CN107006085B - microwave heating device - Google Patents

Abstract

The waveguide structure antenna (5) has a front opening (13), and a top surface (9) and side wall surfaces (10a, 10b, 10c) that define a waveguide structure (8), and radiates microwaves from the front opening (13) to an object to be heated. The waveguide structure section (8) has a coupling section that is joined to the top surface (9) and couples microwaves into the internal space of the waveguide structure section (8). The waveguide structure part (8) has at least one microwave suction opening (14) formed in the top surface (9), and radiates circularly polarized waves into the heating chamber from the microwave suction opening (14). The waveguide structure section (8) has a step region (9a) having a height different from that of the other portion of the top surface (9) at a portion of the top surface (9) on the side closer to the coupling section than the microwave suction opening (14). According to this configuration, the object placed on the central region of the placement surface can be uniformly heated.

Description

microwave heating device

technical field

The disclosure herein relates to microwave heating apparatuses such as microwave ovens that microwave heating objects such as foodstuffs by microwaves.

Background technique

In a microwave oven, which is a typical microwave heating device, microwaves generated by a magnetron, which is a typical microwave generating unit, are supplied into a metal heating chamber, and the object to be heated placed in the heating chamber is microwave-heated.

In recent years, microwave ovens capable of using the entire flat bottom surface of the heating chamber as a mounting table have been put into practical use. In such a microwave oven, in order to uniformly heat the object to be heated in the entire range of the mounting table, a rotating antenna is provided below the mounting table (for example, refer to Patent Document 1). The rotary antenna disclosed in Patent Document 1 has a waveguide structure that is magnetically coupled to a waveguide that propagates microwaves from a magnetron.

FIG. 12 is a front cross-sectional view showing the structure of the microwave oven 100 disclosed in Patent Document 1. As shown in FIG. As shown in FIG. 12 , in the microwave oven 100 , the microwaves generated by the magnetron 101 propagate in the waveguide 102 and reach the coupling shaft 109 .

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

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

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

In addition to the function of uniformly heating the entire heating chamber (uniform heating), for example, when frozen food and room temperature food are placed in the heating chamber, in order to simultaneously complete the heating of these foods, it is necessary to locally and intensively heat the food. The function of radiating microwaves to the area where the frozen food is placed (local heating).

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

FIG. 13 is a front cross-sectional view showing the structure 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 microwaves generated by the magnetron 201 reach the rotating antenna 203 of the waveguide structure via the waveguide 202 .

The rotating antenna 203 has radiation ports 207 formed on one side and radiating microwaves, and low-impedance portions 206 formed on the other three sides, when viewed from above. The microwaves radiated from the radiation port 207 are supplied into the heating chamber 204 via the power supply chamber 209 , and microwave heating of the object to be heated placed in the heating chamber 204 is performed.

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

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

prior art literature

Patent Literature

Patent Document 1: Japanese Patent Publication No. 63-53678

Patent Document 2: Japanese Patent No. 2894250

SUMMARY OF THE INVENTION

In the microwave oven 100 disclosed in Patent Document 1, the rotating antenna 103 is configured to rotate about a coupling shaft 109 arranged below the mounting table 108 as a center. The microwaves are radiated from the radiation port 107 at the front end of the rotating antenna 103 .

With this configuration, it is not possible to directly irradiate the object to be heated placed in the central region of the mounting table 108 with microwaves, and it is not always possible to uniformly heat the object.

According to the microwave oven 200 disclosed in Patent Document 2, it is possible to uniformly heat and locally heat the object to be heated. However, since this structure requires a mechanism for rotating and moving the rotating antenna 203 below the mounting table 208, there is a problem that the structure is complicated and the size of the apparatus is increased.

The present disclosure solves the above-mentioned conventional problems, and aims to provide a system capable of uniformly heating the object to be heated placed on the placing surface in the heating chamber, especially the central region of the placing surface placed in the heating chamber. Small microwave heating device.

A microwave heating apparatus according to one embodiment disclosed herein includes a heating chamber that accommodates an object to be heated, a microwave generating portion that generates microwaves, and a waveguide structure antenna having a front opening and a top surface and a side surface defining the waveguide structure portion. The wall surface radiates microwaves from the front opening to the heating chamber. The waveguide structure portion has a coupling portion that is joined to the top surface and couples microwaves to the inner space of the waveguide structure portion.

The waveguide structure portion has at least one microwave suction opening formed on the top surface, and circularly polarized waves are radiated into the heating chamber from the microwave suction opening. A portion of the top surface of the waveguide structure portion on the side closer to the coupling portion than the microwave suction opening has a level difference region having a height different from that of the other portion of the top surface.

According to this aspect, it is possible to configure a more compact microwave heating device that can uniformly heat the object to be heated placed on the placing surface in the heating chamber, particularly, the object to be heated placed on the central region of the placing surface in the heating chamber.

Description of drawings

FIG. 1 is a cross-sectional view showing a schematic configuration of a microwave heating apparatus according to an embodiment disclosed herein.

FIG. 2A is a perspective view showing a power supply chamber in the microwave heating device of the present embodiment.

FIG. 2B is a plan view showing a power supply chamber in the microwave heating apparatus of the present embodiment.

FIG. 3 is an exploded perspective view showing the rotating antenna in the microwave heating device of the present embodiment.

FIG. 4 is a perspective view showing a general square waveguide.

