Searcharxiv⌕ Search

arXiv subjects

Arthur D. Yaghjian

Publications and source records attributed to Arthur D. Yaghjian.

14 recordsLinked to original sources
arXiv2026

Conservation of Momentum and Energy in the Lorenz-Abraham-Dirac Equation of Motion

After a brief review of the modified (by transition forces) causal Lorentz-Abraham (LA) classical equation of motion for an extended charged sphere and its limit to the mass-renormalized modified causal Lorentz-Abraham-Dirac (LAD) equation of motion as the radius of the charged sphere approaches zero, a concise derivation is given for the conditions on the velocity and external force required for these modified equations of motion to satisfy conservation of momentum and energy. The effects of mass renomalization on the radiated momentum-energy is clarified. The solutions to the unmodified LAD equation of motion, the causal modified LA and LAD equations of motion, and the Landau-Lifshitz approximate solution to the unmodified LAD equation of motion are obtained for a charge traveling through a parallel-plate capacitor.

physics.class-ph↗
arXiv2026

Reply to "Comment on 'Absence of a consistent classical equation of motion for a mass-renormalized point charge'" (arXiv:2511.02865v1, 3 Nov 2025)

By means of a brief review of the derivation of the causal modified Lorentz-Abraham-Dirac classical equation of motion from the renormalization of the mass in the modified equation of motion of an extended charged sphere as its radius approaches zero, it is shown that Zin and Pylak's objection that the jumps in velocity allowed across transition intervals near nonanalytic points in time of the externally applied force produce delta functions in the radiated fields is incorrect.

physics.class-ph↗
arXiv2025

Fundamentals of Antenna Bandwidth and Quality Factor

After a brief history of the development of quality factor, useful expressions are derived for the robust input-impedance Qz(w) quality factor that accurately determines the VSWR fractional bandwidth of antennas for isolated resonances and a small enough bandwidth power drop. For closely spaced multiple resonances/antiresonances, a definitive formula is given for the increase in fractional bandwidth enabled by Bode-Fano tuning. Methods are given for determining the conventional and complex-energy quality factors of antennas from RLC circuit models. New field-based quality factors Q(w) are derived for antennas with known fields produced by an input current. These Q(w) are remarkably robust because they equal Qz(w) when the input impedance is available. Like Qz(w), the field-based Q(w) is independent of the choice of origin of the antenna fields and is impervious to extra lengths of transmission lines and surplus reactances. These robust field-based quality factors are used to derive new lower bounds on the quality factors (upper bounds on the bandwidths) of spherical-mode antennas that improve upon the previous Chu/CR (Collin-Rothschild) lower bounds for spherical modes. A criterion for antenna supergain is found by combining the Harrington maximum gain formula with the recently derived formula for the reactive power boundaries of antennas. Maximum gain versus minimum quality factor for spherical antennas are determined using the improved lower bounds on quality factor for different values of electrical size ka. Lastly, reduced antenna quality factors allowed by dispersive tuning overcome the traditional Chu/CR lower bounds for lower radiation efficiencies and small enough bandwidth power drops.

physics.class-ph↗
arXiv2023

Electromagnetic Force and Momentum in Classical Macroscopic Dipolar Media

Using realistic classical models of microscopic electric-charge electric dipoles and electric-current (Amperian) magnetic dipoles, it is proven that the Einstein-Laub macroscopic electromagnetic force on a macroscopic-continuum volume of these classical dipoles equals the sum of the microscopic electromagnetic forces on the discrete classical dipoles in that volume. The internal (hidden) momentum of the discrete Amperian magnetic dipoles is rigorously derived and properly included in the determination of the macroscopic force from the spatial averaging of the microscopic forces. Consequently, the Abraham/Einstein-Laub rather than the Minkowski macroscopic electromagnetic-field momentum density gives the total microscopic electromagnetic-field momentum in that volume. The kinetic momentum is found for the volume of the macroscopic continuum from Newton's relativistic equation of motion. It is shown that the difference between the kinetic and canonical momenta in a volume of the macroscopic continuum is equal to the sum of the "hidden electromagnetic momenta" within the electric-current magnetic dipoles and within hypothetical magnetic-current electric dipoles replacing the electric-charge electric dipoles in the classical macroscopic continuum. To obtain the correct unambiguous value of the force on a volume inside the continuum from the force-momentum expression, it is mandatory that the surface of that volume be hypothetically separated from the rest of the continuum by a thin free-space shell. Two definitive experiments performed in the past with time varying fields and forces are shown to conclusively confirm the Einstein-Laub/Abraham formulation over the Minkowski formulation.

physics.class-ph↗
arXiv2020

Stellar speckle and correlation derived from classical wave expansions for spherical antennas

