Shuping Gong

Grain-oriented sodium bismuth titanate-based lead-free piezoelectric ceramics prepared using the pulsed strong magnetic field and template grain growth

In this paper, 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNBT6) lead-free piezoelectric ceramics have been prepared using the gelcasting technology. The dielectric and piezoelectric properties of these ceramics have been investigated. The specimens were sintered at 1100–1200u2009°C after grain-oriented under the pulsed strong magnetic field during the solidification of the green bodies. Compared with the BNBT6 samples without applying magnetic field, the ceramics textured by applying 5 T pulsed magnetic field has a coercive field with reduction of 400 V/mm, which makes the polarization process easier. Meanwhile, it is noted that the orientation degree increases with increasing sintering temperature, whereas the piezoelectric constant and electromechanical coupling coefficients are improved. If SrTiO3 seed grain is introduced, the orientation degree can reach 0.70 and the relative density of the sintered ceramics is up to 96%. The dielectric properties are anisotropic in directions vertical and parallel to the applied ma...

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.

Effect of reoxidation annealing on the PTCR behaviour of multilayer Nb5+-doped BaTiO3 ceramics with a Ni internal electrode

The effects of reoxidation annealing on the electrical properties and the positive temperature coefficient of resistance (PTCR) effects of multilayer Ba1.005(Ti1−x Nbx)O3 (BTN) ceramics sintered at different temperatures from 1100 to 1160xa0°C for 2xa0h in a reducing atmosphere and reoxidized at various temperatures in the range 500–900xa0°C were investigated. The results indicated that the room-temperature (RT) resistance of the BTN ceramics reoxidized at different temperatures first increased slowly and then quickly with the increase in the reoxidation temperature. Meanwhile, the resistance jump of the samples increased first and then decreased with the increase in the reoxidation temperature. In addition, the PTCR effect could be improved by prolonging the reoxidation time. Finally, the samples reoxidized at a low temperature of 600xa0°C after sintering at 1160xa0°C in a reducing atmosphere exhibited a significant PTCR effect, with a resistance jump of 3.5 orders of magnitude, along with a low RT resistance of 0.38xa0Ω. Additionally, the influences of the reoxidation temperature and time on the grain resistance and grain-boundary resistance were investigated using complex-impedance spectroscopy.

Positive temperature coefficient effects of carbon blackfilled polytetrafluoroethylene composites

Abstract Carbon black (CB)-filled polytetrafluoroethylene (PTFE) composites were prepared by compact molding of a dry-mixture of CB and polymer powders followed by a sintering technology. The composites show a very low percolation threshold about 5 vol. %, which can be attributed to the segregated distribution of CB in the interfacial regions of PTFE particles. The PTFE/CB composites exhibit a high PTC transition temperature (>300 0C), high PTC intensity (3.5) and no NTC effects. The absence of NTC effect of the composites was attributed to the extremely high viscosity of PTFE at temperatures above its melting point, which restricts the migration of CB particles and prevents the formation of new conductive networks.

An investigation of the voltage-withstanding mechanism of BaTiO3 ceramic semiconductors

The voltage‐withstanding behavior of a BaTiO3 ceramic semiconductor is closely related to the grain boundary structure of this kind of ceramic. This mainly depends on the height of the potential barrier in the grain boundary. A novel concept of the barrier height per unit width is proposed, by which the voltage‐withstanding mechanism can be satisfactorily explained. Positive temperature coefficient devices of high performance have been developed, which possess resistivity ( 300 V/mm).