5A is a plan view showing an H-plane of a waveguide having a rectangular slot-shaped opening for radiation polarized waves.

5B is a plan view showing an H-plane of a waveguide having an opening in a cross-groove shape for radiating circularly polarized waves.

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 in the case of the waveguide shown in FIG. 5A .

FIG. 6B is a characteristic diagram showing experimental results in the case of the waveguide shown in FIG. 5B .

FIG. 7 is a characteristic diagram showing experimental results in the case of “with food”.

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 showing the planar shape of an example of the rotating antenna used in the experiment.

FIG. 9B is a schematic diagram showing the planar shape of an example of the rotating antenna used in the experiment.

FIG. 9C is a schematic diagram showing the planar shape of an example of the rotating antenna used in the experiment.

FIG. 10A is a schematic diagram showing the planar shape of an example of the rotating antenna used in the experiment.

FIG. 10B is a schematic diagram showing the planar shape of an example of the rotating antenna used in the experiment.

FIG. 11 is a plan view showing the waveguide structure part of the present embodiment.

FIG. 12 is a front cross-sectional view showing the microwave oven disclosed in Patent Document 1. FIG.

13 is a front cross-sectional view showing the microwave oven disclosed in Patent Document 2. FIG.

Detailed ways

The microwave heating device of the first aspect disclosed herein includes a heating chamber that accommodates an object to be heated, a microwave generating portion that generates microwaves, and a waveguide structure antenna having a front opening and a top surface defining the waveguide structure portion, The side wall surface radiates microwaves to the heating chamber from the front opening. The waveguide structure portion has a coupling portion that is joined to the top surface and couples microwaves to the inner space of the waveguide structure portion.

The waveguide structure portion has at least one microwave suction opening formed on the top surface, and circularly polarized waves are radiated into the heating chamber from the microwave suction opening. A portion of the top surface of the waveguide structure portion on the side closer to the coupling portion than the microwave suction opening has a level difference region having a height different from that of the other portion of the top surface.

According to this aspect, it is possible to configure a more compact microwave heating device that can uniformly heat the object to be heated placed on the placing surface in the heating chamber, particularly, the object to be heated placed on the central region of the placing surface in the heating chamber.

In addition to the first aspect, according to the microwave heating device of the second aspect, the level difference region includes a joint region corresponding to a joint portion of the coupling portion and the waveguide structure portion.

According to this aspect, the to-be-heated object mounted in the center area|region of a mounting surface can be heated more uniformly.

In addition to the first aspect, according to the microwave heating device of the third aspect, the level difference region is provided in a part of the top surface on the side closer to the coupling part than the microwave suction opening, and has a lower height than the other parts of the top surface. According to this aspect, the circularly polarized wave can be radiated from the microwave suction opening more reliably.

In addition to the first aspect, the microwave heating apparatus of the fourth aspect further includes a drive unit that rotates the waveguide structure antenna. The coupling portion includes a coupling shaft that is connected to the driving portion and includes the center of rotation of the waveguide structure antenna, and a flange that is provided around the coupling shaft and constitutes a joint portion. The length of the flange in the direction of the pipe axis is shorter than the length in the direction perpendicular to the direction of the pipe axis.

According to this aspect, the to-be-heated object mounted in the center area|region of a mounting surface can be heated more uniformly.

In addition to the first aspect, according to the microwave heating device of the fifth aspect, the microwave suction opening has an intersecting groove shape in which two slits intersect, and the microwave suction opening is provided at a position deviated from the tube axis. According to this aspect, the to-be-heated object mounted in the center area|region of a mounting surface can be heated more uniformly.

In addition to the first aspect, according to the microwave heating device of the sixth aspect, the waveguide structure portion has at least two microwave suction openings symmetrical with respect to the tube axis. The distance between the two microwave extraction openings in the region near the coupling portion is longer than the distance between the two microwave extraction openings in the region away from the coupling portion. According to this aspect, the to-be-heated object mounted in the center area|region of a mounting surface can be heated more uniformly.

Hereinafter, preferred embodiments of the microwave heating apparatus disclosed herein will be described with reference to the accompanying drawings.

In the following embodiments, a microwave oven is used as an example of the microwave heating apparatus disclosed herein, but it is not limited to this, and includes a heating apparatus using microwave heating, a household waste disposer, a semiconductor manufacturing apparatus, and the like. The disclosure herein is not limited to the specific configurations shown in the following embodiments, and includes configurations based on the same technical idea.

In addition, in the following drawings, the same or equivalent parts may be denoted by the same reference numerals, and overlapping descriptions may be omitted.

FIG. 1 is a front cross-sectional view showing a schematic configuration of a microwave oven as a microwave heating device according to an embodiment disclosed herein. In the following description, the left-right direction of the microwave oven refers to the left-right direction in FIG. 1 , and the front-rear direction refers to the depth direction in FIG. 1 .

As shown in FIG. 1 , the microwave oven 1 of the present embodiment includes a heating chamber 2 a , a feeding chamber 2 b , a magnetron 3 , a waveguide 4 , a rotating antenna 5 , and a mounting table 6 . The placing table 6 has a flat upper surface on which a to-be-heated object (not shown) such as food is placed. 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 feeding chamber 2b in which the rotating antenna 5 is installed, and defines the bottom surface of the heating chamber 2a by dividing the heating chamber 2a and the feeding chamber 2b. Since the upper surface (the mounting surface 6a) of the mounting table 6 is flat, it is easy to take out and put in the object to be heated, and it is easy to wipe off the dirt and the like adhering to the mounting surface 6a.

