Microwave irradiation device

Abstract

To provide a microwave irradiation device capable of suppressing generation of uneven heating.SOLUTION: A microwave irradiation device includes: a retainer 66 for retaining an irradiated object 90; a power supply fixture 20 configured to conduct with an oscillator 10; and an antenna 40 of a loop antenna 51, which makes an irradiation surface 42 an opening surface 54, configured to irradiate microwaves from an irradiation source 44 within an irradiation surface 42 by means of power supply by conduction through the power supply fixture 20.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

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

[0003] For example, Patent Document 1 discloses a microwave heating device in which a microwave reaction vessel into which an irradiated object is placed is arranged in a conductive storage container, and a plurality of dipole antennas are evenly arranged 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 irradiated microwave 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 irradiated object 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. The 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, a microwave irradiation device comprises a holder for holding an object to be irradiated, a power supply device configured to be electrically connected to an oscillator, and a loop antenna whose irradiation surface is an aperture surface, configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply via electrical connection through the power supply device. [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 1] Figure 1 is a schematic diagram showing an example of the configuration of a microwave irradiation apparatus according to the first embodiment. [Figure 2] Figure 2 is a schematic diagram illustrating the orientation of the antenna in the first embodiment. [Figure 3] Figure 3 is a schematic diagram illustrating the orientation of the antenna in the comparative example. [Figure 4A] Figure 4A is a schematic front view showing an example of the configuration of a microwave irradiation apparatus according to the second embodiment. [Figure 4B] Figure 4B is a schematic plan view showing an example of the configuration of a microwave irradiation apparatus according to the second embodiment. [Figure 4C] Figure 4C is a schematic diagram showing an example of the configuration of the end face as viewed from the side at the antenna position of the microwave irradiation device according to the second embodiment. [Figure 5] Figure 5 is a schematic diagram showing an example of a loop antenna configuration. [Figure 6] Figure 6 is a schematic diagram illustrating the positional relationship between the electric field strength generated by the antenna according to the second embodiment and the object being irradiated. [Figure 7] Figure 7 is a schematic diagram illustrating the positional relationship between the electric field strength and the irradiated object in the comparative example. [Figure 8] Figure 8 is a schematic diagram showing an example of the configuration of a microwave irradiation apparatus according to the third embodiment. [Figure 9] FIG. 9 is a schematic diagram for explaining the positional relationship between the electric field strength generated by the antenna according to the third embodiment and the irradiated object. [Figure 10] FIG. 10 is a schematic diagram showing the magnitude of the effective electric field value according to the position along the directivity irradiation axis of the antennas provided opposite to each other. [Figure 11A] FIG. 11A is a front view schematically showing an outline of a configuration example of a microwave irradiation device according to the fourth embodiment. [Figure 11B] FIG. 11B is a plan view schematically showing an outline of a configuration example of a microwave irradiation device according to the fourth embodiment. [Figure 12] FIG. 12 is a plan view schematically showing an outline of a configuration example of a microwave irradiation device according to the fifth embodiment. [Figure 13] FIG. 13 is a schematic diagram showing an outline of a configuration example of a test apparatus used in Experimental Example 1. [Figure 14] FIG. 14 is a diagram showing an example of test results obtained by heating an object to be heated according to Experimental Example 1 with it placed vertically. [Figure 15] FIG. 15 is a diagram showing an example of test results obtained by heating an object to be heated according to Experimental Example 1 with it placed horizontally. [Figure 16] FIG. 16 is a diagram showing an outline of a configuration example of a test apparatus used in Experimental Examples 2, 3, and 6. [Figure 17] FIG. 17 shows a photograph of a food model after heating at an output of 150 W using the test apparatus in Experimental Example 2. [Figure 18] FIG. 18 shows a photograph of a food model after heating at an output of 250 W using a commercial microwave oven as a comparative experiment. [Figure 19] FIG. 19 is a diagram showing an outline of the implementation status of Experimental Example 3. [Figure 20] FIG. 20 shows a photograph of a food model after heating in Experimental Example 3. [Figure 21A] FIG. 21A is a diagram showing the thermo - coupled analysis results according to Experimental Example 4 in a perspective view. [Figure 21B] FIG. 21B is a diagram showing the thermo - coupled analysis results according to Experimental Example 4 in a cross - sectional view. [Figure 22A] Figure 22A is a diagram showing the results of a thermal coupling analysis when the distance according to Experimental Example 5 is 166.5 mm. [Figure 22B] Figure 22B is a diagram showing the results of a thermal coupling analysis when the distance according to Experimental Example 5 is 56.5 mm. [Figure 23] Figure 23 is a diagram showing the results of temperature measurements of the central part (solid line) and the outer peripheral part (dashed line) of the object to be heated according to Experimental Example 6. [Figure 24] Figure 24 is a diagram showing an outline of a configuration example of the test apparatus used in Experimental Example 7. [Figure 25] Figure 25 shows images obtained by thermography of the first object to be heated, the second object to be heated, and the third object to be heated heated using the test apparatus according to Experimental Example 7. [Figure 26] Figure 26 shows an image obtained by thermography of an object to be heated heated using a commercial microwave oven as a comparative experiment. [Figure 27] Figure 27 is a diagram showing an outline of a model of the microwave irradiation apparatus according to Experimental Example 8. [Figure 28] Figure 28 shows the analysis results of the electric field strength formed between each antenna in the model according to Experimental Example 8. [Figure 29] Figure 29 shows the analysis results of the electric field strength with respect to the irradiation distance from the oscillator in the waveguide as a comparative analysis. [Figure 30] Figure 30 is a diagram showing the results of a thermal coupling analysis of the heat generation distribution of the object to be heated when the object to be heated according to Experimental Example 8 is heated.

