Numerical methods for electromagnetic wave propagation and scattering in complex media

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Vita.Includes bibliographical references (p. 227-242).Numerical methods are developed to study various applications in electromagnetic wave propagation and scattering. Analytical methods are used where possible to enhance the efficiency, accuracy, and applicability of the numerical methods. Electromagnetic induction (EMI) sensing is a popular technique to detect and discriminate buried unexploded ordnance (UXO). Time domain EMI sensing uses a transient primary magnetic field to induce currents within the UXO. These currents induce a secondary field that is measured and used to determine characteristics of the UXO. It is shown that the EMI response is difficult to calculate in early time when the skin depth is small. A new numerical method is developed to obtain an accurate and fast solution of the early time EMI response. The method is combined with the finite element method to provide the entire time domain response. The results are compared with analytical solutions and experimental data, and excellent agreement is obtained. A fast Method of Moments is presented to calculate electromagnetic wave scattering from layered one dimensional rough surfaces. To facilitate the solution, the Forward Backward method with Spectral Acceleration is applied. As an example, a dielectric layer on a perfect electric conductor surface is studied. First, the numerical results are compared with the analytical solution for layered flat surfaces to partly validate the formulation. Second, the accuracy, efficiency, and convergence of the method are studied for various rough surfaces and layer permittivities. The Finite Difference Time Domain (FDTD) method is used to study metamaterials exhibiting both negative permittivity and permeability in certain frequency bands.(cont.) The structure under study is the well-known periodic arrangement of rods and split-ring resonators, previously used in experimental setups. For the first time, the numerical results of this work show that fields propagating inside the metamaterial with a forward power direction exhibit a backward phase velocity and negative index of refraction. A new metamaterial design is presented that is less lossy than previous designs. The effects of numerical dispersion in the FDTD method are investigated for layered, anisotropic media. The numerical dispersion relation is derived for diagonally anisotropic media. The analysis is applied to minimize the numerical dispersion error of Huygens' plane wave sources in layered, uniaxial media. For usual discretization sizes, a typical reduction of the scattered field error on the order of 30 dB is demonstrated. The new FDTD method is then used to study the Angular Correlation Function (ACF) of the scattered fields from continuous random media with and without a target object present. The ACF is shown to be as much as 10 dB greater when a target object is present for situations where the target is undetectable by examination of the radar cross section only.by Christopher D. Moss.Ph.D

Surface electrical properties experiment, Part 3

A complete unified discussion of the electromagnetic response of a plane stratified structure is reported. A detailed and comprehensive analysis of the theoretical parts of the electromagnetic is given. The numerical problem of computing numbers of the electromagnetic field strengths is discussed. It is shown that the analysis of the conductive media is not very far removed from the theoretical analysis and the numerical difficulties are not as accute as for the low-loss problem. For Vol. 1, see N75-15570; for Vol. 2 see N75-15571

Recent Advances in Antenna Design for 5G Heterogeneous Networks

The aim of this book is to highlight up to date exploited technologies and approaches in terms of antenna designs and requirements. In this regard, this book targets a broad range of subjects, including the microstrip antenna and the dipole and printed monopole antenna. The varieties of antenna designs, along with several different approaches to improve their overall performance, have given this book a great value, in which makes this book is deemed as a good reference for practicing engineers and under/postgraduate students working in this field. The key technology trends in antenna design as part of the mobile communication evolution have mainly focused on multiband, wideband, and MIMO antennas, and all have been clearly presented, studied and implemented within this book. The forthcoming 5G systems consider a truly mobile multimedia platform that constitutes a converged networking arena that not only includes legacy heterogeneous mobile networks but advanced radio interfaces and the possibility to operate at mm wave frequencies to capitalize on the large swathes of available bandwidth. This provides the impetus for a new breed of antenna design that, in principle, should be multimode in nature, energy efficient, and, above all, able to operate at the mm wave band, placing new design drivers on the antenna design. Thus, this book proposes to investigate advanced 5G antennas for heterogeneous applications that can operate in the range of 5G spectrums and to meet the essential requirements of 5G systems such as low latency, large bandwidth, and high gains and efficiencies

Wideband directional complex electrical conductivity of geomaterials : a mechanistic description

