Papers by Author: Wei Gao

Abstract: Bi-frequency modulation can effectively solve the contradiction between high frequency and efficiency, but it will bring the problem of the current ripple. In this paper, use Buck circuit as the prototype, adopt phase shift parallel technology, make theoretical analysis and simulation studies on the bi-frequency circuit that the high and low frequencies units are operating in a state of continuous inductor current. Analysis and simulation results show that phase shift parallel can effectively inhibit the output current ripple. ^aMitsui86425@163.com ^bZ1960113@VIP.sina.com ^cdepkia@163.com

Abstract: Taking the relative tip clearance as the variable, we numerically simulated the effect of tip clearance size on the performance of a straight-blade axial flow fan using the 3-D viscous flow solver. The tip clearance is referenced in the relative value. By comparing the flow field corresponding to five different values of the tip clearance 0, 0.5%, 1.0%, 1.5% and 2.0% with other parameters kept constant, we concluded that the changing of the tip clearance has a great influence on the performance of the axial flow fan. Both the efficiency and the total pressure decrease with the increase of the tip clearance.

Abstract: AZ61 alloy is an important magnesium (Mg) alloy which can be rolled at elevated temperature. However, the insufficient ductility of as-extruded alloys limits their design and applications. Pb or Pb+Sn additions lead to a high ductility (~18% at room temperature) and good tensile strength (~250 MPa). This paper discusses the mechanism of property enhancement and the influence of Pb addition on the solidification process of AZ61 alloy.

Abstract: The mechanical properties of the single ZnO nano-/micro-rod were studied using nanoindentation. The nanoindentation measurements were carried directly on these ZnO crystals on glass substrate without any further treatment. The hardness and Young’s modulus of the polar (0001) and nonpolar (011 ̅0) faces were tested and the results demonstrate a face dependence variation in both properties. The mechanical behaviour of the ZnO nano/micro-rod is discussed in conjunction with its morphology, structure and defect effects.

Abstract: A novel silicon-based light emitting structure comprising a lithium doped zinc oxide film and a high energy electrons generating silicon structure is presented. Red light emission with wavelength of ~630 nm is generated and recorded in electroluminescent spectrum under an applied DC voltage of 8.5 V.

Abstract: Positron annihilation spectroscopy is a nondestructive evaluation method which is sensitive to study the microdefects of materials. In this article, hypereutectic Al-20Si-0.35RE (wt.%) pre-alloyed powders was synthesized by using the water atomization method. The pre-alloyed powders were subsequently hot extruded with pressure of 250~500 MPa at 300°C. The effect of pressure of hot-extrusion on the evolution of microdefects in Al-20Si-0.35RE alloy was investigated by positron annihilation spectroscopy, electrical conductivity tests and hardness tests. It was shown that the accretion of pressure led to an apparent increase in conductivity and microhardness. For all samples, the hot-extrusion causes a pronounced change in positron annihilation related parameters signaling the variation of microdefects. The results of hardness tests and the electrical conductivity tests are varied following with the positron annihilation spectroscopy. Possible mechanisms of the influence of hot-extrusion on the behavior of microdefects are discussed.

Abstract: The limited sensitivity of thinfilm based sensors has motivated the search for sensing structures and materials with greater sensing performance. Although thinfilm based SAW devices have been used as force, pressure, chemical and gas sensors so far. It is limited by the exposed sensing surface of the thinfilm. A feasibility study has been done by implementing the ZnO nanorods (NRs) to enhance the device sensitivity by greatly increase the exposed sensing surface. The implementation of these ZnO NRs as sensing elements is expected to enhance the sensing power due to the large surface to volume ratio. The sensing mechanism in this design is by detecting the minute change of seismic mass for ZnO NRs using surface acoustic wave before and after the attachment of reacting chemical liquid and gas substance.

Abstract: Castings may be used more as structural components if friction stir (FS) processing could refine the microstructures satisfactorily. For this, material flow and the formation of various microstructural regions during FS were studied. It was found that -Al dendrites and eutectic Al-Si were sheared into the thread spaces and the microstructures were significantly modified and refined. Material merely dragged into the FS zone remains microstructurally segregated. The volume of each flow was affected by rotation speed and forward speed and the reason for this is explained. Finally, textures determined together with the strain values estimated are presented to discuss further the microstructual development in various stir zones.

Abstract: Low-k dielectric improves the switching speed by reducing the parasitic capacitance in integrated circuits. However it suffers the problem of copper diffusion. Forming gas (H2 + N2) plasma treatment on the surface of HSG-7000 low-k dielectric thin film has demonstrated to improve copper diffusion resistance. Two techniques using X-ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectroscopy (SIMS) have been used to examine the copper diffusion on this thin film. A thin layer of 10 nm with C-N bonds near the HSG-7000 surface were believed to be created by the plasma treatment and confirmed with XPS and SIMS and acts as barrier.

Abstract: This paper describes a new optical switching concept using the deflection of a piezoelectric tube manufactured by an electrophoretic deposition process. A prototype optical switch has been assembled and some of the performance characteristics have been measured, such as an insertion loss of 0.9dB, crosstalk of -47dB and switching speed from 5-15ms. The system for measuring deflection has been custom-designed and built with a measurement accuracy of 1μm. Future work involves the improvement of the piezoelectric tube performance characteristics and combining all switching components in one case so that the switch can be tested in a real network environment.