EP3771290A1

EP3771290A1 - Radio frequency heating device

Info

Publication number: EP3771290A1
Application number: EP19770268.1A
Authority: EP
Inventors: Toshiyuki Okajima; Yoshiharu Oomori; Kazuki Maeda
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2018-03-22
Filing date: 2019-02-18
Publication date: 2021-01-27
Also published as: CN111034357A; EP3771290A4; CN111034357B; WO2019181318A1; JP7249491B2; JPWO2019181318A1

Abstract

Surface wave transmission line (103) provided near installation table (101) is formed to have an inclination with respect to a transmission direction of radio frequency power. Accordingly, a distance between surface wave transmission line (103) and installation table (101) becomes large on a side of radio frequency power supply unit (120). This makes absorbance of radio frequency power propagating on surface wave transmission line (103) into object (102) to be heated larger as a portion of object (102) to be heated becomes away from a side of surface wave transmission line (103) from which radio frequency power is supplied. This enables to uniformly heat object (102) to be heated even when a plurality of objects (102) to be heated are aligned and installed or even when object (102) to be heated having a long length is installed with respect to a propagation direction of radio frequency power of surface wave transmission line (103). This also enables to keep installation table (101) horizontal, making it possible to prevent occurrence of a malfunction such as rolling of object (102) to be heated.

Description

TECHNICAL FIELD

The present invention relates to a radio frequency heating device for heating an object to be heated via a surface wave transmission line that uses a periodic structure.

BACKGROUND ART

Conventionally, a technique has been disclosed of a radio frequency heating device that subjects an object to be heated such as food to heat treatment by supplying radio frequency power to a surface wave transmission line that uses a periodic structure.
Typically, when an object to be heated is heated by using radio frequency power such as micro wave that concentrates and propagates near a surface of a surface wave transmission line, radio frequency power propagating on the surface wave transmission line is absorbed into the object to be heated placed near the surface wave transmission line. This attenuates radio frequency power as radio frequency power propagates on the surface wave transmission line.
Accordingly, when a plurality of objects to be heated are aligned and installed or when an object to be heated having a long length is installed with respect to a propagation direction of radio frequency power of the surface wave transmission line, the object to be heated is heated strongly on a power supply side of the surface wave transmission line. Then, heating of the object to be heated becomes weak as a portion of the object to be heated is away from the power supply side. This causes uneven heating in the object to be heated with respect to the propagation direction of radio frequency power of the surface wave transmission line.
In order to eliminate the above-mentioned uneven heating, a following radio frequency thawing and heating device has been disclosed (e.g., see PTL 1).
The radio frequency thawing and heating device described in PTL 1 has a configuration in which one end of an installation table for placing an object to be heated on a side of supplying radio frequency power to a surface wave transmission line is made movable up and down and the installation table is inclined in an upper direction. This reduces that the object to be heated is heated strongly at a portion of the object to be heated on a power supply side of the surface wave transmission line and that heating becomes weak as a portion of the object to be heated is away from the power supply side. This is supposed to make rice of Frozen Sushi be efficiently thawed or heated using the surface wave transmission line.
However, in the configuration of the above-mentioned conventional radio frequency thawing and heating device, the installation table for placing an object to be heated is movable up and down, which may disadvantageously cause a malfunction such as rolling of the object to be heated placed on the installation table.

