WO2016103586A1

WO2016103586A1 - Microwave heating device

Info

Publication number: WO2016103586A1
Application number: PCT/JP2015/006018
Authority: WO
Inventors: 吉野　浩二; 貞平　匡史; 昌之久保; 大森　義治; 早川　雄二
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2014-12-22
Filing date: 2015-12-04
Publication date: 2016-06-30
Also published as: EP3240364A1; CN107006083A; JP2016119251A; EP3240364B1; JP6414683B2; CN107006083B; TW201635857A; TWI686104B; EP3240364A4

Abstract

A waveguide structure antenna (5) has a top surface (9) and side wall surfaces (10a, 10b, 10c) defining a waveguide structure part (8), and a forward aperture (13), with microwaves being radiated from the forward aperture (13) toward an object being heated. The waveguide structure part (8) has a connecting part (7) that is connected to the top surface (9) of the waveguide structure part (8), and that allows the microwaves to be coupled to an internal space in the waveguide structure part (8). The waveguide structure part (8) radiates circularly polarized waves into a heating chamber from one or more microwave extraction openings (14) formed in the top surface (9). The microwave extraction openings (14) has a cross-slot shape wherein two slits (20a, 20b) intersect each other, and the openings are provided at a position offset from the tube axis (V). Among the distances from the center point (P1) in the intersection region of the cross-slot to the ends of the slits (20a, 20b), the distance to the end closest to the connecting part is the shortest. By means of this embodiment an object being heated that is placed in the central region of the placement surface can be heated uniformly.

Description

Microwave heating device

The present disclosure relates to a microwave heating apparatus such as a microwave oven that heats an object to be heated such as food using microwaves.

In a microwave oven, which is a typical microwave heating device, microwaves generated by a magnetron, which is a typical microwave generation unit, are supplied into a metal heating chamber and placed in a heating chamber. The heated object is heated by microwave.

Recently, a microwave oven in which the entire flat bottom surface in the heating chamber can be used as a mounting table has been put into practical use. In such a microwave oven, a rotating antenna is provided below the mounting table in order to uniformly heat the object to be heated over the entire mounting table (see, for example, Patent Document 1). The rotating antenna disclosed in Patent Document 1 has a waveguide structure magnetically coupled to a waveguide that propagates microwaves from a magnetron.

FIG. 12 is a front sectional view showing the configuration of the microwave oven 100 disclosed in Patent Document 1. As shown in FIG. 12, in the microwave oven 100, the microwave generated by the magnetron 101 propagates through the waveguide 102 and reaches the coupling axis 109.

The rotating antenna 103 has a fan shape in plan view from above, is connected to the waveguide 102 by a coupling shaft 109, and is driven by a motor 105 to rotate. The coupling shaft 109 couples the microwave propagating through the waveguide 102 to the waveguide-structured rotating antenna 103 and functions as the rotation center of the rotating antenna 103.

The rotating antenna 103 has a radiation port 107 for radiating microwaves and a low impedance portion 106. The microwave radiated from the radiation port 107 is supplied into the heating chamber 104, and the object to be heated (not shown) placed on the placing table 108 of the heating chamber 104 is microwave-heated.

The rotating antenna 103 is rotated below the mounting table 108 to make the heating distribution in the heating chamber 104 uniform.

Separately from the function of heating the entire heating chamber uniformly (uniform heating), for example, when frozen food and room temperature food are placed in the heating chamber, to complete heating of these foods simultaneously Needs a function (local heating) to radiate microwaves locally and intensively to the region where the frozen food is placed.

In order to realize local heating, a microwave oven is proposed that controls the stop position of the rotating antenna based on the temperature distribution in the heating chamber detected by an infrared sensor (see, for example, Patent Document 2).

FIG. 13 is a front cross-sectional view showing the configuration of the microwave oven 200 disclosed in Patent Document 2. As shown in FIG. As shown in FIG. 13, in the microwave oven 200, the microwave generated by the magnetron 201 reaches the rotating antenna 203 having a waveguide structure via the waveguide 202.

The rotary antenna 203 has a radiation port 207 that is formed on one side and radiates microwaves in a plan view from above, and a low impedance part 206 that is formed on the other three sides. The microwave radiated from the radiation port 207 is supplied into the heating chamber 204 through the power supply chamber 209, and the object to be heated placed in the heating chamber 204 is heated by microwaves.

The microwave oven disclosed in Patent Document 2 has an infrared sensor 210 for detecting the temperature distribution in the heating chamber 204. The control unit 211 controls the rotation and position of the rotating antenna 203 and the direction of the radiation port 207 based on the temperature distribution detected by the infrared sensor 210.

A rotating antenna 203 disclosed in Patent Document 2 is configured to move on an arc-shaped track while rotating inside a power feeding chamber 209 formed below a mounting table 208 of a heating chamber 204 by a motor 205. . According to the microwave oven 200, the radiation port 207 of the rotating antenna 203 moves while rotating, and the low temperature portion of the object to be heated detected by the infrared sensor 210 can be heated intensively.

Japanese Patent Publication No. 63-53678 Japanese Patent No. 2894250

In the microwave oven 100 disclosed in Patent Document 1, the rotating antenna 103 is configured to rotate around a coupling shaft 109 disposed below the mounting table 108. The microwave is radiated from the radiation port 107 at the tip of the rotating antenna 103.

With this configuration, the object to be heated placed in the central region of the placing table 108 could not be directly irradiated with microwaves, and uniform heating was not always possible.

According to the microwave oven 200 disclosed in Patent Document 2, uniform heating and local heating can be performed on an object to be heated. However, this configuration requires a mechanism for moving the rotating antenna 203 while rotating it below the mounting table 208, and thus has a problem that the structure becomes complicated and the apparatus becomes large.

The present disclosure solves the above-described conventional problems, and provides a smaller microwave heating apparatus capable of uniformly heating an object to be heated placed on a placement surface in a heating chamber, particularly a central region thereof. The purpose is to provide.

A microwave heating apparatus according to one embodiment of the present disclosure includes a heating chamber that stores an object to be heated, a microwave generation unit that generates a microwave, a ceiling surface and a side wall surface that define a waveguide structure unit, and a front opening. And a waveguide structure antenna that radiates microwaves from the front opening to the heating chamber. The waveguide structure portion is joined to the ceiling surface and has a coupling portion that couples the microwave to the internal space of the waveguide structure portion.

