The electric field integral equation (EFIE) is used with the moment method to develop a simple and efficient numerical procedure for treating problems of scattering by arbitrarily shaped objects. For numerical purposes, the objects are modeled using planar triangular surfaces patches. Because the EFIE formulation is used, the procedure is applicable to both open and closed surfaces. Crucial to the numerical formulation is the development of a set of special subdomain-type basis functions which are defined on pairs of adjacent triangular patches and yield a current representation free of line or point charges at subdomain boundaries. The method is applied to the scattering problems of a plane wave illuminated flat square plate, bent square plate, circular disk, and sphere. Excellent correspondence between the surface current computed via the present method and that obtained via earlier approaches or exact formulations is demonstrated in each case.

Electromagnetic scattering by surfaces of arbitrary shape

A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped-circuit elements, and distributed in a two-dimensional lattice. The surface can be described using solid-state band theory concepts, even though the periodicity is much less than the free-space wavelength. This unique material is applicable to a variety of electromagnetic problems, including new kinds of low-profile antennas.

/pdf/high-impedance-electromagnetic-surfaces-with-a-forbidden-3vtu72a5an.pdf

High-impedance electromagnetic surfaces with a forbidden frequency band

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

The particle swarm optimization (PSO), new to the electromagnetics community, is a robust stochastic evolutionary computation technique based on the movement and intelligence of swarms. This paper introduces a conceptual overview and detailed explanation of the PSO algorithm, as well as how it can be used for electromagnetic optimizations. This paper also presents several results illustrating the swarm behavior in a PSO algorithm developed by the authors at UCLA specifically for engineering optimizations (UCLA-PSO). Also discussed is recent progress in the development of the PSO and the special considerations needed for engineering implementation including suggestions for the selection of parameter values. Additionally, a study of boundary conditions is presented indicating the invisible wall technique outperforms absorbing and reflecting wall techniques. These concepts are then integrated into a representative example of optimization of a profiled corrugated horn antenna.

Particle swarm optimization in electromagnetics

Electromagnetic Bandgap (EBG) structures are increasingly utilized by a variety of microwave and optical devices as filters for unwanted signals. One such application is their incorporation in power distribution network (PDN) of electronic circuits where the EBG structure replaces one of the reference voltage planes thus forming a shielded EBG structure. The EBG induces a wide (on the order of few GHz) omni-directional stopband in the operating frequency range of the PDN which mitigates the so called simultaneous switching noise (SSN) on the power plane. The challenging aspect in designing an EBG for such applications is to achieve a wide stopband centered at low GHz frequencies while maintaining a reasonably small unit cell size and a low profile. Indeed, the dimensions of the unit cell of the EBG structure for low frequency designs can become relatively large with respect to the size of the host dielectric substrate. Therefore, availability of a systematic design approach that can provide a fast and accurate means of performance prediction to enable geometry tweaking and design optimization will be of critical importance in utilizing EBG structures in such applications.

A novel strategy for broadband and miniaturized EBG designs: hybrid MTL theory and PSO algorithm

Overview In recent years, electromagnetic band gap (EBG) structures have attracted increasing interest in the electromagnetic community. Because of their desirable electromagnetic properties, they have been widely studied for potential applications in antenna engineering. Hundreds of EBG papers have been published in various journals and conferences. To illustrate the rapid increase of research interest, a simple search using the keywords “EBG” and “antenna” was performed on IEEE Xplore on 1/18/2008 and the data are plotted in Fig. A.1 based on the available number of publications. It is clear that the number of papers has steadily increased over the years with an apparent peak of publications in 2005. Here we provide a comprehensive overview of these publications so that readers can establish a clear picture of EBG development. It will also help readers to easily find papers related to their own research interests. Since the scope of this book is EBG metamaterials, papers on double negative property, left-handed propagation, and negative refractive index are not covered in this overview. We also regret if we have missed some papers as there have been so many international conferences with sessions on this topic. To start with, we would like to emphasize several special issues organized in microwave and antenna journals that relate to EBG research. These special issues provide the readers with background and information for EBG research. They summarize the latest research progress at the time of publication, and have greatly stimulated EBG research afterwards.

Electromagnetic Band Gap Structures in Antenna Engineering: Appendix: EBG literature review

CubeSat will play a key role in Earth Science missions wherein multiple copies of the same RADAR instrument are launched in desirable formations. This will allow for the measurement of atmospheric processes over a short, evolutionary timescale. Such RADAR instruments require a high-gain antenna that fits in a constrained and limited volume. This paper introduces a 42.6 dBi gain mesh deployable antenna folding in a 1.5U stowage volume suitable for 6U class CubeSats.

Earth science RADAR CubeSat deployable Ka-band mesh reflector antenna

The topic of approximate impedance boundary conditions is examined using a spectral-domain approach. New forms for general approximate impedance boundary conditions with broader applicability than the SIBC, TIBC or GIBC (standard, tensor, or generalized impedance boundary condition) are derived. Using the spectral-domain approach, higher-order boundary conditions for coatings which cannot be handled by the existing approximate impedance boundary conditions can be addressed. They include complicated coatings containing anisotropic and nonreciprocal materials as well as those with more complicated constitutive relations such as chiral media. >

Higher order impedance boundary conditions for anisotropic and nonreciprocal coatings

Measurements of deep and subcanopy soil moisture are critical in understanding the global water and energy cycle, as well as the interaction of the carbon and water cycles, but are presently not available on a synoptic basis. In this paper, a low-frequency UHF/VHF radar mission concept is presented and technology challenges to implement it are discussed. This mission concept is currently being studies under a NASA/ESTO instrument incubator program (IIP) project. The progresses of several aspects of the project are discussed.

Yahya Rahmat-Samii

Papers

A novel strategy for broadband and miniaturized EBG designs: hybrid MTL theory and PSO algorithm

Electromagnetic Band Gap Structures in Antenna Engineering: Appendix: EBG literature review

Earth science RADAR CubeSat deployable Ka-band mesh reflector antenna

Higher order impedance boundary conditions for anisotropic and nonreciprocal coatings

Microwave Observatory of Subcanopy and Subsurface (MOSS): a low-frequency radar for global deep soil moisture measurements