The utilization of an open-ended coaxial probe for characterization of dielectric properties or quantitative nondestructive detection of defects in materials firstly requires evaluating the aperture admittance. For the case that the probe is terminated into low-loss dielectrics backed by a conducting sheet, however, the admittance expression encounters poles in the vicinity of the path of integration, resulting in low convergence rate or even overflow in numerical quadrature. In this study, locations and properties of the singularities of the integral formulation for generally lossy, low-loss, and lossless dielectric slabs backed by a perfectly conducting sheet are investigated above all. Subsequently, making use of the contour integral technique, a fast and stable integration method is put forward to calculate the admittance integral formulation. Finally, numerical experiments are conducted to justify the validity and efficiency of the proposed integration method for low-loss dielectric cases by comparison with the traditional integration method as well as commercial FEM software.
There is growing interest in the use of nanocomposites based on carbon nanotubes (CNT) due to their excellent mechanical, thermal and electrical properties. The electromagnetic characteristics of nanocomposites with different types of multi-walled carbon nanotubes were investigated. CNTs with different geometries (length and diameter) were chosen in order to analyze the effect of the geometrical parameters on the electromagnetic properties. Nanocomposites with various percentages of CNT were made and the number of CNTs per cm3 in the composite was computed. CNTs were characterized by Field Emission Scanning Electron Miscroscopy (FESEM) and Raman spectroscopy. The complex permittivity of the NCs was measured with two different techniques, and the variation of the permittivity with the number of CNT per cm3 was investigated.
The possibility of employing highly-elliptical-orbit (HEO) satellites for SAR imaging is investigated. A constellation of two satellites in the Tundra orbits, which are capable of covering all the high-latitude areas, are chosen as the platforms for SAR imaging. The received signals are processed with an improved frequency-domain algorithm (FDA) to reconstruct the image. Simulation results verify that the proposed method can produce better SAR images with less computational load and memory than the conventional FDA.
A metal-insulator-metal (MIM) plasmonic waveguide coupled with two nanodisks as a resonator has been examined and numerically simulated with the finite-difference-time-domain (FDTD) and analytically by the Temporal Coupling Mode Theory (CMT). Based on the three-level system, the strong destructive interference between the two resonators leads to the distinct mode splitting response. The characteristics of mode splitting show that there is anomalous dispersion with the novel fast-light feature at the resonance. Meanwhile, the slow light characteristic can also be achieved in the system at wavelengths of the split modes. The relationship between the transmission characteristics and the geometric parameters is examined. The results show that the modulation depth of the mode splitting transmission spectrum of 80% with 0.175 ps fast-light effect of resonance can be achieved, while for the two modes these values are around 30% with -0.18 ps slow light-effect can be achieved. There is a good agreement between the FDTD simulated transmission features and CMT. The characteristics of the system indicate critical potential applications in integrated optical circuits such as slow-light and fast-light devices, optical monitoring, an optical filter, and optical storage.
We propose a structural optimization method based on a real-coded micro-genetic algorithm to realize a weakly guided 2 × 2 multimode interference (MMI) coupler with low imbalance and excess loss over a wavelength range from 1520 to 1580 nm. The proposed method was applied to silica-based 2×2 MMI couplers with a relative refractive index difference of 5.5%. The optimized result showed an imbalance of less than 8.4×10−3 dB, an excess loss of less than 0.14 dB, and a normalized output power of more than 48% over the operation wavelength range. The proposed method achieved an optimized 2×2 MMI coupler after 250 times of propagation analysis per wavelength, which is less than 6.7% of those by the conventional methods for 4×4 and 1×4 MMI couplers, and was proven to be more effective than the conventional methods. To consider realistic optical devices, 2×2 MMI couplers whose values of structural parameters are close to the optimized values within the accuracy of typical fabrication tolerance are also analyzed. The results are comparable to those of the optimized 2×2 MMI coupler.
Linear equations must be solved at each time step as the explicit finite element time-domain (FETD) method is used to solve time dependent Maxwell curl equations, which leads to a huge amount of computational cost in a long period time simulation. A new scheme to accelerate the iteration solution for matrix equation is proposed based on compressed sensing (CS), in which a low rank measurement matrix is established by randomly extracting rows from mass matrix. Meanwhile, to reduce the number of measurements required, a sparse transform is constructed with the help of prior knowledge offered by the solution results of previous time steps. Numerical results of homogeneous cavity and inhomogeneous cavity are discussed to validate the effectiveness and accuracy of the proposed approach.
This work deals with the evaluation of the efficiency and optimal control of conductive fluids by using electromagnetic forces. An electromagnetic actuator based on a succession of electrodes and magnets annuli is implemented on the surface of the rotating cylinder of a Taylor-Couette device. Considering a laminar flow, the magnetohydrodynamic (MHD) problem is formulated and solved analytically. The different MHD powers, control efficiency and optimal values of the control parameters are evaluated.
