A non-resonant microwave method has been proposed for complex permittivity determination of low-loss materials with no prior information of sample thickness. The method uses two measurement data of maximum/minimum value of the magnitude of transmission properties of the sample. An explicit expression for sample thickness and two expressions for inversion of the complex permittivity of the sample are derived. The method has been validated by transmission measurements at X-band (8.2--12.4 GHz) of a low-loss sample located into a waveguide sample holder.
In this paper propagation losses of body implanted antennas are studied at the ISM bands of 433 MHz, 915 MHz, 2450 MHz and 5800 MHz. Two body models are used, one based on a single equivalent layer and the other based on a three layer structure, showing the advantages and limitations of each one. Firstly, the antenna pair gain at different implanted antenna depths is analyzed. Next, we show the effects of the thickness of the different body tissue layers. Finally, we discuss the consequences of using a coating layer to isolate the antenna from the harsh environment of the human body.
This paper presents a new unequally spaced and excited resonant slotted-waveguide antenna array. It is realized by employing an improved resonant-slot coupled cavity chain composite right/left-handed (CRLH) waveguide. As the CRLH waveguide works at the infinite wavelength frequency, all the slot elements along the waveguide wall are excited in-phase. Thus both the element spacings and excitation amplitudes are introduced into the synthesis to realize a resonant slotted-waveguide antenna array. A seven-element unequally spaced and excited antenna array which generates pencil beam is synthesized, simulated and fabricated. The results show, with comparison to the equally spaced but unequally excited resonant slotted-waveguide antenna array, the proposed unequally spaced and excited array produces a lower peak sidelobe level (PSLL).
A canonical problem is used to investigate the effects of various radar parameters on the performance of both steppedfrequency and short-pulse through-barrier radar imaging systems. For simplicity, a two-dimensional problem is considered, consisting of a perfectly conducting strip located behind a lossy dielectric slab of infinite extent illuminated by line sources. To assess the impact of the parameters on system performance, images of the target are created using the reflected field computed at several positions in front of the barrier and adjacent to the sources. Specific parameters considered include sample rate, A/D bit length, pulse width, and SNR for a time-domain system. For a stepped-frequency system, A/D bit length, bandwidth, and SNR are considered.
Charges and fields in a rotating non-magnetic conducting sphere under stationary conditions are investigated by using Minkowski's electrodynamics of moving media and the Lorentz force equation, taking into account the electric permittivity of the sphere. Starting from the assumption that the magnetic field inside the sphere is constant, exact solutions of the corresponding field equations are obtained in a first-order theory. However, it is found that there is a range of values of the sphere's net charge for which the physical interpretation of the results is difficult within a continuum model. Outside that range, our solution to the classic electromagnetostatic problem appears plausible.
A novel class of electromagnetic media called that of SQ-media is defined in terms of compact four-dimensional differential-form formalism. The medium class lies between two known classes, that of Q-media and SD-media (also called self-dual media). Eigenfields for the defined medium dyadic are derived and shown to be uncoupled in a homogeneous medium. However, energy transport requires their interaction. The medium shares the nonbirefringence property of the Q-media (not shared by the SD media) and the eigenfield decomposition property of the SD media (not shared by the Q-media). Comparison of the three medium classes is made in terms of their three-dimensional medium dyadics.
In recent years, through the wall imaging has become a topic of intense research due to its promising applications in police, fire and rescue or emergency relief operations. In this paper, we propose to use the DORT method (French acronym for Decomposition of the Time Reversal Operator) to detect and localize a moving target behind a wall. One of the DORT method major strengths is that detection remains possible through a distorting medium. In this paper, the DORT method is successfully applied to detect and track moving human beings behind a thick concrete wall. The smallest detectable displacement is also investigated.
Evaluation of electric and magnetic fields due to lightning discharge is important in determination of lightning induced voltage and power system protection especially to the distribution system. In this paper, by using dipole method, Maxwell equations and second order finite-difference time domain (later referred as a 2nd FDTD method) on two realistic return stroke currents, an algorithm for evaluation of electric fields is proposed, which is based on numerical methods in the time domain. Besides proving greater accuracy, it also allows the evaluation of electric and magnetic fields away from lightning channel. In addition, the comparison between simulation results and measured fields' wave shape showed that the proposed algorithm is in good agreement for evaluation of electric and magnetic fields due to lightning channel.
