JP2015049943A - Microwave heating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microwave heating apparatus capable of downsizing a waveguide for transmitting a 915 MHz microwave and downsizing the microwave heating apparatus itself including the waveguide.SOLUTION: A microwave heating apparatus 1 includes a metal heating box 30 having an inner space capable of storing an object to be heated and a 915 MHz waveguide 20 for transmitting 915 MHz microwave power to the metal heating box 30. A length of one side of the metal heating box 30 is equal to or more than a free space wavelength of the 915 MHz microwave, and in the 915 MHz waveguide 20, a width dimension W of an aperture 20a is 165-180 mm close to a 915 MHz cut-off frequency, a height dimension h of the aperture 20a is 45-54.6 mm, and a metal reflector 21 position (BP dimension) based on a position of a magnetron antenna 58 to be inserted into the 915 MHz waveguide 20 is 130-140 mm.

Description

  The present invention relates to a microwave heating apparatus that irradiates an object to be heated with microwave power.

In the heating method using the microwave power, the microwave energy is directly transmitted to the inside of the irradiation object, so that rapid and highly efficient heating can be realized. A magnetron is generally used for a microwave oscillation device.
In conventional magnetrons, two types of oscillation frequency of 915 MHz and 2450 MHz which is an ISM (Industry Science Medical) band have been put into practical use. In the market, magnetrons with an oscillation frequency in the 2450 MHz or 915 MHz band are the mainstream, and in particular, those with 2450 MHz are frequently used. Since the 2450 MHz magnetron has the feature that the size of the processing chamber and the object to be heated, the size of the waveguide, etc. can be reduced, not only a heating apparatus such as a microwave oven for business use and home use, but also a semiconductor manufacturing apparatus. As a thin film dry etching apparatus and a microwave plasma CVD (Chemical Vapor Deposition) apparatus.

  In recent years, the demand for 900 MHz band microwaves has increased. For example, a 915 MHz magnetron is a large electromagnet type magnetron, and is used in industrial heating devices having a large output of several tens of kW or more. It is also conceivable to mount a 915 MHz magnetron on a heating device such as a microwave oven. However, the 915 MHz magnetron itself is large, and in order to be mounted on the heating device, the heating device itself must be enlarged, and is difficult to use in practice. The 915 MHz band magnetron is only commercialized in a large electromagnet type, and thus becomes heavier and larger than the 2450 MHz band magnetron in which the permanent magnet type is generalized (Patent Document 1). reference).

JP 2002-124196 A

  By the way, the spatial wavelength of the 915 MHz microwave is about 33 cm, which is longer than the spatial wavelength of about 12.2 cm of the 2450 MHz microwave. For this reason, the waveguide size for microwave transmission into the metal heating box that houses the object to be heated must be increased. For example, the opening size of the 915 MHz waveguide is 247.65 Wmm × 123.83 hmm in the JIS model name WRJ-1. Since the 915 MHz waveguide cannot be reduced in size, it is difficult to mount such a large 915 MHz waveguide in a small microwave oven or the like. The present condition is that the small microwave heating apparatus which mounted the 915 MHz waveguide is not implement | achieved.

  This invention is made | formed in view of such a situation, The waveguide which transmits 915 MHz microwave can be reduced in size, and the microwave heating apparatus which has the waveguide can be reduced in size. It is an object of the present invention to provide a microwave heating device that can be used.

  In order to solve the above problems, a microwave heating apparatus of the present invention includes a heating box having an internal space in which an object to be heated can be stored, and a 915 MHz waveguide that transmits 915 MHz microwave power to the heating box. The heating box has a side length equal to or greater than a free space wavelength of 915 MHz microwave, and the 915 MHz waveguide has an opening width dimension that is approximately half of the cutoff frequency close to the 915 MHz cutoff frequency. It is the width dimension.

  ADVANTAGE OF THE INVENTION According to this invention, the microwave heating apparatus which can miniaturize the waveguide which transmits 915 MHz microwave and can reduce the microwave heating apparatus which has the waveguide is provided.

