The measuring systems use the principle of the eddy current
effect. Therefore, a high-frequency magnetic field is generated
and the sample is placed in the magnetic field.
The conductive material acts on the resonant circuit, such as a
resistive load, and thus leads to a change in the power
consumption in the oscillator circuit.
Now, the difference in power is determined and according to
findings by Miller (GL Miller, DAH Robinson, and JD Wiley,
"Contactless measurement of semiconductor conductivity by
radio frequency-free-carrier power absorption", Rev. Sci.
Instrum, Vol . 47 (1976) the difference is proportional to the
conductance of the material.