textSubsurface electromagnetic (EM) measurements in shaly sands, sand-shale laminations, and organic-rich mudrocks, to name a few examples, exhibit directional and frequency dispersive characteristics primarily due to the effects of electrical conductivity anisotropy, dielectric permittivity anisotropy, and interfacial polarization phenomena. Conventional resistivity interpretation techniques for laboratory and subsurface EM measurements do not account for the effects of dielectric permittivity, dielectric loss factor, dielectric dispersion, and dielectric permittivity anisotropy arising from interfacial polarization phenomena. Furthermore, laboratory measurements on 1.5-inch-diameter, 2.5-inch-long core plugs acquired at discrete depths in wells are generally utilized to improve the estimation of petrophysical properties based on conventional resistivity interpretation of subsurface EM measurements. Electrical measurements performed on 4-inch-diameter, 2-feet-long whole core samples represent closer approximations to the electrical properties of subsurface formations compared to widely-used galvanic measurements of core plugs. The first objective of this dissertation is to develop a non-contact and non-invasive, laboratory-based EM induction apparatus, referred to as the WCEMIT, to measure the complex-valued electrical conductivity tensor of whole core samples at high resolution and at multiple frequencies for improved core-well log correlation. The tensor functionality of the WCEMIT is sensitive to the directional nature of electrical conductivity, dielectric permittivity, and dielectric loss factor, while its multi-frequency functionality is sensitive to the frequency-dispersive electrical properties of the samples. Finite-element and semi-analytic EM forward models of the WCEMIT are used to calibrate WCEMIT measurements and to estimate various effective electrical properties. WCEMIT measurements are successfully applied to the estimation of directional conductivity, dielectric permittivity, formation resistivity factor, Archie's porosity exponent, relative dip, azimuth, and anisotropy ratio. It is found that brine-saturated samples containing pyrite and graphite inclusions exhibit a negative X-signal response, large frequency dispersion in the R-signal response, large effective permittivity, and significant frequency dispersion of effective conductivity and permittivity in the frequency range of 10 kHz to 300 kHz. Further, graphite-bearing samples exhibit significantly different frequency dispersion properties compared to pyrite-bearing samples. Estimated values of effective relative permittivity of samples containing uniformly distributed 1.5-vol% of pyrite inclusions were in the range of 10³ to 10⁴, while those containing uniformly distributed 1.5-vol% of graphite inclusions were in the range of 10⁵ to 10⁶. At an operating frequency of 58.5 kHz, samples containing 1.5-vol% of graphite inclusions and those containing 1.5-vol% of pyrite inclusions exhibited effective conductivity values that were 200% and 95%, respectively, of the host conductivity. True conductivity and permittivity of hydrocarbon-bearing host media can be determined by processing the estimated effective conductivity and permittivity of conductive-mineral-bearing samples. Accordingly, the second objective of this dissertation is to develop a mechanistic electrochemical model, referred to as the PPIP-SCAIP model, that quantifies the directional complex electrical conductivity of geomaterials containing electrically conductive mineral inclusions, such as pyrite and magnetite, that are uniformly distributed in a fluid-filled, porous matrix made of non-conductive grains possessing surface conductance, such as silica, clay-sized particles, and clay minerals. PPIP-SCAIP model predictions successfully reproduce several laboratory measurements of multi-frequency complex electrical conductivity, relaxation time, and chargeability of mixtures containing electrically conductive inclusions in the frequency range of 100 Hz to 10 MHz. The mechanistic model predicts that the low-frequency effective electrical conductivity of geomaterials containing as low as 5% volume fraction of disseminated conductive inclusions will vary in the range of 70% to 200% of the host conductivity for operating frequencies between 100 Hz to 100 kHz, while its high-frequency effective relative permittivity will vary in the range of 190% to 90% of the host relative permittivity for operating frequencies between 100 kHz and 10 MHz. The model indicates high sensitivity of subsurface EM measurements to the electrical properties, shape, volumetric concentration, and size of the inclusion phase, and to the conductivity of pore-filling electrolyte.Petroleum and Geosystems Engineerin

Final technical report on the Surface Electrical Properties Experiment Part 3

This report consists of a series of reports, reprints and preprints that in themselves constitute a self-explanatory record of the work performed by the University of Toronto on the Surface Electrical Properties Experiment. Areas discussed include: data handling and processing, installation and external signal application, operation of the equipment, and digital output. Detailed circuit descriptions are included. A complete unified discussion of the electromagnetic response of a plane stratified structure is reported. A detailed and comprehensive analysis of the theoretical parts of the electromagnetic is given. The numerical problem of computing numbers of the electromagnetic field strengths is discussed. It is shown that the analysis of the conductive media is not very far removed from the theoretical analysis and the numerical difficulties are not as acute as for the low-loss problem.Submitted to MIT in fulfillment of the subcontract on NASA contract NAS9-1154

The National Aeronautics and Space Administration interdisciplinary studies in space technology at the University of Kansas

A broad range of research projects contained in a cooperative space technology program at the University of Kansas are reported as they relate to the following three areas of interdisciplinary interest: (1) remote sensing of earth resources; (2) stability and control of light and general aviation aircraft; and (3) the vibrational response characteristics of aeronautical and space vehicles. Details of specific research efforts are given under their appropriate departments, among which are aerospace engineering, chemical and petroleum engineering, environmental health, water resources, the remote sensing laboratory, and geoscience applications studies

