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

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Rfid Handbook Fundamentals And Applications In Contactless Smart Cards And Identification

Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Gain enhancement methods for printed circuit antennas

As stated in Chapter 1, one of the many advantages of microstrip patch technology over its competitors is its low profile and hence small volume. Another key advantage of this printed antenna is the relative ease in which it can be connected to the feed network, as was highlighted in Chapter 2. For these reasons antenna design engineers deduced that microstrip patch antennas could be utilized for applications requiring where there was very limited space to mount the antenna. One such global application is for wireless communication handset terminals.

Small microstrip patch antenna

In electrical impedance tomography an approximation for the internal resistivity distribution is computed based on the knowledge of the injected currents and measured voltages on the surface of the body. It is often assumed that the injected currents are confined to the two-dimensional (2-D) electrode plane and the reconstruction is based on 2-D assumptions. However, the currents spread out in three dimensions and, therefore, off-plane structures have significant effect on the reconstructed images. In this paper we propose a finite element-based method for the reconstruction of three-dimensional resistivity distributions. The proposed method is based on the so-called complete electrode model that takes into account the presence of the electrodes and the contact impedances. Both the forward and the inverse problems are discussed and results from static and dynamic (difference) reconstructions with real measurement data are given. It is shown that in phantom experiments with accurate finite element computations it is possible to obtain static images that are comparable with difference images that are reconstructed from the same object with the empty (saline filled) tank as a reference.

Three-dimensional electrical impedance tomography based on the complete electrode model

Reciprocity theorem based phased array hyperthermia applicator design

A hybrid technique for the analysis of pyramidal and conical horn antennas is presented based on an exact vector Dirichlet to Neumann (DtN) mapping mathematical formalism. The transition from the feeding waveguide to the radiating aperture is analyzed by using the mode matching technique (MMT) employing a stepped- waveguide approach. Love's field equivalence principle is employed for the definition of equivalent electric and magnetic current densities at the horn aperture. Explicitly, these currents are located at a plane parallel to the aperture but slightly shifted inwards in order to implement an offset Moment Method for their discretization, which is free of integral singularities. The unbounded area field generated by these sources is enforced to be continuous with the internal mode matching field by strictly following DtN principles. Besides that, this procedure mimics a By-moment approach ensuring the decoupling of the required number of modes from that of the sources discretization degrees of freedom. Finally, the implemented hybrid method is validated against published experimental and numerical results for a number of pyramidal and conical horn antennas including various corrugated geometries.

/pdf/a-dirichlet-to-neumann-map-based-hybridization-of-a-mode-2s72lp82gb.pdf

A Dirichlet to Neumann Map Based Hybridization of a Mode Matching and Offset Moment Method for Horn Antennas Analysis

Summary form only given. Since a lot of low loss and often used dielectric substrates exhibit a dielectric anisotropy, (especially of the uniaxial type), it is thus important to study the patch antennas printed on them. Moreover, the anisotropy offer an additional degree of freedom, which can be properly exploited to increase the efficiency and the gain of the antenna. Thus, the aim of this work is to study the resonance characteristics of rectangular and wraparound antennas as well as wide microstrip lines printed on anisotropic cylindrical substrate. Results for the resonant frequency of both rectangular and wraparound patches are presented, along with a comparison with the corresponding results from numerical simulations performed with the HP-HFSS finite element software.

http://ieeexplore.ieee.org/iel5/7493/20382/00943259.pdf

A study of microstrip antennas printed on electrically thin cylindrical uniaxially anisotropic dielectric substrate

A reconstruction algorithm for three dimensional electrical impedance tomography

Summary form only given. During the past 30 years a lot of research effort has been directed toward the estimation of the heart electrical sources from the body surface potentials. This subject is now very well known as "inverse electrocardiography". The most widespread models for these sources can be identified as the "epicardial potentials" and the "equivalent dipoles or multipoles". Especially, the epicardial potentials seems to be very important for the clinicians, since they can identify the cardiac state (e.g. arrhythmias). The solution of the inverse problem is usually based on iterative solutions of the forward problem. Namely, for a given geometry, a conductivity distribution and a specified internal source, calculate the body surface potentials. Similarly, in the inverse problem the body surface potentials are measured, the conductivity and geometry are assumed known (physiological values) and the internal source is sought. This present work is restricted to the forward problem. What is in turn needed is a realistic 3-D volume conductor FEM model which accurately reflects the internal structure, but keeping in mind that this must be fast enough to be included within the inverse problem. For this purpose we have improved our previous model, with about 5-times finer mesh especially around the heart region. Some typical epicardial potential distributions and typical cardiac dipole sources are simulated and their effects on the surface potentials are presented. The next step is to include the present forward problem within an optimization scheme in order to solve the inverse one.

George A. Kyriacou

Papers

Reciprocity theorem based phased array hyperthermia applicator design

A Dirichlet to Neumann Map Based Hybridization of a Mode Matching and Offset Moment Method for Horn Antennas Analysis

A study of microstrip antennas printed on electrically thin cylindrical uniaxially anisotropic dielectric substrate

A reconstruction algorithm for three dimensional electrical impedance tomography

A realistic 3-D FEM human torso model for electrocardiography applications