This paper presents two simple analytical models of the switched reluctance motor. The first model is constructed on two flux linkage-current characteristics, the aligned position one calculated via finite element analysis (FEA), and the unaligned position characteristic calculated by using motor geometry data. The second model is based on three flux linkage-current characteristics, the aligned, unaligned and average one, obtained by employing the FEA. In both cases the direct and inverse models are defined. The models consider the core nonlinearity and the influence of the rotor position on the motor behavior. The estimated magnetizing and torque characteristics are compared with that calculated via two dimensions FEA for a switched reluctance motor (SRM) sample and with the test bench obtained ones. The merits and the drawbacks of the models are evinced.
Low loss circular birefringence is found in three-dimensional artificial triple helices. High values of chirality index are generated. Within the transmission bandwidth, there is a significant difference in the refractive index value of the right- and left- polarized waves. The outgoing waves from a wedge structure designed from these triple helices are proved to split with a wide angle. The wave polarizations agree with earlier simulation results.
This paper presents a design of perforated nanoantenna reflectarray. The use of metallic nanostructures made of Silver and/or Gold at appropriate wavelength cause fascinating unusual electromagnetic effects. Reflectarray consists of an array of unit cell made from Silver is investigated. The effect of the number of perforated holes in the unit cell configurations is investigated for proper reflection coefficient phase compensation. A linearly polarized pyramidal nano-horn is used to feed the perforated nanoantenna reflectarray. The radiation characteristics of 9 × 9 perforated nanoantenna reflectarray are illustrated. A high gain of 20.5 dB is obtained at the designed frequency of 735 THz. A comparison between solid Silver sheet with no perforation holes and the proposed perforated reflectarray is explained.
In this paper, the network expression is proposed for finite-length multiple transmission lines in arbitrary directions. Crosstalk between two bent transmission lines is analyzed using the proposed approach as an example of application. The resultant network function is obtained in the form of an ABCD matrix for two bent transmission lines is obtained. The validity of the proposed approach was confirmed by comparing experimental results with computed results and those simulated by a commercial electromagnetic solver for some bent-line models.
Present work deals with the microwave absorption characteristics of BaFe12O19 of interest as radar absorbing material (RAM). There are very few reported works available where particle size has been critically analyzed for absorbing characteristics at microwave frequencies, therefore, in this paper microwave absorption properties of the BaFe12O19 with different particle sizes were investigated. The results showed that the particle size had significant influence on the dielectric and absorption properties of the composites in the 8.2-12.4 GHz frequency range. BaFe12O19 powder of different particle sizes were synthesized by varying the annealing time and it was observed that the real part of permittivity of the composite increases from 5.18 (average value) to 7.50 (average value) and imaginary part increases from an average value of 0.20 to an average value of 2.33, whereas the real part of permeability increases from 0.95 (average value) to 1.11 (average value) and imaginary part of permeability was measured in the range of 0.02 to 0.07. These changes in permittivity and permeability affects microwave absorption application. It is observed that the maximum bandwidth for average particle size of 240 nm is 3.02 GHz and with the increase in average particle size, microwave absorption properties increased.
Recently, a new boundary condition is introduced in which surface shows different impedances for TE and TM electromagnetic fields. This new boundary condition is called mixed-impedance (MI) boundary condition and can be expressed in terms of normal components of electromagnetic fields. In this paper, the cylindrical structures with MI boundary condition were investigated and the scattering of such structures was obtained for both normal and oblique incidence and both TEZ and TMZ polarizations. The interesting feature of MI boundary condition was that the boundary conditions of PEC, PMC, DB, D'B', and isotropic impedance boundaries were special cases of the MI boundary. Therefore, by calculating the electromagnetic scattering from a MI boundary, scattering from various boundary conditions could be easily obtained. It was also demonstrated that, by proper choice of boundary conditions the forward or backward RCS (radar cross section) could be significantly increased or decreased.
A Ka-band two-dimensional synthetic aperture interferometric radiometer called BHU-2D has been developed by Electromagnetic Engineering Laboratory of Beihang University. The radiometer obtains images in real-time benefiting from the adoption of a 1bit/2level FPGA-based correlator unit. The design and implementation of the correlator unit in BHU-2D are presented in this paper. The calibration procedures of the correlation coefficients are also presented. For the purpose of simplifying the calibration procedure, a closed form approximation is introduced and applied to BHU-2D, which is used to correct the errors caused by threshold offset of the quantizer. Error analysis of this approximation shows that the method is applicable in SAIRs. In order to verify the design and calibration method, a series of validation experiments have been conducted. Measurement results have proved that the performance of the correlation unit could meet the requirements of BHU-2D.
