In this paper, we reformulate the quasi-static spectral domain analysis (SDA) applicable to a lossy anisotropic multilayer asymmetric coplanar waveguide (ACPW). The SDA formulation also incorporates two-layer model of a conductor thickness and the concept of effective permeability to account for the low frequency dispersion due to the magnetic field penetration in an imperfect conductor. The paper further presents the single layer reduction (SLR) formulation and circuit model to compute frequency dependent line parameters of a lossy anisotropic multilayer ACPW. The accuracy of formulation is comparable to that of the HFSS and CST, without using complex and time consuming full-wave methods. The results of CST for ε_{eff}, Z_{0}, α_{d}, α_{c} of multilayer ACPW, in the frequency range 1 GHz-100 GHz, deviate from results of HFSS up to 0.49%, 1.53%, 2.06% and 10.73% respectively; whereas corresponding deviations of the present SDA and SLR combined formulation are up to 1.38%, 2.09%, 3.57% and 8.87%.
In the present paper a novel mathematical model of physical processes of transient electromagnetic waves excitation and propagation in a biconical transmission line with radially inhomogeneous magneto-dielectric filling is proposed. The model is based on time domain mode expansions over spherical waves. The basis functions of the mode expansions are calculated analytically. The mode expansion coefficients are governed by Klein-Gordon-Fock equation with coefficients depending on a radial spatial coordinate. The explicit finite difference time domain computational scheme is derived to calculate the mode expansion coefficients. Dependences of cutoff frequencies of higher modes of TE and TM waves on the line geometry and dielectric filling are studied. In order to calculate electromagnetic field in the line with higher accuracy, just finite number of terms in the mode expansions is required. Electromagnetic field excited by the transient electric ring current is calculated in both homogeneous and radially inhomogeneous biconical transmission line. It is shown that there is a possibility to increase the bandwidth of the line via introduction of partial dielectric filling without changing the line geometrical size.
A 2D finite element electromagnetic model that permits the simulation of a cage induction machine, involving the effects of eddy currents and coupling the field equation with the stator field-circuit equation, has been presented in this paper. Transformation matrix has been derived to incorporate specialized stator winding scheme called the bridge configured winding (BCW) in the coupled field circuit equation. The bridge configured winding scheme is capable of producing controllable transverse force by deliberately imparting asymmetric flux distribution in the machine air-gap. Steady state stator currents have been calculated using the time-stepping scheme with the rotor motion at constant speed allowing the FE model to take into account the harmonics due to the eccentricity (static) of the rotor. This work has furnished us with the 2D magnetic flux distribution in the whole finite element domain as well as sets out an electromagnetic model to study the electromechanical interaction between the eccentric rotor motion and the electromagnetic field. The results, in terms of variation of terminal currents (phase and bridge) and unbalanced magnetic pull (UMP) due to rotor eccentricity as well as asymmetric field (deliberately imparted by exciting the bridge), obtained from the simulation have been compared with analytical formulations as well as already published experimental results.
This paper considers an electromagnetic waveguide composed of two periodic, perfectly conducting, rippled surfaces. This periodic system has a band structure given by a dispersion relation that allows us characterize eigenmodes of the system. We considered the cases of both smooth and rough surfaces, using an integral numerical method to calculate field intensities corresponding to eigenmodes over a wide frequency range. Under certain conditions, the system presents disordered patterns of field intensities with smooth surfaces. We believe that the explanation of disordered patterns is the following: for smooth surfaces, the phenomenon of electromagnetic chaos; and for rough surfaces, the speckle phenomenon. Since it is well known that the surfaces of materials always have a certain degree of roughness, it can be concluded that both chaos and speckle contribute to the presence of disordered field patterns.
This work deals with the behavior of a patch antenna equipped with squared electromagnetic bandgap (EBG) structures and subjected to various mechanical deformations (twisting and bending deformations). The EBG structures have a stop band frequency (rejection) feature, allowing the coupling and the undesired electromagnetic interferences to be reduced. The influences of the deformations on the mutual coupling and radiation patterns of an antenna equipped of those EBG elements are experimentally studied.
