JP2024037681A - Microwave irradiation method and irradiation device - Google Patents

Abstract

[Problem] To suppress uneven heating during heating by microwave irradiation. [Solution] A microwave irradiation method includes radiating microwaves from a microwave radiating unit along an irradiation axis, and changing the relative positional relationship between the object and the microwave radiating unit along the irradiation axis while the thickness direction of the object is tilted with respect to the irradiation axis. [Selected Figure] Figure 1

Description

The present invention relates to a microwave irradiation method and an irradiation device.

Generally, heating devices are known that dielectrically heat an irradiated object by irradiating the irradiated object with microwaves. In dielectric heating, the object to be irradiated may not be heated evenly for various reasons. Therefore, various efforts have been made to achieve even heating.

For example, Patent Document 1 discloses a heat treatment apparatus in which two microwave irradiation chambers are provided along a conveyance path for horizontally conveying an object to be irradiated, and the two microwave irradiation chambers are irradiated with microwaves of different frequencies. In this apparatus, waveguides are provided above and below the object to be irradiated in each of the two microwave irradiation chambers, and microwaves are irradiated from above and below the object to be irradiated, which is being transported in a horizontal direction. In the first microwave irradiation room, relatively low frequency microwaves are emitted from a waveguide arranged so that the distance between the waveguide and the object to be irradiated is the same as or shorter than the wavelength of the microwave. The object to be irradiated is irradiated. As a result, the central portion of the object to be irradiated is heated. In the second microwave irradiation chamber, relatively high frequency microwaves are irradiated onto the object to be irradiated. The waveguide placed on the upper side is placed so that the distance from the object to be irradiated is equal to or longer than the wavelength of the microwave, and the peripheral portion of the object to be irradiated is heated. The lower waveguide is arranged so that the distance to the object to be irradiated is the same as or shorter than the wavelength of the microwave, and the central portion of the object to be irradiated is heated.

Japanese Patent Application Publication No. 7-255388

The above is just an example, and there may be various methods of suppressing heating unevenness in dielectric heating. An object of the present invention is to suppress uneven heating in heating by microwave irradiation.

According to one aspect of the present invention, a microwave irradiation method includes radiating microwaves from a microwave radiating section along an irradiation axis, and a state in which a thick wall direction of an object is tilted with respect to the irradiation axis. and changing the relative positional relationship between the object and the microwave radiating section along the irradiation axis.

According to the present invention, uneven heating can be suppressed in heating by microwave irradiation.

FIG. 1 is a diagram schematically showing a configuration example of a microwave irradiation device according to an embodiment. FIG. 2 is an enlarged view schematically showing an example of the configuration of the loading conveyor and the ascending conveyor of the microwave irradiation device. FIG. 3 is a schematic diagram for explaining the first loop antenna and the second loop antenna of the microwave irradiation device. FIG. 4A is a diagram for explaining the thinner direction of the irradiated object and the target object. FIG. 4B is a diagram for explaining the thinner direction of the irradiated object and the target object. FIG. 4C is a diagram for explaining the thinner direction of the irradiated object and the target object. FIG. 4D is a diagram for explaining the thinner direction of the irradiated object and the target object. FIG. 5A is a diagram schematically showing the configuration of a test device according to a comparative example. FIG. 5B is a diagram schematically showing the configuration of a test device according to an experimental example. FIG. 6 is a diagram showing an example of a thermography image obtained through an experiment. FIG. 7 is a diagram showing the temperature of each region shown in the thermography image and the maximum temperature difference. FIG. 8 is a diagram schematically showing an outline of a configuration example of a microwave irradiation device according to a modification. FIG. 9 is a diagram schematically showing a configuration example of a microwave radiating section using a waveguide according to a modification.

One embodiment will be described with reference to the drawings. This embodiment relates to a microwave irradiation device and a microwave irradiation method using the same. The microwave irradiation device of this embodiment is configured to irradiate an object with microwaves to internally heat the object. The object to be irradiated may be, but is not limited to, food, for example. Therefore, this microwave irradiation device and the microwave irradiation method using the same can be used, for example, in the production of foods including packaged foods. The microwave irradiation device of this embodiment is configured to reduce uneven heating of the object to be irradiated. For this reason, the microwave irradiation device is configured such that the thin direction of the object to be irradiated intersects the irradiation axis along which microwaves are mainly irradiated. Further, the microwave irradiation device is configured to transport the object to be irradiated along the irradiation axis.

