WO2024095425A1

WO2024095425A1 - Microwave irradiation device

Info

Publication number: WO2024095425A1
Application number: PCT/JP2022/041080
Authority: WO
Inventors: 友樹丸山; 真司山田; 隆明山崎
Original assignee: 東洋製罐グループホールディングス株式会社
Priority date: 2022-11-02
Filing date: 2022-11-02
Publication date: 2024-05-10

Abstract

A microwave irradiation device 1 is provided with: a power supply tool 20 configured to conduct to an oscillator 10; a directional antenna group 34 including at least one directional antenna 40 configured to radiate microwaves through power supply by the conduction via the power supply tool 20; and a secondary radiation antenna group 35 including at least one secondary radiation antenna 50 configured to secondly radiate the microwaves.

Description

Microwave irradiation device

The present invention relates to a microwave irradiation device.

　Generally, heating devices are known that apply microwaves to an object to dielectrically heat it. However, with dielectric heating, the object may not be heated evenly for a variety of reasons. For this reason, various efforts have been made to ensure even heating.

For example, Patent Document 1 discloses the following microwave heating device. In this microwave heating device, microwaves are supplied to the heating chamber from a power supply port through a waveguide. The heating chamber is divided into an upper space and a lower space by a mounting shelf. The periphery of the mounting shelf is located at the center in the vertical direction of the power supply port. The mounting surface has multiple parallel lines with openings and a length that is an integer multiple of 1/2 wavelength, and is configured so that microwaves are secondarily radiated from these parallel lines. An equal amount of objects to be heated is placed in the upper space and the lower space, and the objects to be heated and the mounting shelf are simultaneously heated by microwaves while rotating. Microwaves supplied from the power supply port at the periphery of the mounting surface are evenly distributed to the upper space and the lower space, and microwaves are secondarily radiated above and below from the parallel lines, so that the objects to be heated are heated evenly and efficiently.

Japanese Patent Application Laid-Open No. 11-40339

The microwave heating device described above has the effect of evenly distributing microwaves to the upper and lower spaces, but it is not possible to control the uniformity of heating of the objects placed in each space, and there is a risk of uneven heating depending on the shape and type of the objects. The object of the present invention is to appropriately control heating in a microwave irradiation device.

According to one aspect of the present invention, a microwave irradiation device includes a power supply device configured to be conductive with an oscillator, a directional antenna group including at least one directional antenna configured to irradiate microwaves by power supply through the power supply device, and a secondary radiation antenna group including at least one secondary radiation antenna configured to secondarily radiate microwaves.

According to the present invention, heating can be appropriately controlled in a microwave irradiation device.

FIG. 1A is a front view diagrammatically illustrating an outline of a configuration example of a microwave radiating device according to a first embodiment. FIG. FIG. 1B is a right side view diagrammatically illustrating an outline of a configuration example of the microwave radiating device according to the first embodiment. FIG. FIG. 2A is a diagram for explaining the operation of the microwave radiating device of the first embodiment, showing a current at a certain moment. FIG. 2B is a diagram for explaining the operation of the microwave radiating device of the first embodiment, showing a magnetic field in an xz cross section including the radiation axis of the loop antenna at a certain moment. FIG. 2C is a diagram for explaining the operation of the microwave radiating device of the first embodiment, and is a diagram for explaining an electric field formed at a certain moment. FIG. 2D is a diagram for explaining the operation of the microwave radiating device of the first embodiment, showing the electric field in an xy cross section passing through the secondary radiation antenna at a certain moment. FIG. 2E is a diagram for explaining the operation of the microwave radiating device of the first embodiment, and is a diagram showing the electric field in a yz cross section passing through an object to be radiated at a certain moment. FIG. 3 is a diagram showing an example of a simulation result of a temperature distribution when an irradiated object is heated by the microwave irradiating device of the first embodiment, and showing respective results when the length of the secondary radiation antenna is different. FIG. 4A is a diagram showing an example of a model used in a simulation of a temperature distribution when an irradiated object is heated by the microwave irradiating device of the first embodiment. FIG. 4B is a diagram showing an example of a simulation result of a temperature distribution when an irradiated object is heated by the microwave irradiating device of the first embodiment. FIG. 4C is a diagram showing an example of a simulation result of a temperature distribution when an irradiated object is heated by the microwave irradiating device of the first embodiment. FIG. 5 is a diagram showing an example of a test result in which an object to be irradiated is heated by the microwave irradiating device of the first embodiment. FIG. 6 is a diagram showing an example of a simulation result of the temperature distribution when an irradiated object is heated by a microwave irradiation device according to a modified example, and shows the results for different lengths of the secondary radiation antenna perpendicular to the irradiation axis. FIG. 7A is a front view that diagrammatically illustrates an example of the configuration of a microwave radiating device according to a second embodiment. FIG. FIG. 7B is a right side view diagrammatically illustrating an outline of a configuration example of the microwave radiating device according to the second embodiment. FIG. 8A is a diagram for explaining the operation of the microwave radiating device of the second embodiment, showing a current at a certain moment. FIG. 8B is a diagram for explaining the operation of the microwave radiating device of the second embodiment, showing a magnetic field in an xz cross section including the radiation axis of the loop antenna at a certain moment. FIG. 8C is a diagram for explaining the operation of the microwave radiating device of the second embodiment, showing a current at a certain moment. FIG. 8D is a diagram for explaining the operation of the microwave radiating device of the second embodiment, and is a diagram showing the electric field in an xy cross section passing through the secondary radiation antenna at a certain moment. FIG. 8E is a diagram for explaining the operation of the microwave radiating device of the second embodiment, and is a diagram showing the electric field in a yz cross section passing through an object to be radiated at a certain moment. FIG. 9A is a diagram showing an example of a simulation result of a temperature distribution when an irradiated object is heated by the microwave irradiating device of the second embodiment. FIG. 9B is a diagram showing an example of a simulation result of a temperature distribution when an irradiated object is heated by the microwave irradiating device of the second embodiment. FIG. 10 is a diagram showing an example of a test result in which an object to be irradiated is heated by the microwave irradiating device of the second embodiment. FIG. 11 is a diagram showing an example of a simulation result of temperature distribution when an irradiated object is heated by the microwave irradiating device of the third embodiment, and showing respective results when the position of the secondary radiation antenna is different. FIG. 12 is a front view diagrammatically illustrating an outline of a configuration example of a microwave radiating device according to the fourth embodiment.

