A magnetic field sensor relies on variations in permeability of magnetic material to detect an external field. An exemplary magnetic field sensor includes a lengthwise extending sensing element, and a coil wound about the sensing element. The sensing element may be formed as a number of geometrically and magnetically similar or identical conductive cores that are ferromagnetic, driven by an AC magnetic field. The multiple conductive cores are connected in parallel. An external magnetic field changes the magnetic characteristics of the sensing element and induces a change in electric potential of the induction coil. The sensor output is proportional to the number of conductive cores.