We use both FEM (finite element method) and FDTD (finite difference time domain method) to simulate the field distribution in Maxwell's fish eye lens with one or more passive drains around the image point. We use the same Maxwell's fish eye lens structure as the one used in recent microwave experiment [arXiv:1007.2530]: Maxwell's fish eye lens bounded by PEC (perfect electric conductor) is inserted between two parallel PEC plates (as a waveguide structure). Our simulation results indicate that if one uses an active coaxial cable as the object and set an array of passive drains around the image region, what one obtains is not an image of the object but only multiple spots resembling the array of passive drains. The resolution of Maxwell's fish eye is finite even with such passive drains at the image locations. We also found that the subwavelength spot around the passive drain is due to the local field enhancement of the metal tip of the drain rather than the fish eye medium or the ability of the drain in extracting waves.
The research in the paper puts forward a novel method for synthesizing conformal arrays and optimizing low cross-polarizations including the effects of element mutual coupling and mounted platform. Starting from the far-field superposition principle, an efficient approach with active element pattern technique is proposed to calculate the far-field patterns. Coordinate transform is used to create polarization quantities, and a general process for the element polarized pattern transformation is proposed. The two numerical examples are proposed, and the desired sidelobe levels and low cross-polarizations are optimized. Numerical results denote the proposed method is valid.
The objective of this paper is to establish the properties of the electromagnetic wave propagation in a diversity of situations in material media with magnetic monopoles and even in the situations of entities simultaneously containing electric and magnetic charges. This analysis requires the knowledge and solutions of the ``Maxwell" equations in material media compatible with the existence of magnetic monopoles and the extended concepts of linear responses (conductivity, split-charge susceptibility, kinetic susceptibility, permittivity and magnetic permeability) in the case of presence of electric and magnetic charges. This analysis can facilitate insights and suggestions for electrical and optical experiments according a better knowledge of the materials whose behaviour can be analyzed under the consideration of the existence of entities with equivalent properties of the magnetic monopoles.
In this work, magnetic metallic cobalt nanoparticles with an average particle size of 28 nm were processed as a dry powder with surface coating material and other organic additives to form a screen-printable ink to be cured at 110 °C. EFTEM and TGA-DSCMS-analyses were used to measure the thickness of the polymer, its coverage on cobalt nanoparticles and the inorganic solid content of the ink. The resolution of the printed patterns and the print quality were evaluated by surface profiler, FESEM and optical microscopy. The relative permeability of the thick film patterns with good printability was measured with a shorted microstrip structure over the frequency range of 0.2 to 4 GHz and complex permeability values were calculated from measured scattering parameter data. The ink attained real part of complex permeability values of up to 5.13 at 200 MHz with 70 wt.% of magnetic filler. The developed ink can be utilized in various printed electronics applications such as antenna substrates and magnetic sensors.
In this paper, we consider the imaging of thin dielectric inclusions completed embedded in the homogeneous domain. To image such inclusion from boundary measurements, topological derivation concept is adopted. For that purpose, an asymptotic expansion of the boundary perturbations that are due to the presence of a small inclusion is considered. Applying this formula, we can design only one iteration procedure for imaging of thin inclusions by means of solving adjoint problem. Various numerical experiments without and with some noise show how the proposed techniques behave
In this paper the definition of characteristic impedance for lossless microstrip and coplanar lines has been considered. It has been shown that due to a significant value of the displacement current related to longitudinal component of the electric field, impedance definition becomes ambiguous. Such ambiguity can cause considerable errors in design procedure. This effect is especially noticeable in the coplanar lines, in opposite to microstrip ones. To confirm the validity of the applied algorithm (spectral domain approach) the propagation coefficients and characteristic impedances have been compared to values obtained from commercial software.
