Papers by Author: Huan Liu

Abstract: This paper presents blind source separation of rolling bearing based on particle swarm optimization. The algorithm combines the advantages of both blind source separation and particle swarm optimization. Through the experiment it is shown that the algorithm can separate the signals collected from rolling bearing and gearbox effectively, which can provide a new method for fault diagnosis and signal processing of machinery equipment.

Abstract: The quality of the project depends firstly on the design. Selected excellent design units can help the owner to realize the projects quality, cost and schedule target. The principles of the evaluation in design bidding were discussed in this paper. The design quality, design fees quotation, design teams service commitments, design teams ability, design institutions strength, and design institutions reputation were given as the six aspects of evaluation index system. last, the organization of evaluator was discusses.

Abstract: Semiconducting barium titanate powderss with an average particle size less than 40 nm were used for tape casting. Green tapes with a thickness of 100-500 μm were tape-cast from aqueous slurry of barium titanate powders using polyvinyl alcohol (PVA) as binder and polyelectrolyte ammonium salt as dispersant. The solid loading, viscosity and rheological properties of the ceramic slurries were investigated. Slurries with low viscosity were obtained when the concentration of dispersant was 1.5-2.0 wt% (based on ceramic powders weight) with fixed 75 wt% solid loading. The highest solid loading and optimum dispersion were determined through the proper viscosity to cast. Microstructure and PTC effect of the ceramic chips were studied as a function of firing temperature. Yttrium ions were homogeneously diffused into barium lattices at a low temperature of 1240 °C, and fine-grained PTC ceramics with grain size of 1-2 μm were developed successfully. These results can be explained by the higher rate of reactivity of finer powders and stable behavior of the suspension.

Abstract: Dense PTC ceramics were prepared with BaTiO3 nanopowders synthesized by hydrothermal method. BaCO3 and Ti(OC4H9)4 were used as barium and titanium sources, and Y(NO)3·6H2O as the donor dopant respectively. The average grain size of the powders obtained after hydrothermal treatment at 160°C for 9h was about 30nm with cubic structure. Mn(NO3)2 was introduced to the as-prepared nanopowders in order to improve the PTC effect. After sintered at 1280°C, the PTC ceramic samples exhibited sufficient resistance jump ratio(1.086×103) around Curie temperature, the density of which was 5.81g/cm3(96.5% of the theoretical density).

Abstract: BaTiO3 nanopowders prepared by sol-gel process were used for multilayer PTCR ceramics in order to utilize grain boundary effect and lower sintering temperature. The precursor gel was calcined at different temperatures and the powders were characterized by XRD and TEM. The average grain size was about 26nm when calcined at 800°C for 2h. Effects of acceptor/donor concentration and sintering temperature on PTCR ceramics were also investigated. The optimal concentration of the donor was found to be 0.6mol with the acceptor concentration being 1/8 of the donor. Multilayer PTCR elements were fabricated by tape-casting technique. The jump ratio of PTCR chips sintered at 1240°C was above 103 with the average grain size smaller than 1~2 μm, which is suitable for the multilayer PTCR elements.

Abstract: Nanocrystalline thick-film gas sensor was fabricated by screen printing method with CuO-doped tin oxide powder synthesized by hydrothermal method. Average grain size of the CuO-doped tin oxide powders was typically below 10 nanometers and the thick-films had a narrow grain size distribution typically below 50 nanometers. Effect of the amount of CuO on the sensing properties was investigated and the optimal value was found to be 3 wt%. The nanocrystalline CuO-SnO2 thick-film gas sensors were more sensitive to H2S than those based on commercial micro SnO2 powders, which were attractive to the detection of low concentrations of H2S gas at relative low temperatures.

Abstract: The wireless passive surface acoustic wave (SAW) impedance-loaded sensors offer new and exciting perspectives for remote monitoring and controlling of moving parts, even in harsh environments. However, the classical simulation models such as equivalent circuit model (ECM) and coupling of modes (COM) model are not rigorous enough for these sensors since these sensors usually work in the RF band. We try to make it more accurate by using FEM/BEM (combined finite element method and boundary element method) model to determine some key parameters used in the COM model of impedance-loaded SAW sensors. In this paper, we use periodic Green function which is the basis of FEM/BEM model to determine the key parameters. The result of measurements on real SAW is nearly in accordance with that of simulations.

Abstract: We describe the fabrication of chip-type PTC elements (BaTiO3-based) by roll-forming process. Crack-free green tapes with good malleability are successfully obtained with the thickness typically in the range of 0.20~1.0mm. We also focus on reducing the room-temperature resistance of the chip-type PTC element without deteriorating its PTC effect, both by controlling the firing schedule and by introducing multilayer structure with electrode-bonding method. The typical size of the 5-layered chip-type PTC sample obtained is 8.0mm×5.0mm×1.95mm with R25=1.97- and Rmax/Rmin=4.8×105.

Abstract: Chip-type PTC thermistors with multilayer stacked structure have been fabricated by bonding sintered ceramic chips with internal electrodes to offer low resistance at room temperature and correspondence to surface mounted technology. The resistance-temperature characteristics of multiplayer stacked PTC thermistors made up of different numbers (N = 1, 3, 5) of layers were experimentally investigated (the typical size of each layer was 10 mm × 7.0 mm × 0.38 mm). The selection and extraction of additives in roll-forming process were also discussed. This resulted in a crack-free multiplayer stacked PTC thermistor.

Abstract: Copper-doped tin oxide nanopowder has been synthesized via the hydrothermal route, in which pure metallic Sn, diluted nitric acid solution and Cu(NO3)2 are used as the starting materials. The hydrothermal treatment at about 200°C for 10 h results in rutile crystalline SnO2 particles with a narrow size distribution typically in the range of 3~6 nm. The average crystallite size of 5 wt% CuO-doped SnO2 particles remains smaller than 12.5 nm even after annealing at 800°C. The evaluation of the sensitive properties of the synthesized powder with various amount of CuO doping is conducted on the thick-film samples fabricated by screen-printing method. The high sensitivity toward H2S as shown by the sensor test results show the possibility of using this material for gas sensor fabrication.