JP2023153587A - Electrode for dielectric heating, high-frequency dielectric heating device, and method - Google Patents

Abstract

To provide a small-size electrode for dielectric heating excellent in heating efficiency and less uneven heating with a low cost, and a high-frequency dielectric heating device.SOLUTION: The electrode for dielectric heating dielectrically heats an object to be heated by the electric field generated between upper and lower electrodes by applying a high-frequency voltage between the upper and lower electrodes of a parallel plate. In the electrode for dielectric heating, a spiral-shaped electrode is provided on either or both of the lower surface of the upper electrode and the upper surface of the lower electrode, and the spiral-shaped electrode is connected to the parallel plate electrode at the outer peripheral end, and the inner peripheral end side is an open end.SELECTED DRAWING: Figure 1

Description

The present invention relates to a dielectric heating electrode, a high-frequency dielectric heating device, and a method, and particularly to a dielectric heating electrode, a high-frequency dielectric heating device, and a method for applying a high-frequency electric field in the MHz band to frozen food to thaw the frozen food by dielectric heating. Regarding.

In food processing factories, frozen foodstuffs are sometimes thawed and processed into foods. A high-frequency dielectric heating device (high-frequency thawing device), which is a type of thawing machine used in food processing factories, applies a high-frequency electric field in the MHz band to the frozen food placed between opposing electrodes, and thaws the frozen food by dielectric heating. It has been known.

High-frequency dielectric heating refers to applying a high-frequency voltage to a dielectric object, which is the object to be heated, and heating the object from within through self-heating (dielectric loss) caused by vibrations of polar molecules that make up the object. It's technology. In dielectric heating using microwaves (GHz band) in a microwave oven, there is a large difference in heat generation between ice and water, so the melted portion of the surface layer of the food generates significant heat, resulting in uneven heating. However, high-frequency dielectric heating, which uses a lower frequency band than microwaves, has the advantage that uneven heating is less likely to occur because the energy penetrates deeper than microwaves and the difference in calorific value between ice and water is small. It is generally known that there is.

FIG. 17 shows an example of dielectric heating using a high frequency electric field in the MHz band, which is realized by, for example, Patent Document 1. The high-frequency decompressor 10 in FIG. 17 includes a high-frequency power supply 1 that outputs MHz bands such as ISM bands of 13.56 MHz, 27.12 MHz, and 40.68 MHz, a reflected power detection circuit 16, a matching circuit 11, an upper electrode 3, and a lower The matching circuit 11 is composed of an electrode 6, and further composed of variable capacitors C12, C13 and a variable coil L10.

A high frequency signal (RF signal) in the MHz band from the high frequency power supply 1 is matched with the equivalent impedance of the heated object 7 placed between the upper electrode 3 and the lower electrode 6 by the matching circuit 11 via the reflected power detection circuit 16. The object 7 to be thawed is thawed by efficiently transmitting power from the high frequency power source 1.

In addition, in high-frequency dielectric heating, if the dielectric constant of the frozen food changes during thawing and the impedance between the electrodes changes, the impedance matching will shift and the heating efficiency will deteriorate. The matching state is determined by detecting the incident power and the reflected power, and calculating the difference in VSWR (Voltage Standing Wave Ratio) obtained from these ratios, and adjusting the matching circuit 11 so that matching can be achieved. It is stated that

Furthermore, in Patent Document 2, a plurality of power transmission amplifiers with relatively small power ratings are used, and their outputs are combined by a power combining circuit, so that the combined output of the power transmission amplifiers is used as the decompression power. Since the decompression power can be increased and the time required for decompression can be shortened, it is also possible to obtain an input impedance with a lower impedance matching than the impedance suitable for the power transmission amplifier, so the configuration of the impedance matching circuit can also be improved. It is stated that it is easy.

If we compare the description of Patent Document 2 with reference to FIG. 17, by configuring multiple power transmission amplifiers built into the high frequency power supply 1 to operate in parallel, the output impedance of the amplifiers is lowered, so that the intermediate impedance can be set to a value lower than 50Ω. The input impedance of the matching circuit 11 can be lowered. In addition, since the equivalent series resistance between the electrodes is also low compared to 50Ω, the impedance conversion ratio of the matching circuit 11 can be made small, making it possible to simplify the matching circuit and use relatively low voltage circuit components. .

Japanese Patent Application Publication No. 2020-145114 Japanese Patent Application Publication No. 2003-17238

In Patent Document 1 shown in FIG. 17, in dielectric heating using parallel plate electrodes of the upper electrode 3 and the lower electrode 6, in order to shorten the thawing time, dielectric heating in the MHz band, which is said to be less likely to cause uneven heating when the output power is increased, is used. Even with heating, the electric field concentrates on the edges of the object to be thawed, causing thawing at the tip to progress more than at the center, resulting in uneven heating, where the temperature at the edges rises more than necessary.

Furthermore, since the phases of the voltages generated between the variable coil C13 of the matching circuit 11, the upper electrode 3, and the lower electrode 6 differ by 180 degrees, and a resonance phenomenon occurs in which they cancel each other out, a large voltage of several thousand V or more is applied between these ends. Voltage is generated. As a result, a large current of several amperes or more flows through the parasitic capacitance between the electrode and the casing, resulting in loss and deterioration of heating efficiency.Furthermore, a high voltage is generated, which causes the variable capacitors C12 and C13 to flow. Since it is necessary to use high-voltage, high-cost vacuum variable capacitors, high-voltage relays, etc., the problem is that the circuit components become large and expensive.

On the other hand, as in Patent Document 2, when aiming to reduce the output impedance by combining multiple power transmission amplifiers in parallel to increase output and lower the impedance of the variable matching circuit, the electrode A problem arises in that reflected power and incident power cannot be accurately measured to detect the matching state between the two.

This is because the power detection circuit 16 that detects reflected power and incident power in FIG. 17 detects incident and reflected power by comparing it with a reference resistance, so in Patent Document 2, the impedance is reduced. If the impedance between the electrodes changes depending on the thawing state of the frozen food, the detection accuracy of the reflected power will decrease and the heating efficiency will deteriorate.

In view of the above, an object of the present invention is to provide a dielectric heating electrode, a high frequency dielectric heating device, and a method that are small, low cost, have excellent heating efficiency, and have little heating unevenness.

From the above, in the present invention, "a dielectric heating electrode that dielectrically heats the object to be heated by the electric field generated between the upper electrode and the lower electrode by applying a high frequency voltage between the upper electrode and the lower electrode of a parallel plate. A spiral electrode is provided on one or both of the lower surface of the upper electrode and the upper surface of the lower electrode, and the outer peripheral end of the spiral electrode is connected to the parallel plate electrode, and the inner peripheral end is open. ``A dielectric heating electrode characterized by having an edge.''

