Nicolson–Ross–Weir method
Nicolson–Ross–Weir method is a measurement technique for determination of complex permittivities and permeabilities of material samples for microwave frequencies. The method is based on insertion of a material sample with a known thickness inside a waveguide, such as a coaxial cable or a rectangular waveguide, after which the dispersion data is extracted from the resulting scattering parameters.
Source: Wikipedia — Nicolson–Ross–Weir method (CC BY-SA 4.0)