Embodiments 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 an object to be irradiated with microwaves to heat the object from the inside. The object to be irradiated is not limited to this, but is an example of food. Therefore, this microwave irradiation device and the microwave irradiation method using it can be used, for example, in the manufacture of food products, including packaged foods.

[0010] Figure 1 is a schematic diagram showing an example of the configuration of a microwave irradiation device 1 according to this embodiment. As shown in this figure, the microwave irradiation device 1 includes a holder 66 for holding an object to be heated, which is an object to be irradiated with microwaves, 90. The holder 66 may be, for example, a stand on which the object to be irradiated 90 is placed. The microwave irradiation device 1 includes an antenna 40 configured to irradiate microwaves onto the object to be irradiated 90 held by the holder 66. The antenna 40 is a directional antenna, such as a loop antenna or a patch antenna. That is, the 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 the antenna 40 is along the mounting surface of the holder 66. The antenna 40 is powered by an oscillator 10 which is conductive via a power supply device 20, such as a coaxial cable. The area around the antenna 40 is covered with metal to shield against microwaves. In other words, the holder 66 and the antenna 40 are located inside the metal housing 82.

[0011] The orientation of the antenna 40 will now be described. Figure 2 is a schematic diagram 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 holder 66 on which the object to be irradiated 90 is placed, for example, as shown in Figure 2. Alternatively, the antenna 40 is positioned such that at least the directional irradiation axis 45 does not intersect with any structure in the holder 66 that reflects microwaves.

[0012] The microwaves emitted from the directional antenna 40 spread out to some extent, as shown as the diffuse irradiation axis 46 in Figure 2, but their irradiation angle is relatively narrow, and an electric field with the strongest intensity is formed 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 produced.

[0013] Figure 3 is a schematic diagram showing a comparative example. As shown in Figure 3, when the directional irradiation axis 45 intersects with the surface of the holder 66, the microwaves are reflected by the surface of the holder 66. As a result of the strong reflected waves, the incident waves and reflected waves interfere, and standing waves are generated. When standing waves are generated, the electric field strength differs greatly, especially at the antinodes and nodes of the standing waves, which can cause uneven heating of the irradiated object 90.

[0014] In the microwave irradiation device 1 of this embodiment, as explained with reference to Figure 2, standing waves are not generated due to interference between incident waves and reflected waves, thus preventing uneven heating of the irradiated object 90. The microwave-reflecting structure mentioned above refers to a structure that reflects microwaves to the extent that standing waves are generated to the extent that the uneven heating described above occurs.

[0015] 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. The object to be irradiated 90, which is placed on the holder 66 in front of the antenna 40, is irradiated with microwaves from the antenna 40. The object to be irradiated 90 is dielectrically heated by these microwaves.

[0016] As described above, in this embodiment, a directional antenna 40 is used as the antenna for irradiating microwaves, and the directional irradiation axis 45 is designed so as not to intersect with the microwave-reflecting structure of the holder 66. 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.

[0017] 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.

[0018] 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.

[0019] Furthermore, for more uniform heating, the holder 66 may be moved back and forth along the directional irradiation axis 45 of the antenna 40, or rotated in a plane parallel to the directional irradiation axis 45. By moving the object to be irradiated 90 in such directions, the object to be irradiated 90 can be heated more uniformly. Alternatively, the same can be achieved by moving the antenna 40 instead of the holder 66.

[0020] [Second Embodiment] A second embodiment will now be described. Here, the differences from the first embodiment will be explained, and the same parts will be denoted by the same reference numerals and their descriptions will be omitted. The microwave irradiation device of this embodiment is configured to irradiate an object to be irradiated, such as food, with microwaves to heat the object from the inside. The microwave irradiation device has a transport device, and multiple objects to be irradiated are transported one after another and heated one after the other.

