A visibility-domain processing for optical interferometric imaging (VP-OII) method is proposed to model the visibility distribution of an image, and a phase retrieval technique is proposed to acquire additional visibility data from the powerspectrum and closure-phase data. This method requires only a few tunable parameters, and can be easily extended to include more data acquired from different instruments. By simulating the reconstruction of an LkHα 101 image, the proposed method proves a few hundreds times faster and is more resilient to noises than the conventional MIRA, and the image quality is comparable to noise that of conventional MIRA.
The improvement in the power density in the double stator configurations is feasible with increase in the electrical loading of the electrical machines. This type of newer configuration is finding significant applications in improvising energy generation, more commonly for renewable energy generation. Various double stator configurations with non-arc permanent magnet machines for power density are modelled and analyzed in this paper. Finite Element Method (FEM) is used to simulate for the generation capability including the electromagnetics parameters such as flux linkage and open circuit voltage. A new slotted rotor structure is evolved based on the magnetic flux flow control inside the machine. The proposed structure is then fabricated in the laboratory and tested for operating characteristics with load circuit. The proposed machine produces a maximum power of 600 W at speed of 2000 rpm with 75% of maximum efficiency with the micro-hydro generation unit.
Imaging and scaling of precession targets are very important in spatial target surveillance. The bistatic wideband radar echo model of the spatial precession cone-shaped target is induced, and bistatic ISAR imaging method based on time-frequency analysis is described. Combined with the monostatic and bistatic scattering characteristics of cone-shaped targets, the cross scaling method is presented through range instantaneous Doppler (RID) image matching using T/R-R bistatic radar observations, and the correct scaled monostatic and bistatic two-dimensional images can be obtained at the same time, which can reflect the actual size of the target. The algorithm is validated by dynamic simulation with electromagnetic computation data and provides a feasible way for the stable recognition of spatial targets.
An effective fast equivalent cable bundle modeling method is proposed in this paper to study electromagnetic pulse response of complex cable bundle. Compared with traditional equivalent cable bundle method (ECBM), the complete cable bundle is equivalent to only one cable by modification of cable grouping method, which leads to reduction in number of cables and computation progress. The proposed method can perform well not only in pure resistance case, but also in frequency dependent load case by weighted average method (WAM). The computation time and memory acquirement for complete cable bundle model terminated in arbitrary loads have been further reduced by fast equivalent method compared to ECBM, and calculation precision is maintained to meet fast application need. Numerical simulation of coupled currents in observed cable located at a certain distance away from cable bundle by CST software is given to verify accuracy of the method under illumination of high altitude electromagnetic pulse (HEMP).
In this paper, a portable frequency domain electromagnetic system CEM-2 is presented for shallow metal targets detection. This paper discusses the detection principle of frequency domain electromagnetic system, introduces hardware implementation, presents test results of each module, and gives the system's imaging results in field tests. Sinusoidal pulse width modulation technique is employed in this system to produce single-frequency or multi-frequencies synthetic electromagnetic signals with signal to noise ratio of about 85 dB. After integration, the CEM-2 system's in-phase noise level is about 90 ppm while the quadrature response is about 100 ppm. The experiment results of CEM-2 agree well with the simulation ones both from signatures and amplitudes. The experiment for detecting targets of different sizes and materials conducted in field indicates that CEM-2 system can be used to distinguish metallic and ferrous objects.
In order to improve the angle measurement precision with a low computational complexity, a 2-D direction of arrival (DOA) estimation algorithm UCA-TF-MI-ESPRIT is proposed in this paper. This algorithm is based on the mode space algorithm and the time-frequency (TF) multiple invariance rotational invariance technique (MI-ESPRIT). Firstly, a uniform circular array (UCA) is equivalent to a virtual uniform linear array (ULA) by utilizing mode-space algorithm. Then, the smoothed pseudo Wigner-Ville distribution (SPWVD) of the ULA output is calculated. The spatial time-frequency matrix can be obtained through the average of multiple time-frequency points in the time-frequency plane, and the signal subspace can also be obtained through using eigen decomposition. Then a simple and effective subarray dividing approach is proposed, and the multiple rotational invariant equation of the array is obtained by using the Bessel function. Finally, the closed-form solution is obtained using multi-least-squares (MLS) criterion so that the 2-D DOA estimation of LFM signals in UCA is completed. The simulation results verify the effectiveness of the algorithm proposed by this paper.