It is a figure which shows the structure of the microwave heating apparatus which concerns on the 1st Embodiment of this invention. It is a perspective view which shows the structure of the 915MHz waveguide of the microwave heating device which concerns on the said 1st Embodiment. It is a figure which shows the structure of the 915 MHz waveguide of the microwave heating device which concerns on the said 1st Embodiment. It is a block diagram of 915MHz magnetron of the microwave heating device which concerns on the said 1st Embodiment. It is a figure which shows the frequency characteristic of the 915MHz waveguide of the microwave heating device which concerns on the said 1st Embodiment. It is a figure explaining the simulation analysis model of the microwave electric field distribution of the microwave heating device which concerns on the said 1st Embodiment. It is a figure which shows the microwave electric field distribution by the simulation analysis model of FIG. It is a figure which shows the structure of the microwave heating apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows the experimental result which verified the simulation result of FIG. It is a figure which shows the simulation result of the microwave absorbed electric power distribution of the to-be-heated object at the time of installing the 2450MHz microwave source of the microwave heating device which concerns on the said 2nd Embodiment in the bottom face of a metal heating box, and microwave irradiation. It is a figure which shows the microwave absorption distribution at the time of irradiating a temperature-sensitive gel agent with a moisture of 99% as a to-be-heated object of the microwave heating apparatus which concerns on the said 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram illustrating a configuration of a microwave heating apparatus according to a first embodiment of the present invention. The microwave heating apparatus of this embodiment is an example applied to a high-frequency heating apparatus having a waveguide that transmits microwave power from a microwave oscillation device in a metal heating box that houses an object to be heated.
As shown in FIG. 1, the microwave heating apparatus 1 includes a 915 MHz magnetron 10, a 915 MHz waveguide 20 that is coupled to the 915 MHz magnetron 10 and transmits 915 MHz microwave power generated by the 915 MHz magnetron 10, and an object to be heated. And a metal heating box 30 that has a storable internal space and irradiates an object to be heated with 915 MHz microwave power transmitted from the 915 MHz waveguide 20.
The 915 MHz magnetron 10 and the 915 MHz waveguide 20 constitute a 915 MHz microwave source 15. The 915 MHz microwave source 15 is disposed on the upper surface side of the metal heating box 30 and irradiates the metal heating box 30 with microwaves.

<915MHz magnetron 10>
The 915 MHz magnetron 10 is a microwave oscillation device that oscillates and outputs a 915 MHz microwave.
The 915 MHz magnetron 10 includes a magnetron antenna 58 (see FIGS. 2 and 3) as an output unit. The generated 915 MHz microwave is radiated by the magnetron antenna 58 and transmitted to the 915 MHz waveguide 20. As will be described later, the magnetron antenna 58 is inserted into a predetermined position of the 915 MHz waveguide 20. The height of the magnetron antenna 58 is the same height as the antenna of the 2.450 GHz magnetron.

<915 MHz waveguide 20>
The 915 MHz waveguide 20 is a transmission circuit that is coupled to the 915 MHz magnetron 10 and transmits 915 MHz microwave power to the metal heating box 30. The 915 MHz waveguide 20 is a rectangular waveguide and has a rectangular opening 20a. The width and height of the opening 20a, the depth of the waveguide, and the like have the following characteristics.

  The 915 MHz waveguide 20 has an opening 20a width dimension of 165 to 180 mm close to the 915 MHz cutoff frequency. The 915 MHz waveguide 20 has an opening 20a having a height dimension of 45 to 54.6 mm which is adopted in the 2.450 GHz waveguide. Therefore, for example, the 915 MHz waveguide 20 has an opening 20a width dimension and height dimension of 167 mmW × 54 mmh.

  Further, the 915 MHz waveguide 20 has a mounting portion for the 915 MHz magnetron 10 on the side opposite to the opening 20a of the surface 20b (see FIGS. 2 and 3) orthogonal to the opening 20a. A magnetron antenna (microwave output antenna) 58 of the 915 MHz magnetron 10 is inserted into this attachment portion in the height dimension direction of the 915 MHz waveguide 20. The antenna height of the magnetron antenna 58 is not more than 45 to 54.6 mm in the height dimension of the opening 20a.

Further, the 915 MHz waveguide 20 includes a metal reflector 21 for reflecting and guiding the microwave introduced into the waveguide toward the opening 20a inside the waveguide opposite to the opening 20a. . The metal reflector 21 is attached at a position of 130 to 140 mm on the opposite side of the microwave traveling direction as a position reference for the magnetron antenna 58 inserted into the 915 MHz waveguide 20.
The depth dimension (full length) of the 915 MHz waveguide 20 and the dimension from the opening 20a to the magnetron antenna 58 are arbitrary.

  As described above, the 915 MHz waveguide 20 is compared with the commonly adopted 915 MHz waveguide (based on the JIS standard of the waveguide type name WRJ-1) opening size 247.65 Wmm × 123.83 hmm. The size is reduced to about 67% in width and about 44% in height.

<Metal heating box 30>
The metal heating box 30 has an internal space in which an object to be heated can be stored, and has a rectangular parallelepiped structure in which one side has a length of 915 MHz microwave free space wavelength (about 33 cm) or more. Specifically, the metal heating box 30 has a rectangular tube shape of 411 Wmm × 235 hmm × 320 Dmm in which the length of one side is not less than the free space wavelength of 915 MHz microwave (here, 411 mm). This size and shape is the same basic shape as a general microwave oven. In the metal heating box 30, a door (not shown) for taking in and out the object to be heated is attached to a surface of 411 Wmm × 235 hmm.

