Abstract
When an ac-exited coil faces a non-magnetic moving metal foil, an eddy current is induced in the conductor and the coil impedance is influenced by speed and thickness. By examining this speed and thickness characteristics, a coil is used as the thickness sensor.
In this paper, we derive rigid theoretical formulas for magnetic field and coil impedance of a circle coil facing a standstill or movement foil conductor. And we present several characteristics with regard to coil inductance and resistance by calculations. The good agreement between the theoretical value and measured value demonstrates the validity of the method. We found that there is not an influence with speed at tens of micrometers thickness, and that the exciting frequency upper limit is 1 kHz.