In this paper, an open cavity is proposed to measure the permittivity of dielectrics. The cavity consists of an ellipsoidal mirror and two planar mirrors. The relationship between the parameters of the beam in the open cavity and the cavity geometrical parameters is presented. The transcendental equation of dielectric loaded cavity is presented, from which the permittivity of the dielectric can be solved. The resonance frequencies of the vacuum cavity and loaded cavity are computed by the resonance frequency formula and the transcendental equation. they are compared to the results from FDTD simulation. The results from two methods are almost same with each other. The advantage of the proposed open cavity over the conventional open cavity composed of spherical mirror and planar mirror is demonstrated.
The paper presents an assessment of human exposure to extremely-low-frequency (ELF) electric field generated by a power line using the rotationally-cylindrical body model. The formulation is based on the Laplace type continuity equation. The induced current density in the three-dimensional (3D) model human body is obtained by solving the Laplace equation via the Finite element method (FEM). The main objective is to highlight some parameters influencing the distribution of the induced current density, such as the ohmic contact between the feet and the soil due to the soles of the shoes, and the electrical parameters of the soil. Furthermore, the influence of internal organs (the human model) to the induced current density distribution. The human body is represented by a homogeneous model and also by an inhomogeneous model composed of several organs namely brain, heart, lungs, liver and intestines, whose shapes were spheroid. The proposed model has been validated through comparison to either the experimental results or the theoretical results available in literature being computed by the aid of a homogeneous body model.
Millimeter-wave (MMW) radiation characteristics of solid targets are very complicated, and this paper starts with the research on modeling and simulation of the simple solid metal target. On the basis of the optical property of MMW, the two-ray propagation (direct reflection and ground secondary reflection of the solid target surface) is analyzed by means of the ray tracing theory in the geometrical optics, the radiation temperature calculation model is established; Furthermore, in combination with the panel-method-based geometric model and in accordance with the spatial analytic geometry and vector algebra theory, model calculation of the intersection movement between the radiometer and the target is analyzed and the MATLAB simulation platform for MMW radiation characteristics of the solid target is built. Under the assumed simulation conditions, simulation experiments on three types of solid metal targets (sphere, cylinder and cone) are performed to verify the proposed method in this paper. Meanwhile, comparative analysis between the MMW radiation characteristics of the circular metallic plate and those of the metallic ball with the same radius indicates that the spherical metallic target is equivalent to the non-ideal metallic circular planar target which is increased about 1.3 times in the linear size, and the result is validated through the measured data, which provides more accurate and effective data and theoretical support for target recognition and location in the millimeter-wave passive detection.
Simple internal multiband monopole antenna with low SAR for most of wireless mobile communication applications is presented in this paper. The proposed antenna is a unequal arms monopole antenna with a meander strip in the other substrate side. The antenna has a simple structure and is sufficiently small in size to be easily fit on the housing of mobile or USB dongle with size 18 × 15 × 0.8 mm3. The antenna is designed to operate at multi-bands to occupy most of allocated wireless communication devices by using high frequency structure simulator ver. 13 (HFSS). The proposed antenna has acceptable gain and efficiency while providing broadside radiation pattern that covers the horizontal plane. The antenna design and experimental results are in agreement. Moreover, the specific absorption rate (SAR) in the human head is investigated by CST 2012 Microwave Studio Hugo Voxel Model.
Numerical methods based on solutions of Maxwell's equations are usually adopted for the electromagnetic characterization of Magnetic Resonance (MR) Radiofrequency (RF) coils. In this context, many different numerical methods can be employed, including time domain methods, e.g. the Finite-Difference Time-Domain (FDTD), and frequency domain methods, e.g. the Finite Element Methods (FEM) and the Method of Moments (MoM). We provide a quantitative comparison of performances and a detailed evaluation of advantages and limitations of the aforementioned methods in the context of RF coil design for MR applications. Specifically, we analyzed three RF coils which are representative of current geometries for clinical applications: a 1.5 T proton surface coil; a 7 T dual tuned surface coil; a 7 T proton volume coil. The numerical simulation results have been compared with measurements, with excellent agreement in almost every case. However, the three methods differ in terms of required computing resources (memory and simulation time) as well as their ability to handle a realistic phantom model. For this reason, this work could provide "a guide to select the most suitable method for each specific research and clinical applications at low and high field".
