Classification, identification, and modeling of unexploded ordnance in realistic environments

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 205-218).Recovery of buried unexploded ordnance (UXO) is very slow and expensive due to the high false alarm rate created by clutter. Electromagnetic induction (EMI) has been shown to be a promising technique for UXO detection and discrimination. This thesis uses the EMI response of buried targets to identify or classify them. To perform such discrimination, accurate forward models of buried UXO are needed. This thesis provides a survey of existing target models: the dipole model, the spheroid model, and the fundamental mode model. Then the implementation of a new model, the spheroidal mode model, is described and validated against measurements of a UXO. Furthermore, an in-depth study of the effects of permeable soil, modeled as a permeable half space, is presented. This study concludes that the discontinuity created by the air to permeable soil interface produces minimal effect in the response of a buried object. The change is limited to a magnitude shift of the real portion of the EMI response and can be reproduced by superposition of a permeable half space response on the response of the same object in frees pace. Accurate soil modeling also allows one to invert for soil permeability values from measured data if such data are in known units. However, the EMI sensor used in this study provides measurements in consistent but unknown units. Furthermore, the instrument is from a third party and is proprietary. Therefore, this thesis describes the development of a non-invasive method to model and calibrate non-adaptive instruments so that all measurements can be converted into units consistent with modeled data. This conversion factor is shown to be a constant value across various conditions, thus demonstrating its validity.(cont.) Given that now a more complete model of the measurable response of a buried UXO is implemented, this study proceeds to demonstrate that EMI responses from UXO and clutter objects can be used to identify the objects through the application of Differential Evolution (DE), a type of Genetic Algorithm. DE is used to optimize the parameters of the UXO fundamental mode model to produce a match between the modeled response and the measured response of an unknown object. When this optimization procedure is applied across a library of models for possible UXO, the correct identity of the unknown object can be ascertained because the corresponding library member will produce the closest match. Furthermore, responses from clutter objects are shown to produce very poor matches to library objects, thus providing a method to discriminate UXO from clutter. These optimization experiments are conducted on measurements of UXO in air, UXO in air but obscured by clutter fragments, buried UXO, and buried UXO obscured by clutter fragments. It is shown that the optimization procedure is successful for shallow buried objects obscured by light clutter contributing to roughly 20 dB SNR, but is limited in applicability towards very deeply buried UXO or those in dense clutter environments. The DE algorithm implemented in this study is parallelized and the optimization results are computed with a multi-processor supercomputer. Thus, the computational requirement of DE is a considerable drawback, and the method cannot be used for real time, on-site inversion of measured UXO data. To address this concern, a different approach to inversion is also implemented in this study. Rather than identifying particular UXO, one may do a discrimination between general UXO and general clutter items. Previous work has shown that the expansion coefficients of EMI responses in the spheroidal coordinate system can uniquely characterize the corresponding targets.(cont.) Therefore, these coefficients readily lend themselves for use as features by which objects can be classified as likely to be UXO or unlikely to be UXO. To do such classification, the relationship between these coefficients and the physical properties of UXO and clutter, such as differences in size or body-of-revolution properties or material heterogeneity properties, must be found. This thesis shows that such relationships are complex and require the use of the automated pattern recognition capability of machine learning. Two machine learning algorithms, Support Vector Machines and Neural Networks, are used to identify whether objects are likely to be UXO. Furthermore, the effects of small diffuse clutter fragments and uncertainty about the target position are investigated. This discrimination procedure is applied on both synthetic data from models and measurements of UXO and clutter. It is found that good discrimination is possible for up to 20 dB SNR. But the discrimination is sensitive to inaccurate estimations of a target's depth. It is found that the accuracy must be within a 10 cm deviation of an object's true depth. The general conclusion forwarded by this work is that while increasingly accurate discrimination capabilities can be produced through more detailed forward modeling and application of robust optimization and learning algorithms, the presence of noise and clutter is still of great concern. Minimization or filtering of such noise is necessary before field deployable discrimination techniques can be realized.by Beijia Zhang.Ph.D

