Design and fabrication of optical code generating devices based on plastic optical fiber (POF) for security access-card system is presented. The POF waveguide coupler will utilize two basic designs: 1 × 2 Y-branch coupler as the main device structure and 1 × 2 asymmetric coupler which allows non-symmetric optical power splitting. The Y-branch coupler are based on two designs: A metalbased POF coupler with a hollow taper waveguide and an acrylicbased POF coupler with optical glue for the taper waveguide region. The Y-branch device is composed of input POF fiber, middle taper waveguide and output POF fibers. Simulation based on non-sequential ray tracings have been performed on both types of POF couplers. Low cost aluminum and acrylic based materials are used for the substrates. Fabrications of the POF couplers are done by producing the device mold insert using CNC machining tool and POF fibers are then slotted into the Y-branch coupler mold insert. The insertion loss for both devices are about 8 dB.

An analytical investigation of the lightwave propagation through dielectric optical fibers with helical clads is presented with the emphasis on their field patterns. The helical clad section is effectively realized by introducing conducting windings on the core-clad boundary. Using Maxwell's equations, a rigorous analytical approach is implemented to determine the field patterns in such fibers. For simplicity, two particular values of the helix pitch angle are considered, viz. 0°and 90°. The nature of fields is presented in both the situations corresponding to different allowed values of the propagation constants and the fiber diameters. The radial distributions of fields are presented under different situations, which exhibit the patterns like spikes. The observed smooth match of the fields at the core-clad interface validates of our analytical approach. The presence of a little higher amount of field in the fiber clad section is essentially attributed to the helical windings introduced over the fiber core. Further, the existence of considerable amount of evanescent waves in such fibers opens up the possibility of their applications in optical sensing.

This paper presents some improved three-dimensional expressions of the magnetic field created by tile permanent magnets uniformly and radially magnetized for the design of ironless loudspeaker structures. All the expressions determined have been reduced to compact forms. We use these expressions for the optimization of ironless loudspeaker structures in which the radial field must be radially uniform. Indeed, as ring permanent magnets radially magnetized are rather difficult to manufacture, these magnets are replaced by assemblies of tile permanent magnets radially and uniformly magnetized. We present an example of ironless loudspeaker structure that has been optimized with our threedimensional approaches.

High frequency methods resort to numerical ray tracing for application to complex environments. A new method based on the geometrical projection performed by a ray-congruence has been developed as a preconditioning of the ray tracing procedure. It builds a visibility tree, i.e., a database, storing information on all possible ray paths inside a scenario. The method gives a solution to a class of open problems of ray tracing techniques: ray missing, double (multiple) counting, termination criterion, calculation upgrade. Other features of the method are the multipath map and the multipath classification that allow the user to know the relevance of multipath at any point of the scenario in advance, before ray-tracing calculation. The method can be systematically applied to scenarios pertaining to different applications provided that the objects belong to the class of polyhedrons. Reflected and diffracted contributions in a scene are modelled as secondary sources which are handled with an off-line electromagnetic field calculation. Numerical analysis is provided showing the efficiency of the method.

In this paper, we present new expressions for calculating the magnetic field produced by either tile permanent magnets tangentially magnetized or by radial currents in massive disks. These expressions are fully analytical, that is, we do not use any special functions for calculating them. In addition, they are three-dimensional and can be used for calculating the magnetic field for all regular points in space. The expressions commonly used for calculating the magnetic field produced by radial currents in massive disks are often based on elliptic integrals or semi-analytical forms. We propose in this paper an alternative analytical method that can also be used for tile permanent magnets. Indeed, by using the analogy between the coulombian model and the amperian current model, radial currents in massive disks can be represented by using the fictitious magnetic pole densities that are located on two faces of a tile permanent magnet tangentially magnetized. The two representations are equivalent and thus, the shape of magnetic field produced is the same for all points in space, with a smaller value in the case of it is produced by radial currents in massive disks. Such expressions can be used for realizing easily parametric studies.

Scattering from a two-dimensional (2-D) perfectly electrically conducting (PEC) cylinder partially embedded in a random dielectric rough surface interface is studied using the method of moments (MoM) with pulse basis functions and the point matching technique, for the case of horizontal polarization. The random rough surface is modeled using Gaussian statistical characteristic for the rough surface height and surface correlation function, and generated by the spectralmethod. The tapered plane-wave incidence is used to avoid artificial edge diffraction due to the truncation of the rough surface into finitelength rough surface in the numerical simulations. With the developed algorithms, the interactions between the dielectric rough surface and the partially buried PEC cylinder are investigated using the Monte Carlo simulation, and are expressed as a function of the root mean square (rms) height of a random dielectric rough surface and the moisture content of the soil. The numerical results show that the bistatic scattering coefficients are dependent upon the moisture content, the rms height of a rough surface, and other parameters.

