Through-the-Wall Imaging systems are a promising method for on-line applications,especially in disaster areas, where victims are buried under collapsed walls. These applications require such systems to identify the shape of thetarget. The foremost step while performing the task of shape recognition of stationary targets behind a wall is to first detect the target position, its approximate shape and size, and then, subsequent processing of these images with the use of signal processing techniques for the shape recognition of targets. For determining highly accurate information about target location and its approximate shape, a high-resolution image of the target is required. In literature, various imaging algorithms have been reported, some of which are back projection, delay sum, and frequency-wavenumber imaging algorithm. However, the use of these algorithms for shape detection of the target has not been explored so far. Therefore, it becomes essential to explore the use of these algorithms on TWI data to select an effective imaging algorithm for detecting approximate shape and size of the target. For this purpose, an experiment has been performed. The performances of these imaging algorithms have been analyzed and evaluated. The detected target images do not correspond to the actual shape and size of targets; therefore, a novel methodology using an artificial neural network has been presented for predicting the actual shape of the target. From the experimental data, the retrieved result of shape has been found in good agreement with the target original shape.
This paper presents the design, manufacture, and experimental validation of a novel 3-D pixel antenna with volume-filling characteristics, and the design is based on our Method of Moments (MoM) solver that is efficiently coupled with a global/local optimizer for tailoring the antenna shape and concurrently selecting the location of the feeding port and shorting straps. The design, aimed at operating in the ISM bands of 2.45 GHz and 5.8 GHz, has dimensions under one-tenth of wavelength at the lowest frequency of operation. The optimization results are cross-validated using a commercial full-wave simulator, with a deviation of the reflection coefficient across the operating bands within 3%, showing also a high antenna efficiency of 99.6% and a gain of 1.06 and 4.53 dBi at the matching frequencies, with radiation patterns predominantly oriented towards the top hemisphere. Tolerance and parameter sensitivity studies were also performed. A scaled-up prototype of the antenna was built at a very low cost using standard additive manufacturing techniques, featuring a very good agreement between simulation and measurements, which proves the feasibility of this new kind of complex shape antennas in further applications where compact internal antennas are required.
A novel gain-enhanced microstrip antenna (MSA) with metamaterial planar lens for long-range radio frequency identification (RFID) applications for the 902-928 MHz UHF frequency band is proposed in this paper. The antenna is a combination of a new general-purpose circularly polarized MSA and a novel effective negative refractive index metamaterial (NIM) slab of 25 unit cells, arranged in a 5 x 5 layout, working as a planar lens for gain enhancement. The general-purpose MSA has an impedance frequency band of 828-1015 MHz, a maximum gain of 8.43 dBi at 915 MHz, an axial ratio frequency band of 896-931 MHz and excellent performance for short and medium range RFID applications. The new infinite periodicity NIM slab has a negative refractive band of 886-1326 MHz, a negative electric permittivity band of 888-3406 MHz, and a negative magnetic permeability of band 885-1065 MHz. Together, the general-purpose MSA and the NIM planar lens results in the low-cost gain-enhanced antenna for long-range RFID applications, with an 843-993 MHz impedance frequency band and a maximum broadside gain enhancement of 48.27%, resulting in a 12.5 dBi gain at 902 MHz. Finally, the parametric studies conducted during the design process of the gain-enhanced antenna with metamaterial planar lens are presented.
Electromagnetic scattering from the sea surface is of great significance in ocean remote sensing especially under high wind conditions. A novel volume-surface composite scattering model of nonlinear rough sea surfaces with breaking waves and foam layers under high wind conditions is presented in this study. Based on the semi-deterministic facet scattering model (SDFSM), using a ray tracing method combined with impedance equivalent edge currents (RT-IEEC) and vector radiative transfer theory (VRT), the backscattering characteristics of the sea surface with breaking waves and foam layers are investigated. The crest- and static-foam coverage was introduced to determine the breaking point and foam coverage distribution. The dependence of the backscattering coefficient of thesea surface with and without breaking waves and foam layers on the incident angle, wind speed, and the polarization are discussed in detail. The results of thenumerical simulations are analyzed and compared with the measured data from the relevant references which verifies the validity of our volume-surface composite scattering model. The synthetic aperture radar (SAR) image simulations of the surface with and without the breaking waves and foam layers are compared, and the combined effects of the breaking waves and whitecaps are analyzed.
Since electromagnetic compatibility studies intend to predict the compliance with electromagnetic standards, an accurate computation of both common and differential mode conducted noises is necessary. Modern networks-such as in automobiles that are known for supplying many electrical actuators-include many power converters and long cables (conductors) to efficiently manage power transfer. However, the presence of both converters and cables creates new electromagnetic compatibility issues. For example, the interaction between cables and converters becomes a noise source. For this reason, electromagnetic compatibility study becomes more complex. Therefore, the purpose of this paper is an attempt to propose an analytical model that computes noise sources by generating conducted signals within the network at any site, meaning all along the cable according to the CISPR16 standard. Our approach primarily consists of modeling conducted noise sources generated by converters connected to the DC-network, which are extracted and identified in both frequency and time domains. The electromagnetic compatibility modelling of converter's behaviour is performed by defining a mathematical switching function. The model is assessed with time domain simulations and identified by experimental measurements. Secondly, the extracted converter's model, based on equivalent noise sources, is used to predict the conducted noise inside a defined network at any location of the cable. The process of the network's modelling is realised through using the Multi-Transmission Line Method of lossless lines. This network's model is crucial for EMC analysis in order to evaluate the interaction degree between noise sources and cable parameters.
