JP2018152275A - Microwave heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microwave heating device capable of partially heating a part of an object to be heated when the object to be heated is heated by being irradiated with a microwave.SOLUTION: In a microwave heating device, an object 100 to be heated is heated by being irradiated with a microwave radiated from a planar antenna. In the planar antenna, a radiation electrode 120 is formed on one surface of a plate-shaped antenna substrate 140 in a square shape whose side has a length of substantially 1/4 of the wavelength λ of the microwave, and a ground electrode 130 is provided on another surface of the plate-shaped antenna substrate 140.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a microwave heating apparatus.

  A microwave heating device heats an object to be heated by placing the object to be heated in a heating chamber, irradiating the object to be heated with microwaves generated by a microwave generation source, and absorbing the object. (For example, Patent Document 1). In such a microwave heating apparatus, the microwave radiated into the heating chamber is repeatedly reflected on the wall surface of the heating chamber and is irradiated to the object to be heated.

  Generally, a magnetron, which is a kind of vacuum tube, is used as a microwave generation device in a microwave heating device. However, by using a semiconductor element instead of a magnetron, the microwave heating device is reduced in size and weight. Output controllability can be improved. As such a semiconductor element, for example, a semiconductor element using gallium nitride or the like capable of flowing a large current with a high breakdown voltage even in a high frequency region can be given.

JP 2009-16149 A JP 2016-110750 A JP 59-44794 JP 2010-92794 A

  In the microwave heating apparatus, the object is usually to uniformly heat the object to be heated, but there are cases where it is desired to heat only a part of the object to be heated. For example, when a lunch box containing food, such as salad, rice, and meat, is heated, rice and meat are desired to be heated, but the salad is not desired to be heated. In this case, if the whole lunch box is heated uniformly in the microwave heating apparatus, the salad that is not desired to be heated will be heated.

  Therefore, there is a demand for a microwave heating apparatus that can partially heat a part to be heated when the object to be heated is heated by irradiation with microwaves.

  According to one aspect of the present embodiment, a microwave heating apparatus that heats an object to be heated by irradiating the object to be heated with microwaves radiated from the planar antenna, the radiation electrode of the planar antenna Is characterized in that one side is formed in a square shape having a length substantially ¼ of the wavelength λ of the microwave.

  According to the disclosed microwave heating apparatus, when the object to be heated is irradiated with microwaves, a part of the object to be heated can be partially heated.

Explanatory drawing of patch antenna (1) Illustration of patch antenna (2) Structure diagram of microwave heating device used in the experiment Reflection characteristic diagram showing relationship between frequency obtained by experiment and reflection loss S11 Structure diagram of microwave heating apparatus in this embodiment Explanatory drawing (1) of the microwave heating apparatus in this Embodiment Explanatory drawing of the patch antenna in this embodiment Explanatory drawing of the to-be-heated material heated with the microwave heating apparatus in this Embodiment Explanatory drawing (2) of the microwave heating apparatus in this Embodiment Structure diagram of semiconductor device used for microwave heating device Explanatory drawing of the modification of the patch antenna in this Embodiment Explanatory drawing of the modification of arrangement | positioning of the patch antenna in this Embodiment

  The form for implementing is demonstrated below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

(Flat antenna)
The microwave heating device in this embodiment uses a planar antenna called a patch antenna. First, the patch antenna will be described.

  In the microwave heating apparatus, a microwave that is an electromagnetic wave having a frequency of 2.45 GHz is usually used. For example, in the case where microwaves of this frequency are freely radiated using a patch antenna, in general, a patch antenna having a square radiation electrode whose one side is λ / 2 is considered preferable from the viewpoint of efficiency.

  As shown in FIG. 1, the patch antenna 10 includes a radiating electrode 20 and a ground electrode 30, and the radiating electrode 20 is provided with a power feeding unit 21. A space may be provided between the radiation electrode 20 and the ground electrode 30, and a plate-like antenna base 40 formed of a dielectric may be provided as shown in FIG. That is, in the patch antenna shown in FIG. 2, the radiation electrode 20 is formed on one surface of the plate-shaped antenna base 40, and the ground electrode 30 is formed on the other surface.

