JP2014116175A - Microwave heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microwave heating device in which heating is carried out efficiently while ensuring uniformity of heating distribution, without using a drive section.SOLUTION: When microwaves are radiated from a plurality of openings 105a, 105b, 105c, 105d, 105e, 105f to a heated object mounted substantially in the center of a heating chamber bottom surface, uniformity of heating distribution is ensured without using a drive section. Since a drive section is not used, reflection is suppressed by eliminating variation of load impedance, when viewed from a magnetron 103. Furthermore, heating can be carried out efficiently by generating the anti-node of a standing-wave inside in the central part of the heating chamber bottom surface 108, thereby exposing the heated object to the standing-wave inside.

Description

  The present invention relates to a microwave heating apparatus such as a microwave oven that radiates microwaves to an object to be heated and performs dielectric heating.

  A microwave oven of a typical microwave heating apparatus supplies microwave radiated from a magnetron, which is a typical microwave generation means, to the inside of a metal heating chamber through a waveguide, and into the inside of the heating chamber. The object to be heated is dielectrically heated. Therefore, if the microwave electromagnetic field distribution in the heating chamber is not uniform, the object to be heated cannot be heated uniformly.

  Therefore, as a method of uniformly heating the object to be heated, a structure that rotates the object itself by rotating the table, a structure that rotates the antenna that emits microwaves while the object to be heated is fixed, etc. A general method has been to use a drive unit to heat and uniformize the direction of the microwave radiated to the object to be heated.

  On the other hand, in order to simplify the configuration, a method of uniformly heating without a driving unit is expected, and a method using circularly polarized waves in which the polarization plane of an electric field rotates with time is proposed. Originally, since dielectric heating is based on the principle of heating an object to be heated having dielectric loss with a microwave electric field, rotation of the electric field is considered to have an effect on uniformity. For example, as a specific method of generating circularly polarized waves, Patent Document 1 discloses a method of generating one circularly polarized wave with an X-shaped opening 2 intersecting on the waveguide 1 as shown in FIG. In Patent Document 2, as shown in FIG. 9, one circularly polarized wave is generated by disposing two rectangular slit-shaped openings 3 and 4 that are orthogonal to each other on the waveguide 1 while facing each other. Patent Document 3 describes a method of generating one circularly polarized wave by providing a notch 6 in the planar shape of the patch antenna 5 coupled to the waveguide 1 as shown in FIG. ing.

  Although not related to circular polarization, Patent Document 4 shows an example in which a plurality of rectangular slits are arranged at intervals of ¼ of the wavelength as shown in FIG. ing.

U.S. Pat. No. 4,301,347 Japanese Patent No. 3510523 Japanese Patent Laying-Open No. 2005-235772 Japanese Patent Laid-Open No. 10-284246

However, the conventional microwave heating apparatus has a problem that in any case of Patent Documents 1 to 3, the circularly polarized wave is used, but there is no uniform effect that can be achieved without a driving unit. . Both patent documents only describe that the synergistic effect of the circularly polarized wave and the drive unit makes it more uniform than the conventional drive unit alone. Specifically, Patent Document 1 has a rotating body called a phase shifter 7 at the end of the waveguide as shown in FIG. 8, and Patent Document 2 has a turntable (not shown) for rotating an object to be heated. Patent Document 3 describes a configuration in which the patch antenna 5 is also rotated in addition to the turntable 8 to be used as a stirrer. In any case, it is not described that a circularly polarized wave can be used without a drive unit. This is because if the drive unit is not provided with circular polarization, the uniformity is inferior to a general configuration with a drive unit (for example, a configuration in which a table is rotated or an antenna is rotated).

  On the other hand, it is said that the heating efficiency is in a trade-off relationship with uniformity. This is because it is better to rotate the table or antenna in order to improve the uniformity, but the load impedance seen from the magnetron changes greatly according to the rotation operation, so there is always little reflection (impedance and load on the magnetron side) The magnetron cannot be operated in a state where the impedance on the side is matched), and the heating efficiency tends to decrease.

  The present invention solves the above-described problems, and an object thereof is to provide a microwave heating apparatus that can uniformly and efficiently heat an object to be heated without using a driving unit.

  In order to solve the above-described conventional problems, a microwave heating apparatus of the present invention includes a heating chamber for storing an object to be heated, microwave generation means for generating microwaves, a waveguide for transmitting microwaves, The heating chamber has a plurality of microwave radiating portions that radiate microwaves, and a configuration is provided in which the antinode of the standing wave in the chamber is generated at the center of the bottom of the heating chamber on which the object to be heated is placed.

  With the above configuration, the heating distribution of the object to be heated placed generally at the substantially central portion of the bottom surface of the heating chamber is radiated from a plurality of microwave radiating units without using a driving unit. In addition to suppressing the reflection by eliminating the fluctuation of load impedance seen from the microwave generation means by ensuring that the drive unit is not used while ensuring uniformity, an antinode of the standing wave in the chamber is generated at the center of the bottom of the heating chamber. By doing so, the object to be heated can be efficiently heated by being exposed to the antinodes of the standing wave in the cabinet.

