High-frequency dielectric heating device

Abstract

To suppress overheating at the ends, corners, and protrusions of frozen foods, shorten thawing time and improve thawing quality in a high frequency dielectric heating device that thaws the frozen foods by applying a high-frequency electric field in the MHz band.SOLUTION: A high frequency dielectric heating device includes: a heating room that stores a heating object; a pair of electrodes that is arranged so as to be opposed to each other with the heating object held therebetween; a temperature sensor that detects the temperature of the heating object; a high-frequency power supply that outputs high-frequency power in the MHz band; an amplification part that amplifies the output of the high-frequency power supply to apply the output between the pair of electrodes; a voltage detection part that detects the voltage value applied between the pair of electrodes; an arithmetic part that calculates the heat quantity generated in the heating object; and a control part that reduces the amplification rate of the amplification part when the heat quantity calculated by the arithmetic part turns from increasing to decreasing.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a high-frequency dielectric heating device, and particularly to a high-frequency thawing device that applies a high-frequency electric field in the MHz band to frozen food and thaws the frozen food by dielectric heating.

Background Art

[0002] In food processing factories and the like, there are cases where frozen food ingredients are thawed and then processed into food. As one type of food thawing machine used in this type of factory and the like, a high-frequency thawing device is known that applies a high-frequency electric field in the MHz band to frozen food placed between opposing electrodes and thaws the frozen food by dielectric heating (for example, Patent Document 1).

[0003] Here, high-frequency dielectric heating is a technique in which a high-frequency electric field is applied to a dielectric (food ingredient) that is the object to be heated, and the object to be heated is heated from the inside by self-heating (dielectric loss) caused by the vibration of polar molecules (such as water molecules) that make up the object to be heated.

[0004] In general household microwave ovens, dielectric heating using microwaves (electric fields in the GHz band) is utilized. However, since the difference in heat generation between ice and water is large in dielectric heating by microwaves, when thawing frozen food in a household microwave oven, there is a problem that significant heating unevenness occurs due to the melted part on the surface layer of the food generating a large amount of heat.

[0005] On the other hand, in high-frequency dielectric heating devices mainly for commercial use that use a high-frequency electric field in a frequency band lower than microwaves (MHz band), the penetration depth of high-frequency energy into food ingredients is deeper than that of general household microwave ovens, and also the difference in heat generation between ice and water is small. Therefore, there is an advantage that heating unevenness is less likely to occur.

[0006] For example, the abstract of Patent Document 1 states, "The high-frequency thawing device comprises a heating chamber 1, an upper electrode 2a and a lower electrode 2b arranged parallel to each other in the heating chamber 1 with the object to be thawed 3 inserted between them, a high-frequency power supply 4 and a matching circuit 6 that apply a high-frequency voltage between the upper electrode 2a and the lower electrode 2b, a power detection circuit 5 that detects the reflected power of the applied high-frequency voltage, and a control device 7 that estimates the progress of the object to be thawed based on the change in the detection signal of the power detection circuit 5 from the start of thawing, determines when thawing is complete, and controls the high-frequency power supply 4 based on the determination." Paragraph 0002 of the same document states, "High-frequency thawing devices are known that thaw objects to be thawed, such as food frozen by dielectric heating, by applying a high frequency of MHz or higher (for example, Patent Documents 1 and 2). The high-frequency thawing device comprises an upper electrode and a lower electrode in the heating chamber, and a high-frequency electric field is applied between the two electrodes from a high-frequency power supply, and thawing is performed by the dielectric loss of the object to be thawed. Because the dielectric heating method allows the parallel electric field to reach the inside of the frozen food uniformly, it is more suitable for thawing large objects to be thawed compared to thawing using microwaves in a microwave oven."

[0007] In other words, the high-frequency thawing device described in Patent Document 1 uses a high-frequency electric field in the MHz band, which allows for nearly uniform thawing of the inside of the object being thawed compared to thawing in a microwave oven using microwaves (GHz band).

[0008] Furthermore, during the thawing of food using high-frequency dielectric heating, there is a problem in that the impedance on the load side, including the food and electrodes, changes significantly due to the change in dielectric loss of the food as thawing progresses. Therefore, in order to improve the heating efficiency of food by making the output impedance of the high-frequency power supply and the impedance of the load side, including the food and other objects being heated, approximately the same, a matching circuit consisting of a variable capacitor and a variable coil is provided between the high-frequency power supply and the electrodes, thereby almost eliminating reflected power (reflected waves) returning to the high-frequency power supply, and maintaining impedance matching between the output side and the load side.

