A distance sensor has a capacitive element in turn having a first armature which is positioned facing a second armature whose distance is to be measured. In the case of fingerprinting, the second armature is defined directly by the skin surface of the finger being printed. The sensor comprises an inverting...http://www.google.com/patents/US6320394?utm_source=gb-gplus-sharePatent US6320394 - Capacitive distance sensor