Classification of Metallic Targets Using a Walk-Through Metal Detection Portal

Metal detectors have been used for a long time for treasure hunting, security screening, and finding buried objects such as landmines or unexploded ordnance. Walk-through metal detection (WTMD) portals are used for making sure that forbidden or threatening metallic items, such as knives or guns, are not carried into secure areas at critical locations such as airports, court rooms, embassies, and prisons.The 9/11 terrorist act has given rise to stricter rules for aviation security worldwide, and the ensuing tighter security procedures have meant that passengers face more delays at airports. Moreover, the fear of terrorism has led to the adoption of security screening technology in a variety of places such as railway and coach stations, sports events, malls, and nightclubs.However, the current WTMD technology and scanning procedures at airports require that all metallic items be removed from clothing prior to scanning, causing inconvenience. Furthermore, alarms are triggered by innocuous items such as shoe shanks and artificial joints, along with overlooked items such as jewellery and belts. These lead to time- consuming, manual pat-down searches, which are found inconvenient, uncomfortable, and obtrusive by some.Modern WTMD portals are very sensitive devices that can detect items with only small amounts of metal, but they currently lack the ability to further classify the detected item. However, if a WTMD portal were able to classify objects reliably into, e.g., “knives”, “belts”, “keys”, the need for removing the items prior to screening would disappear, enabling a paradigm shift in the field of security screening.This thesis is based on novel research presented in five peer-reviewed publications. The scope of the problem has been narrowed down to a situation in which only one metallic item is carried through the portal at a time. However, the methods and results presented in this thesis can be generalized into a multi-object scenario. It has been shown that by using a WTMD portal and the magnetic polarisability tensor, it is possible to accurately distinguish between threatening and innocuous targets and to classify them into 10 to 13 arbitrary classes. Furthermore, a data library consisting of natural walk-throughs has been collected, and it has been demonstrated that the walk-through data collected with the above portal are subject to phenomena that might affect classification, in particular a bias and the so-called body effect. However, the publications show that, by using realistic walk-through data, high classification accuracy can be maintained regardless of the above problems. Furthermore, a self-diagnostics method for detecting unreliable samples has also been presented with potential to significantly increase classification accuracy and the reliability of decision making.The contributions presented in this thesis have a variety of implications in the field of WTMD-based security screening. The novel technology offers more information, such as an indication of the probable cause of the alarm, to support the conventional screening procedure. Moreover, eliminating the need for removing all metallic items prior to screening enables design of new products for scenarios such as sports events, where conventional screening procedures might be inconvenient, creating thus new business possibilities for WTMD manufacturing companies.The positive results give rise to a variety of future research topics such as using wideband data, enabling simultaneous classification of multiple objects, and developing the portal coil design to diminish signal nonlinearities. Furthermore, the ideas and the basic principles presented in this thesis may be applied to other metal detection applications, such as humanitarian demining

Thermal dosimetry for bladder hyperthermia treatment. An overview.

The urinary bladder is a fluid-filled organ. This makes, on the one hand, the internal surface of the bladder wall relatively easy to heat and ensures in most cases a relatively homogeneous temperature distribution; on the other hand the variable volume, organ motion, and moving fluid cause artefacts for most non-invasive thermometry methods, and require additional efforts in planning accurate thermal treatment of bladder cancer. We give an overview of the thermometry methods currently used and investigated for hyperthermia treatments of bladder cancer, and discuss their advantages and disadvantages within the context of the specific disease (muscle-invasive or non-muscle-invasive bladder cancer) and the heating technique used. The role of treatment simulation to determine the thermal dose delivered is also discussed. Generally speaking, invasive measurement methods are more accurate than non-invasive methods, but provide more limited spatial information; therefore, a combination of both is desirable, preferably supplemented by simulations. Current efforts at research and clinical centres continue to improve non-invasive thermometry methods and the reliability of treatment planning and control software. Due to the challenges in measuring temperature across the non-stationary bladder wall and surrounding tissues, more research is needed to increase our knowledge about the penetration depth and typical heating pattern of the various hyperthermia devices, in order to further improve treatments. The ability to better determine the delivered thermal dose will enable clinicians to investigate the optimal treatment parameters, and consequentially, to give better controlled, thus even more reliable and effective, thermal treatments

