Searcharxiv⌕ Search

arXiv subjects

Tom G. Mackay

Publications and source records attributed to Tom G. Mackay.

At least 91 records · Page 5Linked to original sources
arXiv2007

Integral Equation for Scattering of Light by a Strong Magnetostatic Field in Vacuum

When a strong magnetostatic field is present, vacuum effectively appears as a linear, uniaxial, dielectric-magnetic medium for small-magnitude optical fields. The availability of the frequency-domain dyadic Green function when the magnetostatic field is spatially uniform facilitates the formulation of an integral equation for the scattering of an optical field by a spatially varying magnetostatic field in vacuum. This integral equation can be numerically treated by using the method of moments as well as the coupled dipole method. Furthermore, the principle underlying the strong-property-fluctuation theory allows the homogenization of a spatially varying magnetostatic field in the context of light scattering.

physics.optics↗
arXiv2007

Scattering loss in electro-optic particulate composite materials

The effective permittivity dyadic of a composite material containing particulate constituent materials with one constituent having the ability to display the Pockels effect is computed, using an extended version of the strong-permittivity-fluctuation theory which takes account of both the distributional statistics of the constituent particles and their sizes. Scattering loss, thereby incorporated in the effective electromagnetic response of the homogenized composite material, is significantly affected by the application of a low-frequency (dc) electric field.

physics.optics↗
arXiv2006

Depolarization regions of nonzero volume for anisotropic, cubically nonlinear, homogenized nanocomposites

An implementation of the strong-permittivity-fluctuation theory (SPFT) is presented in order to estimate the constitutive parameters of a homogenized composite material (HCM) which is both cubically nonlinear and anisotropic. Unlike conventional approaches to homogenization, the particles which comprise the component material phases are herein assumed to be small but not vanishingly small. The influence of particle size on the estimates of the HCM constitutive parameters is illustrated by means of a representative numerical example. It is observed that, by taking the nonzero particle size into consideration, attenuation is predicted and nonlinearity enhancement is somewhat diminished. In these respects, the effect of particle size is similar to that of correlation length within the bilocally-approximated SPFT.

physics.optics↗
arXiv2006

On the effective permittivity of silver-insulator nanocomposites

The Bruggeman formalism provides an estimate of the effective permittivity of a composite material comprising two constituent materials, with each constituent material being composed of electrically small particles. When one of the constituent materials is silver and the other is an insulating material, the Bruggeman estimate of the effective permittivity of the composite exhibits resonances with respect to volume fraction that are not physically plausible.

physics.optics↗
arXiv2006

On the Bergman-Milton bounds for the homogenization of dielectric composite materials

The Bergman-Milton bounds provide limits on the effective permittivity of a composite material comprising two isotropic dielectric materials. These provide tight bounds for composites arising from many conventional materials. We reconsider the Bergman-Milton bounds in light of the recent emergence of metamaterials, in which unconventional parameter ranges for relative permittivities are encountered. Specifically, it is demonstrated that: (a) for nondissipative materials the bounds may be unlimited if the constituent materials have relative permittivities of opposite signs; (b) for weakly dissipative materials characterized by relative permittivities with real parts of opposite signs, the bounds may be exceedingly large.

physics.optics↗
arXiv2006

Simultaneous negative- and positive-phase-velocity propagation in an isotropic chiral medium

The phase velocity of plane waves propagating in an isotropic chiral medium can be simultaneously positive for left-circularly polarized light and negative for right-circularly polarized light(or vice versa). The constitutive parameter regimes supporting this phenomenon are established for nondissipative and dissipative mediums. The boundary between positive and negative phase velocity is characterized by infinite phase velocity.

physics.optics↗
arXiv2006

Concealment by uniform motion

The perceived lateral position of a transmitted beam, upon propagating through a slab made of homogeneous, isotropic, dielectric material at an oblique angle, can be controlled through varying the velocity of the slab. In particular, by judiciously selecting the slab velocity, the transmitted beam can emerge from the slab with no lateral shift in position. Thereby, a degree of concealment can be achieved. This concealment is explored in numerical calculations based on a 2D Gaussian beam.

physics.optics↗
arXiv2006

Counterposition and negative refraction due to uniform motion

Refraction of obliquely incident plane waves due to the interface of a vacuous half-space and a half-space occupied by a simply moving, nondissipative, isotropic dielectric-magnetic medium is considered, when the medium's velocity lies parallel to the interface and in the plane of incidence. Counterposition of the refracted wavevector and time-averaged Poynting vector occurs when the medium's velocity is sufficiently large in magnitude and makes an obtuse angle with the incident wavevector. The counterposition induced by relative motion occurs whether the refraction is negative or positive when the medium is at rest.