[0021] Figure 4A is a schematic front view showing an example of the configuration of the microwave irradiation device 2 according to the second embodiment. Figure 4B is a schematic plan view showing an example of the configuration of the microwave irradiation device 2 according to the second embodiment. Figure 4C is a schematic diagram showing an example of the configuration of the end face of the microwave irradiation device 2 according to the second embodiment, as viewed from the side at the position of the antenna 40.

[0022] As shown in these figures, the microwave irradiation device 2 includes a transport device 60 as a holder for transporting the object to be heated, which is the object to be irradiated with microwaves, 90. The transport device 60 includes, for example, a belt 61 and rollers 62. The belt 61 is placed 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 object to be irradiated 90 is placed on the belt 61 and transported in the transport direction 91 by the movement of the belt 61. Upstream of the transport direction 91 of the transport device 60, a supply device 84 is provided to supply the objects to be irradiated 90 one after another onto the belt 61. Downstream of the transport direction 91 of the transport device 60, an unloading device 86 is provided to unload the transported objects to be irradiated 90 from the belt 61.

[0023] The microwave irradiation device 2 includes an antenna 40 configured to irradiate microwaves onto an object 90 to be irradiated, which is transported by a transport device 60. The antenna 40 is, for example, a loop antenna, which is a type of directional antenna. The antenna 40 is powered by an oscillator 10 that is conductive via a power supply device 20, such as a coaxial cable.

[0024] The loop antenna will be described with reference to Figure 5. Figure 5 is a schematic diagram showing an example of the 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.

[0025] 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.

[0026] Let's return to Figures 4A to 4C and continue the explanation. In the microwave irradiation device 2 of this embodiment, the belt 61 of the transport device 60 is provided so as to penetrate the irradiation surface 42, which is the opening surface 54 of the antenna 40, which is the loop antenna 51. That is, the object to be irradiated 90 is transported in the transport direction 91 so as to pass through the antenna 40. For example, the irradiation surface 42 of the antenna 40 is perpendicular to the transport direction 91, and the directional irradiation axis 45 of the antenna 40 is parallel to the transport direction 91.

[0027] The antenna 40 is surrounded by metal to shield it from microwaves. In other words, the transport device 60 is positioned to pass through the metal housing 82, and the antenna 40 is located inside the metal housing 82.

[0028] In the microwave irradiation device 2 of this embodiment, the directional irradiation axis 45 of the antenna 40 does not intersect with the microwave-reflecting structure among the structures constituting the transport device 60. As a result, standing waves that may be generated by interference between incident and reflected waves are not generated. In the microwave irradiation device 2 of this embodiment, because such standing waves are not generated, uneven heating of the irradiated object 90 is prevented.

[0029] Furthermore, in the microwave irradiation device 2 of this embodiment, the object to be irradiated 90 passes through the irradiation source 44 of the antenna 40, thereby achieving efficient and uniform heating of the object to be irradiated 90. Figure 6 schematically shows the electric field strength according to location using the amplitude of the dashed line 92. As shown in this figure, in the microwave irradiation device 2 of this embodiment, the center of the object to be irradiated 90 passes through the irradiation source 44 of the antenna 40, which has a strong electric field strength. Therefore, the object to be irradiated 90 generates heat at its center and is efficiently heated from the inside. In other words, it is not necessary to consider the power half-depth, as when microwaves are irradiated from the outside of the object to be irradiated 90. Also, since the object to be irradiated 90, which is placed on the belt 61 of the conveying device 60, moves in the conveying direction 91, the heat generation location changes within the object to be irradiated 90, resulting in uniform heating.

[0030] A comparative example is shown in Figure 7. Figure 7 schematically shows a heating device in which the antenna 40 is positioned laterally to the transport direction 91 of a generally known transport device 60. As schematically shown by the dashed line 92 indicating the electric field strength, in the arrangement shown in Figure 7, the object to be irradiated 90 is far from the irradiation source 44 of the antenna 40, making it difficult for power to reach the center of the object to be irradiated 90. For this reason, the center may not be heated well. In contrast, in the microwave irradiation device 2 of this embodiment, the electric field strength becomes stronger at the center of the object to be irradiated 90.

[0031] The operation of the microwave irradiation device 2 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 these, but for example, it may be 2.45 GHz, 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.

[0032] 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 them through the opening 54 of the antenna 40, which is a loop antenna 51 inside the metal housing 82. Microwaves are irradiated from the antenna 40 onto the objects to be irradiated 90 as they pass through the opening 54 of the antenna 40. These microwaves cause the objects to be irradiated 90 to be dielectrically heated. The heated objects to be irradiated 90 are conveyed to the outside of the metal housing 82 by the conveying device 60. The discharge device 86 discharges the heated objects to be irradiated 90 from the conveying device 60.

