Papers by Author: Wei Zhao

Abstract: Aiming at the pressure control of hydraulic transformer (HT), the fractional order PID (FOPID) controller is proposed for the control of the position of the valve plate. The assignment system of the HT is carefully modeled. To optimally determine the parameters of the FOPID controller, a self-adapting differential evolution algorithm is employed. Numerical simulation is conducted to investigate the proposed control strategy. Both step response and sinusoidal command signal tracking of the servo system is assessed, and the results demonstrate that the proposed control strategy is obviously superior to the conventional PID, Fuzzy Logic Controller (FLC) and fuzzy-PID control strategy, and can afford precise tracking performances. It is suitable for the precise adjustment of the output pressure of the HT.

Abstract: Ultrafine (1-x)BiScO3-xPbTiO3 ferroelectric ceramics were successfully prepared by employing nanocrystalline ceramic powder. The average ceramic grain sizes range from 0.4μm to 1.2μm with different phases and different proceeds. The studies show the average grain sizes vary with the calcining and sintering temperature as well as the compositions in different phases. Ceramics, sintered at 1020°C for 3h, in morphotropic phase boundary (MPB) have the smallest grain sizes around 0.4 μm, those in tetragonal phase and rhombohedral phase have larger grains around 0.9μm. Meanwhile, the piezoelectric property and Curie temperature were founded size-dependent when the grain sizes are smaller than 1μm.

Abstract: High <001>-textured Na1/2Bi1/2TiO3-BaTiO3 (6mol%BaTiO3) ceramics were fabricated by reactive-templated grain growth (RTGG), using plate-like Bi4Ti3O14 particles prepared by a molten salt method as the templates. The effect of template concentration on the texture development and microstructure evolution was studied, and the mechanisms of grain orientation and densification were also discussed. The design of Bi element reaction has important impact on the texture development.

Abstract: Pure barium strontium titanate (Ba0.65Sr0.35TiO3) and MnO2-modified barium strontium titanate (Ba0.65Sr0.35TiO3-MnO2) thick films were fabricated by electrophoretic deposition technique. The structures and morphologies of the films were analyzed. The dielectric measurements were conducted on metal-insulator-metal capacitors using platinum as the bottom electrodes and gold as the top electrodes. The dielectric constants and dissipation factors of Ba0.65Sr0.35TiO3 and Ba0.65Sr0.35TiO3-15wt% MnO2 thick films were measured at a frequency of 1 MHz. The tunabilities of 12.5% and 9.3% were obtained for Ba0.65Sr0.35TiO3 and Ba0.65Sr0.35TiO3-MnO2 thick films under an applied electric field of 15 kV/cm, respectively. The dielectric properties of the present thick films were suitable for tunable microwave device applications.

Abstract: Lead-free Na1/2Bi1/2TiO3-6BaTiO3 (BNT-6BT) ceramics with different dopants were prepared by a conventional ceramic fabrication technique. The influence of doping CeO2, La2O3, Nb2O5 and Co2O3 on the structure was studied, and the mechanism of soft and hard additives with A-site or B-site substitute changing the piezoelectric properties was discussed. It was found that the rhombohedral-tetragonal morphotropic phase boundary (MPB) of the Na1/2Bi1/2TiO3-6BaTiO3 was not changed obviously.

Abstract: Al2O3 ceramic fillers were incorporated into polyetheretherketone (PEEK) to improve the mechanical property in order to suit its aerospace application. To get the high performance composite, it is important to control the dispersion of the nano-Al2O3 among the PEEK matrix. As a pre-fabrication process, the dispersion behaviors of the nano-Al2O3 particles in the liquid medium were studied. Thestability of suspensions was characterized by zeta potential, sediment volume, viscosity and TEM analysis. The mechanism of dispersing nano-Al2O3 aqueous suspension has been investigated including single-electronic stabilization, steric stabilization, and electrostatic stabilization. The highly dispersed and stabilized nano-Al2O3 aqueous suspensions were obtained at acidic condition (pH=3) with PEG-400 and tri-ammonium citrate (TAC).

Abstract: The purpose of this study was to investigate the in vitro degradation and release behaviors of calcium phosphate powders (Ca/P) containing Chinese Medicine for bone graft. Two kinds of Ca/P powders, one with the Chinese Medicine, Salvia Miltiorrhiza Bunge (SMB) and the other with Polyacrylic Acid (PAA) and SMB, were soaked in simulated body fluid (SBF) for up to 150h. The in vitro release of SMB was measured by UV-VIS spectroscopy. The Ca2+ concentrations and pH of SBF soaked Ca/P powders were measured by AAS and pH meter. TA and XRD were employed to analyze various Ca/P powders before and after soaked in SBF, respectively. The results demonstrated that a faster SMB release occurred during the first 24 hours, while a slow release was sustained up to150h. Furthermore, the released of SMB in Ca/P-PAA-SMB was faster than that of Ca/P-SMB. It was concluded that a controllable release of Chinese Medicine from Calcium phosphate may be carried out by the addition of suitable surfactant. Accordingly, calcium ions were released into SBF, which was benefit for bone tissue repairing and reconstructing. Additionally, the TA results showed that there was 1.66% SMB released from Ca/P-SMB-PAA powders. XRD confirmed that various Ca/P powders possessed poorer crystallinity and smaller grain size.