JP6671005B2 - Microwave heating equipment - Google Patents

Description

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

  In a microwave oven, which is a typical microwave heating device, a microwave generated by a magnetron, which is a typical microwave generating unit, is supplied into a metal heating chamber, and a microwave placed in the heating chamber. The heated material is microwave heated.

  2. Description of the Related Art In recent years, a microwave oven in which the entire flat bottom in a 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 (for example, see 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 in the waveguide 102 to the rotating antenna 103 having the waveguide structure and functions as a rotation center of the rotating antenna 103.

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

  By rotating the rotating antenna 103 below the mounting table 108, the heating distribution in the heating chamber 104 is made uniform.

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

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

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

The rotating antenna 203 has a radiation port 207 formed on one side thereof for radiating microwaves and a low impedance section 206 formed on the other three sides in a plan view from above. The microwave radiated from the radiation port 207 passes through the heating chamber 204 via the power supply chamber 209.
The heating target supplied in the heating chamber 204 is microwave-heated.

  The microwave oven disclosed in Patent Literature 2 includes an infrared sensor 210 for detecting a temperature distribution in the heating chamber 204. The control unit 211 controls the rotation and the 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.

  The rotating antenna 203 disclosed in Patent Document 2 is configured to move on an arc-shaped orbit while rotating the inside of a power supply 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 rotary antenna 203 moves while rotating, so that the low-temperature portion of the object to be heated detected by the infrared sensor 210 can be intensively heated.

JP-B-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 arranged 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 mounting table 108 cannot be directly irradiated with microwaves, and uniform heating is not always possible.

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

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

  A microwave heating apparatus according to an embodiment of the present disclosure has a heating chamber that stores an object to be heated, a microwave generation unit that generates a microwave, and a ceiling surface and a side wall surface that define a waveguide structure unit. It has a coupling part that is joined to the ceiling surface and couples the microwave to the internal space of the waveguide structure.

  The waveguide structure has at least one microwave suction opening formed in the ceiling surface, and emits circularly polarized waves into the heating chamber from the microwave suction opening. The joint between the coupling portion and the waveguide structure is configured such that the length in the tube axis direction is shorter than the length in the direction orthogonal to the tube axis direction.

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

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a microwave heating device according to an embodiment of the present disclosure. FIG. 2A is a perspective view showing a power supply chamber in the microwave heating device 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 the rotating antenna in the microwave heating device 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 for emitting linearly polarized light. FIG. 5B is a plan view showing an H-plane of a waveguide having a cross-slot-shaped opening for emitting 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 an experimental result 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 illustrating an experimental result in the case of “with load”. FIG. 8A is a cross-sectional view schematically illustrating the suction effect in the present embodiment. FIG. 8B is a cross-sectional view schematically illustrating 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 a 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.

  A microwave heating device according to a first aspect 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, and A waveguide structure antenna having a front opening and emitting microwaves from the front opening to the heating chamber. The waveguide structure has a coupling portion that is joined to the ceiling surface and couples the microwave to the internal space of the waveguide structure.

  The waveguide structure has at least one microwave suction opening formed in the ceiling surface, and emits circularly polarized waves into the heating chamber from the microwave suction opening. The joint between the coupling portion and the waveguide structure is configured such that the length in the tube axis direction is shorter than the length in the direction orthogonal to the tube axis direction.

  According to this aspect, it is possible to configure a smaller microwave heating device capable of uniformly heating the placement surface in the heating chamber, particularly the object to be heated placed in the central region thereof. .

The microwave heating apparatus according to the second aspect further includes, in addition to the first aspect, a driving unit that rotates the waveguide structure antenna. The joint has a joint shaft and a flange. The coupling axis is connected to the driving unit and includes a rotation center of the waveguide structure antenna. The flange is provided around the coupling axis and forms a joint. The flange has a length in the tube axis direction shorter than the length in a direction orthogonal to the tube axis direction.

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

  A microwave heating device according to a third aspect further includes, in addition to the first aspect, a driving unit that rotates the waveguide structure antenna. The coupling unit is coupled to the driving unit and has a coupling axis including a rotation center of the waveguide structure antenna. The cross section of the joining portion at the joining portion has a length in the tube axis direction shorter than the length in the direction orthogonal to the tube axis direction.

