Nonreciprocal transmission spectrum of a ferrite plate-resonant element grating metasandwich with split resonance

It is established that, when microwaves propagate in a structure comprising a ferrite plate and a grating of conducting resonant elements (situated on or close to the plate), the nonreciprocal wave transmission is accompanied by a nonreciprocal splitting of the microwave resonance at the grating frequency and by an expansion of the resonance bandwidth upon application of a constant magnetic field with a magnitude about one order smaller than that of the field exciting the ferromagnetic resonance (FMR). The sign of the nonreciprocity changes when the ferrite is arranged on the opposite side of the grating and/or when the applied constant magnetic field reaches a level at which the difference between the FMR and the grating resonance frequencies changes sign.     

Nonreciprocal left-handed transmission characteristics of microstriplines on ferrite substrate

In this paper, a nonreciprocal left-handed transmission line has been investigated. It is composed of a normally magnetised ferrite microstripline periodically loaded with lumped capacitances and inductive stubs. Based on the simple equivalent circuit model for a predominant edge guided mode, the dispersion relation of the ferrite left-handed transmission line has been estimated, providing the backward wave characteristic in the positive and negative permeability frequency regions. With the aid of the finite element method, it is confirmed that specific three-dimensional structures do show left-handed characteristics as well as the nonreciprocity. Nonreciprocal transmission characteristics with the isolation of more than 30 dB are obtained numerically and demonstrated experimentally in the positive and negative permeability frequency regions, for the edge guided modes. It is explained that the nonreciprocity of the ferrite left-handed transmission line is caused by the leaky wave phenomenon from the microstrip to the ferrite substrate     

Nonlinear suppression of microwave signals in a resonant magnetostatic wave transmission line

We have studied the phenomenon of suppression of a microwave signal in a magnetostatic wave (MSW) resonant transmission line comprising a microstrip resonator with a tangentially magnetized ferromagnetic film. Distinctions are revealed between the observed effects and those reported for a matched MSW line transmitting one microwave signal or two signals with different power levels.     

Dispersion of magnetostatic waves in a tangentially magnetized ferrite wafer with normal uniaxial anisotropy

A dispersion law is obtained and analyzed for the first time for magnetostatic waves in a tangentially magnetized ferrite wafer with uniaxial anisotropy where the axis is perpendicular to the plane of the wafer and the applied static magnetic field is weaker than the anisotropy field. This model qualitatively describes the dispersion of magnetostatic waves in hexa-and orthoferrite wafers and also in an unsaturated ferrite wafer. Pis’ma Zh. Tekh. Fiz. 25, 73–78 (November 26, 1999)     

Axisymmetric stress distribution in a transversely isotropic thick plate with a circular hole

Summary An exact solution for the stresses in a transversely isotropic infinite thick plate having a circular hole and subjected to axisymmetric uniformly distributed load on the plane surfaces has been given. The solution is in the form of Fourier-Bessel series and integrals. Numerical results for the stresses are given using the elastic constants for magnesium, and are compared with the isotropic case.

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Achsensymmetrische Spannungsverteilung in einer transversal isotropen, dicken Platte mit einem kreisförmigen Loch

Zusammenfassung Eine exakte Lösung für die Spannungen in einer transversal isotropen, unendlich ausgedehnten, dicken Platte mit einem kreisförmigen Loch, belastet durch eine achsensymmetrische, gleichmäßig verteilte Last an der ebenen Oberfläche, wird angegeben. Die Lösung ist in Form von Fourier-Bessel Reihen und Integralen dargestellt. Numerische Ergebnisse für die Spannungen werden unter Verwendung der elastischen Konstanten für Magnesium angegeben und mit dem isotropen Fall verglichen.

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With 4 Figures     

Axisymmetric stagnation-point flow impinging on a transversely oscillating plate with suction

The viscous fluid motion generated by axisymmetric stagnation-point flow of strain rate a impinging on a flat plate oscillating in its own plane with velocity amplitude U0 and frequency , including uniform suction of strength W0 is considered. A coordinate decomposition transforms the full Navier-Stokes equations into a primary equation describing the steady flow and a secondary equation describing the unsteady motion coupled to the primary solution. The solution to the boundary-value problem is governed by two dimensionless groups: the suction parameter S = W0 a and the frequency parameter = /a, where is the kinematic viscosity. Numerical integrations performed with a Runge-Kutta routine provide an exact solution to the Navier-Stokes equations. Values of the steady shear stress are found to agree with asymptotic results for large values of |S|, with S>0 representing suction and S<0 representing blowing. The magnitude and phase of the unsteady shear stress are given over a range of frequencies sufficient to recover analytical asymptotic results at large values of . The unsteady shear stress lags the wall motion by radians for 0 and by 5/4 radians when . Velocity profiles at selected parameter values during a period of plate oscillation are presented and discussed.     