The waveguide structure has at least one microwave suction opening formed on the ceiling surface, and radiates circularly polarized waves from the microwave suction opening into the heating chamber. At least one microwave suction opening has a cross slot shape in which two slits intersect, and is provided at a position shifted from the tube axis of the waveguide structure portion.

The at least one microwave suction opening includes a microwave suction opening having the shortest length from the center point of the crossing region of the cross slot to each tip of the slit to the tip closest to the coupling portion.

According to this aspect, it is possible to configure a smaller microwave heating apparatus that can uniformly heat the object to be heated placed on the placement surface in the heating chamber, particularly the central region thereof.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a microwave heating apparatus according to an embodiment of the present disclosure. FIG. 2A is a perspective view showing a power supply chamber in the microwave heating apparatus according to the present embodiment. FIG. 2B is a plan view showing a power supply chamber in the microwave heating apparatus according to the present embodiment. FIG. 3 is an exploded perspective view showing a rotating antenna in the microwave heating apparatus according to the present embodiment. FIG. 4 is a perspective view showing a general rectangular waveguide. FIG. 5A is a plan view showing an H-plane of a waveguide having a rectangular slot-shaped opening that radiates linearly polarized waves. FIG. 5B is a plan view showing an H-plane of a waveguide having a cross-slot-shaped opening that radiates circularly polarized waves. FIG. 5C is a front view showing the positional relationship between the waveguide and the object to be heated. FIG. 6A is a characteristic diagram showing experimental results for the waveguide shown in FIG. 5A. FIG. 6B is a characteristic diagram showing an experimental result in the case of the waveguide shown in FIG. 5B. FIG. 7 is a characteristic diagram showing experimental results in the case of “with load”. FIG. 8A is a cross-sectional view schematically showing a suction effect in the present embodiment. FIG. 8B is a cross-sectional view schematically showing the suction effect in the present embodiment. FIG. 9A is a schematic diagram illustrating a planar shape of an example of the rotating antenna used in the experiment. FIG. 9B is a schematic diagram illustrating a planar shape of an example of the rotating antenna used in the experiment. FIG. 9C is a schematic diagram illustrating a planar shape of an example of the rotating antenna used in the experiment. FIG. 10A is a schematic diagram illustrating a planar shape of an example of the rotating antenna used in the experiment. FIG. 10B is a schematic diagram illustrating a planar shape of an example of the rotating antenna used in the experiment. FIG. 11 is a plan view showing the waveguide structure according to the present embodiment. FIG. 12 is a front sectional view showing the microwave oven disclosed in Patent Document 1. FIG. 13 is a front sectional view showing the microwave oven disclosed in Patent Document 2. As shown in FIG.

A microwave heating apparatus according to a first aspect of the present disclosure includes a heating chamber that houses an object to be heated, a microwave generation unit that generates a microwave, a ceiling surface and a side wall surface that define a waveguide structure, and A waveguide structure antenna having a front opening and radiating microwaves from the front opening to the heating chamber. The waveguide structure portion is joined to the ceiling surface and has a coupling portion that couples the microwave to the internal space of the waveguide structure portion.

According to this aspect, it is possible to configure a smaller microwave heating apparatus that can uniformly heat the object to be heated placed on the placement surface in the heating chamber, particularly the central region thereof. .

According to the microwave heating apparatus of the second aspect, in addition to the first aspect, at least one microwave suction opening includes two microwave suction openings that are symmetrical with respect to the tube axis. The distance between the two microwave suction openings in the region near the coupling portion is longer than the distance between the two microwave suction openings in the region away from the coupling portion.

According to this aspect, the object to be heated placed in the central region of the placement surface can be heated more uniformly.

According to the microwave heating apparatus of the third aspect, in addition to the second aspect, the distance between the two microwave suction openings is 1 of the wavelength of the microwave propagating in the internal space of the waveguide structure. / 8 or more. According to this aspect, it is possible to radiate circularly polarized waves more reliably from the microwave suction opening.

In the microwave heating apparatus of the fourth aspect, in addition to any of the first to third aspects, the microwave suction opening is provided in the vicinity of the coupling portion. According to this aspect, the object to be heated placed in the central region of the placement surface can be heated more uniformly.

According to the microwave heating apparatus of the fifth aspect, in addition to any of the first to fourth aspects, the ceiling surface has a recess provided at a joint portion between the coupling portion and the waveguide structure portion. . According to this aspect, the object to be heated placed in the central region of the placement surface can be heated more uniformly.

Hereinafter, preferred embodiments of the microwave heating apparatus according to the present disclosure will be described with reference to the accompanying drawings.

In the following embodiments, a microwave oven is used as an example of a microwave heating apparatus according to the present disclosure, but the present invention is not limited to this, and a heating apparatus, a garbage disposal machine, or a semiconductor manufacture using microwave heating is not limited thereto. Including devices. The present disclosure is not limited to the specific configurations shown in the following embodiments, and includes configurations based on the same technical idea.

In the following drawings, the same or equivalent parts are denoted by the same reference numerals, and redundant description may be omitted.

FIG. 1 is a front sectional view showing a schematic configuration of a microwave oven that is a microwave heating apparatus according to an embodiment of the present disclosure. In the following description, the left-right direction of the microwave oven means the left-right direction in FIG. 1, and the front-back direction means the depth direction in FIG.

As shown in FIG. 1, the microwave oven 1 according to the present embodiment includes a heating chamber 2a, a power feeding chamber 2b, a magnetron 3, a waveguide 4, a rotating antenna 5, and a mounting table 6. The mounting table 6 has a flat upper surface for mounting an object to be heated (not shown) such as food. The heating chamber 2 a is an upper space of the mounting table 6, and the power supply chamber 2 b is a lower space of the mounting table 6.

The mounting table 6 covers the power supply chamber 2b provided with the rotating antenna 5, partitions the heating chamber 2a and the power supply chamber 2b, and constitutes the bottom surface of the heating chamber 2a. Since the upper surface (mounting surface 6a) of the mounting table 6 is flat, it is easy to put in and out the object to be heated, and it is easy to wipe off dirt and the like attached to the mounting surface 6a.

Since the mounting table 6 is made of a material that easily transmits microwaves, such as glass and ceramic, the microwave radiated from the rotating antenna 5 passes through the mounting table 6 and is supplied to the heating chamber 2a.

