Heating devices, in which a semi-conductor pattern is carried on an insulating surface and a pair of spaced apart electrodes are electrically connected to the semi-conductor pattern, are characterized in that the semi-conductor pattern in at least one heating area of the device defines a two-dimensional...http://www.google.es/patents/US4892998?utm_source=gb-gplus-sharePatente US4892998 - Semi-conductive electrical heating device with voids
Semi-conductive electrical heating device with voids
