Leaky Rayleigh waves on a layered halfspace

Abstract

Experimental and theoretical results on the nonspecular reflection of finite acoustic beams incident at and near the Rayleigh angle onto a fluid-solid interface loaded by an elastic layer are presented. Measurements with Gaussian-shaped acoustic beams have been performed on the reflected field amplitude distribution and surface wave speed dispersion in copper-loaded stainless-steel specimens where the fluid medium is water. It is shown that existing theory can be utilized to explain the results by constructing and solving boundary condition equations for the Rayleigh wave pole appropriate for the lossless layered halfspace with the fluid. Excellent agreement with the exact treatment is observed in most aspects of the measurements. In the model calculation the imaginary part of the Rayleigh wave pole is found to display an unexpected maximum at a value of layer thickness over wavelength where the real part corresponds nearly to the transverse wave speed in the layer.

On Nonspecular Reflection of Bounded Beams for Layered Half Spaces Under Water

“…9 We have found that when a pole of R in the complex a-plane is sufficiently near the real axis to correspond to a mode that causes non specular reflections, it will be associated with a zero also near the real axis. The poles always have positive imaginary parts in the presence of the liquid, but the zeros can have positive or negative imaginary parts.…”

“…In Ref. 9 the loading case of copper on stainless steel was studied. Nonspecular reflections were measured and calculated corresponding to the lowest Rayleigh mode.…”

Interaction of Ultrasonic Waves with Composite Plates.

“…These lead to six solutions for a which we further label as a 2 = -a,, a4 -a3anda 6 = -a5 (11) Using superposition, together with the relation (9) …”

Simulation of Acoustic Wave Propagation in Aluminium Coatings for Material Characterization

“…Considering a broad-band Rayleigh wave, the lower frequency part of the wave propagates more in the substrate, whereas higher frequency components travel mainly in the coating due to their lower penetration depth. Consequently, the Rayleigh wave velocity becomes dispersive (i.e., depends on frequency); this effect has been extensively studied in the past (e.g., [13][14][15]). The dispersion of the Rayleigh wave can be used to extract elastic mechanical parameters like the Young´s modulus, because the Rayleigh wave velocity depends on the density as well as the elastic constants.…”