A 3-D shaped prolate ellipsoidal dielectric lens is designed to produce multiple asymmetric beams in Ka-band. Such radiation characteristics are useful in applications where the antenna system is mounted on platforms flying above Earth and the shape of the footprints have to be carefully controlled for different elevation angles. A set of design rules is introduced and the final designs are optimized using full-wave time-domain methods. A fully operational Ka-band antenna subsystem has been prototyped and measured. The final antenna lens has axes lengths of 62.3 mm and 57.8 mm and provides a maximum gain of 21 dB. When mounted on a stabilized platform at the altitude of 21 Km (a typical HAPS scenario), this antenna provides 19 circular ground footprints of 5 Km diameter each. Radiation pattern measurements show that such a lens reduces the natural beam footprint elongation unavoidable with traditional spherical lenses and confirm the validity of the proposed system.
This paper presents experimental results in the study of Space-surface Bistatic SAR (SS-BSAR) with global navigation satellite system (GNSS) and stationary receiver. The system uses GNSS as the transmitter of opportunity and a self-built, low cost receiver being set-up and fixed on the earth. It is potentially useful at remote sensing applications such as earth monitoring. The system prototype and signal processing at each stage leading to final image are described. Experimental image analysis is the core of this paper, and therefore performed in details finally.
Space spectral domain approach (SSDA) is a full-wave analysis method that combines the advantages of the spectral domain analysis (SDA) with that of the one dimensional method of lines (MOL). This approach is very efficient to solve 3D MIC/MMIC circuits with higher convergence, higher accuracy and minimized computation time. However, arbitrary shaped structures involving non-homogenous metallization distribution in the resonator patch could hardly be solved using this method. In this paper, the analysis of the space spectral domain approach (SSDA) is developed using non-equidistant MOL discretization as well as modified current basis functions to reduce the computation time window and to sense also accurately the fine metallization details of arbitrary shaped resonators. The modified SSDA approach is applied to solve ten arbitrary shaped resonators with a reduction of computation time less than 10%. Design curves are also presented for these shapes and good agreement is achieved between numerical and experimental results.
It is well known that additional space harmonics in the air-gap magnetomotive force (mmf) distribution of the concentrated non-overlapping windings (CW) cause additional losses in the machine. This is especially so for machines used for traction applications where the machine requires to operate over its rated speed and frequency. In this paper, the authors investigates losses present in an interior permanent magnet (IPM) machine with CW designed to achieve a very wide field weakening range. Losses were quantified analytically and also using finite element methods. Loss estimations were experimentally verified in a constructed prototype machine. Based on the analysis, key losses were identified. The optimization process to minimize these losses and of improving efficiency were discussed in details. The segregation of the losses in the studied machine indicates that the losses in the magnet are much smaller compared to the rotor and stator core losses caused by the slot harmonics. Therefore, core loss minimization techniques for this type of machine will involve reduction of slot harmonics. Also, copper loss is found to be the most dominating component of the total loss. Hence, copper loss minimization should be part of the design optimization process.
An extensive error analysis for arbitrary near-field antenna measurements is performed. Expressions are derived to estimate the far-field uncertainty using the available near-field data together with the measurement inaccuracy but, most importantly, without the knowledge of the reference far field. Error analysis techniques presented so far either assume a specific set of antennas or a specific measurement surface and are difficult to generalize. We present a generalized approach providing realistic error estimates using the recently developed Fast Irregular Antenna Field Transformation Algorithm (FIAFTA). FIAFTA utilizes equivalent plane wave sources to represent radiated antenna fields and is able to process near-field data collected on arbitrary measurement grids. The unknown plane wave coefficients are determined by solving a linear system of equations. The error model is applied to planar, cylindrical, and spherical near-field measurements and is also valid for arbitrary measurement grids. The estimated far-field uncertainties show good agreement with the real far-field errors.
