JP2014044944A - Microwave heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microwave heating device capable of more uniformly heating a heated object without using a drive mechanism such as a table, an antenna and a phase shifter.SOLUTION: A waveguide 106 has a first terminal end part 107 arranged at a side close to a microwave output part 109, and a second terminal end part 108 arranged at a side distant from the microwave output part. The whole length of the waveguide 106 is set to a value obtained by adding a length of an even-number times as long as a quarter a guide wavelength in the waveguide 106 (λg/4) to a length twice as long as an interval between the first terminal end part 107 and the center of the microwave output part 109.

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 induction heating, and particularly relates to a microwave heating apparatus characterized by the structure of a microwave radiating portion.

  A typical microwave heating apparatus that heats an object using a microwave is a microwave oven. In a microwave oven, microwaves generated in a microwave generator are radiated into a metal heating chamber, and an object to be heated in the heating chamber is dielectrically heated by the radiated microwaves.

  A magnetron is used as a microwave generator in a conventional microwave oven. Microwaves generated by the magnetron are radiated into the heating chamber through the waveguide. If the electromagnetic field distribution (microwave distribution) of the microwave in the heating chamber is not uniform, the object to be heated cannot be heated by microwaves uniformly.

  As a means of uniformly heating the object to be heated inside the heating chamber, a mechanism for rotating the object to be heated by rotating the table on which the object to be heated is rotated, and an antenna for emitting microwaves by fixing the object to be heated are rotated. To be heated by changing the direction of the microwave radiated to the object to be heated using some kind of drive mechanism, such as a mechanism to change the phase of the microwave generated from the microwave generator by the phaser A method of uniformly heating an object is common.

  For example, in a conventional microwave heating apparatus, a rotatable antenna, an antenna shaft, and the like are disposed inside a waveguide. By driving the magnetron while rotating the rotating antenna by an antenna motor, a microwave in the heating chamber is obtained. It is configured to reduce the non-uniformity of the wave distribution.

  In JP-A-62-64093 (Patent Document 1), a rotating antenna is provided at the lower part of a magnetron, and cooling air from the blower fan is applied to the blades of the rotary antenna so that the fan is rotated by the wind force of the blower fan. There has been proposed a microwave heating device that rotates the antenna to change the microwave distribution in the heating chamber.

  In addition, US Pat. No. 4,301,347 (Patent Document 2) discloses a microwave heating apparatus having a rotary phase shifter and a single microwave radiating unit that radiates circularly polarized waves inside a heating chamber. Proposed.

JP 62-064093 A U.S. Pat. No. 4,301,347

  A microwave heating apparatus such as the microwave oven having the above-described conventional configuration is required to have a simple structure as much as possible, and to efficiently heat an object to be heated efficiently and uniformly. However, the conventional configurations proposed so far are not satisfactory, and have various problems in terms of efficiency and uniformity in terms of structure.

  In microwave heating devices, particularly microwave ovens, technological development for higher output has progressed, and products with a rated high-frequency output of 1000 W have been commercialized in Japan. Microwave ovens are notable for heating food by heat conduction, but the convenience of being able to heat food directly using dielectric heating is a major feature of this product. However, in a microwave oven, increasing the output in a state where non-uniform heating has not been solved has a big problem that non-uniform heating becomes more obvious.

  In the conventional configuration, the following two points are given as structural problems of the microwave heating device having a driving mechanism.

  The first point requires a drive mechanism for rotating the table or antenna in order to reduce heating unevenness. Therefore, a rotation space for the table or antenna, and a drive source such as a motor for rotating the table or antenna. It was necessary to secure an installation space for preventing the miniaturization of the microwave heating apparatus.

  The second point is that in order to rotate the antenna stably, it is necessary to provide the antenna above or below the heating chamber, which is structurally limited.

