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]

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]

A pixelated bicontrollable metasurface tunable in the complete X band was designed with its meta-atoms comprising yttrium iron garnet (YIG)-patched pixels and conductive rubber (CR)-patched pixels on a metal-backed silicon substrate. Maximum absorptance of a normally incident plane wave greater than 0.99 is achievable and tunability with absorptance exceeding 0.9 is realizable, with the help of an external magnetostatic field and temperature. The YIG-patched pixels provide magnetostatic control modality with sensitivity of 0.04 MHz A − 1 m and the CR-patched pixels provide thermal control modality with sensitivity of 1 MHz K − 1 . The proposed metasurface absorber can be used to improve the performance of weather radar, police speed radar, and direct broadcast television. [ABSTRACT FROM AUTHOR]

Terahertz metasurfaces with pixelated meta-atoms were designed for linear-polarization conversion and absorption. The differences between the two functionalities emerged from the number and arrangement of metal-dielectric combos patching some but not necessarily every pixel of each meta-atom. A patching arrangement for a meta-atom with 3 × 3 pixels yielded polarization conversion ratio (PCR) > 0.9 over the 10.20–16.08 THz band, whereas another yielded absorptance (A) > 0.9 over the 27.67–28.73 THz band. A third patching arrangement delivered both functionalities, albeit in different spectral regimes: high PCR and high A at 13.92 THz and 29.1 THz, respectively. The spatial profiles of the electric and magnetic fields in each meta-atom suffice to explain the display of these functionalities. The generality of the pixelated meta-atom approach was supported by a meta-atom with 4 × 4 pixels. [ABSTRACT FROM AUTHOR]

The propagation of compound plasmon-polariton (CPP) waves was investigated for the canonical boundary-value problem involving a metal film sandwiched between a homogeneous uniaxial dielectric material and a periodically nonhomogeneous isotropic dielectric material. Attention was focused upon exceptional CPP waves whose decay in the uniaxial dielectric material is governed by the product of a linear and an exponential function of distance from the uniaxial dielectric/metal interface. For physically realistic constitutive-parameter values, up to three exceptional CPP waves were found to exist, each with different propagation directions and with different wavenumbers, in each quadrant of the interface plane. The number of exceptional CPP waves, and their natures, were found to be sensitive to the period of the nonhomogeneous material, the thickness of the metal, as well as the constitutive properties of all three materials involved. [ABSTRACT FROM AUTHOR]

Transmission of a normally incident plane wave through a pixelated metasurface with meta-atoms made up of graphene-patched and InSb-patched pixels on a silicon substrate was simulated using CST Microwave StudioTM2019 software. This metasurface is electrically controllable due to the graphene-patched pixels, and it is magnetically as well as thermally controllable due to the InSb-patched pixels. A tricontrollable stopband with minimum transmittance as low as 0.05 can be achieved for operation in the terahertz gap. [ABSTRACT FROM AUTHOR]

The finite-difference time-domain method was employed to simulate the propagation of a pulse-modulated surface-plasmon-polariton (SPP) wave along a planar silicon/silver interface in the near-infrared spectral regime. The signal energy on the silicon side varies with the carrier frequency, decreases with the propagation distance, and fans away from the interface as the propagation distance increases. Yet a large fraction of the signal energy on the silicon side is confined to within 250 nm of the interface even for a propagation distance of 800 nm. [ABSTRACT FROM AUTHOR]

The two-angle conformally evaporated-film-by-rotation technique (TA-CEFR) was devised to coat the wings of the monarch butterfly with nickel in order to form a 500-nm thick bioreplica thereof. The bioreplica exhibits structural colours that are completely obscured in actual wings by pigmental colours. Thus, the TA-CEFR technique provides a way to replicate, study and exploit hidden morphologies of biological surfaces. [ABSTRACT FROM AUTHOR]

