Electromagnetic radiation is discussed from the analytical perspective that charge acceleration i... more Electromagnetic radiation is discussed from the analytical perspective that charge acceleration is necessary to produce an electromagnetic field that falls off with distance R as 1/R from a radiating source. The discussion begins with the Lienard-Wiechert potentials that show a radiation field is proportional to charge acceleration. A graphical construction known as the E-field kink model is discussed as a second way to illustrate the connection between charge acceleration and radiation. A generic wire object is introduced as a means to demonstrate the various ways that charge acceleration and subsequent radiation will occur. These features include: exciting sources; wire-radius discontinuities; impedance loads; wire bends; wire curvature; open ends; and straight-wire sections. Each of these is explored in various levels of detail in the discussion that follows which are illustrated with numerous computed examples using the frequency domain model NEC (Numerical Electromagnetics Code) and the time-domain model TWTD (Thin-Wire Time Domain). A technique called FARS (Far-field Analysis of Radiation Sources) is also introduced as a means of showing quantitatively where radiation originates from the generic wire model.
Abstract: The design of an experiment is given which employs an inverted coaxial diode geometry t... more Abstract: The design of an experiment is given which employs an inverted coaxial diode geometry to investigate absorption of electromagnetic radiation below and above the plasma frequency. Data obtained when a pure electron stream is introduced into the ...
Skip to main content. CERN Logo CERN Document Server. Related links. CDS; Indico; Library; Bullet... more Skip to main content. CERN Logo CERN Document Server. Related links. CDS; Indico; Library; Bulletin; EDMS. Main navigation links: Search; Submit; Help; Your CDS: Your alerts; Your baskets; Your searches. login. Home > Computational electromagnetics. ...
In the ACES 2015 meeting, the author presented a method for synthesizing array patterns using a m... more In the ACES 2015 meeting, the author presented a method for synthesizing array patterns using a matrix that relates element excitations with the lobe maxima of a desired pattern [1]. The method is applied here to the synthesis of both a Dolph-Chebyshev scanning array and one that has nonuniformly spaced elements.
Proceedings of the 32nd Midwest Symposium on Circuits and Systems
A widely used computer model in electromagnetics is the method of moments (MM) whereby an integra... more A widely used computer model in electromagnetics is the method of moments (MM) whereby an integral equation is discretized and approximated as a matrix whose solution yields a sampled representation of the physical problem of interest. The computer time T required to evaluate a MM model at a single frequency depends on the number of unknowns or equations N as
Electromagnetic radiation is discussed from the analytical perspective that charge acceleration i... more Electromagnetic radiation is discussed from the analytical perspective that charge acceleration is necessary to produce an electromagnetic field that falls off with distance R as 1/R from a radiating source. The discussion begins with the Lienard-Wiechert potentials that show a radiation field is proportional to charge acceleration. A graphical construction known as the E-field kink model is discussed as a second way to illustrate the connection between charge acceleration and radiation. A generic wire object is introduced as a means to demonstrate the various ways that charge acceleration and subsequent radiation will occur. These features include: exciting sources; wire-radius discontinuities; impedance loads; wire bends; wire curvature; open ends; and straight-wire sections. Each of these is explored in various levels of detail in the discussion that follows which are illustrated with numerous computed examples using the frequency domain model NEC (Numerical Electromagnetics Code) and the time-domain model TWTD (Thin-Wire Time Domain). A technique called FARS (Far-field Analysis of Radiation Sources) is also introduced as a means of showing quantitatively where radiation originates from the generic wire model.
Abstract: The design of an experiment is given which employs an inverted coaxial diode geometry t... more Abstract: The design of an experiment is given which employs an inverted coaxial diode geometry to investigate absorption of electromagnetic radiation below and above the plasma frequency. Data obtained when a pure electron stream is introduced into the ...
Skip to main content. CERN Logo CERN Document Server. Related links. CDS; Indico; Library; Bullet... more Skip to main content. CERN Logo CERN Document Server. Related links. CDS; Indico; Library; Bulletin; EDMS. Main navigation links: Search; Submit; Help; Your CDS: Your alerts; Your baskets; Your searches. login. Home > Computational electromagnetics. ...