Dependence of the electromagnetic shielding effectiveness on filler volume fraction has been investigated from attenuation upon reflection measurements over a broad frequency range in hybrids based on Poly(vinylidene fluoride)-Aluminum nanoparticles. The loss of reflectivity with relation to the incident radiation in these nanocomposites compared with the pristine polymeric matrix shows the maximum value for the sample with an aluminum content of 10% in volume. Furthermore, the morphological aspects of all the specimens as well as their thermal properties, viscoelastic behavior and dielectric response have been evaluated. The nanocomposite that incorporates an Al content of 10% in volume exhibits the best balance in properties including, in addition to its shielding behavior, its processability and mechanical performance.
This paper presents a rigorous approach for the propagation of electromagnetic (EM) fields along a straight hollow waveguide with a circular cross section. The objectives are to present the technique to calculate the dielectric profiles and their transverse derivatives in the inhomogeneous cross section of the cylindrical hollow waveguide, and to understand the influence of the spot-size and cross section on the output fields and output power density. The derivation is based on Maxwell's equations. The longitudinal components of the fields are developed into the Fourier-Bessel series. The transverse components of the fields are expressed as functions of the longitudinal components in the Laplace plane and are obtained by using the inverse Laplace transform by the residue method. The separation of variables is obtained by using the orthogonal-relations. These objectives contribute to the application of the model for the straight hollow waveguide.
This paper presents a convex meshfree framework for solving the scalar Helmholtz equation in the waveguide analysis of electromagnetic problems. The generalized meshfree approximation (GMF) method using inverse tangent basis functions and cubic spline weight functions is employed to construct the first-order convex approximation which exhibits a weak Kronecker-delta property at the waveguide boundary and allows a direct enforcement of homogenous Dirichlet boundary conditions for the transverse magnetic (TM) mode analyses. Three arbitrary waveguide examples are analyzed to demonstrate the accuracy of the presented formulation, and comparison is made by the analytical, finite element and meshfree solutions.
A through wall image enhancement scheme based on Takagi Sugeno fuzzy system and principal component analysis is proposed. The scheme incorporates spectral properties of image and textural properties of eigen components of image to assign weights. The scheme overcomes the empirical setting of inference engine and output membership functions. Simulation demonstrates the effectiveness of proposed scheme in terms of accuracy.
Within the framework of the composite surface scattering model, analytical formulas for Doppler shift and bandwidth of radar echoes backscattered from time-varying sea surface are derived in the forms of three-dimensional integrals. In our derivations, the influences of the tilt modulation (TM), the hydrodynamic modulation (HM), the shadow and the curvature of large-scale undulating waves are all taken into account for achieving more reasonable results. Comparisons between our theoretical curves and the results obtained directly by exact numerical method demonstrate that our formulas can improve the simulated results. On the other hand, the simulations by our formulas can also help to estimate the effects of the TM, the HM, and the shadow of large-scale waves on Doppler behaviors individually. We find that the predicted Doppler shifts are always larger in HH-polarization than in VV-polarization due to the TM. Meanwhile, the simulations also show that the predicted Doppler shifts for both HH- and VV-polarizations would become larger when the HM is considered. In addition, at low-grazing angles (LGA), the shadow effect results in a rapid increase in the predicted Doppler shift, and on the contrary makes the bandwidth narrower.
In this paper, the characteristics of electromagnetic waves supported by three dimensional (3-D) periodic arrays of multilayer multimaterial spheres are theoretically investigated. The spherical particles have the potential to offer electric and magnetic dipole modes, where their novel arrangements engineer the desired metamaterial performance. Multilayer spheres are designed for controlling both electric and magnetic Mie scattering resonances around the same spectrum. A full wave spherical modal formulation is applied to express the electromagnetic fields in terms of the electric and magnetic multipole modes. Imposing boundary conditions will determine the required equations for obtaining dispersion characteristics ωa/2πc-ka/2π. A metamaterial constructed from unit-cells of multilayer multimaterial sphere is created. It is demonstrated such compositions can exhibit negative-slope dispersion diagram metamaterial properties in frequency spectrums of interest, where both electric and magnetic Mie scattering resonances occur. Different coatings such as silver, gold, indium-tin-oxide (ITO), Al:ZnO, (AZO) and Ga:ZnO (GZO) are used and the operating range and the losses of the resulting metamaterials are compared. It is presented that by adding the third layer to the core-shell structure, due to increased degrees of freedom, the metamaterials operation range will be tunable to the desired frequency.
