The essential cause of Multiple Sclerosis (MS) remains to be unknown until present. Although the relevance of racial, genetic, immunological and environmental causal factors has been accepted and expressed by various researchers, there has not been an elaborate study as to the essential cause of MS. This study aims to explain the importance of the environmental causal factor on the occurrence of MS compared to the racial, immunological and genetic factors. In this study, especially the Extreme Low Frequency (ELF) electromagnetic fields and electromagnetic fields at a frequency band (10⁹-10¹³) Hz in terms of dielectrophoretic effect on myelin in dispersive gray matter and white matter are regarded as the essential causal factor of MS regardless of the fact, whether their sources are artificial or natural. There are epidemiological and experiment-based studies that support this view. In order to support my view, I made use of several comparative studies and obtained computational data. Dielectrophoretic force in the human body, especially in gray and white matter can affect on the myelin basic proteins and be the cause of accumulating them.

Active microwave imaging techniques are aimed at reconstructing an unknown region under test by means of suitable inversion algorithms starting from the measurement of the scattered electromagnetic field. Within such a framework, this paper focuses on an innovative strategy that fully exploits the information arising from the illumination of the investigation domain with different configurations as well as radiation patterns of the probing sources. The proposed approach can be easily integrated with multiview techniques and, unlike multifrequency methods, it does not require additive a-priori information on the dielectric nature of the scatterer under test. A large number of numerical simulations concerned with 2D geometries confirms the effectiveness of the inversion strategy as well as its robustness with respect to noise on data. Moreover, the results of a comparative study with single-source methodologies further point out the advantages and potentialities of the new approach.

A disk-loaded monopolee array antenna with coplanar waveguide (CPW) feeding systems that has the capability of beam switching has been successfully demonstrated. The antenna utilises the advantages of CPW and the transmission line of input impedance equation and is integrated with RF/Microwave devices to enable beam switching in the elevated and azimuthal planes. The measured gain of the antenna in the direction of the open-circuited parasite element is in the range of 5.10 to 5.60 dBi. It has good input return loss at 2.45 GHz and produces useful gain in the direction of the open circuited element. The E- and H-plane patterns show that the beam can be steered by pin diodes switching.

In this article, a novel wideband planar monopole antenna for applications in 2.4 GHz WLAN and UWB bands is presented and investigated. The proposed antenna is composed of a gourd-like radiation element fed by a 50 Ohm microstrip line and a step-shaped ground plane. A pair of slot lines is etched symmetrically on the ground plane to obtain the 5 GHz band-notched characteristic, and the notched band can be tuned. The proposed antenna is successfully simulated, designed, and measured. The measured results agree reasonably with the simulated ones. According to the measured results, the proposed antenna yields a wide bandwidth ranging from 2.2 to 11 GHz for VSWR less than 2, except the notched band of 5.1-6.2 GHz for 5 GHz WLAN. Moreover, it exhibits nearly omnidirectional radiation patterns, stable gain, and small group delay variation across the operation band, which meets the requirements of 2.4 GHz WLAN and UWB applications.

In microwaves, ferrites are characterized by a tensorial permeability which represents their anisotropy under a constant magnetic field. We present, in this article, a rigorous study of the formulation of the transverse operator method (TOM) with an extension to the case of the guides of rectangular waves partially charged with longitudinally magnetized ferrite. We show the existence of the complex modes in these types of structures with ferrite. A good agreement of the constant of propagation with the literature is obtained.

Local Area Augmentation System (LAAS) based on multi-constellation GNSS can provide improved accuracy, availability and integrity needed to support all weather category II and III precision approach landing of aircraft. In order to receive satellite signals of GNSS, an antenna working over wide frequency band and high phase center stability is preferred. Commonly used antennas like crossed dipoles, patch etc. are inherently narrow band. This paper describes the design and development of half-cardioid shaped dual arm, wide band printed circuit antenna. The antenna has low VSWR of < 3:1, a stable phase center and good right hand circularly polarized radiation patterns covering full L-band frequencies. The simulated and measured results compare well. This compact antenna can also be used on ground, ship and airborne platforms to receive signals from multiple GNSS satellites above the horizon.

We propose a kind of novel photonic crystal fibers (PCFs) based on a super-lattice structure. Uniform air holes are used to form the basic cell structure. Using the uniform air holes in the PCF has the advantage of minimizing the structural distortion during fabrication while forming a complex-structure cross section. We propose an effective-circular-hole PCF with similar properties of the conventional circular-hole PCF to address the concept of the super-lattice structure PCF. An effective-elliptical-hole PCF based on a super-lattice structure is proposed and investigated, which has the similar birefringent and confinement loss characteristics as the previously reported elliptical-hole PCF. Other PCFs based on super-lattice structures such as the effective-triangular-hole PCF and effective-rectangular-hole PCF can also be achieved by using the design method proposed in this paper.