In the ACES 2015 meeting, the author presented a method for synthesizing array patterns using a m... more In the ACES 2015 meeting, the author presented a method for synthesizing array patterns using a matrix that relates element excitations with the lobe maxima of a desired pattern [1]. The method is applied here to the synthesis of both a Dolph-Chebyshev scanning array and one that has nonuniformly spaced elements.
Proceedings of the 32nd Midwest Symposium on Circuits and Systems
A widely used computer model in electromagnetics is the method of moments (MM) whereby an integra... more A widely used computer model in electromagnetics is the method of moments (MM) whereby an integral equation is discretized and approximated as a matrix whose solution yields a sampled representation of the physical problem of interest. The computer time T required to evaluate a MM model at a single frequency depends on the number of unknowns or equations N as
The Lienard-Wiechert potentials show explicitly that charge acceleration, i.e. a change in charge... more The Lienard-Wiechert potentials show explicitly that charge acceleration, i.e. a change in charge velocity, causes radiation of an electromagnetic field. The purpose of this brief note is to explore the rate of energy loss due to radiation from current and charge flowing on a circular loop as a function of the loop's curvature and wire radius. The results presented are obtained using a thin-wire, time-domain (TWTD) computer model with Gaussian-pulse excitation. Analytical estimates for the curvature and wire-radius effects are developed from best-fits expressions to the computed results. 1
One of the most time-consuming tasks associated with developing and using computer models in elec... more One of the most time-consuming tasks associated with developing and using computer models in electromagnetics is that of verifying software performance and vali- dating the model results. Some of the errors that occur in modeling, the need for quantitative error measures, and some of the validation tests such as convergence behavior and boundary- condition checks are discussed. Use of model-based para- meter estimation to develop error estimates or to control uncertainty in an observable is illustrated. It is recommended that the Computational ElectroMagnetics community adopt a policy of requiring some minimal standards concerning the ac- curacy of numerical results accepted for journal articles and meeting presentations.
Because of its interest in the electromagnetic pulse (EMP) protection-engineering problem, Lawre... more Because of its interest in the electromagnetic pulse (EMP) protection-engineering problem, Lawrence Livermore Laboratory is publishing this set of external coupling modules. The work in this manual has been conducted under Subtask R99QAXEB088 from the Defense Nuclear Agency. The modules may be used either by electromagnetic specialists or by engineers who may not have a great deal of knowledge of the subject. Module in this context denotes a self-contained package of information about the EMP response of a generic class of structures. In each module a canonical model represents a generic class of systems such missiles, ships, airplanes, etc. The intent is to provide pertinent external coupling information to permit reasonable cost-effective estimates of the quantities (currents, voltages, energies, etc.) involved in estimating the hardness of a system to the effects of EMP. Where possible, we have included specific simulation results from tests performed on real systems. In cases where real system data are not available, we have used detailed scale (representative) models or computer codes to verify the appropriateness of our canonical models. The agreement of data from other models with that obtained on real systems indicates that the results presented modules are quite useful for prediction relating to real systems and will greatly aid the protection engineer in in system assessment and experimental design. Up to the present, emphasis of the modules has been on the external coupling aspects of systems of interest to the EMP engineers and others in this field. This is reflected in the list of modules generated for this manual.
Although this book focuses on radiation, a fundamental property of electromagnetic fields, it doe... more Although this book focuses on radiation, a fundamental property of electromagnetic fields, it does not follow the usual analytical kind of approach to be found in the typical book on electromagnetics. Rather than developing and presenting a formal theoretical foundation of electromagnetic theory, this book instead focuses on various aspects of EM radiation from a variety of perspectives. The goal is to provide the reader with a conceptual basis for thinking about and understanding EM radiation and to introduce some associated computational tools for obtaining relevant quantitative results. This is done as an alternative to a rigorous mathematical formalism that may obscure the simple physical reality of the radiation process. The approach taken here seeks to be relevant about how engineers routinely model and design radiating structures as boundary-value problems.
It has been long established that charge acceleration causes electromagnetic radiation, whether from isolated charges like electrons in free space or from the charge distributions on a dipole antenna or radar target. But finding the fields radiated by such PEC objects does not require knowledge of charge acceleration per se. Solving for the current and charge distributions induced on such objects by some specified excitation, typically a tangential electric field, is usually formulated as a boundary-value problem. The fields produced by these induced sources are then obtained by integrating them over the surface of the object being modeled. Whatever charge acceleration may be associated with these induced sources is not specifically involved in determining the radiated field. This is probably why engineering electromagnetics texts rarely mention charge acceleration as the root cause of the radiated field. Knowing that charge acceleration causes electromagnetic radiation may seem to be irrelevant.