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

The magnetron 3 is an example of a microwave generating portion that generates microwaves. The waveguide 4 is an example of a propagating portion that is provided below the feeding chamber 2 b and transmits the microwaves generated by the magnetron 3 to the coupling portion 7 . The rotary antenna 5 is installed in the inner space of the feeding chamber 2b, and radiates the microwaves transmitted through the waveguide 4 and the coupling portion into the feeding chamber 2b from the front opening 13.

The rotary antenna 5 is a waveguide structure antenna having a waveguide structure portion 8 having a box-shaped waveguide structure through which microwaves propagate, and a coupling portion 7 that allows the waveguide 4 to propagate. The microwaves inside are coupled to the inner space of the waveguide structure 8 . The coupling portion 7 has a coupling shaft 7 a coupled to the motor 15 as a driving portion, and a flange 7 b for joining the waveguide structure portion 8 to the coupling portion 7 .

The motor 15 is driven according to a control signal from the control unit 17 to rotate the rotary antenna 5 around the coupling shaft 7 a of the coupling unit 7 and stop in a desired direction. Thereby, the radiation direction of the microwaves from the rotating antenna 5 is changed. A metal such as an aluminum-plated steel sheet is used for the coupling portion 7 , and a fluororesin is used for the connection portion of the motor 15 connected to the coupling portion 7 , for example.

The coupling shaft 7a of the coupling portion 7 penetrates through the opening that communicates the waveguide 4 and the feeding chamber 2b, and there is a predetermined (for example, 5 mm or more) gap between the coupling shaft 7a and the penetrating opening. The waveguide 4 is coupled to the inner space of the waveguide structure portion 8 of the rotating antenna 5 by the coupling shaft 7 a, and microwaves are efficiently propagated from the waveguide 4 to the waveguide structure portion 8 .

The infrared sensor 16 is provided in the upper part of the side surface 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 object to be heated placed on the mounting table 6 as the state of the object to be heated. The infrared sensor 16 detects the temperature of each area|region of the heating chamber 2a which is virtually divided into a plurality of, and transmits these detection signals to the control part 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 .

The present embodiment includes 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, an image sensor that captures an image of the object to be heated, or the like can be used as the state detection unit. In the configuration in which the state detection unit is not provided, the control unit 17 can perform oscillation control of the magnetron 3 and drive control of the motor 15 according to a pre-stored program and user's selection.

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

As shown in FIGS. 2A and 2B , a rotating antenna 5 is provided in a power feeding chamber 2b which is arranged below the heating chamber 2a and is partitioned from the heating chamber 2a by the mounting table 6 . The rotation center G of the coupling shaft 7a in the rotary antenna 5 is positioned below the center in the front-rear direction and the left-right direction of the feeding chamber 2b, that is, the center in the front-rear direction and the left-right direction of the mounting table 6 .

The power supply chamber 2b has an inner space constituted by the bottom surface 11 thereof and the lower surface of the mounting table 6 . The inner space of the feeding 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 feeding chamber 2b. A convex portion 18 protruding inward is formed on the side wall surface of the inner space of the power supply chamber 2b. 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.

The 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 portion 8 through the coupling portion 7 .

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

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

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

The arc-shaped edge portion is not provided with a side wall surface, and an opening is formed below it. This opening functions as a front opening 13 that radiates microwaves propagating in the inner space of the waveguide structure portion 8 . That is, the side wall surface 10b is provided so as to face the front opening 13, and the side wall surfaces 10a and 10c are provided so as to face each other.

The lower edge portion of the side wall surface 10a is provided with a low-impedance portion 12 which is located outside the waveguide structure portion 8 and extends 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 feeding chamber 2b with a slight gap therebetween. The microwaves leaking in the direction perpendicular to the side wall surface 10 a are suppressed by the low impedance portion 12 .

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

On the low-resistance portion 12, a plurality of slits 12a are provided to periodically extend from the side wall surface 10a in the vertical direction at constant intervals. The leakage of microwaves in the direction parallel to the side wall surface 10a is suppressed by the plurality of slits 12a. The interval between the slits 12 a is appropriately determined according to the wavelength propagating in the waveguide structure portion 8 .

In the same manner as the side wall surface 10b and the side wall surface 10c, the low-resistance portion 12 having the plurality of slits 12a is provided in the lower edge portion, respectively.

The rotary antenna 5 of the present embodiment has the front opening 13 formed in a circular arc shape, but the disclosure herein is not limited to this shape, and may have a linear or curved front opening 13 .

As shown in FIG. 3 , the top 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 microwaves propagating in the inner space of the waveguide structure portion 8 are radiated from the front opening 13 and the plurality of microwave suction openings 14 .

The flange 7b formed on the coupling portion 7 is joined to the lower surface of the top surface 9 of the waveguide structure portion 8 by, for example, caulking, spot welding, screwing, or welding, and the rotary antenna 5 and the coupling portion 7 are fixed.

In this embodiment, since the rotating antenna 5 has the waveguide structure part 8 mentioned later, the to-be-heated object mounted on the mounting table 6 can be heated uniformly. In particular, in the central region of the mounting surface 6a located above the rotation center G (refer to FIGS. 2A and 2B ) of the rotating antenna 5 , heating can be efficiently and uniformly performed. Hereinafter, the waveguide structure in this embodiment will be described in detail.