In addition, in the present invention, an electric field is generated between the upper electrode and the lower electrode by applying a high frequency voltage from a high frequency power supply between the upper electrode and the lower electrode of the parallel plate through a matching circuit that variably adjusts the impedance. This is a high-frequency dielectric heating device that dielectrically heats an object to be heated, and a spiral electrode is provided on either or both of the lower surface of the upper electrode and the upper surface of the lower electrode, and the outer peripheral edge of the spiral electrode is parallel. A high-frequency dielectric heating device characterized in that it is connected to a flat plate electrode and that its inner peripheral end is an open end.

In addition, in the present invention, an electric field is generated between the upper electrode and the lower electrode by applying a high frequency voltage from a high frequency power supply between the upper electrode and the lower electrode of the parallel plate through a matching circuit that variably adjusts the impedance. A high-frequency dielectric heating method for dielectrically heating an object to be heated, in which a spiral electrode is provided on either or both of the lower surface of the upper electrode and the upper surface of the lower electrode, and the outer peripheral edge of the spiral electrode is parallel. It is connected to a flat plate electrode, and its inner peripheral end is an open end, and it can be connected to a parallel plate electrode via multiple switch circuits at multiple locations on the outer peripheral end of the spiral electrode. , a high-frequency dielectric heating method characterized by detecting a high-frequency voltage or high-frequency power from a high-frequency power supply and controlling the impedance of a matching circuit and one or both of a plurality of switch circuits according to the temperature of the object to be heated. That is.

The high-frequency dielectric heating device of the present invention provides a high-frequency dielectric heating device that is small, low cost, has excellent heating efficiency, and has little heating unevenness.

1 is a diagram showing a configuration example of a high-frequency dielectric heating device according to Example 1 of the present invention. FIG. 2 is a configuration diagram showing the distribution of standing waves and electric fields generated by the spiral of the dielectric heating electrode of the present invention. FIG. 7 is a diagram showing another example of the spiral arrangement of the high-frequency dielectric heating device according to the first embodiment of the present invention. FIG. 1 is a cross-sectional configuration diagram showing the configuration of a dielectric heating electrode of the present invention. FIG. 2 is an equivalent circuit diagram showing the configuration of the dielectric heating electrode of the present invention. The impedance characteristic diagram showing the electromagnetic field analysis results of the upper and lower spiral electrodes constructed using the conventional technology. FIG. 3 is an impedance characteristic diagram showing the electromagnetic field analysis results of the dielectric heating electrode according to Example 1 of the present invention. A diagram showing the results of calculating the heat generation density distribution of food during thawing using electromagnetic field analysis using conventional parallel plate electrodes. FIG. 3 is a diagram showing the results of the present invention, in which the heat generation density distribution of foodstuffs during thawing was calculated by electromagnetic field analysis. FIG. 3 is a diagram showing an example of the configuration of a high-frequency dielectric heating device according to a second embodiment of the present invention. FIG. 3 is a circuit diagram showing an example of a MOS FET switch circuit for switching the length of a spiral electrode according to a second embodiment of the present invention. FIG. 7 is a diagram showing a configuration example of a dielectric heating device according to Example 3 of the present invention. The figure which shows the result of the electric field distribution of the flat plate electrode at the time of thawing calculated by electromagnetic field analysis with the conventional parallel plate electrode. The figure which shows the result of this invention which calculated the electric field distribution of the flat plate electrode at the time of thawing by electromagnetic field analysis. FIG. 4 is a diagram showing a configuration example of a high-frequency dielectric heating device according to a fourth embodiment of the present invention. FIG. 4 is a circuit diagram showing an example of a capacitance switching circuit of a high-frequency dielectric heating device according to Example 4 of the present invention. FIG. 4 is a diagram showing an equivalent circuit configured to convert into a current source by a current source conversion circuit according to a fourth embodiment of the present invention, and cancel the imaginary part of an electrode by a variable matching circuit. FIG. 7 is a diagram showing the results of calculating the voltage value of the variable matching input terminal when the capacitance value of the variable matching circuit according to the fourth embodiment of the present invention is varied by circuit simulation. FIG. 7 is a flowchart showing the flow from the start to the end of dielectric heating in the high-frequency dielectric heating device according to Example 4 of the present invention. FIG. 3 is a schematic cross-sectional view showing a configuration example of a high-frequency dielectric heating device according to Example 5 of the present invention. FIG. 7 is a diagram illustrating an example of the configuration of the back side of a high-frequency dielectric heating device according to Example 5 of the present invention. FIG. 7 is a schematic perspective view showing a configuration example of the surface and interior of a high-frequency dielectric heating device according to Example 5 of the present invention. 1 is a block diagram showing an example of a circuit configuration of a high-frequency dielectric heating device according to the prior art.

Embodiments of the present invention will be described below with reference to the drawings.

The high-frequency dielectric heating device can be widely used in heating objects to be heated, but when used specifically for thawing, it is sometimes referred to as a high-frequency thawing device. The device will be explained.

In addition, in an embodiment of the present invention, a high-frequency dielectric heating device is installed in the backyard of a retail store such as a convenience store or a supermarket to store frozen lunch boxes, prepared foods, etc. according to the number of customers entering the store. It is assumed that frozen foods will be thawed and displayed as chilled items on store shelves, or that thawed foods will be provided to customers.

However, the following explanations show specific examples of the content of the present invention, and the present invention is not limited to these explanations, and the present invention is not limited to these explanations. Various changes and modifications may be made by the manufacturer.

FIG. 1 is a diagram showing a schematic configuration example of a high frequency decompression device according to a first embodiment of the present invention. The high-frequency decompression device 10 includes a high-frequency power source 1 that outputs MHz bands such as 13.56 MHz, 27.12 MHz, and 40.68 MHz, which are ISM bands, a housing 2, an upper flat plate electrode 3, a lower flat plate electrode 6, an upper spiral 4, It is composed of a lower spiral 5 and thaws frozen food 7. Further, the length (total length) of the upper spiral 4 and the lower spiral 5 is around λ/4 of the output frequency of the high frequency power source 1, and the outer peripheral end of the upper spiral 4 is connected to the upper flat plate electrode 3. The inner peripheral end is in an open state, and similarly, the outer peripheral end of the lower spiral 5 is connected to the lower flat plate electrode 6, and the inner peripheral end is in an open state.

