Planar and Conformal Analysis of Frequency Selective Surface Loaded with Lumped Elements

This work presents an analysis of frequency selective surfaces (FSSs) with Dürer's pentagon pre-fractals patch elements. The proposed FSSs are composed by a 2-D periodic array of metal pre-fractals elements printed on a dielectric substrate. A parametric analysis is performed using Ansoft Designer commercial software in terms of the FSS periodicity and of the fractal iteration number used in the FSS elements. The structures are proposed to behave like stop-band spatial filters and exhibit interesting features to be used in the design of compact FSSs with broadband or dual band responses.

A simple analysis technique for a concept in frequency selective surfaces (FSSs) basis from Babinet's principle, of two closely coupled conducting elements is presented. A layer of conducting patch elements and a layer of slot elements are designed on either side of a substrate, named as complementary FSS (CFSS). An equivalent circuit (EC) model in conjunction with transmission line (TL) model is employed to analyze the response of the structure. This method can predict the scattering parameters with high accuracy at a normal and oblique angle of incidence for both parallel and perpendicular polarizations. A parametric study of CFSS array aimed at their EC model optimization is presented. The CFSS exhibits a highly stable passband for normal and oblique incidences. The validity of the proposed method is verified with commercial simulation software package. It is observed that the results obtained by both methods are very good in agreement.

This paper presents an analysis of the characteristics of the frequency selective surface (FSS) by means of equivalent circuit models. In order to determine the circuit element parameters of the FSS with resonant elements of arbitrary shape, the eigenvalue problem of the matrix equation is solved and the Q curve of each resonance is derived from the frequency dependence of the reactance obtained from the characteristic current distributions at resonance. By equating this Q curve with that for the equivalent circuit, the circuit parameters are derived. As an example of analysis by the present method, the circuit element parameters of patch-type resonant elements designed by us using the genetic algorithm (GA) are derived. The characteristics of the dielectric-loaded FSS for the C/Ka band are analyzed by means of the equivalent circuit. The usefulness of the proposed method is verified by comparison of the frequency characteristics obtained by the method of moments and by the equivalent circuit. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(6): 9–17, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20162

The problem of scattering of an obliquely incident plane acoustic wave from an infinite solid elastic clad rod is formulated. Numerical calculations show the effects of the variations of the cladding thickness on both the backscattered pressure spectrum and individual normal modes. It is shown that various resonance frequencies have different levels of sensitivity to variations of the cladding thickness. Experimental measurements are also performed at both normal and oblique incident angles on a copper-clad aluminum rod; good agreement is observed between the calculated and the measured results. These results demonstrate the potential of acoustic resonance scattering procedures for application in nondestructive evaluation (NDE) of clad rods.

A large-area superhydrophobic and omnidirectional antireflective nanostructured organically modified silica coating has been designed and prepared. The coating mimics the self-cleaning property of superhydrophobic lotus leaves and omnidirectional broad band antireflectivity of moth compound eyes, simultaneously. Water contact and sliding angles of the coating are around 160° and 10°, respectively. Coating improves the transmittance of the glass substrate around 4%, when coated on a single side of a glass, in visible and near-infrared region at normal incidence angles. At oblique incidence angles (up to 60°) improvement in transmission reaches to around 8%. In addition, coatings are mechanically stable against impact of water droplets from considerable heights. We believe that our inexpensive and durable multifunctional coatings are suitable for stepping out of the laboratory to practical outdoor applications.

Recent backscattering interferometry studies utilise a single channel microfluidic system, typically approximately semicircular in cross-section. Here, we present a complete ray tracing model for on-chip backscattering interferometry with a semicircular cross-section, including the dependence upon polarisation and angle of incidence. The full model is validated and utilised to calculate the expected fringe patterns and sensitivities observed under both normal and oblique angles of incidence. Comparison with experimental data from approximately semicircular channels using the parameters stated shows that they cannot be explained using a semicircular geometry. The disagreement does not impact on the validity of the experimental data, but highlights that the optical mechanisms behind the various modalities of backscattering interferometry would benefit from clarification. From the analysis presented here, we conclude that for reasons of ease of analysis, data quality, and sensitivity for a given radius, capillary-based backscattering interferometry affords numerous benefits over on-chip backscattering interferometry.

The mean penetration depths and stopping profiles of positrons with incident energies up to 10 keV impinging on semi-infinite aluminum with normal and oblique angles of incidence are stochastically modelled within a Monte-Carlo framework. The elastic scattering cross sections have been obtained from a partial wave expansion. To model inelastic core and valence electron excitation, we have used the Gryzinski's expression. Our simulated results agree very well with the available experimental data and clearly demonstrate that the mean penetration depths are not adequately described by the simple power law commonly used in defect profiling. This suggests that both mean penetration depths and stopping profiles cannot generally be modelled by material-independent parameters as was proposed previously. The mean penetration depth decreases non-monotonically with increasing the angle of incidence from 0° to 80°. This can be seen from the reduction of the width of the implantation profiles.