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

  According to the microwave heating apparatus of the fourth aspect, in addition to any one of the first to third aspects, the microwave suction opening has a cross slot shape in which two slits intersect, and is shifted from the tube axis. It is provided in the position which was set. According to this aspect, it is possible to more reliably radiate circularly polarized waves from the microwave suction opening.

  According to the microwave heating apparatus of the fifth aspect, in addition to any one of the first to fourth aspects, the waveguide structure has at least two microwave suction openings symmetric with respect to the tube axis, The distance between the two microwave suction openings in a region near the joint is longer than the distance between the two microwave suction openings in the region remote from the joint.

  According to this aspect, the heating chamber can be more uniformly heated by the circularly polarized waves radiated from the microwave suction opening.

  According to the microwave heating apparatus of the sixth aspect, in addition to any one of the first to fifth aspects, the ceiling surface of the waveguide structure has the concave portion provided at the joint. 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 a microwave heating device 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 microwave oven is not limited thereto, and a heating apparatus using microwave heating, a garbage disposal machine, or a semiconductor manufacturing apparatus is used. It includes devices and the like. The present disclosure is not limited to the specific configurations described in the following embodiments, but includes configurations based on similar technical ideas.

  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 cross-sectional view illustrating a schematic configuration of a microwave oven that is a microwave heating device 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-rear 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 supply 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 2a is a space above the mounting table 6, and the power supply chamber 2b is a space below the mounting table 6.

  The mounting table 6 covers the power supply chamber 2b provided with the rotating antenna 5 and partitions the heating chamber 2a and the power supply chamber 2b, and also forms a 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 take 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.

  For the mounting table 6, a material such as glass or ceramic that easily transmits microwaves is used. Therefore, the microwave radiated from the rotating antenna 5 is transmitted through the mounting table 6 and supplied to the heating chamber 2 a.

  The magnetron 3 is an example of a microwave generation unit that generates a microwave. The waveguide 4 is provided below the power supply chamber 2b, and is an example of a propagation unit that 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 room 2b, and radiates the microwave transmitted by the waveguide 4 and the coupling portion from the front opening 13 into the power supply room 2b.

  The rotating antenna 5 has a waveguide structure 8 having a box-shaped waveguide structure through which microwaves propagate in the internal space, and the microwave in the waveguide 4 is connected to the internal space of the waveguide structure 8. This is a waveguide structure antenna having a coupling portion 7 to be coupled. The coupling portion 7 has a coupling shaft 7a connected to the motor 15 as a driving portion, and a flange 7b for joining the waveguide structure portion 8 and the coupling portion 7.

  The motor 15 is driven in response to a control signal from the control unit 17, rotates the rotary antenna 5 about the coupling shaft 7a of the coupling unit 7, and stops 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 connecting portion 7, and, for example, a fluorine resin is used for a connecting portion of the motor 15 connected to the connecting portion 7.

  The coupling shaft 7a of the coupling portion 7 penetrates an opening communicating the waveguide 4 and the power supply chamber 2b, and the coupling shaft 7a has a predetermined (for example, 5 mm or more) clearance between the coupling shaft 7a and the penetrating opening. The coupling shaft 7a couples the waveguide 4 with the internal space of the waveguide structure 8 of the rotating antenna 5, and microwaves propagate efficiently from the waveguide 4 to the waveguide structure 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 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 of the heating chamber 2 a virtually divided into a plurality of sections, and transmits the detection signals to the control unit 17.

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

  In the present embodiment, the infrared sensor 16 is provided as an example of the state detection unit. However, 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 may be used as the state detection unit. In a 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 according to a program stored in advance and selection by the user.

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

  As shown in FIGS. 2A and 2B, a rotating antenna 5 is provided in the power supply chamber 2 b which is disposed below the heating chamber 2 a and is separated from the heating chamber 2 a 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 power supply 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 power supply chamber 2 b has an internal space defined 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 shape symmetrical with respect to a center line J (see FIG. 2B) in the left-right direction of the power supply chamber 2b. A convex portion 18 protruding inward is formed on a side wall surface in the internal space of the power supply chamber 2b. The protrusion 18 includes a protrusion 18a provided on the left side wall surface and a protrusion 18b provided on the right side wall surface.