  As shown in FIG. 2, a coaxial cable 50 is connected to the patch antenna 10, and an internal conductor of the coaxial cable 50 is connected to the power feeding portion 21 of the radiation electrode 20 to be supplied with a signal. The outer conductor is connected to the ground electrode 30 and has a ground potential. When the electromagnetic wave having the wavelength λ is radiated using this patch antenna, as described above, the shape of the radiation electrode 20 is preferably formed as a square having a side length of λ / 2. Specifically, when a microwave having a frequency of 2.45 GHz is radiated, since the wavelength λ of the microwave having a frequency of 2.45 GHz is about 122 mm, the radiation electrode 20 is about 61 mm whose one side is λ / 2. It is preferable that it is formed by a square.

  By the way, when a part of the object to be heated is partially heated, if the heated region can be set finely, only the region to be heated can be efficiently heated. Therefore, in the microwave heating apparatus, if the size of the patch antenna can be reduced, the area to be heated can be set finely, and only the area to be heated can be efficiently heated.

  Next, an experiment conducted by the inventor in a state where the patch antenna and the object to be heated are brought close to each other will be described. Specifically, as shown in FIG. 3, the patch antenna 10 is installed in the recess 61 of the bottom surface 60 a of the heating chamber 60, and the plate-like dielectric is covered so as to cover the patch antenna 10 installed in the recess 61. The body substrate 70 is installed, and the object to be heated 100 is installed on the dielectric substrate 70. The distance L1 from the radiation electrode 20 of the patch antenna 10 to the object to be heated 100 is about 15 mm, and the thickness t of the dielectric substrate 70 is about 3 mm. The radiation electrode 20 in the patch antenna 10 is formed of a square having a side of about 60 mm, and the length of one side of the square is a value corresponding to λ / 2 of 2.45 GHz.

  FIG. 4 shows reflection characteristics obtained by measuring the reflection loss S11 when an electromagnetic wave having a frequency of 1.0 GHz to 3.0 GHz is supplied to the patch antenna 10 in such an apparatus. When the electromagnetic wave is absorbed by the article to be heated 100, the electromagnetic wave that returns is reduced accordingly, so the value of S11 becomes low. Therefore, in FIG. 4, the electromagnetic wave having a frequency at which the value of S11 is low is absorbed by the article to be heated 100.

  As shown in FIG. 4, when the frequency is about 2.31 GHz, which is close to 2.45 GHz, the value of S11 is about −13.5 dB, and the electromagnetic wave of this frequency is absorbed by the object to be heated 100. . Further, even when the frequency is about 1.225 GHz, the value of S11 is about −27.5 dB, and the electromagnetic wave of this frequency is absorbed by the object to be heated 100. The value of S11 is lower for electromagnetic waves having a frequency of about 1.225 GHz than for electromagnetic waves having a frequency of about 2.31 GHz. Therefore, the electromagnetic wave having a frequency of about 1.225 GHz is larger in the object to be heated 100 than the electromagnetic wave having a frequency of about 2.31 GHz.

  By the way, 1.225 GHz is half the frequency of 2.45 GHz. Therefore, when the shape of the radiation electrode 20 of the patch antenna 10 is a half of λ / 2 with a side of 2.45 GHz, that is, a square of λ / 4 with 2.45 GHz, the object to be heated 100 has 1.225 GHz. It is presumed that 2.45 GHz electromagnetic waves that are twice as much as the above are absorbed. In other words, when the length of one side of the square of the radiating electrode of the patch antenna is half of λ / 2 of 2.45 GHz, that is, λ / 4 of 2.45 GHz, the horizontal axis shown in FIG. The value is doubled, and it is presumed that 2.45 GHz electromagnetic waves are absorbed by the object to be heated 100. As described above, by arranging the patch antenna in which the radiation electrode is formed by the square of λ / 4 having a side length of 2.45 GHz, near the object to be heated 100, the microwave of 2.45 GHz is heated. The object 100 can be efficiently absorbed and heated.

  As described above, the object to be heated 100 absorbs electromagnetic waves having a frequency in the vicinity of a wavelength twice as long as one side of the square of the radiation electrode 20 of the patch antenna 10. Electromagnetic waves with double wavelength frequencies are also absorbed. In addition, in the object to be heated 100, an electromagnetic wave having a wavelength four times the length of one side is longer than an electromagnetic wave having a frequency in the vicinity of a wavelength twice the length of one side of the square of the radiation electrode 20 of the patch antenna 10. But absorption is great.

  This is caused by bringing the distance between the patch antenna 10 and the object to be heated 100 closer than a predetermined distance. Therefore, when the distance between the patch antenna 10 and the object to be heated 100 increases, the electromagnetic wave having a wavelength four times the length of one side of the radiation electrode 20 of the patch antenna 10 is rapidly absorbed by the object to be heated 100. Disappear.