Never the less, given that charge acceleration is the cause of all electromagnetic radiation, the question arises about where such acceleration occurs on objects typically modeled and analyzed by electromagnetic engineers. Charge acceleration as the cause of radiation from the typical kinds of objects modeled and analyzed by engineers is examined here on a quantitative basis. This question is considered throughout this book using various analytical and numerical tools primarily developed by the author. The goal is to provide the reader with computational tools for determining quantitatively why and where radiation is emitted by simple wire objects excited as antennas and scatterers. More specifically, this is achieved by demonstrating ways of answering the question “From where, and in what quantity, does EM radiation originate on a per-unit length or per-unit area basis from an perfect electric conductor (PEC) excited as an antenna or scatterer?” Answering this question is shown to be possible using the numerical solutions routinely provided by typical computer models of such problems via straightforward post- processing of their results.
While the analytical and numerical tools for determining the basic properties of a variety of ant... more While the analytical and numerical tools for determining the basic properties of a variety of antenna types have been long-established, there remains some continuing curiosity about how electromagnetic radiation is launched by such a simple antenna as a dipole. The following article discusses this problem in both the frequency domain and time domain. The sinusoidal current filament is investigated first as a prototype of a wire dipole. The lengthwise distribution of radiated power for the SCF is obtained from the distributed radiation resistance of Schelkunoff and Feldman, the induced electromotive-force (IEMF) method and the far-field analysis of radiation sources (FARS) developed by the author. The FARS approach is next used to analyze a frequency-domain numerical model of a dipole antenna, producing results similar to those for the SCF for a dipole of near-zero radius. Differentiating the decaying on-surface Poynting Vector produces results comparable to those from FARS to explicitly demonstrate the power loss caused by radiation of the propagating current and charge. The lobed distributed radiated power is shown to be closely correlated with the square of the dipole current, confirming the cause of the radiation to be due to a partially reflected charge as the current and charge form standing waves on the dipole. Application of a time-domain version of FARS yields a smoothed lengthwise distribution of radiated energy as opposed to the lobed variation of the frequency domain.
While the analytical and numerical tools for determining the basic properties of a variety of ant... more While the analytical and numerical tools for determining the basic properties of a variety of antenna types have been long-established, there remains some continuing curiosity about how electromagnetic radiation is launched by such a simple antenna as a wire dipole. The following article discusses this problem from both a frequencydomain and time-domain perspective. Contributions from pioneers such as Poynting and Schelkunoff and more recently by J. D. Jackson have discussed this problem. The author's concern with it has been whether the geometry of an object can be determined from its far radiated fields if not all parts of the object radiate. The sinusoidal current filament is investigated first as a prototype of a wire dipole. The lengthwise distribution of radiated power for the SCF is obtained from the distributed radiation resistance of Schelkunoff and Feldman, the induced electromotive-force (IEMF) method and the far-field analysis of radiation sources (FARS) developed by the author. These results are found to agree within a percent for the distributed radiated power from the SCF that occurs as a series of halfwavelength lobes of varying amplitude along the current. The FARS approach is next used to analyze a frequency-domain numerical model of a dipole antenna, producing results similar to those for the SCF. Differentiating the decaying on-surface Poynting Vector produces similar results due to radiation loss of the propagating power. The lobed distributed radiated power is shown to be closely correlated with the square of the dipole current, confirming the cause of the radiation to be due to a partially reflected charge as the current and charge form standing waves on the dipole. Application of a time-domain version of FARS yields a smoothed lengthwise distributed radiated energy. FARS thus provides a quantitative result for where and why the far-field radiation originates from along the dipole.
