Characterization of different shape objects using EM pulse for several different scenarios

Abstract

This thesis presents a thorough investigation into the interaction of electromagnetic pulses (EMP) with various shaped objects, with a particular focus on computational method for characterization. The comprehensive dissertation is anchored in the principles of electromagnetics, with Maxwell's equations serving as the foundation for formulating the theoretical framework essential for analyzing radiation and diffraction phenomena. Initially, the study delves into Maxwell's equations within the context of a uniform dielectric medium characterized by permittivity and permeability. These equations are crucial for describing the behavior of electric and magnetic fields in various media and are presented in their frequency domain forms. The main framework of the thesis revolves around the formulation of problems related to EM radiation and diffraction. By applying the curl operator to Maxwell's equations, the study derives expressions that elucidate how electromagnetic fields propagate and interact with different objects. The thesis meticulously examines the boundary conditions at the surfaces of different objects, essential for deriving the integral equations governing radiation and scattering phenomena. A significant portion of the thesis is devoted to the derivation of functions, which are indispensable for solving the integral equations related to EM problems. These functions assist in characterizing the fields generated by sources in different configurations. The thesis also details the computation of electric and magnetic vector potentials, which are pivotal in understanding how EM fields can be represented and manipulated mathematically. The integral equations, which form the basis for many of the computational methods used in the study, are carefully derived and explained. These foundational steps are critical as they set the stage for the complex simulations and analyses that follow, ensuring that the theoretical underpinnings are robust and reliable. In examining the scattering of EM pulses, the thesis employs various boundary conditions to ensure accurate simulation of the scenarios. These conditions include the continuity of tangential components of electric and magnetic fields across interfaces, which is critical for solving the resulting linear algebraic equations. The inversion of these equations provides the amplitudes of the unknown fields, facilitating the calculation of fields both inside and outside the objects. The handling of boundary conditions is crucial for ensuring the physical accuracy of the simulations, and the thesis provides a detailed account of how these conditions are implemented. This meticulous approach ensures that the simulations reflect realistic physical behaviors, which is paramount for the reliability of the results. The thesis progresses to apply these theoretical constructs to practical problems involving different shapes of objects. The Method of Auxiliary Sources (MAS) is extensively utilized for this purpose. MAS is an efficient computational technique that approximates the scattered fields by placing hypothetical sources around the object. This method's efficacy is particularly highlighted in its application to scenarios where objects need to be rendered invisible over a broad frequency range—a novel extension of MAS within this thesis. Numerical research explores the potential of time domain analysis in addition to frequency domain methods. Moreover, the research extends to shape reconstruction of objects using EM pulses. By analyzing the frequency response of the dielectric objects to EM pulses, the thesis provides a comprehensive characterization of their scattering properties. This dual approach allows for a more detailed understanding of the interactions between EM pulses and objects, offering insights that are not readily apparent from time-domain analysis alone. The frequency-domain analysis also helps identify resonant frequencies at which the scattering characteristics are particularly pronounced, valuable for applications in sensing and detection technologies. In practical applications, the thesis demonstrates the feasibility of using the MAS method for real-time object characterization. The research includes developing algorithm that can quickly process Gaussian EMP signal to reconstruct object shapes and determine material properties. This algorithm is tested using results generated from numerical simulations. The results show that the MAS-based algorithms can accurately and efficiently characterize objects in real-time, making them suitable for deployment in field applications where rapid assessment is required. The thesis delves into shape reconstruction using time-domain analysis, which involves measuring the time delay between the first and second echoes of an incident EMP to determine the object's dimensions. This method proves particularly accurate for objects with low ellipticity. When the object's permittivity is known, both the shape and dimensions can be accurately reconstructed; otherwise, only the shape can be inferred. This technique is vital for non-invasive applications such as medical imaging, where precision and safety are crucial. The research demonstrates how time-domain analysis can significantly enhance shape reconstruction accuracy, offering a promising avenue for further research and practical applications. The thesis also explores the practical implications of its findings, particularly in the field of radar and stealth technology. By optimizing the parameters of objects such as elliptical cylinders and dielectric ellipsoids with high ellipticity, the MAS method effectively minimizes the scattering echoes, making the object less detectable by radar. This has significant implications for military and defense applications, where reducing the radar cross-section of objects is of paramount importance. The thesis provides detailed case studies of how these principles can be applied to real-world scenarios, enhancing the understanding of EMP interactions with various materials and shapes. The case studies are comprehensive, covering different dielectric properties and configurations, and provide valuable insights into the practical applications of the MAS method. One of the other significant applications of the MAS method in this research is the reduction of front echo in Gaussian EMP scattering from 3D dielectric ellipsoids with high ellipticity. By optimizing the parameters of the ellipsoids, such as size and dielectric permittivity, the MAS method effectively minimizes the scattering echoes, making the object less detectable by radar. This has important implications for military and defense applications, particularly in stealth technology and missile design. The thesis presents detailed numerical results to demonstrate the efficacy of the MAS method. Simulations were performed using a specially designed software suite, and the results were visualized to show the electric field amplitudes for dielectric ellipsoids. These results highlight significant reductions in front echo, validating the proposed method's practical utility. Numerical results form a substantial part of the thesis, showcasing the practical applications of the derived formulations. These results not only validate the theoretical models but also demonstrate the capability of the computational method to handle complex scattering problems. The numerical results are presented in a series of detailed graphs and tables, illustrating the effectiveness of the MAS method in reducing computational complexity while maintaining high accuracy. The results highlight the precision with which the MAS method can model the scattering behavior, making it a powerful tool for various applications. Also, the advantages of MAS are demonstrated through a variety of numerical experiments and comparisons with other methods, such as the Method of Moments (MoM) and the Finite-Difference Time- Domain (FDTD) method. These comparisons are essential as they validate the MAS method against established techniques, showcasing its advantages in terms of computational efficiency and accuracy. In summary, this thesis offers a comprehensive analysis of EMP interactions with different shaped objects. It combines rigorous theoretical formulations with advanced computational method, providing significant contributions to the field of electromagnetic research. The methods developed and the numerical results obtained have potential applications in areas such as radar detection, stealth technology, telecommunications, medical imaging, geoscience and material science. The study not only advances technological capabilities but also enriches scientific understanding of electromagnetic interactions with complex objects. The detailed explanations, extensive numerical simulations, and practical applications presented in the thesis make it a valuable resource for researchers and practitioners in the field of electromagnetics. The findings and methodologies presented in this thesis have the potential to influence future research and development in the field, offering new insights and tools for tackling complex electromagnetic problems.