Penny-shaped crack in a transversely isotropic plate of finite thickness

The effects of the material anisotropy on the stress intensity factor and on the crack shape are investigated for a penny-shaped crack in a transversely isotropic plate of finite thickness. The surfaces of the crack are subjected to uniform pressures. The plate surfaces are free from stresses for case I while smooth-clamp conditions are prescribed on the plate surfaces for case II. The techniques of Hankel transforms are used to obtain solutions for both cases. The solutions are largely written in terms of the sum and difference of the characteristic roots so that the results can easily be seen as real-value functions for both real and complex roots.Exact expressions for the stress intensity factor and the crack-shape function are obtained as products of dimensional quantities and nondimensional functions which are the stress intensity correction factor and the normalized crack shape function. The nondimensional functions were calculated numerically for three different typical materials which involved both real and complex characteristic roots. The numerical results clearly reveal the effects of the material anisotropy on the stress intensity factor and on the opening of the crack.

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Résumé On a étudié les effets de l'anisotropie du matériau sur le facteur d'intensité de contrainte et sur la forme d'une fissure dans le cas d'une fissuration en demi-lune située dans une plaque transversalement isotrope d'épaisseur finie. Les surfaces de la fissure ont été soumises à des pressions uniformes. Les surfaces de la plaque étaient libres de contrainte dans le cas I tandis que l'on prévoyait des conditions correspondant à un clamage léger sur les surfaces de la plaque dans un cas II. Les techniques de transformées de Hankel ont été utlisées pour obtenir les solutions dans les deux cas. Les solutions ont été exprimées en terme de somme et de différence de racines caractéristiques, de sorte que les résultats peuvent aisément être déduits comme des fonctions à valeur réelle de racine réelle et de racine complexe.Les expressions exactes pour le facteur d'intensité de contrainte et pour la fonction de forme de la fissure ont été obtenues comme les produits de fonctions à quantité dimensionnelle et non dimensionnelle qui sont le facteur de correction de l'intensité de contrainte et une fonction de forme de la fissure normalisée. Les fonctions sans dimension ont été calculées par voie numérique dans le cas de trois matériaux différents et typiques, mettant en oeuvre des racines caractéristiques réelles et des racines caractéristiques complexes. Les résultats numériques ont montré clairement les effets de l'anisotropie des matériaux sur le facteur d'intensité de contrainte et sur l'ouverture de la fissure.

     

Thermoelastic Lamb waves in a transversely isotropic plate bordered with layers of inviscid liquid

Analysis for the propagation of thermoelastic waves in a homogeneous, transversely isotropic, thermally conducting plate bordered with layers of inviscid liquid or half space of inviscid liquid on both sides, is investigated in the context of coupled theory of thermoelasticity. Secular equations for homogeneous transversely isotropic plate in closed form and isolated mathematical conditions for symmetric and anti-symmetric wave modes in completely separate terms are derived. The results for isotropic materials and uncoupled theories of thermoelasticity have been obtained as particular cases. It is shown that the purely transverse motion (SH mode), which is not affected by thermal variations, gets decoupled from rest of the motion of wave propagation and occurs along an in-plane axis of symmetry. The special cases, such as short wavelength waves and thin plate waves of the secular equations are also discussed. The secular equations for leaky Lamb waves are also obtained and deduced. The amplitudes of displacement components and temperature change have also been computed and studied. Finally, the numerical solution is carried out for transversely isotropic plate of zinc material bordered with water. The dispersion curves for symmetric and anti-symmetric wave modes, attenuation coefficient and amplitudes of displacement and temperature change in case of fundamental symmetric (S₀) and skew symmetric (A₀) modes are presented in order to illustrate and compare the theoretical results. The theory and numerical computations are found to be in close agreement.     

Stochastic instability of the magnetostatic surface wave trajectories in a ferrite film magnetized by a modulated field with a banklike profile

We report on the previously unstudied stochastic process arising when a magnetostatic surface wave (MSSW) propagates in a ferrite film magnetized by a modulated periodic inhomogeneous field with a banklike profile. The shape of the MSSW trajectories and the phase portrait of the stochastic process were established. It is shown that the MSSW trajectory becomes unstable and terminates when the MSSW propagation angle exceeds the cutoff angle.     

Synthesis and microwave absorption studies of ferrite paint

A new hexaferrite composition, BaCo _x Si _x+y Fe_12−2x−y O₁₉ (x=0·90;y=0·05), in fine (∼μ size) powder form, is prepared. Ferrite paint formulations are made by dispersing this powder in different weight proportions in an epoxy resin. X-band (8–12 GHz) microwave absorption behaviour of the paint coatings of different thicknesses is studied. Remarkably high value, ≥10 dB, of signal absorption at 9·5 GHz is observed for a coating thickness of 0·60 mm with a ferrite fill factor of 57 wt%. Most of this work, in a poster form, was presented at the 8th AGM of MRSI, BARC, Mumbai, February 10–12, 1997. The paper was adjudged the best for poster paper award     

Steady microwave heating of a ceramic plate

A model is developed of interaction between microwave radiation and a flat ceramic plate made of alumina. A calculation is performed of the thermal and electromagnetic characteristics of the plate in the air depending on the power and frequency of electromagnetic field.     