[First embodiment]
A first embodiment will be described with reference to the drawings. This embodiment relates to a microwave irradiating device. The microwave irradiating device of this embodiment is configured to irradiate microwaves to an irradiated object to heat the inside of the irradiated object. The irradiated object is, but is not limited to, a food product.

<composition>
1A and 1B are diagrams showing an outline of a configuration example of a microwave irradiation device 1 according to the present embodiment. Fig. 1A is a front view of the microwave irradiation device 1, and is a diagram showing a state in which a plate on the front part of a metal housing 82 described later is removed to make the inside visible. Fig. 1B is a right side view of the microwave irradiation device 1, and is a diagram showing a state in which a plate on the right side part of a metal housing 82 described later is removed to make the inside visible.

As shown in these figures, the microwave irradiation device 1 includes a holder 60. The holder 60 holds an irradiated object 90, which is an object to be heated and is irradiated with microwaves. The holder 60 can be, for example, a table on which the irradiated object 90 is placed. The holder 60 is configured, for example, to be able to hold the irradiated object 90 at an irradiation position where the microwaves are appropriately irradiated.

The microwave irradiation device 1 is equipped with a directional antenna group 34 including two directional antennas 40 configured to irradiate microwaves to an irradiated object 90 held by a holder 60. Each directional antenna 40 is, for example, an antenna such as a loop antenna or a patch antenna. The two directional antennas 40 are arranged opposite each other with the irradiated object 90 in between, with their directional irradiation axes facing each other toward the irradiated object 90. The two directional antennas 40 are arranged along the irradiation axes of these directional antennas 40.

In the example shown in Figures 1A and 1B, the two directional antennas 40 are loop antennas 41. The holder 60 is provided so as to pass through the loops of the two loop antennas 41. In this embodiment, the irradiation position where the microwaves are appropriately irradiated is the midpoint between the two opposing loop antennas 41. In other words, the two loop antennas 41 are arranged symmetrically with the irradiated object 90 in between.

The loop antenna 41 includes a conductor 42 formed in a ring shape with a length of, for example, one wavelength of the microwaves to be irradiated. Both ends of the conductor 42 are power supply points 43. A coaxial cable 21, for example, serving as a power supply device 20, is connected to the power supply point 43. The coaxial cable 21 connects the oscillator 10 and the loop antenna 41 to provide electrical continuity. The oscillator 10 supplies high-frequency power to the loop antenna 41 via the coaxial cable 21. When power is supplied, a current is generated in the conductor 42 as an element, and the loop antenna 41 radiates radio waves to form an electric field.

In the loop antenna 41, the surface formed by the conductor 42 becomes the radio wave irradiation surface, and directional microwaves are emitted from the irradiation source in the center of the irradiation surface toward an irradiation axis perpendicular to the irradiation surface. The loop antenna 41 is arranged perpendicular to the mounting surface of the holder 60, and the irradiation axis is along the mounting surface of the holder 60.

The microwave irradiation device 1 includes a secondary radiation antenna group 35 including two secondary radiation antennas 50. The two secondary radiation antennas 50 are arranged between the two loop antennas 41. In the example shown in FIG. 1A and FIG. 1B, the two thin plate-shaped secondary radiation antennas 50 are arranged so as to extend parallel to the irradiation axis of the loop antenna 41, penetrate both loop antennas 41, and sandwich the irradiated object 90 from the horizontal direction. The loop antenna 41, which is the directional antenna 40, and the secondary radiation antenna 50 are not conductive and are insulated. In this embodiment, the two secondary radiation antennas 50 are arranged symmetrically with respect to the irradiation position where the irradiated object 90 is held. Although not limited to this, since the electric field strength is strong and heating efficiency is good in the middle of the two loop antennas 41, it is preferable that the irradiated object 90 is arranged in the middle of the two loop antennas 41, and the secondary radiation antenna 50 is also arranged in the middle of the two loop antennas 41.

The above-mentioned configuration is covered with metal to block microwaves. That is, the holder 60, the directional antenna 40, the secondary radiation antenna 50, etc. are arranged inside the metal housing 82.

