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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]

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 58–72 °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 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. [ABSTRACT FROM AUTHOR]

Faster communication between electronic devices inside a semiconductor chip may be enabled by optical interconnects based on surface-plasmon-polariton (SPP) waves, as their high localization overcomes the size mismatch between optical and electronic devices. Hence, we solved the Maxwell equations in the time domain to investigate the jump of a pulse-modulated carrier SPP wave across a semi-infinite gap on the metallic side of a planar metal/dielectric interface. The Drude model was used for the susceptibility of the metal and the air was taken as the dielectric material in our calculations. The Pearson correlation coefficient of the appropriate component of the Poynting vector at two points on either side of the gap was calculated. After an abrupt termination of the metal, reflection was very low and the signal continued to propagate in air as a precursor followed by a somewhat distorted version of the launched pulse. Information encoded as the existence of a pulse was found to be strongly and positively correlated with the transmitted signal. When the metal/air interface was restored after a gap of width equal to the carrier wavelength in free space, the signal received across the gap still comprised a precursor and a main pulse that were still strongly and positively correlated with the transmitted signal. Thus, information continued to propagate in the forward direction for a long distance after the gap, a promising result for SPPwave- based optical interconnects. [ABSTRACT FROM AUTHOR]

Faster communication between electronic devices inside a semiconductor chip may be enabled by optical interconnects based on surface-plasmon-polariton (SPP) waves, as their high localization overcomes the size mismatch between optical and electronic devices. Hence, we solved the Maxwell equations in the time domain to investigate the jump of a pulse-modulated carrier SPP wave across a semi-infinite gap on the metallic side of a planar metal/dielectric interface. The Drude model was used for the susceptibility of the metal and the air was taken as the dielectric material in our calculations. The Pearson correlation coefficient of the appropriate component of the Poynting vector at two points on either side of the gap was calculated. After an abrupt termination of the metal, reflection was very low and the signal continued to propagate in air as a precursor followed by a somewhat distorted version of the launched pulse. Information encoded as the existence of a pulse was found to be strongly and positively correlated with the transmitted signal. When the metal/air interface was restored after a gap of width equal to the carrier wavelength in free space, the signal received across the gap still comprised a precursor and a main pulse that were still strongly and positively correlated with the transmitted signal. Thus, information continued to propagate in the forward direction for a long distance after the gap, a promising result for SPP-wave-based optical interconnects. [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]

Metasurfaces containing arrays of thermally tunable metal-free (double-)split-ring meta-atoms and metal-free grids made of vanadium dioxide (VO 2 ), a phase-change material can deliver switching between (1) polarization manipulation in transmission mode as well as related asymmetric transmission and (2) other functionalities in the terahertz regime, especially when operation in the transmission mode is needed to be conserved for both phases of VO 2 . As the meta-atom arrays function as arrays of metallic subwavelength resonators for the metallic phase of VO 2 , but as transmissive phase screens for the insulator phase of VO 2 , numerical simulations of double- and triple-array metasurfaces strongly indicate extreme scenarios of functionality switching also when the resulting structure comprises only VO 2 meta-atoms and VO 2 grids. More switching scenarios are achievable when only one meta-atom array or one grid is made of VO 2 components. They are enabled by the efficient coupling of the geometrically identical resonator arrays/grids that are made of the materials that strongly differ in terms of conductivity, i.e. Cu and VO 2 in the metallic phase. [ABSTRACT FROM AUTHOR]

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 when the source potential is due to either a point charge or a point dipole. [ABSTRACT FROM AUTHOR]

The acoustic scattering characteristics of ∼10 μm-long microfibers of Parylene C embedded in water were investigated, towards the eventual goal of designing polymeric sculptured thin films for biomedical applications. The chosen microfibers were upright circular-cylindrical, slanted circularcylindrical, chevronic, and helical in shape. A combination of numerical and analytical techniques was adopted to examine the scattering of plane waves in a spectral regime spanning the lower few eigenfrequencies of the microfibers. Certain maximums in the spectrums of the forward and back scattering efficiencies arise from the phenomenon of creeping waves. The same phenomenon affects the total scattering efficiency in some instances. The spectrums of all efficiencies exhibit the geometric symmetry of a microfiber in relation to the direction of propagation of the incident plane wave. Similarities in the shapes of the slanted circular-cylindrical and the chevronic microfibers are reflected in the spectrums of their scattering efficiencies. A highly compliant microfiber has shorter and broader peaks than a less compliant microfiber in the spectrums of the total scattering efficiency. The proper design of polymeric sculptured thin films will benefit from the knowledge gained of the directions of maximum scattering from individual microfibers. [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]

