well agreed with the computer model with the bench test diagnostics system. Experimentally, the peak current, peak power and power density are 36 A, 15.6 kW, and 96.7 kW/cm/sup 3/, respectively.
TL;DR: Effects of millimeter waves at the frequency of 51.755 GHz were studied in logarithmic and stationary E. coli cells at various cell densities and provided evidence that intercellular communication in response to MMW depended on cell status and PD of microwaves.
Patent•
01 Nov 2002
TL;DR: In this article, the authors described a neuroprotective effective amount of light energy having a wavelength in the visible to near-infrared wavelength range to that area of the brain containing the area of primary infarct.
Abstract: Therapeutic methods for the treatment of stroke are described, the methods including delivering a neuroprotective effective amount of light energy having a wavelength in the visible to near-infrared wavelength range to that area of the brain containing the area of primary infarct. The neuroprotective effective amount of light energy is a predetermined power density (mW/cm 2 ) at the level of the brain tissue being treated, and is delivered by determining a surface power density of the light energy that is sufficient to deliver the predetermined power density of light energy to the brain tissue.
TL;DR: In this paper, a series of Ni-Cu-YSZ cermet made of oxide raw materials was employed as the anode of a SOFC, and the reducing properties of these materials were first investigated.