Abstract: A self-supporting layer of flexible etchable metal having a thickness of about 1 micron has a plurality of apertures formed therethrough and has a layer of etchant resistant material on each face of the metal layer in a pattern completely overlying the metal layer and the periphery of the plurality of apertures.

Abstract: Selective demetallization of an etchable metal layer supported on a polymeric material or other microwave transparent material, or a self-supporting etchable metal layer, particularly aluminum of thickness at least about 1 micron adhesively joined to a flexible polymeric material substrate, is described. A web of polymeric material bearing the etchable metal layer, or an unsupported etchable metal layer, has a pattern of etchant-resistant material first applied and then the web is immersed in and passed through a bath aqueous etchant, particularly hot aqueous sodium hydroxide solution, for a time at least sufficient completely remove the etchable metal from non-protected areas of the web. The demetallized web is washed and dried. Specific structure incorporating the selectively demetallized etchable metal layer also are described.

Abstract: A method and device for enhancing the heating of a surface layer of an article being heated by microwave energy is characterized by directing the energy through the surface layer into a main portion of the article in such a manner that the modes of the energy are in cut-off in the surface layer.