  A rotating mechanism of a table or a phaser is installed in a space where microwaves are irradiated, which leads to a heating chamber in a conventional microwave heating apparatus, and the installation of such a mechanism is a discharge phenomenon caused by microwaves. This reduces the reliability of the device. Therefore, there is a demand for a highly reliable microwave heating apparatus that eliminates these mechanisms.

  In addition, the microwave heating apparatus having a single microwave radiating unit that radiates circularly polarized waves into the heating chamber as described in Patent Document 2 has an advantage of not having a drive mechanism. There is still room for improvement in terms of heating the object to be heated more uniformly.

  The present invention solves various problems in the above-described conventional microwave heating apparatus, and an object thereof is to provide a microwave heating apparatus that can heat an object to be heated more uniformly without using a drive mechanism. And

In order to solve the problems in the conventional microwave heating apparatus, the microwave heating apparatus according to the present invention is:
A heating chamber for storing an object to be heated;
A placement section for placing the object to be heated;
A microwave generator for generating microwaves;
A waveguide for transmitting microwaves;
A microwave output unit for outputting the microwave generated from the microwave generation unit into the waveguide;
A plurality of microwave radiating portions for radiating microwaves passing through the waveguide into the heating chamber;
With
The waveguide is
A first termination located on the side near the microwave output;
A second termination located on the side far from the microwave output;
With
The total length of the waveguide is a length that is an even multiple of one-fourth of the in-tube wavelength of the waveguide, and a length that is twice the distance between the first terminal portion and the center of the microwave output portion. Is set to the length obtained by adding

  ADVANTAGE OF THE INVENTION According to this invention, the microwave heating apparatus which can heat a to-be-heated material more uniformly without using a drive mechanism can be provided.

Sectional drawing of the microwave heating apparatus of Embodiment 1 which concerns on this invention The perspective view which shows the whole structure of the microwave heating apparatus of Embodiment 1. FIG. The figure explaining the relationship between the microwave radiation | emission part in the microwave heating apparatus of Embodiment 1, a standing wave, and a microwave output part The figure explaining the relationship between the microwave radiation | emission part in the microwave heating apparatus of Embodiment 1, a standing wave, and a waveguide wall current The figure explaining the relationship between the microwave radiated | emitted from the microwave radiation | emission part in the heating apparatus of Embodiment 1 into a heating chamber, and a waveguide wall current The figure explaining the relationship between the microwave radiation | emission part in the microwave heating apparatus of Embodiment 2 which concerns on this invention, a standing wave, and a waveguide wall current The figure explaining the relationship between the microwave radiation | emission part in the 1st modification of the microwave heating apparatus of Embodiment 2, a standing wave, and a waveguide wall current The figure explaining the relationship between the microwave radiation | emission part in the 2nd modification of the microwave heating apparatus of Embodiment 2, a standing wave, and a waveguide wall current The figure explaining the example of a shape of a microwave radiation part

  A microwave heating apparatus according to the present invention includes a heating chamber that houses an object to be heated, a placement unit that places the object to be heated, a microwave generation unit that generates microwaves, and a conductor that transmits microwaves. A microwave output section for outputting a microwave generated from the microwave generation section into the waveguide, and a plurality of microwave radiation sections for radiating a microwave passing through the waveguide into the heating chamber. And the waveguide includes a first termination portion disposed on a side closer to the microwave output portion, and a second termination portion disposed on a side far from the microwave output portion. And the total length of the waveguide is an even multiple of a quarter of the in-tube wavelength of the waveguide and twice the distance between the first termination and the center of the microwave output section. The length is set by adding the length. According to this configuration, the position (waveform) of the standing wave in the waveguide can be stabilized even when an object to be heated that hardly absorbs microwaves, such as frozen foods, is heated. The same amount of microwaves can be stably emitted from the section. As a result, the object to be heated in the heating chamber can be heated more uniformly without using a drive mechanism.

  In addition, it is preferable that the plurality of microwave radiating units are arranged symmetrically on the bottom of the heating chamber in a plan view. According to this configuration, microwaves can be radiated more uniformly over the entire heating chamber, and the object to be heated in the heating chamber can be heated more uniformly without using a drive mechanism.