[Configuration of 915 MHz Waveguide 20]
FIG. 2 is a perspective view showing the configuration of the 915 MHz waveguide 20. 3A and 3B are diagrams showing the configuration of the 915 MHz waveguide 20 of FIG. 2, in which FIG. 3A is a top view and FIG. 3B is a side view.
As shown in FIGS. 2 and 3A and 3B, the 915 MHz waveguide 20 includes an opening 20a for irradiating microwaves and a 915 MHz magnetron 10 in a metal heating box 30 (see FIG. 1). Surface 20b. A 915 MHz magnetron 10 (see FIG. 1) is attached to the surface 20b opposite to the opening 20a, and a magnetron antenna 58 (described later in FIG. 4) connected to the coaxial outer conductor 59 of the 915 MHz magnetron 10 is attached to the attachment position. Is inserted). The 915 MHz waveguide 20 has a metal reflector (short-circuit plate) 21 for reflecting and guiding the microwave toward the opening 20a inside the waveguide opposite to the opening 20a. The metal reflector 21 is attached at a position of 130 to 140 mm on the side opposite to the microwave traveling direction as a position reference for the magnetron antenna 58. The metal reflector 21 may be the bottom of the 915 MHz waveguide 20 on the side opposite to the microwave traveling direction (the bottom of the bottomed tube).

  The 915 MHz waveguide 20 has a width dimension W of the opening 20a of 165 to 180 mm (for example, 167 mm) close to the 915 MHz cutoff frequency, and a height dimension h of 45 to 54.6 mm adopted in the 2450 MHz waveguide. (For example, 54 mm). The 915 MHz waveguide 20 has a length from the magnetron antenna 58 to the metal reflector 21 of 130 to 140 mm (for example, 130 mm). The length from the opening 20a to the magnetron antenna 58 is, for example, 330 mm, and the length from the opening 20a to the metal reflector 21 is, for example, 460 mm.

[Configuration of 915 MHz Magnetron 10]
FIG. 4 is a configuration diagram of the 915 MHz magnetron 10.
As shown in FIG. 4, the 915 MHz magnetron 10 is a permanent magnet type 900 MHz band magnetron.
The 915 MHz magnetron 10 includes a cathode filament (directly heated spiral cathode) 51 serving as a thermionic emission source, a plurality of anode vanes 52, and an anode cylinder portion (anode cylinder) 53.
The 915 MHz magnetron 10 includes annular permanent magnets 54 and 54a, magnetic poles 55 and 55a, yokes 56 and 56a, antenna leads 57, a magnetron antenna 58, a coaxial outer conductor 59, a cylindrical antenna block 60, an insulator such as ceramic. 61, an action space 63, and an output unit 69.
The output unit 69 includes an antenna lead 57, a magnetron antenna 58, a coaxial outer conductor 59, and an antenna block 60. The output unit 69 may have a structure in which only the antenna lead 57 is covered with a dome ceramic.

The 915 MHz magnetron 10 includes a magnetic circuit unit 70, an upper end shield (also referred to as an output side end shield) 71, a lower end shield (also referred to as an input side end shield) 72, a cathode lead center lead 73, and a cathode lead side lead 74. , A terminal plate 76, a cathode portion 78, and an anode portion 79.
The magnetic circuit unit 70 includes permanent magnets 54 and 54a and magnetic poles 55 and 55a, and yokes 56 and 56a, which are magnetic sources. The cathode portion 78 includes a cathode filament 51 serving as a thermionic emission source, upper and lower end shields 71 and 72, cathode leads 73 and 74, and the like. The anode portion 79 is fixed to the plurality of anode vanes 52 and the anode cylindrical portion 53 by brazing or the like, or integrally formed with the anode cylindrical portion 53 by extrusion molding.
The yokes 56 and 56 a constitute the magnetic circuit unit 70, and are also housings for housing the permanent magnets 54 and 54 a, the magnetic poles 55 and 55 a, the antenna lead 57, the cathode unit 78, and the anode unit 79. The yoke 56 has a box shape with an open bottom surface, and the yoke 56a has a lid shape that closes the opening.

  Magnetic poles 55 and 55a made of a ferromagnetic material such as soft iron and cylindrical permanent magnets 54 and 54a are arranged above and below the anode cylindrical portion 53, respectively. The magnetic flux generated from the permanent magnets 54 and 54 a passes through the magnetic poles 55 and 55 a and enters the working space 63 formed between the cathode filament 51 and the anode vane 52, and in the axial direction that is the vertical direction of the 915 MHz magnetron 10. Provide the necessary DC magnetic field.

This DC magnetic field has the following effects. That is, in a state where the main body axis of the 915 MHz magnetron 10 is installed perpendicular to the horizontal plane, the magnetic flux is perpendicular to the electrons flying in the horizontal direction from the cathode filament 51 toward the anode vane 52 (axial direction). Is given, Lorentz force is applied to the electrons. Due to this Lorentz force, electrons fly while spirally turning in the horizontal direction, and a high frequency electric field is formed in the anode vane 52.
The cathode filament 51 emits electrons when a negative high voltage of 4 kV to 8 kV of direct current is applied, and the electrons are subjected to high frequency to each anode vane 52 while being spirally moved under the action of an electric field and a magnetic field as described above. Create an electric field. The formed high frequency electric field is output from the antenna block 58 to the 915 MHz waveguide 20 (see FIG. 1) through the antenna lead 57 and the magnetron antenna 58.

