Microwave irradiation device

Abstract

To provide a microwave irradiation device capable of suppressing generation of uneven heating.SOLUTION: A microwave irradiation device 1 includes a conveyance device 60 for carrying an irradiated object 90 in the conveyance direction 91; a power supply fixture 20 configured to be conducted with an oscillator 10; and a plurality of antennas 40 with directivity configured to irradiate microwaves from an irradiation source 44 within an irradiation surface 42 by power supply by conduction through the power supply fixture 20 and an antenna group 30 in which the plurality of antennas 40 are arranged along the conveyance direction 91.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The present invention relates to a microwave irradiation device.

Background Art

[0002] Generally, a heating device that dielectrically heats an object to be irradiated by irradiating the object with microwaves is known. In dielectric heating, the object to be irradiated may not be heated evenly for various reasons. Therefore, various measures have been taken for uniform heating.

[0003] For example, Patent Document 1 discloses a microwave heating device in which a microwave reaction vessel containing an object to be irradiated is disposed in a conductive storage container, and a plurality of dipole antennas are evenly disposed so as to surround the microwave reaction vessel. In this microwave heating device, each part is arranged such that the distance between each antenna and the inner wall of the conductive storage is approximately 1 / 4 of the wavelength of the microwave to be irradiated in the direction of viewing each dipole antenna from the microwave reaction vessel. With such an arrangement, the microwave radiated from the dipole antenna is directed toward the microwave reaction vessel. As a result, the object to be irradiated in the microwave reaction vessel is heated evenly.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The above is an example, and there can be various methods for suppressing uneven heating in dielectric heating. An object of the present invention is to suppress uneven heating in a microwave irradiation device.

Means for Solving the Problems

[0006] According to one aspect of the present invention, the microwave irradiation device comprises a transport device for transporting an object to be irradiated in a transport direction, a power supply device configured to be electrically connected to an oscillator, and a group of directional antennas configured to irradiate microwaves from an irradiation source in the irradiation surface by power supply via the power supply device, wherein the group of antennas is arranged along the transport direction. [Effects of the Invention]

[0007] According to the present invention, uneven heating can be suppressed in a microwave irradiation device. [Brief explanation of the drawing]

[0008] [Figure 1A] Figure 1A is a schematic front view showing an example of the configuration of a microwave irradiation apparatus according to the first embodiment. [Figure 1B] Figure 1B is a schematic plan view showing an example of the configuration of a microwave irradiation apparatus according to the first embodiment. [Figure 2] Figure 2 is a schematic diagram showing an example of a loop antenna configuration. [Figure 3A] Figure 3A is a schematic diagram illustrating the orientation of the antenna. [Figure 3B] Figure 3B is a schematic diagram illustrating the orientation of the antenna. [Figure 4] Figure 4 is a schematic plan view showing an example configuration of a microwave irradiation apparatus according to the second embodiment. [Figure 5] Figure 5 is a schematic diagram illustrating the magnitude of the effective electric field value according to the position along the directional irradiation axis in an example where antennas are installed facing each other. [Figure 6] Figure 6 is a schematic plan view showing an example configuration of a microwave irradiation apparatus according to the third embodiment. [Figure 7] Figure 7 is a schematic diagram showing an example of the configuration of the test apparatus used in Experimental Example 1. [Figure 8] Figure 8 shows an example of test results when the object to be heated was placed vertically and heated, according to Experimental Example 1. [Figure 9] FIG. 9 is a diagram showing an example of a test result of heating an object to be heated according to Experimental Example 1 while placing it horizontally. [Figure 10] FIG. 10 is a diagram showing an outline of a configuration example of a test apparatus used in Experimental Examples 2, 3, and 6. [Figure 11] FIG. 11 shows a photograph of a food model after heating with an output of 150 W using a test apparatus in Experimental Example 2. [Figure 12] FIG. 12 shows a photograph of a food model after heating with an output of 250 W using a commercial microwave oven as a comparative experiment. [Figure 13] FIG. 13 is a diagram showing an outline of the implementation status of Experimental Example 3. [Figure 14] FIG. 14 shows a photograph of a food model after heating in Experimental Example 3. [Figure 15A] FIG. 15A is a diagram showing the thermo - coupled analysis result according to Experimental Example 4 in a perspective view. [Figure 15B] FIG. 15B is a diagram showing the thermo - coupled analysis result according to Experimental Example 4 in a cross - sectional view. [Figure 16A] FIG. 16A is a diagram showing the thermo - coupled analysis result when the distance is 166.5 mm according to Experimental Example 5. [Figure 16B] FIG. 16B is a diagram showing the thermo - coupled analysis result when the distance is 56.5 mm according to Experimental Example 5. [Figure 17] FIG. 17 is a diagram showing the results of temperature measurement of the central part (solid line) and the outer peripheral part (dashed line) of the object to be heated according to Experimental Example 6.

MODE FOR CARRYING OUT THE INVENTION

[0009] [First Embodiment] A first embodiment will be described with reference to the drawings. This embodiment relates to a microwave irradiation device. The microwave irradiation device of this embodiment is configured to irradiate a microwave to an irradiated object and internally heat the irradiated object. The irradiated object is not limited to this, but for example, it is food. 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 has a conveyance device, and a plurality of irradiated objects are successively conveyed and successively heated. A plurality of directional antennas that emit microwaves are arranged along the conveyance direction.

