Tzuu-Hsing Ueng

Electrical and impact properties of the hybrid knitted inlaid fabric reinforced polypropylene composites

A range of conductive knitted fabric reinforced polypropylene composites have been developed and their electromagnetic shielding effectiveness (EMSE), electrostatic discharge (ESD) and impact properties have been investigated. Carbon and aramid fibers are used as the reinforcement phase in the composites, while copper and stainless steel wires are incorporated as conductive fillers to provide the ESD and EMSE properties of the composite materials. The hollow spindle spinning system has been used to make SS/PP, Cu/PP, SS/C/PP, Cu/C/PP and Cu/K/PP uncommingled yarns. The double plain knitted fabric and its inlaid fabrics were fabricated from the yarns using a 5G traverse knitted machine. Changing the yarn composition, fabric knit structure, and stitch density varies the amount of copper and stainless steel conductive fillers in the composites. 4 layer cross-ply laminates were laid-up by hand, then formed into 3-mm thick conductive thermoplastic composites using a compression molding. It was observed that the EMSE and ESD of the composites increase with increasing the incident frequency, especially at higher frequency range. The effects of inlaid ends, materials and yarn constitutions on the EMSE of the conductive thermoplastic composites were investigated. The results indicate that the composites can be used for the purpose of electromagnetic shielding and ESD attenuation, as well as for some microwave applications.

Effects of additives on the microstructure and dielectric properties of Ba 2 Ti 9 O 20 microwave ceramic

Preparation of dense and phase-pure Ba 2 Ti 9 O 2 0 is generally difficult to achieve using a solid-state reaction, due to the presence of several thermodynamically stable compounds in the vicinity of the desired composition. This work investigated the effects of various additives (TiO 2 , MnO, and ZrO 2 ) on the densification, microstructural evolution, phase stability, and dielectric properties of Ba 2 Ti 9 O 2 0 . Ceramics with theoretical density of ≥95% were achieved in all cases after sintering at 1300 °C. A pure Ba 2 Ti 9 O 2 0 phase was obtained by treating the material with TiO 2 additions (≤5.6 wt.%) and sintering at temperatures ranging between 1200 and 1350 °C. Ba 2 Ti 9 O 2 0 is a nonstoichiometric compound that can accommodate an excess amount of TiO 2 . As the temperature was increased, pure Ba 2 Ti 9 O 2 0 partially decomposed and formed a mixture of BaTi 4 O 9 and Ba 2 Ti 9 O 2 0 . The ceramic with excess TiO 2 sintered at 1390 °C possessed a higher permittivity and a lower quality factor due to the larger grain size and lower density. For ceramic with the addition of ZrO 2 (≤6 wt.%), pure Ba 2 Ti 9 O 2 0 phase was obtained after sintering between 1200 and 1390 °C, and the quality factor was improved. The decomposition temperature of the Ba 2 Ti 9 O 2 0 phase was greater than 1390 °C. For sintering temperatures ≥ 1350 °C, the extent of Ba 2 Ti 9 O 2 0 phase decreased with MnO additions. As the MnO content reached 0.5 wt.%, only BaTi 4 O 9 and TiO 2 phases existed, suggesting a decrease in the decomposition temperature of Ba 2 Ti 9 O 2 0 with the addition of MnO. The microwave properties of the ceramics degraded significantly at the sintering temperature of 1390 °C.

ELECTRICAL PROPERTIES OF THE CONDUCTIVE KNITTED FABRIC REINFORCED THERMOPLASTIC COMPOSITES

ABSTRACT This paper reports a study to develop conductive thermoplastic composite materials for attenuation of the electrostatic discharge and immunity of the electromagnetic shielding effectiveness applications. In general, most of the plastics and composites are subjected to conductivity and electrostatic. To overcome these bottleneck, recently stainless steel/polyester/glass/ polypropylene (SS/PET/G/PP) knitted fabrics made from 5G flat knitting machine and their composites were developed successfully. Primary objects of this research are to develop a new material, which could be used in automobile, aerospace, electronic and electrical fields, for avoiding the electromagnetic and electrostatic discharge interference. Stainless steel wires are incorporated as conductive fillers to facilitate the electrostatic discharge (ESD) and electromagnetic shielding properties of the knitted fabric. To facilitate the knitting and reduce the material cost the uncommingled yams comprising stainless steel/polyester/glass/polypropylene yams are produced using a hollow spindle spinning method. The attenuation of the ESD for the various knitted fabric reinforced composites was obtained using an ESD immunity tester in the voltage range of 8kV and 12 kV. Typical waveforms of the output electrostatic discharge voltage on the oscilloscope have also been reported. The electromagnetic shielding effectiveness (EMSE) of various knitted composites was obtained using a coaxial transmission line holder in the frequency range of 300 kHz to 3 GHz. The variations of EMSE and ESD of knitted composites with the fabric structure, stitch density, number of plies, and the amount of stainless steel are described. Suitability of the knitted composites developed in this study for electromagnetic shielding applications is also discussed.