A simplified expression for the eddy current loss in laminated rectangular core is obtained using linear electromagnetic field analysis. The treatment takes cognizance of current interruption phenomena, by considering capacitive effects of insulation regions. Analysis presented in this paper assumes identical field distribution in each lamination and ignores eddy currents in insulation regions.
This paper presents a novel method for microwave breast cancer detection using a parallel-plate waveguide probe. The method is based on detecting the dielectric contrast between a malignant tumor and its surrounding tissues. Our analysis and simulations indicate that scattered signals from a tumor (modelled as a lossy dielectric sphere with higher dielectric constant than the surrounding tissues) received in the form of S parameter S11 have resonating characteristics in the frequency range of 1 to 7 GHz. A frequency scan of the resonant scattered signals provides data of the presence and location of the tumor. Through numerical examples, the effectiveness of the proposed methodology to detect breast tumors of different sizes, embedded at different depths and to distinguish a tumor from clutter items is demonstrated.
In this contribution, a two step strategy for the inversion of amplitude-only data in microwave imaging applications is analyzed. At the first step of the proposed method, the illuminating source is synthesized according to a line sources model in order to compute the incident field in the investigation domain starting from the values available in the measurement domain. The second step is aimed at reconstructing the profile of the objects under test thanks to the iterative multi-scaling approach integrated with the Particle Swarm Optimizer, an effective evolutionary minimization technique. The reconstruction accuracy of the proposed phaseless retrieval strategy is analyzed using synthetic data concerned with a multiple scatterer configuration and successively further assessed inverting experimental data.
This paper presents comprehensive measurements of radar backscatter from rice crops using a ground-based 6 GHz C-band scatterometer system. The measurements were conducted over an entire season from the early vegetative stage of the plants to the ripening stage with full polarization combinations of HH, VV, HV and VH at the incident angle range from 0o to 60o. The objective of this paper is to access the use of the ground-based scatterometer data for the investigation of temporal variation of different incident angle in the rice growth monitoring application. A further study on the angular response for different rice growth stages was also performed in order to have a better understanding of the backscattering behavior of the rice crops and therefore, monitoring of rice crops growth using operational scatterometer system.
In this paper we study the behavior of wave radiation of a horizontal electric dipole antenna with grounded metamaterial substrates formed by using coordinate transformation technology. From theoretical analysis and simulation results, we can find that such metamaterial substrates not only improve the directive emission but also enhance the radiation efficiency as the dipole antenna gets closer and closer to the metallic ground plane. We thus demonstrate that the transformation medium can offer a theoretical basis for designing a compact planar antenna with transformation media as substrates.
New electromagnetic models for the rods and cones that are the photoreceptors at the back of the retina are developed and simulated in order to explain the roles of dimension, geometrical structure, directional sensitivity and visual pigments of the photoreceptors in the reception of visible light. The rods and cones are modeled as uniform and quasi-tapered helical antennas, respectively. The results of the model study show that if the model antennas have the original photoreceptor cell dimensions, the frequency responses of the model antennas and the spectral sensitivities of the photoreceptors would be very close to each other. In addition, it's observed that the spectral sensitivities of L, M and S cones are broadband over the visible light spectrum, and there are secondary peaks beside main peaks in the spectral sensitivity curves of the cones, because of the conical shape of the cones. It's also observed that there is only one main peak in the spectral sensitivity curves of the rods, because of the uniform and cylindrical shape of the rods. Finally, an array of the novel modeled antennas is also discussed to be used in biomedical applications of artificial retinal photoreceptors in medicine, although the main scope is not designing artificial retinal photoreceptor prosthesis.
By properly exciting higher order modes at an aperture it is possible to achieve higher aperture efficiencies. High efficiency antennas are mandatory in many applications, as discrete lenses, since the single element efficiency deeply affects the efficiency of the whole lens. In this contribution a genetic algorithm is applied to the mode matching analysis of square horns to achieve high radiation efficiency over a relatively wide band.
Anew wideband and compact bandstop filter using one dimensional (1-D) mushroom-like electromagnetic bandgap (EBG) structures is proposed in this paper. Although the proposed structure can not be fabricated as easy as defected ground structure (DGS) filters, it has several winning features such as more compactness, better characteristics and no backward radiation. A5-cell 1-D mushroomlike EBG filter is compared with 5-cell and 9-cell circular DGS filters. The 1-D mushroom-like EBG filter is found to be more compact as it requires fewer cells for the same characteristics and also as it has 0.44 times shorter cell length. The proposed EBG filter has a 10-dB bandwidth of 39% while the 5-cell and 9-cell DGS filters have 10-dB bandwidth of 20% and 27%, respectively. Also, the 1-D mushroom-like EBG filter is studied for various number of cells and compared with a two dimensional (2-D) structure. The simulated and measured results are found to be in good agreement.