[0010] 〈Device Configuration〉 FIG. 1A is a front view schematically showing an outline of a configuration example of the microwave irradiation device 1 according to this embodiment, and FIG. 1B is a plan view schematically showing an outline of a configuration example of the microwave irradiation device 1 according to this embodiment. As shown in these figures, the microwave irradiation device 1 includes a conveyance device 60 that conveys an irradiated object 90 that is a heating target and is irradiated with microwaves. The conveyance device 60 includes, for example, a belt 61 and rollers 62. The belt 61 is hung on the rollers 62. The rollers 62 are rotated by a motor (not shown) and move the belt 61 in the longitudinal axis direction. The irradiated object 90 is placed on the belt 61 and conveyed in the conveyance direction 91 by the movement of the belt 61. On the upstream side in the conveyance direction 91 of the conveyance device 60, a supply device 84 for successively supplying the irradiated object 90 onto the belt 61 is provided. On the downstream side in the conveyance direction 91 of the conveyance device 60, a carry-out device 86 for carrying out the conveyed irradiated object 90 from the belt 61 is provided.

[0011] The microwave irradiation device 1 includes an antenna group 30 having a plurality of antennas 40 configured to irradiate microwaves onto an object to be irradiated 90 being transported by a transport device 60. The plurality of antennas 40 are arranged along the transport direction 91. Each antenna 40 is a directional antenna, such as a loop antenna or a patch antenna. That is, each antenna 40 has an irradiation surface 42 and is configured to irradiate microwaves from an irradiation source 44 within the irradiation surface 42 in the direction of a directional irradiation axis 45. The direction of the directional irradiation axis 45 of each antenna 40 is directed toward the object to be irradiated 90 being transported by the transport device 60. Each antenna 40 is powered by an oscillator 10 that is conductive via a power supply device 20, such as a coaxial cable.

[0012] The antenna group 30 is surrounded by metal to shield it from microwaves. Specifically, the transport device 60 is installed either passing through the metal housing 82 or inside the metal housing 82, and the antenna group 30 is located inside the metal housing 82.

[0013] Regarding antenna 40, a loop antenna will be described as an example. Figure 2 is a schematic diagram showing an example configuration of a loop antenna 51. The loop antenna 51 includes, for example, a conductor 52 formed in an annular shape with a length equal to one wavelength of the microwave to be irradiated. Both ends of the conductor 52 are feed points 53. A coaxial cable 21, for example, is connected to the feed points 53 as a feeding device 20. The coaxial cable 21 connects the oscillator 10 and the loop antenna 51, creating conductivity. The oscillator 10 supplies high-frequency power to the loop antenna 51 via the coaxial cable 21. When fed, a current is generated in the conductor 52 as an element, and the loop antenna 51 radiates radio waves and forms an electric field.

[0014] In the annular loop antenna 51, the aperture 54 formed by the conductor 52 becomes the irradiation surface 42, and the center of the aperture 54 becomes the irradiation source 44. A directional irradiation axis 45 is formed passing through the irradiation source 44 and perpendicular to the aperture 54, and microwaves are radiated in both directions along the directional irradiation axis 45. Note that the shape formed by the conductor 52 is not limited to an annular shape; it may also be an annular shape such as a square.

[0015] The orientation of the antenna 40 will be explained further. Figures 3A and 3B are schematic diagrams illustrating the orientation of the antenna 40. In this embodiment, the antenna 40 is positioned such that its directional irradiation axis 45 is parallel to the surface of the belt 61 of the transport device 60 on which the object to be irradiated 90 is placed, as shown in Figure 3A, for example. Alternatively, as shown in Figure 3B at least, the antenna 40 is positioned such that its directional irradiation axis 45 does not intersect with any microwave-reflecting structures among the structures constituting the transport device 60.

[0016] The microwaves emitted from the directional antenna 40 spread to some extent, as shown as the diffuse irradiation axis 46 in Figures 3A and 3B, but their irradiation angle is relatively narrow, forming an electric field where the intensity is strongest along the directional irradiation axis 45. Because the directional irradiation axis 45 does not intersect with structures that reflect microwaves, strong reflected waves are not generated. As a result, standing waves that can be generated by interference between incident and reflected waves are not generated. If standing waves are generated by interference between strong incident and reflected waves, the electric field strength will differ significantly, especially at the antinodes and nodes of the standing waves, which can cause uneven heating of the irradiated object 90. In the microwave irradiation device 1 of this embodiment, such standing waves are not generated, thus preventing uneven heating of the irradiated object 90.

[0017] Furthermore, the microwave-reflecting structure mentioned above refers to a structure that reflects microwaves to such an extent that standing waves are generated, resulting in the uneven heating described above.

[0018] <Operation> The operation of the microwave irradiation device 1 of this embodiment will now be described. The oscillator 10 outputs high-frequency power corresponding to the microwave frequency. The frequency is not limited to this, but for example, it could be 2.45 GHz or 915 MHz, or 450 MHz. The high-frequency power output from the oscillator 10 is supplied to the antenna 40 via the power supply device 20. Based on this power supply, the antenna 40 irradiates microwaves in the direction of the directional irradiation axis 45.

[0019] The conveying device 60 rotates the belt 61 by the rotation of the rollers 62. The supply device 84 supplies the objects to be irradiated 90 onto the belt 61 of the conveying device 60, for example, at regular intervals. The conveying device 60 conveys the supplied objects to be irradiated 90 in the conveying direction 91, passing in front of multiple antennas 40 inside the metal housing 82. Microwaves are irradiated from the antennas 40 to the objects to be irradiated 90 as they pass in front of the antennas 40. These microwaves cause dielectric heating of the objects to be irradiated 90. The heated objects to be irradiated 90 are conveyed by the conveying device 60 to the outside of the metal housing 82. The discharge device 86 discharges the heated objects to be irradiated 90 from the conveying device 60.

