Wave Propagation in Non‐Uniform Media by Linear Expansion of the Refraction Law

ABSTRACT The propagation of mechanical waves in an unbounded, non‐uniform medium can be described by using curvilinear coordinates centered at the source position. The Frenet coordinate system, with origin on a point riding a wave, is used as a basis for the curvilinear coordinates. In this way a principal coordinate stating the evolution of the wave field and running along a ray, orthogonally to the successive wave fronts, is determined. A linear expansion of the refraction law at the rider point connects the gradient of the speed of sound field to the curvatures of the wave path and of the wave front. We use this connection in developing a numerical solution for the wave field, after recalling recent developments about the historical determination of the refraction law.