G. N. Shkerdin

Slab plasmon polaritons and waveguide modes in four-layer resonant semiconductor waveguides

This paper presents a detailed study of the waveguide and plasmon polariton properties of four-layer systems involving highly doped semiconductor material. The dispersion relations of waveguide and plasmon polariton modes are calculated for different geometrical parameters and material properties. Special attention is paid to the transition region between the latter modes, which exhibits a complex behavior. Slab plasmon polaritons at wavelengths slightly larger than the plasma wavelength, yielding a positive real part of the permittivity, have been found. Finally, applications at wavelengths near the transition region and near the plasma wavelength are proposed and discussed.

Lamb mode conversion in a plate with a delamination

A theoretical study of Lamb mode propagation through a part of a plate containing a finite-length, delamination parallel with the surface is presented. In the delamination boundary region, which is taken parallel with the free plate surface, noncontact boundary conditions are assumed. The calculation is based on a modal decomposition method. As a result of diffraction on a delamination the incident Lamb mode is efficiently converted into Lamb modes with wave numbers close to the wave number of incident mode. The transmission coefficient of a Rayleigh wave incident on a delamination located near the surface has an oscillating dependence on the delamination parameters and has a pronounced minimum where there is a strong conversion into transmitted Lamb modes. Inversely, using the method of phase conjugation, a proper incident Lamb mode combination can be efficiently converted into a single transmitted Lamb or Rayleigh wave.

Bounded beam interaction with thin inclusions. Characterization by phase differences at Rayleigh angle incidence

A theoretical study of the reflection of a bounded Gaussian ultrasonic beam, incident onto a rectangular inclusion located near a fluid/solid half-space interface, is presented. The thickness of the inclusion is assumed to be much smaller than the ultrasonic wavelength in the solid. It is shown that, at critical Rayleigh angle incidence, the phase in the point of maximum amplitude of the shifted reflected lobe is very sensitive to dimension variations of the inclusion, and thus useful for inclusion characterization. The modelization of the problem is based on mode theory.

Conversion of a Stoneley wave at the extremity of a fluid loaded plate

A theoretical model, based on mode theory, is presented in order to study the behavior of the Stoneley wave when it reaches the extremity of a thick plate immersed in a liquid. The superposition of two phenomena is established: the first one being the simple forward diffraction of the Stoneley wave in the liquid and the second one being its conversion into two generalized Rayleigh waves which propagate on the same plane as the incident Stoneley wave or along the vertical end face of the solid support. The theoretical analysis is in good agreement with the experimental observations of Tinel [Ph.D. Thesis, Universite Le Havre, France (1991)].

Lamb mode conversion in an absorptive bi-layer with a delamination

A theoretical study of Lamb mode propagation through an absorptive composite plate consisting of two parallel layers with a finite-length delamination dividing these layers is presented. In the delamination boundary region, noncontact boundary conditions are assumed. The calculation is based on a modal decomposition method. In thin composite plates containing a few propagating Lamb modes, as a result of diffraction on a delamination, the incident Lamb mode can be efficiently converted into transmitted Lamb modes. Delaminations in absorptive composite plates result in a considerable change of transmitted acoustic energy if the plate is characterized by substantially different absorption coefficients in the layers of the plate. In particular, the delamination can considerably increase the transmission coefficient of the incident Lamb mode if the layer where the incident Lamb mode is mainly concentrated is much less absorptive than the other one.

Nonlinear modulation of Lamb modes by clapping delamination

The nonlinear interaction between a high frequency probing Lamb wave and a bilayer containing a tangential delamination at the interlayer interface, whose contact conditions are dynamically changing due to a high amplitude Lamb wave with a long wavelength, is modeled in a quasistationary approach. The impact of the evolution of the contact condition on the mode conversion coefficients that describe the interaction of the probing wave with the delamination region leads to spectral enrichment due to cross-modulation spectral components between the probing wave and the modulating wave. The dynamical behavior of the normal displacement at the externally accessible surfaces is investigated for two different types of incident probing wave, both for an absorbing and a nonabsorbing bilayer structure, for variations in the contact quality modulation and as a function of defect size. The results can serve as a parametric guide for experimentalists considering the use of nonlinear harmonic generation of Lamb waves as a tool for nondestructive testing of bilayers, such as rubber-steel composites, in storage tanks and pipelines.

Mode theory as a framework for the investigation of the generation of a Stoneley wave at a liquid–solid interface

A theoretical model, based on mode theory for acoustic waves, is presented in order to describe the complicated scattering of an ultrasonic volume or surface wave at the boundary between two adjacent liquids abutting a single solid. Analytical expressions for the displacement fields of the scattered and mode‐converted waves are derived. In particular, it is shown that a volume wave incident from the liquid of the first liquid/solid structure can generate a Stoneley wave along the interface of the second liquid/solid structure. The relative amplitude of the displacement of the excited Stoneley wave is calculated for several (liquid–liquid)/solid configurations. The angle of most efficient excitation can be derived from the maximum of the function describing the interaction between a radiation mode and a Stoneley eigenmode in the division plane separating both liquid/solid structures.

Effect of loading a plate with different liquids on the propagation of lamb-like waves studied by laser ultrasonics

Three experimental laser ultrasonic configurations-line excitation with scanning detection, grating excitation with single point detection, and grating excitation with scanning probe beam- are shown to consistently reveal the modified propagation properties of Lamb waves on a polyethylene terephthalate (PET) film that is in contact with different liquids on its two sides. Theoretical predictions concerning the physical nature of different wave modes in symmetric and asymmetric film loading configurations (i.e., their existence, velocity, damping, and polarization) are confirmed by the experimental results.

Comparative study of the intra- and intervalley contributions to the free-carrier induced optical nonlinearity in n-GaAs

We performed a theoretical study about the optical nonlinearity connected with the redistribution of free electrons between the Γ and L valley of highly doped n-GaAs. An extended comparison was made between the intravalley (or nonparabolicity) and the intervalley contribution. In the energy relaxation process, intravalley transitions in the Γ and L valley by means of the emission of optical phonons and equivalent intervalley transitions in the L valley by means of intervalley phonons were considered as the main mechanism of energy transfer to the lattice. It is demonstrated that when the frequency of light matches with the plasma frequency of the n-doped GaAs the nonlinearity is quite big. At a doping concentration of 7×1018 cm−3 we calculated a nonlinear refractive index n2=1.74×10−8 cm2/W at 10.6 μm. The doping and intensity dependent energy relaxation times of electrons are calculated: for Γ-valley electrons τenΓ∼(3–5) ps and for L-valley electrons τenΓ∼(0.3–0.5) ps. It is believed that the response ti...

Extension of the mode method for viscoelastic media and focused ultrasonic beams

In the present study viscoelasticity is introduced in the mode model and the orthogonality condition is adapted for viscous media. The expansion of convergent acoustic Gaussian beams in terms of radiation modes for viscoelastic media is studied as well. The effects on the reflected and transmitted profiles of acoustic beams incident from an ideal liquid onto a viscoelastic plate are shown and physically explained. It is shown that focusing the incident beam can suppress divergence effects and gives the possibility to measure shear wave attenuation coefficients.