In the example of FIG. 1, spiral electrodes are provided on both the lower surface of the upper electrode and the upper surface of the lower electrode, but these are not provided on either the lower surface of the upper electrode or the upper surface of the lower electrode. There may be. In addition, it is best for the length (total extension) of the spirals 4 and 5 to be λ/4 of the output frequency of the high-frequency power source 1 or an integral multiple of λ/4, but the length near λ/4 is best. In the following description of the present invention, lengths around λ/4 will be included and treated as λ/4, since the effects of the present invention can be achieved even if the length is λ/4.

In the overall configuration roughly described above, MHz band high frequency power from the high frequency power supply 1 of FIG. 1 is applied between the upper flat plate electrode 3 and the lower flat plate electrode 4, thereby generating an electric field within the flat plate electrode. Due to this electric field, each spiral is excited by the potential difference between the upper spiral 4 and the lower flat plate electrode 6, and the lower spiral 5 with the upper flat plate electrode 3, and a standing wave is generated, and the spirals 4 and 5 are opened from the outer peripheral ends. The electric field is concentrated at the center of the electrode, which is the edge. As a result, the frozen foodstuff 7 can have an electrode configuration in which heating unevenness that occurs at the end portions is less likely to occur due to the central portion being heated more.

In the present invention, the combination of the upper flat plate electrode 3, the lower flat plate electrode 6, the upper spiral 4, and the lower spiral 5 is collectively referred to as a dielectric heating electrode. The dielectric heating electrode includes a flat plate electrode and a spiral electrode.

FIG. 2a is a diagram showing the distribution of standing waves and electric fields generated on a λ/4 spiral in the high-frequency decompression device of FIG.

The lower spiral 5 of the upper and lower spirals 4 and 5 is illustrated in the upper part of FIG. 2a. In the upper part of FIG. 2A, the length l of the lower spiral 5 is set to a quarter of the wavelength λ, the outer peripheral end is connected (short-circuited) to the lower flat plate electrode 6, and the inner peripheral end is left open. An open-short standing wave of λ/4 is excited in the spiral 5 due to the potential difference with the upper plate electrode 3, and the spiral 5 is in an open state than the outer peripheral end, which is connected to the lower plate electrode 6 and has the same potential as the lower plate electrode 6. Since the potential at the inner circumferential edge becomes higher by the amplitude of the standing wave, the electric field E at the center becomes higher.

The middle part of FIG. 2a shows the relationship between the distance r from the inner circumferential end to the outer circumferential end of the spiral 5 and the electrolytic field E in the vicinity of the spiral electrode, and shows that the electric field E in the central part is higher. Further, the lower part of FIG. 2a shows the position when the spiral is extended and the relationship between the voltage V and the current I of the spiral electrode at that position. There is a tendency for the voltage to increase and the current to decrease as the distance from the outer peripheral edge increases.

In addition, in FIG. 2a, the lower spiral 5 is connected to the lower flat plate electrode 6, but the same applies to the upper flat plate electrode 3 side. Furthermore, by connecting the spirals 4 and 5 to the upper and lower flat plate electrodes 3 and 6, the electric field can be further improved. You can get a concentration effect.

At this time, the equivalent length of λ/4 is different depending on whether the magnetic flux generated by the current flowing in the winding direction of the upper and lower spirals 4 and 5 is the same direction and the opposite direction. In FIG. 1, when the winding directions of the upper and lower spirals 4 and 5 are opposite, the generated magnetic fluxes are in the same direction and strengthen each other, so the upper and lower spirals are slightly shortened by the amount of mutual coupling. On the other hand, if the winding directions of the upper and lower spirals are the same but the magnetic fluxes are in opposite directions, it is necessary to increase the length of the spiral by the amount of mutual coupling.

Further, FIG. 2b shows another example of the spiral arrangement, which includes lower spirals 5a and 5b. The outer peripheral ends of the lower spirals 5a and 5b are connected to the lower flat plate electrode 6, and the inner peripheral ends thereof are open, and a plurality of frozen foods 7a and 7b are placed on these spirals. As shown in FIG. 2b, the same effect can be obtained even if a plurality of spirals are arranged, so it is possible to thaw a plurality of foodstuffs or when it is desired to partially accelerate heating. Furthermore, even if the length of the spiral is shorter than λ/4, the electric field concentration effect will be reduced, but heating unevenness can be reduced.

FIG. 3a is a cross-sectional configuration diagram showing a dielectric heating electrode of the high-frequency thawing device shown in FIG. 1, and FIG. 3b shows an equivalent circuit thereof. Parts that overlap with those in FIG. 1 are given the same numbers and explanations are omitted. The impedance characteristics and matching method between electrodes will be explained using these figures.

In FIG. 3a, the capacitance C1 between the upper flat plate electrode 3 and the frozen food 7, the capacitance C2 between the lower flat plate electrode 6 and the frozen food 7, the capacitance C3 between the upper spiral 4 and the frozen food 7, and the capacitance C3 between the upper spiral 4 and the frozen food 7, the lower spiral A capacitance C4 is generated between the frozen food 5 and the frozen food 7. Furthermore, since the lower flat plate electrode 6 is connected to the GND-connected casing, a parasitic capacitance C5 is generated between the upper flat plate electrode 3 and the casing 2.

Further, FIG. 3b is a diagram showing an equivalent circuit of the configuration shown in FIG. 3a, and the frozen food 7 is represented by an equivalent series capacitance C6 and an equivalent series resistance R6. In FIG. 3b, capacitances C1 and C2 are generated at both ends of the frozen food 7, and a parasitic capacitance C5 with the housing is generated on the upper spiral 5 side. Furthermore, a series resonant circuit is formed by the inductor L1 of the upper spiral 5, the capacitance C3, the equivalent capacitance C6, the equivalent series resistance R6, the capacitance C4, and the inductor L2 of the lower spiral 6.

Therefore, when the resonant frequency is close to a frequency band close to the power transmission frequency, the impedance between the electrodes is series-resonant, so the impedance decreases and matching becomes easier. Furthermore, by lowering the impedance, the voltage applied between the flat electrodes can be lowered, so the current flowing through the parasitic capacitance C5 with the housing is also reduced, reducing loss due to the coupling between the housing and the electrodes, increasing heating efficiency. improves.

In addition, when the distance between the spirals increases, the capacitances C3 and C4 become smaller, so the Q value, which indicates the state of loss in the resonant circuit, is calculated by setting the inductance to L, the capacitance to C, and the resistance to R. , Q=ωL/R=1/(ωCR), so the loss of the resonant circuit becomes equivalently smaller. For this reason, as the distance between the spirals increases, the Q value of the resonant circuit increases, so that it is possible to reduce the decrease in heating efficiency when the distance increases.

