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 Hybrid technique for the analysis of conical horn antennas is presented based on a rigorous description of the horn aperture-free space discontinuity. The transition from the feeding waveguide to the radiating aperture is analyzed by using the mode matching technique (MMT) employing a stepped-waveguide approach. The discontinuity between the horn aperture and free space is modeled by combining an offset Moment Method with the MMT for the last waveguide section. Results for the input standing wave ratio are given and compared with commercial software results which demonstrate the very good performance of the method.

Conical Horn Antennas Employing an Offset Moment Method and Mode Matching Technique

A novel quadruple feeding mechanism for a rectangular patch antenna is proposed. A successive phase shift caused by path inequality between four possible symmetrical feeding points is introduced, in order to achieve wideband operation at the 2 GHz frequency band. This work is an extension to the idea of acquiring a pair of resonances and forcing them to behave in a consolidated way. This concept is verified in previous work and is herein stretched to the limit that a rectangular patch could provide speaking in terms of symmetry, i.e. using four feeding points. The proposed antenna exhibits a fractional bandwidth of 3.46 %, almost four times as much as the conventional single-fed patch does. Furthermore, the antenna presents circular polarization and an elevationuniform radiation pattern. VSWR, Impedance matching as well as Antenna and Radiation Efficiency are also presented and annotated.

http://ieeexplore.ieee.org/iel7/7357693/7365982/07366060.pdf

A novel quadruple-fed rectangular patch antenna with improved bandwidth performance

Simplistic numerical methodology for magnetic field prediction in open air type substations

The design of passive circulators/duplexers for RFID applications in the UHF band is presented. The design idea is based on the use of simple passive directional couplers, offering simplicity and low cost compared to ferrite devices or active architectures. The Tx/Rx isolation problem is solved exploiting a mismatched load, which creates a cancelling signal on the Rx port. Additional impedance matching is applied at the Tx port, in order to balance the effects of the mismatch load at the input (Tx). Both branch-line and ring couplers are alternatively used, designed mainly for unequal power division between output ports. A variety of design examples is presented, including miniaturized topologies, aiming at the reduction of size and cost. Design frequency is chosen at 900MHz, trying to cover both 860MHz and 910MHz bands.

Design of passive UHF RFID circulators/duplexers using directional couplers

A two-dimensional finite difference frequency domain eigenvalue method employing orthogonal curvilinear co-ordinates is established. Its main strength is the accurate modelling of curved interfaces enabling the accurate evaluation of the complex propagation constants of curved waveguides. Numerical results for multilayer-multiconductor microstrip lines printed on curved substrates prove the validity of the method.

George A. Kyriacou

Papers

Conical Horn Antennas Employing an Offset Moment Method and Mode Matching Technique

A novel quadruple-fed rectangular patch antenna with improved bandwidth performance

Simplistic numerical methodology for magnetic field prediction in open air type substations

Design of passive UHF RFID circulators/duplexers using directional couplers

Eigenvalue analysis of curved waveguides employing FDFD method in orthogonal curvilinear co-ordinates