  The magnetron 3 is provided below the protrusion 18b. The microwave radiated from the antenna 3a of the magnetron 3 propagates in the waveguide 4 provided below the power supply chamber 2b, and is transmitted to the waveguide structure 8 by the coupling unit 7.

  The side wall surface 2c of the power supply chamber 2b has an inclination for reflecting the microwave radiated in the horizontal direction from the rotating antenna 5 toward 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 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). ). From the three linear edges of the ceiling surface 9, side wall surfaces 10a, 10b, and 10c are formed by bending downward, respectively.

  No side wall surface is provided on the arc-shaped edge portion, and an opening is formed below the side wall surface. This opening functions as a front opening 13 for radiating microwaves propagated in 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, a low impedance portion 12 extending outside the waveguide structure portion 8 and perpendicular to the side wall surface 10a is provided. The low impedance portion 12 is formed in parallel with the bottom surface 11 of the power supply chamber 2b with a slight gap. The low impedance portion 12 suppresses microwaves leaking in the direction perpendicular to the side wall surface 10a.

  In order to secure 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.

  In the low impedance section 12, a plurality of slits 12a are provided so as to periodically extend from the side wall surface 10a at regular intervals in the vertical direction. The plurality of slits 12a suppress leakage of microwaves in a direction parallel to the side wall surface 10a. The interval between the slits 12a is appropriately determined according to the wavelength propagating through the waveguide structure 8.

  Similarly, regarding the side wall surface 10b and the side wall surface 10c, low impedance portions 12 each having a plurality of slits 12a at the lower edge are provided.

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

  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 propagating in 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 joint 7 is joined to the lower surface of the ceiling surface 9 of the waveguide structure 8 by, for example, caulking, spot welding, screw fastening, welding, or the like. Is fixed.

  In the present embodiment, since the rotating antenna 5 has the waveguide structure 8 as described later, the object to be heated mounted on the mounting table 6 can be uniformly heated. 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, efficient and uniform heating is possible. Hereinafter, the waveguide structure according to the present embodiment will be described in detail.

[Waveguide structure]
First, a general waveguide 300 will be described with reference to FIG. 4 in order to understand the features of the waveguide structure 8. 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 depth having a depth along the tube axis V of the waveguide 300. It is a waveguide. The tube axis V is a center line of the waveguide 300 that extends through the center of the cross section 303 and extends in the microwave transmission direction Z.

  When the wavelength a of the microwave in free space is λ0 and the width a and the height b are selected from the range of λ0> a> λ0 / 2 and b <λ0 / 2, the inside of the waveguide 300 is It is known that microwaves propagate in the TE10 mode.

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

  The wavelength λ0 of the microwave in free space is obtained by Expression (1).

  In the formula (1), the light speed c is about 2.998 × 108 [m / s], and the oscillation frequency f is 2.4 to 2.5 [GHz] (ISM band) in the case of a microwave oven. It is. Since the oscillation frequency f varies depending on the variation of the magnetron and the load conditions, the wavelength λ0 in free space varies between a minimum of 120 mm (at 2.5 GHz) and a maximum of 125 mm at 2.4 GHz. I do.

  In the case of the waveguide 300 used for a microwave oven, the width a of the waveguide 300 is designed to be 80 to 100 mm and the height b is designed to be 15 to 40 mm in consideration of the range of the wavelength λ0 in free space. There are many.

  In general, in the waveguide 300 shown in FIG. 4, the wide surface 301 as the upper surface and the lower surface thereof is referred to as an H surface in the sense that the magnetic field spirals in parallel, and the narrow surfaces 302 as the left and right side surfaces are referred to as H surfaces. The plane is parallel to the electric field. For simplicity, in the plan views shown below, a straight line on the H plane where the tube axis V is projected on the H plane may be referred to as a tube axis V.

