The coupling factor or the core sensitivity (S_C) is a coefficient used in order to characterize the proportional relation between the magnetic field measurement and the current going through the conductor. However, this coupling factor is only constant over a limited range of current and frequency. Any change of this coefficient leads to input current measurement error. Eddy currents are a direct effect of Lenz’s law which states that the direction and magnitude of the current induced in a conductor by a varying magnetic field is such that it creates a magnetic field that opposes the change that produced it. In an AC current sensor application using a ferromagnetic core, eddy currents are induced inside the core as a response of the tangential varying magnetic field. These eddy currents generate an induced magnetic field, H_eddy, opposite to the exciting magnetic field, H_exc. This is measured at the sensor level as a reduced core sensitivity or otherwise said, a current measurement error. In order to reduce eddy currents, it is necessary to cut the current paths in the core. This is achieved by using a laminated core with thin sheets. These sheets must be electrically isolated from each other. The lamination can be done in the Y direction by rolling or in the Z direction by stacking sheets. Eddy currents still flow, but with a reduced magnitude.