  The microwave heating apparatus of the present invention generally does not use a driving unit by radiating microwaves from a plurality of microwave radiating units to an object to be heated that is placed substantially at the center of the bottom of the heating chamber. However, while ensuring the uniformity of the heating distribution, the use of the drive unit eliminates load impedance fluctuations seen from the microwave generation means and suppresses reflections. By generating the antinode of the wave, the object to be heated can be exposed to the antinode of the standing wave in the cabinet and heated efficiently.

The perspective view of the microwave heating apparatus in Embodiment 1 of this invention Sectional drawing (a) plane sectional view (b) front sectional view of microwave heating apparatus in Embodiment 1 of the present invention Schematic diagram illustrating a waveguide of a microwave heating apparatus according to Embodiment 1 of the present invention. Schematic diagram illustrating cylindrical standing wave stabilizing means of the microwave heating apparatus according to the first embodiment of the present invention. Schematic diagram illustrating hemispherical standing wave stabilizing means of the microwave heating apparatus according to the first embodiment of the present invention. Sectional drawing (a) plane sectional view (b) front sectional view explaining the standing wave in a warehouse of the microwave heating apparatus in Embodiment 1 of this invention The schematic diagram explaining the opening shape of the microwave heating apparatus in other embodiment of this invention Configuration diagram of a microwave heating device that generates circularly polarized waves with a conventional X-shaped opening Configuration diagram of a conventional microwave heating device that generates circularly polarized waves with two orthogonal rectangular slits Configuration diagram of a microwave heating device that generates circularly polarized waves with a conventional patch antenna Configuration of conventional waveguide and rectangular slit

  A microwave heating apparatus according to a first aspect of the present invention is a heating chamber for storing an object to be heated, a microwave generating means for generating microwaves, a waveguide for transmitting microwaves, and radiating microwaves into the heating chamber. And a plurality of microwave radiating portions that are configured to generate an antinode of standing waves in the center of the bottom of the heating chamber on which the object to be heated is placed.

  With the above configuration, the heating distribution of the object to be heated placed generally at the substantially central portion of the bottom surface of the heating chamber is radiated from a plurality of microwave radiating units without using a driving unit. In addition to suppressing the reflection by eliminating the fluctuation of load impedance seen from the microwave generation means by ensuring that the drive unit is not used while ensuring uniformity, an antinode of the standing wave in the chamber is generated at the center of the bottom of the heating chamber. By doing so, the object to be heated can be efficiently heated by being exposed to the antinodes of the standing wave in the cabinet.

  In the microwave heating apparatus of the second invention, in particular, in the first invention, the standing wave in the cabinet is in a mode in which an odd number of antinodes are generated in the width direction and the depth direction of the heating chamber (odd number, odd number). In this way, the antinode of the standing wave inside the chamber is generated at the center of the bottom surface of the heating chamber. Accordingly, the object to be heated can be exposed to the antinode of the standing wave in the chamber and heated efficiently by reliably generating the antinode of the standing wave in the chamber at the center of the bottom of the heating chamber with a simple configuration.

  The microwave heating apparatus according to a third aspect of the invention is particularly the first or second aspect of the invention, wherein the standing wave in the tube is generated in the waveguide, and at least one of the antinodes of the standing wave in the tube is at the center of the bottom of the heating chamber. It is set as the structure arrange | positioned facing. In the first place, since the waveguide and the heating chamber are connected to the microwave radiation section at multiple locations, the antinodes and nodes of the standing wave inside the waveguide coincide with the antinodes and nodes of the standing wave inside the heating chamber. It becomes easy. Therefore, by making the antinode of the standing wave in the pipe face the center of the bottom of the heating chamber, the antistatic of the standing wave in the chamber is easily generated, and the antinode of the standing wave in the chamber is reliably generated in the center of the bottom of the heating chamber with a simple configuration. By doing so, the object to be heated can be efficiently heated by being exposed to the antinodes of the standing wave in the cabinet.

  The microwave heating apparatus according to the fourth aspect of the invention is particularly configured in any one of the first to third aspects, in which at least one of the microwave radiating portions is arranged at the center of the bottom of the heating chamber. In the first place, the microwave radiating portion connects the waveguide and the heating chamber, and if there is no microwave radiating portion, it is an outlet for radiating the microwave that should be confined in the waveguide to the heating chamber. For this reason, in the microwave radiation part, the electric field of the microwave tends to become strong, and it tends to become an antinode of the standing wave in the tube and an antinode of the standing wave in the warehouse. Therefore, by arranging the microwave radiating part at the center of the bottom of the heating chamber, the object to be heated is placed in the center of the bottom of the chamber by reliably generating an antinode of the standing wave in the center of the bottom of the heating chamber with a simple configuration. It can be heated efficiently by exposure to the belly.