  Moreover, it is preferable that the center part of the bottom part of the said heating chamber is arrange | positioned in the position away from the said 2nd termination | terminus part the distance of the integral multiple of 1/4 of the said in-tube wavelength. According to this configuration, the antinode or node of the standing wave can be positioned at a position corresponding to the center portion of the bottom portion of the heating chamber, and a more uniform micrometer having symmetry with respect to the center portion of the bottom portion of the heating chamber. Wave radiation can be performed. As a result, microwaves can be emitted more uniformly over the entire heating chamber, and the object to be heated in the heating chamber can be heated more uniformly without using a drive mechanism.

  Further, the microwave radiating portion disposed closest to the second termination portion is disposed at a position away from the second termination portion by an odd multiple of a quarter of the guide wavelength. It is preferable. According to this configuration, the microwave radiating portion disposed closest to the second terminal portion is located at a position corresponding to the antinode of the standing wave generated in the waveguide. The position (waveform) of the standing wave in the tube can be further stabilized.

  Moreover, it is preferable that the said microwave radiation | emission part is comprised by the opening shape which radiates | emits a circularly polarized wave. According to this configuration, an electric field that rotates 360 degrees in all directions, which is peculiar to circularly polarized waves, is generated around the microwave radiating portion, and the microwave is radiated into the heating chamber so as to wind a vortex from the center of the microwave radiating portion. Thus, the circumferential direction can be heated more uniformly. As a result, microwaves can be emitted more uniformly to the entire heating chamber, and the object to be heated in the heating chamber can be more uniformly heated without using a drive mechanism.

  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)
FIG. 1 is a cross-sectional view of the microwave heating apparatus according to the first embodiment of the present invention.

  As shown in FIG. 1, the microwave heating apparatus according to the first embodiment mounts a casing 101, a heating chamber 103 provided in the casing 101 for storing the article to be heated 102, and the article to be heated 102. Placement unit 104, microwave generation unit 105 that generates a microwave, waveguide 106 that transmits the microwave, and a microwave that outputs the microwave generated from microwave generation unit 105 into waveguide 106 A wave output unit 109 and a plurality of microwave radiation units 110 that radiate microwaves that pass through the waveguide 106 into the heating chamber 103 are provided. The waveguide 106 includes a first terminal unit 107 disposed on the side close to the microwave output unit 109 and a second terminal unit 108 disposed on the side far from the microwave output unit 109.

  In addition, as the mounting part 104, a glass plate can be used, for example. As the microwave generation unit 105 and the microwave output unit 109, for example, a magnetron can be used.

  FIG. 2 is a perspective view showing the overall configuration of the microwave heating apparatus of the first embodiment. As shown in FIG. 2, the housing 101 is provided with a door 201 for taking the article to be heated 102 into and out of the heating chamber 103.

  Next, (1) the schematic operation of the microwave heating apparatus of the first embodiment, (2) the standing wave generated in the waveguide 106, and the overall length of the waveguide 106, (3) the waveguide (4) Microwave radiated from the microwave radiating unit 110 into the heating chamber 103 and the waveguide wall. The relationship with current will be described.

  Here, it is assumed that a rectangular waveguide most commonly used as the waveguide 106 is used. Here, it is assumed that the microwave radiating unit 110 includes an opening formed so as to communicate the inside of the heating chamber 103 and the inside of the waveguide 106.

  First, (1) the schematic operation of the microwave heating apparatus of the first embodiment will be described.

