portion of the current flowing in metalized layer 14 is indicated by the vertical arrows shown in fig1 b as current flows metalized layer 14 begins to heat as a function of the current generated and the surface impedance z s of layer 14 however it has been observed that metalized layer 14 does not heat uniformly rather hot spots such as spots 20 and 22 develop as illustrated in fig1 b as metalized layer 14 continues to heat and as hot spots 20 and 22 grow hotter heat transfers throughout the susceptor 10 and the temperature of substrate 12 also increases discontinuities such as thinned areas holes or cracks are formed in metalized layer 14 at the hot spots 20 and 22 fig1 c shows a top view of susceptor 10 with the discontinuities at hot spots 20 and 22 having expanded into lateral cracks or thinned areas as the temperature of susceptor 10 continues to rise more spots on susceptor 10 approach the temperature where additional lateral cracks form in substrate 12 thereby driving the formation of more discontinuities in metalized layer 14 the lateral cracks and discontinuities which form in substrate 12 and metalized layer 14 substantially destroy the electrical continuity in metalized layer 14 this decreases the responsiveness of susceptor 10 to microwave energy and susceptor 10 begins to cool despite continued exposure to microwave energy thus the ability of susceptor 10 to provide further heating is essentially destroyed it should be noted that the electric field in a microwave oven has random direction thus discontinuities.