Power-conversion efficiency is a critical factor for the wider adoption of solar-cell modules. Thin-film solar cells are cheap and easy to manufacture, but their efficiencies are low compared to crystalline-silicon solar cells and need to be improved. A thin-film solar cell with two absorber layers (instead of only one), with bandgap energy graded in both, can capture solar photons in a wider spectral range. With a 300-nm-thick CuIn 1 − ξ 1 Ga ξ 1 Se 2 absorber layer and an 870-nm-thick Cu 2 ZnSn (S ξ 2 Se 1 − ξ 2 ) 4 absorber layer, an efficiency of 34.45% is predicted by a detailed optoelectronic model, provided that the grading of bandgap energy is optimal in both absorber layers. [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]

As vector wavefunctions are available to represent incident and scattered fields in an isotropic dielectric-magnetic medium endowed with magnetoelectric gyrotropy, a transition matrix can be conceptualized to relate the scattered field coefficients to the incident field coefficients for scattering by an arbitrary scatterer composed of a linear medium. The elements of the transition matrix must satisfy certain conditions for zero backscattering. For a scatterer composed of a uniaxial dielectric-magnetic medium endowed with magnetoelectric gyrotropy, the extended boundary condition method (EBCM) can be formulated to determine the transition matrix. The numerical results obtained thereby lead to the formulation of a sufficient set of three zero-backscattering conditions: (i) the scatterer is a body of revolution with the incident plane wave propagating along the axis of revolution; (ii) the impedances of both mediums are identical; and (iii) the magnetoelectric-gyrotropy vectors of both mediums are aligned along the axis of revolution, whether or not both magnetoelectric-gyrotropy vectors are co-parallel. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 plane wave 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. [ABSTRACT FROM AUTHOR]

CDs and DVDs are forensically important substrates for latent fingermarks. To enhance the visualization of fingermarks on CDs and DVDs, columnar thin films (CTFs) of either nickel or chalcogenide glass were deposited. The CTFs were deposited by directing a collimated vapor flux towards the substrate placed at an angle and made to rotate rapidly. The resulting CTFs of upright columnar morphology were grown conformally over these substrates. This process was shown to significantly enhance the visual quality of fingermarks. The fingermarks were aged for either 24 h or 72 h prior to the deposition of the CTF and both the latent and depleted fingermarks were used. 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. [ABSTRACT FROM AUTHOR]

The simple Lorentz-nonreciprocal medium described by the constitutive relations D = ε 0 ε r E − Γ × H and B = μ 0 μ r H − Γ × E is inspired by a specific spacetime metric, Γ being the magnetoelectric-gyrotopy vector. Field representations in this medium can be obtained from those for the isotropic dielectric-magnetic medium. When a plane wave is incident on a half space occupied by the Lorentz-nonreciprocal medium with magnetoelectric gyrotopy, theory shows that the transverse component of the magnetoelectric-gyrotopy vector is responsible for a rotation about the normal axis; furthermore, left/right reflection asymmetry is exhibited. Additionally, left/right transmission asymmetry is exhibited by a planar slab composed of the Lorentz-nonreciprocal medium with magnetoelectric gyrotopy. The left/right asymmetries are of interest for one-way devices. [ABSTRACT FROM AUTHOR]

The propagation of Dyakonov surface waves guided by the planar interface of (i) an isotropic dielectric material and (ii) a homogenized uniaxial dielectric composite material comprising both passive and active component materials was theoretically investigated, under the assumption that the optic axis of the uniaxial partnering material lies wholly in the interface plane. For a certain range of the volume fraction of the active component material, the uniaxial partnering material is neither wholly dissipative nor wholly active and the Dyakonov surface waves propagating in certain directions amplify but the Dyakonov surface waves propagating in other directions attenuate. [ABSTRACT FROM AUTHOR]

Examines the electromagnetic signature of a polymer model that is consisted of tiny point-polarizable spheres strung on helical strands. Characteristics of chiral medium; Formula for the helical arrangement; Discussion on the result of the study.