  In the microwave heating apparatus according to the fifth aspect of the invention, in particular, in any one of the first to fourth aspects of the invention, the microwave radiating unit radiates circularly polarized waves. As a result, an electric field that rotates in a 360-degree omnidirectional characteristic of circularly polarized waves is generated around the microwave radiation part, and microwaves are radiated from the center so as to vortex, thereby heating the circumferential direction uniformly. Can do. Therefore, by radiating circularly polarized waves from a plurality of microwave radiating sections, microwaves can be radiated evenly to the entire heating chamber, and heating can be performed without using a drive section by simply arranging a plurality of microwave radiating sections. The object to be heated in the room can be heated uniformly.

  In the microwave heating apparatus of the sixth invention, in particular, in the fifth invention, the microwave radiating portion that radiates circularly polarized waves has a substantially X-shaped configuration in which two long holes intersect. Thereby, circularly polarized waves can be reliably radiated from the waveguide with a simple configuration.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of a microwave heating apparatus according to the invention will be described with reference to the accompanying drawings. In the microwave heating apparatus of the following embodiment, a microwave oven will be described. However, the microwave oven is an example, and the microwave heating apparatus of the present invention is not limited to the microwave oven, and uses dielectric heating. And a microwave heating device such as a garbage processing machine or a semiconductor manufacturing device. Further, the present invention is not limited to the specific configurations of the following embodiments, and configurations based on similar technical ideas are included in the present invention.

(Embodiment 1)
1 and 2 are explanatory diagrams of the microwave heating apparatus according to Embodiment 1 of the present invention. FIG. 1 is a perspective view showing the overall configuration, FIG. 2A is a sectional view seen from above, and FIG. 2B is a sectional view seen from the front.

  A microwave oven 101, which is a typical microwave heating apparatus, includes a heating chamber 102 that can store food (not shown) that is a typical object to be heated, and a typical microwave generation means that generates microwaves. A certain magnetron 103, a waveguide 104 that guides the microwave radiated from the magnetron 103 to the heating chamber 102, and the waveguide 104 as a microwave radiating unit that radiates the microwave in the waveguide 104 into the heating chamber 102. There are six openings 105a, 105b, 105c, 105d, 105e, and 105f provided on the upper surface of the, and a mounting table 106 on which food (not shown) is mounted.

  The heating chamber 102 is a horizontally long rectangular parallelepiped, and the mounting table 106 is configured to cover the entire bottom surface of the heating chamber 102. The mounting table 106 is closed so that the openings 105a, 105b, 105c, 105d, 105e, and 105f are not exposed in the heating chamber 102, and the user can easily take in and out food (not shown) by flattening the top surface. It is easy to wipe off when it gets dirty. Here, the mounting table 106 is made of a material that easily transmits microwaves, such as glass or ceramic, in order to radiate the microwaves from the openings 105a, 105b, 105c, 105d, 105e, and 105f into the heating chamber 102.

  The waveguide 104 and the heating chamber 102 are connected with the microwave transmission direction of the waveguide 104 directed in the width direction of the heating chamber 102. The openings 105 a, 105 b, 105 c, 105 d, 105 e, and 105 f are openings that can radiate circularly polarized waves by an X-shaped shape that intersects the long holes, and are formed at the center (tube axis) 107 in the width direction of the waveguide 104. They are arranged symmetrically in the width direction so as not to be applied. The tube axis 107 does not coincide with the center 109 in the front-rear direction of the heating chamber bottom surface 108 of the heating chamber 102, and the centers of the openings 105 a, 105 c, 105 e coincide with the center 109 in the front-rear direction of the heating chamber bottom surface 108. Further, the six openings 105a, 105b, 105c, 105d, 105e, and 105f are arranged symmetrically with respect to the center 110 in the left-right direction of the heating chamber bottom surface 108 of the heating chamber 102, and as described above, with respect to the heating chamber bottom surface 108 of the heating chamber 102. Thus, the opening 105c is arranged at the center in the front, rear, left, and right. Further, the openings 105a, 105b, 105c, 105d, 105e, 105f are arranged in the transmission direction of the waveguide 104 at an interval of approximately ½ of the guide wavelength λg. An in-tube standing wave is generated in the waveguide 104, which repeats the belly and node every 1/2 of the in-tube wavelength λg determined by the oscillation frequency of the magnetron 103 and the shape of the waveguide 104. The terminal portion 111 of the wave tube 104 is always a node.

