Showing papers on "Power density published in 2007"

A micro electromagnetic generator for vibration energy harvesting

Abstract: Vibration energy harvesting is receiving a considerable amount of interest as a means for powering wireless sensor nodes This paper presents a small (component volume 01 cm3, practical volume 015 cm3) electromagnetic generator utilizing discrete components and optimized for a low ambient vibration level based upon real application data The generator uses four magnets arranged on an etched cantilever with a wound coil located within the moving magnetic field Magnet size and coil properties were optimized, with the final device producing 46 µW in a resistive load of 4 k? from just 059 m s-2 acceleration levels at its resonant frequency of 52 Hz A voltage of 428 mVrms was obtained from the generator with a 2300 turn coil which has proved sufficient for subsequent rectification and voltage step-up circuitry The generator delivers 30% of the power supplied from the environment to useful electrical power in the load This generator compares very favourably with other demonstrated examples in the literature, both in terms of normalized power density and efficiency

Graphite Fiber Brush Anodes for Increased Power Production in Air-Cathode Microbial Fuel Cells

Abstract: To efficiently generate electricity using bacteria in microbial fuel cells (MFCs), highly conductive noncorrosive materials are needed that have a high specific surface area (surface area per volume) and an open structure to avoid biofouling. Graphite brush anodes, consisting of graphite fibers wound around a conductive, but noncorrosive metal core, were examined for power production in cube (C-MFC) and bottle (B-MFC) air-cathode MFCs. Power production in C-MFCs containing brush electrodes at 9600 m2/m3 reactor volume reached a maximum power density of 2400 mW/m2 (normalized to the cathode projected surface area), or 73 W/m3 based on liquid volume, with a maximum Coulombic efficiency (CE) of 60%. This power density, normalized by cathode projected area, is the highest value yet achieved by an air-cathode system. The increased power resulted from a reduction in internal resistance from 31 to 8 Ω. Brush electrodes (4200 m2/m3) were also tested in B-MFCs, consisting of a laboratory media bottle modified to h...

PWM Converter Power Density Barriers

Abstract: Power density of power electronic converters in different applications has roughly doubled every 10 years since 1970. Behind this trajectory was the continuous advancement of power semiconductor device technology allowing an increase of converter switching frequencies by a factor of 10 every decade. However, today's cooling concepts, and passive components and wire bond interconnection technologies could be major barriers for a continuation of this trend. For identifying and quantifying such technological barriers this paper investigates the volume of the cooling system and of the main passive components for the basic forms of power electronics energy conversion in dependency of the switching frequency and determines switching frequencies minimizing the total volume. The analysis is for 5 kW rated output power, high performance air cooling, advanced power semiconductors, and single systems in all cases. A power density limit of 28 kW/dm3@300 kHz is calculated for an isolated DC-DC converter considering only transformer, output inductor and heat sink volume. For single-phase AC-DC conversion a general limit of 35 kW/dm3 results from the DC link capacitor required for buffering the power fluctuating with twice the mains frequency. For a three-phase unity power factor PWM rectifier the limit is 45 kW/dm3@810 kHz just taking into account EMI filter and cooling system. For the sparse matrix converter the limiting components are the input EMI filter and the common mode output inductor; the power density limit is 71 kW/dm3@50 kHz when not considering the cooling system. The calculated power density limits highlight the major importance of broadening the scope of research in power electronics from traditional areas like converter topologies, and modulation and control concepts to cooling systems, high frequency electromagnetics, interconnection technology, multi-functional integration, packaging and multi-domain modeling and simulation to ensure further advancement of the field along the power density trajectory.

