A tag structure suitable for attachment to an object includes one or more bimorphs comprised of a thin strip of a magnetostrictive material attached to a thicker bar of hard magnetic material. The tag is preferably excited using either magnetic or acoustic fields, tuned to the resonance of the bimorphs....http://www.google.de/patents/US5552778?utm_source=gb-gplus-sharePatent US5552778 - Multibit bimorph magnetic tags using acoustic or magnetic interrogation for identification of an object coupled thereto