  If the wavelength of the microwave from the magnetron is defined as the wavelength λ0 and the wavelength of the microwave propagating in the waveguide is defined as the guide wavelength λg, λg can be obtained by equation (2).

  Therefore, the guide wavelength λg changes depending on the width a of the waveguide 300, but is independent of 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 rotary antenna 5, the ceiling surface 9 and the bottom surface 11 of the power supply chamber 2b are H-planes, and the side wall surfaces 10a and 10c are E-planes.

  The side wall surface 10b serves as a reflection end for reflecting all the microwaves in the rotating antenna 5 toward 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 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 displaced from the tube axis V of the waveguide structure 8 (more precisely, a straight line on the ceiling surface 9 that projects the tube axis V onto the ceiling surface 9). With this structure, it is possible to more reliably radiate circularly polarized waves from the microwave suction opening 14. The radiation of the circularly polarized microwave enables uniform heating of the central area of the mounting surface 6a.

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

  In the present embodiment, each of the microwave suction openings 14 is provided so as not to extend over the tube axis V. However, the present disclosure is not limited to this, and it is possible to emit circularly polarized waves even in a configuration in which a part of these openings straddles the tube axis V. In this case, distorted circularly polarized waves occur.

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

  Circularly polarized waves are microwaves in which the plane of polarization of an electric field rotates with time in the direction of travel, and has the characteristic that 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 is expected that the object to be heated can be uniformly heated, especially in the circumferential direction of the circularly polarized wave, as compared with the conventional microwave heating by linearly polarized wave. It should be noted that the same effect can be obtained regardless of right-handed polarization or left-handed polarization.

  Circularly polarized waves are primarily used in the field of telecommunications, and are intended for radiation to open space. Therefore, they are generally discussed as so-called traveling waves without reflected waves. On the other hand, in the present embodiment, there is a possibility that a reflected wave is generated in the heating chamber 2a, which is a closed space, and the generated reflected wave and traveling wave are combined to generate a standing wave.

  However, in addition to the fact that the food absorbs the microwave to reduce the reflected wave, the standing wave is lost at the moment when the microwave is radiated from the microwave suction opening 14, and the standing wave is generated again. It is thought that a traveling wave will be generated until this time. Therefore, according to the present embodiment, it is possible to use the feature of the circularly polarized wave described above, and it is possible to uniformly heat the heating chamber 2a.

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

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

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

[Suction effect of microwave]
Here, the effect of microwave absorption from the rotating antenna, which is a feature of the present embodiment, will be described. In this embodiment, the microwave suction effect means that microwaves in the waveguide structure are sucked 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 a 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 emits linearly polarized microwaves. As shown in FIG. 5B, each of the two openings 501 is a cross slot-shaped opening composed of 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.

  Both apertures are symmetric with respect to the waveguide axis V of the waveguide, and have a width of 10 mm and a length of L mm. In these configurations, the case of “no load” where the object to be heated 22 is not arranged and the case of “with load” where the object to be heated 22 is arranged were analyzed using CAE.

  In the case of “with load”, as shown in FIG. 5C, the height of a fixed object to be heated 22 is 30 mm, the bottom areas (100 mm square, 200 mm square) of two kinds of objects to be heated 22, and three types of heated objects The material D (frozen beef, chilled beef, water) of the object 22 was measured using the distance D from the waveguides 400 and 500 to the bottom surface of the object 22 to be heated as a parameter.

  FIGS. 6A and 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.

  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 represents the length L [mm] of the opening, and the vertical axis represents the radiation radiated from the openings 401 and 501 when the power propagating in the waveguide is 1.0 W. Microwave power [W].

  For comparison with the case of “with load”, the length L at which the radiated power is 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. 6B, the case where the length L is 46.5 mm was selected.

  FIG. 7 shows three types of foods having two types of bottom areas (100 mm square, 200 mm square) when the length L is the above-mentioned length (45.5 mm, 46.5 mm) and “with load”. 6 graphs showing the results of analysis performed on frozen beef, chilled beef, and water.