Presents a study which examined the effect of surface profile modelling errors in investigating the scalar scattering responses of impenetrable, periodic surfaces. Method; Numerical results and discussion; Factors that can alter the maximum surface slope.

Analyzes the scattering of ultrasonic waves by oblate spheroidal voids of very high aspect ratios using the T-matrix method. Significance of the scattering characteristics of smooth and rough oblate spheroidal voids; Schematic of the geometry of the ultrasonic scattering problem; Utilization of the T-matrix properties.

Discusses a general T-matrix formulated to study the scalar scattering response of an impenetrable, biperiodic surface in the presence of a z-directed medium inhomogeneity and reductions thereof. Definition of the incident field; Green's function used for surface scattering problems; Potential reflection coefficients; Matrix equations.

Presents a study which examined the interaction of electromagnetic waves with isotropic chiral media. Discussion on the Maxwellian electromagnetism; Origin of optically active media; Equations describing noncentrosymetric, isotropic micropolar solids; Details on the sourceless volume in which a planewave is propagating in the + z direction.

A rigorous treatment of the scattering of atoms by a stationary periodic hard wall in (n+1) dimensions is presented using the T-matrix approach. The normalized Fourier expansion of the surface field used in this formalism is shown to be computationally superior to the GR method of Garcia and the technique used by Goodman. This improvement comes because the surface field representation used here allows one to bypass the restrictions of the Rayleigh hypothesis. [ABSTRACT FROM AUTHOR]

The plane wave 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 4 × 4 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 ≥ 0. 9 over a 100-MHz spectral regime in the X band, with 360 MHz kA − 1 m magnetostatic controllability rate and 1 MHz V − 1 μ m electrostatic controllability rate. Notably, electrostatic control via graphene in the GHz range is novel. [ABSTRACT FROM AUTHOR]

Abstract: The characteristics of multiple cascaded metasurfaces comprising H‐shaped, magnetostatically controllable, subwavelength terahertz (THz) resonators made of InAs were systematically investigated, using a commercial solver based on the finite‐integration method, for the design of tunable filters. Three configurations of the biasing magnetostatic field were compared with each other as well as with the bias‐free configuration for filtering of normally incident linearly polarized plane waves. A close study of only one metasurface was found sufficient to broadly determine the sensitivity to the direction of the magnetostatic field and the bandwidth of a stopband. Furthermore, the effects of metasurface geometry and biasing field can be considered separately for initial design purposes. All features in the transmittance spectra for the bias‐free configuration that are related to the number of cascaded metasurfaces are also observed when the biasing magnetostatic field is applied. The coupling of adjacent metasurfaces in a cascade is strongly affected by the relative permittivity and the thickness of the spacer between the two metasurfaces. The spectral locations of stopbands scale with respect to the spacer's relative permittivity, the scaling rule being different from a classical one. The stopbands are redshifted when the spacer thickness is increased, with the redshift dependent on the polarization of the incident plane wave. Inter‐metasurface coupling and inter‐resonator coupling on the same metasurface affect the spectral location of a stopband in opposite ways. On‐off type switching can be obtained by changing the orientation of magnetostatic field. The elucidated characteristics are expected to be important for not only filters but also other tunable THz devices. [ABSTRACT FROM AUTHOR]

The energy extinction cross section of a concentrically layered sphere varies with velocity as the Doppler shift moves the spectral content of the incident signal in the sphere's co-moving inertial reference frame toward or away from resonances of the sphere. Computations for hollow gold nanospheres show that the energy extinction cross section is high when the Doppler shift moves the incident signal's spectral content in the co-moving frame near the wavelength of the sphere's localized surface plasmon resonance. The energy extinction cross section of a three-layer sphere consisting of an olivine-silicate core surrounded by a porous and a magnetite layer, which is used to explain extinction caused by interstellar dust, also depends strongly on velocity. For this sphere, computations show that the energy extinction cross section is high when the Doppler shift moves the spectral content of the incident signal near either of olivine-silicate's two localized surface phonon resonances at 9.7 μm and 18 μm. [ABSTRACT FROM AUTHOR]