[Waveguide structure]

First, in order to understand the characteristics of the waveguide structure portion 8 , a general waveguide 300 will be described using FIG. 4 . As shown in FIG. 4 , the simplest and most common waveguide 300 is a square waveguide with a rectangular section 303 having a width a and a height b and a depth along the tube axis V of the waveguide 300 . The tube axis V passes through the center of the section 303 and is the centerline of the waveguide 300 extending along the transmission direction Z of the microwaves.

Assuming that the wavelength of the microwave in free space is λ ₀ , it can be seen that when the width a and the height b are selected from the ranges of λ ₀ >a>λ ₀ /2 and b<λ ₀ /2, the microwave is in the TE10 mode in the waveguide. Propagation within the tube 300.

The TE10 mode refers to a transmission mode of an H wave (TE wave; Transverse Electric Wave) in which a magnetic field component and no electric field component exist in the microwave transmission direction Z in the waveguide 300 .

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

λ ₀ =c/f ...(1)

In the formula (1), the speed c of light 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 according to the deviation of the magnetron and the load conditions, the wavelength λ ₀ in free space varies from a minimum of 120 [mm] (at 2.5 GHz) to a maximum of 125 [mm] (at 2.4 GHz) .

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

In general, in the waveguide 300 shown in FIG. 4 , the wide surface 301 as its upper surface and the lower surface refers to the surface in which the magnetic field vortexes in parallel, which is called the H surface, and the narrow width is used as the left and right side surfaces. The plane 302 refers to the plane parallel to the electric field, referred to as the E plane. For simplicity, in the plan view shown below, a straight line on the H plane obtained by projecting the pipe axis V on the H plane may be referred to as the pipe axis V.

If 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 in-tube wavelength λg, λg is obtained by equation (2).

Therefore, the in-tube wavelength λg varies according to the width a of the waveguide 300 , but does not depend on the height b. In the TE 10 mode, the electric field is zero at both ends (E planes) in the width direction W of the waveguide 300 , that is, on the narrow surface 302 , and the electric field is the largest at the center in the width direction W .

In this embodiment, the same principle as that of the waveguide 300 shown in FIG. 4 is applied to the rotating antenna 5 shown in FIGS. 1 and 3 . In the rotating antenna 5, the top surface 9 and the bottom surface 11 of the feeding chamber 2b are H surfaces, and the side wall surfaces 10a and 10c are E surfaces.

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

A plurality of microwave suction openings 14 are formed on the top surface 9 . The microwave suction opening 14 includes two first openings 14a and two second openings 14b. The two first openings 14 a are symmetrical 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 symmetrical with respect to the pipe axis V. As shown in FIG. The first opening 14a and the second opening 14b are formed so as not to straddle the pipe axis V. As shown in FIG.

By arranging the first opening 14 a and the second opening 14 b at positions deviated from the tube axis V of the waveguide structure portion 8 (precisely, a straight line on the ceiling surface 9 obtained by projecting the tube axis V onto the ceiling surface 9 ) With this configuration, circularly polarized waves can be more reliably radiated from the microwave suction opening 14 . By radiating microwaves of circularly polarized waves, it is possible to uniformly heat the central region of the placement surface 6a.

In addition, the rotation direction of the electric field, that is, a right-handed polarized wave (CW: Clockwise) or a left-handed polarized wave (CCW: Counterclockwise) is determined according to which region on the left and right of the tube axis V the first opening 14a and the second opening 14b are provided. .

In the present embodiment, the microwave suction openings 14 are respectively provided so as not to cross the tube axis V. As shown in FIG. However, the disclosure herein is not limited to this, and even in a structure in which a part of these openings spans the tube axis V, circularly polarized waves can be radiated. In this case, a deformed circularly polarized wave is generated.

[Circularly polarized wave]

Next, circularly polarized waves will be described. Circularly polarized waves are a technology widely used in the fields of mobile communications and satellite communications. As an example of usage around, for example, ETC (Electronic Toll Collection System), that is, a non-stop toll collection system is mentioned.

Circularly polarized waves are microwaves in which the plane of polarization of the electric field rotates with time with respect to the traveling direction, and the direction of the electric field continuously changes with time, and the magnitude of the electric field intensity does not change.

When this circularly polarized wave is applied to a microwave heating device, it can be expected to uniformly heat the object to be heated in the circumferential direction of the circularly polarized wave, in particular, compared to conventional microwave heating using linearly polarized waves. In addition, the same effect can be obtained for both right-handed polarized waves and left-handed polarized waves.

Originally, circularly polarized waves are mainly used in the field of communications, but since they are radiated into open spaces, so-called traveling waves are usually studied without reflected waves. On the other hand, in the present embodiment, reflected waves are generated in the heating chamber 2a, which is a closed space, and the generated reflected waves may be combined with traveling waves to generate standing waves.

However, since the food absorbs microwaves, in addition to weakening the reflected waves, the balance of the standing waves is disrupted at the moment when the microwaves are radiated from the microwave suction opening 14, and it is considered that the standing waves are generated during the period until the standing waves are generated again. Wave. Therefore, according to the present embodiment, uniform heating in the heating chamber 2a can be performed by utilizing the above-mentioned feature of the circularly polarized wave.