Citation List

Patent Literature

PTL 1: Unexamined Japanese Patent Publication No. H08-166133

SUMMARY OF THE INVENTION

The present invention provides a radio frequency heating device that uniformly heats an object to be heated with respect to a propagation direction of radio frequency power of a surface wave transmission line as well as prevents rolling of the object to be heated.
The present invention is of a radio frequency heating device that heats an object to be heated placed on an installation table. The radio frequency heating device includes at least one surface wave transmission line provided near the installation table, at least one radio frequency power generator that generates radio frequency power, and at least one radio frequency power supply unit that directly supplies the radio frequency power to the surface wave transmission line. The surface wave transmission line is formed to have an inclination with respect to a propagation direction of the radio frequency power to make a distance between the surface wave transmission line and the installation table large on a side of the radio frequency power supply unit, the surface wave transmission line being installed on the surface wave transmission line.
This configuration makes the distance between the installation table and the surface wave transmission line shorter as a position becomes away from the side of supplying the radio frequency power of the surface wave transmission line without moving the installation table. In this context, absorbance of radio frequency power propagating on the surface wave transmission line into the object to be heated becomes larger as the radio frequency power becomes away from the side from which the radio frequency power of the surface wave transmission line is supplied. This enables to uniformly heat the object to be heated with respect to the propagation direction of the radio frequency power of the surface wave transmission line even when a plurality of objects to be heated are aligned and installed or even when an object to be heated having a long length is installed with respect to the propagation direction of the radio frequency power of the surface wave transmission line. This also enables to keep the installation table horizontal, making it possible to prevent occurrence of a malfunction such as rolling of the object to be heated placed on the installation table.
The radio frequency heating device according to the present invention may have a configuration in which a radio frequency supplying unit is disposed at both ends of the surface wave transmission line, and the surface wave transmission line has a mountain-shaped inclination to substantially have a highest part in a middle with respect to the propagation direction of the radio frequency power.
This configuration enables to supply the radio frequency power from the both ends of the surface wave transmission line. This also enables to make the distance between the installation table and the surface wave transmission line shorter as a position becomes away from the side of supplying the radio frequency power of the surface wave transmission line without moving the installation table. This enables to more uniformly heat the object to be heated with respect to the propagation direction of the radio frequency power of the surface wave transmission line even when a plurality of objects to be heated are aligned and installed or even when an object to be heated having a long length is installed with respect to the propagation direction of the radio frequency power of the surface wave transmission line. This also enables to keep the installation table horizontal, making it possible to prevent occurrence of a malfunction such as rolling of the object to be heated placed on the installation table.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a basic configuration of a radio frequency heating device according to a first exemplary embodiment of the present invention.
FIG. 2A is a plan view illustrating a configuration of a radio frequency power supply unit of the radio frequency heating device.
FIG. 2B is a side view illustrating the configuration of the radio frequency power supply unit of the radio frequency heating device.
FIG. 3 is a diagram illustrating an example of a shape of a surface wave transmission line of the radio frequency heating device.
FIG. 4 is a diagram illustrating an example of an electric field strength distribution of radio frequency power propagating on a typical surface wave transmission line.
FIG. 5 is a diagram illustrating an electric field strength distribution of radio frequency power during a heating operation of an object to be heated by the surface wave transmission line illustrated in FIG. 4.
FIG. 6 is a diagram illustrating a heating operation of an object to be heated by the surface wave transmission line of the radio frequency heating device according to the exemplary embodiment.
FIG. 7 is a diagram illustrating another example of a shape of the surface wave transmission line of the radio frequency heating device according to the exemplary embodiment.
FIG. 8 is a block diagram illustrating a basic configuration of a radio frequency heating device according to a second exemplary embodiment of the present invention.
FIG. 9 is a diagram illustrating an example of a shape of a surface wave transmission line of the radio frequency heating device.
FIG. 10 is a diagram illustrating a heating operation of an object to be heated by a surface wave transmission line of a typical radio frequency heating device.
FIG. 11 is a diagram illustrating a heating operation of an object to be heated by the surface wave transmission line of the radio frequency heating device according to the exemplary embodiment.
FIG. 12 is a diagram illustrating another example of a shape of the surface wave transmission line of the radio frequency heating device.

DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. Note that the exemplary embodiments do not limit the present invention.

(First exemplary embodiment)

