JP2020013761A - Electromagnetic wave heating device - Google Patents

Abstract

To improve the efficiency of heating by electromagnetic waves in an electromagnetic wave heating device that dielectrically heats an object to be heated using electromagnetic waves.SOLUTION: An electromagnetic wave heating device 10 includes a heating chamber 12 in which an object to be heated 1 is placed, a first side surface antenna 22 disposed on a first inner side surface of the heating chamber 12, a second side surface antenna 23 disposed on a second inner side surface facing the first inner side surface in the heating chamber 12, and oscillating devices 16b and 16c that oscillate electromagnetic waves with which the heating chamber 12 is irradiated for each of the first side surface antenna 22 and the second side surface antenna 23. The electromagnetic wave heating device 10 is configured such that the first side surface antenna 22 has directivity on the bottom side of the heating chamber 12.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electromagnetic wave heating device that performs dielectric heating of an object to be heated using electromagnetic waves.

  2. Description of the Related Art Conventionally, various developments have been made in an electromagnetic wave heating device such as a microwave oven in order to improve the heating efficiency of a heating object.

  Patent Literature 1 describes an electromagnetic wave heating device provided with a planar antenna provided on a wall surface of a heating chamber. In this device, the planar antenna includes a plurality of small antennas arranged in an array. The control device detects the shape or temperature distribution of the object to be heated based on the reflected power generated when radiating electromagnetic waves from the plurality of small antennas, and feeds each of the plurality of small antennas based on the detection result. Determine the size of the microwave to be applied.

International Publication No. WO 2017/022271

  By the way, in the conventional electromagnetic wave heating device, there is a possibility that mutual electromagnetic waves may interfere with each other between the antennas facing each other. That is, the energy of the electromagnetic wave radiated from one of the antennas facing each other is easily received by the other antenna and consumed by the transmission line of that antenna. Therefore, there is a possibility that the heating efficiency due to the electromagnetic wave is reduced.

  The present invention has been made in view of such circumstances, and an object of the present invention is to improve the efficiency of heating by electromagnetic waves in an electromagnetic wave heating device that dielectrically heats an object to be heated using electromagnetic waves.

  In order to solve the above-mentioned problems, a first invention is an electromagnetic wave heating device that heats an object to be heated by using an electromagnetic wave, wherein a heating chamber in which the object to be heated is arranged, and a first inner surface in the heating chamber A first side surface antenna disposed on the second side surface antenna disposed on the second inner side surface facing the first inner side surface in the heating chamber, and a heating chamber for each of the first side surface antenna and the second side surface antenna. And an oscillating device that oscillates electromagnetic waves radiated to the heating chamber. The electromagnetic wave heating apparatus is configured such that the first side antenna has directivity on the bottom side of the heating chamber.

  In a second aspect based on the first aspect, the directivity of the second side antenna is lower than that of the first side antenna. In a third aspect based on the first or second aspect, the first side surface antenna is formed in a plate shape, and the first side surface antenna is disposed in a concave portion of the first inner side surface in the heating chamber. Assuming that the wavelength of the electromagnetic wave supplied to the one-side antenna is λ, when viewed from the front of the first-side antenna, the lower portion of the outer periphery of the first-side antenna has a distance of λ / It is 10 or more and λ / 4 or less. In a fourth aspect based on any one of the first to third aspects, in the first side surface antenna, an input terminal of an electromagnetic wave is disposed at a lower portion, and a hole constituting a resonator is provided above the input terminal. Is formed. In a fifth aspect based on any one of the first to fourth aspects, the outer periphery of the first side surface antenna has a lower straight portion and an arc portion extending upward from the straight portion in an arc shape. .

  In the present invention, the first side surface antenna and the second side surface antenna are disposed on the first inner surface and the second inner surface facing each other. The electromagnetic wave heating device is configured such that the first side antenna has directivity on the bottom side of the heating chamber. Therefore, the electromagnetic wave radiated from the first side antenna is less likely to be received by the second side antenna, and the heating efficiency by the electromagnetic wave can be improved.

FIG. 1 is a schematic configuration diagram showing a longitudinal section and the like of the electromagnetic wave heating device according to the present embodiment. FIG. 2 is a top view of the bottom of the heating chamber of the electromagnetic wave heating device from which the bottom surface with the shielding plate removed is viewed from directly above. FIG. 3 is a front view of the right side surface of the heating chamber of the electromagnetic wave heating device from which the shielding plate is removed, as viewed from the front. FIG. 4 is a front view of the left side surface of the heating chamber of the electromagnetic wave heating device from which the shielding plate is removed, as viewed from the front. FIG. 5 is a block diagram of a control system of the electromagnetic wave heating device. FIG. 6 is an example of a graph showing the frequency characteristics of the reflected wave intensity of the microwave at each antenna. FIG. 7 is another example of a graph showing the frequency characteristic of the reflected wave intensity of the microwave at each antenna.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. The following embodiment is an example of the present invention, and is not intended to limit the scope of the present invention, its application, or its use.

[Schematic configuration of electromagnetic wave heating device]
The electromagnetic wave heating device 10 according to the present embodiment is a microwave oven that dielectrically heats an object to be heated 1 such as a food. As shown in FIG. 1, the electromagnetic wave heating device 10 includes a box-shaped member 14 that forms a heating chamber 12 in which the heating target 1 is arranged, a plurality of oscillators 16a to 16c that oscillate microwaves, and oscillators 16a to 16c. A plurality of antennas 21 to 23 provided for each of the oscillators 16a to 16c and radiating microwaves radiated from the oscillators 16a to 16c to the heating chamber 12, and a plurality of antennas provided for each of the oscillators 16a to 16c from the oscillators 16a to 16c to the antennas 21 to 23. It has a plurality of transmission lines 18a to 18c for transmitting waves. Each of the antennas 21 to 23 is formed of a conductive metal plate, and is arranged at a position facing the heating chamber 12.

