Method and apparatus for controlled broadband microwave heating
First Claim
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1. A broadband microwave heating apparatus, comprising:
- an applicator cavity for exposing a workpiece to microwave energy;
a microwave power supply connected to the cavity, the power supply comprising;
a small-signal RF source comprising at least a voltage controlled microwave oscillator and a voltage controlled attenuator that are both thermally stabilized at a selected temperature above ambient;
a two port microwave amplifier to amplify a signal from the small-signal RF source to a usable power level for heating;
forward and reflected power detectors, the detectors separated from one another by a microwave isolator, wherein the forward power detector is located upstream of the microwave isolator;
a power regulator configured to determine a difference between a forward power detected by the forward power detector and a power setting of the microwave power supply; and
a control system including a power control loop and configured to use an output of the power regulator to adjust an output power of the microwave power supply based on the determined difference between the forward power detected by the forward power detector and the power setting of the microwave power supply,a heater;
at least one of a temperature sensor or a thermostat;
wherein all of the small-signal RF source are mounted on a common thermal platform and maintained at a common temperature above an ambient temperature, wherein the heater is controlled by the at least one of a temperature sensor or the thermostat.
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Abstract
A materials processing system comprises a thermal processing chamber and a broadband microwave power source. The power source includes an ovenized small-signal RF circuit, a high power microwave amplifier, and forward and reflected power detectors separated from one another by an isolator. The power detectors are also preferably ovenized. A control system provides control signals to the thermally stabilized VCO and VCA in the small-signal circuit to control output power based on detected forward power compared to demanded forward power. The system may be run in either open-loop or closed-loop modes.
42 Citations
17 Claims
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1. A broadband microwave heating apparatus, comprising:
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an applicator cavity for exposing a workpiece to microwave energy; a microwave power supply connected to the cavity, the power supply comprising; a small-signal RF source comprising at least a voltage controlled microwave oscillator and a voltage controlled attenuator that are both thermally stabilized at a selected temperature above ambient; a two port microwave amplifier to amplify a signal from the small-signal RF source to a usable power level for heating; forward and reflected power detectors, the detectors separated from one another by a microwave isolator, wherein the forward power detector is located upstream of the microwave isolator; a power regulator configured to determine a difference between a forward power detected by the forward power detector and a power setting of the microwave power supply; and a control system including a power control loop and configured to use an output of the power regulator to adjust an output power of the microwave power supply based on the determined difference between the forward power detected by the forward power detector and the power setting of the microwave power supply, a heater;
at least one of a temperature sensor or a thermostat;
wherein all of the small-signal RF source are mounted on a common thermal platform and maintained at a common temperature above an ambient temperature, wherein the heater is controlled by the at least one of a temperature sensor or the thermostat. - View Dependent Claims (2, 3, 15, 16)
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4. A broadband microwave power supply, comprising:
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a small-signal RF source comprising at least a voltage controlled microwave oscillator (VCO) and a voltage controlled attenuator (VCA) that are both thermally stabilized at a selected temperature above ambient; a microwave amplifier to amplify a signal from the small-signal RF source to a usable power level for heating; forward and reflected power detectors, the detectors separated from one another by a microwave isolator, wherein the forward power detector is located upstream of the microwave isolator; a power regulator configured to determine a difference between a forward power detected by the forward power detector and a power setting of the microwave power supply; and a control system including a power control loop and configured to use an output of the power regulator to adjust an output power of the microwave power supply based on the determined difference between the forward power detected by the forward power detector and the power setting of the microwave power supply, a heater;
at least one of a temperature sensor or a thermostat;
wherein all of the small-signal RF source are mounted on a common thermal platform and maintained at a common temperature above an ambient temperature, wherein the heater is controlled by the at least one of a temperature sensor or the thermostat. - View Dependent Claims (5, 6, 7, 8, 9, 17)
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10. A method of heating materials using broadband microwave power, comprising:
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placing a selected workpiece in a multi-mode microwave applicator cavity; providing a microwave power supply in communication with the cavity, the power supply including a small-signal RF generating circuit, a microwave amplifier, and forward and reflected power detectors, the detectors separated from one another by an isolator; heating at least some of the components of the small-signal RF generating circuit to a selected temperature above ambient, a heater;
at least one of a temperature sensor or a thermostat;
wherein all of the small-signal RF source are mounted on a common thermal platform and maintained at a common temperature above an ambient temperature, wherein the heater is controlled by the at least one of a temperature sensor or the thermostat;providing a control system to perform the following functions; run an automatic power leveling routine to automatically generate an autolevel table and download the autolevel table to the control system; provide an automatic power control system to limit the rate of power adjustment; and
,applying microwave power into the applicator cavity under the control of the control system to heat the workpiece, wherein the control system uses a power regulator to adjust an output power of the microwave power supply based on a comparison between a forward power detected by the forward power detector and a power setting of the microwave power supply. - View Dependent Claims (11, 12, 13, 14)
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Specification