Two active dielectric materials may be blended together to realize a homogenized composite material (HCM) which exhibits more gain than either component material. Likewise, two dissipative dielectric materials may be blended together to realize an HCM which exhibits more loss than either component material. Sufficient conditions for such gain/loss enhancement were established using the Bruggeman homogenization formalism. Gain/loss enhancement arises when (i) the imaginary parts of the relative permittivities of both component materials are similar in magnitude and (ii) the real parts of the relative permittivities of both component materials are dissimilar in magnitude. [ABSTRACT FROM PUBLISHER]

Infrared spectroscopy experiments in the 15–149 THz spectral regime were performed in the transmission mode on a thin film of bulk Parylene-C polymer at normal incidence. The relative permittivity of bulk Parylene-C polymer in this regime was modeled as comprising a frequency-independent term as well as contributions from 32 Lorentz oscillators. A least-squares minimization algorithm and a hybrid genetic algorithm were used to determine the frequency-independent term as well as all parameters characterizing the Lorentz oscillators from the measured transmittance spectrum itself. [ABSTRACT FROM AUTHOR]

The homogenization of a composite material comprising three isotropic dielectric materials was investigated. The component materials were randomly distributed as spherical particles, with the particles of two of the component materials being coupled to form dimers. The Bruggeman and Maxwell Garnett formalisms were developed to estimate the permittivity dyadic of the homogenized composite material (HCM), under the quasi-electrostatic approximation. Both randomly oriented and identically oriented dimers were accommodated; in the former case the HCM is isotropic, whereas in the latter case the HCM is uniaxial. Representative numerical results for composite materials containing dielectric–dielectric dimers demonstrate close agreement between the estimates delivered by the Bruggeman and Maxwell Garnett formalisms. For composite materials containing metal–dielectric dimers and metal–metal dimers with moderate degrees of dissipation, the estimates of the two formalisms are in broad agreement, provided that the dimer volume fractions are relatively low. In general, the effects of intradimer coupling on the estimates of the HCM’s permittivity are relatively modest but not insignificant, these effects being pronounced by anisotropy when all dimers are identically oriented. [ABSTRACT FROM PUBLISHER]

The planar interface of an ordinary, isotropic, homogeneous, dielectric material and a hyperbolic, dielectric, structurally chiral material can support the propagation of one or multiple Dyakonov–Tamm waves, at a specified frequency and along a specified direction in the interface plane. When multiple Dyakonov–Tamm waves can exist, they differ in phase speed, propagation length, degree of localization to the interface, and spatial profiles of the associated electromagnetic fields. Dependence on the relative permittivity scalar of the isotropic partnering material suggests exploitation for optical sensing of analytes in fluids. [ABSTRACT FROM AUTHOR]

All three methodologies of engineered biomimicry – bioinspiration, biomimetics, and bioreplication – are represented in current research on harvesting solar energy. Both processes and porous surfaces inspired by plants and certain marine animals, respectively, are being investigated for solar cells. Whereas dye-sensitized solar cells deploy artificial photosynthesis, bioinspired nanostructuring of materials in solar cells improves performance. Biomimetically textured coatings for solar cells have been shown to reduce optical reflectance and increase optical absorptance over a broad spectral regime. Compound lenses fabricated by a bioreplication technique offer similar promise for reduced reflectance by increasing the angular field of view. [ABSTRACT FROM AUTHOR]

A Tamm wave is guided by the interface of a homogeneous dielectric material and a periodically nonhomogeneous dielectric material, both isotropic. We found theoretically that multiple Tamm waves of different linear polarization states can be guided by such an interface incorporated in a prism-coupled configuration. The Tamm waves have different linear polarization states, phase speeds, and spatial profiles, but the same frequency. The narrow absorptance peaks associated with the excitation of Tamm waves in the prism-coupled configuration offer the application as chemical sensors with very high sensitivity. [ABSTRACT FROM AUTHOR]

