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Content available Propagation in dielectric rectangular waveguides
EN
We present a fundamental and accurate approach to compute the attenuation of electromagnetic waves propagating in dielectric rectangular waveguides. The transverse wave numbers are first obtained as roots of a set of transcendental equations developed by matching the fields with the surface impedance of the wall. The propagation constant is found by substituting the values of transverse wave numbers into the dispersion relation. We have examined the validity of our model by comparing the computed results with those obtained from Marcatili’s equations and the finite element method. In our results, it is shown that the fundamental mode is identical with that found in a perfectly conducting waveguide. Our analysis also shows that a hollow waveguide is found to have much lower attenuation than its dielectric counterparts. Since the cutoff frequency is usually affected by the constitutive properties of the dielectric medium, for a waveguide designed for wave with the same cutoff frequency, hollow waveguides turn out to be relatively larger in size.
2
Content available remote Dispersion of waves in coated poroelastic circular cylinders
EN
The phenomenon of crack initiation due to dynamic contact loading is referred to as fretting fatigue. This situation is commonly encountered in mechanical couplings subjected to vibration. Whenever a material has good mechanical properties but poor fretting resistance it is advantageous to provide a layer of material having good fretting resistance instead of changing the entire material. This extra layer of material can be provided by coating or by any other surface treatment methods. Wave propagation in coated poroelastic cylinders of infinite extent is investigated employing Biot's theory. The coated poroelastic cylinder consists of two poroelastic cylinders of different poroelastic materials bonded at the curved surface such that the liquids in the poroelastic materials are immiscible. Frequency equations of coated poroelastic cylinders are derived both for pervious and impervious surfaces. Let the infinite coated poroelastic cylinder be homogeneous and isotropic and the outer boundary is free from stress. At the interface of the core and coating, the stresses and displacements are continuous. For motions having infinite wavelength or when the wavenumber is zero, the axial shear and radial modes of the coated poroelastic cylinder are uncoupled each for a pervious and an impervious surface. The frequency equation of axial shear vibrations is same for pervious and impervious surfaces. Non-dimensional phase velocity for propagating modes is computed as a function of propagation constant in the absence of dissipation. The results are presented graphically for two types of coated poroelastic cylinders and then discussed.
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