Magnetic resonant wireless power transfer (WPT) is an emerging technology that may create new applications for wireless power charging. However, the output voltage and efficiency fluctuations resulting from lateral misalignments are main obstructing factors for promoting this technology. In this paper, a structure of tower-type coils is proposed. The mathematical model of the proposed structure is built based on equivalent circuit method. The expressions of the output voltage and efficiency are then derived by solving the system equivalent equations. In addition, a method of optimizing the mutual inductance between the transmission coil and intermediate coil and the strong-coupling parameters between the intermediate coil and receiving coil is proposed. The mutual inductance between the transmission coil and intermediate coil can be kept nearly constant with lateral misalignments, and the optimum strong-coupling parameter between the intermediate coil and the receiving coil can be obtained by the proposed method. Therefore, the output voltage and efficiency can be kept nearly constant with different lateral misalignments. The WPT system based on tower-type coils via magnetic resonance coupling is designed. Simulated and experimental results validating the proposed method are given.
A high isolation broadband dual-polarized omnidirectional antenna comprising two low profile orthogonally polarized omnidirectional radiating elements is presented. A modified monopole using loadings to broaden impedance bandwidth is applied to vertical polarization (VP), while four printed concentrically arranged Yagi-Uda-like antennas are employed for horizontal polarization (HP). Both the simulated and measured results indicate that the operating bands of the proposed antenna with its reflection coefficient less than -10 dB are 1.48 to 3.16 GHz for VP and 1.69 to 2.7 GHz for HP. A good port isolation larger than 40 dB and omnidirectional patterns with the out-of-roundness less than 2 dB in horizontal plane are obtained. This paper explains the radiation mechanism by investigating the simulated surface current distributions for VP element and establishing a radiation model for HP element, and also analyzes the performance of the proposed antenna. This antenna design can be applied to 4G (LTE) communication system.
The generation mechanism of the geomagnetic field perturbations associated with tsunami wave propagation in ocean is examined. The geomagnetic perturbations are produced by electric currents generated in both the seawater and conductive layers of the ionosphere. The electric current in conductive seawater is caused by the seawater motion due totsunami wave propagation whereas the current in the ionospheric plasmais generated by acoustic gravity wave (AGW) incident on the ionosphere from the atmosphere. The AGW is originated from vertical displacements of seawater surface due to the tsunami wave propagation. Although the ionospheric plasma conductivity is much lower than the seawater conductivity, the electric current in the ionosphere can be greater than that in the seawater due to an exponential increase of amplitude of the upward-propagating AGW. Our calculations are indicative of the possibility of space monitoring of tsunami wave based on onboard measurements of the geomagnetic field perturbations.
Step-like perfect electric conductor (PEC) structures are studied in both electrostatic and electrodynamic cases implementing Method of Moments. The canonical geometries included in these step-like structures such as edges, wedges and corners as well as the unique charge and current behaviors are characterized and discussed. Both 2D and 3D electrostatic problems are studied. In 2D electrostatic problem, a constant is introduced to the traditional 2D Green's function which effectively adjusts the zero potential reference embedded in the Green's function. This modification alleviates the contradiction between 2D and 3D definitions of electrostatic quantities and avoids unrealistic charge solutions obtained by Method of Moments. In 2D electrodynamic problem, the occasional appearance of singular surface current near the step's right angle bends is observed, discussed and then linked with the analytical solution of a canonical wedge scattering problem. Physical Optics approximation is also utilized as a comparison to Method of Moments in solving the 2D scattering problems.
A non-iterative inverse-source solver is introduced for the 2D Helmholtz boundary value problem (BVP). Microwave imaging within a chamber having electrically conducting walls is formulated as a time-harmonic 2D electromagnetic field problem that can be modelled by such a BVP. The novel inverse-source solver, which solves for contrast sources, is the first step in a two-stage process that recovers the complex permittivity of an object of interest in the second step. The unknown contrast sources, as well as the (permittivity) contrast, are represented using the eigenfunction basis associated with the chamber's shape; canonical shapes allowing for analytically defined eigenfunctions. This whole-domain eigenfunction basis allows the imposition of constraints on the contrast-source expansion at virtual spatial points or contours outside the imaging domain. These constraints effectively regularize the inverse-source problem and the result is a well-conditioned matrix equation for the contrast-source coefficients that is solved in a least-squares sense. The contrast-source coefficients corresponding to different illuminating fields are then utilized to recover the contrast expansion coefficients using one more well-conditioned matrix inversion. The performance of this algorithm is studied using a series of synthetic test problems. The results of this study are promising as they compare very well with, and at times out-perform, state-of-the-art inversion algorithms (both in terms of reconstruction quality and computation time).
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