Strip Grating Research Articles

Electromagnetic beam diffraction by a finite strip grating

We study the diffraction of an electromagnetic beam by a finite strip grating. The fields are expressed in terms of their angular spectra. These spectra verify an integral equation which is derived by means of the combined boundary conditions method introduced in (F. Montiel, M.Nevière, Opt. Commun. 101 (1993) 151).

Analysis of Electromagnetic Wave Diffraction By a Semi-Infinite Strip Grating and Evaluation of End-Effects - Abstract

Diffraction of electromagnetic wave by a semi-infinite strip grating is analyzed and end-effects contribution is investigated. In the formulation, the current induced on each strip is divided into periodic current on an infinite strip grating and the correction current induced by the truncation of the periodic structure. These currents are determined by solving a set of integral equations under the assumption that each strip is narrow relative to the wavelength. Far field representation obtained by the asymptotic evaluation of the radiation integral indicates that the scattered field by the semi-infinite grating is expressed as a sum of the Floquet's modes and the cylindrical wave diffracted at the edge of the semi-infinite grating. In order to evaluate the end-effect contributions, numerical computations are carried out for current distribution, diffraction patterns, and radiated powers by the induced correction currents.

Analysis of Electromagnetic Wave Diffraction by a Semi-Infinite Strip Grating and Evaluation of End-Effects

Analysis of Electromagnetic Wave Diffraction by a Semi-Infinite Strip Grating and Evaluation of End-Effects

半無限平行平板格子の散乱界の空間一波数解析

In order to reveal the end-effects of a finite grating in pure form, scattering problem of electromagnetic waves by a semi-infinite strip grating is analyzed, and scattered fields are investigated in space-wavenumber domain by using the Gaussian Windowed Fourier Transform (GWT). The GWT used here is a powerful tool for the spacewavenumber analysis of scattering data, because it can provide better insights into scattering mechanisms that are not immediately apparent in the space domain. In the resultant space-wavenumber displays, the Floquet's modes excited by the periodic structure and the cylindrical wave diffracted at the edge of the grating are resolved and identified, and the behavior of them are clearly observed.

Transmission waveguide resonator with dissipative and polarization-sensitive elements

The diffraction of Ep and Hp waves due to the inhomogeneous step expansion of a planar waveguide is analyzed. The resonant region consists of magnetodielectric layers, a resistive film, and a grating of parallel metal strips. The eigenmodes of the system are defined by the method of moments on the basis of equivalent boundary conditions and scattering characteristics. The solution is represented in the form of infinite systems of linear algebraic equations. The grating considerably increases the Q-factor of the trapped modes for Hp waves, decreases the velocity of such waves and affects differently the degree of intermode (Ep⇆En, Hp⇆Hn) transformation of the fields. A film with average conductance adds some dissipative losses but retains the dispersion dependences by selective action on the Q-factor of the trapped modes. The distinct boundary between attenuation and propagation regimes is absent.

An Analysis of Periodic Leaky Surface Acoustic Waveguides Using the Hybrid Finite Element Method

A numerical approach based on the hybrid finite element method (HFEM) is described for the analysis of leaky surface acoustic waves (LSAWs) in periodic waveguides with electric-flux leakage into vacuum. Employing superelements and conventional rectangular elements, we evaluate a functional corresponding to the entire region: the substrate region, the inhomogeneous region with electrodes, and the vacuum region. Hence, in this method, all the effects of piezoelectric perturbation, mechanical perturbation, energy storage due to nonradiated bulk waves, and radiation loss of LSAWs are automatically taken into account. Computed results for aluminum strip gratings on a 36° Y–X LiTaO3 substrate are presented. The convergence of solutions are investigated in detail and the dispersion curves and radiation losses of LSAWs are evaluated. Numerical results show that the electric-flux leakage into the vacuum affects the complex wavenumbers, especially in the higher frequency region over the upper edge of the stopband.

Propagation of longitudinal leaky surface waves under periodic metal grating structure on lithium tetraborate

The dispersion properties of longitudinal leaky surface waves propagating under the periodic Al strip grating on lithium tetraborate (Li(2)B(4)O(7); LBO) are described theoretically and experimentally for applications of the mode to high frequency SAW devices. A theoretical method developed here is based on Floquet's theorem using space harmonics as an orthogonal function set and real boundary integral equations derived from the method of weighted residuals for a period of each region, i.e., substrate, metal, and free space. The boundary integral equations are solved by using the Galerkin procedure. The periodic strip gratings with both single-electrodes and double-electrodes are investigated, considering the convergency of the numerical computation for the number of the space harmonics. As a result, the propagation loss for shorted gratings was found to be relatively low in the thickness range of the Al strip below about 1% for the single-electrodes and 2% for the double-electrodes, although it greatly increases for a thickness over 2% for the single-electrodes and 3% for the double-electrodes.