  In this embodiment, the electromagnetic wave heating device 10 includes three microwave oscillators of a first oscillator 16a, a second oscillator 16b, and a third oscillator 16c. A first antenna 21 and a first transmission line 18a are provided for the first oscillator 16a, a second antenna 22 and a second transmission line 18b are provided for the second oscillator 16b, and a third antenna 16c is provided for the third oscillator 16c. An antenna 23 and a third transmission line 18c are provided.

  The box-shaped member 14 is a substantially rectangular box whose front side is open. The front side of the box-shaped member 14 is closed by an opening / closing door 30 (see FIG. 2 and the like) attached to a housing described later. In the box-shaped member 14, concave portions 14a to 14c serving as accommodation rooms for the antennas 21 to 23 are formed on the bottom surface and the left and right side surfaces. The concave portion 14a on the bottom surface serves as an accommodation room for the first antenna 21. The concave portion 14b on the right side surface is an accommodation room for the second antenna 22. The concave portion 14c on the left side surface is a housing room for the third antenna 23. The left and right sides of the electromagnetic wave heating device 10 refer to the directions viewed from the front side.

  The recesses 14a to 14c are covered by shield plates 15a to 15c made of an insulator that transmits microwaves (for example, an insulator having heat resistance such as ceramics) so that the antennas 21 to 23 cannot be seen from the heating chamber 12 side. Is peeling. The heating chamber 12 is a substantially rectangular parallelepiped space formed inside the shielding members 15a to 15c that close the recesses 14a to 14c in the box-shaped member 14. The bottom surface of the heating chamber 12 (the upper surface of the shielding plate 15a) serves as a mounting table 13 on which the object to be heated 1 is placed.

  The box-shaped member 14 is made of a material (metal or the like) that reflects microwaves. The box-shaped member 14 is provided in a housing (not shown) serving as an exterior of the electromagnetic wave heating device 10. On the front surface of the housing, an opening / closing door 30 for taking the object 1 to be heated into and out of the heating chamber 12 is provided. The inner surface of the door 30 is processed to reflect microwaves. The heating chamber 12 is defined by six surfaces that reflect microwaves. In the heating chamber 12, a unique electromagnetic field distribution is generated due to reflection of microwaves or the like.

  The concave portions 14b and 14c on each side surface of the box-shaped member 14 are formed in a substantially rectangular shape when viewed from the front (see FIGS. 3 and 4). Each of the recesses 14b and 14c is a truncated quadrangular pyramid-shaped depression, and extends toward the heating chamber 12 in a longitudinal sectional view in FIG. Each of the recesses 14b and 14c has a length on one side of the bottom surface of one wavelength or more and a depth (corresponding to the height of the truncated pyramid) within a range from a quarter wavelength to a sixteenth wavelength. Designed. The wavelength here is the electrical length at the antennas 22 and 23 provided in the respective recesses 14b and 14c.

  The first antenna 21 corresponds to a bottom antenna disposed on the bottom of the heating chamber 12. The first antenna 21 is arranged in the recess 14 a of the box-shaped member 14 on the bottom surface of the heating chamber 12 behind the mounting table 13 (mounting area of the object to be heated). The first antenna 21 is provided substantially parallel to the shielding plate 15a. The outer peripheral shape of the first antenna 21 is substantially circular as shown in FIG. An input terminal 51 is attached to the center of the first antenna 21. Details of the first antenna 21 will be described later. The outer peripheral shape of the first antenna 21 may be other than a substantially circular shape.

  The second antenna 22 corresponds to a first side antenna disposed on a first inner side surface (right side surface) of the heating chamber 12. The second antenna 22 is disposed inside the recess 14b of the box-shaped member 14 behind the shielding plate 15b. The second antenna 22 is provided substantially parallel to the shielding plate 15b. As shown in FIG. 3, the second antenna 22 is formed in a substantially fan-shaped plate shape (specifically, a substantially semi-circular plate shape). An input terminal 52 is attached to a lower part of the second antenna 22. Details of the second antenna 22 will be described later. The second antenna 22 may have a shape other than a substantially fan-shaped plate.

  The third antenna 23 corresponds to a second side surface antenna disposed on a second inner side surface (left side surface) facing the first inner side surface in the heating chamber. The third antenna 23 is arranged in the recess 14c of the box-shaped member 14 on the back side of the shielding plate 15c. The third antenna 23 is provided substantially parallel to the shielding plate 15c. As shown in FIG. 4, the third antenna 23 is formed in a horizontally elongated substantially rectangular shape. An input terminal 53 is mounted below the third antenna 23. Details of the third antenna 23 will be described later. Note that the third antenna 23 may have a shape other than a horizontally long substantially rectangular shape.

  Each of the oscillators 16a to 16c is a variable frequency semiconductor oscillator using a power semiconductor device (not shown) as a microwave oscillation source. Each of the oscillators 16a to 16c can oscillate a microwave while repeatedly sweeping the oscillation frequency at a high speed in a predetermined frequency band (hereinafter, referred to as a "sweepable range"). For example, in the three oscillators 16a to 16c, the sweepable range of the oscillation frequency of the microwave is the same. The sweepable range is, for example, a range from 2.35 GHz to 2.55 GHz. The first oscillator 16a constitutes a bottom-side oscillator. The second oscillator 16b constitutes a first side oscillator. The third oscillator 16c constitutes a second side oscillator.