The magnetron 3 is an example of a microwave generation unit that generates a microwave. The waveguide 4 is an example of a propagation unit that is provided below the power supply chamber 2 b and transmits the microwave generated by the magnetron 3 to the coupling unit 7. The rotating antenna 5 is provided in the internal space of the power supply chamber 2b, and radiates the microwave transmitted by the waveguide 4 and the coupling portion into the power supply chamber 2b from the front opening 13.

The rotating antenna 5 includes a waveguide structure portion 8 having a box-shaped waveguide structure in which microwaves propagate in the internal space, and a microwave in the waveguide 4 and the internal space of the waveguide structure portion 8. It is a waveguide structure antenna having a coupling portion 7 to be coupled. The coupling unit 7 includes a coupling shaft 7 a coupled to the motor 15 that is a driving unit, and a flange 7 b that joins the waveguide structure unit 8 and the coupling unit 7.

The motor 15 is driven in accordance with a control signal from the control unit 17 to rotate the rotating antenna 5 around the coupling shaft 7a of the coupling unit 7 and stop it in a desired direction. Thereby, the radiation direction of the microwave from the rotating antenna 5 is changed. A metal such as an aluminum-plated steel plate is used for the coupling portion 7, and, for example, a fluororesin is used for a coupling portion of the motor 15 coupled to the coupling portion 7.

The coupling shaft 7a of the coupling portion 7 passes through an opening that communicates the waveguide 4 and the power supply chamber 2b, and the coupling shaft 7a has a predetermined clearance (for example, 5 mm or more) between the penetrating opening. The coupling shaft 7 a couples the waveguide 4 and the internal space of the waveguide structure portion 8 of the rotating antenna 5, so that the microwave propagates efficiently from the waveguide 4 to the waveguide structure portion 8.

An infrared sensor 16 is provided on the upper side of the heating chamber 2a. The infrared sensor 16 is an example of a state detection unit that detects the temperature in the heating chamber 2a, that is, the surface temperature of the heated object placed on the mounting table 6 as the state of the heated object. The infrared sensor 16 detects the temperature of each region of the heating chamber 2 a virtually divided into a plurality of parts, and transmits those detection signals to the control unit 17.

The control unit 17 performs oscillation control of the magnetron 3 and drive control of the motor 15 based on the detection signal of the infrared sensor 16.

This embodiment has the infrared sensor 16 as an example of the state detection unit, but the state detection unit is not limited to this. For example, a weight sensor that detects the weight of the object to be heated or an image sensor that captures an image of the object to be heated may be used as the state detection unit. In the configuration in which the state detection unit is not provided, the control unit 17 may perform the oscillation control of the magnetron 3 and the drive control of the motor 15 in accordance with a program stored in advance and a selection by the user.

FIG. 2A is a perspective view showing the power supply chamber 2b in a state where the mounting table 6 is removed. FIG. 2B is a plan view showing the power supply chamber 2b in the same situation as FIG. 2A.

As shown in FIGS. 2A and 2B, a rotating antenna 5 is provided in a power supply chamber 2b that is disposed below the heating chamber 2a and is separated from the heating chamber 2a by the mounting table 6. The rotation center G of the coupling shaft 7a in the rotating antenna 5 is located below the center of the feed chamber 2b in the front-rear direction and the left-right direction, that is, below the center of the mounting table 6 in the front-rear direction and the left-right direction.

The feeding chamber 2 b has an internal space constituted by the bottom surface 11 and the lower surface of the mounting table 6. The internal space of the power supply chamber 2b includes the rotation center G of the coupling portion 7 and has a symmetrical shape with respect to the center line J (see FIG. 2B) in the left-right direction of the power supply chamber 2b. On the side wall surface in the internal space of the power supply chamber 2b, a convex portion 18 protruding inward is formed. The convex portion 18 includes a convex portion 18a provided on the left side wall surface and a convex portion 18b provided on the right side wall surface.

A magnetron 3 is provided below the convex portion 18b. The microwave radiated from the antenna 3 a of the magnetron 3 propagates in the waveguide 4 provided below the feeding chamber 2 b and is transmitted to the waveguide structure 8 by the coupling portion 7.

The side wall surface 2c of the feeding chamber 2b has an inclination for reflecting the microwave radiated from the rotating antenna 5 in the horizontal direction toward the upper heating chamber 2a.

FIG. 3 is an exploded perspective view showing a specific example of the rotating antenna 5. As shown in FIG. 3, the waveguide structure 8 has a ceiling surface 9 and side wall surfaces 10a, 10b, and 10c that define its internal space.

The ceiling surface 9 includes three linear edges, one arc-shaped edge, and a concave portion 9a to which the coupling portion 7 is joined, and is disposed to face the mounting table 6 (see FIG. 1). ). Side wall surfaces 10a, 10b, and 10c are formed by bending downward from the three linear edges of the ceiling surface 9, respectively.

The side wall surface is not provided at the arc-shaped edge, and an opening is formed below the side wall surface. This opening functions as a front opening 13 that radiates the microwave propagated through the internal space of the waveguide structure 8. That is, the side wall surface 10b is provided to face the front opening 13, and the side wall surfaces 10a and 10c are provided to face each other.

At the lower edge of the side wall surface 10a, there is provided a low impedance portion 12 extending outwardly of the waveguide structure 8 and in a direction perpendicular to the side wall surface 10a. The low impedance portion 12 is formed in parallel with the bottom surface 11 of the power supply chamber 2b with a slight gap therebetween. The low impedance portion 12 suppresses microwaves that leak in the direction perpendicular to the side wall surface 10a.

In order to ensure a certain gap with the bottom surface 11 of the power supply chamber 2b, a holding portion 19 for mounting an insulating resin spacer (not shown) may be formed on the lower surface of the low impedance portion 12.

The low impedance portion 12 is provided with a plurality of slits 12a extending periodically from the side wall surface 10a at regular intervals. The plurality of slits 12a suppress microwave leakage in a direction parallel to the side wall surface 10a. The interval between the slits 12 a is appropriately determined according to the wavelength propagating through the waveguide structure 8.

Similarly, the low impedance portion 12 having a plurality of slits 12a at the lower edge portion is also provided for the side wall surface 10b and the side wall surface 10c.