<Configuration of microwave irradiation device>
FIG. 1 is a diagram schematically showing an outline of a configuration example of a microwave irradiation device 1 according to the present embodiment. The microwave irradiation device 1 is configured to successively heat the irradiation target 90 that is transported by the transport device 70. The conveyance device 70 includes, for example, a carry-in conveyor 71, an ascending conveyor 72, a transfer conveyor 73, a descending conveyor 74, and an unloading conveyor 75.

The irradiation object 90 carried into the microwave irradiation apparatus 1 is conveyed horizontally by an inlet conveyor 71, which is, for example, a belt conveyor, is conveyed vertically in the upward direction by an ascending conveyor 72, and is conveyed by a transfer conveyor 73, which is, for example, a belt conveyor. It is conveyed horizontally again, vertically conveyed in the descending direction by a descending conveyor 74, and conveyed horizontally again by a discharge conveyor 75, which is a belt conveyor, for example, and is discharged. In this embodiment, the object 90 to be irradiated is heated by microwaves while being vertically conveyed by the ascending conveyor 72 and the descending conveyor 74. In this manner, in this embodiment, the transport device 70 functions as a holder that holds the irradiated object 90 at the holding position.

The ascending conveyor 72 and the descending conveyor 74 each have two rows of conveyors 72a that move up and down synchronously. FIG. 2 is an enlarged view of the carry-in conveyor 71 and the ascending conveyor 72. As shown in FIG. 2, each of the two rows of conveyors 72a of the ascending conveyor 72 is provided with a plurality of fingers 72b. The object to be irradiated 90 transported by the carry-in conveyor 71 is placed or held on the fingers 72b and is transported vertically.

Returning to FIG. 1, the explanation will be continued. The ascending conveyor 72 is provided with an antenna 40 that radiates microwaves so that the object 90 to be irradiated, which is vertically conveyed by the ascending conveyor 72, is heated by microwaves. More specifically, in the example shown in FIG. 1, the first loop antenna 41 and the second loop antenna 42 are provided so that the object 90 to be irradiated, which is vertically conveyed by the ascending conveyor 72, passes through the opening surface thereof. The portion where the first loop antenna 41 and the second loop antenna 42 are provided is covered with a metal casing 80 for shielding so that microwaves are not emitted to the outside. The number of loop antennas can be changed as appropriate. In the ascending conveyor 72, although not shown, the conveyor 72a of the ascending conveyor 72 is covered with a protective cover 82, as shown in the descending conveyor 74. In this way, the ascending heating unit 2 is mainly formed by the ascending conveyor 72, the antenna 40, and the like.

The oscillator 10 outputs microwave power according to the frequency of the microwave. The frequency is, for example, but not limited to, 200 MHz to 500 MHz, 915 MHz, or 2.45 GHz. High frequency power is supplied from the oscillator 10 to the first loop antenna 41 and the second loop antenna 42 via a coaxial cable (not shown).

The loop antenna will be explained with reference to FIG. 3. FIG. 3 is a schematic diagram showing an outline of a configuration example of the first loop antenna 41 and the second loop antenna 42. The first loop antenna 41 and the second loop antenna 42 have similar configurations. The first loop antenna 41 and the second loop antenna 42 each include, for example, a conductive wire 52 formed in an annular shape and having a length corresponding to one wavelength of the microwave to be irradiated. Both ends of the conducting wire 52 serve as power feeding points 53. For example, a coaxial cable as a power supply device is connected to the power supply point 53. The coaxial cable connects and conducts the oscillator 10 and the loop antenna. Oscillator 10 supplies high frequency power to the loop antenna via a coaxial cable. When power is supplied, a current is generated in the conducting wire 52 as an element, and the loop antenna radiates radio waves to form an electric field.

In the annular loop antenna, an aperture 54 formed by the conducting wire 52 serves as an irradiation surface 55 , and the center of the aperture 54 serves as an irradiation source 56 . That is, the irradiation source 56 at the center of the aperture 54 becomes a microwave radiator. An irradiation axis 57 is formed that passes through the irradiation source 56 and is mainly irradiated with microwaves in a direction perpendicular to the aperture surface 54, and the microwaves are radiated in both directions along the irradiation axis 57.

Note that the shape formed by the conducting wire 52 is not limited to a circular ring, but may be a ring of other shapes such as a square, a triangle, or an asymmetrical shape. In a loop antenna, the position of the irradiation source and the direction of the irradiation axis can change depending on the shape and the position of the feeding point. However, in any case, the loop antenna provides the concept that an irradiation source, which is a source from which radio waves are radiated when power is supplied, is formed on the aperture surface. Furthermore, the concept of forming an irradiation axis indicating the direction in which radio waves are mainly radiated from the irradiation source when power is supplied can be obtained.