A novel and compact planar ultra-wideband wide-slot antenna with dual band-notched function is proposed. The method of creating dual band-notch function is unique from traditional ones. By embedding a U-shaped parasitic strip and a pair of T-shaped stubs in the wide slot, dual bandstops around 3.5 GHz and 5.5 GHz can be obtained. The measured results demonstrate that the proposed antenna, with a compact size of 20X32.5 mm, has a large bandwidth over the frequency band from 3.1 to 10.6 GHz with voltage standing wave ratio (VSWR) less than 2, except the bandwidths of 3.3~3.7 GHz for WIMAX and 5~6 GHz for WLAN. In addition, the radiation pattern has an excellent omni-directional characteristic in the H-plane and a typical monopole like pattern in the E-plane.

A hybrid technique based on finite-difference frequency domain (FDFD) and particle swarm optimization (PSO) techniques is proposed to reconstruct the angular crack width and its position in the conductor and ability to detect the crack width, position, and its depth in single and multilayer dielectric objects. FDFD is formulated to calculate the scattered field after illuminating the object by a microwave transmitter. Two-dimensional model for the object is used. Computer simulations have been performed by means of a numerical program; results show the capabilities of the proposed approach. This paper presents a computational approach to the two dimensional inverse scattering problem based on FDFD method and PSO technique to determine the crack position, width and depth. By using the scattered field, the specifications of the crack are reconstructed.

New solutions of the homogeneous wave equation of the type usually referred to as relatively undistorted waves are presented. Such solutions relate to the so-called "splash modes", from which indeed they can be generated by applying the Laguerre polynomial operator. Accordingly, the solutions here presented resort to the relativistic Laguerre polynomials --- introduced about one decade ago within a purely mathematical context --- which in fact appear as modulating factor of the basic "splash mode" waveform. Similar solutions of the homogeneous spinor wave equation are also suggested.

We study the radio wave propagation at VHF frequencies in a forested environment using a three-layer anisotropic slab model. The analytical solution to the slab model is implemented numerically to generate broadband data. The data are then transformed into the time domain. The various propagation mechanisms including the direct wave, the lateral wave, the multi-reflected slab waves and the multi-bounce lateral waves are investigated based on their respective times-of-flight. Our results show that the dominant propagation mechanisms are highly dependent on the effective permittivity and conductivity of the forest layer. We then utilize the numerical solution to extract the effective medium parameters of the forest based on the published measurement data of Hicks et al. Good agreement between the fitted model and the measurement data is achieved. The extracted effective permittivity and conductivity of the forest layer show considerable anisotropy and frequency dependence.

Transitions from circular waveguides to rectangular waveguides are used in many situations. One particular case is between the feed of a circular corrugated horn antenna and following rectangular waveguide structures. Since the field patterns are not the same on both sides the conversion from rectangular to circular waveguide always results in a certain amount of power reflected back in one waveguide. Much effort has been put in designing special converters which reduce this effect. For many designs, reflection is reduced by introducing a certain number of waveguide steps. By adjusting the distance between these steps, one can get destructive interference of the returned signal at specific frequencies. In this paper, an alternative approach, the constant impedance structure (CIS) has been chosen. This eliminates the need to design a waveguide converter for minimum return loss at discrete frequencies. The transition obtained by this approach is compared to a transition based on linear surface interpolation.

This paper uses a three-dimensional analytical approach based on the Coulombian model for studying the magnetic field produced by cylindrical Halbach structures. Such structures, commonly used in magnetic couplings or in electrical machines, are composed of tile permanent magnets with rotating magnetizations. Such assemblies of tile permanent magnets allow one to easily optimize the radial field shape in the air gap of electrical machines. In addition, Halbach structures can be used in magnetic couplings for improving the torque transmitted between the two rotors. Analytical studies dealing with the optimization of such structures generally use a twodimensional analytical approach for calculating either the magnetic field produced by tile permanent magnets or the forces exerted between them. These two-dimensional expressions are useful because they have a very low computational cost. However, their accuracy depends greatly on the structure dimensions. We propose in this paper to use a three-dimensional analytical model based on the Coulombian model for determining the exact shape of the magnetic field produced by a Halbach structure. Such an approach also allows one to determine the demagnetizing magnetic field inside the tile permanent magnets. This element of information is important for the design of tile permanent magnets. In addition, we show that some effects cannot be predicted with the linearized analytical model. This implies that a linearized dimensional optimization is not accurate. This study has been carried out without any simplifying assumptions. Therefore, the calculations of the three magnetic field components are exact for all points in space, whatever the magnet dimensions. We can say that such a three-dimensional analytical approach is a good alternative to a finite element one because it has a lower computational cost and is more accurate.