FIG. 4a shows an example of a known technique in which two spiral electrodes with a length of λ/4 formed on a GND plane are opposed to each other, the outer circumferential ends of these spirals are connected, and one inner circumferential end is in an open state. Figure 4b shows the electromagnetic field analysis results of the impedance of the electrode configured to thaw the frozen food placed between the spirals by applying a high frequency power source from the other end. The electromagnetic field analysis results of the impedance of the electrode configuration are shown.

Both analyzes were conducted with a distance between the spirals of 40 mm and 80 mm, the size of the spiral was 250 mm x 185 mm, the number of turns was 3.5 turns, the pattern width was 15 mm, the pattern thickness was 0.3 mm, and the frequency was 40.68 MHz. Analyzed. In addition, as a frozen food material, a simulated food material measuring 200 mm x 100 mm and 25 mm in height that was frozen to -20°C was used as an analytical model.

In the known technique shown in Fig. 4a, spirals of λ/4 are connected to each other to have a length of λ/2, so the reflected waves are in phase and the impedance becomes very large near the transmission frequency, but at a distance of 40 mm, the frozen food The impedance is equivalently reduced by the amount consumed for decompression, and matching using a matching circuit is considered possible. However, in the case of 80 mm, matching is difficult because the efficiency of heating the frozen food becomes poor and the electrode impedance becomes extremely high.

On the other hand, the electrode structure of the present invention shown in Fig. 4b has a series resonant operation, so the impedance is low, and even if the distance between the spirals is large, the Q value of the resonant circuit increases, so the change in impedance is small. It can be said that even at a distance of 80 mm, impedance matching with 50Ω, which is generally used in high frequency power sources, is easier to achieve than with the conventional technology.

Figure 5a shows the heat generation distribution inside the food when the simulated food is heated using the known technique shown in Figure 17, and Figure 5b shows the heat generation distribution when heated with the dielectric heating electrode of Example 1 shown in Figure 1. The results obtained by electromagnetic field analysis are shown.

In the known technique of FIG. 5a, a pseudo food material with a plate electrode of 300 mm x 260 mm, a distance between electrodes of 40 mm, a pseudo food material of 200 mm x 150 mm, and a height of 25 mm frozen to -20 ° C. was used as an analysis model.

In addition, the electrode structure of Example 1 shown in FIG. 5b is a flat plate electrode of 300 mm x 260 mm, a spiral electrode of 250 mm x 185 mm, the number of turns is 3.5 turns, the pattern width is 15 mm, the pattern thickness is 0.3 mm, and the frozen food The same shape as the known technique was used. Both frequencies were analyzed at 40.68 MHz.

Comparing these, it is found that the parallel plate electrode of the known technology promotes heat generation at the edges of the pseudo food material, whereas the structure in which a spiral is connected to the flat plate promotes heat generation at the center of the food material, This makes it possible to reduce uneven heating of the parts.

In the configuration of Example 1 above, in addition to reducing heating unevenness by concentrating the electric field at the center, it is also possible to reduce loss due to coupling between the flat electrode and the casing, and it is possible to maintain alignment even if the distance between the electrodes is large. A dielectric heating electrode that is easy to remove can be obtained. Furthermore, by suppressing heating unevenness, it is possible to shorten the thawing time by increasing the output.

FIG. 6 is a block diagram schematically showing a high frequency decompression device according to a second embodiment of the present invention. The high-frequency defrosting device 10 includes a matching circuit 11, a variable capacitor C12, a control circuit 13, switch circuits SW1 to SW3, and a temperature sensor 17, and other parts that overlap with the first embodiment of the high-frequency decompressing device shown in FIG. The same numbers will be given and explanations will be omitted.

In comparison with the high frequency defrosting device 10 of the first embodiment shown in FIG. 1, FIG. A plurality of switch circuits SW1 to SW3 are connected between the lower plate electrodes 6 connected to the GND-connected case 2, and the spiral length of the lower spiral 6 is adjusted by turning on and off the switch circuits SW1 to SW3 by the control circuit 13. The difference is that it has been made possible.

With this configuration, for example, the temperature sensor 17 detects the thawing state of the frozen food 7, and the control circuit 13 switches the switch circuits SW1 to SW3, thereby adjusting the impedance between the electrodes due to the dielectric constant that changes due to thawing. It has been made possible to maintain consistency with respect to fluctuations. Furthermore, if matching cannot be achieved by switching the switch circuits SW1 to SW3, adjustment can also be made using the variable capacitor C12 of the matching circuit 11.

With the above configuration, the same effect as in the first embodiment shown in FIG. In addition, since the voltage amplitude of the upper flat plate electrode 3 is approximately several hundred volts, there is no need to use a high voltage vacuum variable capacitor for the variable capacitor C12, and the cost of the matching circuit 11 can be reduced. I can figure it out.

FIG. 7 shows a circuit configuration when MOS FETs are used in place of the switch circuits SW1 to SW3 shown in FIG. 6. In FIG. 7, the switch circuit SW connects the sources of MOS FETs 75 and 76 in common, and connects both drain terminals 72 and 73 between the vicinity of the outer peripheral end of the lower spiral 5 and the lower flat plate electrode 6. Further, each gate is connected to the control circuit 13 from a control terminal 74 via gate protection resistors R7 and R8. By using the MOS FETs shown in FIG. 7 for the switch circuits SW1 to SW3, it is possible to further reduce the size and cost.

FIG. 8 is a block diagram schematically showing a high frequency decompression device according to a third embodiment of the present invention. The high-frequency decompressor 10 includes an RF signal source 80 that outputs MHz bands such as 13.56 MHz, 27.12 MHz, and 40.68 MHz, an attenuator 82, a power transmission amplifier 81, a low-pass filter circuit 85, a reflected power detection circuit 16, and a variable matching circuit. It is constituted by a circuit 11, a power supply circuit 14, and a control circuit 13, and other parts that overlap with those of the first embodiment of the high-frequency decompression device shown in FIG. 1 are given the same numbers and their explanations are omitted.

In the high-frequency decompression device shown in FIG. 8, the high-frequency power source 1 includes an RF signal source 80, an attenuator 82, a power transmission amplifier 81, and a low-pass filter 85, a variable matching circuit as the matching circuit 11, and a reflected power detection circuit as the power detection circuit. 16 is applied, and is different from FIG. 1 in that it is added.

The power transmission amplifier 81 in FIG. 8 is composed of a distribution circuit 815, an amplification element 816, a synthesis circuit 817, and a power supply terminal 812, and amplifies the RF signal input from the RF signal input terminal 811 and sends it to the RF signal output terminals 813 and 814. Output. Furthermore, the low-pass filter 85 is configured to attenuate harmonics generated by the power transmission amplifier 81.

