Waves In Layered Structures Research Articles

Stability of shock waves in layered structures (part 2)

The authors continue the study of shock waves stability in layered structures started in [1]. The ill-posedness of a linear initial-boundary value problem on shock waves stability is proven with the help of Hadamard-type ill-posedness examples.

Shock waves stability in layered structures

Equations of a hydrodynamical model in layered structures are studied. A linear initial boundary value problem on stability of shock waves in layered structures is formulated. Ill-posedness of this problem is proven, thus instability of shock waves for chosen model of layered structures is shown.

Propagation of waves in layered structures viewed as number recognition

We propose to consider multilayer spatial structures as numbers. An arbitrary finite sequence of layers with N values of a material parameter which determines the speed of wave propagation is considered as a number written in the numeration system with base N. Within the framework of this approach propagation of classical waves and quantum particles can be treated as number recognition. A problem is formulated of identification of a type among spatial sequences featuring unique spectral portraits versus spatial structure. It is shown possible to perform certain arithmetic operations by means of sequential propagation of waves through several structures. Using fractal Cantor structures as a representative example, spectral properties of waves are shown to reproduce certain properties of the corresponding numbers. A possibility is outlined to use the above approach for data storage. If a set of numbers possessing unique spectral portraits forms a complete set, then compact coding of arbitrary numbers will become possible.

Magnetoelastic volume shear waves in a periodically layered medium

An approach is developed for studying the propagation of magnetoelasic waves in layered structures. The structures have the properties of ferrite with interfaces differently covered with a metal coating. The problem is reduced to an infinite equation system within the framework of the linearized theory of magnetoelasticity. Conditions of volume-wave propagation are derived from the condition of existence of a nontrivial solution to this system. Some results are presented in the form of plots

Propagation and Localization of Longitudinal Thermoelastic Waves in Layered Structures

Based on the generalized dynamical theory of thermoelasticity, a transfer matrix formulation including the second sound effect is developed for longitudinal wave component propagation in a thermoelastic layer. The second sound effect is included to eliminate the thermal wave travelling with infinite velocity as predicted by the diffusion heat transfer model. Using this formulation and the periodic systems framework, the attenuation and propagation properties of one-dimensional thermoelastic waves in both continuum and layered structures are studied. Strong localization of thermal waves predicted by the analysis in the transformed domain is demonstrated in the time-spacial domain by an FFT-based transient analysis. Also, a perturbation analysis for identifying leading terms in thermal attenuation is performed, and the role of the thermal elastic coupling term in attenuation is determined. The attenuation factor, defined as the real part of the propagation constant, is obtained in thermoelastic solids. The reflection and transmission coefficients between half-spaces are also calculated to evaluate the potential practical use of the approach in thermal-based nondestructive testing. [S0739-3717(00)00403-7]

Anomalous absorption of electromagnetic waves in a layered structure with complex permittivities

It is shown theoretically that the absorptivity of bulk TE and TM electromagnetic waves by a thin layer with large complex dielectric permittivity has a strong (as much as 100%) maximum at an optimal layer thickness that is usually much smaller than the wavelength and the wave penetration depth (skin-depth) in the layer. The analysis is carried out in the frictional contact approximation, in which the layer can be replaced by a contact of the surrounding media with special boundary conditions that are analogous to the conditions at a contact with linear mechanical friction. The effects of a non-zero real part of the layer permittivity, and non-zero dissipation in the surrounding media on the anomalous absorption are investigated theoretically in detail. Simple analytical equations for the absorptivity maximum, optimal layer thickness and optimal incidence angles are derived and analysed. Differences in the anomalous absorption of TE and TM waves in layered structures with complex permittivities are described and explained from the physical point of view.

Spin Waves in Layered Structures of Antiferromagnetic F.C.C. MnTe

Spin waves in single thin films and exchange-coupled bilayers of f.c.c. MnTe are analyzed theoretically in the low temperature limit. Long-range antiferromagnetic order of AF-III type is assumed. The spin-wave Hamiltonian includes exchange interactions between nearest and next nearest neighbours, magnetic anisotropy and Zeeman term.

Spin Waves in a Bilayer with Biquadratic Interlayer Coupling

Linear spin waves in layered structures consisting of two ferromagnetic films coupled at the interface by a biquadratic exchange interaction are analysed theoretically within the localized spin model and in the low-temperature limit. Magnetizations of both films are assumed to be parallel to the film plane, but perpendicular one to another. The limit of two semi-infinite ferromagnets is also considered. In both cases interfacial modes have been found.