A boundary-value problem was formulated to investigate the reflection and transmission of light by a device consisting of an orthorhombic dielectric material that sits atop a 1D grating and is coated with a 3D topological insulator. In view of the periodicity of the grating, the electromagnetic field phasors were represented in terms of Floquet harmonics and the analysis was conducted by using the rigorous coupled-wave approach. We found that the device can exhibit bilaterally asymmetric reflection and transmission in the mid-infrared wavelength regime, provided that the surface admittance of the topological insulator is sufficiently high. This bilateral asymmetry is exhibited in narrow regimes for both the free-space wavelength and the angle of incidence. Bilateral asymmetry is exhibited more significantly by the specular components than by the nonspecular components of the reflected and transmitted plane waves. [ABSTRACT FROM AUTHOR]

Although humans have long been imitating biological structures to serve their particular purposes, only a few decades ago engineered biomimicry began to be considered a technoscientific discipline with a great problem-solving potential. The three methodologies of engineered biomimicry-viz., bioinspiration, biomimetic, and bioreplication-employ and impact numerous technoscientific fields. For producing fuels and electricity by artificial photosynthesis, both processes and porous surfaces inspired by plants and certain marine animals are under active investigation. Biomimetically textured surfaces on the subwavelength scale have been shown to reduce the reflectance of photovoltaic solar cells over the visible and the near-infrared regimes. Lenticular compound lenses bioreplicated from insect eyes by an industrially scalable technique offer a similar promise. [ABSTRACT FROM AUTHOR]

Mathematical statements of the Huygens principle relate the electric and magnetic field phasors at an arbitrary location in a source-free region enclosed by a surface to the tangential components of the electric and magnetic field phasors over that surface, via the dyadic Green functions applicable to the linear homogeneous medium occupying that region. We have mathematically formulated the Huygens principle for the electric and magnetic field phasors when the permittivity and permeability dyadics of the medium are symmetric, the symmetric parts of the two magnetoelectric dyadics of the medium are negative of each other, and both magnetoelectric dyadics also contain anti-symmetric terms. We have also formulated the Huygens principle for the electric (resp. magnetic) field phasor in a medium whose permittivity (resp. permeability) is scalar, the permeability (resp. permittivity) is symmetric, the symmetric parts of the two magnetoelectric dyadics reduce to dissimilar scalars, and anti-symmetric parts of the two magnetoelectric dyadics are identical. [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]

ABSTRACT Chiral sculptured thin films of zinc selenide with different helical periods were deposited on both sides of a glass slide using the serial bideposition technique in order to fabricate a dual-band circular-polarization filter polarizer that exhibits two distinct circular Bragg regimes for a wide range (about 45°) of the angle of incidence. This device can be angle tuned within a ±8% spectral range. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2381-2384, 2016 [ABSTRACT FROM AUTHOR]

• Thermal hysteresis surface-plasmon-polariton (SPP) wave propagation. • SPP-wave propagation possible over the entire thermal-hysteresis regime. • Phase speed higher on the cooling branch. • Attenuation rates higher on the heating branch. • Useful to sense if the temperature is increasing or decreasing. Propagation of surface-plasmon-polariton (SPP) waves guided by a metal/dielectric interface can be greatly affected by thermal hysteresis in the dielectric material. Calculations for the silver/vanadium-dioxide interface show that, while SPP-wave propagation is possible over the entire thermal-hysteresis regime 58 ° C * * , 72 ° C if the wavelength ≲ 1100 nm, at higher frequencies SPP-wave propagation is possible only in a low-temperature portion of the same regime. The phase speed is higher and the attenuation rates are lower on the cooling branch than on the heating branch, which may be used to sense whether the temperature is increasing or decreasing. [ABSTRACT FROM AUTHOR]

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]

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]

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]

We considered the experimental realization of a Tamm medium that is optically equivalent to the collision of two linearly polarized gravitational plane waves as a piecewise-homogeneous metamaterial. Our formulation was based on the homogenization of remarkably simple arrangements of oriented ellipsoidal nanoparticles of isotropic dielectric-magnetic mediums. The inverse Bruggeman homogenization was used to estimate the constitutive parameters, volume fractions, and shape parameters for the component mediums. The presented formulation is appropriate for the regions of spacetime where the two gravitational plane waves interact, excluding the immediate vicinity of the nonsingular Killing–Cauchy horizon at the focusing point of the two plane waves. [ABSTRACT FROM PUBLISHER]