Here, FIG. 2B shows an image of the standing wave in the waveguide 104. The standing wave stabilizing means 112a, 112b, and 112c are made of a conductive material protruding into the waveguide 104, and have a configuration similar to a stub tuner or the like known as a so-called matching element. That is, a total of three are arranged at intervals of approximately ½ each of the in-tube wavelength λg from the terminal end 111, and counted from the terminal end 111 side, the first standing wave stabilizing means 112a and the second standing wave stabilizing means 112b. , Third standing wave stabilizing means 112c. The openings 105a and 105b are arranged between the terminal end 111 and the first standing wave stabilizing means 112a, and the openings 105c and 105d are provided.
Is disposed between the first standing wave stabilizing means 112a and the second standing wave stabilizing means 112b, and the openings 105e and 105f are formed in the second standing wave stabilizing means 112b and the third standing wave stabilizing means 112c. It is arranged in the middle. At this time, the waveguide 104 is configured so that the first standing wave stabilizing means 112a and the second standing wave stabilizing means 112b are symmetrical with respect to the center 110 in the left-right direction of the bottom surface 108 of the heating chamber. As a result, 113b of antinodes 113a, 113b, 113c of the standing wave in the tube immediately below the opening is positioned at the center 110 as shown in FIG. The openings 105a and 105b are located at the antinode 113a of the in-tube standing wave between the end portion 111 and the first standing wave stabilizing means 112a, and the openings 105c and 105d are the first standing wave stabilizing means 112a and the second standing wave stabilizing means 112a. The standing wave antinode 113b between the standing wave stabilizing means 112b and the openings 105e and 105f are arranged in the pipe between the second standing wave stabilizing means 112b and the third standing wave stabilizing means 112c. It will be located at standing wave antinode 113c. That is, in the present embodiment, a standing wave in the tube is generated in the waveguide 104, and at least one antinode 113b of the standing wave in the tube is disposed to face the center portion of the heating chamber bottom surface 108. . In addition, as shown in FIG. 1, a door 114 that can be opened and closed is provided, and by closing the door 114, a microwave forms a closed space between the waveguide 104 and the heating chamber 102, and the confined microwave is always defined in some way. It will cause standing waves.

  The operation will be described based on the above configuration. The microwave radiated from the magnetron 103 is transmitted through the waveguide 104, and a part thereof is radiated into the heating chamber 102 from the openings 105a, 105b, 105c, 105d, 105e, and 105f. It is reflected by. In addition, since the heating chamber 102 is a closed space, it is considered that a part of the microwave in the heating chamber 102 may slightly return to the waveguide 104 from the openings 105a, 105b, 105c, 105d, 105e, and 105f. . As a result, an in-tube standing wave is generated in the waveguide 104 and an in-house standing wave is generated in the heating chamber 102. In particular, with respect to the waveguide 104, it is considered that a standing wave with an in-tube wavelength λg is likely to occur if the reflection at the terminal end 111 is dominant. In general, when there is a certain amount or more of an object to be heated, or under conditions where microwaves are easily absorbed, microwaves returning from the heating chamber 102 into the waveguide 104 through the openings 105a, 105b, 105c, 105d, 105e, and 105f. Because the amount is small, the standing wave is stabilized. On the other hand, under the condition that the object to be heated hardly absorbs a very small amount of microwaves, the heating chamber 102 returns to the waveguide 104 due to the communication between the openings 105a, 105b, 105c, 105d, 105e, and 105f and the heating chamber 102. The standing wave in the tube may be disturbed by the microwave to be tried. However, in the present embodiment, the standing wave stabilizing means 112a, 112b, and 112c are arranged in the waveguide 104, so that the node position of the in-tube standing wave can be fixed, and as a result, the respective opening positions. The amplitude and phase at can also be fixed. Further, the microwave is radiated into the heating chamber 102 as a circularly polarized wave by the configuration of the openings 105 a, 105 b, 105 c, 105 d, 105 e, and 105 f. Circularly polarized light is radiated while rotating an electric field in the circumferential direction around the openings 105a, 105b, 105c, 105d, 105e, and 105f, and is radiated uniformly around the periphery.

  Here, circular polarization will be described. Circular polarization is a technology widely used in the fields of mobile communication and satellite communication. Examples of familiar use include an ETC (Electronic Toll Collection System) “non-stop automatic toll collection system” and the like. Circular polarization is a microwave in which the polarization plane of the electric field rotates with respect to the traveling direction, and when the circular polarization is formed, the direction of the electric field continues to change with time, and the magnitude of the electric field strength Has the characteristic of not changing. If this circularly polarized wave is applied to a microwave heating device, it is expected that the object to be heated will be heated evenly, particularly in the circumferential direction of the circularly polarized wave, as compared with the conventional microwave heating by linearly polarized wave. The Note that circularly polarized waves are classified into two types, ie, right-handed polarization (CW: clockwise) and left-handed polarization (CCW: counterclockwise) from the rotational direction, but there is no particular difference in performance in the field of heating.

As circularly polarized waves, there are those constituted by the opening of the waveguide wall surface as in Patent Literature 1 and Patent Literature 2, and those constituted by the patch antenna as shown in Patent Literature 3, but this embodiment The openings 105a, 105b, 105c, 105d, 105e, and 105f are formed on the upper surface (H surface) of the waveguide 104 and emit circularly polarized waves in the same manner as that disclosed in Patent Document 1.