Thermal energy harvesting device using ferromagnetic materials

Abstract: A unique concept for harvesting electrical energy from thermal energy is presented A thermomechanical actuator was fabricated using ferromagnetic material The device converts thermal energy into mechanical energy, which can be converted into electrical energy using piezoelectric materials Magnetic force and operating frequency were measured on the device Results show that the current power density at ΔT=50K is between 185 and 361mW∕cm2 A thermal finite element analysis model is also presented to understand the influence of thermal interface, suggesting that increases of 185mW∕cm2 or higher are achievable

Impact of power density maximization on efficiency of dc-dc converter systems

Abstract: The demand for decreasing costs and volume leads to a constantly increasing power density of industrial converter systems. In order to improve the power density further different aspects, like thermal management and electromagnetic effects must be considered in conjunction with the electrical design. Therefore, a comprehensive optimization procedure based on analytical models for minimizing volume of DC-DC converter systems has been developed at the Power Electronic Systems Laboratory of the ETH Zurich. Based on this procedure three converter topologies - a phase shift converter with current doubler and with capacitive output filter and a series-parallel resonant converter - are optimized with respect to power density for a telecom supply (400V/48V). There, the characteristic of the power density, the efficiency and the volume distribution between the components as function of frequency is discussed. For the operating points with maximal power density also the loss distribution is presented. Further more, the sensitivity of the optimum with respect to junction temperature, cooling and core material is investigated. The highest power density is achieved by the series-parallel resonant converter. For a 5 kW supply a density of approximately 12 kW/ltr. and a switching frequency of ca. 130 kHz results.

A high power density converter system for the Gamesa G10x 4,5 MW wind turbine

Abstract: One of the main points in the design of a Multi-MW-class turbine is the size and weight of the total turbine. Gamesa has developed a converter system with a very high power density and low weight. The system is designed and tested to withstand very high short circuit currents, high vibrations and other wind turbine typical environmental aspects.

Design, Construction, and Testing of an Inductive Pulsed-Power Supply for a Small Railgun

Abstract: Advances in high-power-density batteries have rekindled interest in using inductive store as a pulse compression system. Although these batteries are considered very power dense, they lack over an order of magnitude of power density to drive a deployable electric gun. However, one can add an inductive circuit to a battery bank to make a hybrid system that has a much higher power density than batteries alone. A battery-inductor hybrid pulsed-power supply boasts several advantages over pulsed alternators, as inductors are static and relatively easy to cool. Inductors are potentially more energy dense than capacitors, making a battery-inductor hybrid pulsed-power supply an attractive alternative to capacitor-based pulsed-power supplies. The opening switch has been a major obstacle in previous inductive store projects, but in simulation, a new circuit topology-the Slow Transfer of Energy Through Capacitive Hybrid (STRETCH) meat grinder-greatly attenuates the problem. This paper discusses the design, construction, and testing of a small-scale STRETCH meat grinder system, which was successfully used to power a miniature railgun

Quantum dot laser with 75 nm broad spectrum of emission.

Abstract: We report on a quantum dot laser having an emission spectrum as broad as 74.9nm at 25°C in the 1.2-1.28 wavelength interval with a total pulsed output power of 750mW in single lateral mode regime and the average spectral power density of >10mW/nm. A significant overlap and approximate equalization of the ground-state and the excited-state emission bands in the laser's spectrum is achieved by means of intentional inhomogeneous broadening of the quantum dot energy levels.

Performance Comparisons Between Carbon Nanotubes, Optical, and Cu for Future High-Performance On-Chip Interconnect Applications