Hereinafter, radio frequency heating device 100 according to a first exemplary embodiment will be described with reference to FIG. 1.
FIG. 1 is a block diagram illustrating a basic configuration of radio frequency heating device 100 according to the first exemplary embodiment.
As illustrated in FIG. 1, radio frequency heating device 100 includes installation table 101, surface wave transmission line 103 provided near installation table 101, for example, provided below installation table 101, radio frequency power generator 110, radio frequency power supply unit 120, and the like. Radio frequency heating device 100 heats object 102 to be heated placed on installation table 101.
In radio frequency heating device 100 illustrated in FIG. 1, although an example is illustrated including one surface wave transmission line, one radio frequency power generator, and one radio frequency power supply unit, the example is not limited thereto. A number of surface wave transmission line, radio frequency power generator, and radio frequency power supply unit is not limited to the above-mentioned number, and may be two or more.
Above-mentioned radio frequency heating device 100 operates as described below.
First, radio frequency power generator 110 generates radio frequency power. The radio frequency power generated is supplied to surface wave transmission line 103 via radio frequency power supply unit 120. The radio frequency power supplied is propagated near a surface of surface wave transmission line 103 by surface wave, or radiated from near the surface. This heats object 102 to be heated placed on installation table 101.
Radio frequency heating device 100 according to the first exemplary embodiment is configured and operated as described above.
Note that radio frequency power generator 110 is formed of a radio frequency oscillator that outputs radio frequency power having frequency (e.g., microwave) and power suited to heat object 102 to be heated.
Specifically, the radio frequency oscillator is formed of, for example, a magnetron and an inverter power circuit, a solid state oscillator and a power amplifier, and the like.
The magnetron is a kind of an oscillation vacuum tube that generates powerful non-coherent microwave, which is a kind of electric wave, and often used for radars, microwave ovens, or the like that provide high output from hundreds of watts to several kilowatts. The inverter power circuit is typically used as a driving power source to drive the magnetron because a high voltage of several kilovolts is needed. The inverter power circuit is formed of a converter circuit having a rectification function, and an inverter circuit having a boost (or step-down) function and an output frequency conversion function. Not that the inverter power circuit is a technique widely used for lightening devices and motor control.
The solid state oscillator is formed of a semiconductor oscillator circuit equipped with a feedback circuit including electronic components for radio frequency such as a transistor, a capacitor, an inductor, and a resistor. Note that the solid state oscillator is a technique widely used in an oscillator for small power output such as communication equipment.
Some solid state oscillators output radio frequency power of about 50 watts recently, but the solid state oscillator typically is an oscillator that outputs radio frequency power of about tens to hundreds of milliwatts. Accordingly, a typical solid state oscillator cannot be used for heat treatment necessary to output power of hundreds of watts. Therefore, the solid state oscillator is used with a power amplifier formed of a transistor and the like that amplify radio frequency power output.
In a radio frequency heating cooker according to the first exemplary embodiment, a configuration of radio frequency power generator 110 is not specifically limited, so that its detailed description will be omitted.
Radio frequency power supply unit 120 corresponds to a power connection unit that supplies radio frequency power generated by radio frequency power generator 110 to surface wave transmission line 103.
Hereinafter, a configuration of radio frequency power supply unit 120 will be described with reference to FIG. 2A and FIG. 2B. Note that FIG. 2A and FIG. 2B illustrate an example of the configuration of radio frequency power supply unit 120.
FIG. 2A is a plan view illustrating a configuration around radio frequency power supply unit 120 viewed from an upper direction. FIG. 2B is a side view around radio frequency power supply unit 120.
In FIG. 2A and FIG. 2B, magnetron 111 is used as radio frequency power generator 110 illustrated in FIG. 1.
Magnetron 111 is disposed such that radio frequency power generated is introduced into radio frequency power supply unit 120 using rectangular waveguide 121.
Rectangular waveguide 121 is formed of a hollow waveguide used for transmitting electromagnetic wave such as microwave. The hollow waveguide is a typical waveguide, and is formed of a metal pipe whose cross-sectional shape is a square (e.g., rectangle). Electromagnetic wave propagates in rectangular waveguide 121 while forming an electromagnetic field that depends on a shape and size of rectangular waveguide 121, and a wavelength or frequency of the electromagnetic wave.
In FIG. 2A and FIG. 2B, the configuration using rectangular waveguide 121 is exemplified, but the present invention is not limited thereto. For example, another power supplying method such as a power supplying method using a loop antenna may be used.
