COMPUTATION OF THE 2ND TERM OF THE PROPAG ATION CONSTANT OF CREEPING WAVES BY THE BOUNDARY-LAYER METHOD

Creeping waves propagate and decay on the boundary of convex obstacles . The propagation constant of these waves has an asymptotic expansion in fractional powers of the wavenumber k. The first term of this expan sion is well-known, but the second term has only been determined for p erfectly conducting objects, and specific shapes : bodies of revolutio n, canonical problems. In this paper, we compute this second term in t he case of a general convex object satisfying an impedance boundary co ndition, by using a boundary-layer method. The result shows the effect s of the geometrical parameters of the geodesic along which the creepi ng wave propagates, and of the variations of the surface impedance.