Current Green's Function Research Articles

Nonlinear Mutual Coupling Compensation Operator Design Using a Novel Electromagnetic Machine Learning Paradigm

We propose a technology that utilizes a unified electromagnetic machine learning (EM-ML) technique to mitigate the effect of mutual coupling in receiving antenna array configurations. The recently developed antenna current Green's function (ACGF) formalism is deployed to explicate the electromagnetic behavior of antennas in the form of an accurate digital signal processing (DSP) model, including mutual coupling interactions between radiators. A deep learning framework is devised and combined with the ACGF-based DSP model to design a novel nonlinear mutual coupling compensation operator providing higher decoupling capabilities in comparison to previously reported linear methods. A direction-of-arrival estimation application is presented to validate the proposed EM-ML system.

The antenna spacetime system theory of wireless communications

A general deterministic spacetime system theory of antennas suitable for the analysis and design of wireless communication links is rigorously developed using the recently introduced antenna current Green's function formalism. We provide the first complete derivation of the antenna spatio-temporal response to a delta source using only electromagnetic Green's functions, effectively eliminating all field and current distributions in the final expressions. While the theory works well in both space and time, it puts into sharper focus how the spatio-temporal structure of electromagnetic processes imposes restrictions on the signal processing capabilities of antenna systems by constraining the allowable mathematical form of the effective impulse response of the global wireless communication link. It is shown that the antenna current Green's functions of both the receive and transmit terminals, plus the propagation environment Green's functions, are the only quantities needed to obtain the single input–single output link response function in closed form. One of the results deduced from the theory is that an exact impulse response cannot be ascribed to an arbitrary antenna in general, but may be approximated for many applications. The theory can be deployed for future antenna systems research to boost up spectral efficiency (without increasing physical bandwidth) by directly incorporating electromagnetic knowledge into the design of the communication system's signal processing functions.

An Upper Bound on Antenna Near-Field Deviations Caused by Mutual Coupling for Applications in Optimization Design Methods

The present letter studies the impact of electromagnetic mutual coupling on the near fields of generic antenna systems. The main objective here is to derive an upper bound on near-fields deviations caused by mutual coupling. The method transforms the problem of near-field coupling from the near zone to the recently introduced antenna current Green's function defined on the antenna itself. Through this upper bound, the formulation presented here can be used to develop automatic algorithms for the design of coupled antenna systems with optimum near-field performance. Numerical examples involving linear wire arrays are given to demonstrate and confirm the approach proposed here.

ANALYSIS OF GENERIC NEAR-FIELD INTERACTIONS USING THE ANTENNA CURRENT GREEN'S FUNCTION

We investigate the problem of near field interactions with general antenna systems using the antenna current Green's function formalism recently proposed by the authors as a framework for the theoretical and computational analysis of the interaction problem. The paper focus is on conceptual and numerical issues related to the analysis of the electromagnetic response of generic devices to arbitrary illumination fields produced, for example, by nearby source or scattered by surrounding objects. We provide some method of moment numerical examples involving wire antenna systems substantiating the ACGF approach to the problem of near field excitations.

The Antenna Current Green's Function Formalism—Part I

This paper generalizes the familiar concept of system function in electrical engineering from the time domain (one dimension) to the spatial domain (three dimensions) for the analysis and design of arbitrary electromagnetic systems, including both radiating structures and circuits elements interacting with each other in the near-field zone. The key concept in the formalism is the antenna current Green's function, which can be considered an exact transfer function in space. We provide a conceptual view of electromagnetic systems framed in terms of three operational modes: Mode A is the excitation of a given antenna element by an externally applied field; Mode B is the radiation of the excited current into the medium surrounding the antenna; and finally Mode C as the receiving mode of antennas immersed in the near-field zone of a nearby antenna or circuit element or the far field of another antenna. It is shown that the antenna current Green's function of Mode A can be obtained in terms of a 2D tensor that depends on the local geometry of the general antenna surface. The core of Part I resides in a distributional construction of the antenna current Green's tensor and its relation to differential manifolds in order to deal with arbitrary antennas and to relate the local and global aspects of their geometrical shape to the electromagnetic performance of the system.

