TiO 2 (titania) reinforced low density polyethylene (LDPE) composite is studied as substrate for microstrip patch antenna that is to be used in microwave X band (8 GHz to 12 GHz). Physical, thermal and microwave characterization of the composite is done to confirm the applicability of the composite material as substrate for microstrip antennas. Microstrip antenna with rectangular radiating patch is fabricated on composites with different volume fraction (VF) of filler in polymer as substrate. S11 measurements are carried out on the antenna designed on different substrates using vector network analyzer. To increase the operational bandwidth of the antenna three layer grading of the composite substrate is done. The bandwidth and S11 parameter performance of the antenna is found to be improved by using graded composite as substrate material. Enhancement of directivity is observed for graded substrate as compared to ungraded substrate.
Low-density polyethylene (LDPE)/titania (TiO 2 ) and polystyrene (PS)/titania (TiO 2 ) composite systems have been developed as alternative substrates for microstrip patch antennas (MPA) for handheld devices. Morphological, thermal, and microwave characterizations of these composites have been conducted for different volume fractions of TiO 2 in the polymer matrix. The size of the titania particles was found to be of the order of 0.5 lm, and their distribution in the composite was quite uniform. Composite materials showed an improvement in thermal and microwave properties over the parent polymer. Verification of these composites as potential substrates for MPA was carried out by fabricating simple rectangular patch X-band antennas. Materials with optimized substrate properties were chosen to design the MPA. The patches were designed with 4% volume fraction TiO 2 in the LDPE composite system and 6% volume fraction TiO 2 in the PS composite system. Return loss of $18 dB was observed for both systems.
The effect of a radially varying parallel equilibrium flow on the stability of the Rayleigh-Taylor ͑RT͒ mode is studied analytically in the presence of a sheared magnetic field. It is shown that the parallel flow curvature can completely stabilize the RT mode. The flow curvature also has a robust effect on the radial structure of the mode. Possible implications of these theoretical findings to recent experiments are also discussed.
A fundamental reality throughout the space and laboratory plasmas is the existence of magnetic field-aligned flows. It is usually believed that the spatial transverse shear in the parallel flow destabilizes many low-frequency instabilities and this may be the origin of low-frequency oscillations in the ionosphere. Here we show that this notion of the destabilizing influence of the shear in the parallel flow can be changed altogether if one takes the effect of the flow curvature (second spatial derivative) into account. The transverse curvature in the parallel flow can overcome the destabilizing influence of the shear and can render the low-frequency ion temperature gradient-type instabilities stable.
A nonlocal theory is formulated to study drift waves in a collisionless multicomponent (dusty) plasma in a sheared slab geometry. The dynamics of dust particles and ions are treated by fluid models, whereas the electrons are assumed to follow the Boltzmann distribution. It is found that the usual stability of drift waves in a sheared slab geometry is destroyed by the presence of dust particles. A drift wave is excited which propagates with a new characteristic frequency modified by dust particles. This result is similiar to our earlier work for the collisional dusty plasma [Chakraborty et al., Phys. Plasmas 8, 1514 (2001)].
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