In this paper a symmetrically structured meander line antenna placed around a T-shaped junction with truncated ground planes is proposed for on-body applications. The designed antenna has a percentage bandwidth of 69.04% covering the GSM 1800 band internationally accepted industrial scientific and medical (ISM) 2.4-2.5 GHz band, 4G LTE band 7 (2.5-2.69 GHz). The antenna is compact in nature with a size of 30×40×1.6 mm3. SAR reduction is achieved without the attachment of any auxiliary unit. It is found that the application of designed truncated ground planes around positions of high electric field (E-field) region is an effective solution in reducing Specific Absorption Rate (SAR) significantly through field cancellation technique. In addition maximum temperature elevation due to electromagnetic wave absorption has also been computed. The antenna is simulated over a homogenous human dry skin model as well as head model. The proposed design is fabricated and measured, and it is found to be compatible for real world applications while considering its miniaturization, radiation patterns and SAR limitations.
Finite Difference Time Domain (FDTD) method is widely used in the simulation of various kinds of antennas. In this paper, research on the numerical simulation of the fragment-type antenna by using FDTD is conducted. The fragment-type antenna structures with different cell sizes and different overlapping sizes are simulated and measured. The validity of the numerical simulation of the fragment-type antenna by using FDTD is verified through the comparison between the simulated and measured return losses. In addition, its efficiency in terms of computation time shows great potential in engineering applications, especially when the design matrix is large enough.
In this work, we show that it is possible to produce a planar electromagnetic jet using a flat structure consisting of elementary cells based on lumped elements and fed with a source line. A combination of elementary cells may represent a gradient index, locating the electromagnetic energy in a small area, consisting of a few cells and having a size of about 0.75λ. The theoretical framework of the study is based on the Wave Concept Iterative Process method (WCIP) formulated in both spectral and spatial domains. An analogy with an optical model based on optical paths equality enables predicting the location of formation of this spot. The use of such a system can provide solutions for the development of new kinds of applications such as engraving sub-wavelength, data storage, improved scalpel optics for ultra-precise laser surgery, and detection of cancer.
This paper presents a novel effective calibration technique applicable to phased array radars. The real embedded patterns of the array elements are measured independently in operating mode, taking antenna coupling and other parasitic effects into account. The proposed calibration technique requires minimal modification of the radar hardware. A set of angular-dependent error coefficients, which are compensated during the calibration process, are extracted for one received pulse for one/each angular direction of interest. The performance and effectiveness of the hereproposed calibration technique are assessed by means of modeling and experimental verification.
In this paper, novel compact low-pass filters using Hi-Lo technique and meander method are proposed. Series of the proposed filters are designed by adding modifications along the microstrip line (meander inductor) and by using U-form topology. The size of the proposed filter can be reduced by 15% compaired to the conventional filter while maintaining the optimal low-pass features. The compact meander LPF consists of two thin microstrip lines, which are connected with 50Ω microstrip feed lines and a microstrip patch placed in the middle of the structure. The thin lines and the microstrip patch correspond to inductance and capacitance, respectively. The proposed meander Hi-Lo topology has been mounted on an RO4003 substrate with a relative dielectric constant εr = 3.38, thickness h = 0.813 mm and loss tangent 0.0027. The compact L-band low-pass structure has a size of (0.263λg×0.175λg) where λg = 57 mm is the wavelength at the cutoff frequency 2.85 GHz. In addition to a good compactness, the structure exhibits a simple design, very low insertion loss in the passband (L-band) of less than 0.3 dB, and it achieves a wide rejection bandwidth with a 20 dB attenuation from 5.3 to 6.3 GHz. The excellent LPF characteristics are verified through simulations and measurements where a good consistency can be observed. Such compact filter structures are expected to be used in various microwave system applications.
The influence of seaming stitches on the shielding effectiveness (SE) of electromagnetic shielding (EMS) fabric is huge, but there is not an ideal computation model for the SE of the EMS fabric with the seaming stitch at present. This paper proposes a computation model of the SE based on the equivalent seaming gap. Firstly, a structure model of the equivalent seaming gap is constructed according to the equivalent dielectric principle. The computation method of the structural size of the equivalent seaming gap model is determined by the parameters of the stitch length, number of the stitch type, needle number, and sewing thread. A computation model of the SE based on the equivalent seaming gap structure is built according to the EMS theory. The method of the correction coefficient of the model determination is given. Finally, the samples with seaming stitches are made to test the SE using the waveguide method. The computation results with the proposed model are compared with the experimental ones. The results show that the proposed model can well calculate the SE of the EMS fabric with the seaming stitch. The study in this paper can provide a foundation for further study of the influence of seaming stitches on the SE of the EMS fabric and possesses reference significance for the design, production, evaluation and related theoretical research of the EMS clothing.
