Eddy Current Sensing
Any change in the environment of a coil of wire will cause a voltage to be induced in the coil, regardless of how the magnetic change is produced.
We force changes in a coil through oscillations which in turn create an oscillating magnetic field which generates Eddy currents on the surface of metal targets. As the volume of the flag changes, resistance to change by Eddy currents cause a change in coil impedance which in turn causes a change in frequency.
Our sensors are immune to magnetic or electromagnetic fields and do not require the use of permanent magnets. Due to this the sensor does not attract any metal debris through its lifetime.