Microwave irradiation device, microwave irradiation method, and food manufacturing method

Abstract

To provide proper impedance matching with an irradiated object.SOLUTION: A microwave irradiation apparatus 1 includes: a retainer such as a carrier device 85, which is constituted to hold an irradiated object in a holding position; a power feeding appliance such as a coaxial cable 21, which is constituted to be electrically connected with an oscillator 10; a power feeding antenna 40 with directivity, which is constituted to apply microwaves by power feeding based on conduction via the power feeding appliance, and which is arranged in the state of directing an irradiation axis to the holding position; and a parasitic antenna 50 which is arranged in the state of facing the power feeding antenna 40 across the holding position, which is arranged in the state of directing the irradiation axis to the holding position, and which is not supplied with electric power while having the directivity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a microwave irradiation device, a microwave irradiation method, and a food manufacturing method. [Background technology]

[0002] Generally, heating devices are known that dielectrically heat an object by irradiating it with microwaves. For efficient heating, impedance matching is required to ensure that energy is input to the object. When heating an object by irradiating microwaves toward the object using a directional antenna without using a waveguide or the like, some ingenuity is required for impedance matching. For example, Patent Document 1 discloses that, taking such impedance matching into consideration, the object and the antenna are repeatedly moved closer to and further away from each other to improve the heating efficiency of a microwave heating device. An example of the distance traveled during this process is shown to be in the range of several millimeters.

[0003] The impedance matching disclosed in Patent Document 1 can be considered a fine adjustment. When impedance matching is performed by adjusting the output frequency of a microwave oscillator that generates microwaves to the resonant frequency of an object to be irradiated, widening the output frequency range of a high-power oscillator involves restrictions on the frequency band of the components, as well as reduced efficiency, increased size, and increased cost, so the variable frequency range is limited. For example, if the type or number of objects to be irradiated changes, or if the position of the objects to be irradiated changes significantly, a different impedance matching mechanism is required. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2019-3868 Summary of the Invention [Problem to be solved by the invention]

[0005] An external matching box may be connected to the device to achieve impedance matching. In impedance matching using an external matching box, the resonant frequency is adjusted with the entire device as a load, so matching may occur not only with the irradiated object but also with other parts of the device.

[0006] An object of the present invention is to achieve good impedance matching with an object to be irradiated in microwave irradiation. [Means for solving the problem]

[0007] According to one aspect of the present invention, a microwave irradiation device includes a holder configured to hold an object to be irradiated at a holding position, a power supply device configured to be electrically conductive with an oscillator, a directional power supply antenna configured to irradiate microwaves by power supply through the power supply device and with its irradiation axis directed toward the holding position, and a directional but unpowered unpowered antenna positioned opposite the power supply antenna across the holding position and with its irradiation axis directed toward the holding position. [Effects of the Invention]

[0008] According to the present invention, good impedance matching with an object to be irradiated can be achieved in microwave irradiation. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram schematically illustrating an example of the basic configuration of a microwave radiating device according to a first embodiment. [Figure 2A] FIG. 2A is a diagram schematically showing the relationship between return loss and frequency when there is no parasitic antenna in FIG. [Figure 2B] FIG. 2B is a diagram showing a schematic diagram of the relationship between the return loss and the frequency when the parasitic antenna is adjusted and installed at an appropriate position. [Figure 3A]FIG. 3A is a diagram schematically illustrating an example in which one antenna is provided as a powered antenna and another antenna is provided as a parasitic antenna. [Figure 3B] FIG. 3B is a diagram schematically illustrating an example in which two antennas are provided as power-fed antennas and one antenna is provided as a parasitic antenna. [Figure 3C] FIG. 3C is a diagram schematically illustrating an example in which two antennas are provided as power-fed antennas and two antennas are provided as parasitic antennas. [Figure 4] FIG. 4 is a diagram schematically showing the positional relationship between the first power-fed loop antenna, the first parasitic loop antenna, and the irradiated object in Experimental Example 1. As shown in FIG. [Figure 5] FIG. 5 is a diagram showing the values ​​of the resonant frequency and the return loss measured in Experimental Example 1 with respect to the distance from the first power-fed loop antenna to the first parasitic loop antenna. [Figure 6] FIG. 6 is a diagram schematically showing the positional relationship between the first power-fed loop antenna, the second power-fed loop antenna, the first parasitic loop antenna, and the object to be irradiated in Experimental Example 2. In FIG. [Figure 7] FIG. 7 is a diagram showing the value of the resonant frequency measured in Experimental Example 2 versus the distance from the first power-fed loop antenna to the first parasitic loop antenna. [Figure 8] FIG. 8 is a diagram schematically showing the positional relationship between the first power-fed loop antenna, the second power-fed loop antenna, the first parasitic loop antenna, the second parasitic loop antenna, and the irradiated object in Experimental Example 3. In FIG. [Figure 9] FIG. 9 is a diagram showing the value of the resonant frequency versus the distance from the powered antenna to the parasitic antenna, measured in Experimental Example 3. [Figure 10] FIG. 10 is a diagram schematically showing the positional relationship between the first power-feeding loop antenna, the second power-feeding loop antenna, and the object to be irradiated in a comparative experimental example. [Figure 11] FIG. 11 shows the value of the resonant frequency versus the distance between the first and second feed loop antennas, measured in a comparative experiment. [Figure 12] FIG. 12 is a diagram schematically showing the positional relationship between the first power-fed antenna, the first parasitic antenna, and the irradiated object in Experimental Example 4. In FIG. [Figure 13] FIG. 13 is a plan view schematically showing a basic configuration of a part of an example of a microwave radiating device according to the second embodiment. [Figure 14] FIG. 14 is a diagram schematically illustrating an example of the basic configuration of a microwave radiating device according to the third embodiment. [Figure 15] FIG. 15 is a diagram schematically showing the arrangement of antennas and the like according to Experimental Example 5. In FIG. [Figure 16] FIG. 16 is a diagram showing the value of the resonant frequency with respect to the distance and length between the two auxiliary antennas. [Figure 17] FIG. 17 is a diagram showing the simulation results of the temperature distribution of the irradiated object when the irradiated object is heated by the microwave irradiating device of each configuration. [Figure 18] FIG. 18 is a diagram showing a change in the resonance frequency when one irradiation object is transported. [Figure 19] FIG. 19 is a diagram showing the change in the resonance frequency when three irradiation objects are transported. DETAILED DESCRIPTION OF THE INVENTION

[0010] [First embodiment] A first embodiment will be described with reference to the drawings. This embodiment relates to a microwave radiating device. The microwave radiating device of this embodiment is configured to radiate microwaves to an irradiated object to heat the inside of the irradiated object. In particular, this microwave radiating device uses a directional antenna, and radiates microwaves with its directional radiation axis directed toward the irradiated object. The irradiated object may be, but is not limited to, food. Therefore, this microwave radiating device and a microwave radiation method using the same can be used in the manufacture of food, including packaged foods. The microwave radiating device of this embodiment has excellent impedance matching capabilities. In particular, the same device can achieve appropriate impedance matching even in various situations where the type, number, and position of the irradiated object vary greatly, and efficient heating can be achieved by the same device.

