Ian Jeffrey

Derivation and comparison of SAR and frequency-wavenumber migration within a common inverse scalar wave problem formulation

Two common Fourier imaging algorithms used in ground penetrating radar (GPR), synthetic aperture radar (SAR), and frequency-wavenumber (F-K) migration, are reviewed and compared from a theoretical perspective. The two algorithms, while arising from seemingly different physical models: a point-scatterer model for SAR and the exploding source model for F-K migration, result in similar imaging equations. Both algorithms are derived from an integral equation formulation of the inverse scalar wave problem, which allows a clear understanding of the approximations being made in each algorithm and allows a direct comparison. This derivation brings out the similarities of the two techniques which are hidden by the traditional formulations based on physical scattering models. The comparison shows that the approximations required to derive each technique from the integral equation formulation of the inverse problem are nearly identical, and hence the two imaging algorithms and physical models are making similar assumptions about the solution to the inverse problem, thus clarifying why the imaging equations are so similar. Sample images of landmine-like targets buried in sand are obtained from experimental GPR data using both algorithms.

A Three-Dimensional Precorrected FFT Algorithm for Fast Method of Moments Solutions of the Mixed-Potential Integral Equation in Layered Media

A three-dimensional pre-corrected fast Fourier transform (PFFT) algorithm for the rapid solution of the full-dyadic Michalski-Zhengs mixed potential integral equation is presented. The integral equation is discretized with the Rao-Wilton-Glisson (RWG) method of moments. Handling the method of moments interactions with the dyadic kernel is simplified via representation of the RWG functions in terms of barycentric shape functions. The proposed three-dimensional precorrected FFT method distributes two-dimensional FFT grids nonuniformly along the direction of stratification according to conductor locations within the layers. For P two-dimensional FFT grids each with an average of Np associated triangular elements the method exhibits O(P 2 Np logNp) computational complexity and O(P Np) memory usage. The low-frequency breakdown of the integral equation is eliminated via loop-tree decomposition. A unique combination of O(N logN) computational complexity, fully three-dimensional boundary-element modeling in layered substrates, and full-wave modeling from dc to multi-gigahertz frequencies makes the algorithm particularly useful for characterizing large interconnect networks embedded in multilayered substrates. The method is implemented as the electromagnetic solver in Cadences Virtuoso RF Designer software.

A Monte Carlo Method for Simulating Scattering From Sea Ice Using FVTD

A scattering model based on a Monte Carlo method and the finite-volume time-domain (FVTD) method has been created for sea ice scattering simulations. Statistical methods were used to generate a Gaussian-distributed randomly rough surface. The Polder-Van Santen-de Loor (PVD) model was used to estimate the sea ice dielectric values with inputs based upon actual measured physical variables obtained during field-based experiments and well-known parameterizations. Scattering simulations were performed through an application of the scattered-field (SF) formulation invoked in an FVTD computational engine. Simulated SFs were compared with C-band scatterometer measurements and showed good agreement for copolarized signals in a series of case studies. The developed simulation method has the potential to be used for a variety of sea ice types under different physical conditions.

Hardware invariant protocol disruptive interference for 100BaseTX Ethernet communications

In this paper, we introduce a new concept that we refer to as hardware invariant protocol disruptive interference (HIPDI). Such interference would pose a severe threat as intentional EMI to the corresponding protocol for which it was designed. In this paper, we consider only the 100BaseTX Ethernet protocol over UTP CAT-5 cable which is used extensively in local-area networks. We show that low power, narrowband, differential-mode voltage levels on a 100BaseTX Ethernet twisted-pair can seriously degrade network throughput independent of the physical features of the network or the protocol interpreter hardware. Moreover, we show that the required parameters of disruptive interference can be derived from the protocol itself using a concept we call hardware aperture. The experimental results reported herein indicate that creating such interference is practically feasible and therefore, is a possible threat to existing communication networks.

Grain bin monitoring via electromagnetic imaging

Feasibility of using electromagnetic waves to monitor stored grain was investigated.Successful synthetic analysis of a 2500 bushels grain bin was performed.A measurement device to find the electrical properties of bulk grain was built and successfully tested.A lab-scale measurement system capable of detecting spoilage region within grain was built and successfully tested.Results show the feasibility of applying EMI to grain bin monitoring. Stored grain monitoring is an important post-harvest stage of the food production chain. Grains are usually stored in large metal containers referred to as bins or silos. During storage, there is a possibility for grain to spoil and become unusable. Therefore, monitoring of grain bins is essential to detect conditions leading to spoilage within the bin. Most current grain bin monitoring techniques lack sensitivity as they require conditions leading to spoilage to surpass a certain limit before detection is possible, and consequently a large amount of stored grain is lost during monitored storage. This paper presents the advances in developing a novel grain-monitoring technique using electromagnetic imaging, a modality that can provide global, quantitative images of grain properties throughout the bin. Side-mounted antennas illuminate the contents of the bin and a set of receivers measures the electromagnetic energy within the bin at discrete locations. Using these measurements an optimization algorithm attempts to reconstruct the contents of the bin - herein a finite-element contrast source inversion (FEM-CSI) algorithm was used. The result is a global map of the electrical properties of the grain throughout the bin. In this work we first present a synthetic validation of the proposed method for a model of a full scale hopper bin using simulations to produce the electromagnetic field data. Next, a scaled experimental system was used to collect data from grain that contained regions of induced contamination. This data was used to produce images that show the applicability of the method in practice. Results suggest that this technology has potential to provide farmers with a reliable and robust method to remotely monitor stored grain, preserving stored food resources and increasing their revenue.

