Metal- and Dielectric-Loaded Waveguide: An Artificial Material for Tailoring the Waveguide Propagation Characteristics

Abstract

In the present chapter a number of loaded structures are studied with circular cross-section to explore the deviation in their dispersion characteristics from their parent circular waveguide. The dielectric and/or metal loading to the waveguide tailors its dispersion characteristics. In general, the dielectric depresses and the metal elevates the dispersion characteristics from the characteristics of their parent circular waveguide. The axial periodicity results in periodic dispersion characteristics with a lower and an upper cutoff frequency (bandpass). However such a characteristic is not reported for the azimuthal periodic structures. The bandpass characteristic arises due to the shaping of the dispersion characteristics. Therefore the dispersion shaping is only possible with axial periodicity and not with the azimuthal periodicity. The sensitivity of the structure (geometry) parameters on the lower and upper cutoff frequencies, the extent of passband and the dispersion shaping are also included. In the axial periodic structures, the periodicity is found to be the most sensitive parameter for tailoring the dispersion characteristics and the disc-hole radius is the most sensitive parameter for shifting the dispersion characteristics over the frequency axis.

Electromagnetic and RF pulse design simulation based optimization of an eight‐channel loop array for 11.7T brain imaging

“…To prevent this radiation loss and hence, improve the power absorbed in the sample at 11.7T, the cutoff frequency of the local RF shield must be increased. Several techniques such as dielectric and metallic loading have been reported in the literature to alter the dispersion characteristic of a circular waveguide 39 . Dielectric lining could be expensive, and it can increase the overall weight of the coil.…”

“…Several techniques such as dielectric and metallic loading have been reported in the literature to alter the dispersion characteristic of a circular waveguide. 39 Dielectric lining could be expensive, and it can increase the overall weight of the coil. Hence, the simplest form of metallic loading in which the ends of the cylindrical shield were folded until the inner tube was implemented.…”

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