[0011] <Basic configuration of microwave irradiation device> FIG. 1 is a diagram schematically illustrating an example of the basic configuration of a microwave irradiation device 1 according to this embodiment. The microwave irradiation device 1 is configured to sequentially heat objects to be irradiated 90 transported by a transport device 85. The transport device 85 is, for example, a belt conveyor. The transport device 85 has a belt 86 that moves in its longitudinal direction. The objects to be irradiated 90 are placed at a holding position on the belt 86 and transported in the longitudinal direction of the belt 86. In this way, in this embodiment, the transport device 85 functions as a holder that holds the objects to be irradiated 90 at the holding position.

[0012] The microwave radiating device 1 includes a power feeding antenna 40 configured to radiate microwaves to an object to be irradiated 90 transported by a transport device 85. The power feeding antenna 40 is a directional antenna such as a loop antenna. In the example shown in FIG. 1, the microwave radiating device 1 includes two loop antennas as the power feeding antenna 40, namely, a first power feeding loop antenna 41 and a second power feeding loop antenna 42. The number of power feeding loop antennas can be changed as appropriate.

[0013] The first and second power-fed loop antennas 41 and 42 are formed of, for example, a metal member having a length equivalent to one wavelength of the microwaves to be radiated, and the metal member has, for example, a circular ring shape. The metal member is not limited to a circular ring, and may have other ring shapes such as a square. Both ends of the metal member serve as power feed points. A power feeder, for example, a coaxial cable 21, is connected to the power feed points. High-frequency power is supplied to the first and second power-fed loop antennas 41 and 42 from the oscillator 10 via the coaxial cable 21. When power is supplied, a current flows through the metal member as an element, and the first and second power-fed loop antennas 41 and 42 radiate radio waves to form an electric field. In the loop antennas, the center of an aperture formed by the metal member serves as the radio wave radiation source, and the aperture serves as the radiation surface, radiating microwaves in both directions along an irradiation axis perpendicular to the aperture surface.

[0014] The microwave irradiation device 1 is configured so that the object to be irradiated 90 is transported by passing through the center of the opening, which is the irradiation surface of the first power-fed loop antenna 41 and the second power-fed loop antenna 42. For this reason, the belt 86 of the transport device 85 is provided so as to pass through the opening surfaces of the first power-fed loop antenna 41 and the second power-fed loop antenna 42. The irradiation surfaces of the first power-fed loop antenna 41 and the second power-fed loop antenna 42 are arranged perpendicular to the longitudinal direction of the belt 86, and the directional irradiation axes of the first power-fed loop antenna 41 and the second power-fed loop antenna 42 are arranged parallel to the longitudinal direction of the belt 86. In this embodiment, the directional irradiation axis of the power-fed antenna 40 is referred to as the reference axis.

[0015] The oscillator 10 outputs high-frequency power corresponding to the microwave frequency. The frequency may be, but is not limited to, 450 MHz, 915 MHz, or 2.45 GHz. The output frequency of the oscillator 10 can be adjusted to some extent, but the range is limited. To efficiently and appropriately heat the object 90, it is necessary to match the impedance of the oscillation system including the oscillator 10 and the power supply antenna 40 with the impedance of the object 90. In other words, the resonant frequency with the object 90 as a load must be within the range of the oscillator 10's oscillating frequencies. The oscillator 10 or an associated device has a function of monitoring reflected power.

[0016] For the above-mentioned impedance matching, the microwave radiating device 1 includes a parasitic antenna 50. In the example shown in Fig. 1, the microwave radiating device 1 includes one loop antenna, i.e., a first parasitic loop antenna 51, as the parasitic antenna 50. The number of parasitic loop antennas can be changed as appropriate.

[0017] The first parasitic loop antenna 51 has a configuration similar to the first power-fed loop antenna 41, etc., except that the coaxial cable 21 is not connected and no power is fed to the first parasitic loop antenna 51. That is, the first parasitic loop antenna 51 is formed of a metal member having a length equivalent to one wavelength of microwaves, and this metal member has a ring shape, etc. The first parasitic loop antenna 51 is not grounded. The first parasitic loop antenna 51 is disposed so that the object to be irradiated 90 passes through the center of the opening of the first parasitic loop antenna 51 and the belt 86 of the conveying device 85 passes through the opening. The first parasitic loop antenna 51 is disposed perpendicular to the longitudinal direction of the belt 86, i.e., perpendicular to the reference axis. Therefore, the irradiation axis of the first parasitic loop antenna 51 is disposed along the reference axis.

[0018] Furthermore, the parasitic antenna 50 is installed so as to be movable along the reference axis. As will be described later, by moving the parasitic antenna 50 along the reference axis, the resonant frequency of the microwave irradiating device 1 with the object 90 to be irradiated as a load changes. In the microwave irradiating device 1, the position of the parasitic antenna 50 is adjusted along the reference axis for impedance matching. In this way, although the position of the object 90 to be irradiated changes due to the transport device 85 and the parasitic antenna 50 moves along the reference axis, the irradiation axes of the powered antenna 40 and the parasitic antenna 50 are directed toward the holding position of the transport device 85 where the object 90 to be irradiated is held.

[0019] In order to adjust the position of the parasitic antenna 50, the microwave irradiator 1 is provided with a position adjustment mechanism 60. In the example shown in FIG. 1 , the position adjustment mechanism 60 has a support part 62 that supports the parasitic antenna 50 and a rail 63 that supports the support part 62 so that the support part 62 can move along a reference axis. The position adjustment mechanism 60 also has a control part 61 that controls the position of the support part 62 on the rail 63. The control part 61 is also connected to the oscillator 10, and acquires information about the return loss measured by the oscillator 10.

[0020] The configuration of the position adjustment mechanism 60 shown here is just one example, and the position adjustment mechanism 60 may have any configuration as long as it can change the position of the parasitic antenna 50. For example, the position adjustment mechanism 60 does not have to be capable of continuously changing the position of the parasitic antenna 50. The position adjustment mechanism 60 may be configured so that the user manually adjusts and fixes the position of the parasitic antenna 50. The position adjustment mechanism 60 may also be configured so that the position of the fed antenna 40 can be changed. That is, the position adjustment mechanism 60 may be configured in any way so long as it can change the relative distance between the fed antenna 40 and the parasitic antenna 50. For example, the position adjustment mechanism 60 may be a fixture that can variably fix the position of the fed antenna 40 or the parasitic antenna 50. However, it is more preferable that the position adjustment mechanism 60 be configured so that the position of the fed antenna 40 is fixed and the position of the parasitic antenna 50 is variable.

[0021] The microwave irradiating device 1 includes a metal housing 80 for blocking microwaves. That is, the power-fed antenna 40 and the parasitic antenna 50 are covered by the metal housing 80. Furthermore, a belt 86 of the conveying device 85 passes through the metal housing 80. More specifically, the metal housing 80 includes a main housing 81. The power-fed antenna 40 and the parasitic antenna 50 are disposed within the main housing 81. Through-holes through which the belt 86 passes are provided on both side surfaces of the main housing 81. A side housing 82 large enough to allow the belt 86 and the object to be irradiated 90 placed thereon to pass through is connected to each of these through-holes.