<motion>
The operation of the microwave irradiation device 1 of this embodiment will be described. The oscillator 10 outputs high-frequency power according to the frequency of the microwave. The frequency is not limited to, but may be, for example, 2.45 GHz, 915 MHz, or 450 MHz. The high-frequency power output from the oscillator 10 is supplied to the directional antenna 40 via the power supply device 20. The directional antenna 40 radiates microwaves based on this power supply.

The secondary radiation antenna 50 is electromagnetically induced by the microwaves radiated from the directional antenna 40. As a result, an electric field is generated by the secondary radiation antenna 50.

Microwaves are irradiated from the directional antenna 40 and the secondary radiation antenna 50 to the irradiated object 90 placed on the holder 60. The irradiated object 90 is dielectrically heated by the microwaves.

<Regarding generated electric fields, etc.>
In the microwave irradiation device 1 of the present embodiment, the directional antenna 40 and the secondary radiation antenna 50 are provided as described above, so that the irradiated object 90 is heated more uniformly. This will be described with reference to Figs. 2A to 2E. Here, as shown in Fig. 2A, the horizontal mounting surface of the holder 60 is defined as the xy plane, and the vertical direction is defined as the z axis. The loop antenna 41 as the directional antenna 40 is provided on the yz plane, and its irradiation axis is along the x axis.

FIG. 2A is a diagram showing the direction and magnitude of the current at a certain moment when high-frequency power is supplied from oscillator 10 to loop antenna 41, using the direction and magnitude of many small vectors. Current flows through loop antenna 41 in the direction shown by the large white arrow. At this time, a magnetic field is generated around loop antenna 41 in the direction shown by the large shaded arrow.

FIG. 2B is a diagram showing the direction and strength of the magnetic field in an xz cross section including the irradiation axis of the loop antenna 41 at this time, using the direction and magnitude of many small vectors. In general, a magnetic field is generated in the direction shown by the large hatched arrow in FIG. 2B.

FIG. 2C is a diagram showing the direction and magnitude of the current, also shown in FIG. 2A, with the direction and magnitude of many small vectors. When a magnetic field such as that shown in FIG. 2B penetrates the secondary radiation antenna 50, eddy currents are generated, and a current is induced in the secondary radiation antenna 50 as a result of the combination of these eddy currents. The direction of the current in the secondary radiation antenna 50 is shown by a large white arrow in FIG. 2C. That is, in one secondary radiation antenna 50, a current is generated toward its center, and in the other secondary radiation antenna 50, a current is generated toward the outside from the center. As shown in FIG. 2C, positive and negative charges accumulate where the induced currents face each other, i.e., in the center of the secondary radiation antenna 50.

FIGS. 2D and 2E are diagrams showing the direction and strength of the electric field generated at this time by the direction and magnitude of many small vectors. FIG. 2D shows an xy cross section passing through the secondary radiation antenna 50, and FIG. 2E shows a yz cross section passing through the irradiated object 90. As shown by the large shaded arrows in FIGS. 2C to 2E, an electric field is generated between the two secondary radiation antennas 50, crossing the irradiated object 90.

As described above, by providing two secondary radiation antennas 50 between two opposing loop antennas 41, the irradiated object 90 is efficiently dielectrically heated.

Simulation of temperature distribution due to dielectric heating
FIG. 3 shows the results of simulating the temperature distribution of the irradiated object 90 when the irradiated object 90 is heated by the microwave irradiation device 1 described above, and shows the results for each case where the length of the secondary radiation antenna 50 is different. The analysis was performed with the diameter of the irradiated object 90 being 80 mm, the frequency of the power supply to the loop antenna 41 being 450 MHz, and the distance between the two loop antennas 41 being 333 mm, which corresponds to 1/2 wavelength. In FIG. 3, the upper part shows the model used in the simulation, showing the arrangement of the secondary radiation antenna 50. In both cases, the width of the secondary radiation antenna 50 is 20 mm, and the interval between them is 95 mm. The secondary radiation antenna 50 is arranged at the center position in the height direction of the irradiated object 90. The analysis was performed for (a) the case where the secondary radiation antenna 50 is not provided, and the case where the length of the secondary radiation antenna 50 is set to a length equivalent to each of (b) 1/32 wavelength, (c) 1/16 wavelength, (d) 1/8 wavelength, and (e) 1/4 wavelength. In the analysis, the electromagnetic field generated for each condition was calculated, and the temperature distribution based on this electromagnetic field was calculated. The lower part of Fig. 3 shows the analysis result of the temperature distribution in the xy cross section including the center of the irradiated object 90 on which the secondary radiation antenna 50 is arranged after the uniform irradiated object 90 is heated for 5 minutes at an output of 150 W.

In both cases, the center of the irradiated object 90 was the hottest, and the temperature decreased the further away from the center. In the case of (a) where the secondary radiation antenna 50 was not provided, the loop antenna 41 radiated radio waves along the irradiation axis 45 connecting the centers of the two loop antennas 41, so a high-temperature area was formed along this irradiation axis 45, and the temperature difference depending on the position became large in the direction perpendicular to the irradiation axis. On the other hand, as the secondary radiation antenna 50 was provided and became longer, the temperature difference depending on the position in the direction perpendicular to the irradiation axis 45 became smaller. In particular, in the cases of (d) and (e) where the length of the secondary radiation antenna 50 was 1/8 wavelength or more, the temperature difference depending on the position was small in both the direction along the irradiation axis 45 and the direction perpendicular to the irradiation axis 45, and it was found that the entire irradiated object 90 was heated more uniformly. It was considered preferable that the secondary radiation antenna 50 has a certain length.