  FIG. 3 is a diagram illustrating the relationship among the microwave radiating unit, the standing wave, and the microwave output unit in the microwave heating apparatus according to the first embodiment. When the user places the object to be heated 102 on the placement unit 104 in the heating chamber 103 and gives an instruction to start heating, the microwave generation unit 105 generates microwaves. The microwave is output from the microwave output unit 109 into the waveguide 106. The microwaves are reflected by the first terminal unit 107 and the second terminal unit 108, so that the microwaves such as the standing wave 303 shown in FIG. Standing waves are generated. The standing wave functions as a microwave supply source, and the object to be heated 102 is heated by radiating the microwave into the heating chamber 103 through the microwave radiating unit 110. In the conventional general microwave heating apparatus, the end portion of the waveguide is open, and no standing wave is generated in the waveguide.

  Next, (2) standing waves generated in the waveguide 106 and setting of the total length of the waveguide 106 will be described.

  The microwave frequency is f [Hz], the vacuum dielectric constant is εo, the dielectric constant of the dielectric constituting the object to be heated 102 is εr, the electric field strength is E [V / m], and the dielectric loss angle is tan δ. Then, the electric power P per unit volume consumed by the to-be-heated material 102 is represented by the following equation (Equation 1).

  As shown in the equation (Equation 1), the electric power P is affected by the relative dielectric constant εr and the dielectric loss angle tan δ determined by the intrinsic properties of the dielectric. Whether or not the object to be heated 102, which is a dielectric material, easily absorbs microwaves can be determined by the magnitude of the dielectric loss coefficient. This dielectric loss coefficient can be calculated by the product of the relative dielectric constant εr and the dielectric loss angle tan δ, as shown in the following equation (2). The smaller the dielectric loss coefficient, the more difficult the dielectric absorbs microwaves, and the larger the dielectric loss coefficient, the easier the dielectric absorbs microwaves.

  Examples of the dielectric having a large dielectric loss coefficient include water (relative permittivity of water εr: about 80, dielectric loss angle tan δ: 0.16). When the object to be heated 102 containing a large amount of water is placed on the placement unit 104, much of the microwave output from the microwave output unit 109 is absorbed into the object to be heated 102. For this reason, the amount of microwaves reflected by the second terminal unit 108 and returning to the microwave output unit 109 is reduced. In this case, the amount of the microwave returning to the microwave output unit 109 is further reflected by the first terminal unit 107, and the standing wave generated in the waveguide 106 is reduced to the first terminal unit. There is almost no influence of the microwave reflected by 107. Therefore, each part may be designed in consideration of only the in-tube wavelength traveling in the waveguide 106.

  On the other hand, the heated object 102 such as frozen food has a small dielectric loss coefficient and hardly absorbs microwaves (relative permittivity of ice εr: 4.2, dielectric loss angle tan δ: 0.0009). When such an object to be heated 102 is placed on the placement unit 104, the microwave output from the microwave output unit 109 is not easily absorbed into the object to be heated 102 and is reflected by the second terminal unit 108. As a result, the amount returned to the microwave output unit 109 increases. In this case, the amount of the microwave returning to the microwave output unit 109 is further reflected by the first terminal unit 107, and the standing wave generated in the waveguide 106 is changed to the first terminal unit. It is affected by the microwave reflected by 107. Therefore, it is necessary to set each part in consideration of the influence of the microwave reflected by the first terminal part 107.

  In recent years, with the spread of microwave heating devices, the types of commercially available frozen foods have increased, and the frozen foods are often heated by microwave heating devices. When heating the frozen object to be heated 102, the thawed portion changes from ice to water and the dielectric loss coefficient increases. On the other hand, the part that has not been thawed remains ice and the dielectric loss coefficient does not change. For this reason, heating concentrates only on the thawed part, and the part may be overheated.