[0022] Impedance matching using the parasitic antenna 50 will be described with reference to FIGS. 2A and 2B. FIG. 2A schematically shows the relationship between return loss and frequency when the parasitic antenna 50 is not provided, i.e., when the parasitic antenna 50 is not provided in FIG. 1. FIG. 2B schematically shows the relationship between return loss and frequency when the parasitic antenna 50 is adjusted and provided in an appropriate position. This relationship can generally be easily obtained using a network analyzer or the like. Note that the shaded range of 445 MHz to 465 MHz in these figures is the frequency range that the oscillator 10 can output.

[0023] In FIG. 2A, several peaks are observed. These peaks are resonant frequencies. Among these peaks, the peak indicated by (a) in the figure is the resonant frequency associated with the irradiated object 90. In FIG. 2A, where the parasitic antenna 50 is not provided, the resonant frequency associated with the irradiated object 90 indicated by (a) is outside the range of frequencies that can be output by the oscillator 10, indicated by the shaded area.

[0024] 2B, in which the parasitic antenna 50 is provided, the resonant frequency of the object 90 shown in (a) is within the range of frequencies that can be output by the oscillator 10, which is shown shaded. If the resonant frequency with the object 90 as a load is within the range of frequencies that can be output by the oscillator 10, the output frequency can be made to match this resonant frequency by adjusting the oscillator 10. In this case, the object 90 can be heated efficiently.

[0025] <Operation of microwave irradiation device> The operation of the microwave radiating device 1 of this embodiment will be described. High frequency power output from the oscillator 10 is supplied to the power feeding antenna 40 via the coaxial cable 21. The power feeding antenna 40 radiates microwaves based on this power supply.

[0026] When the irradiated object 90 is changed, the position of the parasitic antenna 50 is adjusted to match the impedance according to the irradiated object 90. At this time, microwaves are irradiated and the return loss is monitored with the irradiated object 90 placed between the powered antenna 40 and the parasitic antenna 50. The control unit 61 acquires the return loss value measured by the oscillator 10, etc., and the position adjustment mechanism 60 adjusts the position of the parasitic antenna 50 so that the resonant frequency of the irradiated object 90 is within the range of the output frequency of the oscillator 10.

[0027] After impedance matching is performed, the microwave irradiation device 1 is used. That is, heating of the object 90 to be irradiated is performed using the microwave irradiation device 1. The object 90 to be irradiated is transported one after another to a heating position between the powered antenna 40 and the parasitic antenna 50 by the transport device 85, and the object 90 to be irradiated is dielectrically heated one after another by the irradiation of microwaves from the powered antenna 40. The transport device 85 may be moved intermittently so that the object 90 to be irradiated stops at the heating position, or the transport device 85 may be moved continuously so that the object 90 to be irradiated passes through the heating position over a sufficient period of time.

[0028] Here, an example has been shown in which the operation relating to impedance matching is performed before the microwave radiating device 1 is used, but the present invention is not limited to this. The operation relating to impedance matching may be performed while the microwave radiating device 1 is in use.

[0029] <Configuration example of microwave irradiation device> The microwave radiating device 1 described above can be configured in several patterns with different numbers of powered antennas 40 and parasitic antennas 50. Although not limited to these, three examples are shown in Figs. 3A to 3C.

[0030] 3A is an example in which one antenna, i.e., a first power-fed loop antenna 41, is provided as the power-fed antenna 40, and one parasitic antenna, i.e., a first parasitic loop antenna 51, is provided as the parasitic antenna 50. The first parasitic loop antenna 51 is configured to be movable along a reference axis.

[0031] 3B is an example in which two antennas, i.e., a first power-fed loop antenna 41 and a second power-fed loop antenna 42, are provided as the power-fed antenna 40, and one parasitic antenna, i.e., a first parasitic loop antenna 51, is provided as the parasitic antenna 50. The first parasitic loop antenna 51 is disposed between the first power-fed loop antenna 41 and the second power-fed loop antenna 42. The first parasitic loop antenna 51 is configured to be movable between the first power-fed loop antenna 41 and the second power-fed loop antenna 42 along the reference axis.

[0032] 3C is an example in which two antennas, namely, a first power-fed loop antenna 41 and a second power-fed loop antenna 42, are provided as the power-fed antenna 40, and two parasitic antennas, namely, a first power-fed loop antenna 51 and a second power-fed loop antenna 52, are provided as the parasitic antenna 50. The first power-fed loop antenna 51 and the second power-fed loop antenna 52 are arranged between the first power-fed loop antenna 41 and the second power-fed loop antenna 42. The first power-fed loop antenna 51 and the second power-fed loop antenna 52 are configured to be movable between the first power-fed loop antenna 41 and the second power-fed loop antenna 42 along the reference axis, respectively.

[0033] As will be described later, in this example, the first power-fed loop antenna 41 and the first parasitic loop antenna 51 form a pair, and the second power-fed loop antenna 42 and the second parasitic loop antenna 52 form a pair. The first parasitic loop antenna 51 is disposed between the second power-fed loop antenna 42 and the second parasitic loop antenna 52, and the second parasitic loop antenna 52 is disposed between the first power-fed loop antenna 41 and the first parasitic loop antenna 51.

[0034] Experimental Example 1 3A, that is, using a microwave radiating device 1 equipped with one first power-fed loop antenna 41 and one first parasitic loop antenna 51, the resonant frequency and return loss were measured with the irradiated object 90 as a load when the position of the first parasitic loop antenna 51 was changed. In addition, the temperature when the irradiated object 90 was heated using the same device was measured.

[0035] (method) In the microwave irradiation device 1 of the test device, the main housing 81 was made of aluminum and had dimensions of 440 mm in length along the conveying direction, 350 mm in width perpendicular to the conveying direction, and 400 mm in height. Each of the side housings 82 was also made of aluminum and had dimensions of 250 mm in length, 220 mm in width, and 80 mm in height. A resin belt 86 of the conveying device 85 was provided to pass through the metal housing 80, and had a width of 150 mm.

[0036] A circular first power-feeding loop antenna 41 was provided inside the main housing 81 so that the belt 86 could pass through it. The first power-feeding loop antenna 41 was made of aluminum and had an inner diameter of 232 mm, an outer diameter of 258 mm, and a thickness of 2 mm. The oscillator 10 was connected to the first power-feeding loop antenna 41 via a coaxial cable 21. The frequency of the output power of the oscillator 10 was 450 MHz (output wavelength λ = 666 mm).

[0037] Similar to the first power-fed loop antenna 41, a circular first parasitic loop antenna 51 was provided inside the main housing 81 so that the belt 86 could pass through it. The first parasitic loop antenna 51 was made of aluminum and had an inner diameter of 232 mm, an outer diameter of 258 mm, and a thickness of 2 mm.

[0038] The object to be irradiated 90 was a polypropylene (PP) cup having a diameter of 85 mm filled with 140 g of potato salad. The object to be irradiated 90 was placed on the belt 86 so that the distance from the first feeding loop antenna 41 was 167 mm (λ / 4).

[0039] The resonant frequency and return loss were measured using a network analyzer, where the return loss RL is defined as follows: RL = 20 log 10 (b1 / a1) where a1 is the square root of the input power and b1 is the square root of the reflected power.