Crushing of compact elements in impact interaction with a thin plate

On the basis of investigations it was established that the limit speeds of crushing are affected by the scale, the ductility and other physicomechanical properties of materials. Crushing is the result of one or several mutually interacting effects (intense plastic deformation, wave processes, and fields of residual stresses).Translated from Problemy Prochnosti, No. 4, pp. 51–57, April, 1994.     

Formation and evolution mechanisms of transmission dips in a compound metallic grating with perpendicular cut

The transmission properties are investigated of a compound metallic grating in which each period is comprised of two slits but only one is engraved with a perpendicular cut are investigated. Based on Fabry–Parot (FP) resonances and phase resonances, the formation and evolution mechanisms of transmission dips are analyzed. We show that there is a corresponding relationship between the depth of transmission dips and the phase difference of magnetic fields in adjacent slits. In particular, the absorption intensity is powerfully enhanced as phase resonances take place and absorption peaks corresponding to transmission dips exhibit blue-shift or red-shift with an increase in depth of the perpendicular cut. We also show that the variation of transmission peaks and bandwidth of transmission dips can be interpreted by a compound of the transmission spectra of two corresponding simple gratings.     

Stability of a compressed elastic plate with nonlinear supporting elements

An approach for studying the critical loading parameters of stability of an elastic plate with nonlinear supporting elements is developed. A general potential function of the system depending on state variables and control parameters is constructed. Classical methods of catastrophe theory including a determination of the different bifurcational sets and an analysis of the physical meaning of the corresponding stability criteria are used. The influence of the supporting elements on the behaviour of the plate under the loading is determined     

Diffraction characteristics of a submicrometer grating for a light guide plate

The diffraction transmission characteristics of submicrometer gratings (SMGs) designed for coupling tricolor light out of a light guide plate (LGP) are discussed. Three discrete SMGs are designed for three special wavelengths: red (700 nm), green (546.1 nm), and blue (435.8 nm). The propagation direction of the output tricolor light is perpendicular to the surface of the LGP and can pass through the corresponding pixels of liquid crystal. Calculated by the rigorous coupled-wave theory, the first-order transmission efficiency as a function of grating depth is found to be approximate to a sinusoidlike curve and can be utilized to obtain uniform illumination. The theoretical maximum transmission is as much as 44%. The performance of the LGP composed of SMGs is also demonstrated by our experiments. Compared with other types of LGP, the present device has the advantage of flexible control of illumination angle and wavelengths. Additionally, lossy and costly color filters are unnecessary in the proposed configuration.     

Polarization multiplexing of diffractive elements with metal-stripe grating pixels

Diffractive elements with polarization multiplexing for the visible spectral region are demonstrated. The polarization-multiplexing property of the element is based on the polarization-dependent transmission characteristics of metal-stripe subwavelength period gratings. The proper dimensions of these gratings are estimated by rigorous calculations. The principle of polarization multiplexing by use of metal-stripe subwavelength period gratings is described for a diffractive element that has a binary amplitude transmission per polarization channel and is demonstrated by experimental results.     

Numerical study on an asymmetric guided-mode resonant grating with a Kerr medium for optical switching

Optical switching effects of a guided-mode resonant grating (GMRG) with a Kerr medium have been simulated with the nonlinear finite differential time domain (FDTD) method. An asymmetric waveguide grating with a large second spatial harmonic component has been proposed for the optical switch. Resonant reflection occurs at both of the band-edge wavelengths. These wavelengths are used for the pump light and the probe light. The enhanced electric field of the pump light changes the resonant wavelength for the probe light as a result of the Kerr effect. We designed the GMRG with resonant wavelengths of 1489.6 and 1630 nm, which were used for the pump light and the probe light, respectively. When the grating material has a third-order susceptibility chi(3) of 8.5 x 10(-10) esu, the transmittance of the probe light changes from 0 to 80% by increasing the intensity of the pump light from 0 to 60 kW/mm2.     

Extensional thermoelastic waves in transversely isotropic plate according to a higher order theory

The objective of this work is to provide a rigorous analysis of thermoelastic ultrasonic waves in transversely isotropic plates. Characteristic features such as dispersion curves of thermoelastic waves of plates are investigated and the influence of coupling in the heat equation on these features is critically examined. If the propagation of the waves is along the axis of symmetry of the plate, then it is possible to decouple the antisymmetric modes from the symmetric ones. This is conveniently done in approximate theories by retaining and omitting various terms in the expansions for the displacement and temperature. In this work, it is assumed that the wave propagation is along the axis of symmetry of an infinite anisotropic plate. Hence, extensional (symmetric) modes can be investigated apart from the antisymmetric modes. Displacement and temperature are expanded across the thickness of the plate using Legendre polynomials. Obviously, such a theory best fits those applications where a low frequency pulse is employed. Further, keeping only the leading terms in the expansion of displacement and temperature gives rise to a lower order theory, which predicts well the correct behavior of symmetric modes in relatively smaller frequency range. Results also show that the effect of coupling in the heat equation is insignificant for thermoelastic waves and can be ignored.