An apparatus and method for sensing impedances of materials placed in contact therewith. The invention comprises a plurality of drive electrodes and one or more sense electrodes. Both rotating electric fields and differently shaped electric fields are provided for, as are analysis of structure and composition...http://www.google.se/patents/US5602486?utm_source=gb-gplus-sharePatent US5602486 - Impedance sensing of flaws in non-homogenous materials