[0020] As described above, in this embodiment, a directional antenna 40 is used in the antenna group 30, and the directional irradiation axis 45 is designed so as not to intersect with the microwave-reflecting structure of the transport device 60. Therefore, no standing waves originating from reflected waves are generated with respect to the irradiated microwaves. As a result, the irradiated object 90 is heated uniformly.

[0021] As heating devices using dielectric heating, for example, multimode heating devices that heat the object to be heated by reflecting microwaves within a metal casing are known. Also known are single-mode heating devices in which the object to be heated is placed inside a waveguide that carries microwaves. In such devices, microwave reflection is intentionally utilized. That is, standing waves are intentionally created by reflection, and dielectric heating is performed by these standing waves. However, in such standing waves, differences in electric field strength occur depending on the location, which are particularly pronounced at the antinodes and nodal positions. This unevenness in electric field strength causes uneven heating of the object to be heated. In the microwave irradiation device 1 of this embodiment, since it is adjusted so that standing waves are not generated, uniform heating can be achieved.

[0022] Furthermore, heating devices using waveguides tend to be large, especially at low frequencies, as the waveguide itself becomes larger. Also, when combining multiple types of heating devices to achieve uniform heating, the overall device tends to become larger. In contrast, the microwave irradiation device 1 of this embodiment does not use waveguides and does not require the combination of multiple types of devices, making it easy to miniaturize the device. Also, because it does not use waveguides, it is easy to use relatively low-frequency microwaves. By lowering the frequency, the power half-depth can also be increased.

[0023] In the above embodiment, the example given was that the object to be irradiated 90 is placed on the belt 61 of the transport device 60 when microwave irradiation occurs, but the invention is not limited to this. The object to be irradiated 90 may be configured to be placed on a stationary platform. In this case as well, it is preferable that the antenna 40 is positioned so that the directional irradiation axis 45 does not intersect with the structure constituting the platform. In this case as well, the generation of standing waves due to reflected waves is suppressed, and uneven heating due to dielectric heating is suppressed.

[0024] The microwave irradiation device 1 according to this embodiment can be incorporated into processing devices for various applications or configured in an appropriate manner. For example, when used for heat sterilization of sealed food products, the microwave irradiation device 1 would be incorporated into a device configured to pressurize the irradiated object 90, which is the sealed food product, or to keep it warm for the time necessary for sterilization. Alternatively, for use in reaction processing of materials, the irradiated object 90, which is the object to be processed, may be housed in a suitable reaction vessel, or the conveying device 60 may be configured as a pipe through which the object to be processed flows.

[0025] [Second Embodiment] A second embodiment will now be described. Here, the differences from the first embodiment will be explained, and identical parts will be denoted by the same reference numerals and their descriptions will be omitted.

[0026] Figure 4 is a schematic plan view showing an example of the configuration of the microwave irradiation device 2 of the second embodiment. In this figure, the oscillator 10 and the power supply device 20 are not shown. In the microwave irradiation device 1 of the first embodiment shown in Figure 1B, the antenna 40 is arranged on one side of the transport device 60, whereas in the microwave irradiation device 2 of the second embodiment shown in Figure 4, the antennas 40 are arranged on both sides of the transport device 60. Therefore, in the microwave irradiation device 1 of the first embodiment shown in Figure 1B, microwaves are irradiated onto the object to be irradiated 90 from one side, whereas in the microwave irradiation device 2 of the second embodiment shown in Figure 4, microwaves are irradiated onto the object to be irradiated 90 from both sides. In particular, in the microwave irradiation device 2 of the second embodiment, the antennas 40 are provided facing each other with the transport device 60 in between, and the directional irradiation axes 45 of the opposing antennas 40 overlap.

[0027] Figure 5 is a schematic diagram showing the magnitude of the effective electric field value according to the position of the opposing antennas 40 along the directional irradiation axis 45. The antennas 40 are positioned opposite each other at the first position P1 and the second position P2. Therefore, the transport device 60 passes between the first position P1 and the second position P2, and the object to be irradiated 90 passes through it. As shown in Figure 5, the microwave irradiation device 2 of this embodiment is configured such that the effective electric field value is approximately constant between the first position P1 and the second position P2.

[0028] According to this embodiment, since microwaves are irradiated from both sides in a direction that crosses the transport direction 91, even if the size of the object to be irradiated 90 in the direction that crosses the transport direction 91 is relatively large, it can be heated from both sides, and uniform heating can be achieved. This effect can be obtained as long as microwaves are irradiated from both sides to the object to be irradiated 90, so the antennas 40 do not necessarily have to be facing each other.

[0029] In this embodiment, the microwave irradiation device 2 is further configured such that the antennas 40 and antennas 40 face each other, and the electric field strength due to microwaves is substantially constant in the direction traversing the transport direction 91. With this configuration, the heating of the object to be irradiated 90 can be performed more uniformly. A constant electric field strength between the opposing antennas 40 means that the electric field strength is constant to the extent that the requirement for uniform heating of the object to be irradiated 90 is met. According to this embodiment, the heating of the object to be irradiated 90 can be performed more uniformly.

[0030] <Variations of heating methods> Although the microwave irradiation device 2 of this embodiment was described above as an example in which microwaves are irradiated evenly onto the object to be irradiated 90 from both sides by two opposing antennas 40 to heat the object to be irradiated 90, the heating method is not limited to this.

