The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform

Hugh W Hillhouse - One of the best experts on this subject based on the ideXlab platform.

  • simulation and interpretation of 2d diffraction patterns from self assembled nanostructured films at arbitrary Angles of Incidence from grazing Incidence above the critical Angle to transmission perpendicular to the substrate
    Journal of Physical Chemistry B, 2006
    Co-Authors: Michael P Tate, Brian W Eggiman, Vikrant N Urade, Jonathon D Kowalski, Benjamin D Hamilton, Hugh W Hillhouse
    Abstract:

    A method to calculate the location of all Bragg diffraction peaks from nanostructured thin films for arbitrary Angles of Incidence from just above the critical Angle to transmission perpendicular to the film is reported. At grazing Angles, the positions are calculated using the distorted wave Born approximation (DWBA), whereas for larger Angles where the diffracted beams are transmitted though the substrate, the Born approximation (BA) is used. This method has been incorporated into simulation code (called NANOCELL) and may be used to overlay simulated spot patterns directly onto two-dimensional (2D) grazing Angle of Incidence small-Angle X-ray scattering (GISAXS) patterns and 2D SAXS patterns. The GISAXS simulations are limited to the case where the Angle of Incidence is greater than the critical Angle (αi > αc) and the diffraction occurs above the critical Angle (αf > αc). For cases of surfactant self-assembled films, the limitations are not restrictive because, typically, the critical Angle is around 0...

  • order and orientation control of mesoporous silica films on conducting gold substrates formed by dip coating and self assembly a grazing Angle of Incidence small Angle x ray scattering and field emission scanning electron microscopy study
    Langmuir, 2005
    Co-Authors: Michael P Tate, Brian W Eggiman, Jonathan D Kowalski, Hugh W Hillhouse
    Abstract:

    Grazing-Angle of Incidence small-Angle X-ray scattering (GISAXS) and high-resolution field emission scanning electron microscopy have been used to characterize the mesophase symmetry, orientation, and long-range order in PEO20−PPO70−PEO20 (Pluronic P123) templated mesoporous silica thin films on conducting gold substrates as a function of silica-to-ethylene oxide (Si/EO) block ratio and relative humidity (RH). The films are formed by dip-coating followed by evaporation-induced self-assembly under tightly controlled RH. The general evolution of the mesophase follows the trends that are expected based on shape factors due to swelling of the PEO block. However, changes in orientation of the nanostructure relative to the substrate and the degree of long-range order are found to depend on Si/EO ratio. These effects are likely due to the dynamics of evaporation and self-assembly. Generally, at Si/EO ratios lower than 3.29, the films contained regions where the nanostructure was not oriented relative to the plan...

Choonbum Choi - One of the best experts on this subject based on the ideXlab platform.

  • flow past a square cylinder with an Angle of Incidence
    Physics of Fluids, 2010
    Co-Authors: Donghyeog Yoon, Kyungsoo Yang, Choonbum Choi
    Abstract:

    A parametric study has been carried out to elucidate the characteristics of flow past a square cylinder inclined with respect to the main flow in the laminar flow regime. Reynolds number and Angle of Incidence are the key parameters which determine the flow characteristics. Location of separation point is greatly affected by Angle of Incidence, thus determining the flow field around the square cylinder. The critical Reynolds number for periodic vortex shedding at each Angle of Incidence considered is obtained by using Stuart–Landau equation. Attempt is made to classify the related flow patterns from a topological point of view, resulting in three distinct patterns in total. A comprehensive analysis of the effects of Reynolds number and Angle of Incidence on flow-induced forces on the square cylinder is presented. Collecting all the results obtained, contour diagrams of force and moment coefficients, Strouhal number, rms of lift-coefficient fluctuation, as well as a flow-pattern diagram are proposed for the ranges of the two parameters considered in the current investigation. Finally, a Floquet stability analysis is presented to detect the onset of the secondary instability leading to three-dimensional flow. The proposed diagrams and the Floquet stability analysis shed light on better physical understanding of the flow past a square cylinder, which should be useful in many engineering applications.

Kumar Vaibhav Srivastava - One of the best experts on this subject based on the ideXlab platform.

  • bandwidth enhanced dual band dual layer polarization independent ultra thin metamaterial absorber
    Applied Physics A, 2015
    Co-Authors: Somak Bhattacharyya, Saptarshi Ghosh, Devkinandan Chaurasiya, Kumar Vaibhav Srivastava
    Abstract:

    In this paper, a polarization-independent metamaterial absorber with enhanced bandwidth at two separate frequency bands is proposed over wide Angle of Incidence. The proposed structure consists of two layers of dielectric substrate. The unit cell is designed on the top surfaces of both the layers of the dielectric by parametric optimization in such a way that bandwidth-enhanced absorptions occur in C and X bands. The proposed structure is fabricated, and experimental results are in good agreement with the simulated responses. This bandwidth-enhanced dual-band absorption nature is maintained for any Angle of polarization under normal Incidence, thus making the absorber polarization independent in nature. The structure also shows bandwidth-enhanced dual-band absorptions over wide Angle of Incidence up to 45° under TE polarization and 30° under TM polarization. Moreover, the proposed structure is ultra-thin, having total thickness of 3.2 mm, ~λ/14 and λ/10 with respect to the center frequencies of two absorption bands.

