  A low loss propagating electromagnetic wave is shown to exist at a gradual
interface between two lossy conductive media. The electromagnetic frequency
range of this phenomenon may span from UV optics to RF range. In particular, it
is demonstrated that such a surface wave may be guided by a seafloor-seawater
interface and it may be used in radio communication and imaging underwater.
Similar surface waves may also be guided by various tissue boundaries inside a
human body. For example, such surface wave solutions may exist at planar
interfaces between skull bones and grey matter inside a human head at 6 GHz.