The cathode filament 51 is generally made of tungsten wire containing about 1% thorium oxide (ThO ₂ ) in consideration of electron emission characteristics, workability, and the like. The upper end shield 71, the lower end shield 72, and the cathode are used. Supported by leads 73 and 74. The cathode leads 73 and 74 are generally made of molybdenum (Mo) from the viewpoint of heat resistance and workability, and the choke coil is connected via a terminal plate 76 brazed to the upper surface of the input-side ceramic 75 with silver brazing or the like. 81.

  A filter structure 85 including a filter case 83 that supports the choke coil 81 and the feedthrough capacitor 82 and a lid 84 that closes the filter case 83 is attached to the lower part of the 915 MHz magnetron 10. The choke coil 81 connected to the terminal plate 76 forms an L-C filter with the feedthrough capacitor 82 and suppresses low frequency components transmitted from the cathode leads 73 and 74. However, the high frequency component is shielded by the filter case 83 and its lid 84. Further, the cooling mechanism 77 installed on the outer periphery of the anode cylindrical portion 53 is provided with a cooling water passage 77a through which the cold water passes, and heat generated by the operation of the 915 MHz magnetron 10 by the cold water passing therethrough. Spread.

  As described above, the 915 MHz magnetron 10 has a structure in which the cathode portion 78 including the cathode filament 51 which is a thermionic emission source, and a plurality of anode vanes 52 are arranged in an annular shape inside the anode cylindrical portion 53 with a certain interval. , An anode part 79 having a cavity resonator formed by a cavity formed between the anode vanes 52, an output part 69 for sending microwaves stored in the cavity resonator to the outside, a cathode part 78, an anode part 79, and an output And a magnetic circuit unit 70 having magnets disposed at upper and lower ends in the axial direction of the vacuum tube main body enclosing a part of the unit 69. Further, the dimensions and arrangement of the anode cylindrical portion 53, the anode vane 52, and the cathode filament 51 are configured to have a specific relationship. As a result, the cavity resonator and its inductance can be increased, the diameters of the anode cylindrical portion 53 and the anode portion 79 can be reduced, the entire magnetron can be reduced in size, and the oscillation frequency can be lowered. Therefore, the 915 MHz magnetron 10 can be realized with substantially the same outer diameter and substantially the same output as the conventional 2450 MHz band magnetron.

Hereinafter, the downsizing of the 915 MHz microwave source 15 of the microwave heating apparatus 1 configured as described above will be described.
The present inventors recognize that one of the factors hindering the miniaturization of the 915 MHz microwave source 15 is the size (size) of the opening 20a of the 915 MHz waveguide 20, and can make the opening 20a small. We studied whether or not. As a result, it has been found that there is a specific relationship between the cutoff frequency of 915 MHz microwave transmission and the width W dimension of the opening 20a. It has also been found that the transmission efficiency varies depending on the position of the metal reflector 21 when the magnetron antenna 58 is used as a reference position.

<Width of opening 20a>
First, the width dimension of the opening 20a (hereinafter referred to as the width W dimension) will be described.
The 915 MHz waveguide 20 constitutes a 915 MHz microwave source 15. The 915 MHz microwave source 15 is disposed on the upper surface side of the metal heating box 30 and irradiates the metal heating box 30 with microwaves.

  That is, when the width W of the opening 20a for transmitting the microwave is 167 mm, the cutoff wavelength of the 915 MHz waveguide 20 is 2 × 167 mm = 334 mm. On the other hand, the 915 MHz waveguide 20 has a spatial wavelength of 315 MHz of about 330 mm. Accordingly, since the cutoff wavelength 334 mm of the 915 MHz waveguide 20 is close to the spatial wavelength of about 315 MHz of about 315 MHz, the 915 MHz microwave irradiated from the 915 MHz magnetron 10 is efficiently transmitted. As described above, the width W of the opening 20a of the 915 MHz waveguide 20 is set to be approximately half the width of the cutoff frequency close to the cutoff frequency (about 900 MHz) of 915 MHz microwave transmission.

<Height dimension of opening 20a>
Next, the height dimension of the opening 20a (hereinafter referred to as the height h dimension) will be described.
In general, the antenna height of a magnetron for transmitting a microwave generated by a magnetron into a waveguide is λ / 4 of a free space wavelength. With a 2450 MHz microwave, the height of the magnetron antenna is 12.2 cm × 1 / 4≈30 mm. That is, in the 2450 MHz magnetron, the magnetron antenna is inserted about 30 mm in the waveguide height direction.