  Therefore, the present inventors diligently studied, and when the object to be heated 102 having a small dielectric loss coefficient such as frozen food and hardly absorbing microwaves is placed on the placement portion 104, the waveguide 106 has It was found that the generated standing wave has a waveform as shown in FIG. That is, the standing wave generated by the transmission of the microwave into the waveguide 106 having the first termination portion 107 and the second termination portion 108 is converted into the first termination portion 107 and the second termination portion. The amplitude is always 0 at the position of the portion 108. In other words, a node of a standing wave is always located at the first end portion 107 and the second end portion 108. When the object to be heated 102 having a small dielectric loss coefficient is placed on the placement portion 104, the standing wave generated in the waveguide 106 is a standing wave generated on the first termination portion 107 side (FIG. 3). (B) range e) and the standing wave generated on the second terminal end 108 side (range c of FIG. 3B) is a standing wave 303. Hereinafter, the boundary between the standing wave generated on the first terminal end 107 side and the standing wave generated on the second terminal end 108 side is referred to as a boundary point 304. The boundary point 304 can be confirmed by observation of the electric field intensity distribution in the waveguide 106 or an electric field intensity distribution obtained by CAE.

  Since the standing wave generated on the first terminal unit 107 side is formed by the microwave output from the microwave output unit 109 being immediately reflected by the first terminal unit 107, the microwave output unit A standing wave is generated based on the distance d between 109 and the first terminal portion 107. Further, the distance e from the first terminal portion 107 to the boundary point 304 as the first node is twice the distance d between the microwave output unit 109 and the first terminal portion 107.

  The standing wave generated on the second terminal end 108 side is formed by the microwave output from the microwave output unit 109 traveling in the waveguide 106 and reflected by the second terminal end 108. Therefore, a standing wave is generated based on the in-tube wavelength λg when traveling in the waveguide 106. Further, the distance c from the boundary point 304 to the second terminal portion 108 is an even multiple of one-fourth (λg / 4) of the wavelength of the standing wave. The in-tube wavelength λg of the microwave transmitted into the waveguide 106 is λ (λ = (speed of light) / (oscillation frequency)) output from the microwave generation unit 105, and the cutoff wavelength of the waveguide 106. Is λc (λc = 2 × a: a is the waveguide width), it is expressed by the following equation (Equation 3).

  Theoretically, the standing wave generated on the second terminal end 108 side has various lengths c obtained by dividing the length c from the microwave output unit 109, which is a microwave generation source, to the second terminal end 108 by a natural number. Can take a wavelength. In particular, in the inside of the waveguide 106 in the range c of FIG. 3B, the wavelength of the standing wave may fluctuate when microwaves are radiated from the microwave radiating unit 110 into the heating chamber 103. Can happen. That is, the positions of antinodes and nodes of standing waves generated in the waveguide 106 may be unstable and fluctuate. In this case, it is difficult to stably radiate an equivalent amount of microwaves from each microwave radiation unit 110. In FIG. 3, a dotted line 301 indicates the position of the antinode of the standing wave.

  In order to stabilize the position (waveform) of the standing wave generated in the waveguide 106, each part is designed based on the in-tube wavelength λg in which the microwave transmitted in the waveguide 106 is naturally present. Is considered good. That is, it is considered that each part should be designed on the assumption that the wavelength of the microwave transmitted in the waveguide 106 and the wavelength of the standing wave generated in the waveguide 106 are the same wavelength. In this case, even when microwaves are radiated from the microwave radiation unit 110 into the heating chamber 103, the position (waveform) of the standing wave generated in the waveguide 106 can be stabilized. An equal amount of microwaves can be stably emitted from the radiating unit 110.

  For the reason described above, in the first embodiment, the total length of the waveguide 106 (the length from the first termination portion 107 to the second termination portion 108) is set to 4 of the in-tube wavelength of the waveguide 106. The length is set to a length obtained by adding an even multiple of 1 / (λg / 4) and a length twice as long as the distance between the first termination portion 107 and the center of the microwave output portion 109. As a result, the position (waveform) of the standing wave in the waveguide 106 can be stabilized even when the object to be heated 102 having a small dielectric loss coefficient such as frozen foods and hardly absorbing microwaves is heated. Thus, it is possible to stably emit an equal amount of microwaves from each microwave radiation unit 110.

