Patent ID: 8723090

Claim:
A self-supporting field director structure for use in heating an article in a microwave oven, the field director structure comprising: a central support member having a plurality of slots formed therein, and a plurality of vanes, each vane extending radially outwardly from a central axis through one of the slots in the central support member, each vane being angularly adjacent to two other vanes, each vane having a predetermined thickness dimension, wherein each vane has a first major surface, a second major surface, a first minor surface and a second minor surface, and wherein each vane comprises: a substrate formed from an electrically non-conductive material having a predetermined coefficient of thermal expansion, and an electrically conductive sheath having a predetermined coefficient of thermal expansion that is different from the coefficient of thermal expansion of the substrate, the sheath encasing the substrate so that a portion of the first and second major surfaces and a portion of the first and second minor surfaces of each vane are covered by the electrically conductive material of the sheath, the sheath and the substrate being arranged in a laterally symmetric fashion so that thermal expansion effects due to heating are equalized across the thickness of each vane.