On the other hand, with 915 MHz microwave, the antenna height is 330 mm / 4 = 82.5 mm. In the present embodiment, as shown in FIGS. 1 to 3, the height of the 915 MHz waveguide 20 is set to 54.0 mm, which is substantially the same as the height of the 2450 MHz waveguide. The height of the magnetron antenna 58 of the 915 MHz magnetron 10 is about 30 mm, which is the same as that of the 2450 MHz magnetron.
Therefore, the size of the opening 20a of the 915 MHz waveguide 20 is about 67% in width and about 44 in height compared to the JIS standard 247.65 Wmm × 123.83 hmm of the waveguide model name WRJ-1. % Downsizing.

<Transmission efficiency>
2 and 3, the microwave transmission characteristics of the 915 MHz microwave source 15 when the height of the 915 MHz waveguide 20 is 54.0 mm and the height of the magnetron antenna 58 is 32 mm are obtained from simulation.
The structure of the magnetron antenna 58 inserted into the 915 MHz waveguide 20 assumes the output unit 69 (see FIG. 4) of the 915 MHz magnetron 10. The coaxial tube outer conductor 59 has a diameter of 37 mm, and the magnetron antenna 58 serving as an inner conductor has a diameter of 18 mm. The depth of the magnetron antenna 58 inserted into the 915 MHz waveguide 20 (the length of the inserted portion) is 32 mm.

  As shown in FIG. 3, the microwave radiated | emitted from the magnetron antenna 58 which is an inner conductor is transmitted toward a microwave advancing direction (metal heating box 30 direction). The transmission efficiency at this time depends on the distance (BP (back plunger) dimension) from the magnetron antenna 58 to the metal reflection plate (short-circuit plate) 21 on the opposite side of the microwave traveling direction.

FIG. 5 is a diagram illustrating frequency characteristics of the 915 MHz waveguide 20. FIG. 5 shows a simulation result of transmission efficiency in the simulation model of FIGS. In FIG. 5, the horizontal axis indicates the frequency f, the vertical axis indicates the reflection coefficient Γ that is the transmission efficiency of the 915 MHz microwave, and the position of the metal reflector 21 (BP size) is used as a parameter.
The reflection coefficient Γ is minimized to 0.10 at the metal reflector 21 position (BP size) 130.2 to 140.2 mm. Here, the frequency f and the reflection coefficient Γ in the BP dimensions of 90.2 mm, 100.2 mm, 130.2 mm, 140.2 mm, and 150.2 mm are shown at the position of the metal reflector 21. A reflection coefficient Γ = 0 represents 100% transmission of microwaves, and a reflection coefficient Γ = 1 represents 0% transmission of microwaves. All microwaves radiated from the antenna when Γ = 0 are supplied into the metal heating box 30 and absorbed by the object to be heated. When Γ = 1.0, the microwave power absorbed by the object to be heated is zero. At f = 900 MHz, Γ = 1 regardless of the BP dimension, which is the waveguide cutoff frequency determined by the waveguide width dimension.

  Here, in the present embodiment, the width dimension of the opening 20a of the 915 MHz waveguide 20 is determined so that the cutoff wavelength of the 915 MHz waveguide 20 is close to the cutoff frequency (about 900 MHz) of 915 MHz microwave transmission. . Specifically, by setting the width dimension of the opening 20a of the 915 MHz waveguide 20 to 167 mm, the cutoff wavelength of the 915 MHz waveguide 20 is set to 2 × 167 = 334 mm, and the cutoff frequency of the 915 MHz microwave transmission (about 900 MHz). ).

  As shown in FIG. 5, when the position of the metal reflector 21 (BP size) is 140.2 mm, the 915 MHz microwave is best transmitted with the reflection coefficient Γ = 0.10, and the position of the metal reflector 21 (BP size) 130. In the case of 2 mm, the reflection coefficient Γ = 0.12 follows. Therefore, it was confirmed by simulation that the transmission efficiency is good when the position of the metal reflector 21 (BP size) is 130 to 140 mm.

<Distribution of microwave absorption power of the object to be heated>
FIG. 6 is a diagram for explaining a simulation analysis model of the microwave electric field distribution of the microwave heating apparatus 1. FIG. 7 is a diagram showing a microwave electric field distribution (simulation result) based on the simulation analysis model of FIG. 6, and FIG. 7A shows a microwave electric field when the water load A of FIG. 6 is heated by 915 MHz microwaves. FIG. 7B shows the distribution of the microwave electric field when the water load B of FIG. 6 is heated by 915 MHz microwaves. Moreover, FIG.7 (c) shows the microwave electric field distribution at the time of heating the water load A of FIG. 6 by a 2450 MHz microwave as a comparative example, FIG.7 (d) shows the water load of FIG. The microwave electric field distribution when B is heated by 2450 MHz microwave is shown. The numerical values in parentheses in FIG. 6 are examples of analysis models when the 2450 MHz microwave source 45 (see FIG. 8) of the second embodiment described later is used.