[0031] Experiments have shown that when microwaves are irradiated evenly to both sides of the object 90 using antennas 40 positioned on both sides of the object 90, the center of the object 90 may be heated in particular, while when microwaves are irradiated unevenly to one side of the object 90, the outer periphery of the object 90 may be heated in particular. Therefore, by combining even irradiation from both sides and uneven irradiation from one side, the center and outer periphery of the object 90 may be heated respectively, resulting in uniform heating of the entire object 90, or it may be intentionally heated unevenly.

[0032] For example, the first irradiation may be uniform microwave irradiation, and the second and third irradiations may be uneven microwave irradiation. That is, with the object to be irradiated 90 positioned equidistant from two antennas 40 between a pair of antennas 40, the following irradiations may be performed: In the first irradiation, microwaves of equal intensity may be irradiated onto the object to be irradiated 90 from the two antennas 40. In the second irradiation, microwaves may be irradiated onto the object to be irradiated 90 from one of the antennas 40. In the third irradiation, microwaves may be irradiated onto the object to be irradiated 90 from the other antenna 40. By a combination of these first, second, and third irradiations, the object to be irradiated 90 can be heated uniformly. Alternatively, only the first and second irradiations may be performed.

[0033] The first, second, and third irradiations may be performed by the same pair of antennas 40 as described above, or by multiple pairs of antennas 40. When multiple pairs of antennas 40 are used, for example, among the multiple pairs of antennas 40 arranged on both sides of the transport device 60, in some cases microwaves with equal irradiation intensity may be irradiated from two opposing antennas 40, in some cases microwaves may be irradiated from one side of the antenna 40, and in some cases microwaves may be irradiated from the opposite side of the antenna 40. In this case, the first, second, and third irradiations can be performed by transporting the object to be irradiated 90 between these antennas 40 by the transport device 60. In this case, in the part where the first irradiation is performed, a pair of antennas 40 may be provided facing each other, while in the part where the second and third irradiations are performed, the antennas 40 may be provided on only one side, as in the microwave irradiation device 1 of the first embodiment.

[0034] Furthermore, in the second and third irradiations, it is sufficient for uneven microwave irradiation to occur, so the irradiation intensity may differ between one of the opposing pair of antennas 40. Alternatively, the object to be irradiated 90 may be moved closer to one antenna or closer to the other between a pair of antennas 40 with equal or unequal irradiation intensities.

[0035] In order to change the distance between the object to be irradiated 90 and the antenna 40, the transport device 60 may be configured to move the object to be irradiated 90 in a direction perpendicular to the transport direction. Alternatively, the transport device 60 and the antenna 40 may be arranged such that the distance between each antenna 40 and the antenna 40 is different.

[0036] Modifications of the heating method described herein may be performed using an irradiation device different from the microwave irradiation device 2 of the second embodiment. For example, the antennas do not have to be arranged along the transport device. For example, the irradiation device may have only two opposing antennas and may not have a transport device. Alternatively, the transport device may be configured to move the object to be irradiated between the two opposing antennas.

[0037] [Third Embodiment] A third embodiment will now be described. Here, the differences from the first embodiment will be explained, and identical parts will be denoted by the same reference numerals and their descriptions will be omitted.

[0038] Figure 6 is a schematic plan view showing an example of the configuration of the microwave irradiation device 3 of the third embodiment. In this figure, the oscillator 10 and the power supply device 20 are omitted from the illustration. In the microwave irradiation device 3 of this embodiment, a loop antenna 51 is used as the antenna 40 that constitutes the antenna group 30. As described above, in the loop antenna 51, both the front and back sides of the aperture surface 54 become the irradiation surface 42, and microwaves are irradiated in both directions along the directional irradiation axis 45. In the microwave irradiation device 3 of the third embodiment, a first transport device 71 and a second transport device 72, corresponding to the transport device 60 of the first embodiment, are provided on both sides of the multiple loop antennas 51 arranged in a row, forming a transport device group 70.

[0039] According to this embodiment, microwaves radiated from one loop antenna 51 to both sides are irradiated to the object to be irradiated 90 transported by the first transport device 71 and the object to be irradiated 90 transported by the second transport device 72, respectively, so even with a simple configuration, the microwave irradiation device 3 has good energy efficiency.

[0040] Furthermore, in this embodiment as well, antennas may be provided on both sides of the conveying device, similar to the second embodiment. Loop antennas 51 may be provided on both sides of the conveying device, and multiple conveying devices may be arranged in parallel.

[0041] [Experimental Example 1] The uniformity of heating by the microwave irradiation device according to the above embodiment was evaluated using a container of potato salad as the object to be heated.

[0042] <method> Figure 7 shows a schematic example of the configuration of the test apparatus 100 used for evaluation. The test apparatus 100 includes an oscillator 110, two loop antennas 140 and a food holding table 166 arranged inside a metal housing 182.

[0043] The oscillation frequency of the oscillator 110 was set to 450 MHz. For the loop antenna 140, a rectangular loop antenna made of aluminum with a circumference of one wavelength (λ = 666 mm) was used. Two loop antennas 140 were arranged so that their aperture faces faced each other and the directional irradiation axis 145 was parallel to the food holding stand 166. The distance between the two loop antennas 140 was set to λ / 4 = 166.5 mm. Power was supplied to the loop antennas 140 using in-phase feeding. For the food holding stand 166, a polyethylene (PE) plate with a thickness of 5 mm was used. The food holding stand 166 was positioned so as to penetrate the two loop antennas 140.

