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The perturbation of a magnetostatic field by a toroid made of a homogeneous anisotropic magnetic material was formulated using the solutions of the Laplace equation in the toroidal coordinate system. That was straightforward in the region outside the toroid, but an affine coordinate transformation had to be employed inside the toroid. The coefficients of the series expansion of the perturbation potential in terms of appropriate toroidal basis functions were related to the coefficients of the series expansion of the source potential in terms of appropriate toroidal basis functions by a transition matrix. As a result of the solution of this novel problem, the consequences of material anisotropy on perturbing the magnetostatic field are clearly evident in the region near the toroid.

The circular Bragg phenomenon is the circular-polarization-state-selective reflection of light in a spectral regime called the circular Bragg regime. In continuation of an expository review on this phenomenon published in 2014, an album of theoretical results is provided in this decadal update. Spectral variations of intensity-dependent and phase-dependent observable quantities in the reflection and transmission half-spaces are provided in relation to the polarization state and the direction of propagation of the incident plane wave., Comment: 20 pages, 11 figures

The geometric phase has acquired interest for optical devices such as achromatic phase shifters, spatial light modulators, frequency shifters, and planar lenses for wavefront engineering. Numerical work with Reusch piles with a large number of layers per period suggests that the geometric phase of the reflected/transmitted plane wave may be sensitive to nanoscale morphological differences, and the geometric-phase spectrum could contain signatures of morphological details that depend on the fabrication technique.

Closed-form expressions were recently derived for depolarization dyadics for truncated spheres and truncated spheroids, and the formalism was extended to truncated ellipsoids. These results were exploited to develop an implementation of the Maxwell Garnett homogenization formalism for the relative permittivity parameters of homogenized composite mediums (HCMs) arising from an isotropic host medium impregnated with isotropic inclusions that are truncated spheres, spheroids, and ellipsoids. In so doing, the anisotropy of the HCM was related to the geometry of the inclusions: in general, the more the shape of the inclusions deviated from spherical, the greater was the degree of anisotropy exhibited by the HCM.

A slab made of a dielectric structurally chiral medium (DSCM) strongly reflects the co-handed circularly polarized plane wave, but not the cross-handed circularly polarized plane wave, in a spectral regime called the circular Bragg regime. The effect of inserting a central phase defect in a DSCM slab with a modest number of structural periods is a spectral reflection hole in the circular Bragg regime, for co-handed incidence only. However, if the incident plane wave is left-circularly polarized, the geometric phase of the transmitted plane wave contains evidence of both the circular Bragg regime and the spectral reflection hole, regardless of the structural handedness of the DSCM. This evidence is indicative of the type of phase defect. The effect of inserting a central phase defect in a DSCM slab with a large number of structural periods is a spectral transmission hole in the circular Bragg regime, for cross-handed incidence only. The spectral transmission hole may be difficult to observe experimentally because of absorption inside the DSCM slab, but it will still be evident in the geometric phase of the transmitted plane wave, if the incident plane wave is left-circularly polarized., Comment: 8 pages, 8 figures

Depolarization dyadics play a central role in theoretical studies involving scattering from small particles and homogenization of particulate composite materials. Closed-form expressions for depolarization dyadics have been developed for truncated spheres and truncated spheroids, and the formalism has been extended to truncated ellipsoids; the evaluation of depolarization dyadics for this latter case requires numerical integration. The H\"{o}lder continuity condition has been exploited to fix the origin of the coordinate system for the evaluation of depolarization dyadics.These results will enable theoretical studies involving scattering from small particles and homogenization of particulate composite materials to accommodate particles with a much wider range of shapes than was the case hitherto.

Polymer banknotes are being increasingly adopted to replace older banknotes. Since banknotes are forensically important substrates for fingermark detection and identification, we present a single-step process to enhance the visualization of fingermarks on banknotes using columnar thin films (CTFs) of nickel. This single-step vacuum technique enhances the quality grade of fingermarks maximally, whether the fingermarks are aged for one or seven days before CTF deposition. This work represents progress over currently available sequences of diverse techniques for enhancing fingermarks on polymer banknotes., Comment: 11 pages, 3 figures

CDs and DVDs are forensically important substrates for latent fingermarks. Upright columnar thin films (CTFs) grown conformally over these substrates were shown to significantly enhance the visual quality of fingermarks. Enhancement to maximum possible grade for visual quality occurred, even for the samples that were developed three days after the fingermarks were placed on them. The CTFs were deposited by directing a collimated vapor flux of an evaporant material towards the substrate placed at an angle and made to rotate rapidly., Comment: 12 pages, 4 figures

The propagation of surface-plasmon-polariton (SPP) waves at the planar interface of a metal and a dielectric material was investigated for a dielectric material with strongly temperature-dependent constitutive properties. The metal was silver and the dielectric material was vanadium multioxide impregnated with a combination of active dyes. Depending upon the volume fraction of vanadium multioxide, either attenuation or amplification of the SPP waves may be achieved; the degree of attenuation or amplification is strongly dependent on both the temperature and whether the temperature is increasing or decreasing. At intermediate volume fractions of vanadium multioxide, for a fixed temperature, a SPP wave may experience attenuation if the temperature is increasing but experience amplification if the temperature is decreasing.