Integral Equation Analysis of Plane Wave Scattering From Multilayered Resistive Strip Gratings

An accurate and efficient numerical solution is presented for the two-dimensional electromagnetic wave scattering from multilayered resistive strip gratings. Both E- and H-waves are treated. The method is based on the integral equations combined with the moment method with regularization procedure. The numerical experiment reveals the criteria for the truncation numbers. The reflected, transmitted, and absorbed powers are computed for various grating parameters and frequencies. Special attention is paid to maximizing the absorption into the strips, and thereby the relative absorbed power amounts to more than 90%.

Propagation of transverse waves on piezoelectric plates supporting single or double side metal strip gratings

A theoretical model of transverse waves propagating on piezoelectric plates of finite thickness under metal strip gratings is proposed. Different mechanical and electrical boundary conditions are considered and their influence on the propagation characteristics of the waves is emphasized. In all the cases, the dispersion curve relating the angular frequency to the wave number exhibits more than only one stopband as found in the usual analysis of surface transverse waves on semi-infinite substrates. This model has been used to calculate the resonance frequencies of synchronous devices on AT-cut and Z-cut quartz plates. These theoretical predictions are compared to experimental results obtained using synchronous devices built on 128-μm-thick Z-cut plate of quartz and AT-cut plate of quartz and operating at frequency range 80–150 MHz.

Transverse waves trapped by metallic gratings deposited on thin quartz plates

A theoretical model has been developed to predict the properties of transverse waves propagating under periodic metal strip gratings deposited on piezoelectric plates of finite thickness. The reliability of the model is demonstrated by comparing theoretical and experimental resonance frequencies of synchronous devices built on 128 μm thick AT-and Z-cut plates of quartz. Temperature sensitivities have also been measured experimentally. Finally, a theoretical analysis of the gravimetric sensitivity of these devices is reported. The case of a purely elastic load has been considered. Results are compared to state-of-the-art.

Infinite array of printed dipoles integrated with a printed strip grating for suppression of cross-polar radiation. I. Rigorous analysis

A rigorous analysis of an infinite array of printed dipoles integrated with a covering layer of printed strip grating is presented. Such designs can be useful to achieve low to ultra-low levels of cross-polar radiation from printed antennas, which is otherwise difficult to obtain from standard printed antenna designs. The analysis rigorously accounts for coupling between the grating strips and the dipole array in a general multilayered environment. Various demonstrative and design results showing loading effects of the grating on scan and impedance characteristics of the array are presented. Some interesting fundamental effects of the grating on the cross-polarization level and scan-blindness behavior are discussed.

Design of multilayered periodic strip gratings by genetic algorithms

Hybrid coded genetic algorithms are applied to the design of multilayered dielectric structures loaded periodically with thin metal strips for use as frequency-selective surfaces and blazing gratings. The analysis of the devices proceeds via a spectral-domain method-of-moments technique. Results are presented for filter and blazing structures. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 14, 81–85, 1997

Design of multilayered periodic strip gratings by genetic algorithms

Design of multilayered periodic strip gratings by genetic algorithms

Electromagnetic modeling of a resonant commutator

Nonsymmetric inhomogeneous step expansion in a plane-parallel waveguide is studied. Its coupling with the regular channel is arranged through a closely spaced grating of metal strips on the substrate. Scattering characteristics are found from the solution of the electromagnetic problem by use of the double-side equivalent boundary conditions and the method of moments. The influence of the resonant cavity parameters on single-mode and multimode regimes of work is analyzed. © 1997 John Wiley & Sons, Inc.

A perturbation method for modeling the thermal sensitivity of surface transverse waves

A perturbation approach has been developed to predict the sensitivity of surface transverse waves (STW) to quasi-static temperature effects. This approach is based on the combination of unperturbed STW characteristics and thermoelastic properties of the substrate. The unperturbed STW parameters are calculated taking piezoelectricity into account. Both cases of STW propagating under shallow groove or thin metal strip gratings are studied. An analytical expression of the first order temperature coefficient is obtained in the case of grooves. A simplified calculation is proposed for thin metal strip grating devices. Results are compared to available experimental data. Possible improvements of this model are finally discussed.