The reflected power detection circuit 16 detects the amount of reflected power generated due to the matching state with the electrode and outputs it to the control circuit 13 .

The variable matching circuit 11 includes a GND-grounded variable capacitor C12 and a series-connected variable capacitor C13. In addition, the upper and lower spirals 4 and 5 are made slightly longer than λ/4 to make the inter-electrode impedance inductive, taking into account impedance changes due to the thawing state of the frozen food 7, and are variable matching composed only of variable capacitors. Matching is possible with the circuit 11.

In the above configuration, the frozen food 7 placed between the upper and lower spirals 4 and 5 is thawed by dielectric heating using the RF signal amplified by the power transmission amplifier 81. The matching state is detected by the reflected power detection circuit 16 with respect to the inter-electrode impedance that changes depending on the state, and the control circuit 13 adjusts the variable capacitors C12 and C13 of the variable matching circuit 11 to achieve matching, thereby efficiently decompressing. be. Furthermore, completion of thawing is determined by measuring the temperature of the frozen food 7 using the temperature sensor 17.

In the high-frequency defrosting device 10 having the above-described configuration, the present invention aims to provide a high-power, low-cost power transmission amplifier 81, and a variable matching circuit in order to obtain a high-frequency defrosting device 10 that is small, low cost, has excellent heating efficiency, and has little heating unevenness. 11 and other circuits, as well as the connection of the spirals 4 and 5 to the flat plate electrodes 3 and 6, which aims to reduce the heating unevenness that becomes noticeable as the output increases. It is.

In the following explanation, the effects brought about by the configuration based on these ideas will be explained for each component component. First, the power transmission amplifier 81 is constructed from the viewpoint of high output to enable short-time decompression, and the RF signal from the RF signal source 80 is inputted from the RF signal input terminal 811 via the attenuator 82. The input RF signals are input to each amplifying element 816 by a distribution circuit 815, and the amplified RF signals are combined by a combining circuit 817 and output between RF signal output terminals 813 and 814.

In the above configuration, by using a push-pull amplifier circuit with a four-element amplification configuration, the output power can be improved and the withstand voltage required for the amplification element can be lowered, so the cost of the amplification element can be reduced. be able to.

In the variable matching circuit 11, the lengths of the spirals 4 and 5 of the electrodes are made longer than λ/4, so that the impedance between the electrodes is made inductive and matching can be achieved only by the capacitive components of the variable capacitors C12 and C13. As a result, a voltage increase in the flat electrode due to the matching inductor between the upper flat electrode 3 and the lower flat electrode 6 does not occur, and loss due to capacitive coupling between the upper flat electrode 3 and the housing 2 is reduced, resulting in heating efficiency. will improve.

9a shows the result of electromagnetic field analysis of the voltage distribution of the upper plate electrode 3 of the known technique shown in FIG. 17, and FIG. 9b shows the analysis result of the voltage distribution of the upper plate electrode 3 of Example 3 shown in FIG. 8. It is something that

The analysis is similar to the heat generation analysis of the pseudo food material shown in FIGS. 5a and 5b. In FIG. Foods frozen to -20°C were used, and in Figure 9b, the plate electrode was 300 mm x 260 mm, the spiral electrode was 250 mm x 185 mm, the number of turns was 3.5, the pattern width was 15 mm, and the pattern thickness was 0.3 mm. Both frequencies are 40.68 MHz.

In the case of the known technique shown in FIG. 9a, since an inductor is used in the matching circuit 11, the voltage of the upper flat plate electrode 3 is relatively high, whereas in the embodiment 3 shown in FIG. 8, a spiral is connected to the parallel plate electrode in FIG. 9b. It can be seen that since the matching circuit 11 does not use an inductor, the voltage of the upper plate electrode 3 is low.

With the above configuration, in addition to obtaining the same effects as in Example 1, the power transmission amplifier can achieve high output and low cost, and furthermore, the variable capacitors C12 and C13 used in the matching circuit 11 have a high withstand voltage. Since the use of a variable capacitor becomes unnecessary and a general air variable capacitor or capacitance switching using a capacitor and relay can be used, the cost of the matching circuit can be reduced.

Note that the same effect can be obtained by using an electrode having a configuration in which the changeover switch circuit SW of the second embodiment shown in FIG. 6 is added to the lower spiral 5. In this case, since the inductance values connected in series are equivalently adjusted, the variable capacitor C13 connected in series can be omitted.

FIG. 10 is a diagram showing a schematic configuration example of a high frequency decompression device according to a fourth embodiment of the invention. The high-frequency decompressor 10 has a current source conversion circuit 85A that also serves as a low-pass filter, a variable matching circuit 11A, and a voltage detection circuit 16A. Parts that overlap with those in Example 3 are given the same numbers and their explanations are omitted.

When the high-frequency decompression device of FIG. 10 is shown in comparison with the high-frequency decompression device of FIG. 8, the low-pass filter 85 is a current source conversion circuit 85A that also serves as a low-pass filter, the reflected power detection circuit 16 is a voltage detection circuit 16A, and the variable matching circuit 11 8 is configured as a variable matching circuit 11A, and that switch circuits SW1 to SW3 are added to the lower spiral 5.

The current source circuit 85A that also serves as a low-pass filter in FIG. 10 is composed of a π-type filter made up of capacitors C21 and C22 and an inductor L21. f (ω = 2πf), the output voltage of the power transmission amplifier 81 is V, and the reactance at the power transmission frequency is When set, the current I output from the current source output terminal 1012 becomes I=-jV/X, and it can be a constant current source determined by the output voltage V and reactance X. At this time, if the value of X is made equal to the characteristic impedance Z0 (generally 50Ω) of the power transmission amplifier 81, voltage source driving and current source driving become equivalent in the case of a load condition equal to the characteristic impedance.

The variable matching circuit 11A includes variable capacitors C13 connected in series. The voltage detection circuit 16A includes a detection diode D1, a capacitor C23, and resistors R10 and R11, detects the voltage applied to the input terminal 1021 of the variable matching circuit 11A, and detects a matching state in the control circuit 13.

In the above configuration, the output voltage of the power transmission amplifier 81 is converted into a constant current source by the current source conversion circuit 85A which also serves as a low-pass filter, and is matched by the variable matching circuit 11A and the switch circuits SW1 to SW3. The frozen food 7 placed between the electrodes is thawed by dielectric heating.The matching state is detected by the voltage detection circuit 16A, and the matching state is detected by the voltage detection circuit 16A, and the variable matching circuit 11A is controlled by the control circuit 13. By adjusting the capacitor C13 to achieve matching, decompression is performed efficiently.