The planewave response of a bicontrollable metasurface absorber with graphene-patched pixels was simulated in the X band using commercial software. Each square meta-atom is a 4x4 array of 16 pixels, some patched with graphene and the others unpatched. The pixels are arranged on a PVC skin which is placed on a copper-backed YIG substrate. Graphene provides electrostatic controllability and YIG provides magnetostatic controllability. Our design delivers absorptance equal to or in excess of 0.9 over a 100-MHz spectral regime in the X band, with 360 MHz/kA magnetostatic controllabity rate and 1 Hz m/V electrostatic controllability rate. Notably, electrostatic control via graphene in the GHz range is novel., Comment: 9 pages, 4 figures, 1 table

A Huygens bianisotropic medium is a linear homogeneous medium for which the Huygens principle can be formulated. When a bounded 3D scattering object composed of a linear bianisotropic medium, whether homogeneous or not, is embedded in a Huygens bianisotropic medium, the excess field phasors inside that object act as volume current densities, and the tangential components of the internal field phasors on the surface of the same object act as surface current densities, to radiate identical field phasors in the external region.

The Bruggeman homogenization formalism was used to numerically investigate the dielectric properties of a columnar thin film (CTF) made from vanadium dioxide. For visible and near-infrared wavelengths, the CTF is electromagnetically equivalent to a homogeneous orthorhombic material. Over the 58 deg C -- 72 deg C temperature range, the eigenvalues of the CTF's relative permittivity dyadic are highly sensitive to temperature, and vary according to whether the CTF is being heated or cooled. The anisotropy revealed through the eigenvalues, and the anisotropy of the associated hysteresis, were investigated in relation to temperature for CTFs of different porosities and columnar cross sections. When the free-space wavelength is 800 nm, the CTF is a dissipative dielectric material that exhibits temperature-dependent anisotropy and anisotropic hysteresis. In contrast, when the free-space wavelength is 1550 nm, the CTF can be either a dissipative dielectric material, a hyperbolic material or a metal-like material, depending on the temperature and the porosity of the CTF. As the porosity of the CTF decreases from 0.55 to 0.3, the anisotropy of the CTF becomes more pronounced, as does the anisotropy of the hysteresis. Only relatively modest variations in anisotropy and hysteresis arise in response to varying the columnar cross-sectional shape, as compared to the variations induced by varying the porosity.

Vanadium dioxide (VO2) transforms from purely monoclinic to purely tetragonal on being heated from 58 deg C to 72 deg C, the transformation being reversible but hysteretic. Electromagnetically, VO2 transforms from a dissipative dielectric to another dissipative dielectric if the free-space wavelength is less than 1100 nm, but from a dissipative dielectric to a plasmonic metal (or vice versa) if the free-space wavelength exceeds 1100 nm. Calculating the extinction, total scattering, absorption, radiation-pressure, back-scattering, and forward-scattering efficiencies of a VO2 sphere, we found clear signatures of thermal hysteresis in (i) the forward-scattering, back-scattering, and absorption efficiencies for free-space wavelength less than 1100 nm, and (ii) the forward-scattering, back-scattering, total scattering, and absorption efficiencies for free-space wavelength more than 1100 nm. Vacuum and null-permittivity quasistates occur between 58 deg C and 72 deg C, when tetragonal VO2 is a plasmonic metal, once each on the heating branch and once each on the cooling branch of thermal hysteresis. But none of the six efficiencies show significant differences between the two quasistates., Comment: 11 pages, 4 figures

We conceptualized three-array scalable metasurfaces comprising only three thin strip grids and numerically demonstrated their characteristics in the mid-infrared spectral regime for switchable polarization manipulation and related asymmetric diodelike transmission (AT). A few or all of the grids were taken to be made of VO$_2$, a phase-change material. For each proposed metasurface, two effective structures and, therefore, two different functionalities exist, corresponding to the metallic and insulating phases of VO$_2$. The achieved scenarios of functionality switching that depend on the VO$_2$ phase are shown to significantly depend in the way in which VO$_2$ is incorporated to the metasurface. Switchable bands of polarization manipulation are up to 40 THz wide. The AT band can be modulated when Fabry--Perot (anti-)resonances come into play., Comment: 6 pages, 4 figures

The homogenization of vaterite impregnated with gold nanoparticles was accomplished using the extended Maxwell Garnett formalism. The extended formalism takes into account the intrinsic anisotropy of vaterite as well as the size, shape, and orientation of the nanoparticles. Size-dependent permittivity was used for the gold nanoparticles. Numerical studies revealed that the homogenized composite material's permittivity parameters are acutely sensitive to the size, shape, orientation, and volume fraction of the gold nanoparticles.

The extended boundary condition method (EBCM) was formulated for the perturbation of a source electric potential by a 3D object composed of a homogeneous anisotropic dielectric medium whose relative permittivity dyadic is positive definite. The formulation required the application of Green's second identity to the exterior region to deduce the electrostatic counterpart of the Ewald--Oseen extinction theorem. The electric potential inside the object was represented using a basis obtained by implementing an affine bijective transformation of space to the Gauss equation for the electric field. The EBCM yields a transition matrix that depends on the geometry and the composition of the 3D object, but not on the source potential.

The boundary-value problem for the perturbation of an electric potential by a homogeneous anisotropic dielectric sphere in vacuum was formulated. The total potential in the exterior region was expanded in series of radial polynomials and tesseral harmonics, as is standard for the Laplace equation. A bijective transformation of space was carried out to formulate a series representation of the potential in the interior region. Boundary conditions on the spherical surface were enforced to derive a transition matrix that relates the expansion coefficients of the perturbation potential in the exterior region to those of the source potential. Far from the sphere, the perturbation potential decays as the inverse of the distance squared from the center of the sphere, as confirmed numerically.