In this embodiment, as will be described later, the microwave irradiation device 1 is configured such that the microwave irradiation axis 57 is arranged along the thin wall direction of the object 90 to be heated. Further, the microwave irradiation device 1 is configured so that the object 90 to be irradiated is conveyed along the microwave irradiation axis 57.

Since microwaves are generated by a loop antenna within the metal casing 80, the width of the metal casing 80 in the electric field amplitude direction of the microwave is configured to satisfy the following condition. Here, the electric field amplitude direction of the microwave radiated from the annular loop antenna is perpendicular to the straight line passing through the feeding point 53 and the irradiation source 56 among the directions passing through the irradiation axis 57 and perpendicular to it. This is the direction on the surface.

First, the wavelength of the microwave radiated from the loop antenna when microwave power of a predetermined frequency is fed to the loop antenna is defined as the feeding wavelength λ. The feeding wavelength λ is a free space wavelength. As mentioned above, the length of the annular conducting wire 52 constituting the loop antenna is an integer multiple or more of the feeding wavelength λ, and using the integer value at that time, for example, a one-wavelength loop antenna, a two-wavelength loop antenna, etc. is defined as

Since the loop antenna is disposed within the metal housing 80, the effective space within the metal housing 80 is narrowed by the width of the loop antenna. The apparent width L' of the metal housing 80 in the microwave electric field amplitude direction is L' where the width of the metal housing 80 in this direction is L and the width of the loop antenna in this direction is t. =L-2t. Based on this apparent width L' of the housing, the cutoff wavelength λc of the metal housing 80 is defined as λc=2L'=2(L-2t). Furthermore, the length of the conducting wire 52 of the loop antenna described above is n times the feeding wavelength λ (n is an integer, and n is the integer closest to the value obtained by dividing the length of the conducting wire 52 of the loop antenna by the feeding wavelength λ). At some point, the cutoff wavelength λc' in terms of one wavelength of the antenna is defined as λc'=λc/n.

The width L of the metal casing 80 is such that the cutoff wavelength λc′ in terms of one wavelength of the antenna and the feeding wavelength λ are
λc′＞λ
is set to satisfy. That is,
L'=L-2t>nλ/2
The width L of the metal casing 80 is set so as to satisfy the following. Numerical simulations have also confirmed that, in principle, this condition must be satisfied in order to generate microwaves using a loop antenna within the metal casing 80. If this condition is not met, the reproducibility of electric field formation decreases.

Further, the apparent width L' of the metal casing 80 must be larger than nλ/2, but if it is further increased by nλ/2, multiple peak waveforms are formed inside the metal casing 80, and the metal casing Multiple reflections of microwaves may occur within the body 80. When multiple reflections occur, multiple resonant frequencies occur, making it difficult to detect the resonant frequencies for impedance matching. Therefore,
L'=L-2t<nλ/2+nλ/2=nλ
The width L of the metal casing 80 is designed so that.

As described above, the width L of the metal casing 80 in the electric field amplitude direction of the microwave is such that the apparent width of the casing L'=L-2t is nλ/2<L'<nλ
It is designed to satisfy.

Returning to FIG. 1, the explanation will be continued. In the microwave irradiation device 1, the first loop antenna 41 and the second loop antenna 42 are arranged so that the opening surface 54, which is the irradiation surface 55 thereof, is horizontal. The microwave irradiation device 1 is configured such that the object 90 to be irradiated is conveyed through the opening surfaces 54 of the first loop antenna 41 and the second loop antenna 42 . Therefore, the portion of the ascending conveyor 72 provided with the fingers 72b moves so as to pass through the opening surfaces 54 of the first loop antenna 41 and the second loop antenna 42. The first loop antenna 41 and the second loop antenna 42 are arranged so that their irradiation axes 57 are parallel to the conveyance direction of the ascending conveyor 72, that is, vertically. The first loop antenna 41 and the second loop antenna 42 are arranged so that their irradiation axes 57 coincide.

The ascending conveyor 72 conveys the object 90 to be irradiated in an upward direction, whereas the descending conveyor 74 conveys the object 90 to be irradiated in a downward direction. In other respects, the ascending conveyor 72 and the descending conveyor 74 have the same configuration. That is, the descending conveyor 74 is provided with a first loop antenna and a second loop antenna so that the object to be irradiated 90 being conveyed passes through the opening surface thereof. The first loop antenna and the second loop antenna are provided so that their irradiation axes are vertical and parallel to the conveyance direction of the descending conveyor 74. The first loop antenna and the second loop antenna are covered by a metal housing 80. In this way, the descending heating unit 3 is formed mainly by the descending conveyor 74, the antenna 40, and the like.

