A large number of magnetic polymer elements are distributed at random in a base material of a object to be checked. Each magnetic polymer element includes an element main body formed of a high-molecular material, such as an acrylic resin, and magnetic metal powder contained therein. The base material...http://www.google.ca/patents/US5601931?utm_source=gb-gplus-sharePatent US5601931 - Object to be checked for authenticity and a method for manufacturing the same
