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.

It is known that a handclap in front of the stairs of the great pyramid of Chichen Itza produces a chirp echo which sounds more or less like the sound of a Quetzal bird. The present work describes precise diffraction simulations and attempts to answer the critical question what physical effects cause the formation of the chirp echo. Comparison is made with experimental results obtained from David Lubman. Numerical simulations show that the echo shows a strong dependence on the kind of incident sound. Simulations are performed for a (delta function like) pulse and also for a real handclap. The effect of reflections on the ground in front of the pyramid is also discussed. The present work also explains why an observer seated on the lowest step of the pyramid hears the sound of raindrops falling in a water filled bucket instead of footstep sounds when people, situated higher up the pyramid, climb the stairs.

Abstract-This paper gives a historical survey of the development of the inhomogeneous wave theory, and its applications, in the field of ultrasonics. The references are listed predominantly chronologically and are as good as complete. Along the historical description, several scientific features of inhomogeneous waves are described. All topics of inhomogeneous wave research are taken into account, such as waves in viscoelastic solids and liquids, thermoviscous liquids and solids, and anisotropic viscoelastic materials. Also inhomogeneous waves having complex frequency are described. Furthermore, the formation of bounded beams by means of inhomogeneous waves is given and the diffraction of inhomogeneous waves on periodically corrugated surfaces. The experimental generation of inhomogeneous waves is considered as well.

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.

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