Low frequency vibrational modes of pharmaceutical molecules are dependent on the molecule as a whole and can be used for identification purposes. However, conventional Fourier transform far-infrared spectroscopy (FT-IR) and terahertz time-domain spectroscopy (THz-TDS) often result in broad, overlapping features that are difficult to distinguish. The technique of waveguide THz-TDS has been recen...

We describe an experimental and theoretical characterization of rectangular resonant cavities integrated into parallel-plate waveguides, using terahertz pulses. When the waveguide is excited with the lowest-order transverse-electric mode, these cavities exhibit resonances with narrow linewidths. Broadband transmission spectra are compared with the results of mode-matching calculations, for vari...

Experiments with dielectric scatterers in a parallel-plate waveguide have verified for the first time the existence of proximity resonances in two dimensions. A numerical solution to the scattering problem supports the analysis of the experimental data. It has recently been shown that two resonant s-wave scatterers placed close together produce two resonances in the spectrum of the combined sys...

Discrete bends in the propagation direction of plane TEM waves can be achieved utilizing the Brewster angle at a planar interface between media of different uniform isotropic pennittivities. This paper extenda this to cases of multiple dielectric or nonuniform permittivity. The nonuniform case is a generali~tion of the Brewster-angle concept. This is also related to special log-spiral solutions...

The dyadic Green’s functions for magnetic and electric currents immersed in a parallel plate waveguide (PPWG) filled with dielectric-magnetic anisotropic uniaxial media are developed via a field-based approach. First, the principal Green’s function is derived from the forced wave equation for currents immersed in an unbounded uniaxial media. Next, the scattered Green’s function is developed fro...

The TM0 surface mode in an infinitely long parallel-plate waveguide filled with a double-positive (DPS) and epsilon-negative (ENG) metamaterial bi-layer is studied. With proper constitutive parameters and thicknesses of the two layers, the slow-wave factor (SWF) for such a parallel-plate waveguide can tend to infinity as the frequency decreases. A 2-D cavity based on the DPS-ENG bilayer wavegui...

We show that metallic wires embedded in narrow waveguide bends and channels demonstrate resonance behavior at specific frequencies. The electromagnetic energy at these resonances tunnels through the narrow waveguide channels with almost no propagation losses. Under the tunneling behavior, high-intensity electromagnetic fields are produced in the vicinity of the metallic wires. These intense fie...

We show that spoof surface plasmons can be used to control the reflection of terahertz radiation at the output facet of a parallel-plate waveguide. Using a periodic groove pattern on the output face, reflectivity approaching 100% can be achieved within a limited spectral range. Unlike the conventional geometry for plasmon-enhanced transmission, this approach enables a unique method for studying...