The Antenna Current Green's Function Formalism—Part II

This paper generalizes the familiar concept of system function in electrical engineering from the time domain (one dimension) to the spatial domain (three dimensions) for the analysis and design of arbitrary electromagnetic systems, including both radiating structures and circuits elements interacting with each other in the near-field zone. The key concept in the formalism is the antenna current Green's function, which can be considered an exact transfer function in space. We provide a conceptual view of electromagnetic systems framed in terms of three operational modes: Mode A is the excitation of a given antenna element by an externally applied field; Mode B is the radiation of the excited current into the medium surrounding the antenna; and finally Mode C as the receiving mode of antennas immersed in the near-field zone of a nearby antenna or circuit element or the far field of another antenna. It is shown that the antenna current Green's function of Mode A can be obtained in terms of a 2D tensor that depends on the local geometry of the general antenna surface. The core of Part I resides in a distributional construction of the antenna current Green's tensor and its relation to differential manifolds in order to deal with arbitrary antennas and to relate the local and global aspects of their geometrical shape to the electromagnetic performance of the system.

CrusDe: A plug-in based simulation framework for composable Crustal Deformation studies using Green's functions

CrusDe is a plug-in based simulation framework written in C/C++ for Linux platforms (installation information, download and test cases: http://www.grapenthin.org/crusde). It utilizes Green's functions for simulations of the Earth's response to changes in surface loads. Such changes could involve, for example, melting glaciers, oscillating snow loads, or lava flow emplacement. The focus in the simulation could be the response of the Earth's crust in terms of stress changes, changes in strain rates, or simply uplift or subsidence and the respective horizontal displacements of the crust (over time).Rather than implementing a variety of specific models, CrusDe approaches crustal deformation problems from a general formulation in which model elements (Green's function, load function, relaxation function, load history), operators, pre- and postprocessors, as well as input and output routines are independent, exchangeable, and reusable on the basis of a plug-in approach (shared libraries loaded at runtime). We derive the general formulation CrusDe is based on, describe its architecture and use, and demonstrate its capabilities in a test case.With CrusDe users can: (1) dynamically select software components to participate in a simulation (through XML experiment definitions), (2) extend the framework independently with new software components and reuse existing ones, and (3) exchange software components and experiment definitions with other users.CrusDe's plug-in mechanism aims for straightforward extendability allowing modelers to add new Earth models/response functions. Current Green's function implementations include surface displacements due to the elastic response, final relaxed response, and pure thick plate response for a flat Earth. These can be combined to express exponential decay from elastic to final relaxed response, displacement rates due to one or multiple disks, irregular loads, or a combination of these. Each load can have its own load history and crustal decay function.

A Methodology for Mutual Coupling Estimation and Compensation in Antennas

A simple methodology is presented for the estimation and compensation of mutual coupling in antenna systems of arbitrary geometries, including antenna arrays in the vicinity of scatterers. The methodology includes both theoretical and experimental schemes, while also, does not resort to assumptions often encountered in previous mutual coupling estimation approaches. In particular, our methodology uses a matrix representation for the antenna system and is based on a new concept, the antenna current Green's function which uses the recently proven inverse reciprocity theorem, or more intuitively, a relation of the transfer function for the transmitting mode of the antenna system to the corresponding transfer function for the receiving mode. Validation is performed by comparing calculated predictions to measurements and simulations of a practical antenna system as well as a two- and four-element array. An algorithm using matrix interpolation, that aims at exploiting the antenna transfer function, is also developed and experimentally demonstrated for practical array calibrations and coupling compensation techniques in array signal processing. The developed procedures are non-specific and can also be applied to a diversity of antenna systems and other complex scattering problems.

