Variable frequency automated capacitive radio frequency (RF) dielectric heating system
First Claim
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1. A capacitive RF dielectric heating apparatus for treating food products, the apparatus comprising:
- a source of an AC RF signal at an RF frequency not greater than 300 MHz, the source being connected to a pair of electrodes on opposite sides of a product treatment zone to cause an RF signal to generate an AC electric field in the product treatment zone;
a frequency controller to adjust the frequency of the RF signal between different RF frequencies;
a mathematical model that predicts impedance of the food products as a function of temperature;
an impedance sensor to sense an impedance of the food products;
a computer programmed to receive impedance data from the impedance sensor, to process the impedance data using the model for the product, and to apply a control signal to the frequency controller to adjust the frequency of the RF signal to match the sensed impedance to a predetermined impedance.
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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.
205 Citations
28 Claims
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1. A capacitive RF dielectric heating apparatus for treating food products, the apparatus comprising:
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a source of an AC RF signal at an RF frequency not greater than 300 MHz, the source being connected to a pair of electrodes on opposite sides of a product treatment zone to cause an RF signal to generate an AC electric field in the product treatment zone;
a frequency controller to adjust the frequency of the RF signal between different RF frequencies;
a mathematical model that predicts impedance of the food products as a function of temperature;
an impedance sensor to sense an impedance of the food products;
a computer programmed to receive impedance data from the impedance sensor, to process the impedance data using the model for the product, and to apply a control signal to the frequency controller to adjust the frequency of the RF signal to match the sensed impedance to a predetermined impedance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A capacitive RF dielectric heating apparatus for treating food and seed products, the apparatus comprising:
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a source of an AC RF signal at a frequency not greater than 300 MHz;
a first electrode that is connected to the source;
a second electrode that is connected to the source and that is spaced from the first electrode so that a product treatment zone is defined between the electrodes and an RF signal flows through the product treatment zone; and
impedance matching means for matching an impedance of the heated food or seed products to a predetermined constant by adjusting the frequency of the RF signal. - View Dependent Claims (11, 12, 13)
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14. A capacitive dielectric (RF) heating apparatus from treating food products, the apparatus comprising:
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at least one pair of spaced-apart electrodes defining therebetween a food product treatment zone that can accommodate a food product to be treated;
signal generating circuitry connected to the electrodes, the signal generating circuitry being capable of providing an AC RF signal to charge the electrodes and generate an AC electric field in the food product treatment zone;
impedance measuring circuitry connected to the electrodes and to the signal generating circuitry, the impedance measuring circuitry measuring an impedance of the electrodes and the food product within the food product treatment zone; and
a controller linked to the impedance measuring circuitry and the signal generating circuitry, the controller controlling the signal generating circuitry and the AC electric field generated thereby based on the impedance measured by the impedance measuring circuitry. - View Dependent Claims (15, 16)
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17. A capacitive RF dielectric heating apparatus for treating food and seed products, the apparatus comprising:
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a source of an AC RF signal at an RF frequency not greater than 300 MHz, the source being connected to a pair of electrodes on opposite sides of a product treatment zone to cause an RF signal to flow through the product treatment zone;
a frequency controller to adjust the frequency of the RF signal between different RF frequencies;
a mathematical model that predicts Debye resonance frequency as a function of temperature for a product to be heated by the apparatus;
a temperature sensor to measure the temperature of a product located in the zone;
a computer programmed to receive temperature data from the temperature sensor, to process the temperature data using the model for the product, and to apply a control signal to the frequency controller to adjust the frequency of the RF signal to a Debye resonance frequency of the product at the sensed temperature in the zone. - View Dependent Claims (18, 19, 20, 21, 22, 23)
the model provides Debye resonance frequency information for multiple types of products; and
the apparatus further comprises an input device to tell the computer what type of product is located in the zone.
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19. The apparatus of claim 17 further comprising:
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a model that provides Debye resonance frequency information for multiple types of packaging materials; and
an input device to tell the computer whether a product located in the zone is contained in packaging material and, if so, what type of packaging material, the computer being programmed to signal the frequency controller to adjust the frequency of the RF signal to an RF frequency that is not a Debye resonance frequency of the packaging material.
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20. The apparatus of claim 19 wherein the input device input device also tells the computer what type of product is located in the zone.
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21. The apparatus of claim 19 wherein:
the model is a data table that contains Debye resonance frequencies for at least one product at various temperatures.
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22. The apparatus of claim 19 wherein the model is a mathematical model that predicts the Debye resonance frequencies for various products based on the dielectric properties of the products.
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23. The apparatus of claim 19 further comprising a field strength controller that responds to signals from the computer to adjust the power level of the RF signal in the zone.
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24. A capacitive RF dielectric heating apparatus for treating food and seed products, the apparatus comprising:
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a source of an AC RF signal at a frequency not greater than 300 MHz;
a first electrode that is connected to the source;
a second electrode that is connected to the source and that is spaced from the first electrode so that a product treatment zone is defined between the electrodes and an RF signal flows through the product treatment zone;
multiple temperature sensors positioned to measure the temperature at multiple regions of a product located in the zone; and
a computer which receives temperature data from the temperature sensors, processes the temperature data using a model for the product, and adjusts at least one characteristic of the RF signal in response to changes in the sensed temperatures in the zone. - View Dependent Claims (25, 26, 27)
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28. A system for heating a medium that includes a food product, comprising:
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means for subjecting the medium to an AC electrical field generated by an RF waveform applied at a selected frequency that heats the medium;
means for measuring an effective load impedance initially dependent upon the impedance of the medium;
means for comparing the effective load impedance with an output impedance of a signal generating unit that generates the RF waveform; and
means for automatically adjusting the effective load impedance to match the signal generating unit output impedance.
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Specification