[0033] As described above, in this embodiment, a directional antenna 40 is used, 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. In addition, the irradiated object 90 passes through the irradiation source 44 of the antenna 40. Therefore, a strong electric field is generated inside the irradiated object 90, and the irradiated object 90 is efficiently heated from the inside. Other effects similar to those of the first embodiment can be obtained.

[0034] The microwave irradiation device 2 according to this embodiment can be incorporated into processing equipment for various applications or configured in an appropriate manner. For example, when used for heat sterilization of sealed food products, the microwave irradiation device 1 will 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, when used for 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.

[0035] [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.

[0036] Figure 8 is a schematic diagram showing an example of the configuration of a microwave irradiation device 3 according to the third embodiment. As shown in this figure, the microwave irradiation device 3 includes an antenna group 30 including two antennas 40. The antennas 40 are directional antennas such as loop antennas and patch antennas. Although not limited to these, here we assume that the antennas 40 are loop antennas 51. The two antennas 40 of the antenna group 30 are arranged parallel to each other so that their irradiation surfaces 42 face each other. A holder 66 on which the object to be irradiated 90 is placed is provided so as to penetrate the aperture surface 54 that forms this irradiation surface 42. In this way, the object to be irradiated 90 placed on the holder 66 is sandwiched between the two antennas 40. The directional irradiation axes 45 of the two antennas 40 are parallel to the surface of the holder 66 on which the object to be irradiated 90 is placed so as not to generate strong reflected waves. The two antennas 40 are configured to irradiate the object to be irradiated 90 with microwaves from opposite sides. The microwaves emitted from each of the antennas 40 are designed to overlap.

[0037] Figure 9 schematically shows the electric field strength at different locations, indicated by the amplitude of the dashed line 92. As shown in this figure, in the microwave irradiation device 3 of this embodiment, microwaves are irradiated from both sides of the object to be irradiated 90.

[0038] Figure 10 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 object to be irradiated 90 is positioned between the first position P1 and the second position P2. As shown in Figure 10, the microwave irradiation device 1 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.

[0039] According to this embodiment, microwaves are irradiated from both sides of the object to be irradiated 90, and the electric field strengths they form are approximately equal regardless of location, thus enabling uniform heating of the object to be irradiated 90. The fact that the electric field strength between the opposing antennas 40 is constant 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. In addition, the same effects as those of the microwave irradiation device 1 of the first embodiment can be obtained.

[0040] Here, we have explained an example in which the directional irradiation axes 45 of the two antennas 40 are parallel to the surface on which the object to be irradiated 90 is placed on the holder 66 so as not to generate strong reflected waves. It is preferable, but not limited to, that the directional irradiation axes 45 be parallel to the mounting surface of the holder 66. However, it is preferable that the two antennas 40 are arranged such that at least the directional irradiation axes 45 do not intersect with the microwave-reflecting structure that constitutes the holder 66 located between the aperture surfaces 54 of the two antennas 40 facing each other. By doing so, standing waves originating from reflected waves are not generated with respect to the irradiated microwaves, and as a result, the object to be irradiated 90 is heated uniformly.

[0041] [Fourth Embodiment] A fourth embodiment will now be described. Here, the differences from the second embodiment will be explained, and identical parts will be denoted by the same reference numerals and their descriptions will be omitted.

[0042] Figure 11A is a schematic front view showing an example of the configuration of the microwave irradiation device 4 according to the fourth embodiment, and Figure 11B is a schematic plan view showing an example of the configuration of the microwave irradiation device 4 according to the fourth embodiment. As shown in these figures, the microwave irradiation device 4 according to the fourth embodiment, like the microwave irradiation device 2 according to the second embodiment, includes a transport device 60 for transporting the object to be heated, which is the object to be irradiated with microwaves, 90.

[0043] The microwave irradiation device 4 of the fourth embodiment includes an antenna group 30 having a plurality of antennas 40 configured to irradiate an object 90 to be irradiated with microwaves, which is transported by a transport device 60. The plurality of antennas 40 are arranged along the transport direction 91. Each antenna 40 is, for example, a loop antenna 51. The belt 61 of the transport device 60 is arranged to pass through each antenna 40. Each antenna 40 is powered by an oscillator 10 that is conductive via a power supply device 20, such as a coaxial cable. The plurality of antennas 40 are arranged such that the effective field value is approximately constant between adjacent antennas 40 and antennas 40, similar to the antennas 40 of the microwave irradiation device 3 of the third embodiment. The antenna group 30 is surrounded by a metal housing 82 to shield from microwaves.