Michelson phase and Hanbury Brown-Twiss intensity stellar interferometry require expressions for the first- and second-order correlation functions, respectively, of the fields radiated by stars in terms of their diameters and measured quasi-monochromatic wavelengths. Although our sun and most other stars are spherical in shape at optical wavelengths, previous determinations of speckle and correlation functions have modeled stars as circular discs rather than spheres because of the mathematical tools available for partially coherent fields on planar surfaces. However, with the incentive that most stars are indeed shaped like spheres and not discs, the present paper models a star as a spherical antenna composed of a random distribution of uncorrelated volume sources within a thin surface layer (photosphere). Working directly with the time-domain fields, a self-contained, straightforward, detailed derivation of speckle patterns and correlation functions is given based on a novel, angularly symmetric, spherical mode expansion with coefficients determined by the assumed Lambertian nature of the star's radiation and the uniform asymptotic behavior of the spherical Hankel functions. First-order spatially averaged and temporally averaged correlation functions are proven to be identical and the normalized second-order correlation function is shown to equal one plus the square of the normalized first-order correlation function. The direct time-domain approach reveals explicit expressions for the quasi-monochromatic wave-packet fields of stellar radiation as well as new criteria for the validity of the far-field approximation for the fields of incoherent sources that are much less restrictive than the Rayleigh-distance criterion for coherent sources.

astro-ph.IM↗
arXiv2020

Maxwell's derivation of the Lorentz force from Faraday's law

In a brief but brilliant derivation that can be found in Maxwell's Treatise and traced back to his 1861 and 1865 papers, he derives the force on a moving electric charge subject to electromagnetic fields from his mathematical expression of Faraday's law for a moving circuit. Maxwell's derivation in his Treatise of this force, which is usually referred to today as the Lorentz force, is given in detail in the present paper using Maxwell's same procedure but with more modern notation.

physics.hist-ph↗
arXiv2019

Maxwell's definition of electric polarization as displacement

After reaffirming that the macroscopic dipolar electromagnetic equations, which today are commonly referred to as Maxwell's equations, are found in Maxwell's Treatise, we explain from his Treatise that Maxwell defined his displacement vector D as the electric polarization and did not introduce in his Treatise or papers the concept of electric polarization P or the associated electric-polarization volume and surface charge densities, -div P and Pn, respectively. With this realization, we show that Maxwell's discussion of surface charge density between volume elements of dielectrics and between dielectrics and conductors becomes understandable and valid within the context of his definition of electric polarization as displacement D. Apparently, this identification of D with electric polarization in Maxwell's work has not been previously pointed out or documented except very briefly in [2].

physics.class-ph↗
arXiv2018

Force and Hidden Momentum for Classical Microscopic Dipoles

The concept of hidden momentum is reviewed and the first rigorous derivation from Maxwell's equations is provided for the electromagnetic force on electrically small perfect electric conductors of arbitrary shape in bandlimited but otherwise arbitrarily time-varying fields. It is proven for the Amperian magnetic dipoles of these perfect conductors that a "hidden-momentum" electromagnetic force exists that makes the force on these time varying Amperian magnetic dipoles equal to the force on magnetic-charge magnetic dipoles with the same time varying magnetic dipole moment in the same time varying externally applied fields. The exact Mie solution to the perfectly conducting sphere under plane-wave illumination is used to prove that the expressions for the total and hidden-momentum forces on the arbitrarily shaped electrically small perfect conductors correctly predict the forces on perfectly conducting spheres. Remarkably, it is found that the quadrupolar fields at the surface of the sphere are required to obtain the correct total force on the sphere even though the quadrupolar moments are negligible compared to the dipole moments as the electrical size of the sphere approaches zero.

physics.class-ph↗
arXiv2016

Classical power and energy relations for macroscopic dipolar continua derived from the microscopic Maxwell equations

Positive semi-definite expressions for the time-domain macroscopic energy density in passive, spatially nondispersive, dipolar continua are derived from the underlying microscopic Maxwell equations satisfied by classical models of discrete bound dipolar molecules or inclusions of the material or metamaterial continua. The microscopic derivation reveals two distinct positive semi-definite macroscopic energy expressions, one that applies to diamagnetic continua and another that applies to paramagnetic continua. The diamagnetic dipoles are "unconditionally passive" in that their Amperian magnetic dipole moments are zero in the absence of applied fields. The analysis of paramagnetic continua, whose magnetization is caused by the alignment of randomly oriented "permanent" Amperian magnetic dipole moments that dominate any induced diamagnetic magnetization, is greatly simplified by first proving that the microscopic power equations for rotating "permanent" Amperian magnetic dipoles (which are shown to not satisfy unconditional passivity) reduce effectively to the same power equations obeyed by rotating unconditionally passive magnetic-charge magnetic dipoles. The difference between the macroscopic paramagnetic and diamagnetic energy expressions is equal to a "hidden energy" that parallels the hidden momentum often attributed to Amperian magnetic dipoles. The microscopic derivation reveals that this hidden energy is drawn from the reservoir of inductive energy in the initial paramagnetic microscopic Amperian magnetic dipole moments. The macroscopic, positive semi-definite, time-domain energy expressions are applied to lossless bianisotropic media to determine the inequalities obeyed by the frequency-domain bianisotropic constitutive parameters. Subtleties associated with the causality as well as the group and energy-transport velocities for diamagnetic media are discussed.