A similar analysis was also performed for the case where the secondary radiation antenna 50 was positioned so as to penetrate the loop antenna 41, as shown in Figure 4A. Figures 4B and 4C show the analysis results, showing the temperature distribution. Figure 4C shows the temperature distribution on the 4C-4C cross section shown in Figure 4A. As shown in these results, it was confirmed that high uniformity could be obtained in heating the irradiated object 90.

<Experimental result>
The uniformity of heating by the microwave radiating device 1 described above was evaluated by using a containerized potato salad as an object to be heated.

The oscillation frequency of the oscillator 10 was 450 MHz. For the loop antenna 140, a square loop antenna 41 made of aluminum with a circumference equivalent to one wavelength (λ = 666 mm) was used. The distance between the two loop antennas 41 was λ/2 = 333 mm. Power was fed to the two loop antennas 41 in phase. A 5 mm thick polyethylene (PE) plate was used as the holder 60. The food holder 166 was positioned so that it penetrated the two loop antennas 140. A plate-shaped secondary radiation antenna 50 with a width of 40 mm and a length that penetrated the two loop antennas 41 was placed with a gap of 95 mm between them, sandwiching the irradiated object 90.

The irradiated object 90 was a polypropylene (PP) container with a diameter of 80 mm, containing potato salad. The temperature was measured by attaching multiple Thermo Labels (registered trademark) to the surface of the potato salad. The temperature was measured after heating for 5 minutes at an output of 150 W.

The irradiated object 90 after heating is shown in FIG. 5. As shown in this figure, the temperature reached 70°C everywhere along the irradiation axis 45. In addition, in the direction perpendicular to the irradiation axis 45, the center was 70°C and both sides were 80°C. In this way, it was confirmed that the microwave irradiation device 1 is capable of uniform heating. Note that, as a comparative example, when the secondary radiation antenna 50 was not provided, the temperature on both sides in the direction perpendicular to the irradiation axis 45 was lower than that of the center. In other words, the same measurement results as the simulation results in FIG. 3(a) were obtained.

As a heating device using dielectric heating, for example, a multi-mode heating device is known that reflects microwaves inside a metal housing to heat the object to be heated. Also, a single-mode heating device is known in which the object to be heated is placed inside a waveguide that carries microwaves. In a multi-mode heating device, uneven heating is likely to occur. Also, a heating device that uses a waveguide is likely to become large in size, especially when the frequency is low, as the waveguide becomes large. Also, when multiple types of heating devices are combined to achieve uniform heating, the entire device is likely to become large. In contrast, the microwave irradiation device 1 of this embodiment does not use a waveguide and does not need to combine multiple types of devices, so the device can be easily miniaturized. Also, since a waveguide is not used, it is easy to use microwaves of a relatively low frequency. By lowering the frequency, the half-power depth can also be deepened.

<Modification>
FIG. 6 shows the results of a simulation of the temperature distribution of the irradiated object 90 when the irradiated object 90 is heated by the microwave irradiation device 1 according to the modified example. In this modified example, the long axis of the secondary radiation antenna 50 is provided so as to be perpendicular to the irradiation axis 45. Each of FIGS. 6(a) to 6(d) summarizes the analysis of the case where the secondary radiation antenna 50 is not provided (a) and the case where the length of the secondary radiation antenna 50 is set to a length equivalent to each of 1/32 wavelength (b), 1/16 wavelength (c), and 1/8 wavelength (d), as shown in the upper part of the model. In each case, the width of the secondary radiation antenna 50 is 10 mm, and the interval between them is 95 mm. The secondary radiation antenna 50 is disposed at the center position in the height direction of the irradiated object 90. The frequency of the power supply to the loop antenna 41 is 450 MHz, and the analysis is performed with the distance between the two loop antennas 41 being 333 mm, which corresponds to 1/2 wavelength.

The lower part of Figure 6 shows the analysis results of the temperature distribution in the xy cross section including the center of the irradiated object 90 where the secondary radiation antenna 50 is placed after heating a uniform irradiated object 90 with a diameter of 80 mm for 5 minutes at an output of 150 W. In both cases, the center of the irradiated object 90 is the hottest, and the temperature decreases the further away from the center. In the case of (a) where the secondary radiation antenna 50 is not provided, a high-temperature region is formed along the irradiation axis 45 as described above, and the temperature difference depending on the position becomes large in the direction perpendicular to the irradiation axis. On the other hand, when the secondary radiation antenna 50 is provided and becomes longer, a high-temperature region is formed in the direction perpendicular to the irradiation axis. In the case of (c) where the length of the secondary radiation antenna 50 is 1/16 wavelength, the temperature difference depending on the position is relatively small in both the direction along the irradiation axis and the direction perpendicular to the irradiation axis, and it was found that the entire irradiated object 90 is heated relatively uniformly.

In the above-described embodiment and modified example, the thin plate-shaped secondary radiation antenna 50 is arranged so that its main surface is horizontal, but this is not limiting. The secondary radiation antenna 50 may be arranged so that its main surface is vertical.