[0009] In this regard, paragraph 0020 of Patent Document 1 states, "The control device 7 controls the output of the high-frequency power supply 4 so that the power obtained by subtracting the reflected power from the input electrode remains constant, and increases the incident power in accordance with the increase in reflected power." (In the above quoted text, "input electrode" is likely a typo for incident power.) Paragraph 0021 of the same document states, "When the ratio of reflected power (RW) to incident power (FW), RW / FW, exceeds a threshold X, the control device 7 adjusts the variable capacitors 6a, 6b, variable coil 6c, etc., in the matching circuit 6 to set the reflected power to 0W. Such impedance adjustment is repeated each time the ratio exceeds the threshold X." [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2020-145114 [Overview of the project] [Problems that the invention aims to solve]

[0011] As described in Patent Document 1, when thawing food by applying a high-frequency electric field in the MHz band, maintaining impedance matching between the output side and the load side and eliminating reflected power so that almost all of the output power from the high-frequency power supply is continuously supplied to the food improves heating efficiency and shortens thawing time. However, this causes the electric field to gradually concentrate on the edges, corners, and protrusions of the food, resulting in overheating of these areas even with high-frequency dielectric heating in the MHz band. Since the temperature unevenness caused by this overheating directly leads to a decrease in thawing quality, the challenge is to suppress overheating while shortening the thawing time.

[0012] However, Patent Document 1 does not mention any techniques for suppressing overheating of such food edges, corners, and protrusions, making it difficult to achieve both a reduction in thawing time and suppression of overheating.

[0013] Therefore, the present invention aims to provide a high-frequency dielectric heating device that can shorten the thawing time of frozen foods and the like when thawing them using a high-frequency electric field in the MHz band, while suppressing overheating of the edges, corners, protrusions, etc. of the food, thereby improving the thawing quality. [Means for solving the problem]

[0014] The features of the present invention for solving the above problems are, for example, as follows:

[0015] A high-frequency dielectric heating apparatus comprising: a heating chamber for housing an object to be heated; a pair of electrodes arranged opposite each other so as to sandwich the object to be heated; a temperature sensor for detecting the temperature of the object to be heated; a high-frequency power supply that outputs high-frequency power in the MHz band; an amplification unit that amplifies the output of the high-frequency power supply and applies it between the pair of electrodes; a voltage detection unit that detects the voltage value applied between the pair of electrodes; a calculation unit that calculates the amount of heat generated in the object to be heated; and a control unit that reduces the amplification ratio of the amplification unit when the amount of heat calculated by the calculation unit changes from increasing to decreasing. [Effects of the Invention]

[0016] The high-frequency dielectric heating device of the present invention makes it possible to shorten the thawing time of frozen foods, etc., while suppressing overheating of the edges, corners, and protrusions of the food, thereby improving the thawing quality, when thawing frozen foods, etc., using a high-frequency electric field in the MHz band. [Brief explanation of the drawing]

[0017] [Figure 1] A schematic diagram of a high-frequency dielectric heating apparatus according to one embodiment. [Figure 2] Conceptual diagram of dielectric property data for each food ingredient stored in the calculation unit of Figure 1. [Figure 3] A graph showing the relationship between elapsed time and food temperature or voltage between electrodes. [Figure 4] A graph showing the relationship between food temperature and the amount of heat generated by the food. [Figure 5] An example of control that reduces the amplification rate of the amplification unit when the heat output of the food decreases. [Figure 6] A processing flowchart for a high-frequency dielectric heating apparatus in one embodiment. [Modes for carrying out the invention]

[0018] The following describes an embodiment of the high-frequency dielectric heating apparatus of the present invention with reference to the drawings.

[0019] The following description provides specific examples of the content of the present invention, and the present invention is not limited to these descriptions. Various modifications and changes are possible by those skilled in the art within the scope of the technical ideas disclosed herein.

[0020] Furthermore, the present invention envisions scenarios such as installing a high-frequency thawing device in the backroom of restaurants such as steak restaurants, yakiniku restaurants, sushi restaurants including conveyor belt sushi restaurants, izakayas, and family restaurants to quickly thaw pre-stored frozen ingredients and foods (beef, chicken, fish, cakes, desserts, etc.) according to the number of customers entering the restaurant and serve them to customers, or installing a high-frequency thawing device in the backroom of retail stores such as convenience stores and supermarkets to quickly thaw pre-stored frozen foods such as bento boxes and prepared foods according to the number of customers entering the store and display them as chilled products on shelves in the retail store. However, the uses of the high-frequency dielectric heating device of the present invention are not limited to the listed uses.