The present invention is based on the addition of a current source conversion circuit 85A that also serves as a low-pass filter to the high-frequency dielectric heating device 10 having the above-described configuration, in order to obtain a high-frequency dielectric heating device that is small, low cost, has excellent heating efficiency, and has little heating unevenness. Some improvements have been made in various aspects, such as simplifying the control and reducing the size and cost of the circuit by means of the variable matching circuit 11A and the voltage detection circuit 16A.

In the following explanation, the effects brought about by the configuration based on these ideas will be explained for each component component.

First, the current source conversion circuit 85A, which is configured from the viewpoint of simplifying control, simplifies the output control of the power transmission amplifier 81 in response to impedance changes between electrodes due to defrosting. The impedance between the electrodes is relatively low as shown in FIG. 4b due to the vertical spiral connection.

On the other hand, since the power transmission amplifier 81 also has multiple amplification elements connected in parallel and the output impedance is low, it is necessary to increase the characteristic impedance to 50Ω, which is a general characteristic impedance, and then lower it using the matching circuit 11. 11 becomes complicated.

Therefore, the circuit can be simplified by directly driving the electrodes with the low impedance of the power transmission amplifier 81. However, in this case, the equivalent resistance value of the frozen food 7 is about 40Ω at a temperature of -20°C and about 20Ω at a temperature of -5°C, and the resistance value decreases as thawing progresses. For this reason, when the power transmission amplifier 81 is the voltage source V, the heating power is V ² /40 at -20°C and V ² /20 at -5°C, so at -5°C, when defrosting is almost completed. The power consumption will be the highest.

On the other hand, when current source I is used, the heating power is I ² × 40 at -20°C and I ² × 20 at -5°C, so the heating power is high at the time when the most heating power is needed at the start of thawing. Since the heating power gradually decreases as the defrosting progresses, output control of the power transmission amplifier 81 can be simplified.

The variable matching circuit 11A is used to achieve matching when the changeover switch circuits SW1 to SW3 connected to the lower spiral 5 cannot be adjusted by the variable capacitor C13 connected in series, and matches by series resonance including the impedance between the electrodes. Furthermore, as shown in FIG. 11, the variable matching circuit 11A is configured by installing parallel capacitors C32 and C33 to the series capacitor C31 that is always connected. Matching is also possible by switching the capacitance values using the changeover switches SW4 and SW5.

Since the voltage detection circuit 16A is a series-resonant low-impedance circuit compared to the equivalent circuit in the spiral connection shown in FIG. 3B, the detection accuracy is degraded in the reflected power detection circuit 16 that performs detection based on a fixed impedance.

FIG. 12a shows the results of determining the inter-terminal voltage V in the series resonant circuit when driven by a current source. In the figure, when the impedance between electrodes including frozen food is equivalent inductor L, equivalent capacitance C, and the resistance mainly consumed by thawing frozen food is equivalent resistance Rrs, the voltage between terminals V, and the impedance at resonance is Rrs. It becomes equal to and becomes the lowest at this time. Therefore, by adding the voltage detection circuit 1030, it can be determined that the point where the voltage is the lowest is matched.

FIG. 12b shows a case where a load equivalent to the interelectrode impedance including the power transmission amplifier 81, current source conversion circuit 85A, variable matching circuit 11A, and frozen food 7 is connected, and the variable capacitance of the variable matching circuit 11A is changed. The simulation results are shown with inductive or capacitive impedance plotted on the horizontal axis and voltage amplitude plotted on the vertical axis. From the results shown in the figure, it can be seen that the terminal voltage is lowest during resonance (matching).

FIG. 13 is a flowchart showing the process of thawing the frozen food 7 in the high-frequency dielectric heating device 10 according to the fourth embodiment shown in FIG. 10, and will be described with reference to FIG. 10. This flow shows the flow of processing by the control circuit 13 of FIG. 10, which is realized using a computer.

In this process, matching is attempted by adjusting the length of the lower spiral 5, but if matching cannot be achieved with the length of the spiral, matching is achieved by adjusting the variable capacitor C13.

First, in processing step S1, the control circuit 13 adjusts the attenuator 82 for the frozen food 7 placed between the upper spiral 4 and the lower spiral 5, and adjusts the RF signal power output from the power transmission amplifier 81 to normal thawing. Start transmitting power at lower power than required.

Next, in processing step S2, the control circuit 13 turns off all the changeover switches SW1 to SW3 of the lower spiral 5 to maximize the length of the spiral, and maximizes the capacitance value of the variable capacitor C13 of the variable matching circuit 11A. state. At this time, the voltage detection circuit 16A measures the detection voltage corresponding to the voltage amplitude of the variable matching circuit input terminal 1021, and further detects the detection voltage with the changeover switch SW of the lower spiral 5 set to a value one step smaller in processing step S3. Measure voltage.

In processing steps S4 and S5, if the length of the lower spiral is the shortest, the control circuit 13 sets the variable capacitor C13 to a smaller value by one step, and compares the detected voltage results before and after in processing step S6. If the detected voltage has decreased, the process returns to step S3, the length of the lower spiral 5 is shortened by one step, and the detected voltage at that time is measured. If the detection voltage increases in processing step S6, then in processing step S7, if the previous process shortens the length of the lower spiral 5 by one step, the length of the spiral is increased by one step, and the variable capacitor C13 If the capacity value is decreased by one step, it is returned to a value that is one step higher and normal power transmission is started.

Then, in processing step S8, it is determined whether the temperature of the temperature sensor 17 has reached the temperature setting value for thawing completion, and if the temperature has not reached the set temperature, the detected voltage is increased by a loop of processing step S11, processing step S9, and processing step S8. Heating is continued until the detection voltage becomes high, and when the detected voltage becomes high, the imaginary part of the impedance of the electrode changes from capacitive to inductive in processing step S12, so the transmitted power is lowered and the process proceeds to processing step S3. Returning to , power transmission is started with high power by shortening the length of the lower spiral 5 or lowering the capacitance value of the variable capacitor C13 until the imaginary part is canceled out. In processing step S10, these steps are repeated until the set temperature is reached, and when the set temperature is reached, power transmission is stopped, and a notification is given that thawing has been completed, and the process ends.

By measuring the voltage amplitude of the input of the variable matching circuit in this manner, the matching state can be detected, making it possible to thaw frozen foods with relatively simple control.