[0040] 4 is a schematic diagram illustrating the positional relationship between the above-mentioned first power-fed loop antenna 41, first parasitic loop antenna 51, and irradiated object 90. Measurements were performed under conditions where the distance between the first parasitic loop antenna 51 and the first power-fed loop antenna 41 was 42 mm, 83 mm, 125 mm, 167 mm, 208 mm, 250 mm, 292 mm, and 333 mm. That is, measurements were performed with the first parasitic loop antenna 51 placed at each of the positions (a) to (h) indicated by the dashed lines in FIG. 4.

[0041] In the temperature measurement experiment of the irradiated object 90, the initial temperature of the irradiated object 90 was set to 10° C., the output was set to 150 W, and the temperature was measured after heating for 5 minutes.

[0042] (result) FIG. 5 shows the values ​​of the resonant frequency and the return loss as a function of the distance from the first parasitic loop antenna 41 to the first parasitic loop antenna 51. The resonant frequency was lowest at 451 MHz when the distance from the first parasitic loop antenna 51 to the first power-fed loop antenna 41 was 167 mm and 208 mm. The resonant frequency increased as the distance from the first parasitic loop antenna 51 to the first power-fed loop antenna 41 decreased from 167 mm to 42 mm. The resonant frequency increased as the distance from the first parasitic loop antenna 51 to the first power-fed loop antenna 41 increased from 208 mm to 333 mm. The return loss was almost constant when the distance from the first parasitic loop antenna 51 to the first power-fed loop antenna 41 was 167 mm or less, and decreased as the distance increased from 167 mm to 333 mm.

[0043] Since the irradiated object 90 is located at a position where the distance from the first power-fed loop antenna 41 to the first parasitic loop antenna 51 is 167 mm, when the distance from the first power-fed loop antenna 41 to the first parasitic loop antenna 51 is shorter than 167 mm, the irradiated object 90 is located outside the gap between the two antennas, the first power-fed loop antenna 41 and the first parasitic loop antenna 51. When the distance from the first power-fed loop antenna 41 to the first parasitic loop antenna 51 is longer than 167 mm, the irradiated object 90 is located inside the gap between the two antennas, the first power-fed loop antenna 41 and the first parasitic loop antenna 51.

[0044] The temperature of the irradiated object 90 after heating was measured when the resonant frequency was 455 MHz, the median value of the oscillator 10's output frequency range of 445 MHz to 465 MHz. Specifically, the temperature of the irradiated object 90 after heating was measured when the distance between the first power-fed loop antenna 41 and the first parasitic loop antenna 51 was 125 mm and 241 mm. When the antenna distance was 125 mm, the return loss was -8 dB, and when the antenna distance was 241 mm, the return loss was -12 dB. After heating the irradiated object 90 at an initial temperature of 10°C for 5 minutes at 150 W, the temperature reached 32°C when the antenna distance was 125 mm and 74°C when the antenna distance was 241 mm. This suggests that when the irradiated object 90 is placed between the power-fed antenna 40 and the parasitic antenna 50 and the resonant frequencies are matched to achieve impedance matching, the return loss is small and the heating efficiency is improved.

[0045] Experimental Example 2 Using the microwave irradiation device 1 having the configuration shown in Figure 3B, i.e., using the microwave irradiation device 1 having two power-fed antennas 40, the first power-fed loop antenna 41 and the second power-fed loop antenna 42, and one first parasitic loop antenna 51, the resonant frequency was measured with the irradiated object 90 as a load when the position of the first parasitic loop antenna 51 was changed.

[0046] (method) Except for the arrangement of the power-fed antenna 40, the experiment was conducted under the same conditions as in Experimental Example 1. That is, the configurations of the metal housing 80, belt 86, etc. were the same as in Experimental Example 1. The first power-fed loop antenna 41 and the second power-fed loop antenna 42 had the same configuration as the first power-fed loop antenna 41 in Experimental Example 1. The first parasitic loop antenna 51 had the same configuration as the first parasitic loop antenna 51 in Experimental Example 1.

[0047] The distance between the first power-fed loop antenna 41 and the second power-fed loop antenna 42 was 333 mm. The oscillator 10 was connected to the first power-fed loop antenna 41 and the second power-fed loop antenna 42 via a coaxial cable 21. The frequency of the output power of the oscillator 10 was 450 MHz, and power was fed to the first power-fed loop antenna 41 and the second power-fed loop antenna 42 in phase.

[0048] The irradiated object 90 was a polypropylene (PP) cup having a diameter of 85 mm filled with 140 g of potato salad, as in Experimental Example 1. The irradiated object 90 was placed on the belt 86 at a position midway between the first power-feeding loop antenna 41 and the second power-feeding loop antenna 42, i.e., at a distance of 167 mm from each of the first power-feeding loop antenna 41 and the second power-feeding loop antenna 42.

[0049] The resonant frequency was measured under conditions where the distance between the first parasitic loop antenna 51 and the first power-fed loop antenna 41 was 167 mm, 208 mm, 250 mm, and 292 mm. The resonant frequency was also measured under the same conditions except that the first parasitic loop antenna 51 was not placed.

[0050] 6 is a schematic diagram illustrating the positional relationship between the first power-fed loop antenna 41, the second power-fed loop antenna 42, the first parasitic loop antenna 51, and the irradiated object 90. The first parasitic loop antenna 51 was placed at each of the positions (a) to (d) indicated by the dashed lines. In Experimental Example 1, it was found to be meaningful to consider a case where the irradiated object 90 is placed between the power-fed antenna 40 and the parasitic antenna 50. Therefore, the distance between the first parasitic loop antenna 51 and the power-fed antenna 40 was defined as the distance between the first power-fed loop antenna 41 and the first parasitic loop antenna 51, rather than the distance between the second power-fed loop antenna 42, so that the irradiated object 90 is placed between the power-fed antenna 40 and the parasitic antenna 50.

[0051] (result) Fig. 7 shows the value of the resonant frequency versus the distance from the first power-fed loop antenna 41 to the first parasitic loop antenna 51. When the first parasitic loop antenna 51 was not placed, the resonant frequency was 513 MHz, and this value is shown by the dashed line in Fig. 7. When the first parasitic loop antenna 51 was placed, the resonant frequency was lower in all cases than when the first parasitic loop antenna 51 was not placed.

[0052] The resonant frequency was lowest at 460 MHz when the distance from the first parasitic loop antenna 51 to the first power-fed loop antenna 41 was 167 mm. The resonant frequency became higher as the distance from the first parasitic loop antenna 51 to the first power-fed loop antenna 41 increased. This was a similar trend to the results of Experimental Example 1.

[0053] When the first parasitic loop antenna 51 is not placed, the resonant frequency is significantly different from the oscillating frequency range of 445 MHz to 465 MHz of the oscillator 10. However, it has become clear that by placing the first parasitic loop antenna 51, the resonant frequency can be set within the range of the oscillating frequency of the oscillator 10.

[0054] Experimental Example 3 Using a microwave irradiation device 1 having the configuration shown in Figure 3C, i.e., a microwave irradiation device 1 having two power-fed antennas 40, a first power-fed loop antenna 41 and a second power-fed loop antenna 42, and two parasitic antennas 50, a first parasitic loop antenna 51 and a second parasitic loop antenna 52, the resonant frequency was measured with the irradiated object 90 as a load when the position of the parasitic antenna 50 was changed.