In this paper we compare, using ISRO's RISAT-1 FRS-1 mode Compact Polarimetric (CL-Pol) data, two widely used hybrid polarimetric decomposition techniques, m-δ and m-χ decompositions, with regard to classification accuracy for various agricultural crops of north and west India. We show that the classification based on the m-χ decomposition results in better crop separability in general. But the crop stage and existence of orientating structures in the crops affects the efficacy of decomposition; a fact vividly brought out in this paper. Theoretical insights into the effectiveness of these decomposition techniques for different crop geometry are brought forth. We also compare the classification accuracy subsequent to polarimetric speckle filtering vis-a-vis spatial multilooking (downsampling). We show that usage of an appropriate polarimetric filter tends to produce comparable accuracy for most of the agricultural classes, as that of multilook case, without degrading spatial resolution. This work showcases a custom implementation of Stokes parameter based decomposition as well as POLSAR filter based on refined Lee algorithm, written in C and tailored to RISAT-1.
In this paper, a feature fusion algorithm is proposed for automatic target recognition based on High Resolution Range Profiles (HRRP). The proposed algorithm employs Convolution Neural Network (CNN) to extract fused feature from the time-frequency features of HRRP automatically. The time-frequency features used include linear transform and bilinear transform. The coding of the CNN's largest output node is the target category, and the output is compared with a threshold to decide whether the target is classified to a pre-known class or an unknown class. Simulations by four different aircraft models show that the proposed feature fusion algorithm has higher target recognition performance than single features.
A magnetically suspended permanent-magnet motor (MSPMM) system mainly consists of magnetic bearings(MBs), a motor and a rotor assembly. This paper focuses on the system analysis of an MSPMM used for a vacuum turbo-molecular pump (TMP). To ensure a normal levitation and rotation, characteristics of electromagnetic field of MBs and motor are studied. For MSPMM, loss is the main heat source. To ensure the safe and steady operation of MSPMM, loss of the MB and motor are calculated and analyzed by finite element method (FEM). For thermal aspects, temperature field is estimated. Based on these analyses, the system performance can be predictive. Considering the poor heat dissipation conditions in a vacuum environment, this system analysis including loss and temperature field is of great value for MSPMM design.
This paper addresses the CFAR target detection in FM-based passive bistatic radars as a composite hypothesis testing problem, using the mixed signal model. The corresponding generalized likelihood ratio test (GLRT) is derived. It has less computational requirements with respect to the conventional GLRT-based detector, previously developed in the literature, due to the decrease in the row dimension of the interference matrix. The proposed detector is computationally efficient for tracking or short-range-radar applications in which a few range cells are surveyed. The theoretical and simulation-based analysis of detection performances and a thorough discussion on the computational complexity compared with that of the existing detectors are also provided.
This paper presents the effect of solar illumination on the differential potential generated on the surfaces of spacecraft body in space. Two geometrical cases are considered: 1) Cylindrical symmetry and 2) Tilted metallic plates forming an angle with the adjacent side. The capacitance required for estimation of the body potential is computed by Method of Moment. Nonuniform triangular meshing is used for both the geometrical structures. The differential potential generated on surfaces of a geometrical body due to photoelectric effect results in electrostatic discharge. In the case of the tilted plates, the differential potential at various tilt-angles is computed along with the capacitance computation. In the case of the cylindrical object, the estimation of potential at the day-night interface is shown. The variation in the potential for different incident angles of the solar photons and the changing (h/r) ratio is analyzed. The validity of the analysis is established with that obtained in open literature.
In this paper, an effective numerical method based on a new surface impedance model is applied to the accurate calculation of the radar cross section of lossy conducting targets. The problem of determining the scattered electromagnetic fields from rectangular lossy conducting strips is presented and treated in detail. This problem is modeled by the method of moments to resolve integral equations of the first kind of surface current density with an accurate choice of basis and test functions. The illustrative computation results of complex surface impedance, surface current density and radar cross section are given for several cases. The accuracy of the method presented in this paper is verified by comparison with other methods, including the general-purpose full-wave simulators HFSS and CST.
Soliton solutions of a cubic-quintic Ginzburg-Landau equation (CQGLE) are computed and analyzed on a parametric plane, specifically across the transitional zones that separate regions associated with different types of solitons. The transformations of behaviors in these transitional zones between stationary and pulsating regions are characterized by the total pulse energy and its maximum value. It is also found that the initial pulse waveform has little effect on bifurcation and the valid range of initial amplitude.