With the above configuration, the high-frequency decompressing device according to the fourth embodiment can obtain the same effects as the high-frequency decompressing device according to the third embodiment shown in FIG. By using a voltage detection circuit, the reflected power detection circuit can be simplified.

FIG. 14 is a schematic side view showing a configuration example of a high-frequency decompression device according to a fifth embodiment of the present invention, and the configuration of the fifth embodiment of the present invention will be described with reference to FIG. 8.

FIG. 8 mainly shows the electric circuit configuration of the high-frequency defrosting device, and FIG. 14 is a side view showing the structure inside the casing that houses the electric circuit of FIG. 8. Note that the same reference numerals are given to the same parts as those of the high-frequency dielectric heating device according to the third embodiment shown in FIG. 8, and the explanation thereof will be omitted.

In FIG. 14, inside the housing 2 are a reflected power detection circuit 16, a power transmission amplifier 81, a lid 142, a GND shield plate 143, a mounting board 144, a heat sink 145, a heat sink fin 146, an outlet 147, cables 148, 149, An insulator plate 141, a fan 1411, etc. are arranged and configured at the illustrated positions.

In the figure, a distribution circuit 815, an amplifying element 816, and a combining circuit 817 that constitute a power transmission amplifier 81 are mounted on a mounting board 144, a heat sink 145 is attached to the back surface of the mounting board 144, and a heat sink 145 is attached to the back surface of the mounting board 144. A heat sink fin 146 and a fan 1411 are mounted on the heat sink 145.

In addition, by mounting the power transmission amplifier 81 and the heat sink 145 so as to lean against the back of the housing 2 of the high-frequency thawing machine, it is easy to radiate heat from the back, and the power transmission amplifier 81 and the heat sink 145 can be easily dissipated from the back. Since the upper and lower flat plate electrodes 3 and 4 can be connected over a short distance using cables 148 and 149, cable loss can be reduced.

In addition, an insulating plate 141 is laid on the upper part of the lower spiral 6 to ensure a distance between the electrode and the frozen food 7, and a temperature sensor 17 is installed near the center of the lower electrode, and a power transmission amplifier A power supply circuit 14 is mounted below 81.

FIG. 15 is a rear view showing an example of the structure on the back side of the high frequency defrosting device according to the fifth embodiment of the present invention shown in FIG. In the figure, parts that overlap with those of the high-frequency decompression device according to the fifth embodiment shown in FIG. 14 are given the same reference numerals, and their explanation will be omitted.

In FIG. 15, reference numeral 151 denotes a power outlet, and the back side of the housing 2 has a cutout portion where a heat sink 145, heat sink fins 146, and fan 1411 are mounted to improve heat dissipation of the power transmission amplifier. In addition, a power supply circuit 14 is disposed below the power transmission amplifier 81, a control circuit 13 is disposed on the operation panel side (on the left side as viewed from the side), and a variable matching circuit 11 is disposed on the back side of the GND shield plate 143 on the opposite side. is arranged, and the variable matching circuit output terminal 1022 is connected to the upper flat plate electrode 3 via a cable outlet.

FIG. 16 is a schematic perspective view showing an example of the structure of the surface and interior of the high-frequency thawing device according to the fifth embodiment of the present invention shown in FIG. In the figure, the same reference numerals are given to the same parts as those of the high-frequency decompression apparatus according to the third embodiment shown in FIG. 8, and the explanation thereof will be omitted.

According to FIG. 16, shelf supports 1601 and 1602, a display panel 1603, push buttons 1604 and 1605, and an adjustment knob 1606 are arranged at the positions shown on the surface and inside the refrigerator. Furthermore, cables 148 and 149 connected to the electrodes are connected to the GND shield plate 143 provided to reduce the influence of the voltage applied between the upper and lower plate electrodes 3 and 4 on other circuits and the radiated electromagnetic field to the outside. A drawer opening 147 for pulling out is provided, and insulated shelf supports 1601 and 1602 made of resin are attached to both sides of the GND shield plate 143 (the shelf support on the right side is not shown).

This shelf support has a structure that supports the upper and lower flat plate electrodes 3 and 6 and the insulating plate 141 (see FIG. 14), and the height can be changed by changing the position of the shelf support. In addition, the front display panel 1603 can display the current thawing status, temperature settings, etc., as well as buttons 1604 and 1605 for starting and stopping heating, and the temperature at which thawing is complete. Adjustment knobs 1606 are provided to set the parameters, etc., and a control circuit 13 is mounted at the back of these operation panels.

With the above configuration, heat dissipation is excellent against the heat generation that increases with the increase in output power of the power transmission amplifier, and transmission loss can be reduced by shortening the length of the cable between the power transmission amplifier and the upper and lower electrodes. In addition, by adopting a structure in which the height of the electrode can be changed, it is possible to obtain a high-frequency thawing device that can thaw frozen foodstuffs of different heights.

Above, through Examples 1 to 5, we have described measures to reduce heating unevenness, increase output and size, and reduce costs.If we were to organize and enumerate the main points of these measures, we would like to summarize them as follows: It is as follows.

The first point is that by forming a spiral with a length of λ/4 on a parallel flat plate and connecting the outer peripheral end to the flat plate, the electric field is concentrated in the center, so that uneven heating at the end can be reduced. Furthermore, since the voltage generated at the flat electrode is reduced, loss due to coupling between the flat electrode and the casing can be reduced, and heating efficiency is improved.

The second point is a configuration in which matching is achieved by switching the length of the spiral using a switch circuit at the outer peripheral end of the spiral on the GND grounding side. This allows the use of low-voltage MOS FETs, resulting in lower costs and miniaturization of the matching circuit.

The third point relates to the power transmission amplifier, which has a configuration in which a constant current source conversion circuit that also serves as a low-pass filter (LPF) for suppressing harmonics is added to the output of the power transmission amplifier. As a result, while the equivalent series resistance of frozen food tends to decrease with the thawing temperature during thawing, the power transmission amplifier output characteristic can be set such that the amount of heat generated is large at the start of thawing and gradually decreases, so the thawing state can be detected. The detection control that controls the output has been simplified.

The fourth point relates to the variable matching circuit. Conventionally, it was necessary to use two variable elements to match the real and imaginary parts of the electrode impedance in the variable matching circuit that matches the impedance between the electrodes, which changes during thawing. By connecting the variable matching element to one element and canceling out only the imaginary part of the electrode, we achieved miniaturization and cost reduction. By making one element variable, it becomes possible to directly see the relatively low equivalent resistance of the frozen food between the electrodes. The structure can be suitable for directly driving a low equivalent series resistance.