A novel technique to increase the bandwidth of the conventional planar triangular monopole antenna (PTMA) is presented. With two symmetrical corrugations extended from the flat ground plane, a significant improvement on the impedance bandwidth up to about 4:1 can be achieved. The proposed antenna design is a modification from the conventional volcano smoke antenna (VSA) and can be more compact and easily fabricated. The HFSS 3-D EM solver is employed for design simulation. The effects of the ridged ground plane on the impedance bandwidth are studied. A printed PTMA is fabricated on the FR-4 PCB substrate. Measured VSWR of the printed PTMA with the ridged ground plane is less than 2 from 3 to 12 GHz which covers the UWB frequency band. The measured antenna patterns also show the monopole-type omni-directional radiation patterns from 3 to about 10 GHz.
A new technique is proposed to increase the bandwidth (BW) of slot antenna operated at 2.4 GHz and 5 GHz, over the industrial-scientific-medical (ISM) bands and the Hiperlan2 bands. By splitting two side slots of the Z-like slot antenna into two or three fingers, several additional resonances can be created. By properly arranging the geometry of the feeding structure in the multi-slot region, the double-slot and triple-slot antennas have respectively 2.0 and 3.2 times wider bandwidth than the single Z-slot antenna. According to the results, the proposedtriple-slot antenna can provide two separated impedance bandwidths of 672 Hz (about 28.3% centered at 2.4 GHz band) and 2752 MHz (about 53.5% centered at 5.2 GHz band), making it easily cover the required bandwidths for WLAN operation in the 2.4 GHz bandand 5.2/5.8 GHz bands.
In this paper, a novel stochastic approach, i.e., the electromagnetism-like (EM-like) algorithm, is applied to phase-only syntheses of antenna arrays. The goal is to minimize the pattern sidelobe under null-steering constraints by phase-only adjusting. The mechanism of EM-like algorithm results from the Coulomb's Law of Electromagnetics. It does not require gradient calculations, and can automatically converge at a good solution through the virtual charge of each particle. Simulation results show that the EM-like algorithm can well treat the phase-only optimization of antenna arrays. Although the null-steering constraints will affect the optimization in sidelobe reduction, it can be easily included in the EM-like based optimization scheme. The EM-like algorithm can be applied not only to problems of antenna arrays, but also to many other nonlinear optimization problems in electromagnetic waves.
A hybrid empirical-neural (HEN) model, to account for a loading effect of arbitrary raised dielectric slab in a microwave cylindrical metallic cavity, is presented. It is based on combination of an approximate model, as a rough empirical knowledge holder, and multi-layer perceptrons (MLP) neural network. In comparison with the model based only on MLP network, more accurate and efficient resonant frequencies calculation is achieved.
Design of a compact dual frequency microstrip antenna is presented. The structure consists of a slotted circular patch with a dielectric superstrate. The superstrate, not only acts as a radome, but improves the bandwidth and lowers the resonant frequency also. The proposed design provides an overall size reduction of about 60% compared to an unslotted patch along with good efficiency, gain and bandwidth. The polarization planes at the two resonances are orthogonal and can be simultaneously excited using a coaxial feed. Parametric study of this configuration showed that the frequency ratio of the two resonances can be varied from 1.17 to 1.7 enabling its applications in the major wireless communication bands like AWS, DECT, PHS, Wi.Bro, ISM, and DMB. Design equations are also deduced for the proposed antenna and validated.
Hemispherical dielectric resonator (HDR) antenna excited with a thick slot at the short circuited end of waveguide is analyzed theoretically and verified experimentally. The problems are formulated using the Green's function approach; with unknown slot currents solved using the method of moments (MOM). The HDR is modeled using exact magnetic field Green's function due to the equivalent magnetic current in the slot. The field inside the waveguide is expressed in terms of model vectors and modal functions. Thickness of the slot is analyzed using cavity approach. For the analysis of HDR antenna part, the modal series is represented as a sum of particular and homogeneous solutions. The particular solution is computed efficiently using spectral domain approach. In order to determine the effects of varying design parameters on bandwidth and matching, sensitivity analysis is carried out using the code developed. Measurements were carried out to verify the theory, and reasonable agreement between them is obtained.
