- We describe an interesting eddy-current effect which takes place in nonlinear magnetic conductors excited by several alternating fields. The field penetrating into the material contains components of new frequencies which were not present at the excitation on the surface. The phenomenon is significant since the low-frequency fields produced in the material become increasingly emphasized as the field penetrates into the material. This is due to the relative cancelation (filtering) of the originally high-frequency fields by the screening of eddy currents. Potential applications of the effect are suggested.