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.
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.
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.
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.
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.
We present the design, processing and testing of a W-band finite by infinite and a finite by finite Grounded Frequency Selective Surfaces (FSSs) on infinite background. The 3D full wave solver Nondirective Stable Plane Wave Multilevel Fast Multipole Algorithm (NSPWMLFMA) is used to simulate the FSSs. As NSPWMLFMA solver improves the complexity matrix-vector product in an iterative solver from O(N2) to O(N log N) which enables the solver to simulate finite arrays with faster execution time and manageable memory requirements. The simulation results were verified by comparing them with the experimental results. The comparisons demonstrate the accuracy of the NSPWMLFMA solver. We fabricated the corresponding FSS arrays on quartz substrate with photolithographic etching techniques and characterized the vector S-parameters with the free space Millimeter Wave Vector Network Analyzer (MVNA).
A polarimetric scattering from two-dimensional (2-D) rough surface is presented by the finite-difference time-domain (FDTD) algorithm. The FDTD calculations with sinusoidal and pulsed plane wave excitations are performed. As the sinusoidal FDTD is concerned, it is convenient to obtain the scattered angular distribution of normalized radar cross section (NRCS) from rough surface for a single frequency. And the advantage of pulsed FDTD is to calculate the frequency distribution of NRCS from rough surface in a scattered direction of interest. A single frequency scattering from rough surface by sinusoidal FDTD is validated by the result of Kirchhoff Approximation (KA). And the frequency response of rough surface by pulsed FDTD is verified by that of sinusoidal FDTD, which requires an individual FDTD run for every frequency. To save computation time, the MPI-based parallel FDTD method is adopted. And the computation time of parallel FDTD algorithm is dramatically reduced compared to a single-process implementation. Finally, the polarimetric scattering of rough surface with the sinusoidal and pulsed FDTD illumination are presented and analyzed for different polarizations.
Design and optimization of high-power microwave (HPM) feed horn by combining the aperture field with radiation patterns are presented in the paper. The optimized feed horn in C band satisfies relatively uniform aperture field, power capacity higher than 3 GW, symmetric radiation patterns, low sidelobes, and compact length. Cold tests and HPM experiments were conducted to investigate the radiation patterns and power capacity of the horn. The theoretical radiation patterns are consistent with the cold test and HPM experimental results. The power capacity of the compact HPM horn has been demonstrated by HPM experiments to be higher than 3 GW.
In this paper we present a Lanczos-type reduction method to simulate the low-frequency response of multiconductor transmission lines. Reduced-order models are constructed in such a way that low frequencies are approximated first. The inverse of the transmission line system matrix is then required and an explicit expression for this inverse is presented. No matrix factorization needs to be computed numerically. Furthermore, computing the action of the inverse on a vector requires an O(N) amount of work, where N is the total number of unknowns, and the inverse satisfies a particular reciprocityrelated symmetry relation as well. These two properties are exploited in a Lanczos-type algorithm to efficiently construct the low-frequency reduced-order models. Numerical examples illustrate the performance of the method.
The paper deals with the evaluation of the far-field radiated emissions from high-speed interconnects when the frequencies are such that the distribution of the currents along the traces is no longer of TEM-type. Instead of a computationally expensive numerical full-wave model, here a generalized transmission line model is used to obtain the current distributions. This full-wave transmission line model is derived from an integral formulation and is here extended to include in efficient way the layered media Green's Functions. The proposed tool is successfully benchmarked to references given in literature and case-studies of practical interest are carried out, referring to a coupled microstrip, driven either by differential and common mode currents. This analysis highlights the existence of a transition range where the error made by evaluating the emission using the classical transmission line current distribution is still negligible. Here a rule of thumb is derived which provides a simple criterion to estimate this extension of the range of validity of the classical transmission line.
The excitation of an antisymmetric trapped mode on a symmetric metamaterial resonator is experimentally demonstrated. We use an active electronic device to break the electrical symmetry and therefore to generate this trapped mode on a symmetric spilt ring resonator. Even more, with such a tunable mode coupling resonator, we can precisely tune the resonant mode frequency. In this way, a shift of up to 15 percent is observed.
In this paper, the closed-form design method of an N-way dual-band Wilkinson hybrid power divider is proposed. This symmetric structure including N groups of two sections of transmission lines and two isolated resistors is described which can split a signal into N equiphase equiamplitude parts at two arbitrary frequencies (dual-band) simultaneously, where N can be odd or even. Based on the rigorous even- and odd- mode analysis, the closed-form design equations are derived. For verification, various numerical examples are designed, calculated and compared while two practical examples including two ways and three ways dual-band microstrip power dividers are fabricated and measured. It is very interesting that this generalized power divider with analytical design equations can be designed for wideband applications when the frequency-ratio is relatively small. In addition, it is found that the conventional N-way hybrid Wilkinson power divider for single-band applications is a special case (the frequency-ratio equals to 3) of this generalized power divider.