[0055] (method) The experiment was conducted under the same conditions as in Experimental Example 2, except for the placement of the parasitic antenna 50. That is, the configurations of the metal housing 80, belt 86, etc. were the same as in Experimental Example 2. The first power-fed loop antenna 41 and the second power-fed loop antenna 42 had the same configuration as the first power-fed loop antenna 41 and the second power-fed loop antenna 42 in Experimental Example 2. The distance between the first power-fed loop antenna 41 and the second power-fed loop antenna 42 was 333 mm. The first parasitic loop antenna 51 and the second parasitic loop antenna 52 had the same configuration as the first parasitic loop antenna 51 in Experimental Example 2.

[0056] The object to be irradiated 90 was a polypropylene (PP) cup having a diameter of 85 mm filled with 140 g of potato salad, as in Experimental Example 2. The object to be irradiated 90 was placed on the belt 86 at a position midway between the first power-feeding loop antenna 41 and the second power-feeding loop antenna 42, i.e., at a distance of 167 mm from each of the first power-feeding loop antenna 41 and the second power-feeding loop antenna 42.

[0057] In Experimental Example 1, it was found to be meaningful to consider a case where an irradiated object 90 is placed between the power-fed antenna 40 and the parasitic antenna 50. Therefore, the first power-fed loop antenna 41 and the first parasitic loop antenna 51, which are placed on either side of the irradiated object 90, were considered as a pair, and the second power-fed loop antenna 42 and the second parasitic loop antenna 52, which are placed on either side of the irradiated object 90, were considered as a pair. In other words, the first parasitic loop antenna 51 is placed between the second power-fed loop antenna 42 and the second parasitic loop antenna 52, and the second parasitic loop antenna 52 is placed between the first power-fed loop antenna 41 and the first parasitic loop antenna 51.

[0058] The resonant frequency was measured under the following conditions: the distance between the first parasitic loop antenna 51 and the first-fed loop antenna 41, and the distance between the second parasitic loop antenna 52 and the second-fed loop antenna 42 were 208 mm, 250 mm, and 292 mm. FIG. 8 shows a schematic diagram of the positional relationship between the first-fed loop antenna 41, the second-fed loop antenna 42, the first parasitic loop antenna 51, the second parasitic loop antenna 52, and the irradiated object 90. The first parasitic loop antenna 51 and the second parasitic loop antenna 52 were positioned at the positions indicated by dashed lines (a) to (c). As described above, the distance between the parasitic antenna 50 and the fed antenna 40 was defined so that the irradiated object 90 was placed between the fed antenna 40 and the parasitic antenna 50.

[0059] (result) Fig. 9 shows the value of the resonant frequency with respect to the distance from the powered antenna 40 to the parasitic antenna 50. When the parasitic antenna 50 was not placed, the resonant frequency was 513 MHz, and this value is shown by the dashed line in Fig. 9. When the parasitic antenna 50 was placed, the resonant frequency was lower in all cases than when the parasitic antenna 50 was not placed. . salary The greater the distance from the powered antenna 40 to the parasitic antenna 50, the higher the resonant frequency. This was a similar trend to the results of Experimental Examples 1 and 2. However, even though the distance from the powered antenna 40 to the parasitic antenna 50 was the same, the resonant frequency was lower in Experimental Example 3, in which two parasitic loop antennas were arranged, than in Experimental Example 2, in which one parasitic loop antenna was arranged. In other words, the resonant frequency could be adjusted by changing the number of parasitic antennas arranged.

[0060] First parasitic loop antenna 51 and second parasitic loop antenna 52 If the first parasitic loop antenna 51 and the second parasitic loop antenna 52 were not placed, the resonant frequency would be significantly different from the range of 445 MHz to 465 MHz that the oscillator 10 can oscillate at. However, it was revealed that by placing the first parasitic loop antenna 51 and the second parasitic loop antenna 52, the resonant frequency can be set within the range of the oscillator 10's range of oscillation.

[0061] <Example of comparative experiment> Without providing the parasitic antenna 50, the resonant frequency was measured with the object to be irradiated 90 as a load when the distance between the two power-fed antennas 40 was changed.

[0062] (method) An experiment was conducted under the same conditions as in Experimental Example 2, except that the parasitic antenna 50 was not placed and the distance between the first power-fed loop antenna 41 and the second power-fed loop antenna 42 was changed. That is, the configurations of the metal housing 80, belt 86, etc. were the same as in Experimental Example 2. The first power-fed loop antenna 41 and the second power-fed loop antenna 42 had the same configuration as the first power-fed loop antenna 41 and the second power-fed loop antenna 42 in Experimental Example 2.

[0063] The object to be irradiated 90 was a polypropylene (PP) cup having a diameter of 85 mm filled with 140 g of potato salad, as in Experimental Example 2. The object to be irradiated 90 was placed on the belt 86 so as to be midway between the first power-feeding loop antenna 41 and the second power-feeding loop antenna 42.

[0064] The resonance frequency was measured under conditions where the distance between the first power-fed loop antenna 41 and the second power-fed loop antenna 42 was 167 mm, 250 mm, 333 mm, and 417 mm. Fig. 10 is a schematic diagram showing the positional relationship between the first power-fed loop antenna 41, the second power-fed loop antenna 42, and the irradiated object 90. The first power-fed loop antenna 41 and the second power-fed loop antenna 42 were placed at the positions indicated by dashed lines (a) to (d).

[0065] (result) 11 shows the resonant frequency versus the distance between the first power-fed loop antenna 41 and the second power-fed loop antenna 42. The resonant frequency decreased as the distance between the antennas increased. This shows that the resonant frequency can be adjusted by changing the distance between the first power-fed loop antenna 41 and the second power-fed loop antenna 42.

[0066] The reason why the resonant frequency decreases when the distance between the antennas is thought to be because the coupling between the antennas is weakened. Considering this, the reason why the resonant frequency decreases when the parasitic antenna 50 is provided in this embodiment is thought to be due to the following reason. That is, a current is induced in the parasitic antenna 50 in the opposite direction to that in the fed antenna 40. It is thought that this reverse induced current acts to weaken the coupling between the fed antennas 40 and between the fed antenna 40 and other elements. Furthermore, this effect is stronger the closer the parasitic antenna 50 and the fed antenna 40 are, which is thought to be why the results shown in Experimental Examples 1 to 3 above were obtained.

[0067] Although the resonant frequency can be adjusted by changing the distance between the first power-fed loop antenna 41 and the second power-fed loop antenna 42 without using the parasitic antenna 50, this requires a large metal housing 80 to significantly change the antenna positions. Furthermore, adjusting the positions of the first power-fed loop antenna 41 and the second power-fed loop antenna 42 connected to the coaxial cable 21 is more difficult than adjusting the position of the parasitic antenna 50 not connected to the coaxial cable 21. Therefore, this embodiment, which can adjust the resonant frequency by adjusting the position of the parasitic antenna 50 while fixing the position of the power-fed antenna 40, is considered to be advantageous in terms of the size of the device, simplicity of the device configuration, etc.

