Изучение характеристик транзисторов на гетероструктурах нитрида галлия, выращенных методом аммиачной молекулярно-лучевой эпитаксии на подложках сапфира и кремния

AbstractsAmmonia molecular-beam epitaxy has been used to grow gallium nitride (GaN) transistor heterostructures on sapphire and silicon substrates. GaN transistors with a 1.2-mm periphery fabricated on substrates of both types exhibited similar high static characteristics: saturation current density above 0.75 A/mm, transconductance above 300 mS/mm, and breakdown voltage above 120 V. Measurements of the small-signal parameters showed that transistors based on silicon substrates possessed high gain in a frequency range up to 5 GHz; the specific output power at 1 GHz amounted to 5 W/mm for transistors on sapphire substrate and 2 W/mm for transistors on silicon substrate.

Comparison Between a Wideband Fractal-Inspired and a Traditional Multicantilever Piezoelectric Energy Converter

Harvesting energy from ambient vibrations in order to power autonomous sensors is a challenging issue. The aim of this work is to compare the power output from an innovative wideband fractal-inspired piezoelectric converter to that from a traditional multicantilever piezoelectric energy converter. In a given frequency range, the converters are tuned on the same eigenfrequencies. The effect of the input acceleration and of the resistive load applied to the converters is investigated experimentally for each of the three eigenfrequencies in the range between 0 and 120 Hz. The fractal-inspired converter exhibits a significantly higher specific output power at the first and third of the eigenfrequencies investigated.

Experimental Comparison Between a Fractal-Inspired Multi-Frequency Piezoelectric Energy Converter and a Traditional Converter

Harvesting energy from ambient vibrations in order to power autonomous sensors is a challenging issue. The aim of this work is to compare the power output from an innovative multi-frequency fractal-inspired piezoelectric converter to that from a traditional multi-cantilever piezoelectric converter. The converters are designed in order to give the same eigenfrequencies in a given range and a prototype of both is built using commercial materials. The experimental tests investigate both the effect of the acceleration and of the resistive load applied to the converters for each of the three eigenfrequencies in the range between 0 and 120 Hz. The fractal-inspired converter exhibits a significantly higher specific output power at the first and third of the eigenfrequencies investigated.

Fabrication of Components for Solid Oxide Fuel Cells by Tape Casting and Magnetic Pulsed Compaction

Fabrication of dense YSZ electrolytes and porous LSM cathodes in the shape of tubes using a radial magnetic pulsed compaction of multilayered tubular blanks of powder tapes has been investigated. The tapes were prepared with butyral resin binder. The multilayered blanks were compacted magnetically. Magnetic pressures of 0.2-0.3 GPa in amplitude, sintering temperatures as low as 1100-1300 °C (in air) with holding time of 20-540 min have been used. Cathode tubes of 0.2-1.0 mm thick exhibited the reproducible open porosity up to 45 %. YSZ electrolyte tubes with the wall of 100-450 microns thick had near full relative density, 0.97-0.99, and were characterized with grains of 200-500 nm in size on the average depending on the sintering temperature. The electrochemical cells built up of as-prepared tubular electrolytes and traditional research electrodes were tested under the air-hydrogen fuel cell conditions. The specific output power, 0.6 W cm-2, was realized at temperature of 885 °C.

An Experimental Study of Blade Angle Effect on a Micro Axial-Type Turbine Air Grinder

Performance characteristics are experimentally studied with changing nozzles, stators and rotors on a partially admitted small axial-type turbine, which could be applied to a driver of micro air grinders. When air tools adopt axial-type turbines as a driver, they could operate without friction and abrasion because the turbine rotor does not make contact with the casing. In order to maintain these merits on a small axial-type turbine without reducing power, performance characteristics are examined in this study through measuring the specific output power with eight different stators and three different rotors and nozzles. The tested turbine consists of two-stages and its mean radius of flow passage is 9.2mm. Output powers are obtained through measured pressure, temperature, torque, rotational speed, and flow rate. The experimental results show that the output power obtained on the second stage is insignificant comparing with that on the first stage because partially admitted flow is fully diffused in the second stage. Meanwhile, the output power is increased to 16–22% by changing the nozzle blade angle from 60° to 70° because the first stage performance is directly affected by the flow spouted from the nozzle. These results indicate that blade angles greatly influence the performance of a micro turbine operating in partial admission. When an appropriate stator and rotor that are designed in accordance with the flow spouted from the nozzle are installed in the rotating part, the output power is increased to 38% depending on the blade angle.

Digital Control of the WR21 Intercooled Recuperated Gas Turbine

The on-going development of a full authority digital engine control (FADEC) system for the US Navy’s Intercooled Recuperated (ICR) gas turbine requires a high level of system coordination to achieve the primary benefits of reduced specific fuel consumption and improved specific output power relative to a simple cycle engine. This paper describes the system evolution and the hardware and associated control algorithms implemented in the Advanced Development prototype ICR control system design. The ICR control system is required to coordinate the actions of 58 actuator channels using data taken from 141 sensors. Primary control of the engine output power is provided by regulation of the fuel metering valve. Thermal management of the intercooler, recuperator, and variable area power turbine nozzle results in maximum cycle efficiency within safe operating limits. The new electronic engine controller (EEC) is based on an open architecture Futurebus+ backplane and is fully redundant in all operationally critical control functions. The EEC also features an integrated operating panel and video display for local operation and maintenance of the control system. The graphical display and function keys provide access to control functions as well as assist maintenance activities with built-in test diagnostics to trouble shoot failed circuitry.