Abstract: Optical interconnects and carbon nanotubes (CNTs) present promising options for replacing the existing Cu-based global/semiglobal (optics and CNT) and local (CNT) wires. We quantify the performance of these novel interconnects and compare it with Cu/low-kappa wires for future high-performance integrated circuits. We find that for a local wire, a CNT bundle exhibits a smaller latency than Cu for a given geometry. In addition, by leveraging the superior electromigration properties of CNT and optimizing its geometry, the latency advantage can be further amplified. For semiglobal and global wires, we compare both optical and CNT options with Cu in terms of latency, energy efficiency/power dissipation, and bandwidth density. The above trends are studied with technology node. In addition, for a future technology node, we compare the relationship between bandwidth density, power density, and latency, thus alluding to the latency and power penalty to achieve a given bandwidth density. Optical wires have the lowest latency and the highest possible bandwidth density using wavelength division multiplexing, whereas a CNT bundle has a lower latency than Cu. The power density comparison is highly switching activity (SA) dependent, with high SA favoring optics. At low SA, optics is only power efficient compared to CNT for a bandwidth density beyond a critical value. Finally, we also quantify the impact of improvement in optical and CNT technology on the above comparisons. A small monolithically integrated detector and modulator capacitance for optical interconnects (~10 fF) yields a superior power density and latency even at relatively lower SA (~20%) but at high bandwidth density. At lower bandwidth density and SA lower than 20%, an improvement in mean free path and packing density of CNT can render it most energy efficient.

High efficiency and/or high power density wide bandgap transistors

Abstract: Field effect transistors having a power density of greater than 40 W/mm when operated at a frequency of at least 4 GHz are provided. The power density of at least 40 W/mm may be provided at a drain voltage of 135 V. Transistors with greater than 60% PAE and a power density of at least 5 W/mm when operated at 10 GHz at drain biases from 28 V to 48 V are also provided.

High-power pulsed sputtering using a magnetron with enhanced plasma confinement

Abstract: High-power pulsed dc magnetron discharges for ionized high-rate sputtering of metallic films were systematically investigated. The depositions were performed using two unbalanced circular magnetrons of different types with a directly water-cooled planar copper target of 100mm in diameter. The repetition frequency was 1kHz at a fixed 20% duty cycle and an argon pressure of 0.5Pa. Time evolutions of the discharge characteristics were measured to provide information on absorption of energy in the discharge plasma and on transfer of arising ions to the substrate at a target power density in a pulse up to 950W∕cm2. Time-averaged mass spectroscopy was performed at the substrate position to characterize ion energy distributions and composition of total ion fluxes onto the substrate. The deposition rate of the copper films formed on a floating substrate at the distance of 100mm from the target was 2.2μm∕min at an average target power density over a pulse period of 96W∕cm2. Very effective ionization of sputtered c...

Analysis of Piezoelectric Materials for Energy Harvesting Devices under High-g Vibrations

Abstract: We analyzed the miniaturized energy harvesting devices (each volume within 0.3 cm3) fabricated by using three types of piezoelectric materials such as lead zirconium titanate (PZT) ceramic, macro fiber composite (MFC) and poly(vinylidene fluoride) (PVDF) polymer to investigate the capability of converting mechanical vibration into electricity under larger vibration amplitudes or accelerations conditions (≥1g, gravitational acceleration). All prototypes based on a bimorph cantilever structure with a proof mass were aimed to operate at a vibration frequency of 100 Hz. PZT-based device was optimized and fabricated by considering the resonant frequency, the output power density, and the maximum operating acceleration or safety factor. PVDF- and MFC-prototypes were designed to have same resonant frequency as well as same volume of the piezoelectric materials as the PZT prototype. All three devices were measured to determine if they could generate enough power density to provide electric energy to power a wireless sensor or a microelectromechanical systems (MEMS) device without device failure.

Porous carbon electrode with conductive polymer coating

Abstract: An extremely high-performance polyaniline electrode was prepared by potentiostatic deposition of aniline on hierarchically porous carbon monolith (HPCM), which was carbonized from mesophase pitch. A capacitance value of 2200 F g −1 of polyaniline was obtained at a power density of 0.47 kW kg −1 and an energy density of 300 Wh kg −1 . This active material deposited on HPCM also has an advantageous high stability. These superior advantages can be attributed to the backbone role of HPCM. This method also has the advantages of not introducing any binder, thus contributing to the increase of ionic conductivity and power density. High specific capacitance, high power and energy density, high stability, and low cost of active material make it very promising for supercapacitors.