Non-circular properties of non-circular signals can be used to improve the performance of the direction-of-arrival (DOA) estimation. However, most ready-made algorithms are not applicable to the general case in which both non-circular and circular signals exist. In this paper, we present a novel DOA estimation algorithm for mixed signals, namely MS-MUSIC (Mixed Signals - Multiple Signals Classification), which can deal with the two kinds of signals simultaneously. And on this basis, we derive the Cramer-Rao Lower Bound (CRLB) of the azimuth and elevation estimation. The effectiveness of the algorithm is confirmed by the simulation results. Meanwhile, it acquires higher accuracy than the traditional algorithms.
In this paper, we present results of characterization of a bifacial silicon solar cell, under multispectral steady state illumination, using finite elementmethod (FEM). The illumination level (n) and back surface recombination velocities (Sb) effects on solar cell electrical parameters have been highlighted. After solving the continuity equation that describes the solar cell operation, the excess minority carrier's density and current-voltage characteristics are determined for various values of illumination level and recombination velocities on the junction and the back surface of the solar cell. The results obtained are in agreement with those given by analytical methods and prove that the photovoltaic cells can be analyzed only by numerical methods, such asthe FEM, characterized by their robustness and flexibility in their applicationsin a context where those methods take more and more importancein the development of Computer Aided Design (CAD) tools.
In this paper, a frequency reconfigurable Antipodal Vivaldi Antenna (AVA), capable of covering a Band of Interest (BoI) spanning from 3 to 10.6 GHz with four different bandwidth resolutions, is presented. By incorporating four rectilinear resonators and two Split-Ring-Resonators (SRRs) into the AVA, the whole BoI can be covered by one (UWB mode), three (3-sub mode), seven (7-sub mode), or sixteen (16-sub mode) sub-bands. In the UWB-mode, all the six resonators are deactivated by disrupting their structures, so the antenna operates as a classical AVA. In the 3-sub mode, only one rectilinear resonator is activated; the low Q of these resonators allow narrowing the antenna operating band so that the BoI is covered by three sub-bands. In the 7-sub mode, two rectilinear resonators are activated at a time, which narrows the operating bandwidth furthermore, allowing to cover the BoI by seven sub-bands. In the 16-sub mode, one of the two SRRs is activated at a time to be used as a coupling-bridge to very narrow frequency bands that allows covering the BoI by sixteen different bands. To present the work, simulated and measured results are given and discussed.
One-side boundary conditions on the field inside core region are obtained for core-cladding waveguide with anisotropic cladding. The boundary conditions involve two functions acting as components of anisotropic surface impedance for cladding material. These functions are determined in relation to desired values for step-index waveguide and dielectric-lined waveguide with either perfectly or finitely conducting walls. With resulting surface impedance, the perfect analogy between core-cladding and impedance waveguide is achieved. Using this analogy, independent eigenvalue problems are obtained for membrane functions of HE and EH waves of core-cladding waveguide. From this result some conclusions about electromagnetic properties of HE and EH waves are drawn.
In this paper, a novel multiband wearable fractal antenna which suitable for GPS, WiMax and WiFi (Bluetooth) applications is presented. This antenna is designed to operate at four resonance frequencies are 1.57, 2.7, 3.4 and 5.3 GHz. The proposed wearable antenna may be attached to human body, so the specific absorption ratio (SAR) must be calculated. Therefore, another design to reduce SAR value with a spiral metamaterial meandered in the ground plane is introduced. In addition, a wearable fractal antenna system integrated on a life jacket is also presented.
Multilayered dielectric rods are widely used, and the analysis of their electromagnetic scattering properties is very important in practical design. Based on our former work on the single layer dielectric rod forest, the equivalent microwave network method (EMN) is applied to analyse the concentric and eccentric multilayered dielectric rods in this article. The key step is to obtain the reflection matrix of the multilayered dielectric. Based on the EMN method, the electromagnetic scattering properties of a novel electromagnetic band gap (EBG) structure are calculated. The EBG structure is formed by periodically embedding multilayered dielectric rods into the original dielectric between power/ground planes. The accuracy and efficiency of the EMN method are verified by comparing with the simulation results by the FIT simulator CST. In addition, the EMN method takes about 1 minute to obtain the results, while the simulator takes nearly 20 hours with the same computer.
In multi-circular synthetic aperture radar (MCSAR) mode, resolution and sidelobes are two important parameters to consider when representing imaging quality, as in other SAR imaging modes. In this paper, three-dimensional (3-D) resolution and cone-shaped sidelobes of MCSAR are analyzed for a point target in the scene center under the Nyquist sampling criterion. The results of the analysis show that resolution can be improved, and cone-shaped sidelobes can be suppressed by increasing the system bandwidth and the length of synthetic aperture in the elevation direction. But this will make the system of acquiring data more difficult. It turns out that some digital signal processing techniques can enhance 3-D imaging quality of MCSAR. In this paper, a simple method based on spectrum extrapolation and interferometric phase masking is proposed to improve 3-D resolution and suppress cone-shaped sidelobes of MCSAR. Experimental results regarding a tank model in a microwave anechoic chamber demonstrate that this method is effective.