  Since circularly polarized waves are primarily used in the field of communications, they are generally discussed in terms of so-called traveling waves that do not return reflected waves because they are intended for radiation into open spaces. On the other hand, the microwave heating apparatus according to the present embodiment emits radiation into a closed space shielded from the outside by the waveguide 104 and the heating chamber 102, and the reflected wave returns and is synthesized in the waveguide. Although the wave is discussed, it is considered that the standing wave is out of balance at the moment when the microwave is radiated from the aperture, and the traveling wave is generated until it returns to the stable standing wave again. Therefore, by making the opening have a circularly polarized radiation shape, it is possible to utilize the above-described features of circularly polarized waves, and the heating distribution in the heating chamber 102 can be made more uniform.

  In order to output circularly polarized waves from the opening provided in the rectangular waveguide 104, two slits having a width are intersected at the center as shown in the example of FIG. A configuration in which the shape inclined by 45 degrees with respect to the waveguide 104 in the microwave transmission direction is disposed at a position that does not pass through the tube axis 107 is desirable.

  Here, the waveguide will be described with reference to FIG. The simplest and most common waveguide is a rectangular waveguide made of a rectangular parallelepiped having a certain rectangular cross section (width a, height b) extended in the transmission direction as shown in FIG. Is selected in the range of the waveguide width a (microwave wavelength λ0> a> λ0 / 2) and height b (<λ0 / 2). Is known to transmit.

  The TE10 mode refers to a transmission mode in an H wave (TE wave; electrical transverse wave) that has only a magnetic field component in the waveguide transmission direction in the waveguide 104 and no electric field component. Point to. Note that transmission modes other than the TE10 mode are rarely applied to the waveguide 104 of the microwave heating apparatus 101.

  Prior to the description of the guide wavelength λg in the waveguide, the free space wavelength λ0 will be described. The wavelength λ0 in free space is known as about 120 mm in the case of a microwave in a general microwave oven. However, to be precise, the wavelength λ0 of the free space is obtained by λ0 = c / f, and c is a speed and constant at the speed of light 3.0 * 10 ^ 8 [m / s], but f is a frequency of 2. There is a width of 4 to 2.5 [GHz] (ISM band). Since the oscillation frequency f of the magnetron changes depending on variations and load conditions, the wavelength λ0 of the free space also changes eventually, from a minimum of 120 [mm] (at 2.5 GHz) to a maximum of 125 [mm] (at 2.4 GHz). Change to.

  Returning to the description of the waveguide, in consideration of the range of the wavelength λ0 in free space, the width a of the waveguide is generally selected to be 80 to 100 mm and the height b is often set to about 15 to 40 mm. At this time, the upper and lower wide surfaces in FIG. 3 are referred to as H surfaces 126 in the sense that the magnetic fields vortex in parallel, and the left and right narrow surfaces are referred to as E surfaces 127 in the sense that they are parallel to the electric field. Incidentally, the wavelength when the microwave is transmitted through the waveguide is expressed as the waveguide wavelength λg and becomes λg = λ0 / √ (1- (λ0 / (2 × a)) ^ 2), and the width of the waveguide It varies depending on the dimension a, but is determined regardless of the height b. Incidentally, in the TE10 mode, the electric field is zero at both ends (E plane) 127 in the width direction of the waveguide, and the electric field is maximum at the center in the width direction. Therefore, the magnetron 103 is coupled to the center in the width direction of the waveguide (on the tube axis 107 shown in FIG. 2) where the electric field is maximum.

Incidentally, the openings 105a, 105b, 105c, 105d, 105e, and 105f of the present embodiment are X-shaped openings with the long holes orthogonal to each other as shown in FIG. The shape is such that circular polarization can be generated by placing it on one side from the center (tube axis) 107, and the direction of rotation of the electric field differs depending on which of the H planes is approached. It will be divided into.

  Here, there are some differences between the open space communication field and the closed space heating field, so a description will be added. In the communication field, we want to send and receive only the necessary information while avoiding mixing with other microwaves, so the transmitting side is limited to either right-handed polarization or left-handed polarization, and the receiving side also adjusts accordingly. The optimum receiving antenna will be selected. On the other hand, in the field of heating, an object to be heated such as food with no directivity is subjected to microwaves instead of a receiving antenna having directivity, so that it is only important that the microwaves uniformly strike the entire object to be heated. . Therefore, in the field of heating, there is no problem even if right-handed polarization and left-handed polarization are mixed, but conversely, it is necessary to prevent uneven distribution as much as possible depending on the position and shape of the object to be heated. For example, when there is only a single opening as in Patent Document 1, it is preferable to place the object to be heated directly above the opening. However, if the object to be heated is shifted back and forth or left and right, the part close to the opening is apt to be heated and far away. The site is difficult to be heated, resulting in uneven heating. Therefore, it is desirable to have a plurality of circularly polarized apertures. In the present embodiment, as shown in FIG. 2, the six openings 105a, 105b, 105c, 105d, 105e, and 105f are arranged as described above.

