simple closed formulae for the number of the short-range surface-plasma wave guided by a thin, plane metallic film, between claddings with unequal permittivities

Closed formulae are derived for the wave number of a short-range surface-plasma wave guided by a metallic film between two thick dielectric slabs. the respective permittivities of those claddings differ from each other, as much as those of air and silicon carbide do for example. the new formulae are simpler and more accurate than the formulae published previously. contrary to the latter, they are not limited in the range of the film’s thickness, as is illustrated by two examples.