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

In the communication field, in order to transmit and receive information reliably, either a right-handed polarized wave or a left-handed polarized wave is used, and on the receiving side, a receiving antenna having a directivity corresponding thereto is used.

On the other hand, in the field of microwave heating, microwaves are received from objects to be heated that do not have directivity, such as foods, instead of receiving antennas having directivity, and therefore, it is important to irradiate the entire object to be heated with microwaves. Therefore, in the field of microwave heating, it does not matter whether it is right-handed or left-handed polarized waves, and there is no problem even in a state where right-handed polarized waves and left-handed polarized waves are mixed.

[Suction effect of microwave]

Here, the effect of extracting microwaves from the rotating antenna, which is a feature of the present embodiment, will be described. In the present embodiment, the microwave suction effect refers to suction of microwaves in the waveguide structure through the microwave suction opening 14 when a to-be-heated object such as food is in the vicinity.

FIG. 5A is a plan view of a waveguide 400 having an H-plane provided with openings for generating linearly polarized waves. FIG. 5B is a plan view of a waveguide 500 having an H-plane provided with openings for generating circularly polarized waves. FIG. 5C is a front view showing the positional relationship between the waveguide 400 or 500 and the object to be heated 22 .

As shown in FIG. 5A , the opening 401 is a rectangular slit provided to intersect the tube axis V of the waveguide 400 . The opening 401 radiates microwaves of a linearly polarized wave. As shown in FIG. 5B , the two openings 501 are respectively an opening in the shape of a cross slot formed by two rectangular slits intersecting at a right angle. The two openings 501 are symmetrical about the tube axis V of the waveguide 500 .

These openings are all symmetrical about the tube axis V of the waveguide, with a width of 10mm and a length of Lmm. In these structures, the case of "no food" in which the object to be heated 22 is not arranged and the case of "with food" in which the object to be heated 22 is arranged were analyzed using CAE.

In the case of "with food", as shown in FIG. 5C , at a constant height of the object to be heated 22 of 30 mm, the bottom area of the two types of objects to be heated 22 (100 mm square, 200 mm square), and the three types of heated objects 22 Under the conditions of the material (frozen beef, refrigerated beef, and water), the measurement was performed using the distance D from the waveguides 400 and 500 to the bottom surface of the object to be heated 22 as a parameter.

In order to use the radiation power from the opening in the case of "no food" as a reference, the relationship between the length of the opening and the radiation power in the case of "no food" is shown in FIGS. 6A and 6B .

FIG. 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 the power [W] of the microwaves radiated from the openings 401 and 501 when the power propagating in the waveguide is 1.0 W.

For comparison with the case of "with food", the length L when the radiation power is 0.1W in the case of "without food" is selected, that is, in the graph shown in Fig. 6A, the length L of 45.5mm is selected , in the graph shown in FIG. 6B , the case where the length L is 46.5 mm is selected.

Figure 7 contains six graphs representing pairs with 2 base areas (100mm square, 200mm square) with the length L being the above-mentioned length (45.5mm, 46.5mm) and in the case of "with food" The results of the analysis of 3 foods (frozen beef, refrigerated beef, and water).

In each graph included in FIG. 7 , the horizontal axis is the distance D [mm] from the object to be heated 22 to the waveguide, and the vertical axis is the relative radiation power when the radiation power in “no food” is set to 1.0. That is, compared with the case of "no food", in the case of "with food", to what extent microwaves are sucked out from the waveguides 400 and 500 by the object to be heated 22 is shown.

In each of the graphs shown in FIG. 7 , the dotted line indicates the characteristic in the case of the opening 401 having a straight shape (I-shape) (indicated by “I” in the figure), and the solid line indicates two intersecting groove shapes (X-shape). ) in the case of the opening 501 (indicated by "2X" in the figure).

In any of the six graphs, the radiation power of the opening 501 is larger than that of the opening 401, and in particular, when the distance D is 20 mm or less, which is the same distance as that of an actual microwave oven, it can be recognized that there is about 2 times the radiation power. poor. Therefore, regardless of the type and bottom area of the object to be heated 22, it can be seen that the openings that generate circularly polarized waves have a stronger effect of sucking out microwaves than the openings that generate linearly polarized waves.

In detail, regarding the type of the object to be heated 22, especially when the distance D is 10 mm or less, the suction effect of frozen beef with a smaller dielectric constant and dielectric loss is stronger, while that with a larger dielectric constant and dielectric loss The suction effect of water is weak.

In the case of refrigerated beef or water, when the distance D increases, especially the radiation power of the linearly polarized wave drops to 1 or less. The reason is considered to be that the radiated power is canceled by the reflected power from the object to be heated 22 . Regarding the bottom area of the object to be heated 22 , the radiation power is substantially the same when the 100 mm square and the 200 mm square are used, so it is considered that the influence on the microwave suction effect is small.

The inventors studied the conditions of the openings capable of radiating circularly polarized waves through experiments using various opening shapes. As a result, the following conclusions were obtained. Preferable conditions for generating a circularly polarized wave include arranging the opening so as to deviate from the tube axis V of the waveguide, and the opening shape being an opening of a cross-slot shape. The microwaves of circularly polarized waves are most efficiently radiated, that is, the openings having the cross-slot shape have a strong suction effect.