Here, the standing wave stabilizing means will be described with reference to FIGS.
FIG. 4 shows a structure in which standing wave stabilizing means 134 and 135 are arranged in the waveguide 104 described with reference to FIG. The standing wave stabilizing means 134 and 135 are cylindrical and made of a conductive material such as aluminum or stainless steel, and are connected and fixed to the center in the width direction of the H surface 126 of the waveguide 104 by welding or screwing. . The standing wave stabilizing means 134 and 135 having such a configuration is considered to partially prevent transmission of microwaves as a protruding portion in the waveguide 104, but as a result, the standing wave stabilizing means 134 and 135. It has been found that it is easy to become a standing wave node at a position. Therefore, conversely, by providing the protruding portions such as the standing wave stabilizing means 134 and 135 at the position where the standing wave is desired, there is an effect of stabilizing the standing wave without changing the position. The structures of the standing wave stabilizing means 134 and 135 are similar to those of a stub tuner known as a so-called matching element, and by adjusting the shape (particularly the height) and the position, the node of the standing wave can be adjusted. It seems that it is possible to have two functions that can be matched while confirming.

  FIG. 4 shows an example in which the standing wave stabilizing means 134 is higher in height than the standing wave stabilizer 135, but there is no particular limitation, and the shape may be optimized as appropriate. In FIG. 4, the distance between the standing wave stabilizing means 134 and 135 is (λg / 2) × n using the guide wavelength λg, and n is an integer, so that nodes can be created in two places. In particular, a clean standing wave exists between the standing wave stabilizing means 134 and 135. For example, when n = 1, the standing wave stabilizing means 134 and 135 are nodes and the center of both is antinode, and when n = 2, the standing wave stabilizing means 134 and 135 is a node and the center of both is also a node. Therefore, if n is an integer, a beautiful standing wave can be created between the standing wave stabilizing means 134 and 135.

  FIG. 5 shows another example of standing wave stabilizing means, which is not a separate component, but a hemispherical standing wave stabilizing means 136 in which the H surface of the waveguide 104 is squeezed by a press or the like and protruded into the waveguide 104. This is an example of the configuration. In this case, since the standing wave stabilizing means can be formed of the waveguide material itself, there is an effect that a separate component for stabilizing the standing wave is unnecessary compared with the example of FIG.

Here, the internal standing wave generated in the heating chamber will be described with reference to FIG. FIG. 6A is a view of the heating chamber as viewed from above, and the antinodes of the standing waves generated on the top surface (the same applies to the bottom surface) are represented by solid lines and the nodes are represented by broken lines as images. (B) is a sectional view of the heating chamber as seen from the front, and the abdominal node similar to that of FIG. 6 (a) is shown on the top surface, but at the same time, the abdominal node is also represented as a half-wave image. . As described above, when there is nothing to stir as in this embodiment, a standing wave in the chamber is also generated in the heating chamber. If the heating chamber is considered to be a substantially rectangular parallelepiped, the concept of a cavity resonator on a rectangular parallelepiped shape applies. A standing wave of a rectangular parallelepiped cavity resonator in which the length of each side is represented by X, y, z is generally expressed by the following (Equation 1) using the wavelength λ0 of free space.

  The chamber standing wave modes m, n, and p indicate the number of standing waves in the X, y, and z directions. When the size is about the same as a microwave oven, X, y, and z are larger than the wavelength. Some combinations of m, n, and p satisfying the above (Formula 1) coexist. Incidentally, in FIG. 6, m, n, and p are represented as 3, 5, and 1, respectively. In the present embodiment, the standing wave in the cabinet is a mode (odd number, odd number) in which an odd number of antinodes occur in the width direction (X direction) and the depth direction (y direction) of the heating chamber 102 (in this embodiment ( 3, 5)). In particular, the oscillation frequency of the magnetron is not constant (it changes depending on the temperature and also changes due to the reflection of the microwave), and the wavelength also changes depending on the frequency. The actual standing wave inside the chamber can be visualized by drilling a minute hole on the wall surface and actually measuring the electric field strength, or by displaying the electromagnetic field inside the chamber using CAE (for example, the finite element method). Good. However, one of the methods for determining the standing wave in the cabinet is where power is supplied from. This is because the power supply unit tends to get hungry because it emits radio waves one after another. In FIG. 6 (b), there are openings 141, 142, and 143 on the antinodes of the standing waves in the tube, and the in-chamber standing waves are also antinodes. Particularly, the antinode 144 of the standing wave inside the chamber just above the opening 142 is located at the center of the bottom surface of the heating chamber, and the heated object 145 placed at the center of the chamber is located at the antinode, so that it is always efficiently heated with a strong electric field. can do.

Below, the operation and effect of the present embodiment will be described.
A microwave oven 101 according to this embodiment includes a heating chamber 102 that stores an object to be heated, a magnetron 103 that serves as a microwave generation unit that generates a microwave, and a waveguide 104 that transmits the microwave generated by the magnetron 103. And heating chambers having openings 105a, 105b, 105c, 105d, 105e, and 105f serving as a plurality of microwave radiating portions that radiate microwaves from the waveguide 104 into the heating chamber 102, and on which an object to be heated is placed. The structure is such that an antinode 144 of the standing wave in the cabinet is generated at the center of the bottom surface 108.