[0021] <Outline configuration of the high-frequency dielectric heating device 100> Figure 1 is a schematic diagram of a high-frequency dielectric heating apparatus 100 according to one embodiment of the present invention. As shown in this figure, the high-frequency dielectric heating apparatus 100 includes a heating chamber 1, a high-frequency power supply 2, an amplification unit 3, a matching unit 4, a power detection unit 5, a voltage detection unit 6, a calculation unit 7, a control unit 8, and an operation unit and a display unit (not shown). The details of each part will be described in order below.

[0022] The heating chamber 1 is a box-shaped container for storing frozen food (hereinafter referred to as food ingredient F) to be heated and thawing it by dielectric heating. It has electrodes 11, a mounting platform 12, a weight sensor 13, a temperature sensor 14, and a door (not shown) that opens and closes when food ingredient F is inserted or removed.

[0023] The electrodes 11 are a pair of non-magnetic metal plates (aluminum alloy plate, stainless steel plate, etc.) positioned opposite each other so as to sandwich the food item F stored in the heating chamber 1. For example, an upper electrode 11a is positioned at the top of the heating chamber 1, and a lower electrode 11b is positioned at the bottom of the heating chamber 1. In a high-frequency dielectric heating device 100 with this configuration, a high-frequency electric field in the MHz band is generated between the upper electrode 11a and the lower electrode 11b, thereby dielectrically heating and thawing the food item F placed between the two electrodes.

[0024] The upper electrode 11a and the lower electrode 11b may be fixed, or they may be configured to be movable vertically by a lifting device (not shown). To shorten the thawing time, it is desirable to position the upper electrode 11a as close as possible to the food F. In the case of a configuration using a lifting device, the heating efficiency can be improved and the thawing time shortened by bringing the upper electrode 11a closer to the food F depending on the thickness and shape of the food F.

[0025] The mounting platform 12 is a platform for placing food ingredients F, and specifically, it is a container, plate, or board made of ceramic or heat-resistant resin that is not heated by dielectric heating.

[0026] The weight sensor 13 is a sensor that automatically detects the weight of the food item F placed on the mounting table 12 and transmits it to the calculation unit 7, which will be described later.

[0027] The temperature sensor 14 detects the temperature of the food item F placed on the mounting base 12 (hereinafter referred to as the food item temperature T). F This sensor automatically detects the temperature of the food ingredient F and transmits it to the calculation unit 7, which will be described later. F Examples include radiation thermometers that convert to a specific temperature.

[0028] High-frequency power supply 2 is a power supply that outputs high-frequency power in the MHz band.

[0029] The amplification unit 3 is an amplifier circuit that amplifies the high-frequency power output by the high-frequency power supply 2 at an amplification factor specified by the control unit 8, which will be described later. Details of the amplification factor control by the control unit 8 will be described later.

[0030] The matching unit 4 is a circuit that matches the output impedance of the high-frequency power supply 2 with the impedance of the load side, including the food ingredient F and the electrodes 11. As explained in Patent Document 1, the dielectric loss of the food ingredient F changes significantly as the thawing of the food ingredient F progresses, so the impedance of the load (food ingredient F and electrodes 11) also changes significantly during the thawing of the food ingredient F. Therefore, by appropriately adjusting the variable coil and variable capacitor built into the matching unit 4, the output impedance of the high-frequency power supply 2 and the impedance of the load (food ingredient F and electrodes 11) can be made approximately the same, and the reflected power (reflected wave) returning from the matching unit 4 to the high-frequency power supply 2 can be almost eliminated, thereby improving the heating efficiency of the food ingredient F.

[0031] The power detection unit 5 detects the forward power (incident wave) that is incident on the matching unit 4 from the high-frequency power supply 2 and the amplification unit 3, and the reflected power (reflected wave) that returns from the matching unit 4 to the amplification unit 3 and the high-frequency power supply 2, based on the matching state of the matching unit 4, and transmits these to the control unit 8, which will be described later.