As shown in FIG. 6, a 915 MHz microwave source 15 is installed in the center of the upper surface of the metal heating box 30, and a 1L × 2 water load (container: 1L beaker) is placed in the metal heating box 30 as an object to be heated. Put. The water loads A and B are, for example, 102 φmm × 110 hmm.
A simulation was performed on an analysis model in which 915 MHz microwaves were irradiated into the metal heating box 30 via the 915 MHz waveguide 20.

  As shown in FIGS. 7A and 7B, in the case of the 915 MHz microwave, a strong microwave absorption portion is seen in the two water loads A and B at the 1/3 height position from the bottom surface. The case of 2450 MHz will be described later according to the second embodiment.

  As described above, the microwave heating apparatus 1 according to this embodiment includes the metal heating box 30 having an internal space in which an object to be heated can be stored, and the 915 MHz waveguide that transmits 915 MHz microwave power to the metal heating box 30. The metal heating box 30 has a side length equal to or greater than a free space wavelength of 915 MHz microwave, and the 915 MHz waveguide 20 has a width dimension W of the opening 20a of 915 MHz cutoff frequency. The metal reflector 21 position (BP dimension) is 130 to 140 mm with reference to the position of the magnetron antenna 58 inserted into the adjacent 165 to 180 mm, opening 20a height dimension 45 to 54.6 mm, and 915 MHz waveguide. is there.

  With this configuration, the size of the opening 20a of the 915 MHz waveguide 20 can be reduced to the same level as that of the 2450 MHz waveguide.

  Further, the transmission efficiency of the 915 MHz waveguide 20 can be increased by setting the metal reflector 21 position (BP size) to 130 to 140 mm with reference to the position of the magnetron antenna 58 inserted into the 915 MHz waveguide 20.

  Further, since the position (BP dimension) of the metal reflector 21 can be specified, the metal reflector 21 can be configured to be the bottom of the 915 MHz waveguide 20, and the length (full length) of the 915 MHz waveguide 20 can be determined. Can be shortened. Furthermore, since the position of the metal reflector 21 can be specified, the overall design freedom of the 915 MHz waveguide 20 can be expanded.

  As described above, since the 915 MHz waveguide 20 can be downsized, the 915 MHz microwave source 15 constituting the 915 MHz waveguide 20 can also be downsized. Conventionally, since it was difficult to reduce the size of a 915 MHz microwave source, it was difficult to mount the 915 MHz microwave source in a small microwave oven or the like. According to this embodiment, since the 915 MHz microwave source 15 can be downsized, 915 MHz microwaves can be supplied in the conventional metal heating box 30 size of the 2450 MHz microwave oven. As a result, it can be widely used in microwave heating apparatuses such as a small microwave oven as well as an industrial microwave oven.

(Second Embodiment)
The first embodiment is an example in which a 915 MHz microwave source is downsized and applied to a metal heating box. However, a 2450 MHz microwave source can be used in combination by downsizing the 915 MHz microwave source.
The second embodiment is an example in which the microwave heating apparatus according to the present invention is applied to a 915 MHz / 2450 MHz microwave source using both a 915 MHz microwave source and a 2450 MHz microwave source.

FIG. 8 is a diagram showing a configuration of a microwave heating apparatus according to the second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, and description of overlapping portions is omitted.
As shown in FIG. 8, the microwave heating device 2 includes a 915 MHz magnetron 10, a 915 MHz waveguide 20 that transmits microwave power generated by the 915 MHz magnetron 10, a 2450 MHz magnetron 40, and a 2450 MHz generated by the 2450 MHz magnetron 40. A 2450 MHz waveguide 50 that transmits microwave power, and an internal space that can store an object to be heated, and 915 MHz microwave power transmitted from the 915 MHz waveguide 20 and 2450 MHz transmitted from the 2450 MHz waveguide 50 A metal heating box 30 that irradiates the object to be heated with microwave power.
The 2450 MHz magnetron 40 and the 2450 MHz waveguide 50 constitute a 2450 MHz microwave source 45. The 2450 MHz microwave source 45 is disposed on the lower surface side of the metal heating box 30 and irradiates the metal heating box 30 with microwaves through the 2450 MHz microwave irradiation port 50a.

The 2450 MHz magnetron 40 is a microwave oscillation device that oscillates and outputs a 2450 MHz microwave.
The 2450 MHz waveguide 50 is a transmission circuit that is coupled to the 2450 MHz magnetron 40 and transmits 2450 MHz microwave power to the metal heating box 30. The 2450 MHz waveguide 50 is a JIS type name WRJ-2 which is generally adopted, and the microwave irradiation port 50a which is the size of the opening is 109.2 Wmm × 54.6 hmm.
As described above, the height of the opening 20a of the 915 MHz waveguide 20 is the same as 45 to 54.6 mm employed in the 2.450 GHz waveguide 50.

