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US 6,657,173 B2Granted
Variable frequency automated capacitive radio frequency (RF) dielectric heating system
AssigneesState Board of Higher Education on Behalf of Oregon State University, Benjamin A. Flugstad
InventorsBenjamin A. Flugstad, Qingyue Ling, Edward R. Kolbe, John Henry Wells, Yanyun Zhao, Jae W. Park
Life of this patent
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Abstract
A food product is heated by maintaining the food product in an AC electrical field generated by an RF signal. As the heating takes place, maximum energy is delivered to the food product using automatic impedance matching to adjust the rate of the process.
Claims46
A method for heating a medium that includes a food product, the method comprising:
- subjecting the medium to an AC electrical field generated by an RF waveform applied at a selected frequency that heats the medium;
- measuring an effective load impedance initially dependent upon the impedance of the medium;
- comparing the effective load impedance with an output impedance of a signal generating unit that generates the RF waveform;
- and
- automatically adjusting the effective load impedance to match the signal generating unit output impedance.
2 more elements
A method for heating a food product, the method comprising:
- subjecting the food product to an AC field produced by applying an AC waveform at a known frequency with a signal generating unit, the signal generating unit having a known, generally constant output impedance;
- measuring an actual impedance of the food product;
- determining an effective load impedance initially dependent upon the actual impedance of the food product, the effective load impedance being determined by at least one of measuring the voltage and current of the applied RF waveform and computing a phase angle difference, and measuring a forward power level of the RF waveform applied to the food product and a reverse power level of the RF waveform reflected from the food product with the signal generating circuitry;
- comparing the effective load impedance with the signal generating unit output impedance;
- and
- automatically matching the effective load impedance to the signal generating unit output impedance by at least one of adjusting the frequency at which the RF waveform is applied and tuning a tunable impedance matching network such that the effective adjusted load impedance is approximately equal to the signal generating unit output impedance.
3 more elements
A method for heating a food product, the method comprising:
- maintaining a food product that is contained in packaging material in an AC electrical field generated by an RF waveform at a frequency not greater than 300 MHz provided by signal generating circuitry;
- and
- controllably heating the food product by automatically maintaining an impedance match between the food product and the signal generating circuitry.
A method for heating a food product comprising:
- maintaining a food product that is contained in packaging material in an AC electrical field provided by an RF waveform;
- periodically sensing the impedance of the food product and the packaging material to produce a sensor output signal;
- determining impedance mismatch based on a difference between a most recently sensed impedance and a known impedance, and generating a corresponding control signal output that corresponds to the difference with a computer;
- and
- as the food product and the packaging material increase in temperature, adjusting the frequency of the RF waveform by the control signal output of the computer such that the sensed impedance matches the most recently sensed impedance.
2 more elements
A method for killing an undesired organism associated with a food product, the method comprising:
- maintaining a food product that is contained in packaging material in an AC electrical field provided by an RF waveform;
- periodically sensing the impedance of the food product and the packaging material to produce a sensor output signal;
- determining impedance mismatch based on a difference between a most recently sensed impedance and a known impedance, and generating a corresponding control signal output that corresponds to the difference with a computer;
- as the food product and the packaging material increase in temperature, adjusting the frequency of the RF waveform by the control signal output of the computer such that the sensed impedance matches the most recently sensed impedance.
1 more element
A method for heating a food product comprising:
- testing a first sample of a food product to determine impedance of the food product at several different temperatures;
- storing the resulting impedance vs. temperature information for the food product in a memory of a computer;
- flowing a signal through a second sample of the food product, the signal being at an RF frequency not greater than 300 MHz for the food product;
- sensing the impedance of at least one portion of the second sample;
- determining, by operation of the computer, a relationship between the most recently sensed impedance of the food product and a heating rate of the food product;
- and
- adjusting the heating rate of the food products based on the relationship.
4 more elements
A method for treating seeds, the method comprising:
- maintaining seeds in an AC electrical field provided by an RF signal at a frequency not greater than 300 MHz;
- and
- controllably heating the seeds by automatically maintaining an impedance match between an impedance of the seeds and a predetermined constant.
Dependencies are inferred from the claim text.