Sumesh George

CeO2–La0.5Sr0.5CoO3−δ composites for giant permittivity applications

CeO2?La0.5Sr0.5CoO3?? (LSCO) composites with different LSCO loadings were prepared by the conventional solid-state ceramic route. X-ray diffraction and scanning electron microscopy results show that the composite is a mixture of CeO2 and LSCO. The variation of relative permittivity (measured at 27??C) with sintering temperature shows that the permittivity is maximum when sintered at 1150??C for the volume fraction of 0.4 (?r ? 105). The permittivity is decreased when sintering temperature increases above 1150??C. For all volume fractions of LSCO, the relative permittivity of CeO2?LSCO composites is almost independent of temperature in the range ?30 to 70??C. CeO2?LSCO composites can be a suitable substitute for cermets used in electromechanical and embedded passive devices.

Polyethylene-ceramic composites for electronic packaging applications

Summary form only given. The recent rapid progress in microwave communication accelerates the search of new materials to meet the present challenging performance requirements. In order to maintain high signal conveying efficiency, the dielectric substrate should have low relative permittivity and low dielectric loss. Several low loss low permittivity ceramics such as silicates and aluminates have been developed. However, they have high processing temperature and are brittle. Polymers are flexible having low processing temperature and exhibit excellent microwave dielectric properties. However, they have low thermal conductivity and high coefficient of thermal expansion. The composite strategy of combining the advantages of both polymer and ceramic phase can offer excellent property. Polymer ceramic composite offers excellent material characteristics such as flexibility, low processing temperature, and good microwave dielectric and thermal properties. In the present study we have taken polyethylene as the polymer because it has low processing dielectric properties. The relative permittivity of the individual phases and volume fraction of the filler are the most important factors determining the effective dielectric properties of the composites. In this paper we report the effect of ceramic fillers having relative permittivity in the range 10 to 110 (Sm2Si2O7, CeO2, Ca[(Li1/3Nb2/3)0.8Ti0.2]O3-delta, Sr2Ce2Ti5O15) in polyethylene. The effect of frequency and temperature and volume fraction of fillers in polyethylene on the dielectric properties of the composites are studied. The ceramic reinforced polyethylene composites are prepared by melt mixing and hot pressing techniques. The microstructure of the composite is studied using a scanning electron microscope. The dielectric properties at high frequency (8 GHz) are analyzed using the cavity perturbation method. The relative permittivity and dielectric loss increased with increase in the ceramic loading for all the ceramic polymer composites. The experimentally observed results are compared with theoretical models.

Polymer ceramic composites for microwave substrate and antenna applications

The preparation and microwave dielectric properties Ca[(Li<inf>⅓</inf>Nb<inf>⅔</inf>)<inf>0.8</inf>Ti<inf>0.2</inf>]O<inf>3-δ</inf> ceramic filled polymer composites for microwave substrate applications is discussed in this paper. The prediction of the dielectric properties of polymer-ceramic composites using different theoretical models is also discussed. A Coplanar Waveguide Monopole Antenna is designed and fabricated using epoxy-CLNT polymer-ceramic composite and compared its response with standard FR-4 epoxy.

Effect of filler on the microwave dielectric properties of polyethylene/ceramic composites

The present study investigates the effect of various ceramic fillers on the dielectric properties of polyethylene based composites. The fillers used were Sr<inf>9</inf>Ce<inf>2</inf>Ti<inf>12</inf>O<inf>36</inf> (SCT), Ca[(Li⅓Nb⅔)<inf>0.8</inf>Ti<inf>0.2</inf>]O<inf>3-δ</inf> (CLNT) and Sm<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> (SS) with relative permittivities 173, 38 and 12 respectively. The composites were synthesized by melt mixing and hot pressing methods. The effect of different volume fractions of the ceramic (vf = 0 – 0.5) on the dielectric properties of the composites was investigated at 8 GHz. The dielectric properties (relative permittivity and dielectric loss) were found to increase with the ceramic filler content. The relative permittivities obtained experimentally were compared with that of the theoretical predictions.