I need to know the complex permittivity of solutions of NaCl and water when subjected to an alternating electric field. Specifically, I need to know how it changes with salt concentration and applied electric field frequency. We are looking at ac field frequencies between 100 Hz and 1e6 Hz and dilute salt solutions.
This is quite easy I guess. The real permittivity and conductivity of aqueous solutions are nearly constant with frequency at the frequency range you mentioned.
Hence, according to the lossy dielectric model, the complex permittivity eps* is
eps* = eps - i*sigma/omega.
Here, i is sqrt(-1), and sigma is the conductivity of the NaCl solution. Omega = 2*pi*f is the angular frequency. eps = 78 is the permittivity of water.
Here's a table relating conductivity and concentration for NaCl: http://myweb.wit.edu/sandinic/Research/conductivity%20v%20concentration.pdf
addendum: you can replace eps = 78 by Eq. (6) of Stogryn's article and instead of the table I added to my reply you can use Eq. (12) of the paper to calculate sigma of the solution.
Note that you can of course also use Eq. (1) of the paper to estimate the permittivity but this should not necessary because the max. frequency you use is much lower than the frequency at which the permittivity of water drops ..
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