  In each graph included in FIG. 7, the horizontal axis represents the distance D [mm] from the object 22 to be heated to the waveguide, and the vertical axis represents the radiated power at the time of “no load” being 1.0. The relative radiated power at the time. In other words, in the case of “with load”, compared to the case of “without load”, the value indicates how much microwaves the heated object 22 sucks out of the waveguides 400 and 500.

  In each of the graphs shown in FIG. 7, the broken line indicates the characteristic (indicated by “I” in the figure) in the case of the opening 401 having a linear shape (I shape), and the solid line indicates the two cross slot shapes (X shape). The graph shows the characteristics 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. In particular, when there is a difference of about twice at a distance D of 20 mm or less, which is the same as that of an actual microwave oven. Can be recognized. Therefore, regardless of the type and the bottom area of the object 22 to be heated, it is clear that the aperture that generates circularly polarized waves has a higher microwave suction effect than the aperture that generates linearly polarized waves.

  When examined in detail, as for the type of the object to be heated 22, in particular, 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. Has a smaller suction effect.

  In the case of refrigerated beef or water, as the distance D increases, the radiated power drops to 1 or less, especially for linearly polarized waves. This is probably because the radiated power was offset by the reflected power from the object 22 to be heated. Regarding the bottom area of the object 22 to be heated, since the radiation power is almost the same between the 100 mm square and the 200 mm square, it is considered that the influence on the microwave suction effect is small.

  The inventors studied conditions of an aperture capable of emitting circularly polarized waves by experiments using various aperture shapes. As a result, the following conclusions were reached. The preferred conditions for generating circularly polarized waves are that the opening is displaced from the tube axis V of the waveguide, and that the opening shape includes a cross-slot-shaped opening. The aperture having the cross-slot shape 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. 8A and 8B, the front opening 13 of the rotating antenna 5 faces the left direction in the figure. The object 22 to be heated is arranged above the joint 7 in FIG. 8A, and is placed at the left corner of the placing surface 6a in FIG. 8B. That is, in the two states shown in FIGS. 8A and 8B, the distance from the joint 7 to the object 22 to be heated is different.

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

  On the other hand, in the state shown in FIG. 8B, since the object to be heated 22 is separated from the microwave suction opening 14, it is considered that the effect of suction 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 heated object 22 as a linearly polarized microwave, and the heated object 22 is heated. I do.

  As described above, the microwave suction opening 14 according to the present embodiment increases the radiated power when the food is arranged close to the microwave suction opening 14, and the food is located at a position separated from the microwave suction opening 14. Is considered to cause a special phenomenon that the radiated power is reduced when arranged.

[Uniform heating by waveguide structure]
Hereinafter, uniform heating by the waveguide structure 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 optimal for uniform heating.

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

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

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

  As shown in FIG. 9C, the waveguide structure part 800 has two T-shaped first openings 814a different from the waveguide structure part 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 intersection at one of the two rectangular slits.

  9A to 9C are 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. , A second opening having a similar size is provided at a similar location. In particular, the second opening 614b, the second opening 714b, and the second opening 814b are the same.

  Using a rotating antenna having a waveguide structure shown in FIGS. 9A to 9C, an experiment was performed under the same heating conditions using frozen okonomiyaki placed in the central region of the placing surface 6 a, 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 with each other, and the temperature of the portion to be heated located in the central region of the mounting surface 6a above the coupling portion 7 is increased. However, it has been found that a phenomenon that the temperature does not rise abnormally as compared with the surrounding portion (hereinafter, referred to as a temperature decrease near the joint portion 7) occurs.

  In the case of the waveguide structure part 700 shown in FIG. 9B, a decrease in temperature near the coupling part 7 could be suppressed. In the case of the waveguide structure section 800 shown in FIG. 9C as well, a decrease in temperature near the coupling section 7 could be similarly suppressed.

  As described above, an opening is not provided in the vicinity of the coupling portion 7, or the waveguide structure in which only one opening is provided in the vicinity of the coupling portion 7 suppresses a temperature decrease in the vicinity of the coupling portion 7. It was confirmed that uniform heating in the heating chamber 2a was possible.

