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

A reconstruction algorithm for microwave imaging based on the Modifled Pertur- bation Method (MPM) is proposed. Both the object conductivity (ae) and permittivity (") are reconstructed. The original Perturbation method developed for static problems was modifled in order to apply in time harmonic problem in higher frequency. The Jacobian matrix is now calculated in closed form employing an adjoint network theorem in conjunction with the reci- procity theorem of electromagnetics. A number of successful reconstructions were carried out for difierent complex permittivity proflles, but all of them based on a computer phantom approach.

https://www.piers.org/piersonline/pdf/Vol3No8Page1217to1221.pdf

A Sensitivity Matrix Based Microwave Tomography Exploiting an Adjoint Network Theorem

The input impedance of a probe-fed short-circuited microstrip antenna (SCMSA) is presented. The electric field expression under the microstrip patch by using the Wiener-Hopf technique is used and the electromotive force (EMF) method is applied. Analytical and experimental results for the impedance show the dependence on the dimensions and frequency.

Analysis of a probe-fed short-circuited microstrip antenna

A circular patch antenna tuned by a ferrite post is presented. The DC-biasing magnetic field is assumed perpendicular to the patch and the ferrite losses are taken into account. Both right- and left-hand circular polarizations are considered. The “perfect magnetic walls” approximation is employed and the resulting closed-form expressions can be used in the design of patch antennas. Also, this approximate but analytical study offers a clear physical insight with regard to the ferrite effects on the patch antenna's resonance characteristics. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 234–237, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20954

Analysis of Circular Patch Antenna Tuned by a Ferrite Post

Summary form only given. An approach to the design of microwave oscillators is presented which allows both the frequency and power output to be predicted. The main feature of this technique is that it allows the optimum performance to be obtained from the active device. The method overcomes the difficulties associated with one-port techniques, where the passive elements connected to the active device to obtain a negative-impedance one-port are often chosen empirically, which constrains the design and sometimes makes the prespecification of parameters, such as power, impossible. It works better also than design methods using S-parameters, since the last ones are dependent on power levels and bias conditions, so they are not flexible for varied conditions. A design example is given for a 4 GHz MESFET oscillator. The computer-simulated oscillator is developed using the present method and two others, the well-known negative-impedance method and another one using S-parameters, for comparison reasons. The results of the present method were found to be within the predicted values for both frequency and power, without any further optimization.

George A. Kyriacou

Papers

A Sensitivity Matrix Based Microwave Tomography Exploiting an Adjoint Network Theorem

Analysis of a probe-fed short-circuited microstrip antenna

Analysis of Circular Patch Antenna Tuned by a Ferrite Post

A technique for the design of microwave transistor oscillators for optimum power output

Aperture Coupled Microstrip Antennas: A Design Approach