  This is because when the distance between the patch antenna 10 and the object to be heated 100 is large or small, the patch antenna 10 changes to the radiation mode, that is, the far field and the near field change to the radiation mode of the patch antenna 10. This is considered to occur. Based on the inventor's knowledge, it is considered that the radiation mode changes when the distance between the patch antenna 10 and the object to be heated 100 is 20 mm or less. This value of 20 mm corresponds to slightly less than 2λ of the wavelength λ of the microwave of 2.45 GHz, specifically about 1.6λ.

  Therefore, in this embodiment, since the size of the radiation electrode of the patch antenna can be reduced, the area to be heated in the object to be heated 100 can be set finely, and only the area to be heated is efficiently heated. be able to.

  The microwave heating apparatus in the present embodiment is based on the knowledge described above.

(Microwave heating device)
Next, the microwave heating apparatus in this Embodiment is demonstrated. The microwave heating apparatus according to the present embodiment uses a patch antenna having a square-shaped radiation electrode having a side length of λ / 4, and this patch antenna is installed near an object to be heated. As shown in FIG. 5, the microwave heating apparatus in this embodiment has a heating chamber 160 into which the object to be heated 100 is placed, and the object to be heated 100 is placed on the bottom surface 160 a of the heating chamber 160. Placed.

As shown in FIG. 6, in the microwave heating apparatus according to the present embodiment, patch antenna 110 is installed below bottom surface 160 a of heating chamber 160. In the patch antenna 110, a plurality of radiation electrodes 120 are formed on one surface of a plate-shaped antenna base 140, and a ground electrode 130 is formed on the other surface. The radiation electrode 120 and the ground electrode 130 are made of metal such as copper, and the plate-like antenna base 140 is made of a dielectric material such as alumina (Al ₂ O ₃ ) having a thickness of 100 μm to 200 μm. The plate-like antenna base 140 may be formed of a PCB (printed circuit board) having a thickness of 1 to 2 mm.

  As shown in FIG. 7, the radiation electrode 120 of the patch antenna 110 is formed by a square having a side length of λ / 4 of a microwave wavelength λ of 2.45 GHz, that is, a square of about 30 mm. The radiation electrode 120 is provided with a power feeding unit 121. In order to avoid coupling between the adjacent radiation electrodes 120, the distance between the adjacent radiation electrodes 120 is separated by 10 mm or more. Further, the length of one side of the radiation electrode 120 of the patch antenna 110 may be in the range of −5% to + 5% of λ / 4 of the wavelength λ of the microwave.

A dielectric substrate 170 is provided on the plurality of radiation electrodes 120 of the patch antenna 110, and the object to be heated 100 is placed on the dielectric substrate 170. Therefore, the surface of the dielectric substrate 170 on which the object to be heated 100 is placed becomes the bottom surface 160 a of the heating chamber 160. The dielectric substrate 170 is made of alumina (Al ₂ O ₃ ) or the like. In the present embodiment, the distance L from the plurality of radiation electrodes 120 of the patch antenna 110 to the object to be heated 100 is formed to be 20 mm or less. FIG. 6 illustrates a state in which the plurality of radiating electrodes 120 of the patch antenna 110 are in contact with the dielectric substrate 170, but the plurality of radiating electrodes 120 of the patch antenna 110 and the dielectric substrate 170 are separated from each other. A cage space may be provided.

  Next, heating of the object to be heated 100 by the microwave heating apparatus in this embodiment will be described with reference to FIG. It is assumed that the object to be heated 100 is a lunch box or the like, and contains rice, various side dishes, etc., and the temperature and the like that are appropriate for each are different. For example, the first region 100a of the object to be heated 100 is not heated, the second region 100b is slightly heated, the third region 100c is weakly heated, and the fourth region 100d is heated moderately. It is assumed that the fifth region 100e is required to be heated strongly. That is, the first region 100a of the object to be heated 100 is not heated, and the strength of the heating is such that the second region 100b <the third region 100c <the fourth region 100d <the fifth region 100e. It shall be required to be heated.