In this embodiment, the object to be irradiated 90 is arranged so that the microwaves emitted along the irradiation axis 57 easily enter the object to be heated. Specifically, the microwave irradiation device 1 is configured such that the irradiation axis 57 passes through the object in the direction of its thinner wall.

Here, the thin wall direction will be explained with reference to FIGS. 4A to 4D. As shown in FIG. 4A, consider a case where the object 90 to be irradiated is a container 91 containing an object 92 to be heated. The object 92 is, for example, food. Focusing on the object 92, consider a rectangular parallelepiped 96 in which the object 92 is inscribed on all its surfaces, as shown in FIG. 4B. Among the three sets of opposing surfaces of the rectangular parallelepiped 96, the surface with the narrowest interval was defined as a thinner direction forming surface 97, and the direction perpendicular to the thinner direction forming surface 97 was defined as a thinner direction 98. According to this definition, for example, even if the container 91 is the same, if the object 92 is contained only at the bottom of the container 91, as shown in FIG. 4C, the height direction of the container 91 becomes the thin wall direction 98. As shown in FIG. 4D, when the container 91 is filled with objects 92, the thickness direction of the container 91 becomes the thinner direction 98. Moreover, the direction in which two pairs of surfaces of the three pairs of opposing surfaces of the rectangular parallelepiped 96, which are wider apart from each other than the thinner direction forming surfaces, face each other will be referred to as the thicker direction.

Returning to FIG. 1, the explanation will be continued. In this embodiment, the transport device 70 transports the object to be irradiated 90 with the thinner direction of the object to be irradiated 90 in the vertical direction. That is, the thinner direction of the irradiated object 90 is set in the vertical direction, and the irradiation axis of the antenna 40 is also set in the vertical direction. The object 90 to be irradiated is heated by microwaves whose irradiation axis is in the thinner direction while being conveyed in the vertical direction, which is the thinner direction, by the ascending conveyor 72 and the lowering conveyor 74. The ascending conveyor 72 and the descending conveyor 74 convey the irradiated object 90 in the vertical direction so as to pass through the opening of the antenna 40 .

A thermal imaging camera 31 is provided in a portion corresponding to the carry-out conveyor 75. Thermal image camera 31 is configured to photograph the heated object 90 being transported by the carry-out conveyor 75 . Based on the photographic results of the thermal image camera 31, the temperature of the irradiated object 90 is monitored.

Further, when the object 90 to be irradiated is food, steam may be emitted from the food. If such vapor is trapped in the metal housing 80 or in various parts of the microwave irradiation device 1, for example, it may have an adverse effect on the device, the irradiated object 90, and the like. In particular, when paper is used as the material for the container of the irradiated object 90, there is a risk that the steam may have an adverse effect on the container. For this reason, the microwave irradiation device 1 is preferably provided with a steam venting structure, mechanism, etc. so that the steam generated from the irradiation object 90 escapes to the outside of the microwave irradiation device 1.

<Overview of the operation of microwave irradiation equipment>
The operation of the microwave irradiation device 1 of this embodiment will be explained. In the ascending heating unit 2 and the descending heating unit 3, the microwave power output from the oscillator 10 is supplied to the first loop antenna and the second loop antenna via the coaxial cable. The first loop antenna and the second loop antenna radiate microwaves based on this feeding.

The objects 90 to be irradiated that have been carried into the microwave irradiation device 1 are successively transported by the transport device 70 to heating positions where they are irradiated with microwaves radiated from the first loop antenna and the second loop antenna. By this microwave irradiation, the irradiated object 90 is dielectrically heated one after another. The transport device 70 may be moved intermittently so that the object 90 to be irradiated stops at the heating position, or the transport device 70 may be moved continuously so that the object 90 to be irradiated passes through the heating position over a sufficient period of time. may be moved by The temperature of the heated object 90 to be irradiated is monitored using the thermal imaging camera 31 on the carry-out conveyor 75 .

[Experiment example]
In the embodiment described above, the irradiation axis 57 of the microwave radiated from the antenna 40 is aligned with the thinner direction of the object to be heated of the irradiated object 90, and the microwave is aligned with the thinner direction of the object to be heated. irradiated along. The influence of the direction of microwave irradiation on heating of the object 90 to be irradiated was evaluated through experiments.