  • triple band polarization independent ultra thin metamaterial absorber using electric field driven lc resonator
    Journal of Applied Physics, 2014
    Co-Authors: Somak Bhattacharyya, Kumar Vaibhav Srivastava
    Abstract:

    In this paper, a triple band polarization-independent metamaterial absorber using electric field-driven LC resonators is proposed over wide Angle of Incidence. The unit cell is designed by parametric optimization in such a way that triple band absorption occurs in C-band. The proposed structure exhibits triple band absorption property for any Angle of polarization under normal Incidence. It also shows high absorption for wide Angle of Incidence upto 60° for both TE and TM polarizations. The proposed structure is also fabricated and experimental results provide good agreement with the simulated responses. The constitutive electromagnetic parameters viz. effective permittivity and effective permeability are extracted from the simulated response, which support the absorption phenomena at all these three frequencies. The reflection from the structure is numerically computed and verified with simulated response, and it shows good agreement between them.

Somak Bhattacharyya - One of the best experts on this subject based on the ideXlab platform.

  • wideband tunable mid infrared cross polarisation converter using monolayered graphene based metasurface over a wide Angle of Incidence
    Iet Microwaves Antennas & Propagation, 2019
    Co-Authors: Vinit Singh Yadav, Sambit Kumar Ghosh, Santanu Das, Somak Bhattacharyya
    Abstract:

    In this study, the authors have designed and proposed a monolayer graphene-based metasurface, performing as a broadband polarisation converter over a wide Angle of Incidence. The unit cell of the metasurface consists of split ring generated over a perforated single layer of graphene grown over metal-backed silicon dioxide. The structure converts incident linearly polarised wave into its cross-polarised component over a wide bandwidth with peak polarisation conversion exhibits value to unity. The plane of polarisation of the incident electromagnetic wave is rotated orthogonally on reflection from the proposed metasurface over full width at half maxima bandwidth around 72.83% compared with centre frequency of 2.16 THz, which can be maintained up to 40° incident Angles under both transverse electric and transverse magnetic polarisations. The proposed structure is as thin as ~ λ /7.3 with respect to lowermost frequency and the period of the structure is about λ /10.7. The frequency band of polarisation conversion can be tuned by altering chemical doping as well as the electrostatic grating of the graphene sheet. The structure can find applications toward sensing, spectroscopy etc.

  • bandwidth enhanced dual band dual layer polarization independent ultra thin metamaterial absorber
    Applied Physics A, 2015
    Co-Authors: Somak Bhattacharyya, Saptarshi Ghosh, Devkinandan Chaurasiya, Kumar Vaibhav Srivastava
    Abstract:

    In this paper, a polarization-independent metamaterial absorber with enhanced bandwidth at two separate frequency bands is proposed over wide Angle of Incidence. The proposed structure consists of two layers of dielectric substrate. The unit cell is designed on the top surfaces of both the layers of the dielectric by parametric optimization in such a way that bandwidth-enhanced absorptions occur in C and X bands. The proposed structure is fabricated, and experimental results are in good agreement with the simulated responses. This bandwidth-enhanced dual-band absorption nature is maintained for any Angle of polarization under normal Incidence, thus making the absorber polarization independent in nature. The structure also shows bandwidth-enhanced dual-band absorptions over wide Angle of Incidence up to 45° under TE polarization and 30° under TM polarization. Moreover, the proposed structure is ultra-thin, having total thickness of 3.2 mm, ~λ/14 and λ/10 with respect to the center frequencies of two absorption bands.

  • triple band polarization independent ultra thin metamaterial absorber using electric field driven lc resonator
    Journal of Applied Physics, 2014
    Co-Authors: Somak Bhattacharyya, Kumar Vaibhav Srivastava
    Abstract:

    In this paper, a triple band polarization-independent metamaterial absorber using electric field-driven LC resonators is proposed over wide Angle of Incidence. The unit cell is designed by parametric optimization in such a way that triple band absorption occurs in C-band. The proposed structure exhibits triple band absorption property for any Angle of polarization under normal Incidence. It also shows high absorption for wide Angle of Incidence upto 60° for both TE and TM polarizations. The proposed structure is also fabricated and experimental results provide good agreement with the simulated responses. The constitutive electromagnetic parameters viz. effective permittivity and effective permeability are extracted from the simulated response, which support the absorption phenomena at all these three frequencies. The reflection from the structure is numerically computed and verified with simulated response, and it shows good agreement between them.

F Frost - One of the best experts on this subject based on the ideXlab platform.

  • dielectric function of amorphous tantalum oxide from the far infrared to the deep ultraviolet spectral region measured by spectroscopic ellipsometry
    Journal of Applied Physics, 2000
    Co-Authors: E Franke, John A Woollam, C L Trimble, Michael J Devries, Mathias Schubert, F Frost
    Abstract:

    Amorphous tantalum oxide thin films were deposited by reactive rf magnetron sputtering onto [001] silicon substrates. Growth temperature, oxygen partial pressure, and total gas pressure have been varied to obtain thin films with different densities. The thin films were analyzed by glancing Angle-of-Incidence x-ray diffraction, atomic force microscopy, and variable Angle-of-Incidence spectroscopic ellipsometry in the near infrared to vacuum ultraviolet spectral region for photon energies from E=1 to 8.5 eV, and in the infrared region from E=0.03 to 1 eV. We present the dielectric function of amorphous tantalum oxide obtained by line shape analysis of the experimental ellipsometric data over the range from E=0.03 to 8.5 eV (40 μm–145 nm). In the infrared spectral region the ellipsometric data were analyzed using Lorentzian line shapes for each absorption mode observed in the spectra. Amorphous tantalum oxide optical properties in the near infrared to vacuum ultraviolet spectral region were extracted by usin...