[0044] The object to be heated 190 consisted of 150 g of potato salad served in a polypropylene (PP) tray measuring 115 mm in length, 80 mm in width, and 20 mm in depth. The object to be heated 190 was positioned in the center between two loop antennas 140 on the food holding stand 166. The object to be heated 190 was positioned in two ways: vertically, with the length of the tray perpendicular to the directional irradiation axis 145, and horizontally, with the length of the tray parallel to the directional irradiation axis 145. Temperature measurement was performed by attaching multiple thermolabels (registered trademark) to the surface of the potato salad. Temperature measurement was performed after heating at an output of 150 W for 5 minutes.

[0045] Furthermore, a numerical analysis was performed on the electric field strength formed between the two loop antennas 140.

[0046] <result> Numerical simulations of the electric field strength revealed that a uniform electric field, as shown in Figure 5, was obtained between the two loop antennas 140.

[0047] Figure 8 shows the test results when the object to be heated 190 was placed vertically. Thermolabels (a), (b), and (c) placed along the directional irradiation axis 145, that is, along the line connecting the midpoints of the two long sides of the tray, all showed 90°C. On the other hand, thermolabels (d) and (e) placed at a position away from the directional irradiation axis 145, that is, near the center of the short side of the tray, all showed less than 50°C.

[0048] Figure 9 shows the test results when the object to be heated 190 was placed horizontally. Thermolabels (f), (g), and (h) placed along the directional irradiation axis 145, that is, along the line connecting the midpoints of the two short sides of the tray, all showed 100°C. On the other hand, thermolabels (i) and (j) placed at a position away from the directional irradiation axis 145, that is, near the center of the long side of the tray, all showed 80°C.

[0049] The results shown in Figures 8 and 9 clearly demonstrate that uniform heating is possible in a short time along the directional irradiation axis 145. In both cases, a temperature gradient was observed where the temperature decreased as the distance from the directional irradiation axis 145 increased, and the heating efficiency was higher on the directional irradiation axis 145 than on the diffuse irradiation axis. It was revealed that by positioning the highly efficient directional irradiation axis 145 so as not to intersect with structures such as the food holding table 166 (corresponding to the conveying device 60 in the above embodiment), heating is possible while suppressing the generation of standing waves due to microwave reflection and energy loss due to absorption.

[0050] [Experimental Example 2] The heating characteristics of the microwave irradiation device according to the above embodiment were further evaluated using the object to be heated as a thermal indicator gel, which serves as a food model.

[0051] <method> Figure 10 shows a schematic example of the configuration of the test apparatus 200 used for evaluation. This test apparatus 200 corresponds to the configuration of the part of the microwave irradiation apparatus 2 of the second embodiment described with reference to Figure 4, which includes a pair of opposing antennas 40. The configuration of the test apparatus 200 was as follows.

[0052] The test apparatus 200 is equipped with a metal housing 282 that shields against electromagnetic waves. The metal housing 282 is made of aluminum and has dimensions of 500 mm in width, 350 mm in length, and 400 mm in height. A mounting base 266 is horizontally installed inside the metal housing 282. The mounting base 266 is made of glass epoxy and has dimensions of 331 mm in width and 5 mm in thickness. A first loop antenna 240a is attached to one end of the mounting base 266 in the width direction via a first bracket 249a, and a second loop antenna 240b is attached to the other end of the mounting base 266 in the width direction via a second bracket 249b. The first bracket 249a and the second bracket 249b are made of polyethylene (PE). The first loop antenna 240a and the second loop antenna 240b were each formed from aluminum in a rectangular shape, with external dimensions of 214 mm in length, 111 mm in height, and 2 mm in thickness. The first loop antenna 240a and the second loop antenna 240b were positioned facing each other, and installed so that the directional irradiation axis of the emitted microwaves was parallel to the mounting base 266. The distance between the first loop antenna 240a and the second loop antenna 240b was 333 mm.

[0053] Furthermore, the material of the metal housing 282 is not limited to aluminum; it may be other metal materials such as iron or stainless steel. Also, the materials of the mounting base 266, the first bracket 249a, and the second bracket 249b may be other low dielectric constant, low loss materials such as resin materials like polypropylene, polyethylene terephthalate, or polycarbonate.

[0054] A microwave oscillator (not shown) is connected to a first feed port 223a and a second feed port 223b provided on a metal housing 282 via a coaxial cable (not shown). This coaxial cable branches midway, and the power output from the oscillator is supplied in parallel to the first feed port 223a and the second feed port 223b. The first feed port 223a is connected to the first feed point 253a of the first loop antenna 240a. The second feed port 223b is connected to the second feed point 253b of the second loop antenna 240b. By branching from a single oscillator and supplying power to each antenna in parallel, simultaneous illumination is possible without the output from one antenna being mistakenly perceived as a reflection by the other antenna.

[0055] The frequency of the output power of the microwave oscillator was set to 450 MHz. The microwave power output from the microwave oscillator is fed in phase to the first loop antenna 240a and the second loop antenna 240b. Microwaves are radiated from the first loop antenna 240a and the second loop antenna 240b. Here, the distance between the first loop antenna 240a and the second loop antenna 240b is 333 mm as described above, which is half a wavelength of the output wavelength λ = 666 mm.

