Showing papers on "Power density published in 2006"

Polymer electrolyte membranes for the direct methanol fuel cell: A review

Abstract: The direct methanol fuel cell (DMFC) has the potential to replace lithium-ion rechargeable batteries in portable electronic devices, but currently experiences significant power density and efficiency losses due to high methanol crossover through polymer electrolyte membranes (PEMs). Numerous publications document the synthesis and characterization of new PEMs for the DMFC. This article reviews this research, transport phenomena in PEMs, and experimental techniques used to evaluate new PEMs for the DMFC. Although many PEMs do not show significant improvements over Nafion®, the benchmark PEM in DMFCs, experimental results show that several new PEMs exhibit lower methanol crossover at similar proton conductivities and/or higher DMFC power densities. These results and recommendations for future research are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Parts B: Polym Phys 44: 2201–2225, 2006

Micromachined microbial and photosynthetic fuel cells

Abstract: This paper presents two types of fuel cells: a miniature microbial fuel cell (µMFC) and a miniature photosynthetic electrochemical cell (µPEC). A bulk micromachining process is used to fabricate the fuel cells, and the prototype has an active proton exchange membrane area of 1 cm2. Two different micro-organisms are used as biocatalysts in the anode: (1) Saccharomyces cerevisiae (baker's yeast) is used to catalyze glucose and (2) Phylum Cyanophyta (blue-green algae) is used to produce electrons by a photosynthetic reaction under light. In the dark, the µPEC continues to generate power using the glucose produced under light. In the cathode, potassium ferricyanide is used to accept electrons and electric power is produced by the overall redox reactions. The bio-electrical responses of µMFCs and µPECs are characterized with the open-circuit potential measured at an average value of 300–500 mV. Under a 10 ohm load, the power density is measured as 2.3 nW cm−2 and 0.04 nW cm−2 for µMFCs and µPECs, respectively.

All-optical efficient wavelength conversion using silicon photonic wire waveguide

Abstract: We demonstrate efficient wavelength conversion using a four-wave-mixing (FWM) effect in a silicon photonic wire waveguide with spot size converters. Applying a continuously operated 160-mW pump, power density in the waveguide's core was increased up to around 430 MW/cm/sup 2/, and the FWM effect was remarkably enhanced. Internal conversion efficiency obtained in an experiment was -10.6 dB. The efficiency was significantly limited by the free-carrier absorption effect.

Cost structure method including fuel economy and engine emission considerations

Abstract: A powertrain control selects engine operating points in accordance with power loss minimization controls. Power loss contributions come from a variety of sources including engine power losses. Engine power losses are determined in accordance with engine operating metrics such as power production per unit fuel consumption and power production per unit emission production. Engine power losses are combined in accordance with assigned weighting into a single engine power loss term for use in the power loss minimization control and operating point selection.

Optical field concentration in low-index waveguides

Abstract: We present a highly efficient optical field concentrator that is capable of confining optical field in nanometer-thin low-index media with very high optical confinement factor. The structure is made of multiple-layered low-index nanolayers embedded in high-index silicon waveguides. By creating multiple high-index-contrast interfaces, the normal field in the low-index nanolayer regions is significantly enhanced. It subsequently results in a very high optical confinement and power density in these regions. With the help of numerical simulation tools, the guiding and propagating characteristics of the new structure are studied and presented. The optimal structures have demonstrated confinement factors and normalized power densities in the range of 30%-60% and 20-160 mum-2 for the 5-20-nm thin low-index multiple nanolayers

Output power density of 5.1/mm at 18 GHz with an AlGaN/GaN HEMT on Si substrate

Abstract: Microwave frequency capabilities of AlGaN/GaN high electron mobility transistors (HEMTs) on high resistive silicon (111) substrate for power applications are demonstrated in this letter. A maximum dc current density of 1 A/mm and an extrinsic current gain cutoff frequency (F/sub T/) of 50 GHz are achieved for a 0.25 /spl mu/m gate length device. Pulsed and large signal measurements show the good quality of the epilayer and the device processing. The trapping phenomena are minimized and consequently an output power density of 5.1 W/mm is reached at 18 GHz on a 2/spl times/50/spl times/0.25 /spl mu/m/sup 2/ HEMT with a power gain of 9.1dB.

GaN HFET for W-band Power Applications

Abstract: In this paper we report high frequency GaN power device and measured power performance of the first W-band (75 GHz-110 GHz) MMIC fabricated in GaN material system. The first W-band GaN MMIC with 150 ?m of output gate periphery produces 316 mW of continuous wave output power (Power density = 2.1 W/m) at a frequency of 80.5 GHz and has associated power gain of 17.5 dB. By comparison the reported (1) state of the art for other solid state technologies in W-band is 427 mW measured in a pulsed mode on an InP HEMT MMIC with 1600 ?m of output periphery (Power density = 0.26 W/mm). The reported result demonstrates tremendous superiority of GaN device technology for power applications at frequencies greater than 75 GHz.