The rotating antenna 5 according to the present embodiment has a front opening 13 formed in an arc shape, but the present disclosure is not limited to this shape, and has a straight or curved front opening 13. Also good.

As shown in FIG. 3, the ceiling surface 9 includes a plurality of microwave suction openings 14, that is, a first opening 14a and a second opening 14b having an opening smaller than the first opening 14a. The microwave that has propagated through the internal space of the waveguide structure 8 is radiated from the front opening 13 and the plurality of microwave suction openings 14.

The flange 7b formed in the coupling portion 7 is joined to the lower surface of the ceiling surface 9 of the waveguide structure portion 8 by, for example, caulking, spot welding, screw tightening, or welding, and the rotating antenna 5 is joined to the coupling portion 7. And fixed.

In the present embodiment, since the rotating antenna 5 has a waveguide structure portion 8 as will be described later, it is possible to uniformly heat the object to be heated mounted on the mounting table 6. In particular, in the central region of the mounting surface 6a located above the rotation center G (see FIGS. 2A and 2B) of the rotating antenna 5, heating can be performed efficiently and uniformly. Hereinafter, the waveguide structure in the present embodiment will be described in detail.

[Waveguide structure]
First, in order to understand the characteristics of the waveguide structure section 8, a general waveguide 300 will be described with reference to FIG. As shown in FIG. 4, the simplest and most common waveguide 300 has a rectangular cross section 303 having a width a and a height b, and a square having a depth along the tube axis V of the waveguide 300. It is a waveguide. The tube axis V is the center line of the waveguide 300 that passes through the center of the cross section 303 and extends in the microwave transmission direction Z.

The wavelength of the microwave when the lambda ₀ in free space, the width a and height _{b, λ 0>a> λ} 0/2, and, by selecting from a range b <a lambda _0/2, the waveguide It is known that the microwave propagates in the tube 300 in the TE10 mode.

The TE10 mode is a transmission mode in the H wave (TE wave; electrical transverse wave transmission (Transverse Electric Wave)) in the waveguide 300 in the microwave transmission direction Z, in which the magnetic field component exists and the electric field component does not exist. Point to.

The wavelength λ ₀ of the microwave in free space can be obtained by the equation (1).

In the formula (1), the speed of light c is about 2.998 × 10 ⁸ [m / s], and the oscillation frequency f is 2.4 to 2.5 [GHz] (ISM band in the case of a microwave oven). ). Since the oscillation frequency f varies depending on variations in magnetron and load conditions, the wavelength λ ₀ in free space is between a minimum of 120 [mm] (at 2.5 GHz) and a maximum of 125 [mm] (at 2.4 GHz). fluctuate.

In the case of the waveguide 300 used for the microwave oven, the width a of the waveguide 300 is designed in the range of 80 to 100 mm and the height b of 15 to 40 mm in consideration of the range of the wavelength λ ₀ in free space. There are many cases.

In general, in the waveguide 300 shown in FIG. 4, the wide surface 301 that is the upper surface and the lower surface is referred to as the H surface in the sense that the magnetic field vortexes in parallel, and the narrow surface 302 that is the left and right side surfaces. In the sense that it is a plane parallel to the electric field, it is called the E plane. For simplicity, in the plan view shown below, a straight line on the H plane in which the tube axis V is projected on the H plane may be referred to as the tube axis V.

When the wavelength of the microwave from the magnetron is defined as the wavelength λ ₀ and the wavelength of the microwave when propagating in the waveguide is defined as the wavelength λg in the tube, λg can be obtained by Expression (2).

Therefore, the guide wavelength λg varies depending on the width a of the waveguide 300, but is not related to the height b. In the TE10 mode, the electric field is zero at both ends (E plane) of the waveguide 300 in the width direction W, that is, the narrow surface 302, and the electric field is maximum at the center in the width direction W.

In the present embodiment, the same principle as that of the waveguide 300 shown in FIG. 4 is applied to the rotating antenna 5 shown in FIGS. In the rotating antenna 5, the ceiling surface 9 and the bottom surface 11 of the power supply chamber 2b are H surfaces, and the side wall surfaces 10a and 10c are E surfaces.

The side wall surface 10 b serves as a reflection end for reflecting all the microwaves in the rotating antenna 5 in the direction of the front opening 13. In the present embodiment, specifically, the width a of the waveguide 300 is 106.5 mm.

A plurality of microwave suction openings 14 are formed in the ceiling surface 9. The microwave suction opening 14 includes two first openings 14a and two second openings 14b. The two first openings 14 a are symmetric with respect to the tube axis V of the waveguide structure portion 8 of the rotating antenna 5. Similarly, the two second openings 14b are symmetric with respect to the tube axis V. The first opening 14a and the second opening 14b are formed so as not to cross the tube axis V.

The first opening 14a and the second opening 14b are arranged at positions shifted from the tube axis V of the waveguide structure 8 (more precisely, a straight line on the ceiling surface 9 obtained by projecting the tube axis V onto the ceiling surface 9). With this structure, circularly polarized waves can be more reliably radiated from the microwave suction opening 14. By radiating circularly polarized microwaves, the central region of the mounting surface 6a can be uniformly heated.

Depending on whether the first opening 14a and the second opening 14b are provided in the left or right region of the tube axis V, the rotation direction of the electric field, that is, right-handed polarization (CW: Clockwise) or left-handed polarization (CCW: Counterclockwise) It is determined.

In the present embodiment, each of the microwave suction openings 14 is provided so as not to straddle the tube axis V. However, the present disclosure is not limited to this, and even in a configuration in which a part of these openings crosses the tube axis V, circularly polarized light can be emitted. In this case, a distorted circularly polarized wave is generated.

[Circular polarization]
Next, circular polarization will be described. Circular polarization is a technique widely used in the fields of mobile communications and satellite communications. Examples of familiar use include ETC (Electronic Toll Collection System), that is, a non-stop automatic toll collection system.

Circular polarization is a microwave in which the polarization plane of an electric field rotates with respect to the direction of travel, and the direction of the electric field continues to change with time, and the magnitude of the electric field strength does not change. .

If this circularly polarized wave is applied to a microwave heating apparatus, it can be expected that the object to be heated will be heated uniformly, particularly in the circumferential direction of the circularly polarized wave, as compared with the conventional microwave heating by linearly polarized wave. The same effect can be obtained with either right-handed polarization or left-handed polarization.

