Hi Ukjin Jeong , thank you for asking this technical question. A real dielectric may be represented by a capacitance in series with a resistance. Lets consider that the dielectric as a series combination of resistance and capacitance. The real and imaginary parts of dielectric permittivity can be calculated as:

Real part of dielectric permittivity = Cs/(Co[1+(wRsCs)2])

Imaginary part of dielectric permittivity = wRsCs2/(Co[1+(wRsCs)2])

Wish you all the best.

Dear Ukjin Jeong ,

You could see this link (from RG):

https://www.researchgate.net/post/How_do_I_calculate_dielectric_constant_from_impedance_spectroscopy_data

Best,

Fran