[0044] In the microwave irradiation device 4 of the fourth embodiment, the electric field strength due to microwaves along the belt 61 is made almost constant by the multiple antennas 40. The object to be irradiated 90, which is transported by the transport device 60, moves within this electric field of constant strength. Furthermore, the object to be irradiated 90 is configured to pass through the irradiation source 44 of each antenna 40. As a result, the microwave irradiation device 4 can heat the object to be irradiated 90 efficiently and uniformly. Other effects similar to those of the microwave irradiation devices of the first to third embodiments can be obtained.

[0045] [Fifth Embodiment] A fifth embodiment will now be described. Here, the differences from the fourth embodiment will be explained, and the same parts will be denoted by the same reference numerals and their descriptions will be omitted. Figure 12 is a schematic plan view showing an example of the configuration of a microwave irradiation device 5 according to the fifth embodiment. As shown in this figure, the microwave irradiation device 5 according to the fifth embodiment is similar to the microwave irradiation device 4 according to the fourth embodiment, but the orientation of some of the antennas 40 has been changed, and the directional irradiation axis 45 of the antennas 40 is not aligned with the transport direction 91, which is a difference from the microwave irradiation device 4 according to the fourth embodiment.

[0046] When heating the object to be irradiated 90, it is not always preferable for power to be supplied uniformly. For example, if there are areas within the object to be irradiated 90 that are heated easily and areas that are not heated easily, supplying more power to the areas that are not heated easily will result in the entire object to be irradiated 90 being heated uniformly.

[0047] The example shown in Figure 12 is one in which the lower and upper sides of the irradiated object 90 are regions that are less likely to be heated. The two antennas 40 on the supply device 84 side are positioned so that the opposing directional irradiation axes 45 of one antenna are biased toward the lower side of the transport direction 91 and the other is biased toward the upper side of the diagram. As a result, electric fields are formed toward the lower and upper sides of the diagram, respectively, and power is supplied to the irradiated object 90 passing through them from different directions. Consequently, the entire irradiated object 90 is heated uniformly. In addition, the same effects as those of the microwave irradiation device 4 of the fourth embodiment can be obtained.

[0048] [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.

[0049] <method> For the evaluation, a test apparatus having a configuration similar to the microwave irradiation apparatus 3 of the third embodiment described with reference to Figure 8 was used. A schematic example of the configuration of this test apparatus 100 is shown in Figure 13. The test apparatus 100 has an oscillator 110 and two loop antennas 140 and a food holding stand 166 arranged in a metal housing 182.

[0050] 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.

[0051] 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.

[0052] Furthermore, a numerical analysis was performed on the electric field strength formed between the two loop antennas 140.

[0053] <result> Numerical simulations of the electric field strength revealed that a uniform electric field, as shown in Figure 10, was obtained between the two loop antennas 140.

[0054] Figure 14 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.

[0055] Figure 15 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.

[0056] The results shown in Figures 14 and 15 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, heating is possible while suppressing the generation of standing waves due to microwave reflection and energy loss due to absorption.

[0057] [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.

[0058] <method> Figure 16 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 microwave irradiation apparatus 3 of the third embodiment described with reference to Figure 8. This situation also corresponds to the state in the fourth embodiment described with reference to Figures 11A and 11B where the object to be irradiated 90 is positioned between the two antennas 40 by the transport device 60. The configuration of the test apparatus 200 was as follows.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] In addition, as a comparative experiment, food model 290 was heated in a commercial microwave oven (manufactured by Panasonic, output 250 W).

[0066] <result> Figure 17 shows a photograph of the food model 290 after heating with the test apparatus 200 at an output of 150 W. In Figure 17, 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 17, 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 17, the right column shows the longitudinal section of the food model 290 cut along the dashed line shown in the left column.

[0067] As shown in Figure 17, the central part of the food model 290 has turned uniformly brown, indicating that the central part was heated uniformly.

[0068] Figure 18 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 18, 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 18, the left column shows the surface of food model 290 as seen from above. In Figure 18, the right column shows the longitudinal cross-section of food model 290 cut along the dashed line indicated in the left column.

[0069] 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.

[0070] 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.

[0071] [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. This situation corresponds to the state in the fourth embodiment described with reference to Figures 11A and 11B, where the object to be irradiated 90 is transported by the transport device 60 to a position biased relative to the two antennas 40.

[0072] <method> Figure 19 shows a schematic diagram of the implementation of this experiment. In this experiment, the test apparatus 200 shown in Figure 16 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.

[0073] <result> Figure 20 shows a photograph of the food model 290 after heating. In Figure 20, 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, which is closer to the food model 290, and the right side being the second loop antenna 240b side, which is further away from the food model 290. In Figure 20, 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, which is closer to the food model 290, and the right side is the second loop antenna 240b side, which is further away from the food model 290.

