Qiu Yun Fu

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.

The Influence of Donor-Doped Concentration on the PTCR Characteristics of the Ban-xSmxTiO3 Based Ceramics Sintered in Reducing Atmosphere

Positive temperature coefficient of resistivity (PTCR) effect and electrical properties of (Ban-xSmx)TiO3 (BSMT ) samples with different Ba-site/Ti-site ratio (n) and various concentration of the donor-doped Sm3+ (x) sintered in a reducing atmosphere and reoxidized in air are investigated. The results show that the room temperature resistivity (ρRT) of the semiconducting BSMT ceramics first decreases and then increases with increasing of concentration of the donor-doped Sm3+, especially when x is 0.005 mol, the ρRT of the BSMT ceramics is the lowest. Moreover, the ρRT of the Ba-excess BSMT (n = 1.01) specimens reoxidized at 800 oC for 1 h after sintering at 1270 °C for 30 min in a reducing atmosphere is lower than the Ti-excess ones (n = 0.99), in addition, the ρRT of the BSMT specimens increases with an increase of both sintering temperature and reoxidized time.

Gas Sensing Performance of Macroporous SnO2 Thin Film Prepared by Using Carbonaceous Polysaccharide Microspheres as Pore-Forming Agent

The macroporous SnO2 thin film has been successfully prepared on alumina substrate with printed Ag interdigital electrodes by sol-gel dip-coating method. The carbonaceous polysaccharide microspheres synthesized by hydrothermal method were used as pore-forming agent. The SnO2 thin film prepared without using carbon microspheres was also synthesized for comparison. X-ray diffraction and scanning electron microscopy were taken to study the micro-characteristics of samples. The influences of operating temperature, gas concentration and structure feature on the H2S sensing performance of SnO2 thin film samples were systematically studied. Compared with SnO2 thin film prepared without using carbon microspheres, the macroporous SnO2 thin film showed a considerably reduced recovery time and good response-recovery properties.

Aerosol-Assisted CVD of SnO2 Thin Films for the Room-Temperature Detection of Hydrogen Sulfide

High-quality SnO2 thin-film materials capable of detecting H2S gas of low concentrations at room temperature was demonstrated in this paper. We employed aerosol-assisted chemical vapor deposition process for the deposition of SnO2 thin films on alumina substrates with pre-patterned electrodes. The gas-sensing performances of the films prepared under different deposition conditions were systematically compared and analyzed. When SnCl2·2H2O was used as the precursor, a response sensitivity of 98.4 toward 50 ppm of H2S at room temperature was achieved. At room temperatures, the resistance upon the H2S gas exposure could recover to 90% of the initial resistance of the sensor when the H2S gas flow was turned off.

Synthesis and Stabilization of BaTiO3/CoFe2O4 Ferrocolloids

In this article, nanocomposites of BaTiO3/CoFe2O4 have been prepared by sol-gel technique. The samples have been calcined at various temperatures ranging from 500 to 900 °C and then the microstructure of the composite nano-particles was studied. XRD, SEM analysis showed the powders can form the two phase composite system of BaTiO3 and CoFe2O4 and the average particle size of the crystalline phases is 50nm at sintering temperature of 800 °C. In addition, we have studied the effects of different solvents and mixed solvents on the stability of the nanocomposites suspensions. Results of sediment volumes and conductivity showed under ultrasonic agitation for at least 25 min, suspensions of the BaTiO3/CoFe2O4 in ethanol-acetylacetone (1:1 in volume) were most stable (the sediment volumes is 0.6cm3/0.4g, the conductivity is 9μS/cm). Electrophoretic deposition (EPD) was utilized for preparation of magnetoelectric (ME) composite films, the impact of deposition time and deposition voltage on electrophoretic deposition process was investigated. The obtained ME composite films exhibited good ferroelectric and ferromagnetic properties, which can meet the demand of ME devices.

Effect of Ni Electrode on the Characteristics of BaTiO3 Based PTCR Ceramics

In order to achieve cost-effective inner electrodes for the multilayer BaTiO3-based ceramics having a positive temperature coefficient of resistivity (PTCR), we fabricated Ni paste based on Ni powder and investigated the effect of Ni electrode on the performance of semiconducting BaTiO3 ceramics. We adjusted the particle size of Ni powder (0.2μm, 0.6μm and 1μm) and incorporated them as the electrodes into both single-layer and laminated BaTiO3 PTCR devices. The device samples were sintered at 1200oC for 30min in reducing atmosphere consisting of N2 and H2 (97:3 by volume ratio), and went through a post-sintering in-air heat treatment at 700-900oC in air which is necessary for the PTCR effect. The results indicate that Ni powder with lager particle size are more stable against post-sintering heat treatment, and the heating temperature needs to be optimized to overcome the trade-off between ohmic behaviors of Ni electrodes and the PTCR effect of BaTiO3-based semiconducting ceramics.

The Influence of Ba-Ti Ratio on the Electrical Properties and Microstructures of the BaM-0.007Sm0.007TiO3 Based Ceramics Fired in Reducing Atmosphere

Electrical properties, positive temperature coefficient of resistivity (PTCR), and microstructures of (Bam-0.007Sm0.007)TiO3 (BST) with different Ba-site/Ti-site (A/B) ratio sintered in a reducing atmosphere and reoxidized in air are investigated. The results reveal that the room temperature resistivity of the semiconducting BST ceramics first decreases and then increases with increasing of A/B ratio (m), particularly when m is equal to 1.006, the semiconducting BST ceramics which have been sintered in a reducing atmosphere and reoxidized at 800°C exhibit significant PTCR effect with a resistance jumping ratio of 3 orders magnitude, and achieve a lower room temperature resisitivity of 80.8 Ω∙cm, in addition, the grain size distribution of the Ti-excess specimens is much better than that of the Ba-excess ones.

Properties of Nano-ZnO Films Deposited by RF Magnetron Sputtering for SAW Biosensors

Abstract. In this article, nano-ZnO films were deposited on SiO2/Si (100) substrates by RF (radio frequency) magnetron sputtering using high purity (99.99%) ZnO target. The effects of deposition time and annealing temperature have been investigated. XRD (X-ray diffraction) and FSEM (Field Emission Scanning Electron Microscopy) were employed to characterize the quality of the films. The results show that the ZnO film with thickness of 600nm annealed at 900°C has higher quality of both C-axis orientation and crystallization. And for the Zone film with thickness of 300nm annealed at 850°C, the quality of both C-axis orientation and crystallization is higher than that annealed at 900°C and 950°C.