<Method>
5A and 5B are diagrams schematically showing the configuration of the test apparatus 100 according to this experimental example. The test apparatus 100 is configured so that the object 190 to be irradiated is transported in the horizontal direction. The test apparatus 100 includes a metal casing 180 that shields electromagnetic waves. The metal housing 180 was made of aluminum material. The dimensions of the metal casing 180 were as follows: length along the transport direction was 666 mm, width perpendicular to the transport direction was 400 mm, and height was 400 mm. A conveyor 170 made of resin and having a width of 140 mm was provided so as to pass through the inside of the metal casing 180.

A first loop antenna 141 and a second loop antenna 142 were provided in the metal housing 180 so that the conveyor 170 penetrated therethrough. The first loop antenna 141 and the second loop antenna 142 are each formed from an aluminum material. The first loop antenna 141 and the second loop antenna 142 each had a circular ring shape, and had an inner diameter of 232 mm, an outer diameter of 256 mm, a width of 12 mm, and a thickness of 2 mm. The first loop antenna 141 and the second loop antenna 142 were arranged to face each other and to be at the same height with respect to the conveyor 170. The first loop antenna 141 and the second loop antenna 142 were installed so that the irradiation axis of the radiated microwave was parallel to the mounting surface of the conveyor 170. The distance between the first loop antenna 141 and the second loop antenna 142 was 450 mm.

An oscillator (not shown) was connected to the first loop antenna 141 and the second loop antenna 142 via a coaxial cable (not shown). The frequency of the output power of the oscillator was set to 450 MHz. The output power of the oscillator was fed in parallel and in phase to the first loop antenna 141 and the second loop antenna 142 via a coaxial cable. By branching off from one oscillator and feeding power to each antenna in parallel, simultaneous irradiation is possible without the output from one antenna being mistakenly recognized as a reflection by the other antenna.

By feeding power to the first loop antenna 141 and the second loop antenna 142, an irradiation source 156 is formed at the center of the first loop antenna 141 and the second loop antenna 142. Further, an irradiation axis 157 is formed from the irradiation source 156 in the normal direction to the aperture surface 154 . The distance between the first loop antenna 141 and the second loop antenna 142 is 450 mm as described above, which is slightly longer than 1/2 wavelength of the output wavelength λ = 666 mm.

A tray (150 x 115 x 30 mm) made of polypropylene (PP) was filled with 140 g of potato salad, and a sample that was not sealed after filling was designated as irradiated object 190. The object 190 to be irradiated was placed on the conveyor 170, the conveyance speed of the conveyor 170 was set to 1 mm/sec, the output was set to 150 W, and the object was heated for 6 minutes. The surface temperature of the heated potato salad was measured using a thermography camera installed at the exit of the metal casing 180. The average temperature of each area divided into three equal parts along the conveyance direction was calculated using thermal image analysis software.

In the case of the comparative example shown in FIG. 5A, the first loop antenna 141 and the second loop antenna 142 were installed so that the irradiation axis 157 was 146 mm from the bottom surface with respect to the height dimension of the metal housing 180. The object to be irradiated 190 was placed on the conveyor 170 so that the thickness direction of the object to be irradiated 190 coincided with the irradiation axis 157 and the irradiation axis 157 passed through the center of the object to be heated.

On the other hand, in the case of the experimental example shown in FIG. 5B, the first loop antenna 141 and the second loop antenna 142 were installed so that the irradiation axis 157 was 186 mm from the bottom surface with respect to the height dimension of the metal casing 180. . A resin inclined table (not shown) was installed on the conveyor 170 so that the longitudinal direction of the irradiated object 190 was at an angle of 45 degrees along the conveyance direction, and the irradiated object 190 was placed on it. In this way, the irradiation axis 157 passes diagonally through the thinner direction of the object to be irradiated 190, passes through the two opposing thinner direction forming surfaces of the object to be heated, and extends through the central portion of the object to be heated. pass through.

Further, the relationship between the wavelength of microwaves radiated from the first loop antenna 141 and the second loop antenna 142 and the size of the metal casing 180 was also separately studied. In this study, two types of metal casings 180 were prepared. One metal casing 180 had a width of 400 mm similarly to the metal casing 180 described above. The other metal housing 180 had a width of 350 mm.

Furthermore, there were two types of frequencies for the output power of the oscillator. That is, experiments were conducted using two types of metal casings 180 at two different power supply frequencies: one in which the frequency of the output power of the oscillator was 450 MHz, and the other in which the frequency was 915 MHz. Other experimental conditions were the same as in the comparative example shown in FIG. 5A.