Anode‐Supported Tubular Micro‐Solid Oxide Fuel Cell

Abstract: A tubular anode-supported "micro-solid oxide fuel cell" (μSOFC) has been developed for producing high volumetric power density (VPD) SOFC systems featuring rapid turn on/off capability. An electrophoretic deposition (EPD)-based, facile manufacturing process is being refined to produce the anode support, anode functional and electrolyte layers of a single cell. μSOFCs (diameter < 5 mm) have two main potential advantages, a substantial increase in the electrolyte surface area per unit volume of a stack and also rapid start-up. As fuel cell power is directly proportional to the active electrolyte surface area, a μSOFC stack can substantially increase the VPD of an SOFC device. A decrease in tube diameter allows for a reduction in wall thickness without any degradation of a cell's mechanical properties. Owing to its thin wall, a μSOFC has an extremely high thermal shock resistance and low thermal mass. These two characteristics are fundamental in reducing start-up and turn-off time for the SOFC stack. Traditionally, SOFC has not been considered for portable applications due to its high thermal mass and low thermal shock resistance (start-up time in hours), but with μSOFCs' potential for rapid start-up, new possibilities for portable and transportable applications open up.

Microbial fuel cells utilising carbohydrates

Abstract: The paper reports results of a mediatorless microbial fuel cell (MFC), utilising waste carbohydrate (manure) as a fuel, which did not use a catalyst or a proton exchange membrane and is thus environmentally friendly (by using no toxic substances) in treating waste. The cell used a manure sludge in the anode compartment and an aqueous salt solution (seawater) containing dissolved oxygen. The influence of the geometric position of the anode and cathode, both made of carbon cloth, had a major effect on the fuel cell power performance. The maximum power density obtained with the cell was 4.21 mW m−2. The paper also reports results of a mediated MFC using a yogurt bacteria and methylene blue as mediator. This cell produced a maximum power density of over 13 mW m−2. This power output compares quite favourably with that achieved with the same cell using glucose as fuel with E. coli (peak power density of 180 mW m−2). Copyright © 2007 Society of Chemical Industry

Optimizing 13.5 nm laser-produced tin plasma emission as a function of laser wavelength

Abstract: Extreme ultraviolet lithography requires a light source at 13.5nm to match the proposed multilayer optics reflectivity. The impact of wavelength and power density on the ion distribution and electron temperature in a laser-produced plasma is calculated for Nd:YAG and CO2 lasers. A steady-state figure of merit, calculated to optimize emission as a function of laser wavelength, shows an increase with a CO2 laser. The influence of reduced electron density in the CO2 laser-produced plasma is considered in a one-dimensional radiation transport model, where a more than twofold increase in conversion efficiency over that attainable with the Nd:YAG is predicted.

Cooling Concepts for High Power Density Magnetic Devices

Abstract: In the area of power electronics there is a general trend to higher power densities. In order to increase the power density the systems must be designed optimally concerning topology, semiconductor selection, etc. and the volume of the components must be decreased. The decreasing volume comes along with a reduced surface for cooling. Consequently, new cooling methods are required. In the paper an indirect air cooling system for magnetic devices which combines the transformer with a heat sink and a heat transfer component is presented. Moreover, an analytic approach for calculating the temperature distribution is derived and validated by measurements. Based on these equations a transformer with an indirect air cooling system is designed for a 10 kW telecom power supply.

Ion flux characteristics in high-power pulsed magnetron sputtering discharges

Abstract: High-power pulsed dc magnetron discharges for ionized high-rate sputtering of copper films were investigated. The repetition frequency was 1 kHz at a fixed 20% duty cycle and argon pressures of 0.5 Pa and 5 Pa. Time evolutions of the discharge characteristics were measured at a target power density in a pulse up to 950 W/cm2. Time-averaged mass spectroscopy was performed at substrate positions. It was shown that copper ions are strongly dominant (up to 92%) in total ion fluxes onto the substrate. Their energy distributions with a broadened low-energy part at a lower pressure are extended to higher energies (up to 45 eV relative to ground potential for the target-to-substrate distance of 100 mm).