  Each of the transmission lines 18a to 18c is constituted by a coaxial cable capable of transmitting microwaves. The first transmission line 18a has one end connected to the output terminal of the first oscillator 16a and the other end connected to the input terminal 51 of the first antenna 21. The second transmission line 18b has one end connected to the output terminal of the second oscillator 16b and the other end connected to the input terminal 52 of the second antenna 22. The third transmission line 18c has one end connected to the output terminal of the third oscillator 16c and the other end connected to the input terminal 53 of the third antenna 23.

[About the first antenna]
The first antenna 21 is formed in a substantially disk shape. The first antenna 21 has an input terminal 51 to which the microwave from the first oscillator 16a is input. As shown in FIG. 2, the input terminal 51 is arranged at a center position of the first antenna 21. In the first antenna 21, a plurality of main holes 32 (four main holes 32 in the present embodiment) having different resonance frequencies are formed around the input terminal 51. The plurality of main holes 32 are formed point-symmetrically about the input terminal 51. Each main hole 32 is for adjusting a capacitive reactance indicating a relationship between a voltage phase and a current phase.

  In the first antenna 21, a plurality of outer holes 31 (in the present embodiment, a plurality of outer holes 31 that hinder microwave transmission to the outer peripheral side of the first antenna 21) so as to surround the outside of the region where the plurality of main holes 32 are formed. , Eight outer holes 31). The plurality of outer holes 31 are formed at equal angular intervals along the circumferential direction. The plurality of outer holes 31 are substantially equal in distance from the center of the first antenna 21. The shape of each outer hole portion 31 is formed in a substantially fan shape (a donut-shaped fan shape) from which an inner portion is removed. The distance between the outer holes 31 adjacent in the circumferential direction is a distance that maintains high electrical conductivity and structural strength, and can be 3 to 5 times the plate thickness (for example, 3 to 5 mm).

  In the present embodiment, when a microwave is input from the input terminal 51, the main radiation area 21 a that radiates the microwave toward the bottom surface of the heating chamber 12 inside the plurality of outer holes 31 in the first antenna 21. Is formed. In the main radiation region 21a, the vicinity of the center of the radius of the main radiation region 21a (the vicinity of the center between the center and the outer periphery of the main radiation region 21a) is a strong electric field region in the circumferential direction. In the main radiation region 21a, a plurality of main holes 32 are formed in the strong electric field region along the circumferential direction.

  In the main radiation area 21a, a plurality of sub-holes 33 (four sub-holes 33 in the present embodiment) are formed radially from the center in the radial direction. In the main radiation area 21a, one sub-hole 33 is formed between a plurality of main holes 32 adjacent in the circumferential direction. Each sub-hole 33 is formed for impedance matching of a microwave in the first antenna 21. The shape of each sub-hole 33 is a substantially rectangular shape or a substantially elliptical shape with four rounded corners. Each sub-hole 33 extends along the radial direction of the first antenna 21. Each sub-hole 33 has an inner end located inside an inner peripheral portion 32 a (described later) of the main hole 32, and an outer end located outside an outer peripheral portion 32 b (described later) of the main hole 32.

The radius r ₁ of the first antenna 21 is represented by α × λ (α = a value in the range of 1/2 to 3/4), where λ is the electrical length of the microwave in the first antenna 21. You. Radius r ₁ of the first antenna 21 is based on the electrical length in consideration of the electromagnetic field distribution rather than a geometrical dimensions. For example, when the center value of the sweepable range is 2.45 GHz, λ is about 120 mm, and the radius r ₁ of the first antenna 21 is a value in a range of 60 mm to 90 mm. Incidentally, the radius r ₁ is not limited to this length.

  The shape and function of the main hole 32 will be described. The magnified view of the main hole 32 is shown in the lower left wavy line in FIG. The shape of each main hole 32 is substantially a fan shape excluding an inner portion unless there is a convex portion 35 described later. The central angle of each main hole 32 is approximately 90 degrees. The outer periphery of each main hole 32 has an inner periphery 32a, an outer periphery 32b facing the inner periphery 32a, and two connection diameter portions 32c. In each main hole 32, a substantially rectangular convex portion 35 projects inward from the outer peripheral portion 32b. When viewed from the front of the first antenna 21, each main hole 32 is formed with a convex portion 35 that is bent so that the outer periphery of the main hole 32 projects inward toward the input terminal 51. At 32, the protrusion 35 performs the function of tuning the resonance frequency.

  In the first antenna 21, the plurality of main holes 32 are formed such that the resonance frequencies are different from each other. In each main hole 32, the resonance frequency is determined mainly by the capacitance component at the tip of the convex portion 35 and the induced current obtained on the outer periphery of the main hole 32. For example, the plurality of main holes 32 have the same shape, but different sizes, and different peripheral lengths. In the plurality of main holes 32, the lengths and widths of the protrusions 35 are different from each other. Each projection 35 matches the eigenmode (standing wave) of the box-shaped member 14 with the resonance frequency of each main hole 32. Regarding the dimensions of the main hole 32, for example, the outer circumference of the main hole 32 is λ / 2 (40 to 60 mm), the width S of the projection 35 is about 1/3 of the length W of the outer periphery 32 b, The length (projection length) of 35 can be λ / 8 (10 to 15 mm). Here, λ is the electrical length of the microwave at the first antenna 21.