The dimensions of the secondary radiation antenna 50 can be appropriately determined so as to achieve impedance matching, taking into consideration the output frequency of the oscillator 10, etc. In addition, the secondary radiation antenna 50 is preferably positioned reasonably close to the irradiated object 90, since the electric field formed in the area of the irradiated object 90 weakens as it moves away from the irradiated object 90.

Second Embodiment
<composition>
The second embodiment will be described. Here, the differences from the first embodiment will be described, and the same parts will be given the same reference numerals and their description will be omitted. The microwave irradiation device 2 of this embodiment is provided with an additional secondary radiation antenna as a secondary radiation antenna 52 for heat control, compared with the microwave irradiation device 1 according to the first embodiment. That is, in this embodiment, the secondary radiation antenna group 35 includes the secondary radiation antenna 52 for heat control in addition to the two secondary radiation antennas 50 on both sides of the irradiated object 90.

FIGS. 7A and 7B are schematic diagrams showing an example of the configuration of a microwave irradiation device 2 according to this embodiment. FIG. 7A is a front view of the microwave irradiation device 2, and is a schematic diagram showing a state in which the plate on the front part of the metal housing 82 has been removed to make the inside visible. FIG. 7B is a right side view of the microwave irradiation device 2, and is a schematic diagram showing a state in which the plate on the right side part of the metal housing 82 has been removed to make the inside visible.

As shown in this figure, the microwave irradiation device 2 has a secondary radiation antenna 52 for heating control provided below the holder 60. The secondary radiation antenna 52 for heating control extends parallel to the irradiation axis 45, but is positioned so that it does not pass directly below the center of the irradiated object 90, but is offset to the left side in FIG. 7B. That is, in this embodiment, the multiple secondary radiation antennas included in the secondary radiation antenna group 35 are positioned asymmetrically with respect to the irradiation position where the irradiated object 90 is placed. The rest of the configuration of the microwave irradiation device 2 is the same as in the first embodiment.

<Regarding generated electric fields, etc.>
In the microwave irradiation device 2 of this embodiment, the directional antenna 40, the secondary radiation antenna 50, and the heating control secondary radiation antenna 52 are provided as described above, so that the irradiated object 90 is heated unevenly. This will be described with reference to Figures 8A to 8E. Here, as in the description of the first embodiment, as shown in Figure 8A, the horizontal mounting surface of the holder 60 is defined as the xy plane, and the vertical direction is defined as the z axis. The loop antenna 41 is provided on the yz plane, and its irradiation axis is along the x axis.

FIG. 8A is a diagram showing the direction and magnitude of the current at a certain moment when high-frequency power is supplied from oscillator 10 to loop antenna 41, using the direction and magnitude of many small vectors. Current flows through loop antenna 41 in the direction shown by the large white arrow. At this time, a magnetic field is generated around loop antenna 41 in the direction shown by the large shaded arrow.

FIG. 8B is a diagram showing the direction and strength of the magnetic field in the xz cross section including the irradiation axis of the loop antenna 41 at this time, using the direction and magnitude of many small vectors. In general, a magnetic field is generated in the direction shown by the large hatched arrow in FIG. 8B.

FIG. 8C is a diagram showing the direction and magnitude of the current as shown in FIG. 8A, using the direction and magnitude of many small vectors. When a magnetic field such as that shown in FIG. 8B passes through the secondary radiation antenna 50 and the secondary radiation antenna for heating control 52, eddy currents are generated, and currents are induced in the secondary radiation antenna 50 and the secondary radiation antenna for heating control 52 as a result of the combination of these eddy currents. The direction of the currents in the secondary radiation antenna 50 and the secondary radiation antenna for heating control 52 is shown by the large white arrows. Electric charge accumulates where the induced currents face each other.

8D and 8E are diagrams showing the direction and strength of the electric field generated at this time by the direction and magnitude of many small vectors. FIG. 8D shows an xy cross section passing through the secondary radiation antenna 50, and FIG. 8E shows a yz cross section passing through the irradiated object 90. As shown by the large hatched arrows in FIG. 8D and FIG. 8E, an electric field is generated that crosses the irradiated object 90 between the opposing secondary radiation antennas 50, and an electric field is generated that crosses the irradiated object 90 toward the secondary radiation antenna 50 farther from the heating control secondary radiation antenna 52. As a result, the electric field strength is stronger on the side of the secondary radiation antenna 50 farther from the heating control secondary radiation antenna 52 than on the opposite secondary radiation antenna 50. Therefore, the irradiated object 90 is dielectrically heated more strongly on the side of the secondary radiation antenna 50 farther from the heating control secondary radiation antenna 52 where the electric field strength is stronger.

Simulation of temperature distribution due to dielectric heating
9A and 9B are simulation results of the temperature distribution of the irradiated object 90 when the irradiated object 90 is heated by the microwave irradiation device 2 of this embodiment. As in the first embodiment, the analysis was performed with the diameter of the irradiated object 90 being 80 mm, the frequency of the power supply to the loop antenna 41 being 450 MHz, and the distance between the two loop antennas 41 being 333 mm, which corresponds to 1/2 wavelength. The width of the secondary radiation antenna 50 was 40 mm, and the interval between them was 95 mm. The secondary radiation antenna 50 was placed at the center position in the height direction of the irradiated object 90. The width of the heating control secondary radiation antenna 52 was 30 mm, and it was placed under the holder 60 so that the width direction end of the heating control secondary radiation antenna 52 was located at the center position of the irradiated object 90. FIG. 9B shows the temperature distribution of the 9B-9B cross section shown in FIG. 9A. As a result, it was revealed that the irradiated object 90 was heated more strongly on the side of the secondary radiation antenna 50 farther from the heating control secondary radiation antenna 52.