[0056] A thermal indicator gel was used as food model 290. This thermal indicator gel contains xylose and glycine, and is configured to change to brown when the temperature reaches approximately 70°C or higher due to the Maillard reaction between these two substances. The electrical properties of the thermal indicator gel, such as dielectric constant and conductivity, were adjusted to be generally equivalent to those of commercially available potato salad by adjusting the concentrations of added oil, salt, etc. Food model 290 was prepared by filling 150 g of thermal indicator gel into a polypropylene (PP) cup. The cup was not sealed after filling.

[0057] The food model 290 was positioned midway between the first loop antenna 240a and the second loop antenna 240b on the mounting base 266. That is, the distance from the first loop antenna 240a and the second loop antenna 240b to the center of the food model 290 was 166.5 mm. The food model 290 was heated at an output of 150 W.

[0058] In addition, as a comparative experiment, food model 290 was heated in a commercial microwave oven (manufactured by Panasonic, output 250 W).

[0059] <result> Figure 11 shows a photograph of the food model 290 after heating with the test apparatus 200 at an output of 150 W. In Figure 11, the upper row shows the case when the heating time is 4 minutes, and the lower row shows the case when the heating time is 6 minutes. In Figure 11, the left column shows the surface of the food model 290 as seen from above. In this figure, the left-right direction is the direction of the directional irradiation axis of the first loop antenna 240a and the second loop antenna 240b. In Figure 11, the right column shows the longitudinal section of the food model 290 cut along the dashed line shown in the left column.

[0060] As shown in Figure 11, the central part of the food model 290 has turned uniformly brown, indicating that the central part was heated uniformly.

[0061] Figure 12 shows photographs of food model 290 after heating in a commercial microwave oven at an output of 250 W as a comparative experiment. In Figure 12, the upper row shows the result after heating for 3 minutes, and the lower row shows the result after heating for 5 minutes. In Figure 12, the left column shows the surface of food model 290 as seen from above. In Figure 12, the right column shows the longitudinal cross-section of food model 290 cut along the dashed line indicated in the left column.

[0062] When a commercial microwave oven was used, the outer periphery of food model 290 turned a dark brown color, indicating that overheating occurred at the periphery. It is thought that the microwaves were continuously irradiated onto the outer periphery of food model 290 while undergoing multiple reflections within the oven. Furthermore, the heat generated at the outer periphery of food model 290 was not uniform along the circumference of the container, and a heat loss occurred in the area circled 299 in the figure, where no heat was generated. This indicates that the standing wave distribution formed by the reflection of microwaves from the metal casing was not uniform. From this, it was suggested that the heating was not reproducible.

[0063] In contrast, when using the test apparatus 200 according to this embodiment, it was confirmed that the center of the food could be selectively heated by an irradiation method that suppressed standing waves.

[0064] [Experimental Example 3] In the above-described Experimental Example 2, the heating conditions at a position equidistant from the first loop antenna 240a and the second loop antenna 240b were investigated. In this experimental example, the heating conditions at a position biased towards either the first loop antenna 240a or the second loop antenna 240b were investigated.

[0065] <method> Figure 13 shows a schematic diagram of the implementation of this experiment. In this experiment, the test apparatus 200 shown in Figure 10 was used. The food model 290 was placed at a position where the distance from the first loop antenna 240a to the center of the food model 290 was 56.5 mm. The output of the test apparatus 200 was set to 150 W and heated for 5 minutes.

[0066] <result> Figure 14 shows a photograph of the food model 290 after heating. In Figure 12, the left photograph shows the surface of the food model 290 as seen from above. In this figure, the left-right direction is the direction of the directional irradiation axes of the first loop antenna 240a and the second loop antenna 240b, with the left side being the first loop antenna 240a side closer to the food model 290 and the right side being the second loop antenna 240b side further away from the food model 290. In Figure 12, the right photograph shows a longitudinal cross-section of the food model 290 cut at the position indicated by the dashed line in the left photograph. Similarly, the left side is the first loop antenna 240a side closer to the food model 290 and the right side is the second loop antenna 240b side further away from the food model 290.

[0067] Figure 14 shows that in this case, the outer periphery of the food model 290 was generating heat. It was also found that the heat generation area near the antenna was wider and of a greater degree than the heat generation area farther from the antenna. It was found that by positioning the object to be heated asymmetrically with respect to one of the pair of opposing antennas, and irradiating the object with microwaves at different distances from each antenna, the leakage of the electric field to the outer periphery of the object increased, allowing the outer periphery to be heated efficiently without generating heat loss.

[0068] [Experimental Example 4] We performed a numerical simulation analysis of the situation described in Experimental Example 2 above.

[0069] <method> For the analysis, we used CST STUDIO SUITE (manufactured by Dassault Systèmes), a coupled thermal analysis software, to perform a coupled analysis of heat and electromagnetic fields. We constructed an analysis model of the test apparatus 200 shown in Figure 10. The object to be heated was a simulated 150 g of commercially available potato salad packed in a polypropylene (PP) cup. The electrical properties of the object to be heated were based on measured values ​​of commercially available potato salad, with relative permittivity εr = 51, conductivity ρ = 1.2 s / m, and dielectric loss tangent tanδ = 0.95.

[0070] As shown in Figure 15A, which illustrates the analysis results, the object to be heated 390 was positioned midway between the first loop antenna 340a and the second loop antenna 340b, which were facing each other. Specifically, the distance from the center of the object to be heated 390 to each antenna was 166.5 mm.