  In the first antenna 21, the outer periphery of each main hole 32 becomes a microwave transmission line. Each of the main holes 32 can excite a unique mode (standing wave) in accordance with a change in the frequency of the applied microwave, in the presence of many unique modes (standing waves) in the box-shaped member 14. . When the frequency of the microwave input from the input terminal 51 changes, each main hole 32 has an electrical length λ of the microwave (current) flowing on the outer circumference of λ / 2 with respect to the outer circumference of the main hole 32. Resonates at the timing of an integral multiple. In the heating chamber 12, since the electric field effectively rises from the main hole 32 resonating with the microwave, the position of the strong electric field region changes according to the change of the main hole 32 resonating with the microwave. Thus, in the present embodiment, the strong electric field region changes on the mounting table 13 of the heating chamber 12 without rotating the first antenna 21. Thereby, the heating distribution in the heating target 1 can be made uniform.

[About the second antenna]
As shown in FIG. 3, the second antenna 22 is formed in a substantially fan shape (specifically, a substantially semicircular shape). Specifically, the second antenna 22 includes a main body 22a formed in a fan shape (semicircular shape), and a long plate-shaped lower portion 22b continuous below the main body 22a. The second antenna 22 has a substantially semicircular shape, but, more precisely, has a shape in which a lower portion 22b having a low height is added to a semicircular main body portion 22a. In FIG. 3, the boundary between the main body 22a and the lower part 22b is indicated by a dotted line. Further, the second antenna 22 has an input terminal 52 to which the microwave from the second oscillator 16b is input. The input terminal 52 is arranged at a center position of the main body 22a.

  The second antenna 22 differs from the first antenna 21 in that, in addition to the fact that the planar shape is substantially fan-shaped, the second antenna 22 does not include the outer hole 32. When a microwave is input from the input terminal 52, the vicinity of the center of the radius of the second antenna 22 (the vicinity of the center between the center and the outer periphery) is a strong electric field region in the circumferential direction. In the second antenna 22, a plurality of main holes 42 (two main holes 42 in the present embodiment) are formed in the strong electric field region along the circumferential direction.

  In the second antenna 22, a plurality of sub-holes 43 (three sub-holes 43 in the present embodiment) are formed radially from the center in the radial direction. In the present embodiment, one sub-hole 43 is formed between two main holes 42 and below each main hole 42. Each sub-hole 43 is formed for impedance matching of microwaves in the second antenna 22. The shape of each sub-hole 43 is a substantially rectangular shape or a substantially elliptical shape with four rounded corners. Each sub-hole 43 extends along the radial direction of the main body 22a. Each sub-hole 43 has an inner end located inside an inner peripheral portion 42 a (described later) of the main hole 42 and an outer end located outside an outer peripheral portion 42 b (described below) of the main hole 42.

The radius r ₂ of the main body portion 22a in the second antenna 22 is α × λ (α = 1/2 to 3/4, where λ is the electrical length of the microwave in the second antenna 22). ). Radius r ₂ of the second antenna 22 is based on the electrical length in consideration of the electromagnetic field distribution rather than a geometrical dimensions. For example, if the median of the sweep range is 2.45 GHz, lambda is 120 mm, the radius _{r 2} of the main body portion 22a has a value in the range of 60Mm～90mm. Incidentally, the radius r ₂ is not limited to this length.

  The shape and function of the main hole 42 will be described. The magnified view of the main hole 42 is shown in the lower left wavy line in FIG. As in the case of the main hole 32, the shape of each main hole 42 is substantially a fan shape excluding an inner portion unless there is a protrusion 36 described later. The central angle of each main hole 42 is approximately 90 degrees. The outer periphery of each main hole 42 has an inner periphery 42a, an outer periphery 42b facing the inner periphery 42a, and two connection diameter portions 42c. In each main hole portion 42, a substantially rectangular convex portion 36 projects inward from the outer peripheral portion 42b. Each main hole 42 has a convex portion 36 that is bent so that the outer periphery of the main hole 42 projects inward toward the input terminal 52 in a front view of the second antenna 22. In each main hole 42, the convex portion 36 has a function of tuning the resonance frequency. The length of the convex portion 36 is, for example, approximately half the distance between the inner peripheral portion 42a and the outer peripheral portion 42b.

  The second antenna 22 is formed so that the resonance frequencies of the plurality of main holes 42 are equal to each other. The plurality of main holes 42 have the same shape and the same size. In the plurality of main holes 42, the length and the width of the protrusion 36 are the same. Each of the main holes 42 can excite a unique mode (standing wave) in accordance with a change in the frequency of the applied microwave, in the presence of many unique modes (standing waves) in the box-shaped member 14. . Further, each convex portion 36 matches the eigenmode (standing wave) of the box-shaped member 14 with the resonance frequency of each main hole 42.

[About the third antenna]
As shown in FIG. 4, the third antenna 23 is formed in a substantially strip shape extending in the front-rear direction of the electromagnetic wave heating device 10. Specifically, the third antenna 23 includes a substantially rectangular main body 23a, and two protrusions 23b protruding upward from each of a front position and a rear position on the upper side of the main body 23a. ing. The third antenna 23 has an input terminal 53 to which the microwave from the third oscillator 16c is input. The input terminal 53 is arranged at the lower part of the main body 23a at the center in the front-rear direction.