<Experimental result>
Heating by the microwave radiating device 2 of this embodiment was evaluated using a containerized potato salad as an object to be heated. The experimental conditions were the same as those of the first embodiment, except that the microwave radiating device 2 was provided with a secondary radiation antenna 52 for heating control.

The irradiated object 90 after heating is shown in FIG. 10. As shown in this figure, the temperature after heating on the side where the secondary radiation antenna for heating control 52 is located is 70°C, while the temperature after heating on the side opposite the side where the secondary radiation antenna for heating control 52 is located is 90°C. In this way, it was confirmed that the microwave irradiation device 2 is capable of uneven heating. It was made clear that the heating distribution can be controlled by adjusting the location of the secondary radiation antenna for heating control 52.

When heating the irradiated object 90, it is not necessarily desirable to heat it uniformly. For example, when there are areas within the irradiated object 90 that are easily heated and areas that are difficult to heat, the entire irradiated object 90 will be heated uniformly by supplying more power to the areas that are difficult to heat. Also, a single irradiated object 90 may contain areas that you want to heat and areas that you do not want to heat excessively. In such cases, it is necessary to supply power to the areas that you want to heat.

According to this embodiment, the microwave irradiation device 2 can perform appropriate heating by adjusting the position and size of the heating control secondary radiation antenna 52 according to the electric field strength required at each part of the irradiated object 90.

The microwave irradiation device 2 may be configured so that the position of the heating control secondary radiation antenna 52 can be changed. In this way, by changing the position of the heating control secondary radiation antenna 52 according to the irradiated object 90, heating according to the irradiated object 90 becomes possible.

Here, an example is shown in which a secondary radiation antenna 52 for heating control is provided in addition to the secondary radiation antenna 50 of the microwave irradiation device 1 of the first embodiment, but this is not limited to this. By appropriately adjusting the position and size of one or more secondary radiation antennas 50 included in the secondary radiation antenna group 35, regardless of whether they are the secondary radiation antenna 50 or the secondary radiation antenna 52 for heating control, the microwave irradiation device can adjust the electric field strength and control the heating of the irradiated object 90. For example, in the first embodiment, the secondary radiation antenna is provided symmetrically with respect to the irradiated object 90, so that power is uniformly supplied to the irradiated object. In the second embodiment, the secondary radiation antenna is provided asymmetrically with respect to the irradiated object 90, so that power is non-uniformly supplied to the irradiated object. In particular, when the secondary radiation antenna is arranged asymmetrically, the distribution of the electric field strength may vary depending on various conditions.

For example, in the second embodiment, when the secondary radiation antenna 50 farther from the heating control secondary radiation antenna 52 is not provided, that is, when the right-side secondary radiation antenna 50 in FIG. 8E is not provided and only two secondary radiation antennas, the left-side secondary radiation antenna 50 and the heating control secondary radiation antenna 52, are provided, a strong electric field is formed between these two secondary radiation antennas. As a result, unlike the second embodiment, the left side of the irradiated object 90 in FIG. 8E is strongly heated.

[Third embodiment]
The third embodiment will be described. Here, the differences from the first embodiment will be described, and the same parts will be given the same reference numerals and the description thereof will be omitted. In the third embodiment, the position of the secondary radiation antenna 50 of the microwave irradiating device 1 according to the first embodiment will be considered.

Figure 11 shows the results of a simulation of the temperature distribution in the irradiated object 90, which is a tapered cup with a diameter of 80 mm to 85 mm containing an item 91, when the irradiated object 90 is heated by the microwave irradiation device 1. (a) shows the case where the secondary radiation antenna 50 is not provided, (b) shows the case where the secondary radiation antenna 50 is placed at the center of the height of the item 91, and (c) shows the case where the secondary radiation antenna 50 is placed at the same height as the holder 60.

In FIG. 11, the upper and middle sections show the models used in the simulation. The upper section shows a perspective view, and the middle section shows a yz cross section passing through the center of the irradiated object 90. In the cases shown in (b) and (c), the width of the secondary radiation antenna 50 was 20 mm. (b) When the secondary radiation antenna 50 was placed at the center of the height of the contents 91, the spacing between the secondary radiation antennas 50 was 95 mm. (c) When the secondary radiation antenna 50 was placed at the same height as the holder 60, the spacing between the secondary radiation antennas 50 was 140 mm. The frequency of the power supply to the loop antenna 41 was 450 MHz, and the distance between the two loop antennas 41 was 333 mm, which corresponds to 1/2 wavelength, for the analysis. In the analysis, the electromagnetic field generated for each condition was calculated, and the temperature distribution based on this electromagnetic field was calculated.