[0068] Experimental Example 4 Using the microwave irradiation device 1 having the configuration shown in Figure 3A, i.e., using the microwave irradiation device 1 having one first power-fed loop antenna 41 and one first unpowered loop antenna 51, we investigated the relationship between the position of the irradiated object 90 when performing impedance matching and the reflection loss when the irradiated object 90 is heated.

[0069] (method) The length of the main housing 81 of the microwave radiating device 1 along the transport direction was set to 660 mm. The configurations of the side housing 82, belt 86, etc. were the same as in Experimental Example 1. The distance between the first power-fed loop antenna 41 and the first parasitic loop antenna 51 was set to 333 mm. The other configurations of the microwave radiating device 1 were the same as in Experimental Example 1.

[0070] The irradiated object 90 was a polypropylene (PP) cup having a diameter of 85 mm filled with 140 g of potato salad, as in Experimental Example 1. Three irradiated objects 90 were placed on the belt 86 at intervals of 120 mm.

[0071] FIG. 12 schematically illustrates the positional relationship between the first power-fed loop antenna 41, the first parasitic loop antenna 51, and the irradiated object 90. When impedance matching was performed with the irradiated object 90 placed between the first power-fed loop antenna 41 and the first parasitic loop antenna 51, the resonant frequency and the resulting return loss were measured in the state shown in the upper left column of FIG. That is, with one of the three irradiated objects 90 placed between the first power-fed loop antenna 41 and the first parasitic loop antenna 51, the resonant frequency was identified, and the return loss was measured when the output frequency was set to the resonant frequency. With the output frequency fixed at the resonant frequency, three irradiated objects 90 were placed between the first power-fed loop antenna 41 and the first parasitic loop antenna 51, as shown in the lower left column of FIG. 12, and the return loss was measured.

[0072] When impedance matching was performed without an irradiated object 90 being placed between the first power-fed loop antenna 41 and the first parasitic loop antenna 51, the resonant frequency and the resulting return loss were measured in the state shown in the upper right column of Fig. 12. That is, the resonant frequency was identified with the irradiated object 90 placed outside the first power-fed loop antenna 41 and the first parasitic loop antenna 51, at a position 60 mm away from the first parasitic loop antenna 51, and the return loss was measured when the output frequency was set to the resonant frequency. With the output frequency fixed at the resonant frequency, three irradiated objects 90 were placed between the first power-fed loop antenna 41 and the first parasitic loop antenna 51, as shown in the lower right column of Fig. 12, and the return loss was measured.

[0073] (result) As shown in the upper left column of Fig. 12, when impedance matching was performed with one irradiated object 90 placed between the first power-fed loop antenna 41 and the first parasitic loop antenna 51, the resonant frequency was 427 MHz and the return loss at this time was -12 dB. The irradiated object 90 was then moved with the output frequency fixed at 427 MHz, and as shown in the lower left column of Fig. 12, three irradiated objects 90 were placed between the first power-fed loop antenna 41 and the first parasitic loop antenna 51. In this case, the return loss was -18 dB, maintaining a sufficiently small return loss.

[0074] As shown in the upper right column of Fig. 12, when impedance matching was performed without an irradiated object 90 being placed between the first power-fed loop antenna 41 and the first parasitic loop antenna 51, the resonant frequency was 432 MHz and the return loss at this time was -12 dB. The irradiated objects 90 were moved while the output frequency was fixed at 432 MHz, and as shown in the lower right column of Fig. 12, three irradiated objects 90 were placed between the first power-fed loop antenna 41 and the first parasitic loop antenna 51. In this case, the return loss was -4.4 dB, which was large and inefficient.

[0075] These results reveal that, particularly when the microwave output frequency is fixed and the irradiated object 90 is transported and heated, impedance matching can be performed with the irradiated object 90 placed between the first power-fed loop antenna 41 and the first unpowered loop antenna 51, thereby achieving efficient heating with little reflection loss.

[0076] [Second embodiment] Various embodiments will be described as the second embodiment. Here, differences from the first embodiment will be described, and the same parts will be denoted by the same reference numerals and will not be described again. In the first embodiment, the belt 86 of the conveying device 85 is arranged to pass through the power-fed antenna 40 and the parasitic antenna 50, but this is not limiting.

[0077] For example, the reference axis and the longitudinal direction of the belt 86 may be perpendicular to each other. Fig. 13 is a plan view schematically showing one example of this. In this example, the first power-fed loop antenna 41 and the second power-fed loop antenna 42 are arranged to sandwich the belt 86, and the first parasitic loop antenna 51 and the second parasitic loop antenna 52 are arranged between the first power-fed loop antenna 41 and the second power-fed loop antenna 42 to sandwich the belt 86. The first parasitic loop antenna 51 and the second parasitic loop antenna 52 are configured to be movable so that the distance between them can be changed.

[0078] Alternatively, only one of the first parasitic loop antenna 51 and the second parasitic loop antenna 52 may be provided. Alternatively, only the first power-fed loop antenna 41 and the first parasitic loop antenna 51 may be provided.

[0079] In addition, a configuration consisting of the first power-fed loop antenna 41, the second power-fed loop antenna 42, the first parasitic loop antenna 51, the second parasitic loop antenna 52, etc. may be considered as one set, and multiple sets of these may be arranged along the belt 86.

[0080] In these examples, the powered antenna 40 is not limited to a loop antenna, and various directional antennas such as a microstrip antenna may be used. Similarly, the parasitic antenna 50 is not limited to a loop antenna, and other antennas or various conductors that function as antennas may be used. In these examples, since the position of the irradiated object 90 changes depending on the conveying device 85, the irradiation axes of the powered antenna 40 and the parasitic antenna 50 will be directed at the holding position of the conveying device 85 where the irradiated object 90 is held, at least temporarily, if not always.

[0081] Furthermore, in the first and second embodiments, an example has been described in which the irradiation object 90 is transported by the transport device 85, but this is not limiting. Instead of the transport device 85, a table configured to place the irradiation object 90 on a reference axis may be provided. As described above, in these embodiments, various types of holders are used, such as the belt 86 of the transport device 85 or a table, configured to hold the irradiation object 90 on the reference axis between the power-fed antenna 40 and the parasitic antenna 50, even if only temporarily. That is, at least temporarily, the irradiation axes of the power-fed antenna 40 and the parasitic antenna 50 are directed toward the holding position where the irradiation object 90 is held.

[0082] [Third embodiment] A third embodiment will be described. Here, differences from the first embodiment will be described, and the same parts will be assigned the same reference numerals and their description will be omitted. In addition to the configuration of the first embodiment, another parasitic antenna may be provided.

[0083] 14 is a diagram showing a schematic outline of a configuration example of a microwave radiating device 1 according to this embodiment. In this example, elongated, plate-shaped, unpowered auxiliary antennas 56 are provided on both sides of a belt 86 in parallel with the belt 86. The auxiliary antennas 56 are not grounded.