We introduce and investigate the applications of double zero (DZR) metamaterials (having the real parts of permittivity and permeability equal to zero) as radar absorbing materials (RAMs). We consider a perfectly electric conductor (PEC) plate covered by several layers of DZR metamaterial coatings under an oblique plane wave incidence of arbitrary polarization. Several analytical formulas are derived for the realization of zero reflection from such structures. The angle of reflection in the DZR metamaterials becomes complex, which leads to the dissociation of the constant amplitude and equiphase planes. Then several examples of the applications of DZR metamaterials (in nondispersive and dispersive conditions) as RAMs and zero reflection coatings are provided. The characteristics and parameters of the DZR metamaterial media are determined in each case. The method of least squares is used to optimize the DZR coatings for the minimization of reflected power, which uses the combination of genetic algorithm and conjugate gradient method (GA-CG) to benefit from their advantages and avert their short comings.

In this work, we present an inverse scattering approach to address the timely detection of damage and leakage from pipelines via multi-bistatic ground penetrating radar (GPR) surveys. The approach belongs to the class of linearized distorted wave models and explicitly accounts for the available knowledge on the investigated scenario in terms of pipe position and size. The inversion is regularized by studying the properties of the relevant linear operator in such a way to guarantee an early warning capability. The approach has been tested by means of synthetic data generated via a finite-difference timedomain forward solver capable of accurately and realistically modeling GPR experiments. The achieved results show that it is possible to detect the presence of leakage even in its first stages of development.

Most tunneling effects are investigated using a one-dimensional model, but such an approach fails to explain the phenomena of the propagation of wave in a system with geometric discontinuities. This work studies the tunneling characteristics in a waveguide system that consists of a middle section with a distinct cutoff frequency, which is controlled by the cross-sectional geometry. Unlike in the one-dimensional case, in which only the fundamental mode is considered, in a virtually three-dimensional system, multiple modes have to be taken into consideration. High-order modes (HOMs) modify the amplitude and the phase of the fundamental mode (TE₁₀), thus subsequently affecting the transmission and group delay of a wave. The effect of the high-order evanescent modes is calculated, and the results are compared with the simulated ones using a full-wave solver. Both oversized and undersized waveguides reveal the necessity of considering the HOMs. The underlying physics is manifested using a multiple-reflection model. This study indicates that the high-order evanescent modes are essential to the explanation of the phenomena in a tunneling system with geometrical discontinuities.

We consider how an electromagnetic field propagating to a target alters the radar cross section of the target relative to an observer. We derive the optimum high-frequency path for the fields using the calculus of variations and by using a realistic refractive index profile for the atmosphere obtain closed form solutions. It is found that the predicted nulls and peaks in the radar cross section of a scattering object relative to an observer are shifted from those normally expected from just the isolated object. Hence, for predictive purposes at least, radar cross section results need to incorporate the effects of atmospheric propagation.

When compared to the over-simplified classical skin-effect model, the accurate classical relaxation-effect modelling approach for THz structures at room temperature can be mathematically cumbersome and not insightful. This paper introduces various interrelated engineering concepts as tools for characterizing the intrinsic frequency dispersive nature of normal metals at room temperature. This engineering approach dramatically simplifies otherwise complex analysis and allows for a much deeper insight to be gained into the classical relaxation-effect model. For example, it explains simply how wavelength increases with frequency at higher terahertz frequencies. This is the first time that such an approach has been applied for the modelling of intrinsic frequency dispersion within a metal. While the focus has been on the characterization of normal metals (magnetic and non-magnetic) at room temperature, it is believed that the same methodology may be applied to metals operating in anomalous frequency-temperature regions, semiconductors, semiconductors, carbon nanotubes and metamaterials.

A proposal for the new modified W type optical fiber structure with ultra high effective area and small dispersion as well as dispersion slope is presented. For the proposed structure, all these features are achieved due to placing extra depressed cladding layers, which is the key to achieve higher effective area and flat dispersion curve compared with the conventional W structures. Meanwhile, the suggested design method is based on the Genetic Algorithm optimization technique to choose optimal value for the structural parameters. Also, our calculation for extracting optical properties of the proposed structure is evaluated analytically. The designed dispersion flattened single mode fiber has dispersion and its slope respectively within [0.1741-0.9282] ps/km/nm and [(-0.011)-(0.0035)] ps/km/nm² in the spectral range of [1.46-1.625] μm (S+C+L bands) which are noticeably smaller than the reported value for ultra-low dispersion slope fibers [5]. The designed fiber has ultrahigh effective area from 103.56 to 232.26 μm² in the above wavelength interval. Meanwhile, we show that there is a breakthrough in the quality factor of the ultra-low, ultra-flattened chromatic dispersion single mode optical fiber.

