Electromagnetic field detector located within a catheter, for determining the position and orientation of the catheter according to an electromagnetic field generated in the vicinity of the catheter, the electromagnetic field detector including a ferromagnetic core having a perforation and at least one winding wound around the ferrous core, the perforation providing communication between a first side of the ferrous core and a second side of the ferrous core, the first side facing a proximal side of the catheter and the second side facing a distal side of the catheter, the winding producing a current according to the electromagnetic field, wherein the ferrous core increases the sensitivity of the electromagnetic field detector to the electromagnetic field, by increasing a proportionality factor between the current and the electromagnetic field.