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

  According to the first opening 814a of the waveguide structure 800 shown in FIG. 9C, since a so-called distorted circularly polarized wave different from the circularly circularly polarized wave formed by the cross-slot-shaped opening is emitted, the heating is performed. A favorable result was not obtained from the viewpoint of uniform heating in the chamber 2a.

  Therefore, in order to suppress interference between 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 was studied.

  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 diagrams respectively showing the planar shapes of the waveguide structure portion 900A and the waveguide structure portion 900B provided with the above-described 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-section in which, in one of the two rectangular slits, a portion extending from the intersection to the joint 7 has a shorter length than a portion extending from the intersection to the opposite direction of the joint 7. It has a slot shape. As a result of the examination, according to the first opening 914a, in addition to suppressing the interference between the two circularly polarized waves and enabling uniform heating, the above-described suction effect is also improved as compared with the first opening 814a shown in FIG. 9C. It was confirmed that it became higher.

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

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

  Using a rotary 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 placing surface 6a, and the results were verified by CAE.

  As a result, since the first opening 914a has a substantially cross-slot shape, the waveguide structure 900A can suppress interference between two circularly polarized waves and generate circularly polarized waves having a shape close to a circle. Was completed.

  In addition, the first opening 914a increased the suction effect, and was able to suppress a temperature drop near the joint 7. In addition, it was found that the concave joining region formed on the ceiling surface of the waveguide structure 900B can suppress the temperature drop near the joint 7.

[Waveguide structure according to present embodiment]
A specific configuration example of the rotating antenna according to the present embodiment based on the findings from various experiments as described above will be described below. Based on the above findings, various modifications can be used according to the specifications of the microwave heating device.

  FIG. 11 is a plan view showing a rotary 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 displaced from the tube axis V of the waveguide structure 8, the microwave suction opening 14 causes circularly polarized waves. 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 intersection region 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 14a is formed near the recess 9a of the ceiling surface 9. The concave portion 9a is a step region provided 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 closer to the front opening 13 than the first opening 14a is apart from the coupling portion 7. Like the first opening 14a, the two second openings 14b are symmetric with respect to the tube axis V.

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

  As shown in FIG. 3, the flange 7 b provided on 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 8. That is, the length of the coupling unit 7 in 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 center point P1 toward the connecting portion 7 can be formed closer to the connecting 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 protrusion of TOX caulking, welding traces, screws, and nut heads. It is configured to be deeper than the height of the protrusion generated on the surface. According to the present embodiment, there is no problem that the protrusion contacts the lower surface of the mounting table 6.

  The waveguide structure section 8 shown in FIG. 11 has a recess 9a provided on the ceiling surface 9 above the coupling section 7, and has the same configuration as the waveguide structure section 900B shown in FIG. 10B. According to the waveguide structure section 8 shown in FIG. 11, similarly to the waveguide structure section 900B, it is possible to suppress a temperature drop near the coupling section 7. The following are two possible reasons for this.

  First, when an object to be heated is placed above the first opening 14a, a part of the circularly polarized microwave radiated from the first opening 14a is reflected by the object to be heated. The reflected microwaves are repeatedly reflected in a space formed between the upper surface of the concave portion 9a and the lower surface of the mounting table 6, and as a result, heat the object to be heated more strongly.

  Second, in the present embodiment, the internal space of the waveguide structure 8 at the portion where the concave portion 9a is formed is narrower than other portions. When most of the microwave propagating from the coupling shaft 7a into the waveguide structure portion 8 travels from a narrow space near the concave portion 9a to a wide space separated from the concave portion 9a, the first opening 14a is drawn by the suction effect. , And the object to be heated placed in the central region of the placing surface 6a is heated strongly.

  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 that intersects 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 end and a third length C from the center point P1 to the upper left end. Have. The lower right end of the slit 20a is directed toward the coupling portion 7 and approaches the concave portion 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 end and a fourth length D from the center point P1 to the upper right end. That is, the first length A is the length from the center point P1 to the tip of the slits 20a and 20b to the tip closest to the coupling portion 7.

  The third length C and the fourth length D are the same and substantially correspond to １ ／ 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.

