A power microelectromechanical concept, a microthermophotovoltaic system, is described in this work. The system uses hydrogen as fuel and is capable of delivering 4.5 W of electrical power to a microcombustor 0.1 cm3 in volume. It does not involve any moving parts. Its fabrication and assembly are relatively easy. As a result, it can be more commonly used in commercial electronics and microdevices.
A prototype microthermophotovoltaic ͑micro-TPV͒ power generator is described in this letter. The system is made of a SiC ͑silicon carbide͒ emitter, a simple nine-layer dielectric filter, and a GaSb ͑gallium antimony͒ photovoltaic cell array. In a microcombustor of 0.113 cm 3 in volume, when the flow rate of hydrogen is 4.20 g/h, the micro-TPV system is able to deliver an electrical power output of 1.02 W, corresponding to an open-circuit electrical voltage of 2.28 V and a short-circuit current of 0.59 A. The prototype of the micro-TPV system will make it possible for us to substitute batteries with micropower generators in micromechanical devices in the near future.
La 2 ∕ 3 Ca 1 ∕ 3 MnO 3 thin films have been grown on yttria-stabilized zirconia (YSZ) buffered silicon-on-insulator (SOI) substrates by the pulsed laser deposition technique. While full cube-on-cube epitaxy was achieved for the YSZ layer, the top manganite layer was multioriented in plane, with a coexistence of cube-on-cube and cube-on-diagonal epitaxial structures. Due to a combined influence from the magnetocrystalline, shape, and stain-induced magnetic anisotropy, in zero field and low temperatures the local spin orientation varies across the large-angle grain boundaries. As a result, a quite large low-field magnetoresistance (LFMR) based on spin-dependent tunneling was observed. The film shows a resistance change of ∼20% in a magnetic field <1000Oe at 50K, which is promising for real applications.
We use an entropy balance to formulate the entropy generation equation in a flame zone of a cylindrical microcombustor tube. In deriving this equation, we define a nondimensional radius as the ratio of the tube radius to the flame thickness, and we set up a thermal model of the flame zone by applying an energy balance for a steady flow system to the flame zone. Based on this model, we obtain a relationship between the flame temperature and the nondimensional radius. Given this relationship, the effects of the fuel, fuel-air ratio, unburned gas temperature, and tube radius on entropy generation are analyzed. The occurrence of minimum entropy generation is predicted. The efficient operating conditions of the microcombustor are suggested.
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