[0084] When power is supplied to the power supply antenna 40, a current is induced in the auxiliary antenna 56. This induced current also affects the electric field around the irradiated object 90. The length, width, shape, number, and arrangement of the auxiliary antennas 56 can be changed as appropriate. The auxiliary antennas 56 may be fixed or movable. The auxiliary antennas 56 can be used to adjust the state of the electric field around the irradiated object 90. It goes without saying that this embodiment can be applied in combination with the second embodiment.

[0085] Experimental Example 5 Without providing the parasitic antenna 50, two auxiliary antennas 56 were provided, and the resonance frequency was measured with the object to be irradiated 90 as a load when the spacing between the auxiliary antennas 56 was changed.

[0086] (method) The length of the main housing 81 of the microwave radiating device 1 along the conveyance direction was set to 660 mm. The configurations of the side housing 82 and the belt 86, etc. were the same as those in Experimental Example 2. An experiment was conducted under the same conditions as in Experimental Example 2, except that the parasitic antenna 50 was not placed, but two auxiliary antennas 56 were placed, and the spacing between the auxiliary antennas 56 was changed.

[0087] 15 is a diagram showing a schematic diagram of the arrangement of antennas, etc. The distance between the first power-feeding loop antenna 41 and the second power-feeding loop antenna 42 was set to 333 mm. The object to be irradiated 90 was a polypropylene (PP) cup having a diameter of 85 mm filled with 140 g of potato salad, as in Experimental Example 2. The object to be irradiated 90 was placed on the belt 86 so as to be midway between the first power-feeding loop antenna 41 and the second power-feeding loop antenna 42.

[0088] The auxiliary antennas 56 had a width W of 20 mm and three lengths L of 320 mm, 400 mm, and 480 mm. Two auxiliary antennas 56 were placed on either side of the irradiated object 90, with their longitudinal axes parallel to the irradiation axes of the first power-fed loop antenna 41 and the second power-fed loop antenna 42. For each of the auxiliary antennas 56 with different lengths, the resonant frequency was measured under conditions in which the spacing D between the auxiliary antennas 56 was changed from 90 mm to 150 mm.

[0089] (result) FIG. 16 shows the value of the resonant frequency versus the distance and length between the two auxiliary antennas 56. When the auxiliary antenna 56 was not placed, the resonant frequency was 489 MHz. This value is shown by the dashed line in FIG. 16. In both cases where the auxiliary antenna 56 was placed, the resonant frequency was lower than when the auxiliary antenna 56 was not placed. As the distance between the auxiliary antennas 56 increased, the resonant frequency increased. As the length of the auxiliary antenna increased, the resonant frequency decreased.

[0090] It was confirmed that the resonant frequency can be adjusted by changing the spacing or length of the auxiliary antennas 56 without using the parasitic antenna 50. However, the adjustment range for the spacing of the auxiliary antennas 56 is limited by the size of the irradiated object, and changing the length requires replacing parts, making the adjustment complicated and discontinuous.

[0091] FIG. 17 shows the results of a simulation of the temperature distribution of the irradiated object 90 when the irradiated object 90 is heated by the microwave irradiation device described above. In FIG. 17, the upper part shows the model used in the analysis, and the lower part shows the temperature distribution obtained as a result of the analysis. (a) shows the case where only the powered antenna 40 is provided, without the parasitic antenna 50 and auxiliary antenna 56. (b) shows the case where the auxiliary antenna 56 is provided, without the parasitic antenna 50. (c) and (d) show the cases where the parasitic antenna 50 is provided, without the auxiliary antenna 56. Here, (c) shows the case where the parasitic antennas 50 are arranged so that the gaps 54 provided in the two parasitic antennas 50 are both on the upper side, and (d) shows the case where the parasitic antennas 50 are arranged so that the gaps 54 provided in one parasitic antenna 50 are on the upper side and the gaps 54 provided in the other parasitic antenna 50 are on the lower side.

[0092] When the auxiliary antenna 56 shown in (b) was used, the temperature distribution changed significantly compared to when only the powered antenna 40 was used as shown in (a). This suggests that providing the auxiliary antenna 56 to adjust the resonant frequency can affect the temperature distribution. When the parasitic antenna 50 shown in (c) and (d) was used, a temperature distribution relatively similar to that obtained when only the powered antenna 40 was used as shown in (a) was obtained. This confirms that by using the parasitic antenna 50, the resonant frequency can be adjusted while minimizing the effect on the temperature distribution.

[0093] A comparison of (c) and (d) suggests that the temperature distribution when multiple parasitic antennas 50 are used is affected by the position of the gap 54 provided in the parasitic antennas 50. When multiple parasitic antennas 50 are used, by arranging the parasitic antennas 50 so that their gaps 54 are on opposite sides, a temperature distribution closer to that obtained when only the powered antenna 40 is used was obtained than when the parasitic antennas 50 are arranged so that their gaps 54 are on the same side. It was confirmed that by arranging the parasitic antennas 50 so that their gaps 54 are on opposite sides, it is possible to adjust the resonant frequency without affecting the temperature distribution.

[0094] From the above, it is believed that the method of adjusting the resonant frequency by adjusting the position of the parasitic antenna 50 is superior in terms of simplicity of the device configuration and little effect on the temperature distribution.

[0095] Experimental Example 6 The change in resonant frequency when the irradiated object 90 was transported was measured for each device when only the power feeding antenna 40 was arranged, and when the auxiliary antenna 56 or the parasitic antenna 50 was arranged in addition to the power feeding antenna 40.

[0096] (method) The length of the main housing 81 of the microwave radiating device 1 along the transport direction was 660 mm. The configurations of the side housing 82 and belt 86, etc. were the same as in Experimental Example 2. The distance between the first power-fed loop antenna 41 and the second power-fed loop antenna 42 was 333 mm. When the power-fed antenna 40 and the auxiliary antenna 56 were combined, the length of the auxiliary antenna was 480 mm, and the distance between the two auxiliary antennas was 150 mm. When the power-fed antenna 40 and the parasitic antenna 50 were combined, one parasitic antenna 50 was placed equidistantly in the center from the two power-fed antennas 40.

[0097] The object to be irradiated 90 was a polypropylene (PP) cup with a diameter of 85 mm filled with 140 g of potato salad, as in Experimental Example 2. One object to be irradiated 90 was placed on the belt 86. Alternatively, three objects to be irradiated 90 were placed on the belt 86 at intervals of 120 mm. When there was one object to be irradiated 90, the center of the object to be irradiated was taken as the position of the object to be irradiated 90. When there were three objects to be irradiated 90, the center of the middle object to be irradiated was taken as the position of the object to be irradiated 90. The object to be irradiated 90 was transported, and the resonant frequency was measured at each position of the object to be irradiated 90 at intervals of 82.5 mm from the end position of the main housing 81.

[0098] (result) FIG. 18 shows the change in resonant frequency when one irradiated object 90 is transported. For all three antenna configurations, the resonant frequency was lowest when the irradiated object 90 was located at the center of the main housing 81 and highest when it was located at the edge of the main housing 81. When only the powered antenna 40 was used, the resonant frequency had a maximum value of 496 MHz and a minimum value of 489 MHz, with a fluctuation range of 7 MHz. When the auxiliary antenna 56 was used, the resonant frequency had a maximum value of 488 MHz and a minimum value of 469 MHz, with a fluctuation range of 19 MHz. When the parasitic antenna 50 was used, the resonant frequency had a maximum value of 457 MHz and a minimum value of 454 MHz, with a fluctuation range of 3 MHz. That is, when the auxiliary antenna 56 was used, the resonant frequency fluctuation range during transport was larger than when only the powered antenna 40 was used. On the other hand, when the parasitic antenna 50 was used, the resonant frequency fluctuation range during transport was smaller than when only the powered antenna 40 was used.