<Results and discussion>
The experimental results are shown in FIGS. 6 and 7. FIG. 6 shows an image obtained by thermography according to a comparative example using the configuration of the test device 100 shown in FIG. 5A in the upper row, and an experimental example using the configuration of the test device 100 shown in FIG. 5B in the lower row. An image obtained by thermography is shown. FIG. 7 shows the average temperature of each of the regions AC shown in the image of FIG. 6A, and the maximum temperature difference obtained by subtracting the minimum temperature from the highest temperature among the temperatures of each of these regions.

In the case of the comparative example, heat generation was low in region B at the center of the object to be heated, and a temperature difference of 8° C. was generated with respect to region C at the end, which showed the highest temperature. In the case of the comparative example, as the microwave penetrates into the heated object along the thickness direction, power attenuation occurs inside the heated object, resulting in lower heat generation in region B of the heated object. It will be done.

On the other hand, in the case of the experimental example, the heat generation in the central region B of the object to be heated was improved, and the temperature difference with respect to the end region C, which showed the highest temperature, was suppressed to 3°C. That is, the heating uniformity was greatly improved in the experimental example compared to the comparative example. This is considered to be because, in the case of the experimental example, the microwave penetrated into the object to be heated along the thin wall direction, so that the attenuation of the electric power inside the object to be heated was suppressed.

Particularly in the case of the irradiated object 90 having a thin and long shape as used in this experiment, if the microwave irradiation axis and the thickness direction coincide, the central part of the irradiated object 90 will generate heat. It becomes difficult. Therefore, it has become clear that tilting the thickness direction with respect to the microwave irradiation axis contributes to uniform heating.

As described above, it is preferable to configure the microwave irradiation device so that the microwave irradiation axis passes through the thin-wall direction forming surface of the object to be heated, that is, along the thin-wall direction. In particular, it is one preferable aspect that the microwave irradiation axis is orthogonal to the thinner direction forming surface of the heating target as in the above-described embodiment.

Further, the experimental results using two types of power supply frequencies using the test apparatus 100 having two types of metal casings 180 with different widths were as follows. That is, when comparing the temperature of the central region of the heated object after heating, it is found that when the width of the metal casing 180 is 350 mm, the center region of the heated object There was insufficient heat generation in the central region, and the temperature in the central region was low. On the other hand, when the width of the metal housing 180 was 400 mm, the lack of heat generation at the center of the object to be heated was improved, and relatively uniform heating results were obtained including the center region.

This result is thought to be due to the following reasons. First, when the feeding frequency is 450 MHz, the feeding wavelength λ is 667 mm. The first loop antenna 141 and the second loop antenna 142 have a loop length of one wavelength. When the feeding frequency is 915 MHz, the feeding wavelength λ is 328 mm. The first loop antenna 141 and the second loop antenna 142 have a loop length equivalent to two wavelengths.

As shown in FIG. 5A, in this experiment, the feeding points of the first loop antenna 141 and the second loop antenna 142 were provided vertically above. In the case of such a loop antenna arrangement, the electric field amplitude direction of the microwave radiated from the loop antenna is perpendicular to and horizontal to the irradiation axis 157. The two types of metal casings 180 have different widths L in the horizontal direction.

Further, the width t of the first loop antenna 141 and the second loop antenna 142 installed in the metal housing 180 is 12 mm. Therefore, the apparent width L' of the metal casing 180 having a width L of 350 mm is L'=350 mm−12 mm×2=326 mm. Therefore, the cutoff wavelength λc of the metal casing 180 having a width of 350 mm is λc=326 mm×2=652 mm. Further, the apparent width L' of the metal casing 180 having a width L of 400 mm is L'=400 mm−12 mm×2=376 mm. Therefore, the cutoff wavelength λc of the metal casing 180 with a width of 400 mm is λc=376 mm×2=752 mm.

When the feeding frequency is 450 MHz and the feeding wavelength λ is 667 mm, the first loop antenna 141 and the second loop antenna 142 have a loop length of one wavelength. The cutoff wavelength λc' in terms of one wavelength of the antenna of the housing 180 is λc'=652 mm. That is, at this time, λc'<λ, and it is considered that microwaves were not appropriately generated by the first loop antenna 141 and the second loop antenna 142 within the metal casing 180. For this reason, it is considered that the temperature in the central region of the object to be heated became low.

On the other hand, the cutoff wavelength λc' of the metal casing 180 having a width of 400 mm in terms of one wavelength of the antenna is 752 mm. That is, at this time, λc′>λ, and it is considered that microwaves are appropriately generated by the first loop antenna 141 and the second loop antenna 142 within the metal casing 180. For this reason, it is thought that the temperature in the central region of the object to be heated became relatively high.