The fifth point concerns measurement of reflected power. Conventionally, in order to detect the matching state, a reflective electrode detection circuit is used between the power transmission amplifier and the variable matching circuit (input side) to detect the amount of incident power and the amount of reflected power, and the VSWR determined from the voltage amplitude ratio of these is determined. This was used as a threshold value for determining the state, but in a configuration that cancels only the imaginary part of the interelectrode impedance mentioned above, the series equivalent resistance of the frozen food, which is the real part, changes depending on the thawing state, so it is measured by comparing it with the reference resistance value. The matching state cannot be determined by measuring VSWR using a directional coupler. On the other hand, if the configuration is such that only the imaginary part mentioned above is canceled, the voltage amplitude at the input end of the variable matching circuit becomes the lowest when the imaginary part of the electrode impedance is canceled. By adding a detection circuit that detects the voltage amplitude of , it is possible to detect the matching state, and the directional coupler that was previously required is no longer necessary, simplifying the circuit and reducing costs.

1: High frequency power supply 2: Housing 3: Upper plate electrode 4: Upper spiral 5, 5A, 5B: Lower spiral 6: Lower plate electrode 7, 7a, 7b: Frozen food 10: High frequency thawing device 11, 11A: Matching circuit ( variable matching circuit)
13: Control circuit 14: Power supply circuit 16: Reflected power detection circuit 17: Temperature sensor 72, 73: Drain terminal 74: Control terminal 75, 76: MOS FET
80: RF signal source 81: Power transmission amplifier 82: Attenuator 85: Low pass filter 85A: Current source conversion circuit 142: Lid 143: GND shield plate 144: Mounting board 145: Heat sink 146: Fin 147: Outlet ports 148, 149: Cable 141: Insulating plate 811: RF signal input terminal 812: Power supply terminal 813, 814: RF signal output terminal 815: Distribution circuit 816: Amplification element 817: Synthesis circuit 821, 1011, 1021, 1031: Input terminal 822, 1012, 1022 : Output terminals 16A, 1030: Voltage detection circuit R10, R11: Resistor D1: Detection diode 1411: Fan 151: Outlet 1601, 1602: Shelf support 1603: Display panel 1604, 1605: Push button 1606: Adjustment knob C1, C2, C3 , C4, C5: Capacitance C6: Equivalent series capacitance C12, C13: Variable capacitance C21, C22, C23: Capacitor L1, L2, L21: Inductor R6: Equivalent series resistance R7, R8: Gate protection resistor SW1 to SW5: Switch circuit

Claims (12)

A dielectric heating electrode that dielectrically heats an object to be heated by an electric field generated between an upper electrode and a lower electrode by applying a high frequency voltage between an upper electrode and a lower electrode of a parallel plate,
A spiral electrode is provided on one or both of the lower surface of the upper electrode and the upper surface of the lower electrode, and the outer peripheral end of the spiral electrode is connected to the parallel plate electrode, and the inner peripheral end thereof is connected to the parallel plate electrode. A dielectric heating electrode characterized by having an open end. The dielectric heating electrode according to claim 1,
The dielectric heating electrode is characterized in that the length of the spiral electrode is approximately 1/4 of the wavelength λ of the high-frequency voltage or an integral multiple of λ/4. The dielectric heating electrode according to claim 1 or 2,
When the spiral electrodes provided on the upper electrode and the lower electrode are wound in opposite directions and the magnetic fluxes generated from both spiral electrodes are in the same direction, the length of the spiral is equivalently λ/ by the amount of mutual coupling. A dielectric heating electrode characterized by being shorter than an integral multiple of 4. The dielectric heating electrode according to claim 1 or 2,
When the spiral electrodes provided on the upper electrode and the lower electrode have the same winding direction and the magnetic fluxes generated from the spiral electrodes are in opposite directions, the length of the spiral is equivalently λ/ by the amount of mutual coupling. A dielectric heating electrode characterized in that the length is longer than an integral multiple of 4. The dielectric heating electrode according to claim 1,
The length of the spiral electrode is adjusted in stages by connecting the spiral electrode to the parallel plate electrode via a plurality of switch circuits at a plurality of locations on the outer peripheral end side of the spiral electrode. dielectric heating electrode. The dielectric heating electrode according to claim 5,
The dielectric heating electrode is characterized in that the switch circuit uses a relay or a MOS FET. The object to be heated is dielectrically heated by the electric field generated between the upper and lower electrodes by applying a high-frequency voltage from a high-frequency power supply between the upper and lower electrodes of a parallel plate through a matching circuit that variably adjusts the impedance. A high frequency dielectric heating device, comprising:
A spiral electrode is provided on one or both of the lower surface of the upper electrode and the upper surface of the lower electrode, and the outer peripheral end of the spiral electrode is connected to the parallel plate electrode, and the inner peripheral end thereof is connected to the parallel plate electrode. A high frequency dielectric heating device characterized by having an open end. The high frequency dielectric heating device according to claim 7,
The length of the spiral electrode is adjusted in stages by connecting the spiral electrode to the parallel plate electrode via a plurality of switch circuits at a plurality of locations on the outer peripheral end side of the spiral electrode. High frequency dielectric heating device. The high frequency dielectric heating device according to claim 8,
It is characterized by comprising a control circuit that detects a high frequency voltage or high frequency power from the high frequency power supply and controls the impedance of the matching circuit and one or both of the plurality of switch circuits according to the temperature of the heated object. High frequency dielectric heating device. The high frequency dielectric heating device according to any one of claims 7 to 9,
A high frequency dielectric heating device, wherein the high frequency power source is a current source. The object to be heated is dielectrically heated by the electric field generated between the upper and lower electrodes by applying a high-frequency voltage from a high-frequency power supply between the upper and lower electrodes of a parallel plate through a matching circuit that variably adjusts the impedance. A high frequency dielectric heating method comprising:
A spiral electrode is provided on one or both of the lower surface of the upper electrode and the upper surface of the lower electrode, and the outer peripheral end of the spiral electrode is connected to the parallel plate electrode, and the inner peripheral end thereof is connected to the parallel plate electrode. It is said to have an open end, and
The spiral electrode can be connected to the parallel plate electrode via a plurality of switch circuits at a plurality of locations on the outer peripheral end side,
High-frequency dielectric heating characterized in that a high-frequency voltage or high-frequency power from the high-frequency power supply is detected, and the impedance of the matching circuit and one or both of the plurality of switch circuits are controlled according to the temperature of the object to be heated. Method. The high frequency dielectric heating method according to claim 11,
A high frequency dielectric heating method, comprising adjusting the impedance of the matching circuit after adjusting the plurality of switch circuits.

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