Waveguides For Surface Waves Research Articles

Analysis by Asymptotic Boundary Conditions of Strip-Grated Dielectric Pipe Over Dielectric Rod With Wide Total Band-Gap as Multifrequency Cylindrical Leaky-Wave Antennas

In this paper, the method of classical vector potential analysis along with the asymptotic strips boundary conditions (ASBC) is used to treat conducting strip grated dielectric pipes wrapped over core dielectric cylindrical rods. By virtue of the periodically-textured surface, this structure is able to exhibit plasmonic behaviors that facilitate strong surface field localization and wave propagation, thereby offering itself as cylindrical surface-wave waveguides or antennas. It can also be configured to exhibit electromagnetic band-gap (EBG) properties, yielding what is known as cylindrical EBG structures. As opposed to a typical counterpart whose core rod is instead conducting, the core dielectric is herein demonstrated to be vital in realizing wide total band-gaps in which neither slow surface nor fast space waves exist, something that the conducting core rod version is incapable of, being only able to offer surface-wave band-gaps, as do many others in the literature that have neglected the suppression of fast space waves as well. By coaxially connecting various such rod structures, each with its own distinct total band-gap, multi-frequency, multi-functional cylindrical antennas with mitigated inter-band interference even under simultaneous operations can be achieved when the pass-band of any one rod (in which its operating frequency lies) falls within the total band-gaps of all others, as herein investigated. Manufactured prototypes are also measured, yielding experimental results that agree well with theoretical predictions.

EHF Band Linear Antenna Array Based on Surface Wave Transformation

The experience of using of experimental samples of diffraction radiation antennas shows the need to expand the list of options and modifications of the technical solutions for such antennas. One of variants is the modification of a linear dielectric waveguide for rigidly fixation of the dielectric rod. H-shaped surface-wave waveguides in the form of combination of dielectric rod and rigid metal elements have been proposed for a basic element of diffraction radiation antennas designed for operation in conditions of increased mechanical loads and vibrations at frequencies above 80 GHz. The results of experimental studies of the near-field distribution, radiation patterns, gain and energy losses of the antenna are presented. The obtained results show the effectiveness of the implemented constructive approach. The configuration of the linear antenna grating of diffraction radiation with a modified dielectric waveguide is proposed, which can be applied for the development of scanning antennas in the 80–100 GHz frequency range.

Surface Waveguides Supporting Both TM Mode and TE Mode With the Same Phase Velocity

Two kinds of surface-wave waveguide (SWG) topologies are proposed in this paper with the objective to achieve the property of supporting both transverse magnetic (TM) and transverse electric (TE) modes with the same phase velocity. The first type is composed of two frequency-selective surfaces (FSSs) as layers whose dominant modes are TM mode and TE mode, respectively. For illustrationC the combination of loop-type FSS and wire-grid-type FSS is analyzed and its dispersion characteristics are examined as well. The second class also consists of two layers. For the top layer, there are gaps in one direction and continuous conducting strips in the orthogonal direction. The bottom layer is created from a 90° rotation of the top layer. As a particular illustration, a modified bow-tie-like SWG structure is investigated. The simulated results show that the two proposed SWG structures exhibit the property of supporting both TM mode and TE mode with the same phase velocity over a broad bandwidth. In addition, the effects of lattice types on dispersion diagrams are discussed in this paper. Near field measurements are also carried out to validate the simulations and good agreements are achieved.

Multiple modes of surface plasmonic polaritons in transversely-truncated metal/dielectric superlattices

The surface plasmonic polariton (SPP) of a transversely-truncated metal/dielectric superlattice (SL) structure has been solved with an approximate method. The effect of inter-layer interfaces in the SL is taken into consideration efficiently in comparison with the effective-medium method. The silver/air and silver/SiO2 SLs with a shorter period are regarded as two specific examples in numerical calculation. A series of separated SPP modes are found and highly localized at the surface, and the highest-frequency mode is the only one also predicated by the effective-medium method. These results obviously show the effect of inter-layer interfaces in the case of short period, whilst the reliability and limitation of the effective-medium method is presented as well. Because the skin depths of the modes are extremely small, the SLs can be used as ideal surface-wave waveguides.

Nonlinear Power-Dependent Impedance Surface

Impedance surfaces are artificially designed periodic structures that support surface waves. This paper presents a novel concept of a nonlinear impedance surface, whose impedance increases with the surface wave power. The proposed surface consists of a lattice of modified slotted mushroom-like cells loaded with varactor diodes and lumped circuits. The circuits are designed to sense the incoming surface wave power and feed back the signal to control the bias of the varactors, which eventually tunes the surface impedance. Such proposed power-dependent impedance surface has been demonstrated by a prototype consisting of 4 × 10 cells. It is observed from the experiments that as the power varies from 16 to 27 dBm, the surface exhibits a surface impedance range as much as j385 to j710 Ω. This characteristic enables the surface to be potentially useful in self-trapping surface-wave waveguide, power-dependent beam-steering antenna reflector, and other nonlinear applications.