When the feeding frequency is 915 MHz and the feeding wavelength λ is 328 mm, the first loop antenna 141 and the second loop antenna 142 have a loop length of two wavelengths, so they are made of metal with a width of 350 mm. The cutoff wavelength λc' in terms of one wavelength of the antenna of the housing 180 is λc'=λc/2=326 mm. That is, at this time, λc'<λ, and it is considered that microwaves were not appropriately generated by the first loop antenna 141 and the second loop antenna 142 within the metal casing 180. For this reason, it is considered that the temperature in the central region of the object to be heated became low.

On the other hand, the cutoff wavelength λc' of the metal casing 180 having a width of 400 mm in terms of one wavelength of the antenna is λc'=λc/2=376 mm. That is, at this time, λc′>λ, and it is considered that microwaves are appropriately generated by the first loop antenna 141 and the second loop antenna 142 within the metal casing 180. For this reason, it is thought that the temperature in the central region of the object to be heated became relatively high.

The above relationships can be summarized as shown in Table 1 below.

[Modified example]
In the embodiment shown in FIG. 1, two antennas 40 are provided on each of the ascending conveyor 72 and the descending conveyor 74, and the object 90 to be irradiated is heated when it passes through these antennas 40. The number of antennas 40 that the object 90 passes through may be any number. For example, the ascending conveyor 72 and the descending conveyor 74 may be longer in the vertical direction, and more antennas 40 may be provided on one ascending conveyor 72 or descending conveyor 74.

Alternatively, a unit having the same configuration as the unit including the ascending conveyor 72 or the descending conveyor 74, the antenna 40, etc. may be further provided. By increasing the number of units, the power burden on each power supply cable can be reduced. Furthermore, in order to adjust the heating conditions, each unit may be configured to have a different antenna configuration such as antenna size and arrangement, output, etc.

Moreover, a plurality of configurations similar to the microwave irradiation device 1 shown in FIG. 1 may be arranged in parallel. That is, as shown in FIG. 8, the microwave irradiation device 300 includes a first unit 301, a second unit 302, and a third unit 303 having the same configuration as the microwave irradiation device 1 shown in FIG. It may have a configuration arranged in parallel. Each unit includes an ascending heating unit 311 having an ascending conveyor 372 and an antenna 340 disposed thereon, and a descending heating unit 312 having a descending conveyor 374 and an antenna 340 disposed thereon. A thermal imaging camera 330 may be provided in each unit. By providing each unit in parallel, the processing capacity of the microwave irradiation device 300 as a whole can be improved.

Furthermore, the distribution of the electric field formed by feeding power to a loop antenna, the resonant frequency of the system, etc., are affected by the presence of conductors such as unpowered loop antennas, metal plates, metal pieces, etc. placed within the electric field. It can change. Therefore, an appropriate conductor may be placed in, for example, the metal casing 80 of the microwave irradiation device 1, for example, in order to change the electric field distribution or for impedance matching.

In the embodiment described above, an example was shown in which the object 90 to be irradiated is transported along the irradiation axis 57 of the microwave radiated by the antenna 40. If the relative positional relationship between the irradiated object 90 and the antenna 40 changes along the irradiation axis 57, the same phenomenon will occur, so the antenna 40 is moved along the irradiation axis 57 without moving the irradiated object 90 It may be moved along. However, in general, it is often easier to move the irradiated object 90 than to move the antenna 40.

In the above embodiments, an example was shown in which a loop antenna was used as a microwave radiation source. The microwave radiation source is not limited to this. For example, various types of antennas may be used that are supplied with power from an oscillator through conduction through a power supply device and thereby radiate microwaves along the irradiation axis from an irradiation source within the irradiation surface of the antenna. In addition to loop antennas, for example, microstrip antennas are known as such antennas.

In addition to the directional antenna described above, for example, as shown in FIG. 9, microwaves are transmitted from a microwave irradiation source 242 such as a magnetron using a waveguide 244. The object to be irradiated 90 may be irradiated with the microwaves emitted from the wave emitting section 246. At this time, the irradiation axis 248 along which the microwave irradiation unit 246 irradiates the irradiation object 90 is along the thinner direction of the irradiation object 90, and the irradiation object 90 is conveyed along the irradiation axis 248. In this case, the effect of uniformly heating the object to be irradiated can be obtained, similar to the above-described embodiment.