A magnetized thin layer mounted on a PEC surface is considered as an alternative for an absorbing layer. The magnetic material is modeled with the Landau-Lifshitz-Gilbert equation, with a lateral static magnetization having a periodic variation along one lateral direction. The scattering problem is solved by means of an expansion into Floquet-modes, a propagator formalism and wavesplitting. Numerical results are presented, and for parameter values close to the typical values for ferro- or ferrimagnetic media, reflection coefficients below -20 dB can be achieved for the fundamental mode over the frequency range 1-4 GHz, for both polarizations. It is found that the periodicity of the medium makes the reflection properties for the fundamental mode almost independent of the azimuthal direction of incidence, for both normally and obliquely incident waves.
Feed forward neural Network (FNN) has been widely applied to many fields because of its ability to closely approximate unknown function to any degree of desired accuracy. Back Propagation (BP) is the most general learning algorithms, but is subject to local optimal convergence and poor performance even on simple problems when forecasting out of samples. Thus, we proposed an improved Bacterial Chemotaxis Optimization (BCO) approach as a possible alternative to the problematic BP algorithm, along with a novel adaptive search strategy to improve the efficiency of the traditional BCO. Taking the classical XOR problem and sinc function approximation as examples, comparisons were implemented. The results demonstrate that our algorithm is obviously superior in convergence rate and precision compared with other training algorithms, such as Genetic Algorithm (GA) and Taboo Search (TS).
A hybrid array configuration suitable for wideband millimeter-wave applications is presented in this work. The proposed structure is based on the use of circular waveguide elements electromagnetically coupled trough circular apertures to a stripline distribution network. The adopted excitation mechanism avoids the use of transition components generally reducing the overall antenna efficiency. Simulated and measured results on a Ka-band prototype are discussed to prove the wideband radiation behavior.
In the application of two-dimension (2D) finite-difference time-domain (FDTD) to scattering analysis of object embedded in layered media, the incident electromagnetic wave propagation is much more complicated, it can not inject the plane wave source by traditional method. To solve this problem, the Π-shape total-field/scatteringfield (TF-SF) boundary scheme is presented. The side TF-SF boundaries are governed by the modified 1D Maxwell's equations, but the discretization for which to p-wave is more difficult than n-wave. Then an auxiliary magnetic variable is used, which can develop the modified 1D-FDTD to p-wave without any approximately. To truncate the modified 1D-FDTD, the convolutional perfectly matched layer (CPML) absorbing boundary condition (ABC) is also given. Examples showthe feasibility and applicability of proposed Π-shape TF/SF boundaries scheme.
A set of beam shifter which can effectively control the propagation of the beam is proposed. The permittivity and permeability of the beam shifter can be obtained by applying forminvariant, spatial coordinate transformations to Maxwell's equations. We show that the beam is smoothly guided to avoid hitting some irremovable objects, which could be useful in the practical application. Besides, inspired by some phenomenon from the above application, an interesting utilization has been found that by placing a set of beam shifters, electromagnetic detectors can be misled and make mistakes about where the target is located, which is very useful in the antidetection. All our ideas are verified by numerical simulations with finite element method.
A novel approach for the design of a compact multiband planar microstrip antenna is presented. This type of antenna is composed of composite metamaterial resonators (including conditional microstrip resonators and metamaterial resonators), and fed by signal feed. A sample antenna with composite closed-ring resonator and split-ring resonator (SRR) fed by 50Ω coplanar waveguide (CPW) developed on FR4_epoxy substrate for multi-band wireless communication applications is presented. Appropriate design of the composite structure resulted in three discontinuous resonant bands. The fundamental magnetic resonant and electric resonant frequency of SRR and the first electric resonant frequency of the closed-ring resonator were combined to form low, middle, and high resonant band. The properties of this antenna are investigated by theoretical analysis and finite element method (FEM) simulations. The numerical results show that the proposed antenna has good impedance bandwidth and radiation characteristics in the three operating bands which cover the required band widths of the 2.4/5.2/5.8 GHz wireless local-area networks (WLAN) and 3.5/5.5 GHz worldwide interoperability for microwave access (WiMax) with return loss of better than 10 dB. The antenna also has stably omni-directional H-plane radiation patterns within the three operating bands.