[0032] The voltage detection unit 6 detects the voltage value applied between the electrodes 11 (in the configuration shown in Figure 1, where the lower electrode 11b is grounded, the voltage value applied to the upper electrode 11a) and transmits it to the calculation unit 7, which will be described later.

[0033] The calculation unit 7 calculates an estimated thawing time based on the output information from the weight sensor 13, temperature sensor 14, and voltage detection unit 6, as well as dielectric property data for each food item, which will be described later. m It automatically calculates the amount of heat generated in the food F during thawing, Q. m It automatically calculates the amount of heat generated here Q. m Details of the calculation method will be described later.

[0034] Based on the output information from the power detection unit 5 and the calculation unit 7, the control unit 8 performs output adjustment of the amplification unit 3 and alignment adjustment of the alignment unit 4. Details of the output adjustment and alignment adjustment here will be described later.

[0035] Specifically, the calculation unit 7 and the control unit 8 are computers equipped with hardware such as a calculation device like a CPU, a storage device like a semiconductor memory, and a communication device. And by the calculation device executing a predetermined program, each function described later is realized. However, hereinafter, such well-known technologies will be omitted as appropriate for explanation.

[0036] With the high-frequency power supply 2 and the amplification unit 3 having the above-described configuration, high-frequency power in the MHz band is oscillated, and a high-frequency electric field is applied to the food F from the upper electrode 11a through the alignment unit 4. As described above, the high-frequency electric field in the MHz band has the characteristic of being likely to reach deep inside the food F compared to the microwave (GHz band) used in a microwave oven. Therefore, by using the high-frequency power supply 2 of this embodiment, uniform thawing of the food F can be promoted.

[0037] <Calculation method of the heat generation amount Q by the calculation unit 7 m > Next, the calculation method of the heat generation amount Q generated in the food F by the calculation unit 7 m will be described in detail.

[0038] FIG. 2 is a conceptual diagram of dielectric property data for each food stored in the calculation unit 7 of this embodiment. The dielectric property data of the food F illustrated here are the characteristic data of the relative dielectric constant ε’ with respect to the food temperature T F and the characteristic data of the dielectric loss factor ε'' with respect to the food temperature T F . Note that the dielectric loss factor ε'' is an index indicating the ratio of dielectric loss (heat generation) in the food F. All of these dielectric property data take unique values for each food (more precisely, for each part of the food). However, both of them gradually increase slightly with the increase in temperature in the negative temperature range and generally tend to increase rapidly from around -5°C.

[0039] In this embodiment, dielectric property data for each food item to be thawed (three types of food items Fa to Fc in the example of Figure 2) is pre-stored in the calculation unit 7. Therefore, if the user specifies in advance which food item F is stored in the heating chamber 1, the calculation unit 7 will calculate the food item temperature T detected by the temperature sensor 14. F The relative permittivity ε' and dielectric loss rate ε'' can be determined based on the dielectric property data of the specified food ingredient F. Furthermore, the calculation unit 7 calculates the current dielectric heating amount (i.e., heat generation amount Q) of the food ingredient F based on the determined relative permittivity ε' and dielectric loss rate ε''. m The calculation unit 7 can then calculate the heat output Q of the food ingredient F. m The calculation method will be explained in detail.

[0040] The amount of heat Q generated in food ingredient F by dielectric heating. m (W / m 3 ) is given by (Equation 1). Here, f in (Equation 1) is the frequency (Hz) of the high-frequency power output by the high-frequency power supply 2, and ε0 is the permittivity of vacuum (= 8.854 × 10⁻¹⁴). -12 F / m), E m This is the electric field strength (V / m) applied by electrode 11 to the food ingredient F.

[0041]

number

[0042] Furthermore, as shown in the high-frequency dielectric heating apparatus 100 in Figure 1, when food ingredients F and an air layer are placed between the upper electrode 11a and the lower electrode 11b, the electric field strength E applied to the food ingredients F m (V / m) is given by (Equation 2). Here, V in (Equation 2) is the voltage between the upper and lower electrodes (V), d0 is the thickness of the air layer (m), and d F This is the thickness (m) of ingredient F.

[0043]

number

[0044] Substituting (Equation 2) into (Equation 1), we get the amount of heat generated Q. m (W / m3 ) is expressed as (Equation 3).