Dispersion of magnetostatic surface waves in ferrite-htsc structures near the phase transition

We present a detailed study of the dispersion properties of surface magnetostatic waves in layered structures of ferrite and high temperature superconductor (HTSC) layers. We solve the propagation problem for the surface magnetostatic waves under a quasistatic approximation, and obtain the dispersion relation. We present an analysis of this dispersion near the phase transition temperature in the HTSC layer. The calculations show that when the HTSC material transforms to the superconducting state the dispersion properties of the magnetostatic waves changes suddenly: the damping decreases by 4–10 dB and the phase velocity increases by a factor of 2–4. These results support experiments which have been performed, in which surface magnetostatic waves have been studied in a YIG film with gallium impurities and a YBaCuO film on a lithium niobate substrate.

The dynamic susceptibility and spin waves in layered structures

The dynamic susceptibility and spin waves in systems composed of ferromagnetic layers separated by nonmagnetic or nearly nonmagnetic ones are investigated within the framework of tight-binding and random phase approximations. Calculations are based on the multiband model. Layered structures are simulated by changes of the model parameters in the interfilm. The thickness of the spacer is also changed. A reduction of the Coulomb integral in the interfilm as well as an increase in a number of nonmagnetic spacer layers lead to a significant lowering of the effective coupling between magnetic sublayers and therefore strongly influence the spectrum and amplitudes of spin waves. Pairs of modes with very close values of energy are found in the spectrum for low values of U and thick enough nonmagnetic spacer. A distance between two energy levels which correspond to such a pair increases with the energy. The results are well consistent with the ones obtained within the framework of the Heisenberg model.

Transducer Performance for Leaky Wave in Layered Structure of Piezoelectric Ceramic Thin Plate and Acryl Plate

A leaky wave transducer in the combination of a piezoelectric ceramic thin plate and an acryl plate is described, which functions as a transducer for underwater ultrasound. The operation performance of an interdigital transducer in the layered structure is described from the viewpoint of phase velocity, electromechanical coupling constant, mode conversion efficiency and transducer efficiency. The leaky wave transducer has multiple modes with velocity dispersion. Using the second-order anti-symmetrical mode with high transducer efficiency value, a liquid-delay line oscillation is demonstrated.

Shear horizontal waves in layered structure with 180° ferroelectric domain

Theoretical analyses and numerical results describing the propagation characteristics of shear horizontal interface waves in layered structure with 180° ferroelectric domain are presented. A sandwich structure and a multilayered structure with finite layers are considered. It is found that there exist universally strong dispersion and multimode in a multilayered structure. There are N−1 dispersion curves in a structure with N 180° domain layers. For the multimode, some symmetry properties are found. The fundamental mode is a symmetrical one and the higher-order modes are symmetry or antisymmetry. The multimodes are arranged as symmetrical–antisymmetrical alternatively. There exist cutoff frequencies. It is noted that the B–G wave and the M–T wave may be obtained as special cases of the present theory. Three kinds of dispersion curves are found: ferroelectric domain layer wave, ferroelectric domain layer flexure wave, and lovelike wave. The dispersion relations and the multimode characteristics of the SH interface waves in 180° domain finite multilayered structure were verified by experiments. [Work supported by NNSF.]

Stability analysis of stationary nonlinear guided waves in self-focusing and self-defocusing Kerr-like layered media.

In this paper, we develop a linear stability analysis of stationary nonlinear guided waves in self-focusing and self-defocusing Kerr-like layered media. The analysis is applicable to the general problem of the stability of stationary nonlinear guided waves in layered structures including one or more self-defocusing media, a previously unsolved problem. Further, as a demonstration of its use, the technique is applied to the case of the fundamental dark surface wave (FDSW), a wave guided near the interface between two dissimilar defocusing media. We obtain results consistent with a numerical stability analysis of the FDSW performed previously [J. Opt. Soc. Am. B 8, 2265 (1991)]. Finally, the generalization of this technique to arbitrary layered structures of Kerr-like media is discussed.