A Planar and Subwavelength Open Guided Wave Structure Based on Spoof Surface Plasmons

A planar and compact open waveguiding structure based on spoof surface plasmon polaritons (SPPs) was demonstrated. For practicality, instead of the well-known wire medium, the uniaxial strip medium (USM) was proposed and used as the effective bulk material with a negative dielectric constant to support the spoof SPP modes. The relevant formulations, including the modal dispersion relations and the formulation for the waves in a multilayer anisotropic structure, are analytically presented in this paper. Interestingly, instead of taming and suppressing the spatial dispersion (SD), which had been done in most past studies, SD was exploited in the proposed structure to enhance the field confinement of the spoof SPP mode by approximately 41%. Moreover, the thickness of the USM slab could be reduced by 50%, using conductor backing and without perturbing the odd mode. This method and SD can help avoid electromagnetic interactions among various components of a multilayer printed circuit board structure and help miniaturize sensors or surface-wave waveguides in the microwave regime. In this study, the subwavelength thickness of the proposed structure was only 0.09 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> at 1.34 GHz. Additionally, the propagation loss for such slow-wave structures has seldom been discussed analytically and quantitatively. In this study, through calculations and simulations, low attenuation constants in the spoof SPP propagation direction of the proposed structures were investigated. Finally, an experiment was conducted, and an extraction method for obtaining the required reflection spectrum from the measured S-parameter was developed.

3-D Conformal Metasurfaces

This letter presents a method for mapping and fabricating metasurfaces on arbitrary 3-D surfaces. Metasurfaces are used for holographic leaky-wave antennas, reflectarray antennas, coatings for soft horn antennas, artificial magnetic conductors, high-impedance surfaces, frequency selective surfaces, electromagnetic band-gap structures, and surface-wave waveguides. They are typically fabricated as 2-D planar structures by printing a grid of metallic patches on a dielectric substrate, but for some applications, it is desirable to create a metasurface conformal to a 3-D surface. The methods presented here can be used with direct-write printing or with standard printed circuit board (PCB) techniques. The PCB method involves mapping the metasurface to a set of 2-D bands that are laminated to a 3-D substrate. As an example, a 3-D conformal, ellipsoidal, holographic, leaky-wave antenna was designed, fabricated, and measured.

Surface-Wave Waveguides

We present simulations and measurements of surface-wave waveguides (SWGs) for guiding surface waves (SWs) along a constrained path. In its simplest form, the SWG is a two-dimensional analog to a dielectric waveguide where a low-index material surrounds a high-index material. The most common method for realizing materials with differing SW index is to use a grid of metallic patches of varying size on a dielectric substrate. Using asymmetric patches results in a tensor SW index. We show simulations of how the phase front of the guided surface wave can be precisely controlled using a combination of SW-index grading and rotation of the SW-index tensor. We present measurements of straight and curved SWGs showing how SWG width and curvature affect guiding properties.

Generation and Propagation of Electromagnetic Waves in Carbon Nanotubes: New Propositon for Optoelectronics and Bio‐medical Applications

Electromagnetic response properties of carbon nanotubes (CNTs) are discussed. A basic approach to the problem is proposed synthesizing present‐day solid‐state physics and classical electrodynamics of nonhomogeneous mediums.[1] The developed theoretical model predicts the property of CNTs to be a strong slowing‐down system for surface waves[1,2] and allows proposing the physical schemes of the carbon nanotube use as monomolecular optoelectronic devices, such as a surface wave waveguide in IR frequency range, a monomolecular optical nanoantenna, a nanoantenna excitation device based on the Purcell effect, etc. A particular emphasis is given to the stimulated emission of electromagnetic waves by electron beam in nanotube. The significant retardation of the surface wave along with the ballistic character of the electron motion in nanotubes are shown[3] to be underlying the idea of the monomolecular light emitter with the Cherenkov lasing mechanism: the electrons in nanotube imposed to a realistic voltage can be accelerated to the velocities synchronous with the phase velocity of the surface wave. Since the achievable current density in nanotubes exceeds drastically corresponding characteristic values in vacuum electronic devices, the stimulated emission in CNTs is started at a very small, of the order of several microns, length of electron‐photon interaction. A dispersion equation for the electron beam instability in a nanotube is presented and analyzed. The potential of carbon nanotube as traveling wave tube (TWT) and backward wave oscillator (BWO) is demonstrated.

Swihart waves and surface plasmons in a parallel-plate superconducting transmission line

The electromagnetic waves propagating inside a parallel-plate transmission line are investigated. In the case of a finite penetration depth of the electromagnetic field into the metal, a longitudinal electric E wave propagates in the the line instead of a transverse electromagnetic wave. At small thicknesses of the dielectric this wave goes over to a Swihart wave, and at large thicknesses of the dielectric it is converted into a surface wave (plasmon). It is shown that there exists an optimum thickness of the superconducting film coating the parallel-plate transmission line, for which the electromagnetic wave experiences the maximum slowing down. Using waveguides for surface waves, one can construct surface-wave microwave resonators. These resonators have a highly uniform microwave current distribution and, have a high concentration of microwave current in the superconducting film, and they are simple to fabricate.

Measurements of coupled Rayleigh wave propagation in an elastic plate

At frequencies where the thickness of an elastic plate is more than a wavelength, the propagation of the two lowest Rayleigh–Lamb modes in an elastic plate can be viewed as the propagation of a Rayleigh surface wave over two weakly coupled, surface-wave waveguides. That is, a Rayleigh wave launched on one surface gradually transfers to the other and then back. It does so in a length we call the beatlength. Measurements of the beatlength for brass plates are reported as a function of frequency and thickness. This phenomenon is readily excited and persists over a wide range of thicknesses and frequencies

Radiation losses in bent waveguides for surface waves

Radiation losses in bent waveguides for surface waves