NASA SBIR abstracts of 1991 phase 1 projects

The objectives of 301 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1991 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 301, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1991 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

Electromagnetic Composites: from Effective Medium Theories to Metamaterials

Electromagnetic (EM) composites have stimulated tremendous fundamental and practical interests owing to their flexible electromagnetic properties and extensive potential engineering applications. Hence, it is necessary to systematically understand the physical mechanisms and design principles controlling EM composites. In this tutorial, we first provide an overview of the basic theory of electromagnetism about electromagnetic constitutive parameters that can represent the electromagnetic properties of materials. We show how this corpus allows a consistent construction of effective medium theories and allows for numerical simulation of EM composites to deal with structure-property relationships. We then discuss the influence of spatial dispersion of shaped inclusions in the material medium on the EM properties of composites, which has not been systematically illustrated in the context of this interdisciplinary topic. Next, artificial composites or metamaterials with peculiar properties not readily available in nature are highlighted with particular emphasis on the control of the EM interaction with composites. We conclude by discussing appropriate methods of electromagnetic measurement and practical aspects for implementing composites for specific applications are described. Overall, this tutorial will serve the purpose of introducing the basics and applications of electromagnetic composites to newcomers in this field. It is also anticipated that researchers from different backgrounds including materials science, optics, and electrical engineering can communicate to each other with the same language when dealing with this interdisciplinary subject and further push forward this advancement from fundamental science to technological applications.Comment: 63 pages, 20 figure

Modeling EMI Resulting from a Signal Via Transition Through Power/Ground Layers

Signal transitioning through layers on vias are very common in multi-layer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current must switch from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in noise on the power bus that can lead to signal integrity, as well as EMI problems. Numerical methods, such as the finite-difference time-domain (FDTD), Moment of Methods (MoM), and partial element equivalent circuit (PEEC) method, were employed herein to study this problem. The modeled results are supported by measurements. In addition, a common EMI mitigation approach of adding a decoupling capacitor was investigated with the FDTD method

Theory, Modelling, and Applications of Advanced Electromagnetic Materials

PhDA multitude of recent work predicts many novel concepts based on the availability of non-natural materials; some prominent examples include transformation optics (TO) and perfect lens. The interest in this eld has grown dramatically due to spec- ulated possibility to allow for continuously varying material properties to steer the incident wave at will, such as for the TO. The posed challenges for their realisation include the limitations of numerical modelling and manufacturing techniques. A de- sign scheme has been proposed, in this thesis, for composite materials: the desired electromagnetic properties of composites can be engineered by judiciously varying the volume fraction of the inclusion-to-host materials, by manipulating the geomet- ric arrangement of inclusions, or by altering their dielectric contrast. The analysis of the homogenised response of the designed materials at macro-scale requires effective medium modelling techniques. The existing effective medium approximation tech- niques have been discussed, and their pros and cons outlined. A homogenization scheme has been introduced that is based on the interaction of the incident wave and the nanoparticles at the micro-scale, which further requires efficient electromagnetic modelling. The conventional nanoparticle modelling techniques, as well as the state of the art, have been reviewed and a dipole-moment-based method to efficiently solve modern nanoparticle-based electromagnetic problems has been outlined. The appli- cability of the proposed scheme has been demonstrated by employing it to design various EM devices. An improved permittivity extraction scheme has been proposed for the homogenization of composites. Unlike classical homogenization schemes, the extracted parameters, using the proposed technique, follow the relation between the real and imaginary parts, that is, Kramers-Kronig relations. Several random and periodic structures have been simulated for the purpose of extracting the ef- fective electromagnetic properties and interpreting the results so as to establish a connection between them