This paper proposes a radio frequency identification (RFID) based collision-free robot docking in cluttered environment. Physical distance estimation sensors are fused to the developed degree of arrival (DOA) guided robot docking system, and collision-avoidance function is implemented based on the vector field histogram technique. Additionally, new simple but efficient DOA filtering algorithm is developed based on the gain control according to the improved robot control algorithm, which enables the robot to move continuously. The experimental results show that the robot can move to target transponder even though the estimated DOA is blocked by obstacles. The success rate does not reach satisfactory level due to the limitation of the employed sensors and collision-avoidance algorithm, but it is proved that the collision-free docking becomes available without any priori map and reference stations.
An accurate and flexible three-dimensional Volterra Time Domain Integral Equation (TDIE) algorithm is presented and implemented here to model the time-dependent electromagnetic field of arbitrarily shaped dielectric bodies. This development is motivated by the need for a modern high-resolution numerical tool that is capable of providing a full and comprehensive investigation of devices containing a diverse range of feature sizes or boundaries, in all three space dimensions plus time. Stability, accuracy and convergence of the algorithm are discussed and verified by means of canonical working examples.
In this study, a general method for analyzing the multilayer optical planar waveguides with photonic metamaterial is presented. The propagation characteristics of TE waves guided by the film with both the permittivity and permeability less than zero are investigated theoretically. The formulae for the electric fields of TE modes in this structure have been proposed. Typical numerical results for dispersion characteristics are shown. The analytical and numerical results show excellent agreement.
While designing wireless networks, it is crucial to obtain the maximum coverage by using minimum number of transmitting antennas. This paper proposes a new algorithm for determining the minimum number of transmitting antennas as well as their appropriate locations to provide the optimized wireless coverage in the indoor environment. The proposed algorithm uses a ray-tracing method to predict the signal distribution among the sampling points in the indoor area due to one or more transmitters and the genetic algorithm (GA) incorporated with the Breath First Search (BFS) terminology to determine the minimum number of transmitters and their corresponding locations to achieve the optimum wireless coverage. The proposed method outperforms the existing method in terms of both space and time complexities. The results obtained from this study also show that the computation time using the proposed algorithm is much less than that of the existing algorithm.
When employing computational methods for solving problems in electromagnetic scattering the resulting solutions are strongly determined by the geometry of the scatterer. Careful consideration must therefore be given to the computational geometry used in representing the scatterer. Here we show that the solution for a problem as simple as plane wave scattering off a PEC sphere is sensitive to the computational geometry used to represent the sphere. We show this by implementing 4 higher-order computational geometry schemes over 3 different tessellations resulting in 45 different representations of the sphere. Two methods for solving the scattering problem are implemented: the boundary-element method (BEM) based on the MFIE, and the physical optics (PO) method. Results are compared and insights are obtained into the performance of the various schemes to model surfaces accurately and efficiently. The comparison of the different schemes takes into consideration the required computational resources in implementing the schemes. Some unexpected results are discovered and explanations given.
The synthetic aperture radar (SAR) signatures of moving target are the basis of ground moving target indication and imaging (GMTI&Im) in the framework of SAR systems. However, previous studies are mainly based on the 2-D separable SAR processing, and little work has been done to investigate the signatures of moving target after the application of a particular fine resolution SAR image formation algorithm. In this paper, we derive the image spectrum of moving target after two representative fine resolution SAR image formation algorithms, i.e., the range migration algorithm (RMA) and polar format algorithm (PFA), respectively. Based on the spectrum derived, detailed analysis on the SAR signatures of moving target, including the geometric displacement, residual range migration, and defocusing effect in both the range and azimuth dimensions are performed. The presented work might be helpful when considering a SAR system with the capability of ground moving target indication and imaging (GMTI&Im).
