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.

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.

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.

The underlying working principle of detecting impulsive stimulated scattering signals in a differential configuration of heterodyne diffraction detection is unraveled by involving optical scattering theory. The feasibility of the method for the thermoelastic characterization of coating-substrate systems is demonstrated on the basis of simulated data containing typical levels of noise. Besides the classical analysis of the photoacoustic part of the signals, which involves fitting surface acoustic wave dispersion curves, the photothermal part of the signals is analyzed by introducing thermal wave dispersion curves to represent and interpret their grating wavelength dependence. The intrinsic possibilities and limitations of both inverse problems are quantified by making use of least and most squares analysis.

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, Université Le Havre, France ͑1991͔͒.

A model was developed to simulate the effects of heavy charged-particle (HCP) radiation on the information stored in three-dimensional computer optical memories. The model is based on (i) the HCP track radial dose distribution, (ii) the spatial and temporal distribution of temperature in the track, (iii) the matrix-specific radiation-induced changes that will affect the response, and (iv) the kinetics of transition of photochromic molecules from the colored to the colorless isomeric form (bit flip). It is shown that information stored in a volume of several nanometers radius around the particle's track axis may be lost. The magnitude of the effect is dependent on the particle's track structure.

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.

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.