[0099] FIG. 19 shows the change in resonant frequency when three irradiated objects 90 were transported. For all three antenna configurations, the resonant frequency was lowest when the irradiated object 90 was located at the center of the main housing 81 and highest when it was located at the edge of the main housing 81. When only the power-feeding antenna 40 was used, the resonant frequency had a maximum value of 494 MHz and a minimum value of 477 MHz, with a fluctuation range of 17 MHz. When the auxiliary antenna 56 was used, the resonant frequency had a maximum value of 487 MHz and a minimum value of 461 MHz, with a fluctuation range of 26 MHz. When the parasitic antenna 50 was used, the resonant frequency had a maximum value of 455 MHz and a minimum value of 448 MHz, with a fluctuation range of 7 MHz. That is, even when there were three irradiated objects 90, the fluctuation range of the resonant frequency during transportation was larger when the auxiliary antenna 56 was used than when there was only one irradiated object 90, just as in the case of one irradiated object 90. On the other hand, when the parasitic antenna 50 was used, the fluctuation range of the resonant frequency due to the transmission was smaller than when only the powered antenna 40 was used.

[0100] It was confirmed that the use of the parasitic antenna 50 not only adjusts the resonant frequency but also suppresses fluctuations in the resonant frequency due to transportation. Therefore, it became clear that the use of the parasitic antenna 50 enables the adjustment range of the output frequency of the microwave oscillator 10 to be narrowed and enables irradiation with a fixed output frequency.

[0101] [Usage of microwave irradiation equipment] The microwave irradiation device 1 according to each of the above-described embodiments can be incorporated into processing devices for various applications or configured in an appropriate manner. For example, when used for heat sterilization of sealed and packaged food, the microwave irradiation device 1 is incorporated into an apparatus configured to pressurize the irradiated object 90, which is the sealed and packaged food, and to keep it warm for the time required for sterilization. In addition, the microwave irradiation device 1 can be used in the production of food, which includes placing food in a packaging container and sealing the packaging container to produce packaged food, and heating the packaged food using the microwave irradiation device 1.

[0102] The present invention has been described above by showing preferred embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

[0103] In the above-described embodiment, the shape and size of the parasitic antenna 50 are the same as those of the power-fed antenna 40, but this is not limiting. For example, since increasing the diameter of the parasitic loop antenna decreases the resonant frequency, and decreasing the diameter increases the resonant frequency, the size of the parasitic antenna 50 may be changed to cover a required frequency band.

[0104] In the above-described embodiments, the reference axis, which is the directional irradiation axis of the power supply antenna 40, is horizontal. However, this is not limiting. The reference axis may be, for example, vertical or inclined relative to the horizontal. For example, the power supply antenna 40 and the parasitic antenna 50 may be arranged to sandwich the irradiated object 90, which is transported horizontally by the transport device 85, from above and below, and the power supply antenna 40 may be used to irradiate the irradiated object 90 from above, below, or both. Alternatively, the transport device 85 may transport the irradiated object 90 in the vertical direction. For example, the power supply antenna 40 and the parasitic antenna 50 may be loop antennas with their reference axes vertical and their openings horizontal, and the microwave irradiating device 1 may be configured so that the irradiated object 90 transported by the transport device 85 passes through these loop antennas in the vertical direction. Alternatively, the microwave irradiating device 1 may be configured so that the irradiated object 90 is transported vertically by the transport device 85 and passes between antennas arranged with their reference axes horizontal. In this way, the reference axis, the conveying direction, etc. can be set arbitrarily. [Explanation of symbols]

[0105] 1. Microwave irradiation device 10 Oscillators 21 Coaxial cable 40 Powered Antenna 41 First feeding loop antenna 42 Second feeding loop antenna 50 Parasitic antenna 51 First parasitic loop antenna 52 Second parasitic loop antenna 56 Auxiliary Antenna 60 Position adjustment mechanism 61 Control Unit 62 Support part 63 Rail 80 Metal Case 81 Main housing 82 Side housing 85 Transport equipment 86 Belt 90 Irradiated object

Claims

1. a holder configured to hold the object to be irradiated at a holding position; a power supply device configured to be in electrical communication with the oscillator; a first feeding antenna configured to irradiate microwaves by power supply through conduction via the power supply fixture, the first feeding antenna having directivity and an irradiation axis directed toward the holding position; a parasitic antenna that has directionality but is not fed with power, the parasitic antenna being disposed opposite the first fed antenna across the holding position and having an irradiation axis directed toward the holding position; a second feeding antenna having directivity, the second feeding antenna being configured to irradiate microwaves by power supply through conduction via the power supply fixture, the second feeding antenna having an irradiation axis directed toward the holding position, and the parasitic antenna being sandwiched between the second feeding antenna and the first feeding antenna; A microwave irradiation device comprising:

2. The microwave radiating device according to claim 1 , further comprising a position adjustment mechanism configured to change a relative distance between the parasitic antenna and the first power-feeding antenna.

3. The microwave irradiating device according to claim 2 , wherein the position adjustment mechanism is configured to change the position of the parasitic antenna.

4. 2. The microwave irradiation device according to claim 1, further comprising a further unpowered antenna having directionality but not being fed, the further unpowered antenna being arranged opposite the second powered antenna across the holding position and with an irradiation axis directed toward the holding position.

5. The microwave irradiation device according to claim 4 , further comprising a position adjustment mechanism configured to change the position of the further parasitic antenna.

6. The microwave radiating device according to claim 1 or 2, wherein the first feeding antenna, the second feeding antenna, or the parasitic antenna is a loop antenna.

7. The microwave radiating device according to claim 6 , wherein the holder is provided so as to penetrate the loop antenna.

8. The microwave irradiation device according to claim 1 or 2, wherein the holder has a transport device configured to transport the object to be irradiated.

9. A microwave irradiation method comprising: directing an irradiation axis toward an object to be irradiated, feeding power to one of directional antennas arranged opposite to each other across the object to be irradiated, a first feeding antenna, without feeding power to the other parasitic antenna; and further directing an irradiation axis toward the object to be irradiated, feeding power to a second feeding antenna having directionality arranged so as to sandwich the parasitic antenna between the first feeding antenna and the second feeding antenna, thereby irradiating microwaves to the object to be irradiated.

10. The microwave irradiation method according to claim 9, further comprising adjusting impedance by changing the spacing between the opposingly arranged directional antennas.

11. The microwave irradiation method according to claim 10, wherein adjusting the impedance includes moving an unpowered antenna without moving a powered antenna of the opposingly arranged directional antennas.

12. A method for producing food, comprising heating food using the microwave irradiation method according to claim 9 or 10.

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

14. The method for producing a food product according to claim 13, further comprising: placing the food product in a packaging container and sealing the packaging container to produce the packaged food product.

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