[0071] In this analytical experiment example, for convenience, the mounting platform 366 on which the object to be heated 390 is placed is positioned to penetrate the first loop antenna 340a and the second loop antenna 340b. However, since the physical properties of the mounting platform 366 are set to mimic a low dielectric constant, low-loss resin, this model can be considered to effectively reproduce the apparatus configuration of the test apparatus 200 shown in Figure 10.

[0072] Using the above model, we analyzed the temperature distribution when the output was set to 150 W and heated for 5 minutes.

[0073] <result> Figures 15A and 15B show the results of the coupled thermal analysis. Figure 15A is a perspective view of the analysis results, and Figure 15B shows a cross-section passing through the center of the heated object 390 and perpendicular to the directional irradiation axes of the first loop antenna 340a and the second loop antenna 340b. Similar to the results of Experimental Example 2 shown in Figure 11, the center of the heated object 390 was strongly heated and became very hot. The results of this numerical analysis were in good agreement with the experimental results. The reliability of this numerical analysis was confirmed.

[0074] [Experimental Example 5] Numerical simulation analysis was performed on the apparatus configuration of the first embodiment, as described with reference to Figure 1B.

[0075] <method> An analysis similar to that in Experimental Example 4 was performed. As shown in Figure 16A, which illustrates the analysis results, a model was constructed and analyzed of the portion of the microwave irradiation device 1 of the first embodiment described with reference to Figure 1B that includes one antenna 40. Specifically, in this model, the loop antenna 440 was placed on only one side of the object to be heated 490 placed on the mounting table 466. The object to be heated 490 was the same as the object to be heated 390 in Experimental Example 4.

[0076] In the analysis shown in Figure 16A, the distance from the loop antenna 440 to the center of the object 490 was set to 166.5 mm. In the analysis shown in Figure 16B, the distance from the loop antenna 440 to the center of the object 490 was set to 56.5 mm. The temperature distribution was analyzed for each case when the output power was set to 150 W and heated for 5 minutes.

[0077] <result> Figures 16A and 16B show the results of the coupled thermal analysis. As shown in Figure 16A, when the distance from the loop antenna 440 to the center of the object to be heated 490 is 166.5 mm, it was found that the outer periphery of the object to be heated 490, particularly the side closer to the loop antenna 440, generates heat. It became clear that by placing the antenna on only one side of the object to be heated and irradiating the object with microwaves asymmetrically, it is possible to selectively heat the outer periphery of the object on the antenna side.

[0078] Figure 16B shows the results when the distance between the object to be heated 490 and the loop antenna 440 is reduced compared to the case in Figure 16A, with the distance from the loop antenna 440 to the center of the object to be heated 490 being 56.5 mm. By reducing the distance between the object to be heated 490 and the loop antenna 440, the temperature of a wider area of ​​the outer circumference of the object to be heated 490 increased compared to the case in Figure 16A. This result is consistent with the results of Experimental Example 3 shown in Figure 14.

[0079] It has become clear that by irradiating microwaves asymmetrically and further adjusting the distance between the object to be heated and the antenna, it is possible to adjust the area of ​​the object that is heated.

[0080] [Experimental Example 6] We conducted an experiment to investigate heating methods.

[0081] <method> Using the test apparatus 200 shown in Figure 10, the experiment was conducted using a polypropylene (PP) cup filled with 140 g of commercially available potato salad and left unsealed as the object to be heated. The heating conditions were as follows: First, the object to be heated was placed midway between the first loop antenna 240a and the second loop antenna 240b and heated at an output of 150 W for 2.5 minutes. After heating, it was left to stand for an interval of 1.5 minutes. Next, the object to be heated was placed at a position where the distance from the first loop antenna 240a to the center of the object was 56.5 mm and heated at an output of 150 W for 2.5 minutes. The temperature of the object to be heated during this time was measured using an optical fiber thermometer.

[0082] <result> Figure 17 shows the results of temperature measurements at the center (solid line) and outer edge (dashed line) of the object being heated. When the object being heated was placed midway between the first loop antenna 240a and the second loop antenna 240b, the center of the object was heated more than the outer edge, with temperatures of 70°C at the center and 45°C at the outer edge after 2.5 minutes of heating. There was little temperature drop during the 1.5-minute interval, with temperatures of 67°C at the center and 45°C at the outer edge at the end of the interval. Subsequently, when the object being heated was moved closer to the first loop antenna 240a, the outer edge of the object was heated more than the center, with temperatures of 73°C at the center and 100°C at the outer edge after 2.5 minutes of heating.

[0083] It was found that by combining the placement of the object to be heated at an intermediate position between the first loop antenna 240a and the second loop antenna 240b, and the irradiation of microwaves evenly from both antennas, with the placement of the object to be heated closer to the first loop antenna 240a, and the irradiation of microwaves unevenly from both antennas, the center and the outer periphery can be heated separately, thereby enabling even heating of the entire object.

