The radiation mode theory in ultrasonics

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Forming of the Optical Beam with the Rotating Polarization Vector

A method for the optical beam production with the rotating polarization vector based on the interference of two beams with the circular polarizations is proposed. The frequency shift between beams is implemented by means of acousto-optic (AO) diffraction. The method is used for the amplitude light modulation with the frequency nf where f is acoustic frequency and n is integer. AO modulators are fabricated from paratellurite crystal. Modulators allow modulating the optical radiation with wavelength of 0.63 mcm at the quadruple frequency of the acoustic wave. The modulation frequency achieves 180 MHz. Keywords: acousto-optic diffraction, Bragg regime, frequency shift, rotating polarization vector

Interaction of lamb modes with delaminations in plates coated by highly absorbing materials

A theoretical study of Lamb mode propagation through an absorptive bilayer consisting of a steel plate coated by highly absorptive rubber with a finite delamination dividing these layers is presented. Essentially, in such a bilayer structure, steel-like A0 and S0 modes still propagate, although with moderate absorption. Two different types of delaminations are taken into consideration: slip delaminations in which noncontact boundary conditions are assumed only for shear displacement and stress, and stress-free delaminations in which noncontact boundary conditions are assumed for all mechanical displacements and stresses. The calculations, which are based on a modal decomposition method, show that delaminations in absorptive bilayers result in a considerable change of the normal displacement amplitude at the bilayer surfaces inside the delamination region, and for an incident mode steel-like A0 mode, also in the transmission region. Stress-free and slip delaminations can be distinguished exploiting their different effect on the steel-like A0 and S0 incident modes.status: publishe

Planar four layers waveguide structure at sub-THz frequencies comprising metal and garphene: a complex scenery of coupled modes

Abstract In spite of the fact that graphene plasmons were investigated in a number of structures containing a few graphene monolayers or graphene bilayers, the case of coupled graphene plasmons with other types of structure modes (surface metal-plasmon or waveguide modes) has not been thoroughly examined. The coupling of graphene plasmons with surface metal plasmons in a structure containing a graphene layer and metal substrate separated by an air gap was studied We propose a multilayer structure containing a metal substrate, dielectric buffer layer, a monolayer of graphene, and air as the superstrate, aimed to unravel the complex solution space: coupled graphenemetal plasmons and waveguide modes which are supported by this structure. Hereto we present interesting results for these plasmon modes, by employing analytical models [1], we described these plasmon modes behavior at the sub-THz range, to our knowledge, this could be the first study of its kind. The solution of the dispersion relation for the structure is explained in The TM surface plasmons are represented by metal-like and graphene-like branches depending on their behavior for very thick buffer layers. For instance; for frequencies smaller than 0.75 THz (for the concrete structure under study), the metal-like surface plasmons split up into two branches depending on the graphene electron concentration: one of the branches exists in the whole range of the buffer thickness and being a shortrange mode for small thicknesses, another one undergoes cutoff and exists only within a limited range of buffer thicknesses smaller than the cutoff thickness. Further increase of the surface plasmon frequency leads to the disappearance of the splitting effect for metal like surface plasmon, also the TM waveguide modes split up into two branches for small frequencies analogously to that of the metal-like surface plasmo

Nonlinear clapping modulation of Lamb modes by normally closed delamination

The nonlinear interaction between a high-frequency probing Lamb mode, propagating through a bilayer containing an initially closed tangential delamination at the interlayer interface whose contact conditions are dynamically changing because of a high-amplitude Lamb pump wave with long wavelength, is modeled in a quasi-stationary approach. The proposed criterion for the delamination to open is based on the magnitude, with respect to a threshold value, of the pump-wave-induced normal stress components that are pulling on both sides of the interface during part of its cycle. The temporal evolution of the contact condition during the pump wave cycle is calculated and the spectral enrichment caused by cross-modulation spectral components between the probing wave and the modulating wave is predicted. The impact of the cross-modulation on the normal displacement at the externally accessible surfaces is investigated for two different types of incident probing wave in an absorbing bilayer structure, and for different variations of the contact quality modulation. The results can serve as a parametric guide for experimenters considering the use of nonlinear harmonic generation of Lamb waves as a tool for nondestructive testing of bilayers such as rubber-steel composite walls that are typically used in storage tanks and pipelines for corrosive liquids.status: publishe

Interaction of Lamb modes with an inclusion

The interaction of Lamb modes propagating in a steel plate containing a thin inclusion is analyzed for cases where the inclusion material has elastic parameters similar to the ones of the plate, and where the inclusion is in perfect mechanical contact with the surrounding plate material. A modal decomposition method is used to calculate the conversion of an incident Lamb mode to other modes. Hence, the influence of the type of incident mode, of the location and geometry of the inclusion, and of the elastic parameters of the inclusion and plate material on the mode conversion coefficients is analyzed. Besides the expected increase of the conversion efficiency with increasing cross section of the inclusion, it is found that due to reasons of symmetry, the presence of an inclusion leads to an efficient conversion of an incident S0 mode into reflected and transmitted A0 modes, unless the inclusion is located very close to the plate center. On the other hand, the conversion efficiency of an incident A0 mode into a reflected A0 mode is found to be strongly dependent on the depth of the inclusion, this conversion even disappearing for some location depths. For the cases studied, the inclusion location dependence of the mode conversion seems to be correlated with the normal profile of the longitudinal normal stress component. As intuitively expected, the mode conversion efficiency increases with the mismatch of an acoustic impedance like factor between the uniform plate and the inclusion region.status: publishe