Dong Xiang Zhou

Design of triple-band LTCC antenna using meander line structure for mobile handsets

This paper presents the design simulation of compact meander line antenna for GSM/DAB/DCS bands used in mobile handsets. The dimensions of the LTCC chip antenna are 20×10×0.85 mm3. The structure includes two meander patches. The bottom meander patch is tuned to GSM band, and the top meander patch is designed for DCS band. The coupling between the two meander patches is used to obtain DAB band, instead stacking a third meander patch on the two meander patches. It is found that coupling quality varies with the space between two meander patches. With the 2.5:1 VSWR impedance bandwidth definition, the lower, middle, and upper band have the bandwidth of 110, 140, and 60 MHz, respectively. This paper provides a new scheme of designing compact antenna for mobile handsets.

Accurate FEM/BEM Simulation of Wireless Passive Surface Acoustic Wave Sensors

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.

The Properties of Antimony-Doped Tin Oxide Thin Films by the Sol-Gel Approach

Antimony-doped tin oxide thin films have a range of technical applications as conductive coatings, and sol-gel processing seems to offer some advantages over other coating techniques. In this study, the sol was prepared by sol-gel approach from SnO2·H2O and SbCl3 in alcohol. It was found that the heat-treatment temperature and doping level have strong influences on the microstructure and composition of Sb: SnO2 films. The SnO2 crystals exist mainly as tetragonal rutile structure. The optimum heat-treatment temperature is about 450 ~ 500°C, and the film is composed with nanocrystals and nano-pores. Microstructure and the electrical behaviors of Sb-doped SnO2 thin films derived by sol-gel process were investigated.

Fabrication of BaTiO3-Based Semiconducting Ceramic Thick Films by Aqueous Tape Casting

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.

Nanopowder and Fine-Grained Ceramics for Multilayer PTCR Elements

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.

High Piezoelectric Property and Low Dielectric Constant PZN-PZT Ceramics

The influences of the substitution of (Zn1/3Nb2/3) group for Ti as well as addition of Fe2O3 and K2CO3 on d33, kp, εr, and tgδ of the Pb[Zr0.46Ti0.54-x(Zn1/3Nb2/3)x]O3 + y mol%Fe2O3+z mol%K2CO3 (PZNPZT) (0 ≤ x ≤ 0.20, 0 ≤ y ≤ 0.10, 0 ≤ z ≤ 0.20) ceramics were investigated. The experimental results demonstrated that when x increases in Pb[Zr0.46Ti0.54-x(Zn1/3Nb2/3)x]O3+0.3 mol%Fe2O3+0.5mol%K2CO3 ceramics, the d33, kp, εr, and tgδ increase and approach to their maximum values, then eventually decrease. XRD analysis revealed that the perovskite structure of the materials transfers from tetragonal phase to rhombohedral phase. The relative dielectric constant (εr) decreases dramatically in the rhombohedral phase area near the MPB; the d33 and εr decrease with the small amount of added Fe2O3 and K2CO3, which also contributes to densification of the PZN-PZT ceramics. The optimized piezoelectric performances through the experiment were obtained as d33=280 pC/N, kp=0.62, εr=900, tgδ=0.003.

Liquid Desiccant Drying Method for Gelcasting PTC Ceramics Based on BaTiO3

In this work, aqueous gel-casting (AGC) method was used for preparing PTC (positive temperature coefficient) ceramic green body based on BaTiO3. We studied on modeling of liquid desiccant drying method for gelcasting ceramic bodies, and compared with the conventional drying methods.

Synthesis of (1-x) Ca0.4Sm0.4TiO3 – xLi0.5Nd0.5TiO3 Ceramic Powders via Citric Acid Precursor

Using citric acid (CA) as a chelating agent, (1-x)Ca0.4Sm0.4TiO3 –xLi0.5Nd0.5TiO3 (CSLNT) (x = 0.3) ceramic powders were synthesized by the Pechini method. The CSLNT precursor and derived oxide powders were characterized by differential thermal analysis, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy. Only perovskite CSLNT (x=0.3) phase appeared when the CSLNT precursor was calcined at 1050°C for 3 h. Compared with the conventional solid-state reaction method, microwave dielectric ceramics with better properties could be prepared by the Pechini method at lower sintering temperature.

On the Microstructure and Electrical Properties of Undoped and Antimony- Doped Tin Oxide Thin Film Deposited by Sol-Gel Process

Undoped and antimony-doped tin oxide (ATO) thin films were prepared by sol-gel process in the solution of metal salts of tin (II) chloride dehydrate and antimony tri-chloride. The microstructure of the thin films was analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). Compared with undoped tin oxide, doped antimony tin oxide films coated glass substrate were homogeneous in composition and morphology after being sintered at different temperatures. Electrical behavior of the doped films was discussed in terms of sheet resistance measured by four point probe. From the experimental data, the sheet resistance of the films could be as low as 100-200Ω/□

Preparation and Characterization of Semi-Conducting (Ba,Sr)TiO3 Powders by a Wet Chemical Route

Ultrafine (Ba,Sr)TiO3-based powders used for making positive temperature coefficient of resistance (PTCR) were synthesized by two chemical steps: polyacrylamide gel process and liquid phase coating process. First, donor doped (Ba,Sr)TiO3 powders were synthesized by polyacrylamide gel process at rather low temperature, and the physical and chemical characteristics of the gels and the precursorpowders were investigated by DSC, TG, XRD and TEM. Secondly, acceptor and sintering aid were coated by an aqueous solution containing acceptor (Mn) and additive (Si). The characterization and sintering behavior of the semi-conducting powders and the PTC effect of ceramic samples prepared by the as-obtained powders were investigated.