Loss mechanisms and high power piezoelectrics

Abstract: Heat generation is one of the significant problems in piezoelectrics for high power density applications. In this paper, we review the loss mechanisms in piezoelectrics first, followed by the heat generation processes for various drive conditions. Heat generation at off-resonance is caused mainly by dielectric loss tan δ′ (i.e., P-E hysteresis loss), not by mechanical loss, while the heat generation at resonance is mainly attributed to mechanical loss tan ′. Then, practical high power materials developed at Penn State is introduced, which exhibit the vibration velocity more than 1 m/s, leading to the power density capability 10 times of the commercially available “hard” PZTs. We propose a internal bias field model to explain the low loss and high power origin of these materials. Finally, using a low temperature sinterable “hard” PZT, we demonstrated a high power multilayer piezoelectric transformers

Plasma generation using high-power millimeter-wave beam and its application for thrust generation

Abstract: Propagation of an ionization front in the beam channel was observed after plasma was generated using a 170GHz millimeter-wave beam in the atmosphere. The propagation velocity of the ionization front was found to be supersonic when the millimeter-wave power density was greater than 75kWcm−2. The momentum coupling coefficient Cm, a ratio of the propulsive impulse to the input energy, was measured using conical and cylindrical thruster models. A Cm value greater than 350NMW−1 was recorded when the ionization front propagated with supersonic velocity.

A new performance criterion for heat engines: efficient power

Abstract: Many performance analyses have been carried out based on two comparative criteria namely maximum power (mp) and maximum power density (mpd). Researchers involved in power maximization studies have utilized the thermal efficiency at mp (Curzon–Ahlborn efficiency) as an efficiency standard for practical heat engines. On the other hand, maximum power density studies showed that the efficiency at mpd is always greater than that at the mp, while the power output from heat engines reduces. In this study, a new performance analysis is applied to a reversible Carnot cycle based on a new criterion which is proposed for all kind of heat engines. The proposed criterion, called efficient power, is defined as the multiplication of power by efficiency. This criterion considers not only the power output, but also the cycle efficiency. Maximizing the efficient power gives a compromise between power and efficiency. The results showed that the design parameters at maximum efficient power (mep) conditions lead to mo...

Donor‐acceptor pair recombination luminescence from Cu2ZnSnS4 bulk single crystals

Abstract: Photoluminescence from Cu 2 ZnSnS 4 bulk single crystals was studied as a function of temperature and excitation power density. The bulk single crystals showed a broad luminescence between 1.1 and 1.45 eV. The peak energy of the photoluminescence was shifted to higher energy side when the excitation power density was increased. The origon of the photoluminescence was attributed to donor-acceptor pair recombination with an activation energy of 48 meV.

Thermoelectric power generator for variable thermal power source

Abstract: Traditional power generation systems using thermoelectric power generators are designed to operate most efficiently for a single operating condition. The present invention provides a power generation system in which the characteristics of the thermoelectrics, the flow of the thermal power, and the operational characteristics of the power generator are monitored and controlled such that higher operation efficiencies and/or higher output powers can be maintained with variably thermal power input. Such a system is particularly beneficial in variable thermal power source systems, such as recovering power from the waste heat generated in the exhaust of combustion engines.

High Capacity Thermoelectric Temperature Control Systems

Abstract: Recent advances in TE technology enable a new class of solid state cooling, heating, and temperature control systems. The new designs utilize advanced thermodynamic cycles [Bell, LE, 2002] to improve the Coefficient of Performance (COP) by about a factor of two, so that performance levels are comparable to those of two phase compressor based systems in certain important applications. Further improvement has resulted from optimized designs that employ TE components with increased power density [Diller, RW, et. al., 2002] and reduced temperature differentials at the TE/electrode interfaces in the heat transfer path. Together, these improvements enable new system configurations that in important applications are performance competitive with two phase systems for heating and cooling capacities of up to 3,500 watts. By utilizing high power design concepts and system level design optimization [Bell, LE, 2004], TE material costs per watt of thermal power output is reduced by about a factor of four. A system design is presented that is suitable for output thermal power ranging from 50 to 5,000 watts in either heating or cooling modes. The present design is compared with a similar design using conventional TE modules in terms of size, weight, efficiency, and power density. Experimental results are presented that demonstrate good correlation between measured values and the predicted COP performance enhancements and TE material usage reductions

A high-efficiency class-E GaN HEMT power amplifier at 1.9 GHz

Abstract: A single stage class-E power amplifier in GaN high electron mobility transistor (HEMT) technology is reported. The circuit operates at 1.9 GHz. At 30-V drain bias, a power-added-efficiency (PAE) of 57% and a maximum output power of over 37dBm was achieved, corresponding to a power density of 5.25W/mm. At 40-V drain bias, an output power of 38.7dBm is achieved at 50% PAE corresponding to a power density of 7.4W/mm