  In the case where the attachment state of the microwave generation part 105 and the state of the first terminal part 107 and the second terminal part 108 are not ideal, the in-tube wavelength λg in the waveguide 106 is Deviations from values calculated based on the formula can occur. In this case, the in-tube wavelength λg may be determined by actually measuring the amplitude of the electric field in the waveguide 106.

  Next, (3) the waveguide wall current flowing in the waveguide 106 when a standing wave is generated in the waveguide 106 will be described.

  FIG. 4 is a diagram for explaining the relationship among the microwave radiating portion, the standing wave, and the waveguide wall current. As shown in FIG. 4A, the waveguide wall current flowing in the waveguide 106 when the standing wave 303 is generated in the waveguide 106 is the current of the antinode of the standing wave 303. It becomes the point of flowing out and flowing in. As shown in FIG. 4B and FIG. 4C, the waveguide wall current flows between the antinodes of the standing waves 303 adjacent to each other and passes through the side wall of the waveguide 106. And flows between the surface on which the microwave radiating unit 110 is disposed and the opposite surface. The amplitude of the standing wave 303 at the antinode changes so as to alternately repeat the maximum value and the minimum value. When the amplitude at the antinode of the standing wave 303 changes from the maximum value to the minimum value, or from the minimum value to the maximum value, the waveguide wall current is as shown in FIG. 4B and FIG. In addition, the flow direction is reversed.

  Next, (4) the relationship between the microwave radiated from the microwave radiation unit 110 into the heating chamber 103 and the waveguide wall current will be described.

  FIG. 5 is a diagram for explaining the relationship between the microwave radiated from the microwave radiation unit 110 into the heating chamber 103 and the waveguide wall current. As shown in FIG. 5A, a standing wave 303 is generated in the waveguide 106, and as shown in FIG. 5B, a microwave is used to block the current 502, which is a waveguide wall current. In the case where the opening 501 is provided as the radiating portion 110, as shown in FIG. 5C, an electric field 503 generated when the current 502 is blocked by the opening 501 and a magnetic field 504 below the opening 501. Microwaves are radiated in the microwave radiation direction 505 (that is, in the heating chamber 103) orthogonal to. The waveguide wall current flows in a direction orthogonal to the magnetic field.

  As described above, in the first embodiment, the total length of the waveguide 106 is set to an even multiple of ¼ (λg / 4) of the in-tube wavelength of the waveguide 106, and the first termination portion 107. And a length twice as long as the distance between the center of the microwave output unit 109 and the center of the microwave output unit 109. According to this configuration, the position (waveform) of the standing wave in the waveguide 106 is stabilized even when the object to be heated 102 that has a small dielectric loss coefficient such as frozen food and does not easily absorb microwaves is heated. Therefore, an equivalent amount of microwaves can be stably emitted from each microwave radiation unit 110. As a result, the object to be heated 102 in the heating chamber 103 can be heated more uniformly without using a driving mechanism.

  In addition, it is preferable that the plurality of microwave radiating units 110 be arranged symmetrically on the bottom of the heating chamber 103 in plan view. According to this configuration, microwaves can be radiated more uniformly over the entire heating chamber 103, and the object to be heated 102 in the heating chamber 103 can be heated more uniformly without using a drive mechanism.

  Moreover, it is preferable that the plurality of microwave radiating portions 110 are arranged in line symmetry (front-rear symmetry) with respect to the central axis of the waveguide 106 parallel to the microwave transmission direction 302 in plan view. According to this configuration, microwaves can be radiated more uniformly over the entire heating chamber 103, and the object to be heated 102 in the heating chamber 103 can be heated more uniformly without using a drive mechanism. Further, in this case, by configuring the center of the bottom of the heating chamber 103 to be located on the central axis of the waveguide 106, the symmetry of the arrangement of the microwave radiating unit 110 is improved, and the inside of the heating chamber 103 is increased. The object to be heated 102 can be heated more uniformly. In addition, when the position recommended for placing the article to be heated 102 is a position away from the center of the bottom of the heating chamber 103 due to the uneven structure inside the heating chamber 103 or the convenience of the user, The position deviated from the center of the bottom of the heating chamber 103 may be used as a reference for the symmetrical arrangement of the microwave radiating unit 110.