The physics of strong coupling phenomena in semiconductor quantum microcavities is reviewed. This is a relatively new field with most important developments having occurred in the last 5 years. We describe how such microcavities enable both electronic and photonic properties of semiconductors, and the interaction between them, to be controlled in the same structure. The resulting coupled exciton-photon eigenstates, cavity polaritons, have many interesting properties including very low mass for small in-plane wavevectors, and can be studied easily and directly in optical experiments, unlike exciton-polaritons in bulk semiconductors. A wealth of new optical phenomena has been reported in this field in the last few years. This review describes the most important of these phenomena. We discuss the reasons why polaritons have fundamentally different properties in microcavities as compared with those in bulk materials or quantum wells. We explain the factors which control the strength of the exciton-photon coupling and how the resulting optical spectra can be modelled. We then emphasize, in the main body of the review, the particularly important results of reflectivity experiments at both normal and oblique angles of incidence, the effects of external electric and magnetic fields, the results of coherent Raman scattering experiments, the effects of disorder on microcavity spectra, including the observation of motional narrowing over the exciton disorder potential, studies of coupled microcavities, and photoluminescence and time-resolved phenomena.

The amplitude acoustic reflection coefficient of an interface between two lossy biological tissues can be approximated as where is the lossless acoustic reflection coefficient and is the change in (absorption coefficient per wavenumber) across the tissue interface. This approximation is shown to be valid for both normal and oblique angles of incidence.

Elastic-collision spikes in sputtering of metals at normal and oblique incidence

<div class="htmlview paragraph">It has been shown that the combination of a particle velocity (u) sensor and a sound pressure (p) microphone can successfully be used to determine the reflection coefficient of acoustic materials [<span class="xref">1</span>, <span class="xref">2</span>, <span class="xref">3</span> and <span class="xref">4</span>].</div> <div class="htmlview paragraph">In this paper, a practical measurement technique and a so called pu-probe impedance meter are described that require no Kundt's tube or anechoic room. The procedure allows fast (less than 60 seconds) sound absorption measurements under both normal and oblique angles of incidence on small test samples (less than 30*30cm). The total size of the pu-probe impedance meter is 60 centimeters and weights less than 1kg. The method can be used in combination with a sound card based software package.</div> <div class="htmlview paragraph">At first, the pu-probe is calibrated in approximately 20 seconds. The frequency response of the impedance sensor is transformed to an impulse response. This response is time windowed to cancel out the room reflections.</div> <div class="htmlview paragraph">After the calibration, the reflection coefficient (and the real and imaginary part of the impedance) of the acoustic materials are determined by putting the pu-probe in close proximity of the acoustic sample.</div>

In this paper a modified method based on FDTD method is used to analyze frequency selective surfaces with periodic boundary condition. Computation results are compared to that from other scholars. Good agreement has been observed. Multiplexer, which consists of two sheets of FSS, is simulated and good performance has been obtained over a band from 100 GHz to 450 GHz.

In this paper, a submillimetric/THz metasurface polarization/oblique independent absorber is designed and characterized. The absorber is designed using a periodic arrangement of a modified split ring resonator unit cell. The symmetric absorber is insensitive to the variation of incident angles and polarization angles. The results confirm that perfect absorption is achieved (close to 100%) for either TM or TE polarization at 300 GHz. Moreover, the absorber is efficient for normal and oblique incident angle (above 90% for 45° angle of incidence). In all the presented cases, the full width half maximum bandwidth is 20 GHz. The absorber unit cell size is only 0.0052 λ 0 × 0.0052 λ 0 and it has a low-profile thickness = 0.0002 λ 0, at the operating frequency. Also, an absorber-based biosensor is presented. The sensing has proved the coating analyte thickness can be detected by shifting the absorption frequency. The maximum sensitivity is 24.9% RIU−1 with a low-profile maximum of 50 µm thickness. Analytical formulas for the frequency shift have been extracted. The presented results are discussed based on 3D full-wave EM simulations.

A circular polarizer is a single layer or multi-layer structure that converts linearly polarized waves into circularly polarized ones and vice versa. In this communication, a simple method based on transmission line circuit theory is proposed to model and design circular polarizers. This technique is more flexible than those previously presented in the way that it permits to design polarizers with the desired spacing between layers, while obtaining surfaces that may be easier to fabricate and less sensitive to fabrication errors. As an illustrating example, a modified version of the meander-line polarizer being twice as thin as its conventional counterpart is designed. Then, both polarizers are fabricated and measured. Results are shown and compared for normal and oblique incidence angles in the planes φ = 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> and φ = 90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> .

Computer programs for simulation of microwave structures are becoming accessible. However, to understand electromagnetic fields behavior and to comprehend the numerical model limitations, a solid theoretical basis and computational expertise to enable the implementation of the own programs remains indispensable. The wave concept iterative procedure, WCIP, is a numerical technique easy to understand, that can be implemented without great efforts. In this work the WCIP is applied to analysis of frequency selective surface, FSS, with Koch Island patch elements. Obtained numerical results are compared to others obtained by the use of Ansoft Designer <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">™</sup> software and to experimental ones.