function a = skindepth(omega, sigma, epsrel)
% SKINDEPTH returns skin depth asa function of frequency and conductivity
% full expression - not the good conductor approximation

eps = 8.85E-12 * epsrel;
mu = 4E-7 * pi;

a = sqrt( 1 + (sigma ./ (omega .* eps) ).^2 )  - 1;
a = a .* mu .* eps ./ 2;
a = omega .* sqrt(a);
a = 1./a;
