A magnetic marker has a plurality of thin strips or wires of saturatable magnetic material having square .phi.-H characteristics and coercive forces different from each other. Amorphous magnetic material may be used. When the marker is subjected to magnetization reversal by an external magnetic field,...http://www.google.de/patents/US5204526?utm_source=gb-gplus-sharePatent US5204526 - Magnetic marker and reading and identifying apparatus therefor