[Applications of microwave irradiation equipment]
The microwave irradiation device 1 according to each of the embodiments described above can be incorporated into processing devices for various uses or configured in an appropriate manner. For example, when used for heat sterilization of hermetically packaged food, the microwave irradiation device 1 may be used to apply pressure to the irradiated object 90, which is the hermetically packaged food, or for a period of time required for sterilization. It will be incorporated into a device that is configured to maintain heat. In addition, the microwave irradiation device 1 is capable of storing food in a packaging container and sealing the packaging container to produce a packaged food, and using the microwave irradiation device 1 to heat this packaging container food. It can be used in the production of foods containing.

Further, the object 92 to be heated by the microwave irradiation device 1, that is, the object 90 to be irradiated with microwaves by the microwave irradiation device 1 is not limited to food for the purpose of sterilization. The target object 92 is a frozen food as an object to be thawed, and the microwave irradiation device 1 may be used for thawing the frozen food. Furthermore, the object to be heated 92 is not limited to food. For example, the object 92 may be cryopreserved cells, and the microwave irradiation device 1 may be used to thaw the cryopreserved cells. Further, the target object 92 is various reactive substances that are gasified, synthesized, decomposed, etc. by heating, and the microwave irradiation device 1 may be used for gasification, synthesis, decomposition, etc. of various reactive substances. . In this way, there can be various types of irradiated objects 90 to which the microwave irradiation device 1 irradiates microwaves. It may be.

Although the present invention has been described above by showing preferred embodiments, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the present invention. Nor.

1: Microwave irradiation device 2: Rising heating unit, 3: Falling heating unit 10: Oscillator, 20: Power supply device, 31: Thermal image camera, 80: Metal casing, 82: Protective cover 40: Antenna, 41: First Loop antenna, 42: Second loop antenna 52: Conductor, 53: Feeding point, 54: Opening surface, 55: Irradiation surface, 56: Irradiation source, 57: Irradiation axis 70: Conveyance device, 71: Carrying-in conveyor, 72: Elevation Conveyor, 72a: Conveyor, 72b: Finger, 73: Transfer conveyor, 74: Descending conveyor, 75: Unloading conveyor 90: Irradiated object, 91: Container, 92: Target object, 96: Rectangular parallelepiped, 97: Thin wall direction forming surface , 98: Thin wall direction

Claims (14)

radiating microwaves along an irradiation axis from a microwave radiating section;
changing the relative positional relationship between the object and the microwave radiating section along the irradiation axis in a state where the thickness direction of the object is inclined with respect to the irradiation axis. Irradiation method. The irradiation method according to claim 1, wherein changing the positional relationship includes changing the positional relationship in a state where the irradiation axis passes through two thinning direction forming surfaces regarding the target object. Claim: 2. Emitting the microwave includes feeding power from an oscillator to the antenna by conduction through a power feeding device, and radiating the microwave from an irradiation source in an irradiation surface of the antenna along the irradiation axis. The irradiation method according to 1 or 2. The antenna is a loop antenna,
4. The irradiation method according to claim 3, wherein changing the positional relationship includes causing the object to pass through an aperture of the loop antenna. The irradiation method according to claim 1 or 2, wherein changing the positional relationship includes moving at least one of the target object and the microwave radiating section in a vertical direction. A heating method comprising heating the object by irradiating the object with the microwave using the irradiation method according to claim 1 or 2. A method for manufacturing a food product, comprising heating the object, which is a food product, by the heating method according to claim 6. a microwave radiator configured to radiate microwaves along an irradiation axis;
and a conveying device configured to move the target object along the irradiation axis in a state where the thickness direction of the target object is inclined with respect to the irradiation axis. The microwave irradiation device according to claim 8, wherein the conveyance device is configured to convey the object in a vertical direction. According to claim 8 or 9, the conveyance device is configured to move the object along the irradiation axis in a state where the irradiation axis passes through two thinner direction forming surfaces regarding the object. The microwave irradiation device described. The microwave according to claim 8 or 9, wherein the microwave radiating section includes a loop antenna configured to radiate microwaves by supplying power by conduction via a power supply device configured to conduct with the oscillator. Wave irradiation device. The microwave irradiation device according to claim 11, wherein the conveyance device is configured to cause the object to pass through an aperture of the loop antenna. a microwave radiator that radiates microwaves along an irradiation axis provided in the vertical direction;
A microwave irradiation device comprising: a conveying device that conveys a target object in a vertical direction along the irradiation axis. The microwave radiating unit includes a loop antenna configured to radiate microwaves by supplying power by conduction via a power supply device configured to conduct with the oscillator,
The conveyance device is configured to cause the object to pass through an aperture of the loop antenna.
The microwave irradiation device according to claim 13.

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