Rudy Briers

The history and properties of ultrasonic inhomogeneous waves

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 study of special acoustic effects caused by the staircase of the El Castillo pyramid at the Maya ruins of Chichen-Itza in Mexico

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.

Theoretical verification of the backward displacement of waves reflected from an interface having superimposed periodicity

Experiments are reported by Breazeale and Torbett [Appl. Phys. Lett. 29, 456 (1976)] that visualize ultrasonic backward beam displacement due to the excitation of surface waves by means of diffraction. The authors have simulated these experiments using the concept of inhomogeneous waves. Such waves have proven to be well suited in predicting beam displacements on plane interfaces. It is now found that inhomogeneous waves are even capable of predicting the experimentally observed displacement phenomena on periodic rough surfaces.

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)].

Inhomogeneous plane‐wave scattering and mode stimulation on periodic rough surfaces

Medium vibration properties to characterize interface layers and quality of bonding can be examined by an ordinary approach using homogeneous waves or by a more general inhomogeneous (or complex harmonic) wave scattering technique. It is known that only particular inhomogeneous plane waves can stimulate eigenvibrations of a given structure, and not the homogeneous wave. The reflection and transmission of such inhomogeneous waves is investigated for plane parallel interfaces as well as their scattering at periodically corrugated boundaries between liquid and solids. The influence of plate thickness, corrugation periodicity, and height on the occurrence of specific plate modes is examined. Using an alternative description of a bounded ultrasonic beam as a finite superposition of inhomogeneous waves, this theory can be applied to examine the deformation of Gaussian profiles and to explicitly relate this deformation to the stimulation of mode vibrations. The generation of a plate—or interface—mode by an obliq...

Theory of the backward beam displacement on periodically corrugated surfaces and its relation to leaky Scholte-Stoneley waves

A demonstration of the capability of the inhomogeneous wave theory to simulate backward displacement of ultrasonic-bounded beams [M. A. Breazeale and M. Torbett, Appl. Phys. Lett. 29, 456 (1976)] has been demonstrated recently [N. F. Declercq, J. Degrieck, R. Briers, and O. Leroy, Appl. Phys. Lett. 82, 2533 (2003)]. The current report applies the theory of the diffraction of inhomogeneous waves and shows how this theory is capable of simulating, explaining, and understanding the experiments mentioned above. The theory reveals the existence of leaky Scholte-Stoneley waves, a phenomenon suggested theoretically [N. F. Declercq, J. Degrieck, R. Briers, and O. Leroy, J. Acoust. Soc. Am. 112, 2414 (2002)] and observed experimentally [A. A. Teklu, M. A. Breazeale, J. Acoust. Soc. Am. 113, 2283 (2003)]. Moreover, the present paper shows that the classical Fourier decomposition of bounded beams is unable to simulate the backward beam displacement. This work also elucidates the nature of Wood anomalies in Diffracti...

The use of polarized bounded beams to determine the groove direction of a surface corrugation at normal incidence, the generation of surface waves and the insonification at Bragg-angles

Zero order reflected sound from a singly corrugated interface between a solid and a liquid, insonified from the solid side by circular polarized shear waves, can become almost perfect linearly polarized in a direction parallel or perpendicular to the corrugations, depending on the frequency, and can therefore reveal the direction of the corrugations. When narrow bounded beams, formed by a summation of infinite plane waves, are diffracted at certain frequencies, depending on the angle of incidence, or vice versa, one can predict phenomena like backscattering at Bragg-angle incidence and also the creation of Scholte-Stoneley waves.

A theoretical elucidation for the experimentally observed backward displacement of waves reflected from an interface having superimposed periodicity

It has been shown experimentally by Breazeale and Torbet [M. A. Breazeale and M. A. Torbett, Appl. Phys. Lett. 29(8), 456–458 (1976)] that a backward beam displacement can occur when a beam is reflected from an interface having superimposed periodicity. The angle at which the phenomenon occurs was predicted by Bertoni and Tamir [H. L. Bertoni and T. Tamir, Appl. Phys. 2, 157–172 (1973)] with a classical approach dated before the inhomogeneous waves era. However, during that era it has been shown by many scientists that the ultimate theory to describe critical phenomena, such as the generation of surface waves or the existence of a beam displacement, is the inhomogeneous wave theory. In the present research, one applies the inhomogeneous wave theory and shows that the theory predicts extremely well the phenomenon of backward displacement when a bounded beam reflects from a periodically rough surface. The agreement reaches far beyond a prediction of the angle of occurrence. One is able to simulate the entir...

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.