  As a result, microwaves are generally applied from the openings 105a, 105b, 105c, 105d, 105e, and 105f as a plurality of microwave radiating portions to an object to be heated that is placed substantially at the center of the bottom surface 108 of the heating chamber. In addition to ensuring the uniformity of the heating distribution without using the drive unit by radiating, in addition to eliminating the fluctuation of the load impedance viewed from the magnetron 103 and suppressing reflection by using the drive unit, the heating chamber By generating the chamber standing-wave antinode 144 at the center of the bottom surface 108, the object to be heated can be exposed to the chamber standing-wave antinode and efficiently heated.

  In addition, usually the user will put food on something on hand, but it tends to place food in the center of the plate, and the place where the plate is placed on the bottom of the heating chamber tends to be in the center. . In many cases, a circular marking is printed at the center of the mounting table 106 as a recommended position. As a result, the food is very likely to be placed in the center of the bottom of the heating chamber. In particular, when a large plate is used, it can be assumed that it can be placed only in the center. Therefore, the object to be heated can be exposed to the antinode of the standing wave in the chamber and heated efficiently by generating the antinode 144 of the standing wave in the center of the bottom surface 108 of the heating chamber.

Further, in the microwave oven of the present embodiment, the standing wave in the cabinet has an odd number of antinodes (odd number, odd number) in the width direction and depth direction of the heating chamber 102 (in this embodiment, (3, 5 )), An antinode 144 of the standing wave inside the chamber is generated at the center of the bottom surface 108 of the heating chamber. Thereby, the object to be heated is exposed to the antinode 144 of the standing wave in the chamber by efficiently generating the antinode 144 of the standing wave in the center at the center of the heating chamber bottom surface 108 with a simple configuration, and can be efficiently heated. it can.

  In addition, the microwave oven according to the present embodiment generates an in-tube standing wave in the waveguide 104, and at least one antinode 113b of the in-tube standing wave is disposed to face the central portion of the heating chamber bottom surface 108. It is configured. In the first place, the waveguide 104 and the heating chamber 102 are connected to the openings 105 a, 105 b, 105 c, 105 d, 105 e, and 105 f as microwave radiation portions at a plurality of locations. The nodes and the antinodes and nodes of the standing wave in the heating chamber easily match. Therefore, by making the tube standing wave antinode 113b face the central portion of the heating chamber bottom surface 108, the chamber standing wave is likely to be antinoded, and the simple configuration ensures that the chamber standing wave is centrally located in the center portion of the heating chamber bottom surface 108. By generating the wave belly 144, the object to be heated 145 can be exposed to the antinode 144 of the internal standing wave and heated efficiently.

  In addition, the microwave oven according to the present embodiment has a configuration in which at least one opening 105c serving as a microwave radiating portion is arranged at the center of the heating chamber bottom surface 108. In the first place, the microwave radiating part connects the waveguide and the heating chamber, and if there is no microwave radiating part, it is an outlet for radiating the microwave that should be confined in the waveguide 104 to the heating chamber 102. . For this reason, the microwave electric field tends to become strong at the opening as the microwave radiating section, and it tends to become an antinode in the tube and an antinode in the chamber. Therefore, by arranging an opening as a microwave radiating portion at the center of the heating chamber bottom surface 108, the chamber standing wave antinode 144 is reliably generated at the center of the heating chamber bottom surface 108 with a simple configuration. The heated object 145 can be efficiently heated by being exposed to the antinode 144 of the standing wave in the cabinet.

  In the microwave oven of the present embodiment, the microwave radiating unit radiates circularly polarized waves. As a result, an electric field rotating in all 360 ° directions specific to circular polarization is generated around the six openings 105a, 105b, 105c, 105d, 105e, and 105f as the microwave radiating section, and a vortex is wound from the center. Microwaves are radiated to the circumference, and the circumferential direction can be heated uniformly. Therefore, by radiating circularly polarized waves from as many as six microwave radiating portions, the entire heating chamber 102 can be radiated uniformly, and the object to be heated in the heating chamber 102 can be moved without using a drive portion. It can be heated uniformly.

  Furthermore, in the microwave oven according to the present embodiment, the six openings 105a, 105b, 105c, 105d, 105e, and 105f serving as the microwave radiating portions that radiate circularly polarized waves have a substantially X shape in which two long holes intersect. The configuration is as follows. Thereby, circularly polarized waves can be reliably radiated from the waveguide 104 with a simple configuration.

  Note that the dimensions X, y, and z of the heating chamber 102 can be selected to generate the (odd, odd) mode, but actually, the wall surface and the top surface are uneven as shown in FIG. It is not always possible to make an accurate rectangular parallelepiped. It is also effective to use a method of estimating the unevenness to some extent and replacing it with a rectangular parallelepiped. Then, it is preferable to make fine adjustments by actually measuring the electric field strength or confirming the degree of coincidence by CAE.