[0045]

number

[0046] Therefore, the calculation unit 7 of this embodiment uses the voltage V between the upper and lower electrodes detected by the voltage detection unit 6 and the food temperature T detected by the temperature sensor 14. F Then, using dielectric property data corresponding to the food ingredient F being thawed (see Figure 2) and (Equation 3), the current heat output Q of food ingredient F can be calculated. m It is possible to calculate the amount of heat generated Q. m By performing calculations over time, the calculation unit 7 calculates the amount of heat generated Q m It can store the change over time of the heat output Q. m When calculating the value of (Equation 3), F For d0, you should substitute a given standard value corresponding to the food ingredient F being thawed, and for d0, you should substitute a given value determined by the device specifications.

[0047] <Food temperature T during thawing of frozen tuna block F and heat generation Q m Relationship > Next, using Figures 3 and 4, we will discuss the food temperature T when thawing a frozen tuna block. F and heat generation Q m This explains the relationship.

[0048] Figure 3 shows the food temperature T when a frozen tuna block (approximately 200g) is thawed by high-frequency dielectric heating in the MHz band. F This graph shows an example of the time-dependent measurement results of the voltage T over time (dashed line) and an example of the time-dependent measurement results of the voltage V between electrodes (solid line). As described above, during food heating, the control unit 8 adjusts the variable coil and variable capacitor built into the matching unit 4 to suppress reflected power (reflected waves) returning from the matching unit 4 to the high-frequency power supply 2. Due to this effect, the voltage V between electrodes while thawing frozen tuna takes the form of temporarily decreasing and then increasing, as shown in the solid line graph in Figure 3. Note that, as shown in the upper part of the dashed line graph in Figure 3, the food temperature T FThe temperature range of approximately -5°C to -1°C is the temperature range in which the temperature rise during thawing is slow, and is called the maximum ice crystal formation zone.

[0049] In the high-frequency dielectric heating apparatus 100 of this embodiment, the voltage detection unit 6 can acquire the voltage value (electrode voltage V) of the upper electrode 11a, and the temperature sensor 14 can detect the food temperature T F Therefore, the calculation unit 7, which receives the outputs of the voltage detection unit 6 and the temperature sensor 14, uses the data pair exemplified in Figure 3 as material to obtain the food temperature T F Data on the change in the inter-electrode voltage V in response to the change in [the variable] can be obtained.

[0050] Furthermore, in the calculation unit 7 of this embodiment, (1) the food temperature T obtained from dielectric property data of frozen tuna block (see Figure 2) F (2) relative permittivity ε' and dielectric loss ε'', (2) data of the inter-electrode voltage V detected by the voltage detection unit 6, and (3) a predetermined food temperature T F The amount of heat generated in food ingredient F at the time of detection Q m It is possible to perform calculations on this.

[0051] This type of heat generation Q m By continuing the calculation for a predetermined time, the calculation unit 7 determines the food temperature T of the frozen tuna block, as shown in Figure 4. F and heat generation Q m A graph showing the relationship between the food temperature and the food temperature can be obtained. In this example, the food temperature T can be obtained. F During the process of rising from -20°C to -10°C, the amount of heat generated Q m It gradually increased, and then the heat output Q m It can be seen that the amount increases rapidly and reaches its maximum just before the maximum ice crystal formation zone (-5°C to -1°C).

[0052] Therefore, in the high-frequency dielectric heating apparatus 100 of this embodiment, the amplification factor of the amplification unit 3 is set to a large value to start thawing, and the heat output Q of the food ingredient F is reduced. m The point at which the change shifts from increasing to decreasing (heat output Q) mThe calculation unit 7 detects the point of maximum heat output (Q), and at that point, the amplification rate of the amplification unit 3 is reduced, thereby shortening the thawing time of the food ingredient F while reducing the heat output Q of the food ingredient F. m It can be seen that localized overheating of food ingredient F caused by excessive supply of dielectric heating energy in the temperature range where the dielectric energy decreases sharply can be suppressed.

[0053] Note that in Figure 4, the heat generation Q m The food temperature T at which it is maximized F Although the temperature is lower than the maximum ice crystal formation zone, the amount of heat generated Q can vary depending on the type of food F and the voltage between the electrodes. m The food temperature T at which it is maximized F This area is sometimes included in the zone of maximum ice crystal formation.

[0054] <Control method by control unit 8> Next, we will specifically explain the control content of the control unit 8 to suppress localized overheating of the food ingredient F by applying the mechanism described above.