[0074] Figure 20 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.

[0075] [Experimental Example 4] We performed a numerical simulation analysis of the situation described in Experimental Example 2 above.

[0076] <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 16. 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.

[0077] As shown in Figure 21A, 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.

[0078] In this analytical experiment example, 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. In this respect, this model is closer to the microwave irradiation device 3 according to the third embodiment shown in Figure 8 than to the test apparatus 200 shown in Figure 16. On the other hand, since the physical properties of the mounting platform 366 are set to mimic a resin with low dielectric constant and low loss, it can be considered that this model substantially reproduces both the apparatus configuration of the test apparatus 200 shown in Figure 16 and the configuration of the microwave irradiation device 3 according to the third embodiment shown in Figure 8.

[0079] Using the above model, we analyzed the temperature distribution when the output was set to 150 W and heated for 5 minutes.

[0080] <result> Figures 21A and 21B show the results of the coupled thermal analysis. Figure 21A is a perspective view of the analysis results, and Figure 21B 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 17, 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.

[0081] [Experimental Example 5] Numerical simulation analysis was performed on the device configuration corresponding to the microwave irradiation device 1 of the first embodiment described with reference to Figure 1 and the microwave irradiation device 2 of the second embodiment described with reference to Figure 4A, etc.

[0082] <method> An analysis similar to that in Experimental Example 4 was performed. As shown in Figure 22A, which shows the analysis results, a model corresponding to the microwave irradiation device 1 of the first embodiment described with reference to Figure 1 and the microwave irradiation device 2 of the second embodiment described with reference to Figure 4A, etc., was constructed and analyzed. That is, 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.

[0083] In the analysis shown in Figure 22A, the distance from the loop antenna 440 to the center of the object to be heated 490 was set to 166.5 mm. In the analysis shown in Figure 22B, the distance from the loop antenna 440 to the center of the object to be heated 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.

[0084] <result> Figures 22A and 22B show the results of the coupled thermal analysis. As shown in Figure 22A, 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.

[0085] Figure 22B 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 22A, 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 22A. This result is consistent with the results of Experimental Example 3 shown in Figure 20.

[0086] 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.

[0087] [Experimental Example 6] We conducted an experiment to investigate heating methods.

[0088] <method> Using the test apparatus 200 shown in Figure 16, the experiment was conducted using a polypropylene (PP) cup filled with 140 g of commercially available potato salad and not sealed after filling 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 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.

[0089] <result> Figure 23 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.

[0090] 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 even irradiation of microwaves from both antennas, with the placement of the object to be heated closer to the first loop antenna 240a, and the uneven irradiation of microwaves from both antennas, the center and outer periphery can be heated separately, thereby enabling even heating of the entire object to be heated. In other words, as in the microwave irradiation device 2 of the second embodiment and the microwave irradiation device 4 of the fourth embodiment, by moving the object to be irradiated 90 with the transport device 60 and changing the positional relationship between the antenna 40 and the object to be irradiated 90, the center and outer periphery of the object to be irradiated 90 can be heated separately, thereby enabling even heating of the entire object to be irradiated 90.

[0091] [Experimental Example 7] A test apparatus corresponding to the microwave irradiation apparatus 4 of the fourth embodiment was fabricated, and the heating characteristics were evaluated when the object to be heated was heated while being transported.

[0092] <method> Figure 24 is a schematic diagram of an example configuration of the test apparatus 500 related to this experimental example. The test apparatus 500 comprises a first metal casing 582a, a second metal casing 582b, and a third metal casing 582c for shielding electromagnetic waves. The first metal casing 582a is made of aluminum and has dimensions of 440 mm in length along the conveying direction, 350 mm in width perpendicular to the conveying direction, and 400 mm in height. A resin conveyor 561 with a width of 140 mm is provided to pass through the first metal casing 582a. The second metal casing 582b is provided at the entrance of the conveyor 561 of the first metal casing 582a so as to be connected to the first metal casing 582a, and the third metal casing 582c is provided at the exit of the conveyor 561 of the first metal casing 582a so as to be connected to the first metal casing 582a. The second metal casing 582b and the third metal casing 582c were each made of aluminum, with dimensions of 220 mm in length, 248 mm in width, and 80 mm in height.

[0093] Inside the first metal housing 582a, a circular first loop antenna 540a and a second loop antenna 540b were provided so that the conveyor 561 could pass through them. The first loop antenna 540a and the second loop antenna 540b were each made of aluminum, with an inner diameter of 232 mm and a thickness of 2 mm. The first loop antenna 540a and the second loop antenna 540b were positioned facing each other, and installed so that the directional irradiation axis of the emitted microwaves was parallel to the mounting surface of the conveyor 561. The distance between the first loop antenna 540a and the second loop antenna 540b was 333 mm.