It is a proven fact that The Fast Fourier Transform (FFT) extension of the conventional Fast Multipole Method (FMM) reduces the matrix vector product (MVP) complexity and preserves the propensity for parallel scaling of the single level FMM. In this paper, an efficient parallel strategy of a nested variation of the FMMFFT algorithm that reduces the memory requirements is presented. The solution provided by this parallel implementation for a challenging problem with more than 0.5 billion unknowns has constituted the world record in computational electromagnetics (CEM) at the beginning of 2009.

Anechoic chambers which are used for emission and immunity testing require expensive ferrite tiles on their inner surfaces. This paper describes a method to reduce the number of required ferrite tiles, whilst ensuring a reliable and specified test region. In this method, the positions of some ferrite tiles are found optimally to keep the performance of the anechoic chamber as high as possible. An optimum ray-tracing method is presented to predict the electric field in the anechoic chamber. The performance of the proposed method is verified by a comprehensive example simulated by the CST software, which is a full-wave simulator based on time difference method.

This paper presents the design, fabrication and measurement of a polarization insensitive microwave absorber based on metamaterial. The unit cell of the metamaterial consists of four-fold rotational symmetric electric resonator and cross structure printed on each side of a print circuit board to realize both electric and magnetic resonances to achieve efficient absorption of the incident microwave energy. Both the full wave electromagnetic simulation and the measurement on the fabricated absorber demonstrate high microwave absorption up to 97% for different polarized incident electromagnetic waves. To understand the mechanism, analysis is carried out for the electromagnetic field distribution at the resonance frequency which reveals the working mode of the metamaterial absorber. Moreover, it is verified by experiment that the absorption of this kind of metamaterial absorber remains over 90% with wide incident angle ranging from 0° to 60° for both transverse electric wave and transverse magnetic wave.

In this study, annular-ring microstrip patch on uniaxial medium is analysed in Hankel Transform Domain. Equivalent models of the structure are obtained depending on the TE and TM mode decomposition in this domain. For the simplification of the tensor form formulations, equivalent matrix operators are defined in cylindrical coordinates instead of the differential ones. Then, resonant characteristics of the structure is determined via the application of the moment method and compared with the isotropic case for different anisotropy ratio values and structural parameters. Equivalent circuit models for the case of multilayered substrates and superstrates are given in order to be used in the following studies on annular-ring microstrip patch.

This paper presents a simple and innovative deterministic approach to the synthesis of uniformly excited thinned arrays able to fulfill constraints concerning both the sidelobe level and the value of the radiated far field (and/or of the directivity) in a set of given directions. Starting from a reference regular (periodic or even aperiodic) lattice and from an optimal continuous reference source fulfilling at best the required specifications, the proposed approach finds out both the number and the location of the isophoric (i.e., equi-amplitude) radiating elements to withdraw in a fast and effective fashion. In fact, it is based on a deterministic best-fitting procedure which takes inspiration from existing density taper techniques. Examples are provided with reference to the synthesis of large circular arrays and confirm the interest of the proposed procedure.

In this paper, a half mode substrate integrated with folded waveguide (HMSIFW) and a HMSIFW partial H-plane bandpass filter are proposed. The proposed filter employs H-plane slot of open-ended evanescent waveguide and H-plane septa of short-ended evanescent waveguide as admittance inverter and impedance inverter, respectively. The filter has advantages of convenient integration, compact size, low cost, mass-producibility and ease in fabrication. In order to validate the new proposed topology, a four-pole ultra-narrowband bandpass filter, with quarter wavelength resonators, is designed and fabricated using standard printed circuit board process. The tapered line is used as transition between HMSIFW and microstrip-line for easy integration and measurement. The measured results are in good agreement with simulated ones, and good selectivity is achieved.

In this paper, we propose a circularly polarized (CP) stacked annular-ring microstrip antenna (SARMSA) with an integrated feeding network in the UHF RFID band. A circular parasitic patch is suspended above the annular ring to improve the impedance matching and bandwidth. Through the parametric studies on SARMSA, the CP characters of the entire antenna are well understood，and an optimized CP character is obtained. Prototypes are fabricated to confirm the theoretical results. The experimental results indicate the impedance bandwidth for S₁₁<-10 dB is 870-967 MHz (10.6% at 915 MHz)，and the 3 dB AR bandwidth is 893-948 MHz (6%). Meanwhile, the measured CP gain reaches 8.9 dBic at 915 MHz.