physics.class-ph↗
arXiv2009

Absence of a consistent classical equation of motion for a mass-renormalized point charge

The restrictions of analyticity, relativistic (Born) rigidity, and negligible O(a) terms involved in the evaluation of the self electromagnetic force on an extended charged sphere of radius "a" are explicitly revealed and taken into account in order to obtain a classical equation of motion of the extended charge that is both causal and conserves momentum-energy. Because the power-series expansion used in the evaluation of the self force becomes invalid during transition time intervals immediately following the application and termination of an otherwise analytic externally applied force, transition forces must be included during these transition time intervals to remove the noncausal pre-acceleration and pre-deceleration from the solutions to the equation of motion without the transition forces. For the extended charged sphere, the transition forces can be chosen to maintain conservation of momentum-energy in the causal solutions to the equation of motion within the restrictions of relativistic rigidity and negligible O(a) terms under which the equation of motion is derived. However, it is shown that renormalization of the electrostatic mass to a finite value as the radius of the charge approaches zero introduces a violation of momentum-energy conservation into the causal solutions to the equation of motion of the point charge if the magnitude of the external force becomes too large. That is, the causal classical equation of motion of a point charge with renormalized mass experiences a high acceleration catastrophe.

physics.class-ph↗
arXiv2008

Alternative Derivation of Electromagnetic Cloaks and Concentrators

Beginning with a straightforward formulation of electromagnetic cloaking that reduces to a boundary value problem involving a single Maxwell first-order differential equation, explicit formulae for the relative permittivity-permeability dyadic and fields of spherical and circular cylindrical annular cloaks are derived in terms of general compressed radial coordinate functions. The general formulation is based on the requirements that the cloaking occurs for all possible incident fields and that the cloaks with frequency w > 0 have continuous tangential E and H fields across their outer surfaces, and zero normal D and B fields at their inner material surfaces. The tangential-field boundary conditions at the outer surface of the cloak ensure zero scattered fields, and the normal-field boundary conditions at the inner surface of the cloak are compatible with zero total fields inside the interior cavity of the cloak. For spherical cloaks, unlike cylindrical cloaks, these boundary conditions lead to all the tangential components of the E and H fields being continuously zero across their inner surfaces -- cylindrical cloaks having delta functions in polarization densities at their inner surfaces. For bodies with no interior free-space cavities, the formulation is used to derive nonscattering spherical and cylindrical concentrators that magnify the incident fields near their centers. For static fields (w = 0), the boundary value formulation is appropriately modified to obtain a permeability dyadic that will cloak magnetostatic fields. Causality conditions imply that, unlike magnetostatic cloaking, electrostatic cloaking as well as low-frequency cloaking for w > 0 is not realizable.

physics.class-ph↗
arXiv2007

Electrically Small Supergain Arrays

The theory, computer simulations, and experimental measurements are presented for electrically small two-element supergain arrays with near optimal endfire gains of 7 dB. We show how the difficulties of narrow tolerances, large mismatches, low radiation efficiencies, and reduced scattering of electrically small parasitic elements are overcome by using electrically small resonant antennas as the elements in both separately driven and singly driven (parasitic) two-element electrically small supergain endfire arrays. Although rapidly increasing narrow tolerances prevent the practical realization of the maximum theoretically possible endfire gain of electrically small arrays with many elements, the theory and preliminary numerical simulations indicate that near maximum supergains are also achievable in practice for electrically small arrays with three (and possibly more) resonant elements if the decreasing bandwidth with increasing number of elements can be tolerated.

physics.class-ph↗
arXiv2006

Plane-Wave Solutions to Frequency-Domain and Time-Domain Scattering from Magnetodielectric Slabs

Plane-wave representations are used to formulate the exact solutions to frequency-domain and time-domain sources illuminating a magnetodielectric slab with complex permittivity and permeability. In the special case of a line source at z=0 a distance d 2L but also divergent infinite fields in the region 2d 2L and divergent in the region 2d<z<2L. These theoretical results, which are confirmed by numerical examples, imply that divergent fields of the single-frequency solution are not caused by an inherent inconsistency in assuming an ideal lossless -1 DNG material, but are the result of the continuous single-frequency wave (which contains infinite energy) building up infinite reactive fields during the infinite duration of time from t=-infinity to the present time t that the single-frequency excitation has been applied.

math-ph↗