Effective-medium theories for electromagnetic constitutive parameters of particulate composite materials are theories of averages. Standard deviations are absent because of the lack of rigorous theories. But ensemble averages and standard deviations can be calculated from a rigorous theory of reflection by planar multilayers. Average reflectivities at all angles of incidence and two orthogonal polarization states for a multilayer composed of two kinds of electrically thin layers agree well with reflectivities for a single layer with the same overall thickness and a volume-weighted average of the relative permittivities of these two components. But the relative standard deviation can be appreciable depending on the angle of incidence and the polarization state of the incident illumination, and increases with increasing difference between the constitutive parameters of the two layers. This suggests that average constitutive parameters obtained from effective-medium theories do not have uniform validity for all calculations in which they might be used. [ABSTRACT FROM PUBLISHER]

A theoretical approach was applied to compute the reflectance spectrums of semi-infinite rugate filters with a sinusoidal refractive-index profile. Regardless of the linear polarization state of the incident plane wave, the reflectance spectrum of a sufficiently thick rugate filter contains a top-hat feature - indicative of the Bragg regime - with ripples on both flanks. The corresponding reflectance spectrum of a semi-infinite rugate filter also contains the top-hat feature, but is devoid of ripples. [ABSTRACT FROM AUTHOR]

We have analyzed electromagnetic wave propagation in photonic bandgap (PBG) structures comprising alternating layers of isotropic dielectric-magnetic materials with positive phase velocity and negative phase velocity, implemented in different waveguides of uniform cross-section (parallel-plate, rectangular, circular, and coaxial) and perfectly conducting walls. The structures could be either ideal (i.e. of infinite extent along the waveguide axis) or real (i.e. terminated at both ends with homogeneously filled waveguide sections). The spectral locations of the band gaps do not directly depend on the cross-sectional shape and dimensions, but on the cut-off parameter instead, for ideal structures. The band gaps of an ideal structure are located in spectral regions where the reflectance of the corresponding real structure is large. The real structures show four types of band gaps, only one type of which is due to the periodically repetitive constitution of the PBG structure; the remaining three types are not of the Bragg type. [ABSTRACT FROM AUTHOR]

When the electrically thin unit cell of a laminated composite material is made of two bianisotropic sheets whose constitutive properties in the thickness direction are decoupled from the constitutive properties in the interfacial planes, the laminated composite material can be homogenized into a material, not all of whose constitutive parameters are independent of each other. This nonindependence of the constitutive dyadics of the constituent materials and the homogenized composite material is captured by two simple constraints, which may not hold if even one of the two constituent materials has more complicated constitutive properties than stated above. [ABSTRACT FROM AUTHOR]

As the variation of temperature alters the intrinsic carrier density in a semiconductor, numerical simulations indicate that the consequent variation of the relative permittivity in the terahertz regime provides a way to realize thermally tunable split-ring resonators. Electromagnetic metasurfaces and metamaterials that are thermally tunable in the terahertz regime can thus be implemented. [ABSTRACT FROM AUTHOR]

The dyadic Green functions for a uniaxial dielectric-magnetic medium, together with a reversible field transformation, were implemented to derive a formulation of the Huygens principle appropriate to a uniaxial dielectric-magnetic medium with gyrotropic-like magnetoelectric properties. [ABSTRACT FROM AUTHOR]

Electromagnetic fields exert higher radiation pressures over isotropic, achiral, homogeneous, passive spheres made of negative-phase-velocity materials than of positive-phase-velocity materials. The radiation pressure can be very high if a nanoscale sphere has negligible loss, and the real parts of its relative permittivity and/or relative permeability are in the neighborhood of -2. [ABSTRACT FROM AUTHOR]

Surface waves can propagate on the planar interface of a linear electro-optic (EO) material and an isotropic dielectric material for restricted ranges of the orientation angles of the EO material and the refractive index of the isotropic material. These ranges can be controlled by the application of a DC electric field, and depend on both the magnitude and the direction of the DC field. Thus, surface-wave propagation can be electrically controlled by exploiting the Pockels effect. [ABSTRACT FROM AUTHOR]

