A capacity type proximity sensor comprised of a capacitance type sensor, a capacitance type reference, and two independent and mutually opposing driven shields respectively adjacent the sensor and reference and which are coupled in an electrical bridge circuit configuration and driven by a single frequency...http://www.google.fr/patents/US5442347?utm_source=gb-gplus-shareBrevet US5442347 - Double-driven shield capacitive type proximity sensor
Double-driven shield capacitive type proximity sensor