[Directivity of side antenna]
The electromagnetic wave heating apparatus 10 is configured such that the second antenna (first side antenna) 22 has directivity on the bottom surface side (obliquely downward) of the heating chamber 12. Further, the third antenna (second side antenna) does not have high directivity. The directivity of the third antenna 23 is lower than that of the second antenna 22. Hereinafter, a configuration in which the second antenna 22 has directivity on the bottom surface side will be described.

  The outer periphery of the second antenna 22 has a lower straight portion 22c and an arc portion 22d extending upward from the straight portion 22c in an arc shape. The straight portion 22c extends in the front-rear direction substantially parallel to the bottom surface of the heating chamber 12. The straight portion 22c is substantially parallel to the lower side (lower edge) 114a of the outer periphery of the concave portion 14b. Assuming that the wavelength of the microwave supplied to the second antenna 22 is λ, when viewed from the front of the second antenna 22 shown in FIG. The distance X1 to the side edge 114a is not less than λ / 10 and not more than λ / 4, for example, 30 mm. Therefore, the electric field below the second antenna 22 becomes strong.

  The distance X2 from the top of the arc portion 22d to the upper edge 114b on the outer periphery of the concave portion 14b is slightly larger than λ / 2, for example, 70 mm. Since the upper side of the second antenna 22 has an arc shape, the average distance from the arc portion 22d to the upper edge 114b of the concave portion 14b is large. The electric field of both the arc portion 22d of the second antenna 22 and the upper edge portion 114b of the concave portion 14b is substantially zero, and no resonance occurs between them. Further, in the second antenna 22, the main hole 42 forming the resonator is formed above the input terminal 52, so that microwave energy is not easily transmitted to the arc portion 22d. With the above configuration, the second antenna 22 has directivity on the bottom surface side, and the microwave energy input from the input terminal 52 is efficiently supplied to the heating target 1 on the mounting table 13.

[Oscillator control]
As shown in FIG. 5, the electromagnetic wave heating device 10 further includes a control device 40 that controls each of the oscillators 16a to 16c. The control device 40 is configured by an MCU (microwave control unit).

  In each of the transmission lines 18a to 18c, the directional couplers 19a to 19c (the first directional coupler 19a, the second directional coupler 19b, and the third directional coupler 19a to 19c) are provided between the oscillators 16a to 16c and the antennas 21 to 23. A sex coupler 19c) is provided. Each of the traveling wave and the reflected wave extracted from each of the directional couplers 19a to 19c is input to the power meter 25, and the power is measured. The power meter 25 and the three directional couplers 19a to 19c constitute a reflected wave measuring unit for measuring the reflected wave intensity of the microwave reflected on the heating chamber 12 side and returned to each of the oscillators 16a to 16c.

  Each of the oscillators 16a to 16c has an IQ modulator (quadrature modulator) and is configured to be capable of phase modulation. In addition, each wiring connecting the directional couplers 19a to 19c and the power meter 25 includes demodulation units 20a to 20c (first demodulation unit 20a and second demodulation unit) each including an IQ demodulator (quadrature demodulator). 20b and a third demodulation unit 20c). Each of the demodulation units 20a to 20c demodulates the traveling wave and the reflected wave extracted from each of the directional couplers 19a to 19c, and the demodulated signal is input to the power meter 25.

  At the start of the heating operation, the control device 40 first performs a monitoring operation. The monitoring operation is an operation of detecting the resonance frequency of each of the antennas 21 to 23.

  Specifically, in the monitoring operation, the control device 40 oscillates the microwave while repeatedly sweeping the oscillation frequency in the above-described sweepable range (for example, 2.35 GHz to 2.55 GHz) for each of the oscillators 16a to 16c. Execute the sweep operation. During the period of the sweep operation (microwave oscillation period), the control device 40 controls each of the antennas based on the power measurement information of the reflected wave extracted from each of the directional couplers 19a to 19c in the output signal of the power meter 25. As information on the reflected wave intensity (return loss (S11)) in 21 to 23, information on the frequency characteristics of the reflected wave intensity as shown in FIG. 6 is acquired. Then, for each of the antennas 21 to 23, the control device 40 detects a frequency at which a dip in the reflected wave intensity occurs as a resonance frequency.

  When the frequency characteristics of the reflected wave intensity shown in FIG. 6 are obtained, the resonance frequencies of the first antenna 21 are 2.45 GHz and 2.51 GHz, and the resonance frequencies of the second antenna 22 are 2.405 GHz and 2.475 GHz. In addition, the resonance frequencies of the third antenna 23 are 2.415 GHz, 2.455 GHz, 2.46 GHz, 2.495 GHz, and 2.54 GHz. Hereinafter, the resonance frequency detected by the monitoring operation is referred to as “detection frequency”.

  When the monitoring operation is completed during the heating operation, the control device 40 performs a frequency setting operation. The frequency setting operation is an operation of setting an oscillation frequency for each of the oscillators 16a to 16c. By the frequency setting operation, each of the oscillators 16a to 16c starts the sweep operation, oscillates the microwave by fixing the oscillation frequency to one frequency, or switches the oscillation frequency between a plurality of frequencies to generate the microwave. Switching to oscillating operation.

  Specifically, in the frequency setting operation, for the first oscillator 16a, the control device 40 selects and sets one or more values from the detection frequency of the corresponding first antenna 21 as the oscillation frequency, and sets the second oscillator 16a. For the 16b and the third oscillator 16c, one value is selected and set as the oscillation frequency from the detection frequencies of the corresponding second antenna 22 and third antenna 23. Then, the control device 40 instructs each of the oscillators 16a to 16c to oscillate the microwave at the set oscillation frequency. When a plurality of values are set as the oscillation frequency, the first oscillator 16a oscillates the microwave while switching the oscillation frequency between the plurality of values at a high speed.

