Abstract:
We present an accurate approach to compute the attenuation of waves, propagating in circular waveguides with lossy and superconducting walls. A set of transcendental equation is developed by matching the fields at the surface of the wall with the electrical properties of the wall material. The propagation constant kz is found by numerically solving for the root of the equation. The complex conductivity of the superconductor is obtained from the Mattis-Bardeen equations. We have compared the loss of TE11 mode computed using our technique with that using the perturbation and Stratton’s methods. The results from the three methods agree very well at a reasonable range of frequencies above the cutoff. The curves, however, deviate below cutoff and at millimeter wave frequencies. We attribute the discrepancies to the dispersive effect and the presence of the longitudinal fields in a lossy waveguide. At frequencies below the gap, the superconducting waveguide exhibits lossless transmission behavior. Above the gap frequency, Cooper-pair breaking becomes dominant and the loss increases significantly.

Abstract:
We numerically demonstrate that domain walls can be used as spin wave waveguides. We show that gapless spin waves bounded inside a domain wall can be guided by the domain wall. For Bloch walls, we further show that the bound spin waves can pass through Bloch lines and corners without reflection. This finding makes domain-wall-based spin wave devices possible.

Abstract:
It is widely accepted that, on ensemble average, the transmission T of guided modes decays exponentially with the waveguide length L due to small imperfections, leading to the important figure of merit defined as the attenuation-rate coefficient alpha = -/L. In this letter, we evidence that the exponential-damping law is not valid in general for periodic monomode waveguides, especially as the group velocity decreases. This result that contradicts common beliefs and experimental practices aiming at measuring alpha is supported by a theoretical study of light transport in the limit of very small imperfections, and by numerical results obtained for two waveguide geometries that offer contrasted damping behaviours.

Abstract:
In this work we consider stability of recovery of the conductivity and attenuation coefficients of the stationary Maxwell and Schr\"odinger equations from a complete set of (Cauchy) boundary data. By using complex geometrical optics solutions we derive some bounds which can be viewed as an evidence of increasing stability in these inverse problems when frequency is growing.

Abstract:
In this paper the characteristic equations of the E and E modes of the dielectric rectangular waveguide have been derived using the mode matching technique. No assumptions have been taken in the derivations which have been straight forwardly done. Two ratios have been introduced in the characteristic equations and the new set of characteristic equations thus obtained are then plotted and graphical solutions are obtained for the propagation parameters assuming certain numerical values for the introduced ratios. The results have then been compared to those obtained by Marcatilli and Goell for rectangular dielectric waveguides. The comparisons depict a good agreement in the three methods at frequencies well above cut-off.

Abstract:
Quantum interference phenomena in the conductivity of mesoscopic ferromagnets are considered, particularly with regard to the effects of geometric phases acquired by electrons propagating through regions of spatially varying magnetization (due, e.g., to magnetic domain walls). Weak localization and electron-electron interaction quantum corrections to the conductivity and universal conductance fluctuations are discussed. Experiments are proposed for multiply-connected geometries that should reveal conductance oscillations with variations of the profile of the magnetization.

Abstract:
This paper presents the simulation, design and implementation of bandpass filters in rectangular waveguides. The filters are simulated and designed by using a numerical analysis program based on the Wave Iterative Method (WIM) called WFD (Waveguide Filter Design) simulation. This simulation program can analyze the electrical network of filters. The sample waveguide filter is designed based on a proposed structure consisting of three circuits serving as a simple bandpass filter with two inductive irises and three inductive irises in a cascade. We determined that the operating frequency was equal to approximately 4.20-4.84 GHz. The waveguide filters were then implemented using an aluminum material. The analyzed results for the inductive iris obtained with the WFD program agree well with the results of CST Microwave Studio . Finally, the measured results of sample waveguide filters are consistent with the simulation tool.

Abstract:
Marcatili's famous approximate analytical description of light propagating through rectangular dielectric waveguides, published in 1969, gives accurate results for low-index-contrast waveguides. However, photonic integrated circuit technology has advanced to high-index-contrast (HIC) waveguides. In this paper, we improve Marcatili's model by adjusting the amplitudes of the components of the electromagnetic fields in his description. We find that Marcatili's eigenvalue equation for the propagation constant is also valid for HIC waveguides. Our improved method shows much better agreement with rigorous numerical simulations, in particular for the case of HIC waveguides. We also derive explicit expressions for the effective group index and the effects of external forces on the propagation constant. Furthermore, with our method the phenomenon of avoided crossing of modes is observed and studied.

Abstract:
High moisture in mine tunnel can cause the change of the permittivity and conductivity of tunnel walls, therefore influence the characteristics of electromagnetic waves propagation. This paper analyzes the mechanism of humidity influencing the permittivity and conductivity and attenuation of electromagnetic waves propagation in the circular tunnel and rectangular tunnel. The study result shows that, in the interest frequency range, the change of permittivity caused by humidity has little effect on propagation attenuation, but the effect on the conductivity change cannot be ignored. When the humidity is greater than a certain value, the attenuation will be increased significantly.

Abstract:
In our previous works, we have presented one differential method for the efficient calculation of the modal scattering matrix of junctions in rectangular waveguides. The formalism proposed relies on the Maxwell's equations under their covariant form written in a nonorthogonal coordinate system fitted to the structure under study. On the basis of a change of variables, we show in this paper that the curvilinear method and the generalized telegraphist's method lead to the same system of coupled differential equations.