physics.optics↗
arXiv2006

On electromagnetics of an isotropic chiral medium moving at constant velocity

A medium which is an isotropic chiral medium from the perspective of a co-moving observer is a Faraday chiral medium (FCM) from the perspective of a non-co-moving observer. The Tellegen constitutive relations for this FCM are established. By an extension of the Beltrami field concept, these constitutive relations are exploited to show that planewave propagation is characterized by four generally independent wavenumbers. This FCM can support negative phase velocity at certain translational velocities and with certain wavevectors, even though the corresponding isotropic chiral medium does not. The constitutive relations and Beltrami--like fields are also used to develop a convenient spectral representation of the dyadic Green functions for the FCM.

physics.optics↗
arXiv2006

Depolarization regions of nonzero volume in bianisotropic homogenized composites

In conventional approaches to the homogenization of random particulate composites, the component phase particles are often treated mathematically as vanishingly small, point-like entities. The electromagnetic responses of these component phase particles are provided by depolarization dyadics which derive from the singularity of the corresponding dyadic Green functions. Through neglecting the spatial extent of the depolarization region, important information may be lost, particularly relating to coherent scattering losses. We present an extension to the strong-property-fluctuation theory in which depolarization regions of nonzero volume and ellipsoidal geometry are accommodated. Therein, both the size and spatial distribution of the component phase particles are taken into account. The analysis is developed within the most general linear setting of bianisotropic homogenized composite mediums (HCMs). Numerical studies of the constitutive parameters are presented for representative examples of HCM; both Lorentz-reciprocal and Lorentz-nonreciprocal HCMs are considered. These studies reveal that estimates of the HCM constitutive parameters in relation to volume fraction, particle eccentricity, particle orientation and correlation length are all significantly influenced by the size of the component phase particles.

physics.optics↗
arXiv2006

Effect of charge on negative-phase-velocity propagation of electromagnetic waves in the ergosphere of a rotating black hole

The presence of charge promotes the propensity of a rotating black hole to support the propagation of electromagnetic plane waves with negative phase velocity (NPV) in its ergosphere, whether the Kerr-Newman or the Kerr-Sen metric descriptions of spacetime are considered. Striking differences in the NPV characteristics for the Kerr-Newman and Kerr-Sen metrics emerge from numerical studies, particularly close to the outer event horizon when the magnitude of the charge is large.

astro-ph↗
arXiv2006

Electrical control of the linear optical properties of particulate composite materials

The Bruggeman formalism for the homogenization of particulate composite materials is used to predict the effective permittivity dyadic of a two-constituent composite material with one constituent having the ability to display the Pockels effect. Scenarios wherein the constituent particles are randomly oriented, oriented spheres, and oriented spheroids are numerically explored. Thereby, homogenized composite materials (HCMs) are envisaged whose constitutive parameters may be continuously varied through the application of a low-frequency (dc) electric field. The greatest degree of control over the HCM constitutive parameters is achievable when the constituents comprise oriented and highly aspherical particles and have high electro-optic coefficients.

physics.optics↗
arXiv2006

Correlation length and negative phase velocity in isotropic dielectric-magnetic materials

A composite material comprising randomly distributed spherical particles of two different isotropic dielectric-magnetic materials is homogenized using the second-order strong-property-fluctuation theory in the long-wavelength approximation. Whereas neither of the two constituent materials by itself supports planewave propagation with negative phase velocity (NPV), the homogenized composite material (HCM) can. The propensity of the HCM to support NPV propagation is sensitive to the distributional statistics of the constituent material particles, as characterized by a two--point covariance function and its associated correlation length. The scope for NPV propagation diminishes as the correlation length increases.

physics.optics↗
arXiv2005

Positive-, negative-, and orthogonal-phase-velocity propagation of electromagnetic plane waves in a simply moving medium

Planewave propagation in a simply moving, dielectric-magnetic medium that is isotropic in the co-moving reference frame, is classified into three different categories: positive-, negative-, and orthogonal-phase-velocity (PPV, NPV, and OPV). Calculations from the perspective of an observer located in a non-co-moving reference frame show that, whether the nature of planewave propagation is PPV or NPV (or OPV in the case of nondissipative mediums) depends strongly upon the magnitude and direction of that observer's velocity relative to the medium. PPV propagation is characterized by a positive real wavenumber, NPV propagation by a negative real wavenumber. OPV propagation only occurs for nondissipative mediums, but weakly dissipative mediums can support nearly OPV propagation.

physics.optics↗
arXiv2005

Orthogonal-Phase-Velocity Propagation of Electromagnetic Plane Waves

In an isotropic, homogeneous, nondissipative, dielectric-magnetic medium that is simply moving with respect to an inertial reference frame, planewave solutions of the Maxwell curl postulates can be such that the phase velocity and the time-averaged Poynting vector are mutually orthogonal. Orthogonal-phase-velocity propagation thus adds to the conventional positive-phase-velocity propagation and the recently discovered negative-phase-velocity propagation that is associated with the phenomenon of negative refraction.

physics.optics↗