Quantum processes of propagation of electron waves in layered structures

The interaction of electron waves with (001) heteroboundaries in GaAs/AlAs systems is considered using the scattering matrix and pseudopotential methods. The different transmision channels of electrons through one boundary and a two-barrier structure are analyzed. It is shown that the matching matrix contains a 3×3 block of strongly interacting Γ1, X1, and X3 states. Hence a three-trough model is proposed to describe resonant tunneling processes in the corresponding structures. The matching conditions for the wave packets are analyzed. The applicability of the often-used one-through approximation of the effective mass method is analyzed. The effect of mixing of Γ and X state on the transmission coefficient is shown to be important.

Interference Analysis of Photothermal Generation of Waves in Layered Structures

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Surface waves in layered structures with application to vocal-fold vibration

The initiation of surface waves over a layered structure, including an air channel, a thin elastic layer, an inviscid waterlike fluid, and an impedance boundary, is discussed. This structure is a rudimentary picture of the vocal folds near the edges. The initiation of surface waves at the interface between the air and elastic layer is similar to the problems of initiation of wind waves over water and the flutter of panels. Early linear analyses of surface wave initiation considered Kelvin-Helmholtz instability, a static instability, and the use of Jeffreys' sheltering coefficient as a destabilizing mechanism for a dynamic instability. Both static and dynamic instabilities are possible in vocal-fold vibration. However, the dynamic type of instability is the mechanism that usually is operable in a layered structure model of vocal-fold vibration, although Jeffreys' sheltering coefficient does not provide the correct term for negative damping. This is confirmed by the lumped element two-mass model, a very successful model for simulating some aspects of vocal-fold vibration [K. Ishizaka and J. L. Flanagan, Bell Syst. Tech. J. 51, 1233 (1968)]. The two-mass model also illustrates how to incorporate dynamic pressure loss into the layered structure approach to account for the negative stiffness. The layered structure approach has the advantage of allowing for testing of the effects of changing the mechanical properties of various histological layers on the initiation of the surface wave. [Work supported by NIH grants HD-1994, NS-13870, and NS-13617 to Haskins Laboratories.]

A Program for Calculating Refraction Times for Layered Models With Arbitrarily Dipping Discontinuities

A computer program written in Microsoft BASIC for use on personal computers to calculate travel times of refracted waves in layered structures with arbitrarily dipping interfaces is described. Exercises for student use are given to illustrate some of the basic properties of reversed refraction travel-time graphs with different models.

P-polarized nonlinear surface and bounded (guided) waves in layered structures

P-polarized nonlinear surface and bounded (guided) waves in layered structures

Acoustic Surface Wave Excitation in Layered Structures

An analytical and computational procedure for the study of acoustic surface wave excitation in anisotropic layered structures has been developed. The analysis is based upon solution of the coupled wave equations in both layer and substrate and is directed toward materials which can be oriented such that the particle displacements are in the sagittal plane. The admittance characteristics (complex) of interdigital transducers, as used to excite surface waves in such structures, are calculated and found to be in excellent agreement with experimental results. ducers in such structures (g) , ( 181 . However, a basic theoret- ical study of surface wave excitation in layered structures has not yet been published.' This paper attempts to fill this ap- parent gap and to show that the admittance characteristics of the ID transducers used to launch surface waves in layered structures can be accurately predicted from the material con- stants which are determined from bulk wave measurements. The intent of this study is to concentrate on low coupling materials, such as CdS and ZnO, in conjunction with nonpie- zoelectric materials for the layer and substrate, respectively. Thus the analysis is based on a low-coupling approach, and certain crystalline symmetry restrictions are imposed to reduce the mathematical complexity. Nevertheless, the analysis pre- sents a method which could be used for a more general situa- tion if so desired. 11. THEORY

Recent advances in the amplification of surface elastic waves in layered structures

Abstract The emergence of surface elastic waves as an important area of applied research has been largely the result of the successful application of well known principles of physical acoustics rather than the discovery of new phenomena. A number of factors have contributed to the rapid growth of interest in this field, among which may be noted the recent demonstration of terminal gain in an acoustoelectric surface wave amplifier at 100 MHz, the considerable reduction of two port insertion losses, and the recognition that planar acoustic systems offer significant advantages in sophistica- ted signal processing devices such as transversal filters. Most laboratories currently engaged in surface wave work had already developed the necessary facilities and skills during a period devoted to exploring the potential of bulk elastic waves. The single crystal materials of most interest for surface waves, generally low acoustic loss strongly piezoelectric insulators, are also those that have formed the basis for mu...