Two-dimensional microwave band-gap structures of different dielectric materials

Experimental and Numerical Study of Sensitivity Improvement in Near-Field Probes Using Single-Negative Media

Abstract: In this paper, we present experimental verification of the sensitivity improvement of evanescent-field probes using single-negative (SNG) metamaterials. Artificial magnetic materials are designed and fabricated to realize a ?-negative SNG material. The response of an electrically small probe to an electrically small target is investigated numerically and experimentally. The deviation in the phase of reflection coefficient due to the target is measured. When an SNG layer is employed, phase shift due to the presence of a target is improved nine times compared to a probe without an SNG layer.

Linearization of power amplifiers by second harmonics and fourth-order nonlinear signals

Abstract: In this article, a single-stage power amplifier and two-way Doherty amplifier are linearized by the technique that uses second harmonics and fourth-order nonlinear signals. Measurements of the linearization effects on the third- and fifth-order intermodulation products have been carried out. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:425–430, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27294

Sandwich vehicle structure having integrated electromagnetic radiation pathways

Abstract: A sandwich vehicle structure may allow for confined propagation of electromagnetic radiation within the sandwich vehicle structure. The sandwich vehicle structure may include at least one upper conducting plate, at least one lower conducting plate, and a core extending between the upper and lower conducting plates. The core may comprise a core medium, and a plurality of spaced apart core members embedded in the core medium and extending between the upper and lower conducting plates. The core medium and the core members may allow for the propagation of electromagnetic radiation within the core.

Nonlinear properties of a graded-index photonic heterostructure

Abstract: The optical properties of a one-dimensional (1D) photonic heterostructure with graded-index nonlinear materials are demonstrated theoretically. The influence of the gradation profile of the graded-index nonlinear layers on the linear and nonlinear responses of the structure are analysed. It is shown that the Q-factor of the defect mode and the threshold input intensity to achieve the optical bistability in the used photonic heterostructure depend on the gradation profile of the graded-index nonlinear layers.

Sensitivity Enhancement of Near Field Probes Using Negative Materials

Abstract: In the last decade, design and application of negative materials have been one of the most interesting subjects in the electromagnetic research. The extraordinary properties of double negative (DNG) and single negative (SNG) materials have been studied extensively over this period. In this thesis, one of the unusual properties of negative materials, the evanescent amplification, is used to improve the sensitivity of the near field probes. The effect of placing DNG and SNG layers between the near field probes and the targets are investigated theoretically. A sensitivity definition is introduced for evanescent probes and it is shown using quantitative measures that the sensitivity can be increased using DNG and SNG materials for a target in vacuum and for a buried target. The electromagnetic loss of the negative materials and the mismatch between the material properties of the host medium and DNG and SNG materials are studied. Using an unmatched DNG layer or SNG layer enhances the sensitivity within an evanescent spectrum range while a lossless and matched DNG layer improves the sensitivity of entire evanescent spectrum. The idea of using negative materials is implemented over conventional near field probes by numerical experiments. Sensitivities of open-ended waveguides and open-ended coaxial lines for a specific application are studied in the presence of negative materials. In the case of precursor pitting detection on airplane bodies, the sensitivity of an open-ended waveguide probe is increased by 35 times for a λ/10 sized cubic crack. It is also shown that the negative material increases the quality of the image generated by the probe. The sensitivity improvement is also verified for an open-ended coaxial line. A 11 times improvement is achieved for a similar detection practice, with a λ/20 sized crack. The effect of coaxial line size and the dielectric material on the sensitivity enhancement are studied. The improvement is studied theoretically and numerically for an electrically small dipole. Theoretical studies show that when a small dipole is placed within a spherical shell made of DNG materials, the antenna parameters of the dipole becomes more sensitive to the position of a target placed outside the negative material shell. The field distribution generated by a small dipole in a multilayered spherical medium is studied for this purpose. Numerical analysis of a small dipole placed next to a planar DNG layer is presented. The DNG layer increases the sensitivity of the dipole due to a λ/30 sized metallic target by 5.5 times. To provide experimental verification, the sensitivity of an electrically small loop is studied. SNG materials with a negative permeability around 1.25 GHz are designed

Inhibited Spontaneous Emission in Solid-State Physics and Electronics

Abstract: It has been recognized for some time that the spontaneous emission by atoms is not necessarily a fixed and immutable property of the coupling between matter and space, but that it can be controlled by modification of the properties of the radiation field. This is equally true in the solid state, where spontaneous emission plays a fundamental role in limiting the performance of semiconductor lasers, heterojunction bipolar transistors, and solar cells. If a three-dimensionally periodic dielectric structure has an electromagnetic band gap which overlaps the electronic band edge, then spontaneous emission can be rigorously forbidden.

Photonic band structure: The face-centered-cubic case.

Abstract: We employ the concepts of band theory to describe the behavior of electromagnetic waves in three dimensionally periodic face-centered-cubic (fcc) dielectric structures. This can produce a ``photonic band gap'' in which optical modes, spontaneous emission, and zero-point fluctuations are all absent. In the course of a broad experimental survey, we have found that most fcc dielectric structures have ``semimetallic'' band structure. Nevertheless, we have identified one particular dielectric ``crystal'' which actually has a ``photonic band gap.'' This dielectric structure, consisting of 86% empty space, requires a refractive index contrast greater than 3 to 1, which happens to be readily obtainable in semiconductor materials.

Photonic band structure of two-dimensional systems: The triangular lattice

Abstract: By the use of a position-dependent dielectric constant and the plane-wave method, we have calculated the photonic band structure for electromagnetic waves in a structure consisting of a periodic array of parallel dielectric rods of circular cross section, whose intersections with a perpendicular plane form a triangular lattice. The rods are embedded in a background medium with a different dielectric constant. The electromagnetic waves are assumed to propagate in a plane perpendicular to the rods, and two polarizations of the waves are considered. Absolute gaps in the resulting band structures are found for waves of both polarizations, and the dependence of the widths of these gaps on the ratio of the dielectric constants of the rods and of the background, and on the fraction of the total volume occupied by the rods, is investigated.

Tight-binding description of the coupled defect modes in three-dimensional photonic crystals

Abstract: We have experimentally observed the eigenmode splitting due to coupling of the evanescent defect modes in three-dimensional photonic crystals. The splitting was well explained with a theory based on the classical wave analog of the tight-binding (TB) formalism in solid state physics. The experimental results were used to extract the TB parameters. A new type of waveguiding in a photonic crystal was demonstrated experimentally. A complete transmission was achieved throughout the entire waveguiding band. We have also obtained the dispersion relation for the waveguiding band of the coupled periodic defects from the transmission-phase measurements and from the TB calculations.