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, in the ceiling surface 9, a region near the recess 9 a between the two first openings 14 a is wider than a region separated from the recess 9 a.

  If the region between the two first openings 14a is not flat, a disturbed 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 circularly polarized wave with less disturbance is formed by the wider flat region provided between the two first openings 14a, and a high suction effect can be obtained.

  In the present embodiment, the distance between the two first openings 14 a is at least １ ／ of the wavelength of the microwave propagating in the waveguide structure 8. According to the experiments performed by the inventors, favorable results were obtained when the two first openings 14a had a distance substantially matching the axis 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 major axis length 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.

  Although the coupling portion 7 according to the present embodiment has the flange 7b having the above-described shape, 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 made shorter, the first opening 14a can be provided closer to the coupling portion 7. Depending on the shape of the flange 7b, the first opening 14a can be provided closer to the coupling portion 7, such as by using a flange 7b having a notch between the first opening 14a.

  If the shape of the flange 7b is devised, it is possible to strengthen the joining between the coupling portion 7 and the waveguide structure portion 8 without reducing the area of the joining portion, and it is possible to suppress 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, the present embodiment is performed. The same effect as in the embodiment is obtained. According to the configuration without the flange 7b, 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 near the joint 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. The microwave suction opening may have any shape other than the cross slot shape as long as it can generate circularly polarized waves.

  As a result of the experiment, it is presumed that an essential condition for generating circularly polarized waves from the waveguide structure portion is to arrange a combination of two generally elongated openings at positions 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, a circularly polarized wave can be generated.

  Rather, in order to suppress the concentration of the electric field, it is preferable that the corner of the opening is rounded. In the present embodiment, as shown in FIGS. 3, 9A to 9C, 10A, 10B, and 11, the slits included in first opening 14a and second opening 14b have rounded tips and intersections. With flared corners. 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 recess 9a is formed above the joint 7 of the ceiling surface 9, but the waveguide structure 8 of the present disclosure is not limited to this.

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

  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.

  INDUSTRIAL APPLICABILITY The present disclosure is applicable to microwave heating devices for various industrial uses such as a drying device, a heating device for pottery, a garbage disposer, and a semiconductor manufacturing device, in addition to a microwave oven.

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 table 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 Depression 11 Bottom surface 12, 106, 206 Low impedance portion 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 Outside line sensor 17, 211 Control unit 18, 18a, 18b Convex portion 19 Holding unit 22 Heated object 107, 207 Emission port 300 Waveguide 301 Wide surface 302 Narrow surface 303 Cross section 401, 501 Opening

Claims (6)

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, having a coupling portion joined to the ceiling surface and coupling the microwave to an internal space of the waveguide structure portion; ,
The waveguide structure has at least one microwave suction opening formed on the ceiling surface, and emits circularly polarized waves into the heating chamber from the microwave suction opening,
A microwave heating device, wherein a joining portion between the coupling portion and the waveguide structure portion is configured such that a length of the waveguide structure portion in a tube axis direction is shorter than a length in a direction orthogonal to the tube axis direction. . Further comprising a drive unit for rotating the waveguide structure antenna,
The coupling unit is coupled to the driving unit, and includes a coupling axis including a rotation center of the waveguide structure antenna, and a flange provided around the coupling axis and forming the joint portion,
The microwave heating device according to claim 1, wherein the flange has a length in the tube axis direction shorter than a length in a direction orthogonal to the tube axis direction. Further comprising a drive unit for rotating the waveguide structure antenna,
The coupling unit is coupled to the driving unit, and has a coupling axis including a rotation center of the waveguide structure antenna,
2. The microwave heating apparatus according to claim 1, wherein a cross section of the joint portion at the joint portion has a length in the tube axis direction shorter than a length in a direction orthogonal to the tube axis direction. 3. The microwave heating device according to claim 1, wherein the microwave suction opening has a cross slot shape in which two slits intersect, and is provided at a position shifted from the tube axis. The waveguide structure has at least two microwave suction openings symmetric with respect to the tube axis,
The microwave heating apparatus 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. The microwave heating device according to claim 1, wherein the ceiling surface has a concave portion provided in the joining portion.