Unpassivated high power deeply recessed GaN HEMTs with fluorine-plasma surface treatment

Abstract: In this letter, unpassivated high power deeply recessed GaN-based high electron mobility transistors (HEMTs) are reported. The introduction of a thick graded AlGaN cap layer and a novel fluorine-plasma surface treatment reduced the gate-leakage current and increased breakdown voltage significantly, enabling the application of much higher drain biases. Due to excellent dispersion suppression achieved at an epitaxial level, an output power density of more than 17 W/mm with an associated power added efficiency (PAE) of 50% was measured at 4 GHz and V/sub DS/=80 V without SiN/sub x/ passivation. These results demonstrate the great potential of this novel epitaxial approach for passivation-free GaN-based HEMTs for high-power applications.

Lateral power MOSFET for megahertz-frequency, high-density DC/DC converters

Abstract: DC/DC converters to power future CPU cores mandate low-voltage power metal-oxide semiconductor field-effect transistors (MOSFETs) with ultra low on-resistance and gate charge. Conventional vertical trench MOSFETs cannot meet the challenge. In this paper, we introduce an alternative device solution, the large-area lateral power MOSFET with a unique metal interconnect scheme and a chip-scale package. We have designed and fabricated a family of lateral power MOSFETs including a sub-10 V class power MOSFET with a record-low R/sub DS(ON)/ of 1m/spl Omega/ at a gate voltage of 6V, approximately 50% of the lowest R/sub DS(ON)/ previously reported. The new device has a total gate charge Q/sub g/ of 22nC at 4.5V and a performance figures of merit of less than 30m/spl Omega/-nC, a 3/spl times/ improvement over the state of the art trench MOSFETs. This new MOSFET was used in a 100-W dc/dc converter as the synchronous rectifiers to achieve a 3.5-MHz pulse-width modulation switching frequency, 97%-99% efficiency, and a power density of 970W/in/sup 3/. The new lateral MOSEFT technology offers a viable solution for the next-generation, multimegahertz, high-density dc/dc converters for future CPU cores and many other high-performance power management applications.

Development of New Fast Oxide Ion Conductor and Application for Intermediate Temperature Solid Oxide Fuel Cells

Abstract: Solid Oxide Fuel Cell (SOFC) show great promise as new power generators with high efficiency. Decreasing the operating temperature is critically required for the further development of SOFC. This review introduces that oxide ion conductivity in the perovskite oxide of LaGaO 3 , which was found by our group. LaGaO 3 doped with La and Mg exhibits the high oxide ion conductivity over a wide P O2 range; the value is higher than that of Y 2 O 3 -stabilized ZrO 2 by an order of magnitude. When LaGaO 3 -based oxide was used as the electrolyte of SOFC, the power density could be improved greatly, in particular over the low-temperature range. In this study, the power generating property of LSGM using a thin film of LaGaO 3 is also introduced. The maximum power density of the cell using LaGaO 3 -based oxide is as high as 0.6Wcm- 2 at 773 K. This suggests that SOFC could be operable at temperature lower than 773 K.

Nitride based transistors for millimeter wave operation

Abstract: Field effect transistors having a power density of greater than 5 W/mm when operated at a frequency of at least 30 GHz are provided. The power density of at least 5 W/mm may be provided at a drain voltage of 28 V. Transistors with a power density of at least 8 W/mm when operated at 40 GHz at a drain voltage of 28 V are also provided.

AlGaN/GaN $Ka$ -Band 5-W MMIC Amplifier

Abstract: A broadband Ka-band AlGaN/GaN on SiC high electron-mobility transistor monolithic-microwave integrated-circuit (MMIC) power amplifier was developed for millimeter-wave antenna applications. The 0.18-mum gate two-stage 50-Omega matched MMIC produces 13plusmn1 dB of gain from 26 to 36 GHz. At 35 GHz, the measured continuous wave (CW) saturated output power (Pout) was 4 W (5 W pulsed), indicating a CW power density of 3.3 W/mm (4.2 W/mm pulsed). The CW power-added efficiency was 23%. Across the band, the measured CW Pout was >2 W (2.5 W pulsed). While individual (or partially matched single stage) devices have been demonstrated with good output power, to the best of our knowledge, this is the first report of a 10-GHz-bandwidth Ka-band GaN MMIC with high output power and gain. A unique aspect of the design, contributing to the wide bandwidth, is the use of positive feedback in the first stage to increase the gain. RF power stress test and detailed investigation of the channel temperature effect are presented. A preliminary RF power stress test indicates a lifetime of 1000 h at 191 degC channel temperature, and elevated temperature operation indicates that Pout decreases by 0.013 dB/degC