[0055] Figure 5(a) shows the food temperature T detected by the temperature sensor 14. F And the amount of heat generated in the food ingredient F during thawing, calculated by the calculation unit 7, Q m This graph shows the relationship between the two. Note that Q in the figure ma is, at a certain time t a The food temperature T detected Fa This is the maximum heat output calculated based on [the formula / condition]. mb (However, Q ma > Q mb ) is the aforementioned time t a The next control period is time t b The food temperature T detected Fb (However, T Fa < T Fb This is the amount of heat generated based on ( ). Therefore, in this example, time t a and time t b At some point during this time, the calorific value Q of ingredient F m This means that the number has shifted from increasing to decreasing.

[0056] Figure 5(b) also shows the food temperature T detected by the temperature sensor 14. FThis is a graph showing the relationship between the amplification factor of the amplification unit 3 and the amplification factor of the amplification unit 3. As can be seen from the comparison of Figure 5(a) and Figure 5(b), the control unit 8 of this embodiment controls the heat output Q of the food ingredient F. m The calculation unit 7 detects at time t that the value has changed from increasing to decreasing. b At this point, the amplification factor set in the amplification unit 3 is reduced from its initial value.

[0057] By switching the amplification factor set in the amplification unit 3 in this way, the thawing time of the food F is shortened by the high-frequency electric field amplified with the high amplification factor set at the start of thawing, while the heat output Q m After detecting a decrease in the high-frequency electric field, the high-frequency electric field is amplified at a set low amplification factor, which makes it possible to suppress overheating of the edges, corners, and protrusions of the food ingredient F. Therefore, this embodiment makes it possible to achieve both a reduction in thawing time and an improvement in thawing quality of frozen foods.

[0058] Note that while ingredient F is thawing, the thickness of ingredient F F Since the thickness d0 of the air layer is constant, the amount of heat generated Q is calculated using (Equation 3) above. m The increase or decrease of is influenced only by the variables, namely the dielectric properties data of the food ingredient F (relative permittivity ε', dielectric loss rate ε'') and the voltage between electrodes V. Therefore, the thickness d of the food ingredient F is affected. F Even if the thickness d0 of the air layer is unknown, the heat generation Q can be calculated by assuming them to be arbitrary fixed values. m Based on the increase or decrease, the appropriate timing to switch the amplification factor set in the amplification unit 3 (the aforementioned time t) b It can detect ).

[0059] <Flowchart> Next, using the flowchart in Figure 6, we will explain an example of user operation and the defrosting operation by the high-frequency dielectric heating device 100.

[0060] First, in step S1, the user opens the door of heating chamber 1, places the frozen food item F on the placement tray 12, and then closes the door of heating chamber 1.

[0061] In step S2, the weight sensor 13 automatically detects the weight of the food ingredient F, and the temperature sensor 14 detects the initial food ingredient temperature T. F It will be automatically detected. Furthermore, detection by the temperature sensor 14 will continue thereafter.

[0062] In step S3, the calculation unit 7 uses the food weight detected in step S2 and the initial food temperature T to calculate the initial food temperature T. F Based on this, the estimated thawing time is t m The number of seconds is calculated, and the result is displayed on the display unit on the front of the high-frequency dielectric heating device 100.

[0063] In step S4, the user operates the control unit to register a defrosting menu number corresponding to the type of food ingredient F. This allows the calculation unit 7 to select the dielectric property data corresponding to the food ingredient F stored in the heating chamber 1 from a plurality of pre-stored dielectric property data (see Figure 2).

[0064] In step S5, the user operates the control unit to command the start of thawing. Upon receiving this command, the control unit 8 controls the high-frequency power supply 2 to begin outputting high-frequency power in the MHz band. The amplification unit 3 also amplifies the high-frequency power output by the high-frequency power supply 2 at a high amplification factor that has been initially set by the control unit 8. As a result, the thawing of the food item F begins with a certain high-frequency output power.

[0065] In step S6, the calculation unit 7 calculates the food temperature T based on the output of the voltage detection unit 6 and the temperature sensor 14. F Then, begin observing the electrode voltage V (see Figure 3).

[0066] In step S7, the calculation unit 7 uses the dielectric property data selected in step S4 (see Figure 2) and the current food temperature T detected by the temperature sensor 14. F Based on this, the current food temperature T F The relative permittivity ε' and dielectric loss rate ε'' are calculated for T. The calculation unit 7 also calculates the current food temperature T FSubstitute the electrode voltage V, and the relative permittivity ε' and dielectric loss rate ε'' obtained in the first half of this step into (Equation 3) above, and obtain the amount of heat generated in the food ingredient F Q. m Perform the calculation.