Hybrid Finite-Element Analysis of Leaky Surface Acoustic Waves in Periodic Waveguides

A numerical approach based on the hybrid finite-element method (HFEM) is developed for the analysis of leaky surface acoustic wave (LSAW) propagation along periodic waveguides. Only a region corresponding to one period of the waveguide is discretized, and the dispersion relation between complex propagation constants and frequencies around a stop band and the standing-wave distributions at these frequencies are calculated. Using the hybrid variational principle, the region to which HFEM is applied is divided into elements with suitable interpolation functions; the inhomogeneous region including electrodes is divided into conventional quadratic elements of the serendipity class, and the remaining homogeneous substrate region is replaced with a hybrid element with specialized interpolation functions which are derived from modal expansions and satisfy the radiation condition of LSAWs. In this method, all the effects of piezoelectric perturbation, mechanical perturbation, energy storage due to nonradiated bulk waves, and radiation loss of LSAWs are automatically taken into account. Using this method, aluminum strip gratings on an Al/ST-X quartz or a 36° Y–X LiTaO3 substrate are analyzed, and the validity of this method is confirmed.

Scattering of millimeter waves by metallic strip gratings on an optically plasma-induced semiconductor slab

This paper presents the scattering characteristics of a TE electromagnetic plane wave by metallic strip gratings on an optically induced plasma slab in silicon at millimeter-wave frequencies. The characteristics were analyzed by using the spectral domain Galerkin method and estimated numerically. We examined how to control the resonance anomaly by changing the optically induced plasma density for metallic strip grating structures fabricated on highly resistive silicon. The optical control characteristics of the reflection and the forward scattering pattern of the grating structures were measured at Q band and are discussed briefly with theory.

Perfectly Conducting Lamellar Gratings: Babinet's Principle and Circuit Models

We consider rigorous modal formulations for the diffraction of plane electromagnetic waves of infinitesimally thin, perfectly conducting strip gratings. The formulations that are considered involve either modes for expanding fields in the gaps between conducting strips, or for expanding the currents flowing on their surfaces. We express the rigorous diffraction solutions in terms of simple equivalent circuit models and derive a generalized form of Babinet's principle applying to strip gratings on dielectric substrates. Matrix methods are used to simplify derivations and to exhibit explicitly interesting properties relating to the conservation of energy and phase constraints.

Finite-Element Analysis of Periodic Surface Acoustic Waveguides

A numerical approach based on the three-dimensional finite-element method is developed for the analysis of periodic surface acoustic waveguides. Only a region corresponding to one period of the waveguide is discretized using three-dimensional elements of hexahedral form with 20 nodal points, and cutoff frequencies of a stop band and standing-wave distributions at these frequencies are calculated. These data are used for determining the self- and mode-coupling coefficients of coupled-mode equations with which the reflection characteristics of finite periodic surface acoustic waveguides are easily estimated. In this method, all the effects of piezoelectric perturbation, mechanical perturbation, energy storage due to nonradiated bulk waves, and three-dimensional field distributions are automatically taken into account. Using this method, aluminum strip gratings on an Al/45° X-Z Li2B4O7 or 128° Y-X LiNbO3 substrate are analyzed, and the effects of strip width in the aperture direction on the reflection characteristics are investigated.

Angular bandpass filters: an alternative viewpoint gives improved design flexibility

An alternative approach for the design of angular bandpass filters composed of metal strip gratings is proposed. In the classic approach, frequency selective surfaces (gratings) are used as resonant elements and the spacing between them is adjusted to obtain the required electrical performance. Following this implementation, however, the electrical coupling to the individual resonators can not be fully controlled so that very limited design freedom is obtained. Following the approach that we propose, the resonant element is the spacing between surfaces while the individual grating geometries are adjusted to obtain the required inter-resonator couplings. With this arrangement the structure becomes effectively equivalent to a closed waveguide filter, all electrical parameters of interest can be individually controlled and considerably extended design freedom is achieved. The basic resonator performance is analyzed and complete filter design examples are discussed. Furthermore, it is shown that, following the approach proposed, the frequency behavior of the structure is completely decoupled from its angular behavior in the design process thereby further extending the design freedom.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>