DETERMINE: Novel Radar Techniques for Humanitarian Demining

Today the plague of landmines represent one of the greatest curses of modern time, killing and maiming innocent people every day. It is not easy to provide a global estimate of the problem dimension, however, reported casualties describe that the majority of the victims are civilians, with almost a half represented by children. Among all the technologies that are currently employed for landmine clearance, Ground Penetrating Radar (GPR) is one of those expected to increase the efficiency of operation, even if its high-resolution imaging capability and the possibility of detecting also non-metallic landmines are unfortunately balanced by the high sensor false alarm rate. Most landmines may be considered as multiple layered dielectric cylinders that interact with each other to produce multiple reflections, which will be not the case for other common clutter objects. Considering that each scattering component has its own angular radiation pattern, the research has evaluated the improvements that multistatic configurations could bring to the collected information content. Employing representative landmine models, a number of experimental campaigns have confirmed that GPR is capable of detecting the internal reflections and that the presence of such scattering components could be highlighted changing the antennas offset. In particular, results show that the information that can be extracted relevantly changes with the antenna separation, demonstrating that this approach can provide better confidence in the discrimination and recognition process. The proposed bistatic approach aims at exploiting possible presence of internal structure beneath the target, which for landmines means the activation or detonation assemblies and possible internal material diversity, maintaining a limited acquisition effort. Such bistatic configurations are then included in a conceptual design of a highly flexible GPR system capable of searching for landmines across a large variety of terrains, at reasonably low cost and targeting operators safety

A tri-axial electromagnetic induction tool for hydraulic fracture diagnostics

The monitoring and diagnostics of induced fractures are important for the real-time performance evaluation of hydraulic fracturing operations. Previous electromagnetic (EM) based studies show that single backbone tri-axial induction logging tools are promising candidates for the real-time monitoring and diagnosis of fractures in uncased wells. To support the development of field deployable tools, the concept must be tested in experiments, in a controllable environment, before it is tested under field-like conditions. To this end, we have developed numerical tools which can simulate any wellbore environment while logging hydraulic fractures with the induction tool. We have designed and built a prototype induction tool and performed two sets of tests to compare with numerical simulation results. The computational and experimental setup consists of tri-axial transmitter and receiver coils in co-axial, co-planar and cross-polarized configurations. Both lab and shallow earth measurements are shown to be in good agreement with simulations for all examined cases. The average relative and maximum discrepancies of the measured signals from the simulated ones were lower than 3% and 10%, respectively. With the prototype tool, strong signals sensitive to the fracture’s surface area and dip-angle were measured in the co-axial coil configuration, while weaker signals sensitive to the fracture’s aspect ratio were observed in the co-planar configuration. Cross-polarized signals are also shown to be strong and sensitive to the fracture’s dip. Lastly, we resolved the detectable components of the measured signal tensor to obtain parameters for simplified fracture geometries. The inversion algorithm, a derivative free directional search model, uses an objective function defined as a combination of co-axial and cross-polarized signals from different tool spacing, and the function provides a well behaved global minimum. The robustness of the inversion algorithm is tested on synthetic data for single cluster fractures in a homogeneous and heterogeneous background electrical conductivity. All the effective model parameters for different cases, electrical conductivity, size and dip-angle, are shown to be recovered with good accuracy. We also evaluated the effect of neighboring fractures and suggested a multi-cluster inversion path which can recover the proppant distribution in a stage very accurately. Based on the numerical and experimental results we suggest a tool with specifications that can effectively recover far-field proppant distribution in the fractures.Petroleum and Geosystems Engineerin

Microwave scattering from surf zone waves

Wave breaking in the surf zone is an important forcing mechanism on the generation of nearshore currents and in the driving of sediment transport. At the same time, wave breaking can have significant spatial and temporal variability that needs to be accounted for in the description of nearshore processes. Remote sensors are best suited to collect wave breaking measurements due to their large footprint and synoptic capabilities, but in order to extract quantitative wave parameters a proper understanding of the imaging mechanisms is essential. Microwave sensors have been shown to be able to measure wave parameters in deep water, but in the surf zone many of the assumptions the algorithms are based upon do not hold. Additionally, the dynamics of breaking waves are different and may affect in a yet determined way the signal. This dissertation first intends to address an observational gap regarding surf zone microwave measurements. A novel combination of synchronous, large coverage marine radar, calibrated pulsed Doppler radar and video observations from a field site enable the analysis of the evolution and characteristics of the wave signature. The combined data sets yield superior discrimination rates between breaking and non-breaking waves. Discrimination also allows the study of the microwave scattering by source, where active breaking is separated from remnant foam and steepening waves. Results show that the backscattered power from breaking waves, specifically from the wave roller, is a several dB larger than that of foam and steepening waves and independent of the environmental conditions and polarization state. While similar results have been obtained for deep water waves and variety of scattering models have been proposed, it is found that none of the models can describe all the data. Additionally, most of the models neglect the roller morphology. Therefore, in the last section a scattering model is introduced, in which the roller is treated as a volume where a collection of water droplets embedded in air can scatter incoherently. Multiple interactions of the scattered fields between particles and the boundaries are also accounted for. Though the model formulation is complex, it depends on a few physical parameters (diameter, volume fraction, medium permittivity) and no calibration constants. Comparison against data shows that the model does a reasonable job in predicting the observed scattering levels, polarization response and grazing angle dependencies, although is not capable to reproduce the maximum scattered levels observed and predicts polarization ratios always less than unity