Electromagnetic heating
An electromagnetic heater for heating an irregularly shaped object, including: a cavity within which an object is to be placed; at least one feed which feeds UHF or microwave energy into the cavity; and a controller that controls one or more characteristics of the cavity or energy to assure that the UHF or microwave energy is deposited uniformly in the object within ±30% over at least 80% of the volume of the object.
1. A method of electromagnetic heating an object in a cavity, the method comprising:
feeding UHF or microwave energy into the cavity via a plurality of feeds;
determining an efficiency of net transfer of energy into the cavity for each of the plurality of feeds as a function of frequency over a range of frequencies; and
adjusting the frequencies of the energy fed into the cavity, responsive to the determined efficiency of net transfer of energy into the cavity for each of the plurality of feeds;
wherein the method includes adjusting power at each feed, responsive to the determined efficiency of net transfer of energy into the cavity for each of the plurality of feeds, as the frequencies of the energy fed into the cavity are adjusted.
2. A method of electromagnetic heating of an object in a cavity, the method comprising:
feeding UHF or microwave radiation into the cavity for heating the object;
changing a frequency of the UHF or microwave radiation fed into the cavity by at least 1 MHz during the course of the heating; and
adjusting, for each frequency, a power level of the UHF or microwave radiation fed into the cavity, wherein
the change in the frequency of the UHF or microwave radiation is determined based on a measurement of net efficiency of energy transfer to the cavity over a band of frequencies, and
the power level of the UHF or microwave radiation is adjusted for each frequency responsive to the measurement of the net efficiency of energy transfer to the cavity over a band of frequencies.
3. The method of claim 2 , wherein the net efficiency is approximated by a proportion of input power that is absorbed in the object.
4. The method of claim 3 , wherein the net efficiency is approximated by a proportion of input power that is not output from the cavity through the feeds.
5. The method of claim 2 , wherein the frequency of the UHF or microwave radiation fed into the cavity for heating the object is fed via a plurality of feeds.
6. The method of claim 5 , wherein a net efficiency of energy transfer into the object to be heated, as compared to an amount of energy provided to the plurality of feeds, is greater than 40%.
7. The method of claim 5 , wherein the frequencies fed at the same time to two of the feeds differ by at least 8 MHz.
8. The method of claim 2 , wherein a controller is configured to determine the net efficiency of energy transfer to the cavity and cause adjustment of the frequency.
9. The method of claim 8 , wherein the controller is configured to cause the adjustment of the frequency during a period between commencement and ending of heating.
10. The method of claim 8 , wherein the controller is configured to cause feeding of the UHF or microwave radiation into the cavity at two or more different frequencies, each being associated with a different power level of the UHF or microwave radiation.
11. The method of claim 8 , wherein the controller is configured to cause the adjustment of the frequency as heating proceeds.
12. A method to control one or more characteristics of a process of heating an object in a cavity based on measurement of energy absorption efficiency, wherein the method comprises:
measuring an efficiency of energy absorption into the object as a function of frequency; and
adjusting an input power level associated with each of a plurality of transmitted frequencies based on the measured efficiency of energy absorption into the object.
13. The method of claim 12 , wherein the efficiency of energy absorption into the object is approximated based on a proportion of input energy that is absorbed in the object.
14. The method of claim 12 , wherein the transmitted frequencies are supplied via a plurality of feeds.
15. The method of claim 14 , wherein the net efficiency is approximated by a proportion of input power that is not output from the cavity through the feeds.
16. The method of claim 14 , wherein the efficiency of energy absorption into the object to be heated, as compared to an amount of energy provided to the plurality of feeds, is greater than 40%.
17. The method of claim 14 , wherein the transmitted frequencies supplied at any given time by at least two of the plurality of feeds differ by at least 8 MHz.
18. The method of claim 12 , wherein a controller is configured to determine the efficiency of energy absorption into the object and to cause adjustment of the input power level at each of the plurality of transmitted frequencies.
19. The method of claim 18 , wherein the controller is further configured to cause the adjustment of the input power level at each of the plurality of transmitted frequencies during a period between commencement and ending of heating.
20. The method of claim 18 , wherein the controller is configured to cause the adjustment of the input power level at each of the plurality of transmitted frequencies as heating proceeds.