8A and 8B are cross-sectional views schematically showing the suction effect in the present embodiment. The front opening 13 of the rotary antenna 5 is directed to the left in the figures in both FIGS. 8A and 8B . The to-be-heated object 22 is arrange|positioned above the coupling part 7 in FIG. 8A, and is mounted in the left corner of the mounting surface 6a in FIG. 8B. That is, in the two states shown in FIGS. 8A and 8B , the distances from the coupling portion 7 to the object to be heated 22 are different.

In the state shown in FIG. 8A , the object to be heated 22 is close to the microwave suction opening 14, especially the first opening 14a, and it is considered that the suction effect from the first opening 14a is produced. As a result, most of the microwaves traveling from the coupling portion 7 toward the front opening 13 become circularly polarized microwaves from the first opening 14 a and are radiated to the object to be heated 22 to heat the object to be heated 22 .

On the other hand, in the state shown in FIG. 8B , since the object to be heated 22 is far away from the microwave suction opening 14 , it is considered that the suction effect from the microwave suction opening 14 is not produced much. As a result, most of the microwaves traveling from the coupling portion 7 toward the front opening 13 retain the linearly polarized microwaves and are radiated from the front opening 13 to the object to be heated 22 to heat the object to be heated 22 .

As described above, it is considered that the microwave suction opening 14 of the present embodiment causes the following special phenomenon: when the food is placed close to the microwave suction opening 14 , the radiation power increases, and the food is placed at a position away from the microwave suction opening 14 . , the radiation power decreases.

[Uniform heating by waveguide structure]

Hereinafter, uniform heating of the waveguide structure portion according to the present embodiment will be described. The inventors conducted experiments using rotating antennas having waveguide structures of various shapes, and found a waveguide structure most suitable for uniform heating.

9A, 9B, and 9C are schematic diagrams each showing the planar shape of three examples of the rotating antenna used in the experiment.

As shown in FIG. 9A , the waveguide structure portion 600 has two first openings 614a and two second openings 614b. The first opening 614 a has a cross groove 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 614b is smaller than the first opening 614a and is provided away from the coupling portion 7 .

As shown in FIG. 9B , the waveguide structure portion 700 is different from the waveguide structure portion 600 in that it has one first opening 714a having the same intersecting groove shape as the first opening 614a.

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

The waveguide structures shown in FIGS. 9A to 9C have in common that a plurality of microwave suction openings in the shape of intersecting grooves are provided, first openings of the same size are provided at the same position, and second openings of the same size are provided at the same position. s position. 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 , experiments were conducted under the same heating conditions using frozen okonomiyaki placed in the central region of the placement surface 6 a , and verification was performed by CAE. Okonomiyaki is a pancake-like dish made by frying 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 cause the phenomenon that the object to be heated in the central region of the mounting surface 6 a located above the coupling portion 7 is heated. The temperature of the part does not rise abnormally compared with the surrounding part (hereinafter, referred to as the temperature drop in the vicinity of the coupling part 7).

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

As described above, it can be confirmed that the temperature drop in the vicinity of the coupling portion 7 can be suppressed and uniformity in the heating chamber 2a can be achieved by 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. heating.

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

The first opening 814a of the waveguide structure portion 800 shown in FIG. 9C radiates a so-called deformed circularly polarized wave, which is different from the circular circularly polarized wave formed by the opening of the intersecting groove shape. From the viewpoint of uniform heating in 2a, a preferable result could not be obtained.

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

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

FIGS. 10A and 10B are schematic diagrams showing the planar shapes of the waveguide structure portion 900A and the waveguide structure portion 900B in which the first opening 914a is provided, respectively.

As shown in FIGS. 10A and 10B , the waveguide structure portions 900A and 900B have the same first opening 914a and second opening 914b.

The first opening 914a has an intersecting groove shape in one of the two rectangular slits such that the length of the portion extending from the intersecting portion in the direction of the coupling portion 7 is shorter than that of the portion extending from the intersecting portion in the opposite direction to the coupling portion 7 . As a result of the investigation, it was confirmed that the first opening 914a can suppress the interference between the two circularly polarized waves and perform uniform heating, and the above-described suction effect is stronger than that of the first opening 814a shown in FIG. 9C .

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

The waveguide structure portion 900A has an overall flat top surface. On the other hand, in the waveguide structure portion 900B, a concave joint region (recess 909a serving as a level difference region) recessed downward is formed in a joint portion where the flange 7b and the top surface are joined (for example, see FIG. 3 ). Therefore, on the top surface of the waveguide structure portion 900B, the distance between the bonding region and the mounting table is larger than that in other portions.

Similarly, using the rotating antenna having the above-described waveguide structure, an experiment was performed under the same heating conditions using a frozen okonomiyaki placed in the central region of the mounting surface 6a, and verification was carried out by CAE.

As a result, since the first opening 914a has a substantially intersecting groove shape, the waveguide structure portion 900A can suppress the interference between the two circularly polarized waves and generate a circularly polarized wave having a shape similar to a circle.

In addition, the suction effect is enhanced by the first opening 914a, and the temperature drop in the vicinity of the coupling portion 7 is suppressed. In addition, it was found that the temperature drop in the vicinity of the coupling portion 7 can be suppressed by the concave joint region formed on the top surface of the waveguide structure portion 900B.

Hereinafter, a specific configuration example of the rotating antenna of the present embodiment based on the knowledge obtained from various experiments as described above will be described. Based on the above findings, various modifications can be used in accordance with the specifications of the microwave heating apparatus and the like.