This paper suggests a pilot-less residual carrier frequency offset (CFO) estimator for ultra-wideband orthogonal frequency division multiplexing (UWB-OFDM) systems. The basic idea of our approach is based on the fact that two adjacent OFDM symbols carry the identical information in the UWB-OFDM system, thus removing the need of pilot symbols. To demonstrate the efficiency of the proposed pilot-less CFO estimator, analytical expression of the mean square error (MSE) is reported and comparisons are made with the conventional pilot-aided CFO estimator in terms of MSE and throughput.
In this paper an efficient technique for the determination of the resonances of elliptic Substrate Integrated Waveguide (SIW) resonators is presented. The method is based on the implementation of Support Vector Regression Machines trained using a fast algorithm for the computation of the resonant frequencies of SIW structures. Results for resonators with a wide range of parameters will be presented. A comparison with results obtained with Multi Layer Perceptron Artificial Neural Network and with full wave simulations will show the effectiveness of the proposed approach.
This paper presents a method of antenna impedance measurement for RFID tag antenna based on a differential probe. The importance of accurate impedance measurement in optimal design of tag antenna, especially for the metal tags, is first addressed. Afterwards, an overview of the existing methods based on the singleended probe and the balun probe is presented. The proposed method using the differential probe is explained based the well-known two port network model. Experiments for both balanced and unbalanced tag antenna measurement demonstrate the differential probe can provided better agreement with simulated results.
We have investigated the scattering of the Magnetic Resonance Imaging (MRI) radiofrequency (RF) field by implants for Deep Brain Stimulation (DBS) and the resultant heating of the tissue surrounding the DBS electrodes. The finite element method has been used to perform full 3-D realistic simulations. The near field has been computed for varying distances of the connecting portion of the lead from the air-tissue interface. Dissipated powers and induced temperature rise distributions have been obtained in the region surrounding the electrodes. It is shown that the near proximity of the air-tissue interface results in a reduction in the induced temperature rise.
In this paper, the Haar wavelets basis functions are applied to the method of moments to calculate the radar cross section of the resistive targets. This problem is modeled by the integral equations of the second kind. An effective numerical method for solving these integral equations is proposed. The problem is treated in detail, and illustrative computations are given for several cases. This method can be generalized to apply to objects of arbitrary geometry.
In this paper, we consider the resistances and inductances extraction from finite conducting metals. To remedy the weakness of volume integral equation, we extend the usage of a surface integral equation method from analyzing finite conducting rectangular wire strip to analyzing arbitrarily shaped geometry. Moreover the multilevel Green function method (MLGFIM) with a complexity of O(N) is employed to accelerate the matrix-vector multiplications in iterations. The numerical results shows the efficacy of the proposed method.
A three dimensional plano-convex lens which is placed at a certain distance from a plane uniaxial interface has been considered. High frequency fields refracted by the geometry are derived. The treatment is based on Maslov's method. The method combines the simplicity of asymptotic ray theory and generality of the transform method to remedy the problem of geometrical optics around the caustic point of a focusing system. Field patterns are obtained which includes the observation points around the caustic region. The results are found in good agreement with obtained using Huygens-Kirchhoff Principle.
Inspired by the requirement of proper link simulation methods in performance analysis of communication systems, we present in this paper a recipe for channel implementation in simulation environments. Our focus here is the indoor applications of wireless local-area networks (WLANs). Specifically, we describe a procedure that beginning with statistical description of the channel impulse response leads to an efficient multi-input multi-output (MIMO) channel simulating method for arbitrary antenna configurations at both ends. A sample set of distributions for model parameters are also provided at the 5-GHz band, which is the operating frequency band of IEEE 802.11a, HIPERLAN/2, and the emerging IEEE 802.11n standards, and the corresponding software implementation of the simulator is addressed for public use.
This paper presented a novel dual band transmitter which operates as power amplifier or frequency doubler with the stop band characteristic of defected ground structure (DGS). It works as a power amplifier at 2.4GHz which satisfies the 802.11b/g wireless LAN standard or performs as an active frequency doubler at 6.8GHz which depends on the input frequency and. The equivalent circuit and the stop band characteristic of the proposed microstrip DGS are analyzed and simulated. For the proposed transmitter, second harmonic suppression is below -52.6dBc in the amplifier mode, and fundamental suppression is below -41dBc in the frequency doubler mode with the stop band characteristic of DGS. The designed transmitter used GaAs InGaP Heterojunction broadband MMIC. It achieves 13.7dBm of P1dB and its gain is 16.5dB in amplifier mode, and its maximum output power is 7.8dBm at 6.8GHz in frequency double mode.