Radiation is the fundamental physical property of electromagnetic fields from which everything el... more Radiation is the fundamental physical property of electromagnetic fields from which everything else follows. The goal of the book is to explain why and where radiation occurs from simple perfect-electric conducting objects as exemplified by wire antennas and scatterers. Numerous examples to illustrate how radiation occurs and its relationship with the behavior of the current and charge on such objects are presented. The numerical results are primarily derived using two well-known and wellvalidated computer models, TWTD (Thin-Wire Time Domain, described in Appendix A) and NEC (Numerical Electromagnetics Code, described in Appendix B) with which the author has been long associated. Several different methods for determining why and where radiation originates from a perfect electric conductor are examined. While EM radiation is caused by acceleration of electric charge, this fact is rarely mentioned in engineering texts. In spite of that, computing the radiation patterns of complex, perfect-electric conductors (PEC) has been long-established and validated using Maxwell's Equations (ME). Although charge acceleration is not explicitly included for PEC objects in ME, they obviously contain this effect implicitly in far-field computations based on them. Typical physics texts do discuss charge acceleration as the basis of EM radiation, but in terms of free charge in space, rather than in connection with, for example, how a physical antenna operates. The goal of this book is to demonstrate the relationship between charge acceleration and how PEC objects behave when excited by localized sources as antennas or by incident waves as scatterers. Various analytical and numerical techniques developed by the authors provide an answer to the question "Where and in what amount is the power (frequency domain) or energy (time domain) emitted by PEC objects for various representative geometries?" A method called FARS (Far field Analysis of Radiation Sources) is demonstrated to provided an answer in both the frequency and time domains. It follows that the answer to that question also reveals where charge acceleration occurs. These techniques also apply to specified currents such as the sinusoidal current filament, long used as an approximation for a dipole antenna. The techniques described and demonstrated can be incorporated into most computational electromagnetics models with little effort to provide those interested in investigating localized radiation behavior for various situations. Such techniques will be of value in a teaching setting since they will give students a learning tool and unique insight into a fundamental aspect of the electromagnetic discipline. A variety of examples throughout will demonstrate geometrical features that cause charge acceleration or radiation. As a specific example, various published observations that associate current decay along a straight wire with radiation are confirmed to be due to charge reflection, caused by a wave-impedance variation with distance.
─ Model-based parameter estimation (MBPE) using rational-function fitting models (FM) provides a ... more ─ Model-based parameter estimation (MBPE) using rational-function fitting models (FM) provides a way to more efficiently develop electromagnetic frequency responses. These reduced-order FMs can also be used to estimate the quantitative uncertainty of first-principles or generating models (GMs). Using MBPE to Asses the accuracy of EM results is discussed. Index Terms ─ Accuracy of EM computer models, Model-Based Parameter Estimation.
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Papers by Edmund Miller
model NEC (Numerical Electromagnetics Code) and the time-domain model TWTD (Thin-Wire Time Domain). A technique called FARS (Far-field Analysis of Radiation Sources) is also introduced as a means of showing quantitatively where radiation originates from the generic wire model.
model NEC (Numerical Electromagnetics Code) and the time-domain model TWTD (Thin-Wire Time Domain). A technique called FARS (Far-field Analysis of Radiation Sources) is also introduced as a means of showing quantitatively where radiation originates from the generic wire model.
It has been long established that charge acceleration causes electromagnetic radiation, whether from isolated charges like electrons in free space or from the charge distributions on a dipole antenna or radar target. But finding the fields radiated by such PEC objects does not require knowledge of charge acceleration per se. Solving for the current and charge distributions induced on such objects by some specified excitation, typically a tangential electric field, is usually formulated as a boundary-value problem. The fields produced by these induced sources are then obtained by integrating them over the surface of the object being modeled. Whatever charge acceleration may be associated with these induced sources is not specifically involved in determining the radiated field. This is probably why engineering electromagnetics texts rarely mention charge acceleration as the root cause of the radiated field. Knowing that charge acceleration causes electromagnetic radiation may seem to be irrelevant.
Never the less, given that charge acceleration is the cause of all electromagnetic radiation, the question arises about where such acceleration occurs on objects typically modeled and analyzed by electromagnetic engineers. Charge acceleration as the cause of radiation from the typical kinds of objects modeled and analyzed by engineers is examined here on a quantitative basis. This question is considered throughout this book using various analytical and numerical tools primarily developed by the author. The goal is to provide the reader with computational tools for determining quantitatively why and where radiation is emitted by simple wire objects excited as antennas and scatterers. More specifically, this is achieved by demonstrating ways of answering the question “From where, and in what quantity, does EM radiation originate on a per-unit length or per-unit area basis from an perfect electric conductor (PEC) excited as an antenna or scatterer?” Answering this question is shown to be possible using the numerical solutions routinely provided by typical computer models of such problems via straightforward post- processing of their results.