  Moreover, it is preferable that the center part of the bottom part of the heating chamber 103 is disposed at a position away from the second terminal part 108 by a distance that is an integral multiple of one-fourth of the guide wavelength (λg / 4). According to this configuration, the antinode or node of the standing wave can be positioned at a position corresponding to the central portion of the bottom of the heating chamber 103, and is more uniform with symmetry with respect to the central portion of the bottom of the heating chamber 103. Microwave radiation can be performed. As a result, microwaves can be emitted more uniformly over the entire heating chamber 103, and the article to be heated 102 in the heating chamber 103 can be heated more uniformly without using a drive mechanism.

  In addition, the microwave radiating unit 110 disposed closest to the second termination unit 108 is disposed at a position away from the second termination unit 108 by an odd multiple of a quarter of the guide wavelength. It is preferable. According to this configuration, the microwave radiating portion 110 disposed closest to the second terminal portion 108 is located at a position corresponding to the antinode of the standing wave generated in the waveguide 106. Thus, the position (waveform) of the standing wave in the waveguide 106 can be further stabilized.

(Embodiment 2)
Hereinafter, a microwave heating apparatus according to a second embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 6 is a diagram for explaining the relationship among the microwave radiating section, the standing wave, and the waveguide wall current in the microwave oven that is the microwave heating apparatus according to the second embodiment of the present invention. The microwave oven of the second embodiment is different from the microwave oven of the first embodiment in that the microwave radiating unit 110 is configured with an opening shape that radiates circularly polarized waves.

  In the second embodiment, the microwave radiating section 110 is configured in an X-shaped opening shape in which two elongated rectangular long holes (slits) intersect each other at the center point. In addition, the two long holes are inclined by 45 degrees with respect to the microwave transmission direction 302 and are provided so as not to intersect the central axis of the waveguide 106 parallel to the microwave transmission direction 302. By configuring the microwave radiating unit 110 in this way, the microwave is radiated into the heating chamber 103 as circularly polarized waves.

  Circular polarization is a technique 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 of the radio wave, and when the circular polarization is formed, the direction of the electric field continues to change with time. The radiation angle of the microwave radiated into the inside continues to change, and the electric field strength does not change with time. Due to this feature, the microwave heating according to the second embodiment having a microwave radiating unit that radiates circularly polarized waves is compared with microwave heating by linearly polarized waves used in conventional microwave heating devices. Microwaves are dispersed and radiated over a wide range, and the object to be heated can be heated more uniformly. In particular, there is a strong tendency for uniform heating in the circumferential direction of circular polarization. Note that circularly polarized waves are classified into two types, that is, right-handed polarization (CW: clockwise) and left-handed polarization (CCW: counterclockwise) from the direction of rotation, but there is no difference in heating performance.

  As described above, in the second embodiment, the microwave radiating unit 110 is configured to have an aperture shape that radiates circularly polarized waves. The microwave is radiated into the heating chamber 103 so as to wind a vortex from the center of the microwave radiating unit 110, and the circumferential direction can be more uniformly heated. As a result, microwaves can be emitted to the entire heating chamber 103, and the object to be heated 102 in the heating chamber 103 can be more uniformly heated without using a driving mechanism.

  When the object to be heated 102 having a small dielectric loss coefficient is placed on the placement unit 104, a standing wave 303 is normally generated in the induction wave tube 106, but from the microwave radiation unit 110 to the heating chamber 103. When microwaves are radiated in, standing wave 303 may be out of balance. In this case, a traveling wave is generated from when the balance is lost until it returns to the stable standing wave 303 again. Even in such a case, the microwave radiation unit 110 is configured to radiate circularly polarized waves, so that the microwave is radiated into the heating chamber 103 so as to vortex from the center of the microwave radiation unit 110. Thus, the object to be heated 102 in the heating chamber 103 can be heated more uniformly.