We introduce a novel variant of the Lanczos method for computing a few eigenvalues of sparse and/or dense non-Hermitian systems arising from the discretization of Maxwell- or Helmholtz-type operators in Electromagnetics. We develop a Krylov subspace projection technique built upon short-term vector recurrences that does not require full reorthogonalization and can approximate simultaneously both left and rigth eigenvectors. We report on experiments for solving eigenproblems arising in the analysis of dielectric waveguides and scattering applications from PEC structures. The theoretical and numerical results reported in this study will contribute to highlight the potential and enrich the database of this technology for solving generalized eigenvalue problems in Computational Electromagnetics.
The objective of this work is to analyze electronic transport phenomena, due to ionized impurity scattering in δ-MIGFET (Delta-Multiple Independent Gate Field Effect Transistor). In this work, we report theoretical results for electronic transport in a delta-MIGFET using the device electronic structure and analytical expression of mobility and conductivity. The results show that the analytical mobility and conductivity are a good way to analyze transport in this device. We find the relative mobility as a linear and increasing function in different modes; also, we find transconductance as an almost flat function in all the evaluated interval. Finally, we analyze the differential capacitance and resistivity, and we report regions where this device is operating in digital and analogue mode. These regions are delimited in terms of intrinsic and extrinsic parameters of this device in symmetrical mode.
Power strength or Received Signal Strength Indicator (RSSI), a primary technique used in Real Time Location Systems (RTLS), is analyzed in this paper for RFID tracking applications. Critical issues are studied and hardware novelties are introduced in order to improve its performance. The main novelty is the accomplishment of an RFID RTLS through a mesh of individual active radiofrequency (RF) barriers composed by active emitter and receiver nodes/tags that cover only small individual areas. The result is a Sensor Area Network (SAN) that offers some advantages over classical tracking systems, which are based on Wireless Sensor Networks (WSN), especially in the multipath impairment mitigation, such as a controlled power emission, and the chance to warrant privacy regarding the exchange of RFID information. Experimental measurements were done to estimate the influence of the transmitted signal type and the receiver end architecture in the detection of the RF barrier presence. The parameterization of the coverage area of a SAN cell in terms of power is derived for both free-space and log-distance propagation models. The Kalman filtering technique is introduced as a valid tool to severely mitigate the multipath propagation effects that can affect the accurate operation of the proposed SAN for indoor operation conditions. Outcomes show a promising performance for this wireless network design, which has not received enough attention in literature.
In this paper, the hybrid approach to the analysis of electromagnetic wave scattering from arbitrary configuration of body-of-revolution (BOR) posts is presented. The proposed approach is based on the representation of each scatterer or set of scatterers by an effective sphere with the known boundary conditions defined by transmission matrix. In the analysis of each single axially-symmetrical post with irregular shape we utilize the finite-difference frequency-domain/mode-matching technique (FDFD/MM). Then the scattering parameters of investigated set of posts are obtained utilizing the analytical iterative scattering procedure (ISP). This work is an extension of our previously published results where the proposed technique was defined in cylindrical coordinates and was limited to configurations of infinitely long parallel cylinders with arbitrary cross-section. In this paper we extend this method by formulating it in spherical coordinates. This allows us to significantly increase the versatility of the developed approach and in result to include in the analysis the sets of arbitrary located and oriented rotationally-symmetrical posts. The accuracy and efficiency of the proposed technique are discussed. The presented numerical results are verified with the ones obtained from commercial software.
The calibration of the multistatic scattering matrix plays an important part in the construction of a quantitative microwave imaging system. For scattering measurement applications, the calibration must be performed on the amplitude and on the phase of the fields of interest. When the antennas are not completely identical, as for example with a multiplexed antennas array, a specific calibration procedure must be constructed. In the present work, we explain how a complex calibration matrix can be defined which takes advantage of the geometrical organization of the antennas. Indeed, for arrays of antennas positioned on a circle, the inherent symmetries of the configuration can be fully exploited by means of an adequate reorganization of the multistatic scattering matrix. In addition, the reorganization permits to detect antenna pairs which are not properly functioning and to estimate the signal-to-noise ratio. Experimental results obtained within a cylindrical cavity enclosed by a metallic casing are provided to assess the performance of the proposed calibration procedure.This calibration protocol, which is described here in detail, has already been applied to provide quantitative images of dielectric targets [1, 2].
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