Geometrical acoustics

Geometrical acoustics or ray acoustics is a branch of acoustics that studies propagation of sound on the basis of the concept of acoustic rays, defined as lines along which the acoustic energy is transported. This concept is similar to geometrical optics, or ray optics, that studies light propagation in terms of optical rays. Geometrical acoustics is an approximate theory, valid in the limiting case of very small wavelengths, or very high frequencies. The principal task of geometrical acoustics is to determine the trajectories of sound rays. The rays have the simplest form in a homogeneous medium, where they are straight lines. If the acoustic parameters of the medium are functions of spatial coordinates, the ray trajectories become curvilinear, describing sound reflection, refraction, possible focusing, etc. The equations of geometric acoustics have essentially the same form as those of geometric optics. The same laws of reflection and refraction hold for sound rays as for light rays. Geometrical acoustics does not take into account such important wave effects as diffraction. However, it provides a very good approximation when the wavelength is very small compared to the characteristic dimensions of inhomogeneous inclusions through which the sound propagates.