  Such an object to be heated 100 is placed on the bottom surface 160 a of the heating chamber 160 of the microwave heating apparatus in this embodiment, that is, on the dielectric substrate 170. Under the dielectric substrate 170, as shown in FIG. 9, a plurality of radiation electrodes 120 are two-dimensionally arranged. For example, in the case shown in FIG. 9, 36 pieces of 6 × 6 are provided. . A power supply unit 180 is connected to the patch antenna 110. The power supply unit 180 is provided with a microwave generation source 181 that generates a microwave of 2.45 GHz, a plurality of amplifier units 182, a control unit 183 that controls each of the amplifier units 182, and the like.

  In the power supply unit 180, the amplifier unit 182 serving as an amplifier is provided corresponding to each radiation electrode 120, and the output of the microwave supplied to each radiation electrode 120 is controlled. That is, the power supply unit 180 is provided with one amplifier unit 182 for one radiation electrode 120, and the corresponding radiation electrode 120 and the amplifier unit 182 are connected to each other and supplied to each radiation electrode 120. The microwave output is controlled. This control is performed by the control unit 183.

  When heating the object to be heated 100 shown in FIG. 8, the radiation electrode 120a prevents the microwave from being emitted from the radiation electrode 120a of the patch antenna 110 corresponding to the first region 100a of the object to be heated 100. The amplifier unit 182 connected to is controlled. Further, the amplifier unit 182 connected to the radiation electrode 120b is controlled so that the microwave is slightly emitted from the radiation electrode 120b of the patch antenna 110 corresponding to the second region 100b of the object to be heated 100. The In addition, the amplifier unit 182 connected to the radiation electrode 120c is controlled so that a weak microwave is radiated from the radiation electrode 120c of the patch antenna 110 corresponding to the third region 100c of the object to be heated 100. . In addition, the amplifier unit 182 connected to the radiation electrode 120d controls the radiation electrode 120d of the patch antenna 110 corresponding to the fourth region 100d of the object 100 to be radiated so as to emit a moderate microwave. Is done. In addition, the amplifier unit 182 connected to the radiation electrode 120e is controlled so that a strong microwave is radiated from the radiation electrode 120e of the patch antenna 110 corresponding to the fifth region 100e of the article to be heated 100. .

  By performing such control and heating the article to be heated 100, desired heating can be performed in each region of the article to be heated 100. For example, the first region 100a of the object to be heated 100 is not heated, the second region 100b is slightly heated, the third region 100c is weakly heated, and the fourth region 100d is heated moderately. Thus, the fifth region 100e can be heated strongly.

(Semiconductor elements used in power supply units)
In the present embodiment, a semiconductor element is used for the power supply unit in order to generate microwaves having a desired output. Specifically, a HEMT (High Electron Mobility Transistor) using a nitride semiconductor is used. The HEMT using a nitride semiconductor is formed by stacking a nitride semiconductor layer on a substrate 210 such as SiC as shown in FIG. That is, a buffer layer 211 made of AlN, GaN, or the like, an electron transit layer 212, and an electron supply layer 213 are sequentially stacked on the substrate 210. The electron transit layer 212 is made of GaN, and the electron supply layer 213 is made of AlGaN or InAlN. Thereby, in the electron transit layer 212, 2DEG (two dimensional electron gas) 212a is generated in the vicinity of the interface with the electron supply layer 213. The gate electrode 231, the source electrode 232, and the drain electrode 233 are formed on the electron supply layer 213.

(Modification)
In the microwave heating apparatus in this embodiment, a patch antenna in which the shape of the radiation electrode 320 as shown in FIG. 11 is a rectangle may be used. In this case, the length of one side of the rectangular radiation electrode 320, for example, the length of the short side is formed to be λ / 4. The patch antenna of the rectangular radiation electrode 320 as shown in FIG. 11 is larger than the patch antenna as shown in FIG. 7 but smaller than the patch antenna 10 shown in FIG. Can be narrowed.

  FIG. 6 shows a case where a plurality of radiation electrodes 120 are formed on one surface of one antenna base 140 and a ground electrode 130 is formed on the other surface. However, in the present embodiment, as shown in FIG. 12, a patch antenna in which one radiation electrode 120 is formed on one surface of the antenna base 140 and one ground electrode 130 is formed on the other surface is two-dimensionally formed. A plurality of structures may be provided.

  Although the embodiment has been described in detail above, it is not limited to the specific embodiment, and various modifications and changes can be made within the scope described in the claims.

