On the diffraction of sound waves in a viscous medium

The theory of the diffraction of a sound wave at a half-plane barrier is extended to the case of propagation in a viscous medium. It is shown that the singularity in the velocity near the edge of the barrier, a characteristic feature of the classical second order theory, disappears. In the neighbourhood of the edge the velocity attains its maximum, the value of which is determined by a reciprocal power of the viscosity. In the far field a viscous wave occurs, the amplitude of which is proportional to the square root of the viscosity, in contrast to the second order theory, where the introduction of a viscosity gives rise to a linear dependence.