This paper deals with a technique for classifying jet aircrafts from JEM (Jet Engine Modulation) signal. A novel method to recognize an engine model by analyzing JEM spectrum using frequency mask is proposed. The frequency mask extracts and analyses the spectral component at the frequencies that are predicted from the blade number of a jet engine and the estimated spool rate. The proposed method does not need a complicated logical algorithm for finding the chopping frequency or the pre-simulated engine spectra used in previous methods. In addition, we suggest a method to precisely estimate the spool rate in the spectrum domain of JEM signal, which plays an important role in generating the frequency mask. The classification experiments using the JEM signals measured from two fabricated engine models verify that the proposed algorithm has good performance in the recognition of jet aircrafts.
The rectangular wave beams-based geometrical optics (GO) and physical optics (PO) hybrid method is applied to the radar cross section (RCS) simulation of complex target. In the implementation process, the incident wave beam is divided into plenty of regular rectangular wave beams. The RCS of target is subsequently harvested from the sum of the contributions from rectangular wave beams. And Open Graphics Library (OpenGL) is used to accelerate ray tracing for the GO/PO method. Here, each pixel corresponds to a rectangular wave beam, which improves the defect that the pixel number should be larger than the patch number on the model and the efficiency in the general OpenGL based GO/PO method. In addition, the patch size in the presented method can be arbitrary as long as the model is described accurately with these patches. The simulation results prove this point and show that the proposed rectangular wave beam-based GO/PO method is feasible and can keep a high calculation accuracy and efficiency with a low pixel number.
An improved range-Doppler algorithm (RDA) is proposed to reconstruct images from synthetic aperture radar (SAR) data received at high squint angles. At a higher squint angle, a larger synthetic aperture is required to receive sufficient amount of data for image reconstruction, and the range migration also becomes more serious, which demands more computational load and larger memory size. The proposed method can generate better SAR images with less computational load and memory than the conventional RDA, which is verified by simulations.
Principal component analysis is usually used for clutter suppression of ground penetrating radar, but its performance is influenced by the selection of main components of target signal. In the paper, an improved principal component selection rule is proposed for selecting the main components of target signal. In the method, firstly difference spectrum of singular value is used to extract direct wave and strong target signal, and then, Fuzzy-C means clustering algorithm is used to determine the weights of principal component of weak target signal. Finally, the principal components of strong target signal and weak target signal are reconstructed to obtain target signal. Experimental results show that the proposed method can effectively remove the clutter signals and reserve more target information.
In this paper, a 3D quasistatic numerical algorithm for computation of the electric field produced by overhead power lines is presented. The real catenary form of the overhead power line phase conductors and shield wires is taken into account with an arbitrary number of straight thin-wire cylindrical segments of active and passive conductors. In order to obtain more precise results of the charge density distribution, segmentation is conducted for each overhead power line span separately. Moreover, the presence of the towers which distort the electric field and significantly reduce its magnitude is taken into account. Therefore, the towers of overhead power lines are approximated using thin-wire cylindrical segments of passive conductors with electric potential equal to zero. From self and mutual coefficients of these components, system of linear equations for computation of the charge density distribution was obtained. In the numerical example, electric field intensity distribution in the vicinity of towers and under the midspan of overhead power lines is shown. In order to verify the accuracy of the presented model, the obtained results are compared with similar published examples and results available in the literature.
The general principles of design and development of microwave absorbing materials are discussed and analysed in respect to 26-37 GHz frequency range (Ka-band). Dispersive composite materials based on carbon nanotubes in epoxy resin matrix are produced, and their electromagnetic responses are investigated in Ka-band. Both theoretical and experimental results demonstrate that presented composites may be used as compact e ective absorbers in 26-37 GHz range.
In this paper, a rigorous study of rectangular waveguide partially filled with longitudinally magnetized ferrite is presented. The propagation constant as a function of frequency is first obtained by the use of Transverse Operator Method. We show the existence of the complex modes in this type of structures with ferrite. In these problems, the interface between an air filled rectangular waveguide and E-plane ferrite slab loaded rectangular waveguide represent a discontinuity problem. The analysis is based on the Mode Matching Method and the Transverse Operator Method which are combined in such a way as to determine the scattering parameters. The proposed approach is validated by comparing the presented results with the published data and numerical ones obtained from commercial software.
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