In addition to the above description, the following additional notes are disclosed.
(Appendix 1)
A microwave heating apparatus that heats the object to be heated by irradiating the object to be heated with microwaves radiated from a planar antenna,
The microwave heating apparatus according to claim 1, wherein the radiation electrode of the planar antenna is formed in a square shape with one side having a length substantially ¼ of the wavelength λ of the microwave.
(Appendix 2)
A microwave heating apparatus that heats the object to be heated by irradiating the object to be heated with microwaves radiated from a planar antenna,
The microwave heating device according to claim 1, wherein the radiation electrode of the planar antenna is formed in a rectangular shape having a short side having a length substantially ¼ of the wavelength λ of the microwave.
(Appendix 3)
The microwave heating apparatus according to appendix 1 or 2, wherein a distance between the radiation electrode of the planar antenna and the object to be heated is 20 mm or less.
(Appendix 4)
The microwave according to any one of appendices 1 to 3, wherein the planar antenna has a plurality of radiation electrodes arranged two-dimensionally on one surface of a plate-shaped antenna substrate. Heating device.
(Appendix 5)
The microwave heating apparatus according to appendix 4, wherein a ground electrode is provided on substantially the entire surface of the other surface of the antenna base of the planar antenna.
(Appendix 6)
6. The microwave heating apparatus according to any one of appendices 1 to 5, wherein a dielectric substrate is installed between the radiation electrode of the planar antenna and the object to be heated.
(Appendix 7)
A power supply unit is connected to the planar antenna,
The microwave heating device according to appendix 6, wherein the power supply unit is provided with an amplifier connected to each of the radiation electrodes of the planar antenna.
(Appendix 8)
The microwave heating apparatus according to appendix 7, wherein the power supply unit includes a semiconductor element formed of a nitride semiconductor.
(Appendix 9)
A heating chamber in which the object to be heated is placed;
Part or all of the bottom surface of the heating chamber is formed by the dielectric substrate,
The object to be heated is placed on one surface of the dielectric substrate,
9. The microwave heating apparatus according to any one of appendices 6 to 8, wherein the planar antenna is installed on the other surface of the dielectric substrate.

DESCRIPTION OF SYMBOLS 10 Patch antenna 20 Radiation electrode 21 Feeding part 30 Ground electrode 40 Antenna base body 50 Coaxial cable 60 Heating chamber 60a Bottom surface 70 Dielectric substrate 100 Heated object 100a 1st area | region 100b 2nd area | region 100c 3rd area | region 100d 4th Region 100e Fifth region 110 Patch antenna 120 Radiation electrodes 120a, 120b, 120c, 120d, 120e Radiation electrode 121 Feeding portion 130 Ground electrode 140 Antenna base 160 Heating chamber 160a Bottom surface 170 Dielectric substrate 180 Power supply unit 181 Microwave generation source 182 Amplifier unit 183 controller

Claims (8)

A microwave heating apparatus that heats the object to be heated by irradiating the object to be heated with microwaves radiated from a planar antenna,
The microwave heating apparatus according to claim 1, wherein the radiation electrode of the planar antenna is formed in a square shape with one side having a length substantially ¼ of the wavelength λ of the microwave. A microwave heating apparatus that heats the object to be heated by irradiating the object to be heated with microwaves radiated from a planar antenna,
The microwave heating device according to claim 1, wherein the radiation electrode of the planar antenna is formed in a rectangular shape having a short side having a length substantially ¼ of the wavelength λ of the microwave.   The microwave heating apparatus according to claim 1 or 2, wherein a distance between the radiation electrode of the planar antenna and the object to be heated is 20 mm or less.   4. The micro of claim 1, wherein the planar antenna has a plurality of radiation electrodes arranged two-dimensionally on one surface of a plate-like antenna base. 5. Wave heating device.   The microwave heating apparatus according to claim 4, wherein a ground electrode is provided on substantially the entire surface of the other surface of the antenna base of the planar antenna.   The microwave heating apparatus according to any one of claims 1 to 5, wherein a dielectric substrate is disposed between the radiation electrode of the planar antenna and the object to be heated. A power supply unit is connected to the planar antenna,
The microwave heating apparatus according to claim 6, wherein the power supply unit is provided with an amplifier connected to each of the radiation electrodes of the planar antenna. A heating chamber in which the object to be heated is placed;
Part or all of the bottom surface of the heating chamber is formed by the dielectric substrate,
The object to be heated is placed on one surface of the dielectric substrate,
The microwave heating apparatus according to claim 6 or 7, wherein the planar antenna is installed on the other surface of the dielectric substrate.

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