Circular polarization is primarily used in the field of communications, and since it is intended for radiation into open spaces, it is generally discussed as a so-called traveling wave with no reflected wave. On the other hand, in the present embodiment, a reflected wave is generated in the heating chamber 2a that is a closed space, and the generated reflected wave and the traveling wave may be combined to generate a standing wave.

However, in addition to the reduction of reflected waves due to the absorption of microwaves by the food, the balance of standing waves is lost at the moment when the microwaves are radiated from the microwave suction opening 14, and standing waves are generated again. It is considered that a traveling wave is generated until this time. Therefore, according to the present embodiment, it is possible to utilize the above-described features of circularly polarized waves, and uniform heating in the heating chamber 2a is possible.

Here, the difference between the field of communication in an open space and the field of dielectric heating in a closed space will be described.

In the communications field, either right-handed polarization or left-handed polarization is used for accurate transmission / reception of information, and a receiving antenna having directivity suitable for it is used on the receiving side.

On the other hand, in the field of microwave heating, instead of a receiving antenna having directivity, a non-directional object to be heated, such as food, receives microwaves, so that the microwave is irradiated to the entire object to be heated. Is important. Therefore, in the field of microwave heating, whether it is right-handed polarized wave or left-handed polarized wave is not important, and there is no problem even if right-handed polarized wave and left-handed polarized wave are mixed.

[Microwave suction effect]
Here, the microwave suction effect from the rotating antenna, which is a feature of the present embodiment, will be described. In the present embodiment, the microwave suction effect means that the microwave in the waveguide structure is sucked out from the microwave suction opening 14 when an object to be heated such as food is nearby.

FIG. 5A is a plan view of a waveguide 400 having an H plane provided with an opening for generating linearly polarized waves. FIG. 5B is a plan view of a waveguide 500 having an H plane provided with an opening for generating circularly polarized waves. FIG. 5C is a front view showing the positional relationship between the

waveguide

400 or 500 and the object 22 to be heated.

As shown in FIG. 5A, the opening 401 is a rectangular slit provided so as to intersect the tube axis V of the waveguide 400. The opening 401 radiates linearly polarized microwaves. As shown in FIG. 5B, each of the two openings 501 is a cross-slot-shaped opening formed by two rectangular slits that intersect at right angles. The two openings 501 are symmetric with respect to the tube axis V of the waveguide 500.

Each opening is symmetric with respect to the tube axis V of the waveguide, and has a width of 10 mm and a length of Lmm. In these configurations, the case of “no load” in which the object to be heated 22 is not disposed and the case of “with load” in which the object to be heated 22 is disposed were analyzed using CAE.

In the case of “with load”, as shown in FIG. 5C, the height of a constant object to be heated 22 is 30 mm, the bottom areas (100 mm square and 200 mm square) of two kinds of objects to be heated 22, and three kinds of objects to be heated With respect to the material of the object 22 (frozen beef, refrigerated beef, water), the distance D from the

waveguides

400 and 500 to the bottom surface of the object to be heated 22 was measured as a parameter.

FIG. 6A and FIG. 6B show the relationship between the length of the opening and the radiated power in the case of “no load” in order to use the radiated power from the opening in the case of “no load” as a reference.

6A shows the characteristics in the case of the opening 401 shown in FIG. 5A, and FIG. 6B shows the characteristics in the case of the opening 501 shown in FIG. 5B. 6A and 6B, the horizontal axis is the length L [mm] of the opening, and the vertical axis is emitted from the

openings

401 and 501 when the power propagating in the waveguide is 1.0 W. The microwave power [W].

For comparison with the case of “with load”, the length L at which the radiated power becomes 0.1 W in the case of “without load”, that is, the case where the length L is 45.5 mm in the graph shown in FIG. 6A. In the graph shown in FIG. 6B, the case where the length L was 46.5 mm was selected.

FIG. 7 shows three kinds of foods having two kinds of bottom areas (100 mm square and 200 mm square) when the length L is the above length (45.5 mm, 46.5 mm) and “with load” ( Includes six graphs showing the results of analysis on frozen beef, refrigerated beef, and water).

In each graph included in FIG. 7, the horizontal axis represents the distance D [mm] from the object to be heated 22 to the waveguide, and the vertical axis represents the radiated power at “no load” as 1.0. It is the relative radiated power when. In other words, compared to the case of “no load”, the object to be heated 22 indicates how much microwaves are sucked out of the

waveguides

400 and 500 in the case of “with load”.

In each graph shown in FIG. 7, the broken line indicates the characteristics (indicated by “I” in the figure) in the case of the opening 401 having a linear shape (I shape), and the solid line has two cross slot shapes (X shape). The characteristic in the case of the opening 501 (indicated by “2X” in the figure) is shown.

In any of the six graphs, the opening 501 has more radiated power than the opening 401. In particular, when the distance D is 20 mm or less, there is a difference of about twice as much as the actual microwave oven. Can be recognized. Therefore, regardless of the type and bottom area of the object to be heated 22, it is clear that the opening that generates circularly polarized waves has a higher microwave absorption effect than the opening that generates linearly polarized waves.

Examining in detail, with regard to the type of the object to be heated 22, particularly when the distance D is 10 mm or less, frozen beef having a smaller dielectric constant and dielectric loss has a larger suction effect, and water having a larger dielectric constant and dielectric loss. The suction effect is smaller.

In the case of refrigerated beef or water, when the distance D increases, the radiated power drops to 1 or less particularly in linearly polarized waves. This is considered to be because the radiated power was canceled by the reflected power from the object to be heated 22. About the bottom area of the to-be-heated object 22, since radiation power is almost the same at 100 mm square and 200 mm square, it is thought that there is little influence with respect to the microwave suction effect.

The inventors examined the conditions of the aperture that can radiate circularly polarized waves through experiments using various aperture shapes. As a result, the following conclusion was reached. The preferable conditions for generating the circularly polarized wave are that the opening is arranged so as to be shifted from the tube axis V of the waveguide, and that the opening shape includes a cross-slot-shaped opening. It is an opening having a cross slot shape that radiates the circularly polarized microwave most efficiently, that is, has a high suction effect.