A variety of configurations and formats have been devised to exploit the phenomenon of surface plasmon on metal dielectric interfaces for sensing a variety of significant analytes, such as pesticides and explosives, pathogens and toxins, and diseased tissue. Researchers continue to aim at detecting lower concentrations in smaller volumes of samples in real time. A new research field, called nanoplasmnonics, has emerged in this regard. [ABSTRACT FROM AUTHOR]

An analysis [McCall, M.W. J. Mod. Opt. 2007, 54, 119-128] based on the electromagnetic energy-momentum tensor, to explore the prospects for negative-phase-velocity (NPV) propagation in gravitationally affected vacuum, did not consider (i) the total energy-momentum tensor and (ii) the global perspective of curved spacetime. Also, the appearance of NPV was wrongly attributed to a change in signature of the spacetime metric. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The propagation of a surface electromagnetic wave at the interface of identical uniaxial dielectric half-spaces with a relative twist in their orientation about an axis perpendicular to the interface is formulated as a boundary value problem, the direction of propagation being along the bisector of the relative twist angle and both optic axes being tilted to the interface. Only positive uniaxiality supports surface-wave propagation. When the optic axes in both half-spaces are tilted relative to the interface, the range of the relative twist angle which supports surface waves diminishes and eventually disappears at some maximum value of the tilt angle which depends on the degree of uniaxiality. At optical frequencies and with relatively large degree of uniaxiality, the surface waves are localized within 10's to 100's of nm of the interface. [ABSTRACT FROM AUTHOR]

Electromagnetic band gap (EBG) structures of two different configurations implemented inside R120 rectangular waveguides (frequency range 10–15 GHz) are examined. The first configuration has a periodic, piecewise uniform variation of permittivity in the propagation direction. Two types of such one-dimensional (1D) EBG structures are analyzed, one with the unit cell comprising two dielectric layers, the other with three dielectric layers per unit cell. The second configuration is two-dimensional, with the unit cell along the propagation direction containing two sections, each of which is made of alternating pillars of two dielectric materials. The Bloch theorem is invoked for the ideal EBG structures, which are infinitely long in the propagation direction. The mode-matching method (MMM) is used for real 1D-EBG structures, which contain a finite number of unit cells, whereas a combination of the coupled-mode method (CMM) and the MMM is used for real 2D-EBG structures. Spectrums of the transmission coefficient of the fundamental mode for the 1D-EBG structures are computed and shown to compare favorably against experimental data. The effect of inserting a defect in 1D-EBG structures is demonstrated theoretically as well as experimentally. The band gaps computed for real and ideal 2D-EBG structures are compared as well. [ABSTRACT FROM AUTHOR]

We analyse electromagnetic radiation normally incident to a structurally chiral half-space. We adopt two strategies based respectively on the extract electromagnetic solution to the problem, and a more phenomeno-logical approach based on coupled-wave analysis. We find good agreement between the two methods. [ABSTRACT FROM AUTHOR]

Guided wave propagation in a Ku -band rectangular waveguide filled with a series of cells of dielectric materials in the Kronig-Penney morphology is examined. Allowed and forbidden bands in these ideal electromagnetic band-gap (EBG) filters are obtained for the TE z and TM z propagation modes by invoking the Floquet theorem. Real EBG structures, with a finite number of unit cells, are also studied using the scattering matrix technique. As the number of unit cells in a real structure increases, its transmission characteristics converge to those of its ideal analogue. [ABSTRACT FROM AUTHOR]

A theory of reflection and transmission of normally incident plane waves to a chiral sculptured thin film (CSTF) is presented. It is based on a coupled wave approach, in which the handedness-reversing reflections at the medium's interfaces are combined with the handedness-preserving distributed reflection inside the CSTF. Explicit formulas for the various reflection and transmission coefficients are derived. The method is shown to provide acceptable quantitative agreement with the exact full electromagnetic analysis. [ABSTRACT FROM AUTHOR]

Explains why the strong-property-fluctuation (SPFT) has gained prominence in the homogenization of linear composite mediums. Accommodation of the distributional statistics of the component phases; Formulation of the SPFT for cubically nonlinear isotropic chiral composite in mediums.