[0084] Although the present invention has been described above with reference to preferred embodiments, it goes without saying that the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the present invention. [Explanation of symbols]

[0085] 1,2,3 Microwave irradiation device 10 Oscillators 20 Power supply devices 21 Coaxial Cable 30 antenna arrays 40 Antennas 42 Irradiation surface 44 Irradiation source 45 Directional irradiation axis 46 Diffuse irradiation axis 51 Loop Antenna 52 Conductor 53 Power supply point 54 Opening surface 60 Conveying device 61 belt 62 Laura 70 Conveyor System Group 71 First conveying device 72 Second conveying device 82 Metal casing 84 Feeding device 86 Unloading device 90 Irradiated object 91 Conveying direction 100 Test equipment 110 Oscillator 140 Loop Antenna 145 Directional irradiation axis 166 Food Holder 182 Metal casing 190 Objects to be heated 200 Test equipment 223a First power supply port 223b Second power supply port 240a First Loop Antenna 240b Second Loop Antenna 249a First bracket 249b Second bracket 253a First power supply point 253b Second power supply point 266 Mounting platform 282 Metal casing 290 Food Models 340a First Loop Antenna 340b Second Loop Antenna 366 Mounting platform 390 Objects to be heated 440 Loop Antenna 466 Mounting platform 490 Objects to be heated

Claims

1. A conveying device that conveys the object to be irradiated in the conveying direction, A power supply device configured to conduct electricity with an oscillator, The antenna group comprises a plurality of directional antennas configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply via conductivity through the aforementioned power supply device, wherein the plurality of antennas are arranged along the transport direction. Equipped with, The antenna group comprises at least one pair of antennas arranged opposite each other, and the directional illumination axis of each of the paired antennas does not intersect with the directional illumination axis of the other antennas that are not part of the pair. The power supply device is configured to feed power in parallel and in phase from one oscillator to the pair of antennas. Microwave irradiation device.

2. A conveying device for conveying an object to be irradiated in the conveying direction, A power supply device configured to conduct electricity with an oscillator, The antenna group comprises a plurality of directional antennas configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply via conductivity through the aforementioned power supply device, wherein the plurality of antennas are arranged along the transport direction. Equipped with, The antenna is positioned such that the directional irradiation axis of the microwaves irradiated from the irradiation source does not intersect with the structure constituting the transport device. Microwave irradiation device.

3. The microwave irradiation apparatus according to claim 1 or 2, wherein the antenna group has a plurality of antennas arranged on both sides of the transport device.

4. The microwave irradiation apparatus according to any one of claims 1 to 3, wherein the antenna is a loop antenna whose irradiation surface is an aperture surface.

5. A conveying device for conveying an object to be irradiated in the conveying direction, A power supply device configured to conduct electricity with an oscillator, The antenna group comprises a plurality of directional antennas configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply via conductivity through the aforementioned power supply device, wherein the plurality of antennas are arranged along the transport direction. Equipped with, The aforementioned antenna is a loop antenna in which the irradiation surface is an aperture surface. The conveying device group comprises a plurality of conveying devices arranged on both sides of the opening surface of the loop antenna, Microwave irradiation device.

6. A microwave irradiation method comprising irradiating an object to be irradiated with microwaves using a directional antenna configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply, The antennas form at least one pair of opposing antennas, and the directional illumination axis of each of the paired antennas does not intersect with the directional illumination axis of the other antenna that is not part of the pair. This includes supplying power in parallel and in phase from one oscillator to the pair of antennas arranged opposite each other on both sides of the object to be irradiated, thereby simultaneously and evenly irradiating the pair of antennas with microwaves. Irradiation method.

7. An irradiation method in which an object to be irradiated is irradiated with microwaves by a directional antenna configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply, The process involves simultaneously and uniformly irradiating the object to be irradiated with microwaves from the antennas positioned on both sides of the object, The process involves unevenly irradiating the object to be irradiated with microwaves from the antennas positioned on either side or one side of the object to be irradiated. A method of irradiation that includes this.

8. The irradiation method according to claim 7, wherein the uniform irradiation of microwaves includes irradiating the object to be irradiated with microwaves of equal intensity from a pair of antennas positioned facing each other at an equidistant distance from the object to be irradiated.

9. The aforementioned uneven irradiation of microwaves is The process involves irradiating the object to be irradiated with microwaves from one of the pair of antennas, The other of the pair of antennas irradiates the object to be irradiated with microwaves. The irradiation method according to claim 8, including the method described in claim 8.

10. The aforementioned uneven irradiation of microwaves is equivalent to irradiating with microwaves of equal intensity. The irradiation method according to claim 8, further comprising bringing the object to be irradiated closer to one of the pair of antennas.

11. The method further includes transporting the object to be irradiated in the transport direction by a transport device, In the transport device, a pair of antennas are arranged opposite each other at an equidistant distance from the first position, and the uniform irradiation of microwaves includes irradiating the object to be irradiated at the first position with microwaves of equal intensity from each of the pair of antennas. In the transport device, the antenna is positioned at least on one side of the second position, and the uneven irradiation of microwaves includes irradiating the object to be irradiated at the second position with microwaves from the antenna on one side. The irradiation method according to claim 7.

12. A method for manufacturing food, which includes heating food by irradiating it with microwaves, The microwave irradiation is performed by a directional antenna configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply. The antennas form at least one pair of opposing antennas, and the directional illumination axis of each of the paired antennas does not intersect with the directional illumination axis of the other antenna that is not part of the pair. A method for manufacturing food, comprising supplying power in parallel and in phase from one oscillator to a pair of antennas arranged opposite each other on both sides of the food, thereby simultaneously and uniformly irradiating the pair of antennas with microwaves.

13. A method for producing food, comprising heating food by irradiating it with microwaves, The microwave irradiation is performed by a directional antenna configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply, and includes supplying power in parallel from a single oscillator to a plurality of such antennas arranged on both sides of the food, thereby simultaneously and evenly irradiating microwaves from the plurality of antennas. The further includes unevenly irradiating the food with microwaves from antennas positioned on both sides or one side of the food, Food manufacturing methods.

14. The method for producing a food according to claim 12 or 13, wherein the food is a packaged food.

Images