A recently developed technique to design and model an isolated Defected Ground Structure (DGS) has been employed to successfully design and characterize a DGS to be used in between two microstrip patches to reduce their mutual coupling. This is the only technique that can handle isolated DGS and as such has been explored for microstrip antennas in this paper for the firt time. An X-band design has been examined. A prototype is used to obtain measured data which are employed to verify the technique experimentally for microstrip array.
Arrangements of bilayer anisotropic structures are inspected in this paper that manifest wonderful behaviors. One of these arrangements can pass TM & TE modes spontaneously in low frequencies and reflect them in higher frequencies and function as a low-pass filter. Another arrangement can reflect TE mode and pass TM mode in a particular frequency band and vice versa and function as a polarizer. All the analyses are based on the calculations of the hybrid matrix of layers by means of a recursive algorithm. Also the effect of the μ & ε tensors on the specifications of the filters is discussed.
A straightforward approach is proposed to retrieve the effective electromagnetic parameters of a slab of bianisotropic material from the scattering parameters. We first obtain the values of the impedance and refractive index of a slab of metamaterial, followed by the deduction of the expressions for determining these electromagnetic parameters including permittivity, permeability and magnetoelectric coupling coefficient. Then, comparisons between the results coming respectively from retrieval technique and analytical method are made. Finally, we demonstrate the properties of split-ring resonator materials in other two orientations with respect to the incident plane wave and apply the proposed method to anisotropic materials to reveal its generality.
The fuzzy fractal characteristics of return signals from aircraft targets in conventional radars offer a description of dynamic features which induce the targets' echo structure, therefore they can provide a new way for aircraft target classification and recognition with low-resolution surveillance radars. On basis of introducing fuzzy fractal theory, the paper analyzes the fuzzy fractal characteristics of return signals from aircraft targets in a VHF-band surveillance radar by means of the fuzzy fractal analysis, and puts forward a fuzzy-fractal-feature-based classification method for aircraft targets with a low-resolution radar from the viewpoint of pattern recognition. The analysis shows that the fuzzy fractal characteristic parameters such as the local fuzzy fractal dimension (LFFD) and local degree of fractality (LGF) can be used as effective features for aircraft target classification and recognition. The results of classification experiments validate the proposed method.
Small phased-array antennas can be combined with dielectric lenses or planar lens-arrays to form directive beam-steering system. The use of the lens increases the size of the radiating aperture and enhances the directivity of the phased array, but it also reduces its scan field of view. However, the effect can be controlled by properly designing the phase delay profile across the lens. This paper presents the formulation and methodology for designing modified lenses that can allow the desired scan angle. The utility and limitations of the proposed approach will be illustrated by considering several design examples. Simulations suggest that a directivity enhancement of > 2 dB and wide scan field of view (up to 45° off boresight) can be obtained for compact radiation systems employing small lenses and short separations between the lens and phased array. Larger directivity improvements in the range of tens of dB's are possible in systems with limited scanning capability by employing large lenses and greater phased array-lens separation. Ease of implementation and the ability of the proposed topology to adapt to the system requirements make this topology an interesting candidate for various millimeter-wave radio applications.
This paper presents a frequency domain technique for reconstructing the constitutive parameters of inhomogeneous planar layered chiral media based on an optimization approach. The measured co- and cross-reflection and transmission coefficients are used to extract profiles of electromagnetic parameters of the inhomogeneous chiral media. To identify the functions of constitutive parameters of the chiral media, Fourier series expansions and Genetic Algorithm (GA) are utilized. Since the optimization problem is highly non-linear, enhanced GA in which a fuzzy system is used for improving the speed and accuracy of GA. The performance and feasibility of the proposed reconstruction method is proven using two typical examples.
In this paper, the fast Fourier transform (FFT) to perform spatial convolutions of the time domain discrete Green's functions (DGF) method related to the analysis of the antenna with more than one dimension has been proposed. For this aim, the discrete Green's functions and the currents on the antenna have been appropriately defined periodic so as to use the zero padded fast Fourier transform. The computational complexity of this approach is O(NwNxNyNz log(NxNyNz)), contrary to O(NwNx2Ny2Nz2)for direct implementation of the convolutions. Simulation results demonstrate the great efficiency of the FFTbased spatial convolutions in the modeling of planar antennas.
In this paper, we show that the solution of linear coupled mode equations (LCME) is a good approximation to that of the nonlinear coupled mode equations (NLCME) for small times, provided that the nonlinearity is weak. We bound the difference between the two solutions using energy estimates. We illustrate our findings in numerical examples.
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