Reflective temperature compensating microwave susceptors

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The ability of a susceptor to brown or crispen food is largely determined by the complex surface impedance of the susceptor and by changes in the surface impedance during cooking.
Most microwave ovens operate at a microwave frequency of 2.
45 GHz.
The surface impedance of the susceptor can be measured at the frequency of the microwave oven, e.
g.
, 2.
45 GHz, with a network analyzer.
The effect of susceptor breakup on surface impedance can be seen in Table 1, which shows surface impedances for conventional susceptors, measured with a network analyzer before and after microwaving each product according to package directions.
The data in Table 1 show that the dominant electrical effect of breakup is a large increase in the imaginary part of the surface impedance with a concomitant dramatic decrease in susceptor absorption and reflection, and increased microwave transmission.
While not intending to be bound by any particular theory, microscopic examination of conventional aluminized polyethylene terephthalate (PET) susceptors before and after cooking in the microwave shows that the observed electrical changes correlate with the appearance of microscopic and macroscopic cracks and other discontinuities in the conductive, microwave interactive layer of the susceptor.

TABLE 1
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Surface Impedance
Product ohms/square % R % T % A
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Totino's Micro-
wave Pizza
Before MW 73.
4 - j7.
8 51.
7 7.
9 40.
3
After MW 160.
6 - j1101.
6
2.
7 92.
8 4.
5
Van de Kamp's
Microwave Fish
Fillets
#1:
Before MW 84.
0 - j5.
5 47.
8 9.
6 42.
6
After MW 163.
0 - j602.
9
7.
3 80.
1 12.
6
#2:
Before MW 126.
2 - j13.
3 35.
8 16.
2 48.
0
After MW 163.
3 - j596.
3
7.
4 79.
7 12.
8
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Highly significant in the above observations of the heating effects on a conventional susceptor is the substantial decrease in reflection (R) as a result of heating