[0094] An oscillator 510 was connected to the first loop antenna 540a and the second loop antenna 540b via a coaxial cable 521. The frequency of the oscillator 510's output power was set to 450 MHz. The output power of the oscillator 510 was fed in parallel and in phase to the first loop antenna 540a and the second loop antenna 540b via the coaxial cable 521. The distance between the first loop antenna 540a and the second loop antenna 540b was 333 mm, as described above, which is half a wavelength of the output wavelength λ = 666 mm. By branching off from a single oscillator and feeding power to each antenna in parallel, simultaneous illumination is possible without the other antenna misinterpreting the output from one antenna as a reflection.

[0095] A sample of 140 g of potato salad was filled into a polypropylene (PP) cup and left unsealed after filling, which was designated as the object to be heated 590. Three objects were prepared as the object to be heated 590: the first object to be heated 591, the second object to be heated 592, and the third object to be heated 593. These were placed on a conveyor 561 at predetermined intervals. The conveying speed of the conveyor 561 was set to 1 mm / second and the output power to 300 W. The surface temperature of the heated potato salad was measured using a thermographic camera installed at the exit of the third metal housing 582c.

[0096] In addition, as a comparative experiment, the same cup-packaged potato salad was heated in a commercial microwave oven at 150 W for 5 minutes, and the surface temperature was measured using a thermograph.

[0097] <result> Figure 25 shows thermographic images obtained of the first object 591, the second object 592, and the third object 593, which were heated using the test apparatus 500. Figure 26 shows a thermographic image obtained of the object 590, which was heated using a commercial microwave oven, as a comparative experiment.

[0098] As shown in Figure 26, when heated in a microwave oven, the microwaves are thought to be constantly irradiated from the outer periphery of the object being heated 590 while undergoing multiple reflections within the oven chamber, resulting in overheating at the outer periphery of the object being heated 590. In this comparative experiment, the temperature difference between the outer periphery and the center was 33°C. Furthermore, the heat generation at the outer periphery of the object being heated 590 did not show a uniform temperature distribution along the circumference, and low-temperature areas were observed, as shown in the area circled 599 in the figure. This indicates that the standing wave distribution formed by the reflection of microwaves in the metal casing is not uniform. From this, it was suggested that the heating was not reproducible.

[0099] In contrast, as shown in Figure 25, the first object 591, the second object 592, and the third object 593, which were heated using the test apparatus 500, all showed that the outer edges were slightly hotter than the center, but this temperature difference was only about 7°C, indicating high uniformity. As described above, this heating method, which aims to suppress power reflection, can achieve highly uniform heating compared to heating methods that actively utilize power reflection, such as microwave ovens.

[0100] [Experimental Example 8] Numerical simulation analysis was performed on the microwave irradiation device 4 of the fourth embodiment.

[0101] <method> A model of the microwave irradiation device 4 according to the fourth embodiment shown in Figure 27 was fabricated. In this model, the metal housing 682 was made of aluminum, with dimensions of 1320 mm in length, 350 mm in width, and 400 mm in height. A resin conveyor 661 was provided to pass through the metal housing 682. Three loop antennas, a first loop antenna 640a, a second loop antenna 640b, and a third loop antenna 640c, were provided inside the metal housing 682 so that the conveyor 661 could pass through them. All of these loop antennas were made of aluminum, with external dimensions of 214 mm × 111 mm. The frequency of the power supplied to the first feed point 653a of the first loop antenna 640a, the second feed point 653b of the second loop antenna 640b, and the third feed point 653c of the third loop antenna 640c was 450 MHz (wavelength λ = 666 mm). The distance between each loop antenna was set to 333 mm (λ / 2).

[0102] The position of the second loop antenna 640b, located in the center, was used as the coordinate origin, and the electric field strength formed between each antenna was analyzed.

[0103] For comparative analysis, the electric field strength was calculated as a function of irradiation distance from the oscillator when microwave oscillation was performed inside a waveguide at a frequency of 450 MHz and an output electric field of 1 V / m.

[0104] Furthermore, using the model shown in Figure 27, an analysis was performed on a sample consisting of 150 g of potato salad filled in a polypropylene (PP) cup as the object to be heated. For the analysis, coupled thermal and electromagnetic field analysis was performed using CST STUDIO SUITE (manufactured by Dassault Systèmes), a coupled thermal analysis software. The electrical properties of the potato salad object to be heated were set to relative permittivity εr = 51, conductivity ρ = 1.2 s / m, and dielectric loss tangent tanδ = 0.95 based on measured values. The heat generation distribution of the object to be heated was analyzed when microwave heating was performed at an output of 150 W for a heating time of 5 minutes while transporting one object to be heated.