<Antenna height of 915 MHz magnetron 10 and 2450 MHz magnetron 40>
The antenna height of the magnetron for transmitting the microwave generated by the magnetron into the waveguide is λ / 4 of the free space wavelength. In a 2450 MHz microwave, it is 12.2 cm × 1 / 4≈30 mm. Therefore, the magnetron antenna 58 of the 2450 MHz magnetron 40 is inserted about 30 mm in the height direction of the 2450 MHz waveguide 50. In addition, with 915 MHz microwave, the antenna height is 330 mm / 4 = 82.5 mm. In the present embodiment, the height of the 915 MHz waveguide 20 is set to 54.0 mm, which is substantially the same as the height of the 2450 MHz waveguide 50. The antenna height of the 915 MHz magnetron 10 is about 30 mm, which is the same as the 2450 MHz magnetron 40.

  Thereby, the size of the 915 MHz waveguide 20 can be reduced, and the antenna structure of the 915 MHz magnetron 10 can be shared with 2450 MHz. By making the antenna structure of the magnetron common, it is possible to obtain the mass production effect of the magnetron manufacturing cost.

Hereinafter, the internal heating of the microwave heating apparatus 2 configured as described above will be described.
An example of an analysis model using the 2450 MHz microwave source 45 (see FIG. 8) is indicated by a numerical value in parentheses in FIG.
As shown in FIG. 6, a 915 MHz microwave source 15 (see FIG. 1) or a 2450 MHz microwave source 45 (see FIG. 8) is installed in the center of the upper surface of the metal heating box 30, and water is heated as an object to be heated in the metal heating box 30. Loads A and B are placed.
A simulation was performed on an analysis model in which 915 MHz microwave or 2450 MHz microwave was irradiated into the metal heating box 30 via the 915 MHz waveguide 20 or 2450 MHz waveguide 50.

As shown in FIGS. 7A and 7B, in the case of the 915 MHz microwave, a strong microwave absorption portion is seen in the two water loads A and B at the 1/3 height position from the bottom surface.
On the other hand, as shown in FIGS. 7C and 7D, in the case of the 2450 MHz microwave, strong microwave absorption is observed on the upper surface side that is the microwave irradiation surface side. The difference in the microwave absorption distribution between the 915 MHz microwave and the 2450 MHz microwave is clear. From this knowledge, by using the 915 MHz microwave and the 2450 MHz microwave in combination, uniform internal heating can be realized for the object to be heated.

  In order to verify the simulation results described above, an actual operation test was performed using a temperature-sensitive gel with 99% moisture in place of the water loads A and B. The thermosensitive gel becomes white turbid from a high temperature portion, that is, a place where the microwave electric field is strong, and is suitable for investigation of the microwave absorption distribution in the heated object.

FIG. 9 is a diagram showing an experimental result in which a temperature-sensitive gel with a moisture of 99% is adopted as an object to be heated, microwave irradiation is actually performed, and the simulation result of FIG. 7 is verified. FIG. 9A shows an experimental result in the case of the 915 MHz microwave, and FIG. 9B shows an experimental result in the case of the 2450 MHz microwave.
As shown in FIG. 9A, in the 915 MHz microwave, the temperature-sensitive gel 91 is clouded (see the shaded portion) at a position 1/3 from the load bottom surface.
Further, as shown in FIG. 9B, in the 2450 MHz microwave, the temperature-sensitive gel 91 is clouded (see the shaded portion) from the upper surface side that is the microwave irradiation surface.
As a result, an experimental result almost similar to the simulation result of FIG. 7 was obtained.

[Verification example]
The present invention can be applied to the microwave heating apparatus 2 (see FIG. 8) that uses both 915 MHz microwave and 2450 MHz microwave. The microwave heating device 2 is, for example, an industrial microwave oven.
In the case of the structural example of FIG. 8, the 2450 MHz microwave is irradiated from the lower surface of the metal heating box 30. The microwave absorption distribution simulation result in this case is shown in FIG. 10, and the temperature-sensitive gel load actual operation experiment result is shown in FIG.

  FIG. 10 is a diagram showing a simulation result of the microwave absorbed power distribution of the object to be heated when the 2450 MHz microwave source 45 is installed on the bottom surface of the metal heating box 30 and irradiated with microwaves. FIG. FIG. 10B shows the microwave absorbed power distribution viewed from the side, and FIG. 10B shows the microwave absorbed power distribution viewed from above.

FIG. 11 is a diagram showing a microwave absorption distribution when a temperature-sensitive gel having a moisture content of 99% is irradiated with microwaves as an object to be heated, and is a diagram showing experimental results for verifying the simulation result of FIG.
As shown in FIGS. 10 and 11, the temperature-sensitive gel 91 becomes clouded (see the shaded portion) from the lower surface side, which is the irradiation surface side, and has the same result as the simulation of FIG.