  The selection of the detection frequency will be described. The control device 40 selects the detection frequency of the first oscillator 16a when the detection frequency of the first antenna 21 is one, and selects the detection frequency when the detection frequency of the first antenna 21 is plural, when the detection frequency of the first antenna 21 is plural. When a low detection frequency (referred to as “low loss frequency”) is selected, and there is a detection frequency at which the difference between the low loss frequency and the reflected wave intensity is equal to or smaller than the first determination value (for example, the first determination value = 5 dB), The detection frequency is also selected. When the detection frequency of the corresponding antennas 22 and 23 is one for each of the oscillation frequencies of the second oscillator 16b and the third oscillator 16c, the control device 40 selects the detection frequency as the oscillation frequency, and selects the corresponding antenna 22 , 23 are selected, the low loss frequency is selected as the oscillation frequency. In the second antenna 22 and the third antenna 23, even if the number of detection frequencies is one or more, one detection frequency is selected. Note that the second oscillator 16b or the third oscillator 16c may be set to have a plurality of frequencies as oscillation frequencies in the same manner as the first oscillator 16a. In this case, each of the oscillators 16b and 16c oscillates the microwave while switching the oscillation frequency between a plurality of frequencies at a high speed.

  Referring to FIG. 6 as an example, for the first antenna 21 having two detection frequencies, the low loss frequency is 2.45 GHz, and the difference between the low loss frequency and the reflected wave intensity is the first determination value (5 dB). The following detection frequencies (2.51 GHz) exist. Both of the two detection frequencies (2.45 GHz and 2.51 GHz) are selected, and these values are set as the oscillation frequency of the first oscillator 16a. As a result, the first oscillator 16a oscillates the microwave while switching the oscillation frequency between the two values (2.45 GHz and 2.51 GHz) at high speed. During the microwave oscillation period, the main hole 32 that resonates with the microwave changes in the first antenna 21, and the position of the strong electric field region changes in the heating chamber 12 according to the change.

  Further, for the second antenna 22 having two detection frequencies, the low loss frequency is 2.405 GHz. Only the low loss frequency (2.405 GHz) is selected from the two detection frequencies, and this low loss frequency is set as the oscillation frequency of the second oscillator 16b. As a result, the second oscillator 16b oscillates the microwave with the oscillation frequency fixed at one value (2.405 GHz).

  The low loss frequency of the third antenna 23 having five detection frequencies is 2.415 GHz. Only the low loss frequency (2.415 GHz) is selected from the five detection frequencies, and this low loss frequency is set as the oscillation frequency of the third oscillator 16c. As a result, the third oscillator 16c oscillates the microwave with the oscillation frequency fixed at one value (2.415 GHz). In the case of FIG. 6, the detection frequencies selected by the oscillators 16a to 16c do not overlap, and the first oscillator 16a, the second oscillator 16b, and the third oscillator 16c set the oscillation frequencies to different values.

  When the frequency characteristics of the reflected wave intensity shown in FIG. 7 are obtained, the resonance frequencies of the first antenna 21 are 2.45 GHz and 2.51 GHz, and 2.45 GHz is a low loss frequency. The resonance frequencies of the second antenna 22 are 2.41 GHz and 2.48 GHz, of which the low loss frequency is 2.41 GHz. The resonance frequencies of the third antenna 23 are 2.41 GHz, 2.45 GHz, 2.495 GHz, and 2.54 GHz, of which the low loss frequency is 2.41 GHz.

  Here, in the case of FIG. 7, the detection frequencies selected by the oscillators 16a to 16c overlap each other. In this case, the control device 40 sets the oscillation frequency to a value different from each other in the second oscillator 16b and the third oscillator 16c according to a predetermined rule. As a predetermined rule, when the first condition that one antenna 22 or 23 exists with a detection frequency is satisfied, the oscillators 16b and 16c corresponding to the antennas 22 and 23 are prioritized, and the low loss frequency is set as the oscillation frequency. There is a first rule of doing. Further, as another predetermined rule, when the first condition is not satisfied, the oscillator 16b corresponding to the antennas 22 and 23 having the larger difference between the detection frequency having the second lowest reflected wave intensity and the low loss frequency after the low loss frequency. , 16c is prioritized and a low rule is set as the oscillation frequency. Note that the predetermined rule is merely an example, and is not limited to the contents described in this paragraph.

  In the case of FIG. 7, the detection frequency of both the second antenna 22 and the third antenna 23 is not one, and the first condition is not satisfied. In the second antenna 22 and the third antenna 23, the second antenna 22 has a large difference between the detection frequency at which the reflected wave intensity is the second lowest and the low loss frequency next to the low loss frequency. The control device 40 gives priority to the second oscillator 16b corresponding to the second antenna 22 according to the second rule, and sets the low loss frequency (2.41 GHz) of the second antenna 22 as the oscillation frequency of the second oscillator 16b. . On the other hand, as the oscillation frequency of the third oscillator 16c, the detection frequency (2.45 GHz) having the minimum reflected wave intensity is set from among the detection frequencies (2.45 GHz, 2.495 GHz, 2.54 GHz) other than the low loss frequency. . The oscillation frequency of the third oscillator 16c becomes the same as the oscillation frequency of the first oscillator 16a.

