Search

The free-space dyadic Green function in electromagnetics is orthogonal to its own curl on any spherical surface whose center is the source point. [ABSTRACT FROM AUTHOR]

A boundary-value problem was formulated for perturbation of an electrostatic field by a coated dielectric sphere made of two distinct linear anisotropic dielectric (LAD) materials. Specific affine transformations were employed to represent the electric potential inside the core and the coating in terms of the solutions of the Laplace equation. A transition matrix was found to relate the source potential and the perturbation potential in the exterior region. The formulation can be straightforwardly extended to concentrically multilayered spheres made of several homogeneous LAD materials. [ABSTRACT FROM AUTHOR]

An explainable artificial intelligence approach based on consolidating the Local Interpretable and Model-agnostic Explanation (LIME) model outputs was devised to discern the influence of the surface morphology on the colors exhibited by stainless-steel 304 parts polished with a Magnetic Abrasive Finishing (MAF) process. The MAF polishing process was used to create two regions, each appearing either blue or red to the naked eye. The color distribution was microscopically heterogeneous, i.e., some red microscale patches were dispersed in blue regions, and vice versa. The surface morphology was represented in the frequency domain (using a 2D Fourier transform) to capture the harmonic surface patterns, such as the feed and lay marks from the polishing process. A Convolutional Neural Network (CNN) was employed to identify the color of the region from the frequency characteristics of the surface morphology. The CNN was able to predict the observed colors with test accuracies exceeding 99%, suggesting that the frequency characteristics of the surface morphology of the red regions are distinctly different from those of the blue regions. A LIME model was constructed around each small segment within each region of the surface to identify the frequency features that are influential for differentiating between the colors. To deal with the effect of heterogeneity, an algorithm based on the query by experts was used to reconcile the local influences and gather the global explanations of the frequency characteristics that inform the blue versus red regions. We found that the dominant morphological features in the red regions are those that capture the polishing lay patterns underlying surface structure, whereas those in the blue regions capture the non-uniform and high-frequency waveform patterns, such as those result when oxide films form due to the intense polishing conditions. [ABSTRACT FROM AUTHOR]

Complex behaviour associated with metamaterials can arise even in commonplace isotropic dielectric materials. We demonstrate how silver, for example, can support negative phase velocity and counterposition, but not negative refraction, at optical frequencies. The transition from positive to negative phase velocity is not accompanied by remarkable changes in the Abraham and Minkowski momentum densities. In particular, orthogonal phase velocity is associated with nonzero Abraham and Minkowski momentum densities. (Contains 5 footnotes and 8 figures.)

Refraction of light from an isotropic dielectric medium to an anisotropic dielectric material is a complicated phenomenon that can have several different characteristics not usually discussed in electromagnetics textbooks for undergraduate students. With a simple problem wherein the refracting material is uniaxial with its optic axis normal to the interface plane, the phenomena of (i) negative/positive refraction, (ii) negative/positive phase velocity, (iii) counterposition of the phase velocity and the time-averaged Poynting vector, and (iv) "negative refraction" of the energy flux density can be examined. The last-named phenomenon is really negative deflection by refraction. (Contains 7 figures and 1 footnote.)