Electromagnetic heating

Abstract

An apparatus for applying RF energy, via an antenna, to an object placed in a cavity is disclosed. The apparatus includes a Direct Digital Synthesis (DDS) frequency source configured to feed the antenna with RF energy at a plurality of frequencies, and a controller configured to control the DDS frequency source to apply RF energy to the object.

1 - 19 . (canceled) 
     
     
         20 . An apparatus for applying RF energy, via an antenna, to an object placed in a cavity, the apparatus comprising:
 a Direct Digital Synthesis (DDS) frequency source configured to feed the antenna with RF energy at a plurality of frequencies; and   a controller configured to control the DDS frequency source to apply RF energy to the object.   
     
     
         21 . The apparatus of  claim 20 , further comprising an amplifier, wherein said amplifier is connected to the DDS frequency source and is configured to provide an output signal to the antenna. 
     
     
         22 . The apparatus of  claim 21 , wherein said amplifier includes a solid state microwave amplifier. 
     
     
         23 . The apparatus of  claim 21 , further comprising a dual directional coupler between the amplifier and the antenna configured to sample input and output power from the cavity and send power measurement signals to the controller. 
     
     
         24 . The apparatus of  claim 21 , further comprising a dual directional coupler between the amplifier and the antenna configured to sample input and output power from the cavity and send power measurement signals to the controller, wherein the controller is configured to cause the DDS frequency source to sweep a first plurality of RF frequencies to determine one or more characteristics associated with at least one interaction between the RF energy and the object and to cause the DDS frequency source to sweep over a second plurality of RF frequencies and, based on the one or more determined characteristics, apply RF energy to the object at frequencies within the second plurality, and wherein the controller is configured to determine the one or more characteristics based on the power measurement signals. 
     
     
         25 . The apparatus of  claim 20 , wherein the controller is configured to cause the DDS frequency source to sweep a first plurality of RF frequencies to determine one or more characteristics associated with at least one interaction between the RF energy and the object and to cause the DDS frequency source to sweep over a second plurality of RF frequencies and, based on the one or more determined characteristics, apply RF energy to the object at frequencies within the second plurality. 
     
     
         26 . The apparatus of  claim 25 , wherein the one or more characteristics include an RF energy absorption characteristic associated with the object. 
     
     
         27 . The apparatus of  claim 25 , wherein the controller is configured to cause heating of the object through the application of RF energy applied to the object at frequencies within the second plurality. 
     
     
         28 . The apparatus of  claim 25 , wherein the first plurality of RF frequencies and the second plurality of RF frequencies at least partially overlap. 
     
     
         29 . The apparatus of  claim 25 , wherein the one or more characteristics include an RF energy absorption characteristic associated with the object, and wherein one or more power levels at which RF energy is applied to the object at frequencies within the second plurality are selected based on the RF energy absorption characteristic associated with the object. 
     
     
         30 . The apparatus of  claim 25 , wherein the one or more characteristics include an RF energy absorption characteristic associated with the object, and wherein application of the RF energy applied to the object at frequencies within the second plurality is controlled such that a multiplicative product of applied power level and net power efficiency is substantially constant over the second plurality of frequencies. 
     
     
         31 . The apparatus of  claim 25 , wherein the first plurality of frequencies includes a greater number of frequencies than the second plurality of frequencies. 
     
     
         32 . The apparatus of  claim 25 , wherein the sweep over the first plurality of RF frequencies occurs at a scan rate of greater than at least 1 GHz/sec. 
     
     
         33 . The apparatus of  claim 25 , wherein the sweep over the second plurality of RF frequencies occurs at a scan rate of greater than at least 1 kHz/sec. 
     
     
         34 . The apparatus of  claim 20 , further including a plurality of antennas, and wherein the DDS frequency source is configured to feed each of the plurality of antennas with RF energy at a plurality of frequencies. 
     
     
         35 . The apparatus of  claim 20 , further including a plurality of antennas and a plurality of DDS frequency sources, wherein each of the plurality of DDS frequency sources is configured to feed a respective antenna, from among the plurality of antennas, with RF energy at a plurality of frequencies. 
     
     
         36 . A method of applying RF energy, via an antenna, to an object placed in a cavity, the method comprising:
 causing a Direct Digital Synthesis (DDS) frequency source to feed the antenna with RF energy at a plurality of frequencies; and   controlling the DDS frequency source to apply RF energy to the object.   
     
     
         37 . The method of  claim 36 , further comprising:
 causing the DDS frequency source to sweep a first plurality of RF frequencies to determine one or more characteristics associated with at least one interaction between the RF energy and the object;   causing the DDS frequency source to sweep over a second plurality of RF frequencies; and   based on the one or more determined characteristics, applying RF energy to the object at frequencies within the second plurality.   
     
     
         38 . The method of  claim 37 , wherein the one or more characteristics include net power efficiency associated with the object. 
     
     
         39 . The method of  claim 38 , further comprising measuring input reflection coefficients and transfer coefficients, and determining the net power efficiency based on the measurements.