A robust algorithm has been developed for improving the backscattered signal and recognizing the shape of the shallow buried metallic object using Artificial Neural Network (ANN) and image analysis techniques for remote sensing at X-band. An ANN with image analysis technique based on tangent analysis is proposed to recognize the shape of metallic buried objects and minimize the orientation effect of buried object. The experimental setup has been assembled for detecting the buried metallic objects of any size at different depths in the sand pit. The system uses only one pyramidal horn antenna for transmitting and receiving microwave signals at X-band (10.0 GHz). All the data to be processed by this algorithm has been received by moving the transmitter/receiver to different locations at a single frequency in X-band in the far field region. ANN technique has been found to be very efficient. An effective training technique has been used to improve the effectiveness of the algorithm. The retrieved result of shape is in good agreement with original shape.

This work presents a new indoor localization method based on the fingerprinting technique. The proposed method uses a ray-tracing model that provides information about multipath effects. This information is stored in a dataset during the first stage of the fingerprinting method. The direction of arrival (DOA) and received signal strength (RSS) are used in the fingerprinting technique as a hybrid system. The localization estimation is calculated while taking into account the Euclidian distance between the DOA and the RSS from each unknown position and the information of the fingerprints. Numerical calculations were performed to show the mean and the standard deviation of the estimated error.

A new approach to analyze the behavior of a high-gain antenna covered with a frequency selective surface (FSS) superstrate is presented. Using an image theory and effective constitutive parameter retrieval, properties of impedance and a refractive index of the entire cavity structure are investigated. Through the analysis, we show that our antenna inherently operates in the medium whose maximum index of refraction is lower than ‘0.5'. Furthermore, we also demonstrate that the high-gain feature of the Fabry-Perot cavity antenna is not only due to satisfy a conventional cavity resonance condition, but also for a material of an effectively low index of refraction.

A Green's function based methodology has been developed and implemented with the view to optimize the focusing properties and thus the performance of a Microwave Radiometry Imaging System (MiRaIS). The system consists of an ellipsoidal conductive wall cavity and a sensitive radiometric receiver and its operation principal is based on the convergence of the radiation from one focal point, where the subject or phantom is placed, on the other, where the receiver antenna is positioned. A two-layered cylinder is used to model the human head with the semi-analytical Green's function technique. The imaging configuration is enhanced by different matching structures of various materials which are placed on the surface of both the human head model and the antenna inside the ellipsoidal. Numerical code executions have been realized and the results for the electric field distribution inside the head are presented for materials of various dielectric properties and for left handed materials at two different frequencies (0.5 GHz and 1.0 GHz). Increased sensitivity of the system focusing properties is observed using particular matching structures.

A compact Vivaldi antenna array printed on thick substrate and fed by a Substrate Integrated Waveguides (SIW) structure has been developed. The antenna array utilizes a compact SIW binary divider to significantly minimize the feed structure insertion losses. The low-loss SIW binary divider has a common novel Grounded Coplanar Waveguide (GCPW) feed to provide a wideband transition to the SIW and to sustain a good input match while preventing higher order modes excitation. The antenna array was designed, fabricated, and thoroughly investigated. Detailed simulations of the antenna and its feed, in addition to its relevant measurements, will be presented in this paper.

Abstract---In this paper we propose a circularly polarized (CP) microstrip antenna on a suspended substrate with a coplanar capacitive feed and a slot within the rectangular patch. The antenna has an axial ratio bandwidth (< 3 dB) of 7.1%. The proposed antenna exhibits a much higher impedance bandwidth of about 49% (S₁₁ < -10 dB) and also yields return loss better than -15 dB in the useful range of circular polarization. Measured characteristics of the antenna are in good agreement with the simulated results. The radiation patterns indicate good cross polarization rejection and low back lobe radiations. The design proposed here can be scaled to any frequency of interest.

This article describes a compact UWB chip antenna using the coupling concept. The inclined slot is inserted on the rectangular radiating patch of the UWB chip antenna. From experimental results, the measured impedance bandwidth of the antenna (defined by -6 dB return loss) is 2.5 GHz (3-5.5 GHz). Also, the proposed antenna exhibits good radiation patterns with small gain variation (2.5-3.5 dBi) in the operating frequency band. Details of the proposed antenna design and the simulated and measured results are presented and discussed.

An inclined semi-circular slot cut in the narrow wall of a rectangular waveguide has been analyzed. By enforcing the boundary condition of continuity of the tangential magnetic field at the slot aperture, an integral equation with the aperture electric field as the unknown has been obtained and solved by the method of moments (MoM). The equivalent slot admittance is then determined. Different slot parameters, such as scattering coefficients, normalized resonant conductance, resonant length versus tilt angle, and radiation patterns, have been studied. The results obtained by the MoM have been verified by comparing them against those results obtained with HFSS.