[0067] In step S8, the calculation unit 7 calculates the amount of heat generated Q for the current control cycle. m And the amount of heat generated Q calculated during the previous control cycle. m The values ​​are compared to determine if the change in heat output has shifted from an increase to a decrease. If the requirements are not met, step S8 is repeated; if the requirements are met, the process proceeds to step S9.

[0068] In step S9, the control unit 8 switches the amplification factor set in the amplification unit 3 to a value smaller than the initial value (see Figure 5). As a result, the high-frequency output from the amplification unit 3 is reduced compared to the initial value. This suppresses overheating of the edges, corners, and protrusions of the food ingredient F.

[0069] In step S10, the control unit 8 determines that the elapsed time since the start of thawing is the guideline t for thawing time defined in step S3. m Determine if the requirement has been met. If the requirement is not met, repeat step S10; if the requirement is met, proceed to step S11.

[0070] In step S11, the control unit 8 turns off the high-frequency power supply 2 to complete the defrosting process.

[0071] <Effects of this embodiment, etc.> The high-frequency dielectric heating device of this embodiment, as described above, makes it possible to shorten the thawing time of frozen foods, etc., while suppressing overheating of the edges, corners, and protrusions of the food, thereby improving the thawing quality, when thawing frozen foods, etc., using a high-frequency electric field in the MHz band. In the above embodiment, a high-frequency dielectric heating device for thawing food F was exemplified, but the high-frequency dielectric heating device of the present invention may also be used to thaw things other than food. [Explanation of Symbols]

[0072] 100 High-frequency dielectric heating device 1 Heating chamber 11 electrodes 11a Upper electrode 11b Lower electrode 12 Mounting platform 13. Weight sensor 14. Temperature sensor 2 High frequency power supply 3. Amplification section 4 Matching part 5 Power detection unit 6 Voltage detection unit 7 Arithmetic section 8 Control Unit F Ingredients

Claims

1. A heating chamber for housing the object to be heated, A pair of electrodes are arranged opposite each other so as to sandwich the object to be heated, A temperature sensor for detecting the temperature of the object to be heated, A high-frequency power supply that outputs high-frequency power in the MHz band, An amplification unit that amplifies the output of the high-frequency power supply and applies it to the pair of electrodes, A voltage detection unit that detects the voltage value applied between the pair of electrodes, A calculation unit calculates the amount of heat generated in the object to be heated based on the temperature detected by the temperature sensor and the voltage value detected by the voltage detection unit, When the amount of heat generated by the calculation unit changes from increasing to decreasing, the control unit reduces the amplification factor of the amplification unit. A high-frequency dielectric heating apparatus characterized by comprising the following features.

2. In the high-frequency dielectric heating apparatus according to claim 1, The high-frequency dielectric heating apparatus is characterized in that the calculation unit has dielectric property data corresponding to the type of object to be heated stored in advance.

3. In the high-frequency dielectric heating apparatus according to claim 2, The high-frequency dielectric heating apparatus is characterized in that the dielectric property data comprises characteristic data of the relative permittivity with respect to the temperature of the object to be heated and characteristic data of the dielectric loss rate with respect to the temperature of the object to be heated.

4. A heating chamber for housing the object to be heated, A pair of electrodes are arranged opposite each other so as to sandwich the object to be heated, A temperature sensor for detecting the temperature of the object to be heated, A high-frequency power supply that outputs high-frequency power in the MHz band, An amplification unit that amplifies the output of the high-frequency power supply and applies it between the pair of electrodes, A voltage detection unit that detects the voltage value applied between the pair of electrodes, A calculation unit has pre-stored dielectric property data corresponding to the type of object to be heated, and calculates the amount of heat generated in the object to be heated based on the temperature detected by the temperature sensor, the voltage value detected by the voltage detection unit, and the selected dielectric property data. A control unit that reduces the amplification factor of the amplification unit in accordance with the change in the amount of heat generated calculated by the calculation unit, A high-frequency dielectric heating apparatus characterized by comprising the following features.

5. In the high-frequency dielectric heating apparatus according to any one of claims 1 to 4, A high-frequency dielectric heating apparatus further comprising a matching unit that matches the output impedance of the high-frequency power supply with the load-side impedance including the object to be heated.

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