  However, the control device 40 may set the oscillation frequency to a different value for the first oscillator 16a, the second oscillator 16b, and the third oscillator 16c using, for example, a predetermined rule. In this case, in the first antenna 21 and the third antenna 23, the difference between the detection frequency and the low loss frequency where the reflected wave intensity is the second lowest after the low loss frequency is the first antenna 21, and the control device 40 The low loss frequency (2.45 GHz) of the first antenna 21 is set as the oscillation frequency of the first oscillator 16a. Then, as the oscillation frequency of the third oscillator 16c, the detection frequency (2.54 GHz) with the minimum reflected wave intensity is set from the remaining detection frequencies (2.495 GHz and 2.54 GHz).

[Effects of Embodiment]
In the present embodiment, the electromagnetic wave heating device 10 is configured such that the second antenna 22 has directivity on the bottom side of the heating chamber 12. Therefore, the electromagnetic wave radiated from the second antenna 22 becomes difficult to be received by the third antenna 23, and the heating efficiency by the microwave can be further improved.

  In the present embodiment, in the heating operation, a second oscillator (first side oscillator) 16 b for the second antenna (first side antenna) 22 and a third oscillator (second side antenna) 23 for the third antenna (second side antenna) 23 are provided. The oscillating frequencies of the third oscillator (second side oscillator) 16c are set to values different from each other. Also, the first antenna (bottom antenna) 21 is set to have a different oscillation frequency. Therefore, microwave interference hardly occurs between the three antennas 21 to 23, and heating efficiency by microwaves can be improved. In addition, in each of the antennas 21 to 23, since the energy of the microwave radiated from the other antennas 21 to 23 hardly flows, the isolator can be omitted.

  In the present embodiment, a plurality of main holes 32 having different resonance frequencies are formed in the first antenna 21 that radiates the microwave oscillated from the first oscillator 16a. When a plurality of resonance frequencies are detected for the first antenna 21, the first oscillator 16a oscillates microwaves while switching the oscillation frequency between the plurality of resonance frequencies. Therefore, in the first antenna 21, the main hole 32 that resonates with the microwave is switched, and the strong electric field region in the heating chamber 12 changes according to the switching. Therefore, there is no need to rotate a structure such as a waveguide or an antenna, and the uniformity of heating of the object to be heated 1 can be improved with a simple configuration.

  Further, in the present embodiment, the first antenna 21 in which the plurality of main holes 32 having different resonance frequencies are formed is disposed behind the mounting area of the heating target 1 on the bottom surface of the heating chamber 12. In addition, the strong electric field region can be effectively changed in the mounting area of the object 1 to be heated.

  In the present embodiment, the first antenna 21 has a plurality of outer holes 31 that obstruct the transmission of microwaves to the outer periphery thereof so as to surround the outside of the region where the plurality of main holes 32 are formed. Have been. Therefore, the microwave energy supplied to the first antenna 21 close to the heating target 1 can be effectively supplied to the heating target 1.

  In the present embodiment, impedance matching is performed on the antennas 21 to 23 as loads so that the microwaves oscillated from the oscillators 16a to 16c are efficiently absorbed by the object 1 to be heated. However, since the oscillation frequency is set individually for each of the oscillators 16a to 16c, impedance matching between the plurality of antennas 21 to 23 is not performed.

[Modification of Embodiment]
In the present modification, when there are a plurality of oscillation frequency candidates for each of the second antenna 22 and the third antenna 23, the control device 40 complements the result of the phase modulation operation described later in addition to the result of the monitoring operation. To narrow down the oscillation frequency of each of the oscillators 16a to 16c. Hereinafter, the second antenna 22 will be described as an example, but the same control is performed on the third antenna 23. Description of control of the third antenna 23 is omitted.

  Specifically, in the above-described embodiment, when the second antenna 22 has a plurality of detection frequencies, the low loss frequency is selected as the oscillation frequency. However, in this modification, the oscillation frequency is determined prior to the determination of the oscillation frequency. A frequency candidate (hereinafter, referred to as “candidate frequency”) is selected. The control device 40 selects, as the candidate frequency, a detection frequency in which the difference between the low loss frequency and the reflected wave intensity is equal to or less than the second determination value (for example, the second determination value = 5 dB) in addition to the low loss frequency.

  Then, when a plurality of candidate frequencies exist, the control device 40 performs the phase modulation operation immediately after the monitoring operation, and sets the oscillation frequency based on the phase change rate p obtained by the phase modulation operation. That is, when there are a plurality of candidate frequencies, the control device 40 determines that the condition that the oscillation frequency cannot be set only by the reflected wave intensity is satisfied, and also uses the result of the phase modulation operation complementarily.

  In the phase modulation operation, the control device 40 sequentially sets the plurality of candidate frequencies to the oscillation frequency for the second oscillator 16b. Further, during the period in which each candidate frequency is set to the oscillation frequency, the control device 40 changes the phase by a predetermined phase modulation amount (for example, an angle of 30 degrees) by the IQ modulator of the second oscillator 16b while keeping the amplitude at a constant value. Modulate. The second demodulation unit 20b demodulates the traveling wave and the reflected wave extracted from the second directional coupler 19b.

