A method of and apparatus for determining the genuineness of a document such as a currency note printed at least in part with magnetizable ink in which there is produced a first signal as a measure of the saturation magnetization of a portion of the document printed with the ink and a second signal as...http://www.google.co.uk/patents/US5068519?utm_source=gb-gplus-sharePatent US5068519 - Magnetic document validator employing remanence and saturation measurements