A novel configuration for an end-wall microstrip-to-waveguide splitter transition is presented suitable for use in series fed microstrip arrays. The low price, simplicity, manufacturability, low sensitivity, and also wideband operation, up to more than 37%, is the result of positive interaction between double slots and double stubs. The transition is applied to a dual band 1 × 2 array. A wideband non-tilted pattern is achieved.
In this paper, two full-wave simulators (one using finite difference time domain method and the other the method of moments) are developed, in order to analyze wireless communication in boxes with metallic enclosure based on time-reversal ultra-wideband (TR-UWB) technique. Impedance boundary conditions are exploited to model realistic metallic walls, and parallel computing is applied to relieve high computational resources requirements. Focusing on both space and time is exhibited by numerical results in arbitrarily shaped metallic boxes, which demonstrates the feasibility of TR-UWB communication in metallic boxes.
We have developed a proof-of-concept low power free electron maser that is compact and low cost. The design, set-up and results of a novel (without wiggler) low power X-band rectangular waveguide pre-bunched free electron maser (PFEM) are presented in this paper. Our device operates at 10 GHz, with 10 mWatt seeding input power and employs two rectangular waveguide cavities (one for velocity modulation and the other for energy extraction). The electron beam used in this experiment is produced by Thoria coated Iridium filament which can operate at 3 kV and up to 5 mA beam current. The effect of the aperture on the power leaking out of the waveguide is also analyzed. The TE10 mode propagation of the EM standing wave is used to pre-bunch the electron beams in the input cavity. The bunched electron beams are in the same phase as the TE10 mode propagation of the EM wave in the output cavity. This free electron maser could be useful industrially, as it could be used with the commercially available accelerating voltage supplies.
This paper presents a novel approach for designing planar multimode wideband bandpass filters with good selectivity. The multimode resonator is composed of an open-ended microstrip line with length of half-wavelength (λ/2) and several radial-line stubs. By using different kinds of radial-line stub-loaded, different kinds of responses including three-pole and four-pole bandpass filters can be realized. Depending on electric field distribution and equivalent circuit model, the characteristics of the filter are analyzed. To verify the proposed method, two filters are implemented. The measured results exhibit good agreement with the simulation.
In this study, electromagnetic (EM) pollution measurements in crowded residential areas were performed and statistical analysis of values recorded for the EM sources causing pollution was carried out. The actual measurement values and the estimated values by the analysis model obtained through the statistical analysis were compared. Also, amplitude fluctuations of the electromagnetic radiations from EM pollution sources were detected for a long time and statistical analyses were made. EM field levels were measured in the districts of Turkish capital, Ankara where cellular base stations and TV/Radio stations are densely populated. EM radiation levels were measured for the GSM900, GSM1800, FM, UHF4, VHF4 and VHF5 stations for certain spectrum ranges under far-field conditions by utilizing isotropic field probe and selective spectrum analyzer. The measurements were fulfilled by using NARDA SRM3000 radiation meter with isotropic antenna that can be utilized in 100 kHz-3 GHz frequency range. The obtained measurement levels were compared with the limit values given by International Commission for Non-Ionizing Radiation Protection (ICNIRP). The measurement results for each pollution sources were compared and their contributions to the combined radiation were analyzed. The values for the EM pollution in the measurement regions were embedded over the digital maps created for the related places. During this process, comparisons of the pollution maps were made by utilizing Natural Neighbour (NN) interpolation technique.
An optical code generating device has been developed based on 1×2 and 1×4 asymmetric plastic optical fiber (POF) couplers. The code generating device provides a unique series of output power which are successively used as an optical code in a portable optical access-card system. The system is designed where the asymmetric POF coupler is embedded in an all passive portable unit. This device utilizes a tap-off ratio (TOFR) technique based on a simple variation of the tap width of an asymmetric Y-branch splitter design. A hollow-type waveguide structure is used where it eliminates the use of polymeric material for the waveguide core and allows simple fabrication and assembling of the device. The asymmetric POF coupler has been fabricated on metal-based materials using machining technique. The results for the simulated and fabricated 1×2 asymmetric couplers show the same linear characteristics between the TOFR and the tap width. The simulated devices shows a TOFR variation from 18.6% to 49.9% whereas the TOFR for the fabricated metalbased devices varies from 10.7% up to 47.7%, for a tap width of 500 um to 1 mm. The 1×4 coupler designed using simple cascading of a Y-branch splitter with two 1×2 asymmetric couplers has been fabricated and shows similar characteristics as that of the designed 1×4 devices. The insertion loss for the 1×2 asymmetric coupler at the tap line varies from 9 dB to 16 dB whereas for the bus line, the insertion loss is about 9±0.8 dB. The insertion loss for the 1×4 asymmetric coupler at the output ports varies from 14 dB to 22 dB.
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