Gauge theory of topological phases of matter

We study the response of quantum many-body systems to coupling some of their degrees of freedom to external gauge fields. This serves to understand the current Green functions and transport properties of interacting many-body systems. Our analysis leads to a “gauge theory of states of matter” complementary to the well-known Landau theory of order parameters. We illustrate the power of our approach by deriving and interpreting the gauge-invariant effective actions of (topological) superconductors, 2D electron gases exhibiting the quantized Hall- and spin-Hall effect, 3D topological insulators, as well as axion electrodynamics. We also use the theory to elucidate the structure of surface modes in these systems.

A new wave approach for signal and noise modelling of microwave/mm-wave FET based on Green's function concept

Based on the active coupled line concept, a novel approach for calculating the noise performance of microwave/mm-wave field-effect transistors (FETs) is proposed. The voltage and current Green's functions are introduced to determine the correlation matrix of the FET. Some results using this approach have been presented for a microwave MESFET.

NUMERICAL ANALYSIS OF SOME SCATTERING PROBLEMS IN CONTINUOUS RANDOM MEDIUM - ABSTRACT

In this paper, we present numerical analysis for the following scattering problems: the radar cross-section, the backscattering enhancement, and the angular correlation function for waves scattered from practical targets embedded in random media. We assume perfect conducting targets with various cross-sections to study the effect of target configuration on the scattering problems. Also, we consider different random media with taking account of incident wave polarization. The scattering waves from conducting targets in random media can be estimated by a numerical method that solves the scattering problem as a boundary value problem. In this method, we use current generator and Green's function to obtain an expression for the scattering waves.

Three-dimensional Green's functions in anisotropic magneto-electro-elastic bimaterials

In this paper, we derive three-dimensional Green's functions in anisotropic magneto-electro-elastic full space, half space, and bimaterials based on the extended Stroh formalism. While in the full space, the Green's functions are obtained in an explicit form, those in the half space and bimaterials are expressed as a sum of the full-space Green's function and a Mindlin-type complementary part, with the latter being evaluated in terms of a regular line integral over [0,π]. Despite the complexity involved, the current Green's function expressions are surprisingly simple. Furthermore, the piezoelectric, piezomagnetic, and purely elastic Green's functions can all be obtained from the current Green's functions by setting simply the appropriate material coefficients to zero. A special material case, to which the extended Stroh formalism cannot be applied directly, has also been identified.Simple numerical examples are presented for Green's functions in full space, half space, and bimaterials with fully coupled and uncoupled anisotropic magneto-electro-elastic material properties. For given material properties and fixed source and field points, the effect of magneto-electro-elastic coupling on the Green's function is discussed. In particular, we observed that magneto-electro-elastic coupling could significantly alter the magnitude of certain Green's displacement and stress components, with difference as high as 45% being noticed. This result is remarkable and should be of great interest in the material analysis and design.

Translational invariance of the density and current temperature Green’s functions for an electron gas in a uniform magnetic field

In the aim of providing a theoretical basis for conventional calculation, the translational invariance of both the density temperature Green's function and the current temperature Green's function is proved for an interacting electron gas in a uniform magnetic field. The proof is based on the previously proposed nonperturbative canonical method [Phys. Rev. B 50, 18 640 (1994)].

Uma Contribuição ao Estudo da Interação Corrente-onda Progressiva

A mathematical model to evaluate the resultant interaction of a progressive wave, incident to a uniform current is presented and its effects analysed. The model is based on the potential theory wich assumes small amplitude waves, so that the potential velocity can be treated as the addition of the several elementary potentials. For the description of the interaction of motion between waves and current Green's function tecnique is utilized. The solution of the problem is achieved by applying the boundary conditions on the nortex surface. An algorithm is carried out to show the form of the surface in the internal and external regions of the current, and for numeri cally avaluation of ghe model.