The absorption and extinction efficiencies of a sphere covered by InSb coating and illuminated by an incident plane wave in the terahertz gap were computed. Numerical results shows that these efficiencies, for some core materials and in some spectral regimes, can be reduced by adjusting the temperature. This, reduction of absorption and extinction by the InSb coating is not possible for air and metallic spheres, but it is possible for dielectric spheres. Furthermore, the InSb coating is more effective in absorption reduction for more dissipative dielectric materials, whereas it is more effective in extinction reduction for less dissipative dielectric materials. [ABSTRACT FROM AUTHOR]

Recent advances in nanoscale bioreplication processes present the potential for novel basic and applied research into organismal behavioral processes. Insect behavior potentially could be affected by physical features existing at the nanoscale level. We used nano-bioreplicated visual decoys of female emerald ash borer beetles (Agrilus planipennis) to evoke stereotypical mate-finding behavior, whereby males fly to and alight on the decoys as they would on real females. Using an industrially scalable nanomolding process, we replicated and evaluated the importance of two features of the outer cuticular surface of the beetle's wings: structural interference coloration of the elytra by multilayering of the epicuticle and fine-scale surface features consisting of spicules and spines that scatter light into intense strands. Two types of decoys that lacked one or both of these elements were fabricated, one type nano-bioreplicated and the other 3D-printed with no bioreplicated surface nanostructural elements. Both types were colored with green paint. The light-scattering properties of the nano-bioreplicated surfaces were verified by shining a white laser on the decoys in a dark room and projecting the scattering pattern onto a white surface. Regardless of the coloration mechanism, the nano-bioreplicated decoys evoked the complete attraction and landing sequence of Agrilus males. In contrast, males made brief flying approaches toward the decoys without nanostructured features, but diverted away before alighting on them. The nano-bioreplicated decoys were also electroconductive, a feature used on traps such that beetles alighting onto them were stunned, killed, and collected. [ABSTRACT FROM AUTHOR]

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]

Abstract: The versatile oblique-angle deposition (OAD) technique, which is based on traditional vapor-deposition processes, allows the growth of thin films comprising one-, two- and three-dimensional complex nanostructures. The OAD technique has evolved into the conformal-evaporated-film-by-rotation (CEFR) and the modified CEFR (mod-CEFR) techniques, which have been successfully used to coat biotemplates for possible replication. Finally, the Nano4Bio technique – which is the sequential combination of the mod-CEFR technique, electroforming, plasma ashing and stamping/casting – is emerging as a robust and industrially scalable manufacturing process to fabricate bioreplicas. [Copyright &y& Elsevier]

The reflectances of a thin-film solar cell were computed, using the rigorous coupled-wave approach, as functions of the angle of incidence and the free-space wavelength for illumination by linearly polarized plane waves. A tandem solar cell made of amorphous-silicon alloys was considered. The metallic back-reflector was taken to be periodically corrugated. Both the simple and the compound periodic corrugations of the metallic back-reflector (surface-relief gratings) were investigated. Low-reflectance bands in the reflectance spectrums were correlated with the solutions of the underlying canonical boundary-value problem to delineate the excitation of multiple surface-plasmon-polariton (SPP) waves. For the standard AM1.5 solar irradiance spectrum, we found that the light absorption efficiency in the near-infrared spectral regime can be increased up to 100% when multiple SPP waves of both linear polarization states are excited. [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]

Abstract: The prism-coupled excitation of Dyakonov–Tamm waves guided by the planar interface of a homogeneous, isotropic dielectric material and a periodically nonhomogeneous sculptured nematic thin film (SNTF) was investigated. The excitation of Dyakonov–Tamm waves was identified by correlating a high-absorptance band in the plots of absorptance vs. the incidence angle and the direction of propagation in the interface plane with the solutions of the underlying canonical boundary–value problem. Dyakonov–Tamm waves were found to have a much wider angular existence domain than Dyakonov waves, and broader absorptance peaks than both the Dyakonov and Tamm waves in the plots of absorptance vs. the incidence angle. [Copyright &y& Elsevier]