On the Equivalence of RWG Method of Moments and the Locally Corrected Nyström Method for Solving the Electric Field Integral Equation

The first-order locally corrected Nyström (LCN) method for the electric field integral equation is modified to ensure continuity of the current between triangular elements of the mesh. Rao-Wilton-Glisson (RWG) basis functions are used to create a conversion matrix from the LCN representation of the current to the RWG method-of-moments (MoM) representation of the current in order to enforce continuity of current between adjacent triangular flat patches. Benefits of the method are two fold: first, it provides 4 × reduction in degrees of freedom and removes unacceptable error levels in first-order LCN implementations, second, the method can be viewed as a point-based discretization of the RWG MoM offering improved efficiency in its acceleration with the fast multipole algorithm.

Quantifying the impact of dissimilar HPV vaccination uptake among Manitoban school girls by ethnicity using a transmission dynamic model

BACKGROUND Gardasil, a human papillomavirus (HPV) vaccine, began among grade 6 girls in Manitoba, Canada in 2008. In Manitoba, there is evidence that First Nations, Métis, and Inuit women (FNMI) have higher HPV prevalence, lower invasive cervical cancer (ICC) screening, and higher ICC incidence than all other Manitoban (AOM) women. We developed a mathematical model to assess the plausible impact of unequal vaccination coverage among school girls on future cervical cancer incidence. METHODS We fit model estimated HPV prevalence and ICC incidence to corresponding empirical estimates. We used the fitted model to evaluate the impact of varying levels of vaccination uptake by FNMI status on future ICC incidence, assuming cervical screening uptake among FNMI and AOM women remained unchanged. RESULTS Depending on vaccination coverage, estimated ICC incidence by 2059 ranged from 15% to 68% lower than if there were no vaccination. The level of cross-ethnic sexual mixing influenced the impact that vaccination rates among FNMI has on ICC incidence among AOM, and vice versa. The same level of AOM vaccination could result in ICC incidence that differs by up to 10%, depending on the level of FNMI vaccination. Similarly, the same level of FNMI vaccination could result in ICC incidence that differs by almost 40%, depending on the level of AOM vaccination. CONCLUSIONS If we are unable to equalize vaccination uptake among all school girls, policy makers should prepare for higher levels of cervical cancer than would occur under equal vaccination uptake.

Error Controllable Solutions of Large-Scale Problems in Electromagnetics: MLFMA-Accelerated Locally Corrected Nyström Solutions of CFIE in 3D [Open Problems in CEM]

This work provides an overview of a parallel, high-order, error-controllable framework for solving large-scale scattering problems in electromagnetics, as well as open problems pertinent to such solutions. The method is based on the higher-order locally corrected Nystrom (LCN) discretization of the combined-field integral equation (CFIE), accelerated with the error-controlled Multi-Level Fast Multipole Algorithm (MLFMA). Mechanisms for controlling the accuracy of calculations are discussed, including geometric representation, stages of the locally corrected Nystrom method, and the MLFMA. Also presented are the key attributes of parallelization for the developed numerical framework. Numerical results validate the proposed numerical scheme by demonstrating higher-order error convergence for smooth scatterers. For the problem of scattering from a sphere, the developed numerical solution is shown to have the ability to produce a solution with a maximum relative error of the order 10-9. Open-ended problems, such as treatment of general scatterers with geometric singularities, construction of well-conditioned operators, and current challenges in development of fast iterative and direct algorithms, are also discussed.

An Efficient Scattered-Field Formulation for Objects in Layered Media Using the FVTD Method

A technique for efficiently simulating the scattering from objects in multilayered media is presented. The efficiency of the formulation comes from the fact that the sources for the scattered fields (SFs) only occur at the inhomogeneities and, therefore, the SFs impinging on the boundaries are more easily absorbed. To demonstrate the technique, a 1-D-finite-difference time-domain solution to the plane-wave propagation through a multilayered medium is used as an incident-field source for an SF formulation of the finite-volume time-domain method. Practical aspects of the application are discussed and numerical examples for scattering from canonical objects are presented to show the validity of the proposed technique. The simulation scheme described herein can be used for simulations of geophysical media with appropriate specifications of the dielectric properties of the media and the inhomogeneities.

The Barnes–Hut Hierarchical Center-of-Charge Approximation for Fast Capacitance Extraction in Multilayered Media

The Barnes-Hut algorithm is widely used in astrophysics for solving large gravitational N -body problems using O(N logN) time and memory. This reduction in computational cost is achieved by a hierarchical application of the classical center-of-mass approximation. As both gravitational and electrostatic potentials are subject to a 1/R dependence, the Barnes-Hut algorithm is also a natural choice for rapidly evaluating interactions between charged particles. The contribution of this paper is an extension of the Barnes-Hut hierarchical clustering to the acceleration of charge interactions in stratified media. We derive and validate a closed-form expression for the shift of the center-of-charge location induced by the physical inhomogeneities and show that proper positioning of the center-of-charge ensures O(1/R 3) error decay in the field approximation. Hierarchical applications of the proposed clustering approximation is demonstrated for the construction of O(N logN) method-of-moment based capacitance extractors.