Microscopic Theory of Linear Response in Amorphous Materials

This thesis provides an analytical and systematic framework from first-principles to study dielectric and mechanical properties of disordered materials, as well as non-centrosymmetric crystals. The Caldeira-Leggett Hamiltonian opens a route to the (both Markovian and nonMarkovian) fluctuation-dissipation theorem (FDT) and gives rise to the generalised Langevin equation (GLE) in classical dynamics. In the first place, I extend the GLE and the corresponding FDT for more general cases where both the tagged particle and bath oscillators respond to an external oscillatory field. This is the example of a charged or polarisable particle immersed in a bath of other particles that are also charged or polarisable, under an external AC electric field. Being linked to the vibrational density of states (VDOS), the dielectric function calculated based on the GLE is compared with experimental data for the paradigmatic case of molecular glasses: glycerol and Freons 112 & 113, around and above the glass transition temperature, Tg. Moving to the mechanical aspect, the theory of nonaffine lattice dynamics is able to describe the various relaxation processes in the linear viscoelastic response of metallic glasses. In particular, to understand universal properties of relaxation, the VDOS obtained in simulations, or in experiments, is substituted into the model. The nonaffine contribution to elasticity is also important for the pre-stressed/stretched harmonic networks. In order to give an insight on nonaffinity, I compute static elastic constants of α-quartz, taking into account the long-range Coulomb interaction. The nonaffine (softening) correction is found very large, such that the overall elastic constants are at least 3-4 times smaller than the affine Born-Huang estimate. Finally, I formulate the analytical expression of the dynamical structure factor by averaging over all quenched disorder along the acoustic branch, which stores the information of phonon transport in disordered materials. The Rayleigh scattering may be enhanced by a logarithmic factor in an intermediate range of wavenumber. I present a tensorial replica field-theoretic derivation based on heterogeneous or fluctuating elasticity, which suggests that long-range spatial correlations (in power-law decay) of elastic constants (or stress tensors) might be responsible for the logarithmic enhancement to Rayleigh scattering of phonons in amorphous solids.CSC-Cambridge scholarshi

Electromagnetic Interference and Compatibility

Recent progress in the fields of Electrical and Electronic Engineering has created new application scenarios and new Electromagnetic Compatibility (EMC) challenges, along with novel tools and methodologies to address them. This volume, which collects the contributions published in the “Electromagnetic Interference and Compatibility” Special Issue of MDPI Electronics, provides a vivid picture of current research trends and new developments in the rapidly evolving, broad area of EMC, including contributions on EMC issues in digital communications, power electronics, and analog integrated circuits and sensors, along with signal and power integrity and electromagnetic interference (EMI) suppression properties of materials

Inverse problems in electromagnetics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Vita.Includes bibliographical references (p. 155-164).Two inverse problems in electromagnetics are investigated in this thesis. The first is the retrieval of the effective constitutive parameters of metamaterials from the measurement of the reflection and the transmission coefficients. A robust method is proposed for the retrieval of metamaterials as isotropic media, and four improvements over the existing methods make the retrieval results more stable. Next, a new scheme is presented for the retrieval of a specific bianisotropic metamaterial that consists of split-ring resonators, which signifies that the cross polarization terms of the metamaterial are quantitatively investigated for the first time. Finally, an optimization approach is designed to achieve the retrieval of general bianisotropic media with 72 unknown parameters. The hybrid algorithm combining the differential evolution (DE) algorithm and the simplex method steadily converges to the exact solution. The second inverse problem deals with the detection and the classification of buried metallic objects using electromagnetic induction (EMI). Both the exciting and the induced magnetic fields are expanded as a linear combination of basic modes in the spheroidal coordinate system. Due to the orthogonality and the completeness of the spheroidal basic modes, the scattering coefficients are uniquely determined and are characteristics of the object.(cont.) The scattering coefficients are retrieved from the knowledge of the induced fields, where both synthetic and measurement data are used. The ill-conditioning issue is dealt with by mode truncation and Tikhonov regularization technique. Stored in a library, the scattering coefficients can produce fast forward models for use in pattern matching. In addition, they can be used to train support vector machine (SVM) to sort objects into generic classes.by Xudong Chen.Ph.D