Abstract: We explored the effects of relative motion on the excitation of surface-plasmon-polariton (SPP) waves guided by the planar interface of a metal film and a dielectric slab, both materials being isotropic and homogeneous. Electromagnetic phasors in moving and non-moving reference frames were related directly using the corresponding Lorentz transformations. Our numerical studies revealed that, in the case of a uniformly moving dielectric slab, the angle of incidence for SPP-wave excitation is highly sensitive to (i) the ratio β of the speed of motion to speed of light in free space and (ii) the direction of motion. When the direction of motion is parallel to the plane of incidence, the SPP wave is excited by p-polarized (but not s-polarized) incident plane waves for low and moderate values of β, while at higher values of β the total reflection regime breaks down. When the direction of motion is perpendicular to the plane of incidence, the SPP wave is excited by p-polarized incident plane waves for low values of β, but s-polarized incident plane waves at moderate values of β, while at higher values of β the SPP wave is not excited. In the case of a uniformly moving metal film, the sensitivity to β and the direction of motion is less obvious. [Copyright &y& Elsevier]

Abstract: The excitation of multiple surface-plasmon-polariton (SPP) waves—of different linear polarization states, phase speeds and spatial profiles—guided by the interface of a metal film and a rugate filter in the Kretschmann configuration was investigated. A plane wave of either of the two linear polarization states was made incident on the metal-capped rugate filter of finite thickness and the absorptances were calculated using a stable algorithm. The excitation of SPP waves was inferred by the presence of those peaks in the absorptance curves that were independent of the thickness of the rugate filter. The absorptance peaks representing the excitation of s-polarized SPP waves are narrower than those representing p-polarized SPP waves. For efficient excitation of multiple SPP waves, the metal film''s thickness should be close to the penetration depth of the metal. The solution of a canonical boundary-value problem of SPP-wave propagation guided by a metal film, with a semi-infinite homogeneous dielectric material on one side and a semi-infinite rugate filter on the other side, reinforced the results obtained for the Kretschmann configuration. The thin metal film in the Kretschmann configuration may lead to coupling of its two interfaces. [Copyright &y& Elsevier]

While metamaterials offer the potential to realize Tamm mediums that are electromagnetically equivalent to vacuous spacetime subjected to gravitational fields, practical formulations for suitable metamaterials have not hitherto been developed. This matter was addressed by establishing a metamaterial formulation for the Tamm medium representing Schwarzschild-(anti-)de Sitter spacetime. Our formulation is remarkably simple and does not involve a complex nanostructure of the type that is often associated with metamaterials. Instead it is based on the homogenization of only isotropic dielectric and isotropic magnetic component mediums, which are distributed randomly as oriented spheroidal particles. Using the inverse Bruggeman homogenization formalism, we demonstrated that a wide range of constitutive parameter values for the Tamm medium may be accessed through varying the particle shape, volume fraction, or relative permittivity and relative permeability of the component mediums. The presented formulation is appropriate for the regions of spacetime that lie outside the event horizon for Schwarzschild spacetime and inside the cosmological horizon for de Sitter spacetime; there are no such restrictions for anti-de Sitter spacetime. [ABSTRACT FROM AUTHOR]

Various vacuum techniques are employed to develop fingermarks on evidentiary items. In this work, a vacuum was used to deposit columnar thin films (CTFs) on untreated, cyanoacrylate-fumed or dusted fingermarks on a limited selection of nonporous surfaces (microscope glass slides and evidence tape). CTF deposition was not attempted on fingermarks deposited on porous surfaces. The fingermarks were placed in a vacuum chamber with the fingermark side facing an evaporating source boat containing either chalcogenide glass or MgF. Thermal evaporation of chalcogenide glass or MgF under a 1 μTorr vacuum for 30 min formed dense CTFs on fingermark ridges, capturing the topographical features. The results show that it is possible to capture fingermark topology using CTFs on selected untreated, vacuumed cyanoacrylate-fumed or black powder-dusted nonporous surfaces. Additionally, the results suggested this might be a mechanism to help elucidate the sequence of deposition. [ABSTRACT FROM AUTHOR]

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]