Energy harvesting by magnetostrictive material (MsM) for powering wireless sensors in SHM

Abstract: A new class of vibrational energy harvester based on Magnetostrictive material (MsM) Metglas 2605SC is deigned, developed, and tested in building practical energy harvesting wireless sensor networks. Compared to piezoelectric material, Metglas 2605SC offers advantages including ultra-high energy conversion efficiency, high power density, longer life cycles without depolarization issue, and flexibility to operate in strong ambient vibrations. To enhance the energy conversion efficiency and shrink the size of the harvester, Metglas is annealed in the direction normal to the axial strain direction without the need of electromagnet for applying bias (static) magnetic field. To seamlessly integrate with a newly developed wireless sensor at NC State 1 , a prototype design for the MsM harvester is proposed. An analytical model is developed for the harvesting using an equivalent electromechanical circuit. The model resulting in achievable output performances of the harvester powering a resistive load and charging a capacitive energy storage device, respectively, is quantitatively derived. An energy harvesting module, which powers a wireless sensor, stores excess energy in an ultracapacitor is designed on a printed circuit board (PCB) with dimension 25mm x 35mm. The main functionalities of the circuit include a voltage quadrupler, a 3F ultracapacitor, and a smart regulator. The output DC voltage from the PCB can be adjusted within 2.0~5.5V. In experiments, the maximum output power and power density on the resistor can reach 200 mW and 900 mW/cm 3 , respectively. For a working prototype, the average power and power density during charging the ultracapacitor can achieve 576 mW and 606 mW/cm 3 respectively, which are much higher than those of most piezo-based harvesters.

A tubular microbial fuel cell

Abstract: Cell potential and power performance for tubular microbial fuel cells utilising manure as fuel are reported. The microbial fuel cells do not use a mediator, catalysts or a proton exchange membrane. The cell design has been scaled up to a size of 1.8 m in length using electrodes of 0.4 m2 in area. The cell does not require a strictly controlled anaerobic environment and has potential practical applications when adapted into the form of a helix allowing fuel to flow through it. The cell could be used for power generation in remote applications. The peak power density of the cell is over 3 μW cm −2 (30 mW m−2). The performance can be improved by a more effective design of the interface between the anode and cathode chambers.

Catalytic Combustion Systems for Microscale Gas Turbine Engines

Abstract: As part of an ongoing effort to develop a microscale gas turbine engine for power generation and micropropulsion applications, this paper presents the design, modeling, and experimental assessment of a catalytic combustion system. Previous work has indicated that homogenous gas-phase microcombustors are severely limited by chemical reaction timescales. Storable hydrocarbon fuels, such as propane, have been shown to blow out well below the desired mass flow rate per unit volume. Heterogeneous catalytic combustion has been identified as a possible improvement. Surface catalysis can increase hydrocarbon-air reaction rates, improve ignition characteristics, and broaden stability limits. Several radial inflow combustors were micromachined from silicon wafers using deep reactive ion etching and aligned fusion wafer bonding. The 191 mm 3 combustion chambers were filled with platinum-coated foam materials of various porosity and surface area. For near stoichiometric propane-air mixtures, exit gas temperatures of 1100 K were achieved at mass flow rates in excess of 0.35 g/s. This corresponds to a power density of ∼1200 MW/m 3 ; an 8.5-fold increase over the maximum power density achieved for gas-phase propane-air combustion in a similar geometry. Low-order models, including time-scale analyses and a one-dimensional steady-state plug-flow reactor model, were developed to elucidate the underlying physics and to identify important design parameters. High power density catalytic microcombustors were found to be limited by the diffusion of fuel species to the active surface, while substrate porosity and surface area-to-volume ratio were the dominant design variables.