FIG. 11 is a plan view showing a rotating antenna including the waveguide structure portion 8 of the present embodiment.

As shown in FIG. 11 , the waveguide structure portion 8 has a plurality of microwave suction openings 14 provided on the top 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 substantially intersecting groove shapes.

By arranging the center point P1 of the first opening 14a and the center point P2 of the second opening 14b at positions deviated from the tube axis V of the waveguide structure portion 8, the microwave suction opening 14 can radiate circularly polarized waves. 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 straddle the tube axis V of the waveguide structure portion 8 . The longitudinal direction of each rectangular slit of the 1st opening 14a and the 2nd opening 14b has an inclination of 45 degreeC with respect to the pipe axis V substantially.

As shown in FIG. 11 , the first opening 14 a is formed close to the recessed portion 9 a of the top surface 9 . The recessed part 9a is a level difference area|region (refer FIG. 3) provided protruding from the top surface 9 in the direction opposite to the advancing direction (downward) of the microwave radiated from the 1st opening 14a. The two first openings 14a are symmetrical with respect to the pipe axis V. As shown in FIG.

The second opening 14b is farther from the coupling portion 7 than the first opening 14a and is formed in the vicinity of the front opening 13 . Like the first opening 14a, the two second openings 14b are symmetrical with respect to the pipe axis V. As shown in FIG.

The first opening 14a is characterized in that, of the two grooves, the length of the portion extending in the direction from the center point P1 toward the pipe axis V is shorter than the length of the portion extending in the direction from the center point P1 toward the side wall surface 10a .

As shown in FIG. 3 , the flange 7 b provided on the coupling portion 7 has a shape in which the length along the propagation direction Z of the microwave is shorter than the length along the width direction W of the waveguide structure portion 8 . That is, the length of the coupling portion 7 along the propagation direction Z of the microwaves is shorter than the length along the direction perpendicular to the propagation direction Z. As shown in FIG. With the flange 7b, the front end of the slit extending from the center point P1 toward the coupling portion 7 can be formed at a position closer to the coupling portion 7. As shown in FIG.

In the present embodiment, since the flange 7b is joined to the reverse side of the concave portion 9a, the concave portion 9a is configured such that protrusions of TOX caulking, welding marks, heads of screws and nuts, etc. are formed in the concave portion by the joining of the flange 7b The height of the protrusion generated on the front side of 9a is deep. According to the present embodiment, problems such as contact between the protrusions and the lower surface of the mounting table 6 do not occur.

The waveguide structure portion 8 shown in FIG. 11 has a concave portion 9 a provided on the top surface 9 above the coupling portion 7 , and has the same structure as the waveguide structure portion 900B shown in FIG. 10B . According to the waveguide structure portion 8 shown in FIG. 11 , like the waveguide structure portion 900B, the temperature drop in the vicinity of the coupling portion 7 can be suppressed. The following two reasons are considered as the reasons for this.

First, when the object to be heated is placed above the first opening 14a, a part of the microwaves, which are circularly polarized waves radiated from the first opening 14a, is reflected by the object to be heated. The reflected microwaves are repeatedly reflected in the space formed between the upper surface of the concave portion 9 a 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 inner space of the waveguide structure portion 8 in the portion where the recessed portion 9a is formed is narrower than that in the other portions. When most of the microwaves propagating from the coupling shaft 7a into the waveguide structure 8 travel from the narrow space near the concave portion 9a to the wide space away from the concave portion 9a, they are radiated from the first opening 14a by the suction effect, and are strongly opposed to the The to-be-heated object mounted in the center area|region of the mounting surface 6a is heated.

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

As shown in FIG. 11 , the first opening 14a includes slits 20a and 20b, and these have a cross groove shape intersecting at the center point P1. The long axis of each slit of the first opening 14a has an angle of 45 degrees with respect to the tube axis V. As shown in FIG.

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 front end, and a third length C from the center point P1 to the upper left front end. The lower right front end of the slit 20a approaches the concave portion 9a toward the coupling portion 7 .

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 front end, and a fourth length D from the center point P1 to the upper right front end. That is, the first length A is the length to the front end closest to the coupling portion 7 among the lengths from the center point P1 to the front ends of the slits 20 a and 20 b.

The third length C is the same as the fourth length D, and they are substantially equivalent to 1/4 of the substantial wavelength of the microwaves propagating in the waveguide structure portion 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 among them.

Further, the distance X between the slit 20a and the pipe axis V is longer than the distance Y between the slit 20b and the pipe axis V. That is, in the ceiling surface 9, the area|region near the recessed part 9a between the two 1st openings 14a is wider than the area|region away from the recessed part 9a.

When the region between the two first openings 14a is not flat, a disordered electromagnetic field is generated in the waveguide structure portion 8, which adversely affects the formation of circularly polarized waves. A wider flat area is provided between the openings 14a. According to the present embodiment, a circularly polarized wave with less disorder can be formed by the wider flat region provided between the two first openings 14a, and a strong suction effect can be obtained.

In the present embodiment, the distance between the two first openings 14 a is equal to or more than 1/8 of the wavelength of the microwaves propagating in the waveguide structure portion 8 . According to the inventor's experiments, when the two first openings 14a have a distance substantially equal to the shaft diameter (18 mm) of the coupling shaft 7a, preferable results are obtained.