Then, the control device 40 synchronizes the waveform of the traveling wave and the waveform of the reflected wave, which are input to the power meter 25 through the second demodulation unit 20b, and adjusts the phase modulation amount of the traveling wave for the second oscillator 16b. Δφ and the phase change ΔΦ of the reflected wave generated when the phase of the oscillating microwave is modulated are detected. The control device 40 calculates the phase change rate p using Expression 1 from the detection result. Note that the control device 40 calculates the phase change rate p for each candidate frequency.
Equation 1: p = ΔΦ / Δφ

  If the phase change rate p = 1, it indicates a standing wave, and indicates a state where there is no load on the object to be heated 1 or the like. Further, if p> 1, it indicates that the phase change rate is large, and if p <1, it indicates that the phase change rate is small. The reciprocating distance from the second antenna 22 to the heating target 1 is reflected in the phase change rate p.

  When calculating the phase change rate p for each candidate frequency as a result of the phase modulation operation, the control device 40 performs the frequency setting operation. In the frequency setting operation, the control device 40 sets a candidate frequency having the smallest phase change rate p from among a plurality of candidate frequencies as an oscillation frequency. That is, the candidate frequency with the shortest reciprocating distance of the microwave from the second antenna 22 to the heating target 1 is selected as the oscillation frequency.

  Here, even if a resonance frequency (low loss frequency) having the minimum reflected wave intensity is found, the microwave absorption rate of the heating target 1 may not be the highest at the resonance frequency. In other words, depending on the type or size of the heating target 1, various phase changes occur with respect to the standing wave, and the microwave may not be efficiently absorbed by the heating target 1 without being able to cope with the phase change. In this modification, the optimum oscillation frequency can be selected with high accuracy because the magnitude of the phase change rate p is considered in addition to the magnitude of the reflected wave intensity at the resonance frequency.

  When the heating object 1 itself is small and the total area is small, the phase change rate p tends to be large, and when the heating object 1 itself is large and the total area is large, the phase change rate p tends to be small. The control device 40 determines the type and size of the heating target 1 by measuring the phase change rate p using Expression 1 and detecting the total area of the heating target 1 according to the magnitude. Then, from the area of the object 1 to be heated, the control device 40 can also determine what percentage of the region should be locally heated. For example, the controller 40 can be controlled so that 30% of the entire region of the heating target 1 is locally heated, and 70% is entirely uniformly heated.

  Also, when the phase change rate p increases, the heating target 1 tends to be locally heated, and when the phase change rate p decreases, the heating target 1 tends to be uniformly heated. In the heating operation, the control device 40 specifies a point to be locally heated in the same heating target 1 according to the magnitude of the phase change rate p, or sets the point according to the magnitude of the phase change rate p. The frequency of each of the oscillators 16a to 16c can be controlled so as to perform the overall uniform heating process.

[Other Modifications]
In the above-described embodiment, the method of detecting the resonance frequency at which the return loss (S11) has the minimum value has been described. However, the resonance loss at which the insertion loss (S21) detected using another antenna as the reception antenna has the minimum value has been described. The frequency may be detected. Here, when detecting the resonance frequency at which the return loss (S11) has the minimum value, the component reflected by each of the antennas 21 to 23 and the component reflected by the heating target 1 are mixed, so that an accurate heating target is detected. In some cases, the absorption ratio of 1 cannot be calculated. On the other hand, the insertion loss (S21) indicates the absorption amount of the heating target 1, but there is no obstacle such as a wall when compared with the return loss (S11). Therefore, the absorption ratio of the heating target 1 can be calculated more accurately.

  In the above-described embodiment, the resonance frequency of the plurality of main holes 42 may be different from each other for the second antenna 22 as in the first antenna 21.

  In the above-described embodiment, the third antenna 23 may have directivity on the bottom surface side, similarly to the second antenna 22.

  INDUSTRIAL APPLICATION This invention is applicable to the electromagnetic wave heating apparatus etc. which heat an object to be heated dielectrically using an electromagnetic wave.

Reference Signs List 10 electromagnetic wave heating device 12 heating room 16a first oscillator 16b second oscillator (oscillator)
16c Third oscillator (oscillator)
21 First antenna 22 Second antenna (first side antenna)
23 3rd antenna (2nd side antenna)

Claims (5)

An electromagnetic wave heating device that heats an object to be heated using electromagnetic waves,
A heating chamber in which the object to be heated is arranged,
A first side antenna disposed on a first inner side surface of the heating chamber;
A second side surface antenna disposed on a second inner side surface facing the first inner side surface in the heating chamber;
An oscillation device that oscillates an electromagnetic wave radiated to the heating chamber for each of the first side antenna and the second side antenna;
The electromagnetic wave heating device, wherein the first side surface antenna is configured to have directivity on a bottom surface side of the heating chamber.   The electromagnetic wave heating device according to claim 1, wherein the directivity of the second side antenna is lower than that of the first side antenna. The first side antenna is formed in a plate shape,
The first side surface antenna is disposed in a recess of the first inner side surface in the heating chamber,
When the wavelength of the electromagnetic wave supplied to the first side antenna is λ, the lower part of the outer periphery of the first side antenna extends to the lower edge of the outer periphery of the recess in a front view of the first side antenna. 3. The electromagnetic wave heating device according to claim 1, wherein a distance of the electromagnetic wave heater is λ / 10 or more and λ / 4 or less.   4. The electromagnetic wave according to claim 1, wherein in the first side antenna, an input terminal of the electromagnetic wave is arranged at a lower part, and a hole that forms a resonator is formed above the input terminal. 5. Heating equipment.   The electromagnetic wave heating device according to any one of claims 1 to 4, wherein an outer periphery of the first side surface antenna has a lower straight portion and an arc portion extending upward from the straight portion in an arc shape.

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