It is shown that the Bragg centre-wavelength of a polymeric chiral sculptured thin film (STF) can be shifted by the axial tension generated in a cobonded piezoelectric disc by a DC voltage. This attractive possibility can be exploited for tunable optical filters as well as lasers made of chiral STFs, and can be extended to other types of STFs. [ABSTRACT FROM AUTHOR]

Two results about the planewave response of an isotropic, dielectric-magnetic, homogeneous, planar slab are deduced when the real parts of both the permittivity and the permeability are altered from positive to negative. First, the reflection and the transmission coefficients suffer phase reversals without change in their respective magnitudes. Second, the Goos-Hänchen shifts experienced by beams on total reflection reverse their directions. [ABSTRACT FROM AUTHOR]

The problem of the coupling of a surface dielectric grating to a structurally chiral volume grating is formulated and solved. The volume grating is a chiral sculptured thin film, which exhibits the circular Bragg phenomenon in distinct wavelength regimes. Two distinct interactions are involved: (i) those of linearly polarized and circularly polarized modes, and (ii) those of nonspecular modes with the specular Bragg phenomenons. Numerical studies show that the circular Bragg phenomenon is virtually immune to the presence of the surface grating. Hence, chiral STF filters can be diffraction-coupled to other optical elements. [ABSTRACT FROM AUTHOR]

Reported here is the derivation of analytic expressions for the reflection coefficients of a halfspace filled by a chiral sculptured thin film (STF) that is axially excited by a normally incident plane wave at the centrewavelength of the Bragg regime. Although these expressions are correct to the second order with respect to a small parameter that delineates the local anisotropy of the chiral STF, their first-order reductions are particularly simple and very adequate for practical purposes. A small difference between the two cross-polarized reflection coefficients has also been found. The results are explained on the basis of a simple model which utilizes the standard Fresnel equations for a scalar dielectric halfspace, combined with coupled wave theory. [ABSTRACT FROM AUTHOR]

Derived here are four conditions that must be satisfied by the constitutive parameters of a linear, homogeneous, bianisotropic medium for it to support the propagation of a circularly polarized plane wave along a fixed axis. [ABSTRACT FROM AUTHOR]

The viability of combining chiral sculptured thin films with a standard Mach-Zehnder fibre interferometer to produce a passive, lossless, in-line, polarization router and combiner is demonstrated. The spectral response of the device is calculated with respect to the input of orthogonal polarizations which are shown to be either efficiently routed to different output ports or combined at one port. [ABSTRACT FROM AUTHOR]

The Bruggeman approach is implemented to homogenize a collection of identical, similarly oriented, electrically small, ellipsoidal particles with intensity-dependent refractive index that are dispersed randomly and homogeneously in an isotropic, linear, dielectric host material. The homogenized composite medium is assumed to be cubically nonlinear and anisotropic, in the simplest approximation. The anisotropy of nonlinearity may be considerably different from the anisotropy of the linearity. The possible enhancement of nonlinearity is also anisotropic, with the most desirable performance along the shortest principal axis of the ellipsoidal particles. [ABSTRACT FROM AUTHOR]

The coupled wave theory (CWT) for axial propagation of light in dielectric thin-film helicoidal bi-anisotropic mediums is exploited to obtain simple expressions for true and apparent circular dichroisms, true and apparent linear dichroisms, transmission ellipticity, and optical rotation. The effect of weak isotropic absorption on the circular Bragg phenomenon is elucidated, in terms of simple expressions. Comparison is made with exact results obtained with the full electromagnetic analysis (FEMA), any differences between the CWT and the FEMA results being due to the neglect of cross-polarized scattering by the CWT. [ABSTRACT FROM AUTHOR]