The lower part of Figure 11 shows the analysis results of the temperature distribution in the yz cross section including the center of the irradiated object 90 after the irradiated object 90 was heated for 5 minutes at an output of 150 W. (a) When there is no secondary radiation antenna, or (b) when the secondary radiation antenna 50 is placed at the center of the height of the contents 91, the upper edge of the contents 91 generates heat strongly and the temperature becomes high. In contrast, (c) when the secondary radiation antenna 50 is placed at the same height as the holder 60, heat generation at the upper edge of the contents 91 is suppressed.

As in the first embodiment, the experiment was conducted with the irradiated object 90 being a container of potato salad. The irradiated object 90 was a tapered polypropylene (PP) container with a diameter of 80 mm to 85 mm, in which potato salad was placed. Except for the position of the secondary radiation antenna 50, the other experimental conditions were the same as those shown in the first embodiment.

When the secondary radiation antenna 50 was placed at the center of the height of the potato salad, as in (b) of Figure 11, part of the edge of the top surface of the potato salad became burnt. On the other hand, when the secondary radiation antenna 50 was placed at the same height as the holder 60, as in (c) of Figure 11, no burnt occurred on the edge of the top surface of the potato salad. In this way, the experiment produced results similar to the simulation results shown in Figure 11.

As described above, by controlling the temperature distribution by adjusting the position of the secondary radiation antenna, it is possible to prevent defects such as burning of the top edge of the contents, which may occur depending on the shape of the packaging container of the irradiated object and the type of contents.

[Fourth embodiment]
A fourth embodiment will be described. Here, differences from the first embodiment will be described, and the same parts will be given the same reference numerals and their description will be omitted. FIG. 12 is a front view showing an outline of a configuration example of a microwave irradiation device 3 according to a fourth embodiment. The microwave irradiation device 3 of this embodiment is configured to irradiate microwaves to an object to be irradiated 90, such as food, to heat the inside of the object to be irradiated 90. The microwave irradiation device 3 is configured so that a plurality of objects to be irradiated are transported in succession and heated in succession.

The microwave irradiation device 3 includes a conveying device 61 as a holder 60 that conveys an irradiated object 90, which is an object to be heated and irradiated with microwaves. The conveying device 61 includes, for example, a belt 62 and a roller 63. The belt 62 is hung on the roller 63. The roller 63 is rotated by a motor (not shown) to move the belt 62 in the longitudinal direction. The irradiated object 90 is placed on the belt 62 and conveyed in a conveying direction 89 by the movement of the belt 62. A supplying device 84 is provided on the upstream side of the conveying device 61 in the conveying direction 89, which supplies the irradiated object 90 onto the belt 62 one after another. A conveying device 86 is provided on the downstream side of the conveying device 61 in the conveying direction 89, which conveys the conveyed irradiated object 90 from the belt 62.

The microwave irradiation device 3 has the same configuration as the microwave irradiation device 1 according to the first embodiment as a device for heating an irradiated object 90. The microwave irradiation device 3 includes a pair of loop antennas 41 configured to irradiate microwaves to the irradiated object 90 transported by a transport device 61. The loop antennas 41 are powered by an oscillator 10 that is electrically connected via a power supply device 20, such as a coaxial cable.

In the microwave irradiation device 3 of this embodiment, the belt 62 of the conveying device 61 is provided so as to penetrate the irradiation surface, which is the opening surface of the two loop antennas 41. In other words, the irradiated object 90 is conveyed in the conveying direction 89 so as to pass through the loop antennas 41. In addition, the microwave irradiation device 3 is provided with a pair of secondary radiation antennas 50 so as to sandwich the irradiated object 90 conveyed in the conveying direction 89 between them.

The loop antenna 41 and the secondary radiation antenna 50 are surrounded by a metal covering to block microwaves. In other words, the transport device 61 is arranged to pass through the metal housing 82, and the loop antenna 41 and the secondary radiation antenna 50 are disposed within the metal housing 82.

In the microwave irradiation device 3 of this embodiment, the object to be irradiated 90 passes through the loop antenna 41 and between the secondary radiation antennas 50, thereby achieving efficient and uniform heating of the object to be irradiated 90.

The operation of the microwave irradiation device 3 of this embodiment will be described. The oscillator 10 outputs high-frequency power according to the frequency of the microwave. The frequency is, but is not limited to, for example, 2.45 GHz, 915 MHz, or 450 MHz. The high-frequency power output from this oscillator 10 is supplied to the loop antenna 41 via the power supply device 20. Based on this power supply, the loop antenna 41 radiates microwaves in the direction of the irradiation axis 45. In this way, an electric field is formed by the loop antenna 41 and the secondary radiation antenna 50.

The conveying device 61 rotates the belt 62 by rotating the roller 63. The supplying device 84 supplies the irradiated object 90 onto the belt 62 of the conveying device 61, for example at regular intervals. The conveying device 61 conveys the supplied irradiated object 90 in the conveying direction 89 and passes it through the opening surface of the loop antenna 41 in the metal housing 82. The conveying device 61 further passes the irradiated object 90 between a pair of secondary radiation antennas 50 and passes it through the opening surface of the other loop antenna 41. Microwaves are irradiated from the loop antenna 41 and secondary radiation antenna 50 to the conveyed irradiated object 90. The irradiated object 90 is dielectrically heated by the microwaves. The heated irradiated object 90 is conveyed to the outside of the metal housing 82 by the conveying device 61. The conveying device 86 conveys the heated irradiated object 90 out of the conveying device 61.