  Actually, there is a food that is an object to be heated inside the heating chamber 102, and the food is generally made of a dielectric and generally has a high dielectric constant. Since it is known that the microwave wavelength appears to be compressed to the inverse of the root of the dielectric constant in the dielectric, the X, y, and z dimensions are designed to be slightly smaller assuming that. Is considered good.

  As shown in FIG. 2A, in this embodiment, the openings 105a, 105b, 105c, 105d, 105e, and 105f are not symmetrically arranged in the front-rear direction in the heating chamber 102. It is arranged slightly forward. In general, a microwave oven is a box-type structure that opens and closes by a front door 114 and puts food in and out, so that the depth is difficult to understand and even if it is placed in the center, it tends to be placed slightly in front. Also, for users who want to see the progress of cooking during heating as much as possible, they can only see the inside of the cabinet through the punching of the door, so there are times when it is going to be placed slightly in front to make it easier to see. come. Therefore, it can be heated substantially uniformly at the opening disposed slightly closer to the front as shown in FIG.

FIG. 7 is a schematic diagram for explaining an opening shape according to another embodiment of the present invention.
In particular, an aperture configured by at least two slits will be described as the shape of the aperture that radiates circularly polarized waves as the microwave radiation portion. Like the openings 411 to 417, the slits are composed of two or more slits, and the long side of at least one of these slits is inclined with respect to the microwave transmission direction (arrow line 418). Just do it. Therefore, a shape that does not intersect such as the opening 415 and the opening 416 or a shape that includes three slits such as the opening 414 may be used.

  In addition, the following 3 points | pieces are mentioned as conditions of the optimal shape of the opening comprised by two slits.

  The first point is that the length of the long side of each slit is about ¼ or more of the guide wavelength λg in the waveguide 419.

  The second point is that the two slits are orthogonal to each other and the long side of each slit is inclined 45 ° with respect to the transmission direction 418.

  The third point is that the electric field distribution is not axisymmetric when a straight line parallel to the transmission direction 418 of the waveguide 419 and passing through the center of the opening is considered as an axis. For example, in the case of transmitting microwaves in the TE10 mode, the electric field is symmetrically distributed with the tube axis 421 serving as the center line in the width direction 420 of the waveguide 419 being the axis of symmetry, so the shape of the opening is It is the best condition to arrange them so as not to be symmetric with respect to the tube axis 421 (that is, the center of the opening does not come on the tube axis 421).

  In addition, FIG. 7 shows only those in which the long holes are orthogonal, but even when the shape is such that the X shape is crushed by configuring the long holes to be inclined rather than orthogonal, they are deformed from a perfect circle. Although it becomes an ellipse, it can radiate circularly polarized waves.

  In addition, by adopting an L-shaped configuration such as the opening 413 and a T-shaped configuration such as the opening 415 in FIG. According to Patent Document 2, as shown in FIG. 9B, the two slits 3 and 4 do not have to be orthogonal but may be tilted by about 30 degrees.

  Moreover, although it is a long hole, it is not limited to a rectangle. It is possible to generate circularly polarized waves by adding an R to the corner of the opening or making it elliptical. As a basic idea of circularly polarized aperture, it is presumed that two long and narrow shapes that are longer in one direction and shorter in the perpendicular direction may be combined.

As described above, since the microwave heating apparatus of the present invention can uniformly irradiate the object to be heated with microwaves, the microwave heating apparatus can be effectively used for a microwave heating apparatus that performs heating processing or sterilization of food. Can do.

101 Microwave oven (microwave heating device)
102 Heating chamber 103 Magnetron (microwave generating means)
104 Waveguide 105a, 105b, 105c, 105d, 105e, 105f, 141, 142, 143, 411, 412, 413, 414, 415, 416, 417 Opening (microwave radiation part)
108 Heating chamber bottom surface 113a, 113b, 113c Intra-tube standing wave belly 144 In-chamber standing wave belly

Claims (6)

A heating chamber for storing an object to be heated;
Microwave generation means for generating microwaves;
A waveguide for transmitting microwaves;
A plurality of microwave radiating portions for radiating microwaves in the heating chamber;
A microwave heating apparatus having a configuration in which an antinode of a standing wave is generated in the center of the bottom of a heating chamber on which an object to be heated is placed. The chamber standing wave is a mode in which an odd number of antinodes are generated in the width direction and the depth direction of the heating chamber (odd number, odd number), thereby generating an antinode chamber standing wave in the center of the heating chamber bottom. The microwave heating apparatus according to claim 1. The microwave heating device according to claim 1 or 2, wherein an in-tube standing wave is generated in the waveguide, and at least one antinode of the in-tube standing wave is disposed to face the center of the bottom of the heating chamber. The microwave heating device according to any one of claims 1 to 3, wherein at least one of the microwave radiating portions is arranged at the center of the bottom of the heating chamber. The microwave heating device according to any one of claims 1 to 4, wherein the microwave radiating unit radiates circularly polarized waves. The microwave heating apparatus according to claim 5, wherein the microwave radiating portion that radiates circularly polarized waves has a substantially X-shaped configuration in which two long holes intersect.