8A and 8B are cross-sectional views schematically showing the suction effect in the present embodiment. The front opening 13 of the rotating antenna 5 faces leftward in the figure in both FIG. 8A and FIG. 8B. The object to be heated 22 is disposed above the coupling portion 7 in FIG. 8A, and is placed at the left corner of the placement surface 6a in FIG. 8B. That is, in the two states shown in FIGS. 8A and 8B, the distance from the coupling portion 7 to the article to be heated 22 is different.

In the state shown in FIG. 8A, it is considered that the object to be heated 22 is close to the microwave suction opening 14, particularly the first opening 14a, and the suction effect from the first opening 14a occurs. As a result, most of the microwave traveling from the coupling portion 7 toward the front opening 13 is radiated to the object to be heated 22 as a circularly polarized microwave from the first opening 14a, and the object to be heated 22 is emitted. Heat.

On the other hand, in the state shown in FIG. 8B, since the article 22 to be heated is separated from the microwave suction opening 14, it is considered that the suction effect from the microwave suction opening 14 does not occur so much. As a result, most of the microwave traveling from the coupling portion 7 toward the front opening 13 is radiated from the front opening 13 to the object to be heated 22 as a linearly polarized microwave, and heats the object to be heated 22. To do.

As described above, the microwave suction opening 14 according to the present embodiment increases the radiated power when food is placed in the vicinity of the microwave suction opening 14, and the food is located away from the microwave suction opening 14. This is considered to cause a special phenomenon that the radiated power decreases when the is placed.

[Uniform heating by the waveguide structure]
Hereinafter, uniform heating by the waveguide structure according to the present embodiment will be described. The inventors have conducted experiments using rotating antennas having waveguide structures of various shapes, and have found an optimal waveguide structure for uniform heating.

FIG. 9A, FIG. 9B, and FIG. 9C are schematic views respectively showing the planar shapes of three examples of the rotating antenna used in the experiment.

As shown in FIG. 9A, the waveguide structure 600 has two first openings 614a and two second openings 614b. The first opening 614a has a cross slot shape, and each rectangular slit is provided in the vicinity of the coupling portion 7 so as to form an angle of 45 degrees with respect to the tube axis V of the waveguide structure portion 600. The second opening 614 b is smaller than the first opening 614 a and is provided apart from the coupling portion 7.

As shown in FIG. 9B, the waveguide structure 700 has one first opening 714a having a cross slot shape similar to the first opening 614a, unlike the waveguide structure 600.

As shown in FIG. 9C, the waveguide structure 800 has two first openings 814a having a T-shape unlike the waveguide structure 600. That is, unlike the first opening 614a, the first opening 814a does not have a portion extending from the intersecting portion toward the coupling portion 7 in one of the two rectangular slits.

Common to the waveguide structure shown in FIGS. 9A to 9C is that a plurality of cross-slot shaped microwave suction openings are provided, and a first opening having a similar size is provided at a similar location. The second opening having the same size is provided at the same place. In particular, the second opening 614b, the second opening 714b, and the second opening 814b are the same.

Using the rotating antenna having the waveguide structure shown in FIGS. 9A to 9C, an experiment was performed under the same heating conditions using the frozen okonomiyaki placed in the central region of the placement surface 6a, and verified by CAE. Okonomiyaki is a pancake-like dish made by baking dough containing various ingredients.

In the case of the waveguide structure portion 600 shown in FIG. 9A, the circularly polarized waves output from these openings interfere, and the temperature of the part to be heated located in the central region of the mounting surface 6a above the coupling portion 7 However, it has been found that a phenomenon (hereinafter referred to as a temperature drop in the vicinity of the coupling portion 7) that does not rise abnormally as compared with the surrounding portion occurs.

In the case of the waveguide structure 700 shown in FIG. 9B, the temperature drop in the vicinity of the coupling portion 7 could be suppressed. Similarly, in the case of the waveguide structure portion 800 shown in FIG. 9C, the temperature drop in the vicinity of the coupling portion 7 could be suppressed.

As described above, the waveguide structure in which no opening is provided in the vicinity of the coupling portion 7 or only one opening is provided in the vicinity of the coupling portion 7 suppresses a temperature drop in the vicinity of the coupling portion 7. It was confirmed that uniform heating in the heating chamber 2a was possible.

Furthermore, the inventors conducted experiments on the shape of the microwave suction opening and found a waveguide structure capable of further uniforming the heating distribution.

The first opening 814a of the waveguide structure 800 shown in FIG. 9C radiates a distorted circularly polarized wave, which is different from the circularly polarized wave formed by the cross-slot shaped opening. From the viewpoint of uniform heating in the chamber 2a, a preferable result was not obtained.

Therefore, the first opening 914a having the shape shown in FIGS. 10A and 10B was examined in order to suppress the interference between the two circularly polarized waves and to form the circularly polarized wave as close to the circle as possible.

Hereinafter, the waveguide structure having the first opening 914a will be described in detail with reference to the drawings.

FIG. 10A and FIG. 10B are schematic views respectively showing the planar shapes of the waveguide structure portion 900A and the waveguide structure portion 900B provided with the first opening 914a.

As shown in FIGS. 10A and 10B, the

waveguide structures

900A and 900B both have the same first opening 914a and second opening 914b.

The first opening 914a is a cross in which, in one of the two rectangular slits, a portion extending from the intersecting portion in the direction of the coupling portion 7 has a shorter length than a portion extending from the intersecting portion in the opposite direction of the coupling portion 7. It has a slot shape. As a result of the examination, according to the first opening 914a, uniform heating can be achieved by suppressing interference between the two circularly polarized waves, and in addition, the above-described suction effect can be obtained compared to the first opening 814a shown in FIG. It was confirmed that it was higher.

The length of the portion of the first opening 914a extending from the intersecting portion in the direction of the coupling portion 7 is appropriately set according to the specifications so that interference between the two circularly polarized waves does not occur.

The waveguide structure 900A has a flat ceiling surface as a whole. On the other hand, in the waveguide structure portion 900B, a concave joint region (a concave portion 909a which is a step region) is formed in a joint portion where the flange 7b is joined to the ceiling surface (see, for example, FIG. 3). Therefore, on the ceiling surface of the waveguide structure 900B, the distance between the junction region and the mounting table is longer than that of other portions.

Using the rotating antenna having the above-mentioned waveguide structure, an experiment was similarly performed under the same heating conditions using frozen okonomiyaki placed in the central region of the placement surface 6a, and verified by CAE.

