A card configured to output an magnetic field on or at a surface thereof, the card comprising an elongated magnetically conducting material on or at the surface of the card, the magnetically conducting material having a first and a second guide ends, and a field generator positioned so as to feed a magnetic field into the magnetically conducting material. The magnetically conducting material is positioned at the position where the reading head travels and forms a return path for the field generated by the field generator, whereby field from the generator is fed to the reading head via the magnetically conducting material.