I am trying to modeled scattering of layered sphere. For material modeled of one of these layered i should define permittivity as a complex value. So i tried to difined 'er' and 'ei' and created interpolation for both. then difine relative permittivity as ''eps = er - j*ei '' . but comsol gave this error: unknown varibles('er' and 'ei'). I would appreciate it if help me define complex permittivity.
Best regard Amin