As a result, since the first opening 914a has a substantially cross slot shape, the waveguide structure 900A suppresses interference between two circularly polarized waves and generates a circularly polarized wave having a shape close to a circle. I was able to.

In addition, the first opening 914a increases the suction effect, and can suppress the temperature drop in the vicinity of the coupling portion 7. Moreover, it has been found that the temperature decrease in the vicinity of the coupling portion 7 can be suppressed by the concave joining region formed on the ceiling surface of the waveguide structure portion 900B.

A specific configuration example of the rotating antenna according to the present embodiment based on the knowledge from various experiments as described above will be described below. Based on the above knowledge, various modified examples can be used according to the specifications of the microwave heating apparatus.

FIG. 11 is a plan view showing a rotating antenna having the waveguide structure 8 according to the present embodiment.

As shown in FIG. 11, the waveguide structure 8 has a plurality of microwave suction openings 14 provided on the ceiling surface 9. The plurality of microwave suction openings 14 include a first opening 14a and a second opening 14b having an opening smaller than the first opening 14a. The first opening 14a and the second opening 14b have a substantially cross slot shape.

Due to the structure in which the center point P1 of the first opening 14a and the center point P2 of the second opening 14b are arranged at positions shifted from the tube axis V of the waveguide structure 8, the microwave suction opening 14 is circularly polarized. Can radiate. Here, the center point P1 of the first opening 14a and the center point P2 of the second opening 14b are the center points of the intersecting regions of the two slits forming the first opening 14a and the second opening 14b, respectively.

In the present embodiment, the first opening 14 a and the second opening 14 b are arranged so as not to cross the tube axis V of the waveguide structure 8. The longitudinal direction of each rectangular slit of the first opening 14a and the second opening 14b has an inclination of substantially 45 ° C. with respect to the tube axis V.

As shown in FIG. 11, the first opening 14 a is formed close to the recess 9 a of the ceiling surface 9. The recess 9a is a step region provided so as to protrude from the ceiling surface 9 in a direction (downward) opposite to the traveling direction of the microwave radiated from the first opening 14a (see FIG. 3). The two first openings 14a are symmetric with respect to the tube axis V.

The second opening 14b is formed in the vicinity of the front opening 13 at a distance from the coupling portion 7 than the first opening 14a. Similar to the first opening 14a, the two second openings 14b are symmetric with respect to the tube axis V.

In the first opening 14a, in two slots, the length of the portion extending in the direction from the center point P1 toward the tube axis V is shorter than the length of the portion extending in the direction from the center point P1 to the side wall surface 10a. Has characteristics.

As shown in FIG. 3, the flange 7 b provided in the coupling portion 7 has a shape in which the length in the microwave transmission direction Z is shorter than the length in the width direction W of the waveguide structure portion 8. That is, in the coupling unit 7, the length of the microwave transmission direction Z is shorter than the length in the direction orthogonal to the transmission direction Z. According to the flange 7b, the tip of the slit extending from the central point P1 toward the coupling portion 7 can be formed closer to the coupling portion 7.

In the present embodiment, since the flange 7b is joined to the back side of the recess 9a, the recess 9a is formed on the front side of the recess 9a by joining the flange 7b such as a protrusion of TOX caulking, a welding mark, a screw, a nut head, or the like. It is comprised so that it may become deeper than the height of the protrusion which arises. According to the present embodiment, there is no problem such that the protrusion contacts the lower surface of the mounting table 6.

11 has a recess 9a provided in the ceiling surface 9 above the coupling portion 7, and has the same configuration as the waveguide structure 900B shown in FIG. 10B. According to the waveguide structure portion 8 shown in FIG. 11, similarly to the waveguide structure portion 900 </ b> B, a temperature decrease near the coupling portion 7 can be suppressed. There are two possible reasons for this.

First, when an object to be heated is placed above the first opening 14a, a part of the microwave radiated from the first opening 14a and turned into a circular polarization is reflected by the object to be heated. The reflected microwave is repeatedly reflected in the space formed between the upper surface of the recess 9a and the lower surface of the mounting table 6, and as a result, the object to be heated is heated more strongly.

Second, in the present embodiment, the internal space of the waveguide structure portion 8 where the recess 9a is formed is narrower than the other portions. When most of the microwave propagating from the coupling axis 7a into the waveguide structure 8 travels from a narrow space near the recess 9a toward a wide space separated from the recess 9a, the first opening 14a is caused by the suction effect. The object to be heated radiated from the surface and placed in the central region of the placement surface 6a is strongly heated.

Hereinafter, the shape of the first opening 14a in the present embodiment will be described in detail.

As shown in FIG. 11, the first opening 14a includes

slits

20a and 20b, and has a cross slot shape in which these intersect at the center point P1. The major axis of each slit of the first opening 14a has an angle of 45 degrees with respect to the tube axis V.

The slit 20a extends from the lower right to the upper left of the center point P1, and has a first length A from the center point P1 to the lower right tip and a third length C from the center point P1 to the upper left tip. Have. The lower right tip of the slit 20a is directed toward the coupling portion 7 and close to the recess 9a.

The slit 20b extends from the lower left to the upper right of the center point P1, and has a second length B from the center point P1 to the lower left tip and a fourth length D from the center point P1 to the upper right tip. That is, the first length A is the length from the center point P1 to the tips closest to the coupling portion 7 among the lengths from the center point P1 to the tips of the

slits

20a and 20b.

The third length C and the fourth length D are the same, and these correspond to substantially ¼ of the wavelength of the microwave propagating in the waveguide structure 8. The second length B is shorter than the third length C and the fourth length D, and the first length A is the shortest of these.

Further, the distance X between the slit 20a and the tube axis V is longer than the distance Y between the slit 20b and the tube axis V. That is, the ceiling surface 9 has a wider area near the recess 9a between the two first openings 14a than an area spaced from the recess 9a.

If the region between the two first openings 14a is not flat, a turbulent electromagnetic field is generated in the waveguide structure 8 and adversely affects the formation of circularly polarized waves. It is preferable to provide a wider flat area between them. According to the present embodiment, a circular polarization with less disturbance is formed by a wider flat region provided between the two first openings 14a, and a high suction effect is obtained.

In the present embodiment, the distance between the two first openings 14a is 1/8 or more of the wavelength of the microwave propagating in the waveguide structure portion 8. According to the experiments by the inventors, favorable results were obtained when the two first openings 14a have a distance substantially corresponding to the shaft diameter (18 mm) of the coupling shaft 7a.

