Apparatus for resolving movement of a mass within a defined space utilizes at least one electrode proximate to the space to be observed. An AC signal is applied to the electrode, and the current measured from that electrode and also to any other electrodes included in the system, and which are effectively...http://www.google.com/patents/US6066954?utm_source=gb-gplus-sharePatent US6066954 - Apparatus for resolving presence and orientation within a defined space