  In addition, this invention is not limited to the said embodiment, It can implement in another various aspect. For example, in the second embodiment, as shown in FIG. 6, the plurality of microwave radiating units 110 are arranged symmetrically in the left-right direction and in the front-rear symmetry (symmetric with respect to the depth direction). Is not limited to this. For example, as illustrated in FIG. 7, the plurality of microwave radiating units 110 may be disposed asymmetrically in the front-rear direction (asymmetric with respect to the depth direction).

  In the second embodiment, as shown in FIG. 6, all of the plurality of microwave radiating units 110 are arranged at positions facing the antinodes of the standing wave, but the present invention is not limited to this. . For example, as shown in FIG. 8, a part of the plurality of microwave radiating units 110 may be disposed at a position facing a portion deviated from the antinode of the standing wave. Further, as shown in FIG. 8, the intervals between the microwave radiating portions 110 may not be equal.

  Moreover, in the said Embodiment 2, although X shape as shown in FIG. 6 was mentioned as an example as opening shape of the microwave radiation | emission part 110 which radiates | emits a circularly polarized wave, this invention is not limited to this. For example, the microwave radiation | emission part 110 may be comprised by the opening 411-417 of a shape as shown in FIG. In other words, the microwave radiating unit 110 may include at least two long holes and be configured such that the longitudinal direction of at least one long hole is inclined with respect to the microwave transmission direction 418. Further, the at least two long holes constituting the microwave radiating unit 110 may be arranged so that their longitudinal directions intersect like the openings 415 and 416 and do not need to be connected to each other. Further, the shape of the elongated hole is not limited to a rectangle, and may be a shape obtained by rounding a rectangular corner (R shape) or an elliptical shape.

  Since the microwave heating apparatus of the present invention can uniformly radiate microwaves to the object to be heated, it is effective for a heating apparatus that performs heating processing and sterilization of an object to be heated that hardly absorbs microwaves such as frozen foods. Can be used.

DESCRIPTION OF SYMBOLS 101 Case 102 Object to be heated 103 Heating chamber 104 Placement part 105 Microwave generation part 106 Waveguide 107 First termination part 108 Second termination part 109 Microwave output part 110 Microwave radiation part 201 Door 301 Standing Wave antinode 302 Microwave transmission direction 303 Standing wave 304 Boundary point 501 Opening 502 Current (waveguide wall current)
503 Electric field 504 Magnetic field 505 Microwave radiation direction

Claims (5)

A heating chamber for storing an object to be heated;
A placement section for placing the object to be heated;
A microwave generator for generating microwaves;
A waveguide for transmitting microwaves;
A microwave output unit for outputting the microwave generated from the microwave generation unit into the waveguide;
A plurality of microwave radiating portions for radiating microwaves passing through the waveguide into the heating chamber;
With
The waveguide is
A first termination located on the side near the microwave output;
A second termination located on the side far from the microwave output;
With
The total length of the waveguide is a length that is an even multiple of one-fourth of the in-tube wavelength of the waveguide, and a length that is twice the distance between the first terminal portion and the center of the microwave output portion. A microwave heating device set to a length obtained by adding   The microwave heating device according to claim 1, wherein the plurality of microwave radiating portions are arranged symmetrically on a bottom portion of the heating chamber in a plan view.   3. The microwave heating apparatus according to claim 1, wherein a center portion of a bottom portion of the heating chamber is disposed at a position away from the second terminal portion by a distance that is an integral multiple of a quarter of the guide wavelength.   The microwave radiating portion disposed closest to the second termination portion is disposed at a position away from the second termination portion by an odd multiple of a quarter of the guide wavelength. Item 3. The microwave heating apparatus according to Item 1 or 2.   The microwave heating device according to claim 1, wherein the microwave radiating unit is configured in an opening shape that radiates circularly polarized waves.

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