[Application example]
The 915 MHz magnetron 10 of the microwave heating device 2 is a permanent magnet type magnetron. The 2450 MHz magnetron 40 is a general microwave magnetron (800 W).
The basic structure is the same for both the 915 MHz magnetron 10 and the 2450 MHz magnetron 40. The anode structure that determines the oscillation frequency is a cavity resonator type, and a resonator of 915 MHz or 2450 MHz is designed by the inductance L and capacitor C of the cavity. For example, the permanent magnet type magnetron structure shown in FIG. 4 can be used. 4 has a cavity resonator structure. In the case of the 915 MHz magnetron 10, the anode 79 has an outer diameter of about 90 φmm in order to increase the cavity L. In the case of the 2450 MHz magnetron 40, the outer diameter of the anode portion 79 is 40 mm (800 W output) to 52 mm (6 kW output). The specifications of the permanent magnets 54 and 54a and the cathode portion 78 of the 915 MHz magnetron 10 and the 2450 MHz magnetron 40 are the same.

In the 915 MHz magnetron 10 and the 2450 MHz magnetron 40, the resonance frequency of the cavity resonator is significantly different from 915 MHz and 2450 MHz. Therefore, even if both magnetrons are operated simultaneously, no microwave interference occurs.
If the anode voltage is the same 915 MHz magnetron 10 and 2450 MHz magnetron 40, the magnetrons can be connected in parallel with one anode power source and operated simultaneously.

  Thus, according to this embodiment, the microwave heating apparatus 2 includes the 915 MHz magnetron 10, the 915 MHz waveguide 20 that transmits the microwave power generated by the 915 MHz magnetron 10, the 2450 MHz magnetron 40, and the 2450 MHz magnetron 40. From the 2450 MHz waveguide 50 that transmits the 2450 MHz microwave power generated in the above, and the 915 MHz microwave power transmitted from the 915 MHz waveguide 20 and the 2450 MHz waveguide 50 having an internal space in which an object to be heated can be stored. A metal heating box 30 that irradiates the object to be heated with the transmitted 2450 MHz microwave power.

  With this configuration, the 915 MHz waveguide 20 can be reduced in size as in the first embodiment. Since the size of the 915 MHz waveguide 20 can be reduced, the 915 MHz waveguide 20 is mounted together with the 2450 MHz waveguide 50 in the size of the metal heating box 30 of the 2450 MHz microwave oven, and 915 MHz microwave and 2450 MHz microwave are supplied. can do. As shown in FIG. 7, in the case of a 915 MHz microwave with deep microwave penetration, heat treatment can be performed from the inside of the object to be heated, while in the case of a 2450 MHz microwave, heating starts near the surface of the object to be heated. Therefore, extremely excellent uniform internal heating can be performed by irradiation with 915 MHz microwave and 2450 MHz microwave.

  In addition, this invention is not limited to the structure described in each said embodiment, The structure can be suitably changed unless it deviates from the summary of this invention described in the claim.

  For example, as a microwave oscillating device that oscillates and outputs a microwave, an electron tube such as a klystron or a gytron, or a microwave generator using a semiconductor as an oscillation source may be used. Further, the material, shape, structure, and the like of the waveguide and the heating box are examples, and any materials may be applied.

  The above-described exemplary embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. . Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each exemplary embodiment.

DESCRIPTION OF SYMBOLS 1, 2 Microwave heating apparatus 10 915MHz magnetron 15 915MHz microwave source 20 915MHz waveguide 20a Opening part 21 Metal reflector (short circuit board)
30 Metal heating box (heating box)
40 2450 MHz magnetron 45 2450 MHz microwave source 50 2450 MHz waveguide 50a 2450 MHz microwave irradiation port 57 antenna lead 58 magnetron antenna 59 coaxial outer conductor

Claims (6)

A heating box having an internal space capable of storing an object to be heated;
A 915 MHz waveguide that transmits 915 MHz microwave power to the heating box;
The heating box has a side length of 915 MHz microwave free space wavelength or longer,
The microwave heating apparatus, wherein the 915 MHz waveguide has an opening width dimension that is approximately half the width of the cutoff frequency close to the 915 MHz cutoff frequency. The microwave heating apparatus according to claim 1, wherein the substantially half-width dimension is 165 to 180 mm close to a 915 MHz cutoff frequency. The microwave heating device according to claim 1, wherein the height of the opening of the 915 MHz waveguide is 45 to 54.6 mm. 2. The microwave according to claim 1, wherein the position of the reflector provided in the direction opposite to the microwave traveling direction is 130 to 140 mm with respect to the position of the microwave output antenna inserted into the 915 MHz waveguide. Heating device. The microwave heating apparatus according to claim 4, wherein a height of the microwave output antenna inserted into the 915 MHz waveguide is equal to or less than a height dimension of the opening of the 915 MHz waveguide. The microwave heating apparatus according to claim 1, further comprising a 2450 MHz waveguide that transmits 2450 MHz microwave power to the heating box.