The homogenization of a composite medium formed by randomly dispersing electrically small, weakly nonlinear, bianisotropic, ellipsoidal inclusions in a linear bianisotropic host medium is considered. The effective constitutive properties of the homogenized composite medium (HCM) are estimated using the Maxwell Garnett formalism. The linear and nonlinear properties of the HCM are estimated separately because the nonlinearity of the inclusions is weak and the composite medium is dilute. Whereas previously available results were confined to simple dielectric media and spherical inclusions, the reach of the presented formalism is vast and can be significant for numerous technological applications. [ABSTRACT FROM AUTHOR]

A material combining both mirror-conjugated and racemic chirality properties is characterized and classified within the context of linear bianisotropic mediums. Planewave propagation in the chosen material is studied with particular emphasis on the interaction of different and no handedness along certain specified directions. Comparison is made with isotropic chiral mediums as well as uniaxial bianisotropic mediums. [ABSTRACT FROM AUTHOR]

The coupled wave theory (CWT) for axial propagation of light in dielectric thin-film helicoidal bianisotropic media is presented and compared with the full electromagnetic analysis (FEMA). Two sets of formulas are developed for the location and bandwidth of the wavelength regime wherein the circular Bragg phenomenon is exhibited. Multi-layer structures are also analysed using the CWT, the location of the spectral hole in a class of three-layer structures being determined analytically. Absorption and dispersion effects are considered. [ABSTRACT FROM AUTHOR]

We analyse theoretically transmission through two layers of different thin-film helicoidal bianisotropic mediums (TFHBMs), wherein the pitch of each layer bears a precisely determined relation to the overall thickness of the bi-layer. A spectral hole emerges from the interaction of the circular Bragg regimes of both TFHBM layers. Our results generalize a recently discovered scheme for producing spectral holes in fibre-Bragg gratings, with which comparison is made. The proposed TFHBM bi-layers may be useful for the simultaneous production of oppositely polarized beams with narrow bandwidths and a specific amplitude splitting ratio. [ABSTRACT FROM AUTHOR]

We show that the evanescent part of the plane wave representation of the free-space dyadic Green function contributes to the far field only along a distinguished axis. The claim of contribution of evanescence in all directions is incorrect as it arises from a flawed procedure, but alimited version of that claim may have merit. [ABSTRACT FROM AUTHOR]

Homogenization theories foster understanding of the electromagnetic properties of composite materials formed by dispersing electrically small inclusions made of various types of homogeneous media in a homogeneous host medium. In this paper, the Maxwell Garnett approach is applied to homogenize a broad class of nonlinear composites. While the host is a linear bi-isotropic medium, the inclusions are made of a nonlinear anisotropic dielectric medium. Bloembergen's formalism, originally developed for nonlinear isotropic dielectric inclusions dispersed in a linear isotropic dielectric host medium, is employed for the estimation of local fields; and its applicabillity for this considerably more general problem is critically examined and contextualized. The homogenized composite displays a rich behaviour due to the chirality of the host medium, and novel optical applications are therefore anticipated. [ABSTRACT FROM AUTHOR]

The Waterman-Truell approach has been utilized for the homogenization of a chiral composite formed by identical chiral particles randomly dispersed in free space. Comparison is made with the results of applying the Maxwell Garnett approach on the same composite. The Waterman-Truell approach is found to be deficient compared with the Maxwell Garnett approach, as the former yields only a partial characterization of the homogenized composite. [ABSTRACT FROM AUTHOR]

A self-consistent derivation is given for the Maxwell-Garnett model for a very general particulate composite. The bi-anisotropic inclusions are supposed to be randomly embedded in a bi-isotropic host medium. It is seen that the effective medium is also bi-anisotropic in general. [ABSTRACT FROM AUTHOR]