An electrodynamic sensor comprises a high input impedance electrometer adapted to measure small electrical potentials originating from an object under test and having a pair of input probes, characterised in that at least one of said pair of input probes has no direct electrical contact with said object,...http://www.google.co.uk/patents/US20060058694?utm_source=gb-gplus-sharePatent US20060058694 - Electrodynamic sensors and applications thereof
