Broad-band microwave characterization of a tri-layer structure using a coaxial discontinuity with applications for magnetic liquids and films

An analytic technique is described, which allows us to determine simultaneo usly complex permittivity epsilon and permeability mu of magnetic films or magnetic liquids. The cell is a gap in a coaxial line filled with three lay ers (for liquid samples, the two external layers are used as windows, and f or films, the middle layer constitutes the substrate). Permittivity and per meability of the unknown layer(s) are computed from the S-parameters (S-11, S-21), which are measured on the gap, taking into account higher order mod es excited at the discontinuity. epsilon and mu measured for ethanol and a ferrofluid (with an applied magnetic static field) are presented up to 18 G Hz.