On the other hand, the second opening 14b has a cross groove shape in which two slits having the same length are perpendicular to the respective centers. The long axis of each slit of the second opening 14b has an angle of 45 degrees with respect to the tube axis V. As shown in FIG. 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 coupling portion 7 of the present embodiment has the flange 7b of the above-mentioned shape, but the shape of the flange 7b is not limited to this, and can be appropriately changed according to specifications and the like.

For example, if the portion of the flange 7b in the direction along the pipe axis V is shortened, the first opening 14a can be provided closer to the coupling portion 7 . The 1st opening 14a can also be provided closer to the coupling part 7 by using the flange 7b etc. which have a notch between the 1st opening 14a and the shape of the flange 7b.

If the shape of the flange 7b is designed, it is possible to strengthen the bonding between the coupling portion 7 and the waveguide structure portion 8 without reducing the area of the bonding portion, thereby suppressing product variation.

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 portion 8, the same thing as the present embodiment can be obtained. Effect. With the configuration in which the flange 7b is not provided, the space for forming the first opening 14a can be further enlarged.

According to the present embodiment, a strong suction effect is obtained, whereby the temperature drop in the vicinity of the coupling portion 7 can be suppressed, and the central region of the placement surface 6a can be uniformly heated.

In the present embodiment, the microwave suction opening has a cross groove shape, but the microwave suction opening disclosed herein is not limited thereto. Even if the microwave suction opening has a shape other than the cross-groove shape, it may be a shape capable of generating circularly polarized waves.

As a result of the experiment, it was concluded that a necessary condition for generating circularly polarized waves from the waveguide structure is to combine two substantially elongated openings at positions deviated from the tube axis.

The slit constituting the microwave suction opening 14 is not limited to a rectangle. For example, circularly polarized waves can also be generated in the case of openings with rounded corners or elliptical openings.

In order to suppress the concentration of the electric field, an opening with rounded corners is more preferable. 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 have rounded corners at the front end and the intersection. That is, in the two slits included in the microwave suction opening 14, the width in the vicinity of the intersection portion is wider than the width in the vicinity of the end portion.

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

For example, the concave portion 9 a may be provided between the microwave suction opening 14 and the rotation center of the waveguide structure portion 8 in consideration of the propagation conditions of microwaves radiated from the opening. A convex portion protruding toward the inner space of the waveguide structure portion 8 may be provided on the top surface 9 on the side closer to the rotation center of the waveguide structure portion 8 than the microwave suction opening 14 .

That is, the waveguide structure portion 8 only needs to have a step region provided on a part of the top surface 9 on the side closer to the coupling portion 7 than the microwave extraction opening 14 and having a height higher than that of the top surface 9 . other parts are low.

Industrial Availability

In addition to microwave ovens, the disclosure herein can be used in microwave heating apparatuses for various industrial purposes, such as drying apparatuses, ceramic heating apparatuses, household waste disposers, and semiconductor manufacturing apparatuses.

Label description

1, 100, 200: microwave oven; 2a, 104, 204: heating chamber; 2b, 209: power supply chamber; 2c, 10a, 10b, 10c: side wall surface; 3, 101, 201: magnetron; 3a: antenna; 4 , 102, 202, 400, 500: waveguide; 5, 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; 9: top surface; 9a, 909a: recessed part; 11: bottom surface; 12, 106, 206: low impedance part; 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: infrared sensor; 17 , 211: control part; 18, 18a, 18b: convex part; 19: holding part; 12a, 20a, 20b: slit; 107, 207: radiation port; 300: waveguide; face; 303: section; 401, 501: opening.

Claims (6)

1. A microwave heating device, wherein the microwave heating device has: a heating chamber, which accommodates the object to be heated; a microwave generating section that generates microwaves; and A waveguide structure antenna having a waveguide structure portion and a coupling portion, the waveguide structure antenna having a top surface and side wall surfaces defining the waveguide structure portion, the coupling portion being engaged with the top surface so that all the microwaves are coupled to the inner space of the waveguide structure, The waveguide structure part has at least one microwave suction opening formed on the top surface, and circularly polarized waves are radiated into the heating chamber from the microwave suction opening, A part of the top surface of the waveguide structure part on the side closer to the coupling part than the microwave suction opening has a level difference region having a height different from that of the other parts of the top surface. 2. The microwave heating device according to claim 1, wherein, The step region includes a joint region corresponding to a joint portion of the coupling portion and the waveguide structure portion. 3. The microwave heating device according to claim 1, wherein, The height of the level difference region is lower than other parts of the top surface. 4. The microwave heating device according to claim 2, wherein, The microwave heating device further has a drive unit that rotates the waveguide structure antenna, The coupling portion has: a coupling shaft connected to the driving portion and including the center of rotation of the waveguide structure antenna; and a flange provided around the coupling shaft and constituting the joint portion, A length of the flange in a direction along a tube axis of the waveguide structure portion is shorter than a length in a direction perpendicular to the direction of the tube axis. 5. The microwave heating device according to claim 1, wherein, The microwave suction opening has a cross groove shape in which two slits intersect, and the microwave suction opening is provided at a position deviated from the tube axis of the waveguide structure portion. 6. The microwave heating device of claim 1, wherein, the waveguide structure portion has at least two microwave suction openings symmetrical with respect to the tube axis of the waveguide structure portion, 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.

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