The conveying device 61 may move the irradiated object 90 continuously, or may move the irradiated object 90 intermittently, for example, so that the irradiated object 90 stops at the midpoint between the pair of loop antennas 41. The irradiated object 90 is heated evenly by passing between the loop antenna 41 and the secondary radiation antenna 50 that radiate microwaves.

The microwave irradiation device 3 according to this embodiment can be incorporated into processing equipment for various applications, or configured in an appropriate manner. For example, when used for heat sterilization of sealed packaged food, the microwave irradiation device 1 is incorporated into an apparatus configured so that the irradiated object 90, which is the sealed packaged food, is pressurized and kept warm for the time required for sterilization. Alternatively, when used for reaction processing of materials, the irradiated object 90, which is the object to be processed, may be contained in an appropriate reaction container, and the conveying device 61 may be configured as a pipe through which the object to be processed flows, or the like.

In addition, in the microwave irradiation device 3 of this embodiment, the device configuration for heating the irradiated object 90 is similar to that of the microwave irradiation device 1 of the first embodiment, but this is not limited to this. For example, the microwave irradiation device 3 may have a device configuration similar to that of the microwave irradiation device 2 of the second embodiment. By having such a configuration, the microwave irradiation device 3 of this embodiment can also perform biased heating.

In addition, in the microwave irradiation device 3 of this embodiment, an example in which two loop antennas 41 are arranged along the radiation axis has been shown, but this is not limited to this. For example, the device may be configured such that three loop antennas 41, such as a first, second, and third loop antenna 41, are arranged along the radiation axis, a secondary radiation antenna 50 is provided between the first and second loop antennas 41, and a secondary radiation antenna 50 is also provided between the second and third loop antennas 41, so that appropriate heating is performed at two locations. The number of loop antennas 41 may be one or any number of times.

In this embodiment, an example has been shown in which the conveying device 61 changes the position of the irradiated object 90 relative to the loop antenna 41 and the secondary radiation antenna 50. However, this is not limiting, and it is also possible that the position of the loop antenna 41 or the secondary radiation antenna 50 relative to the irradiated object 90 is changed. In other words, the holder 60 may fix the position of the irradiated object 90, and the loop antenna 41 or the secondary radiation antenna 50 may move. In this way, if the relative positional relationship between the loop antenna 41 and the holder 60, or the relative positional relationship between the secondary radiation antenna 50 and the holder 60, is changed, a similar effect can be obtained.

The present invention has been described above by showing preferred embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

REFERENCE SIGNS

LIST

1, 2, 3 Microwave irradiation device 10 Oscillator 20 Power supply device 21 Coaxial cable 34 Directional antenna group 35 Secondary radiation antenna group 40 Directional antenna 41 Loop antenna 42 Conductor 43 Power supply point 45 Irradiation axis 50 Secondary radiation antenna 52 Secondary radiation antenna for heating control 60 Holder 61 Conveyor device 62 Belt 63 Roller 82 Metal case 84 Supply device 86 Carry-out device 89 Conveying direction 90 Irradiated object

Claims

A power supply device configured to be in electrical communication with the oscillator;
A directional antenna group including at least one directional antenna configured to irradiate microwaves by power supply through conduction via the power supply device;
and a secondary radiation antenna group including at least one secondary radiation antenna configured to secondarily radiate microwaves.
The microwave irradiation device of claim 1, wherein the secondary radiation antenna is insulated from the directional antenna.
the directional antenna group includes a plurality of directional antennas;
The plurality of directional antennas are arranged along the radiation axes of the plurality of directional antennas.
The microwave irradiation device according to claim 1 or 2.
The plurality of directional antennas are arranged symmetrically with respect to an irradiation position where an object to be irradiated is held.
The microwave irradiation device according to claim 3.
The secondary radiation antenna is disposed between the directional antennas constituting the directional antenna group.
The microwave irradiation device according to claim 3 or 4.
The microwave irradiation device according to any one of claims 1 to 5, wherein the secondary radiation antenna has a shape that extends along the radiation axis of the directional antenna.
The microwave irradiation device according to any one of claims 1 to 6, wherein the group of secondary radiation antennas includes a plurality of secondary radiation antennas.
The plurality of secondary radiation antennas are arranged symmetrically with respect to an irradiation position where an object to be irradiated is held.
The microwave irradiation device according to claim 7.
The plurality of secondary radiation antennas are arranged asymmetrically with respect to an irradiation position where an object to be irradiated is held.
The microwave irradiation device according to claim 7.
The microwave irradiation device according to any one of claims 1 to 9, wherein the secondary radiation antenna is configured so that its position relative to the directional antenna can be changed.
The microwave irradiation device according to claim 4, 8 or 9, further comprising a holder configured to hold the object to be irradiated at least at the irradiation position.
Further comprising a holder for holding the object to be irradiated;
At least one of the directional antenna and the holder is configured to move along an irradiation axis of the directional antenna and change a relative positional relationship between the directional antenna and the holder.
The microwave irradiation device according to any one of claims 1 to 10.
Further comprising a holder for holding the object to be irradiated;
At least one of the secondary radiation antenna and the holder is configured to move so as to change a relative positional relationship between the secondary radiation antenna and the holder.
The microwave irradiation device according to any one of claims 1 to 10.
The microwave radiating device according to claim 1 , wherein the directional antenna is a loop antenna.