# How to compute complex relative permittivity

1. Sep 28, 2010

### kris287

Greetings. I don't know how to use an equation with a complex frequency term, specifically this one (aka Debye expression) for frequency-dependent permittivity:

epsilon(omega) = epsiloninfinity + delta-epsilon/(1 + j*omega*tau)

where epsilon(omega) is the permittivity at omega angular frequency, epsiloninfinity is the limit of permittivity at high frequency (omega*tau >>1), tau is the time it takes to polarize the dielectric, delta-epsilon = epsilons - epsiloninfinity (where epsilons is the permittivity at omega*tau<< 1), a measure of a permittivity dispersion region that is driven by tau (different factors drive tau at different frequency ranges, q.v., e.g., http://en.wikipedia.org/wiki/Complex_permittivity#Complex_permittivity), and j = -11/2.

How do I put frequency values in for omega, such as in what units, and crank it to get permittivity at a given frequency out? General comments on using complex frequency are welcome, too.

Thanks (and hopefully in my first post I described the problem so it's not gibberish :-).