[0105] <result> Figure 28 shows the results of an analysis of the electric field strength formed between each antenna in the model shown in Figure 27. In this figure, the dashed lines at -333 mm, 0 mm, and 333 mm indicate the positions where the loop antenna is located. Figure 29 shows the results of a comparative analysis of the electric field strength as a function of the irradiation distance from the oscillator within a waveguide.

[0106] As shown in Figure 29, as is well known, antinodes and nodes of standing waves are alternately formed inside the waveguide due to reflection from the metal housing. At the antinode locations, the electric field strength is twice the oscillator output, and at the node locations, the electric field strength is zero. In other words, there is a large difference in electric field strength depending on the location. In contrast, as shown in Figure 28, in the microwave irradiation device according to the fourth embodiment, the electric field strength distribution was highly uniform with no nodes.

[0107] Figure 30 shows the results of an analysis of the heat generation distribution of a heated object 690, which consists of a polypropylene (PP) cup filled with 150 g of potato salad, when heated. The left figure shows a cross-section along the direction of transport by the conveyor 661, and the right figure shows a cross-section perpendicular to the direction of transport by the conveyor 661. A uniform heat generation distribution was confirmed in the heated object 690.

[0108] 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]

[0109] 1,2,3,4,5 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 66 Holder 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 500 Test Equipment 510 Oscillator 521 Coaxial Cable 540a First Loop Antenna 540b Second Loop Antenna 561 Conveyor 582a First metal housing 582b Second metal casing 582c Third metal casing 590 Objects to be heated 591 First object to be heated 592 Second object to be heated 593 Third object to be heated 640a First Loop Antenna 640b Second Loop Antenna 640c Third Loop Antenna 653a First power supply section 653b Second power supply section 653c Third power supply section 661 Conveyor 682 Metal casing 690 Objects to be heated

Claims

1. A holder for holding the object to be irradiated, A power supply device configured to conduct electricity with an oscillator, A loop antenna, whose irradiation surface is an aperture, is configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply via conductivity through the aforementioned power supply device. Equipped with, At least one of the loop antenna and the holder is configured to move along the directional irradiation axis of the microwaves irradiated from the irradiation source, thereby changing the relative positional relationship between the loop antenna and the holder. Microwave irradiation device.

2. A holder for holding the object to be irradiated, A power supply device configured to conduct electricity with an oscillator, A loop antenna, whose irradiation surface is an aperture, is configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply via conductivity through the aforementioned power supply device. Equipped with, The retainer is provided by penetrating the opening surface. Microwave irradiation device.

3. The microwave irradiation apparatus according to claim 2, wherein the holder is configured to move in a direction that penetrates the opening surface.

4. A holder for holding the object to be irradiated, A power supply device configured to conduct electricity with an oscillator, A loop antenna, whose irradiation surface is an aperture, is configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply via conductivity through the aforementioned power supply device. Equipped with, All of the one or more loop antennas are positioned such that the directional irradiation axis of the microwaves irradiated from the irradiation source does not intersect with the structure constituting the holder. Microwave irradiation device.

5. A holder for holding the object to be irradiated, A power supply device configured to conduct electricity with an oscillator, A loop antenna, whose irradiation surface is an aperture, is configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply via conductivity through the aforementioned power supply device. A microwave irradiation device comprising, The antenna group comprises a plurality of loop antennas arranged along the directional irradiation axis of the microwaves irradiated from the irradiation source, Microwave irradiation device.

6. A holder for holding the object to be irradiated, A power supply device configured to conduct electricity with an oscillator, A loop antenna, whose irradiation surface is an aperture, is configured to irradiate microwaves from an irradiation source within the irradiation surface by power supply via conductivity through the aforementioned power supply device. A microwave irradiation device comprising, The antenna group comprises a plurality of the aforementioned loop antennas, The holder is provided so as to penetrate multiple of the opening surfaces of the antenna group. Microwave irradiation device.

7. The microwave irradiation apparatus according to claim 6, wherein the holder is configured to move in a direction that penetrates the opening surface.

8. The microwave irradiation device according to any one of claims 5 to 7, wherein the loop antenna constituting the antenna group is arranged such that the directional irradiation axis of the microwaves irradiated from the irradiation source does not intersect with at least the microwave-reflecting structure constituting the holder, which is located between the aperture surface of the loop antenna and the aperture surface of another loop antenna constituting the antenna group that faces the aperture surface of the loop antenna.

9. A method for manufacturing food, which includes heating food by irradiating it with microwaves, A method for producing food, wherein the microwave irradiation is performed using a microwave irradiation apparatus according to any one of claims 1 to 8.

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