On the other hand, the second opening 14b has a cross slot shape in which two slits having the same length are orthogonal to each other at the center. The major axis of each slit of the second opening 14b has an angle of 45 degrees with respect to the tube axis V. In the present embodiment, the length of the major axis of each slit of the second opening 14b is equal to the third length C and the fourth length D of the first opening 14a.

The connecting portion 7 according to the present embodiment has the flange 7b having the above-mentioned shape, but the shape of the flange 7b is not limited to this, and can be changed as appropriate according to the specifications.

For example, if the portion of the flange 7b in the direction along the tube axis V is made shorter, the first opening 14a can be provided closer to the coupling portion 7. It is also possible to provide the first opening 14a closer to the coupling portion 7 depending on the shape of the flange 7b, such as using a flange 7b having a notch with the first opening 14a.

If the shape of the flange 7b is devised, it is possible to reinforce the joining between the coupling portion 7 and the waveguide structure portion 8 without reducing the area of the joining portion, thereby suppressing variations in products.

Even when the coupling shaft 7a has, for example, a semicircular, elliptical, or rectangular cross section, or when the coupling shaft 7a having such a cross-sectional shape is directly joined to the waveguide structure 8, this embodiment is implemented. The same effect as that of the embodiment can be obtained. According to the configuration in which the flange 7b is not provided, the space for forming the first opening 14a can be further expanded.

According to the present embodiment, since a high suction effect is obtained, a temperature drop in the vicinity of the coupling portion 7 is suppressed, and uniform heating in the central region of the mounting surface 6a becomes possible.

In the present embodiment, the microwave suction opening has a cross slot shape, but the microwave suction opening of the present disclosure is not limited to this. Even if the microwave suction opening has a shape other than the cross slot shape, it may have a shape capable of generating circularly polarized waves.

As a result of the experiment, it is inferred that the essential condition for generating the circularly polarized wave from the waveguide structure part is that the two generally elongated openings are combined at a position shifted from the tube axis.

The slit constituting the microwave suction opening 14 is not limited to a rectangle. For example, even in the case of an opening having a rounded corner or an elliptical opening, it is possible to generate circularly polarized waves.

Rather, in order to suppress the concentration of the electric field, the corners of the opening are preferably rounded. In the present embodiment, as shown in FIGS. 3, 9A to 9C, 10A, 10B, and 11, the slits included in the first opening 14a and the second opening 14b are rounded at the tip and the intersection. Has a cracked corner. That is, the two slits included in the microwave suction opening 14 have a width near the intersection that is wider than the width near the end.

In the present embodiment, the concave portion 9a is formed above the coupling portion 7 of the ceiling surface 9, but the waveguide structure portion 8 of the present disclosure is not limited to this.

For example, in consideration of the propagation state of the microwave radiated from the opening, a recess 9 a may be provided between the microwave suction opening 14 and the rotation center of the waveguide structure 8. A convex portion projecting into the internal space of the waveguide structure 8 may be provided on the ceiling surface 9 closer to the rotation center of the waveguide structure 8 than the microwave suction opening 14.

That is, if the waveguide structure portion 8 is provided in a part of the ceiling surface 9 closer to the coupling portion 7 than the microwave suction opening 14 and has a step region whose height is lower than other portions of the ceiling surface 9. Good.

The present disclosure can be used in microwave heating apparatuses for various industrial uses such as a drying apparatus, a heating apparatus for ceramics, a garbage disposal machine, and a semiconductor manufacturing apparatus in addition to a microwave oven.

1, 100, 200

Microwave oven

2a, 104, 204

Heating chamber

2b, 209

Feed chamber

2c, 10a, 10b, 10c

Side wall surface

3, 101, 201

Magnetron 3a Antenna

4, 102, 202, 400, 500 Waveguide 5, DESCRIPTION OF SYMBOLS 103,203 Rotating antenna 6,108,208 Mounting base 6a Mounting surface 7

Coupling part

7a, 109 Coupling shaft 7b Flange 8,600,700,800,900A, 900B Waveguide structure part 9

Ceiling surface

9a, 909a Concave part 11

Bottom face

12, 106, 206

Low impedance part

12a, 20a, 20b Slit 13 Front opening 14

Microwave suction opening

14a, 614a, 714a, 814a, 914a First opening 14b, 614b, 714b, 814b, 914b

Second opening

15, 105 , 205 Motor 16,210 Red

External line sensor

17, 211

Control unit

18, 18a, 18b Protruding part 19 Holding part 22 Object to be heated 107, 207 Radiation port 300 Waveguide 301 Wide surface 302 Narrow surface 303

Cross section

401, 501 Opening

Claims

A heating chamber for storing an object to be heated;
A microwave generator for generating microwaves;
A waveguide structure antenna having a ceiling surface and a side wall surface defining a waveguide structure portion, and a front opening, and radiating the microwave from the front opening to the heating chamber, wherein the waveguide structure portion A waveguide structure antenna having a coupling portion joined to the ceiling surface and coupling the microwave to the internal space of the waveguide structure portion;
The waveguide structure has at least one microwave suction opening formed in the ceiling surface, and radiates circularly polarized waves from the microwave suction opening into the heating chamber;
The at least one microwave suction opening has a cross slot shape in which two slits intersect, and is provided at a position shifted from the tube axis of the waveguide structure part,
The at least one microwave suction opening is a microwave suction opening having the shortest length from the center point of the crossing region of the cross slot to each tip of the slit to the tip closest to the coupling portion. A microwave heating apparatus.
The at least one microwave suction opening includes two microwave suction openings that are symmetrical about the tube axis;
The microwave according to claim 1, wherein a distance between the two microwave suction openings in a region near the coupling portion is longer than a distance between the two microwave suction openings in a region separated from the coupling portion. Heating device.
The microwave heating apparatus according to claim 2, wherein a distance between the two microwave suction openings is 1/8 or more of a wavelength of a microwave propagating through the internal space of the waveguide structure.
The microwave heating device according to claim 1, wherein the microwave suction opening is provided in the vicinity of the coupling portion.
The microwave heating apparatus according to claim 1, wherein the ceiling surface has a recess provided at a joint portion between the coupling portion and the waveguide structure portion.