Presently, the simulated Delay Doppler Maps (DDMs) of oil slicked sea are limited to simplified scenarios which have the elevation angle of 90° (nadir reflection). In this paper, the detailed simulation process to generate GNSS-R DDMs of oil slicked sea surfaces under general scenarios is presented. The DDM of oil slicked sea surface under general scenarios are generated by combining the mean-square slope model for oil slicked/clean surfaces and the GNSSR Zavorotny-Voronovich (Z-V) scattering model. The coordinate system transformation appropriate for general-elevation-angle scenarios are also incorporated. To validate the proposed approach, a comparison is made between the DDMs of a simplified scenario and a general scenario, which are generated based on the oil slick distribution of the Deepwater Horizon oil spill accident. Theoretical analysis reveals that oil slick may be detected within a 100 km radius coverage area around the specular point for a GNSS-R receiver under the general scenario with elevation angles of 72°.
Time reversal imaging method based on full wave numerical technique for likely breast tumors biological tissue in the Microwave-Induced Thermo-Acoustic Tomography (MITAT) system is discussed. In this paper, the mechanism of microwave-induced thermo-acoustic is strictly described based on thermodynamics and thermo-diffusion principles; the equivalent relationship between the absorbed microwave energy distribution of the biological tissue and the induced thermo-acoustic source distribution is used as the basis of the imaging algorithm. Due to its unique noise suppression feature and the stability of the algorithm, the Time Reversal Method (TRM) based on the Pseudospectral Time-Domain (PSTD) technique is applied to image heterogeneous phantom tissues from low Signal-to-Noise-Ratio (SNR) thermo-acoustic signals. Thereafter, an integrated MITAT prototype system is presented to obtain the thermo-acoustic signals from some biologic tissue with millimeter scale. The proposed TRM method is based on PSTD technique produced two-dimensional images, presented to study the performances of the MITAT in terms of contrast and resolution. These images prove predominant advantages in both contrast and resolution compared with conventional microwave and ultrasound imaging systems for malignant tumor detection. Based on the current results, our TRM-PSTD MITAT system provides evidence to predict breast tumor in an early stage and millimeter scale.
In this paper, we focus on target detection and system configuration optimization of Multiple-input Multiple-output (MIMO) radar in low-grazing angle, where the multipath effects are very abundant. The performance of detection can be improved via utilizing the multipath echoes. First, the reflection coefficient, considering the curved earth effect, is derived. Then, the general signal model for MIMO radar is introduced for low-grazing angle. Using the Neyman-Pearson sense, the detector of MIMO radar with multipath is analyzed. We use the deflection coefficient as a criterion of system configuration both for MIMO radar and phased-array radar. The simulation results show that the performance can be enhanced markedly when the multipath effects are considered, and the optimal configuration of phased-array radar is with the same number of transmitters as that of receivers, however, the optimal configuration of MIMO radar depends on the signal-to-noise ratio (SNR).
Two efficient unconditionally-stable four-stages split-step (SS) finite-difference time-domain (FDTD) methods based on controlling parameters are presented, which provide low numerical dispersion. Firstly, in the first proposed method, the Maxwell's matrix is split into four sub-matrices. Simultaneously, two controlling parameters are introduced to decrease the numerical dispersion error. Accordingly, the time step is divided into four sub-steps. The second proposed method is obtained by adjusting the sequence of the sub-matrices deduced in the first method. Secondly, the theoretical proofs of the unconditional stability and dispersion relations of the proposed methods are given. Furthermore, the processes of obtaining the controlling parameters for the proposed methods are shown. Thirdly, the dispersion characteristics of the proposed methods are also investigated, and numerical dispersion errors of the proposed methods can be decreased significantly. Finally, to substantiate the efficiency of the proposed methods, numerical experiments are presented.