Surface wave transmission line 103 is formed of a metal periodic structure in which impedance elements are periodically arranged on a metal plate, a dielectric plate, or the like. For the metal periodic structure, for example, a stub-type surface wave transmission line or an interdigital-type surface wave transmission line is used. The stub-type surface wave transmission line is formed by aligning a plurality of metal plates on a metal plate at predetermined intervals. The interdigital-type surface wave transmission line is formed by punching a metal plate to have a crossed fingers state. For the dielectric plate, an alumina plate or a bakelite board is used, for example. In FIG. 1, an example is illustrated using the stub-type surface wave transmission line as surface wave transmission line 103.
Surface wave transmission line 103 also makes radio frequency power supplied from radio frequency power generator 110 via radio frequency power supply unit 120 be concentrated near the surface to transmit the radio frequency power with surface wave. Accordingly, surface wave transmission line 103 is disposed near installation table 101. Then, object 102 to be heated is placed on installation table 101. This heats object 102 to be heated on installation table 101 by radio frequency power concentrated and transmitted near the surface of surface wave transmission line 103.
Next, a shape of surface wave transmission line 103 according to the first exemplary embodiment will be described with reference to FIG. 3.
FIG. 3 is a diagram illustrating an example of the shape of surface wave transmission line 103 according to the first exemplary embodiment.
Surface wave transmission line 103 is formed to have a shape inclining at constant inclination angle 105 (e.g., about 10°) in a direction of transmission direction 104 of radio frequency power as illustrated in FIG. 3. This makes surface wave transmission line 103 be disposed to incline to have inclination angle 105 with respect to installation table 101 near installation table 101 disposed in a horizontal state as illustrated in FIG. 1. Specifically, surface wave transmission line 103 is disposed to incline at inclination angle 105 with respect to installation table 101 such that distance d101 between surface wave transmission line 103 on a side of radio frequency power supply unit 120 and installation table 101 becomes larger than distance d102 between surface wave transmission line 103 on another side and installation table 101.
The above-mentioned configuration supplies radio frequency power generated by radio frequency power generator 110 to surface wave transmission line 103 via radio frequency power supply unit 120 in radio frequency heating device 100 according to the first exemplary embodiment. This subjects object 102 to be heated placed on installation table 101 disposed near the surface of surface wave transmission line 103 to heat treatment.
Also, surface wave transmission line 103 is disposed near installation table 101 such that distance d101 between surface wave transmission line 103 near the side of radio frequency power supply unit 120 and end 101a of installation table 101 becomes larger than distance d102 between surface wave transmission line 103 near another side and end 101b of installation table 101. Accordingly, absorbance of radio frequency power propagating on surface wave transmission line 103 absorbed into object 102 to be heated via installation table 101 becomes larger as radio frequency power becomes far from a side of surface wave transmission line 103 supplying radio frequency power. This enables to uniformly heat object 102 to be heated even when a plurality of objects 102 to be heated are aligned and installed or object 102 to be heated having a long length is placed with respect to a propagation direction of radio frequency power of surface wave transmission line 103.
Installation table 101 is disposed to keep a horizontal state as illustrated in FIG. 1. This enables to prevent occurrence of a malfunction that object 102 to be heated placed on installation table 101 is rolled and moved for example. This enables to more surely prevent occurrence of uneven heating associated with movement of object 102 to be heated.
Next, a heat treatment operation of object 102 to be heated in radio frequency heating device 100 equipped with the above-mentioned configuration will be described in detail with reference to FIG. 4 to FIG. 6.
First, a heat treatment operation of object 102 to be heated in a typical radio frequency heating device will be described with reference to FIG. 4 and FIG. 5.
FIG. 4 is a diagram illustrating electric field strength distribution 141 of radio frequency power propagating on typical surface wave transmission line 106. FIG. 5 is a diagram illustrating electric field strength distribution 142 of radio frequency power during the heating operation for object 102 to be heated by surface wave transmission line 106 illustrated in FIG. 4.
Specifically, FIG. 4 illustrates by grayscale a state of electric field strength distribution 141 formed near a surface of surface wave transmission line 106 at a time when radio frequency power generated by radio frequency power generator 110 is supplied to surface wave transmission line 106 via radio frequency power supply unit 120. Also, FIG. 5 illustrates by grayscale a state of electric field strength distribution 142 formed by radio frequency power propagating on surface wave transmission line 106 with surface wave at a time when radio frequency power is supplied to surface wave transmission line 106 illustrated in FIG. 4 in a state where object 102 to be heated is placed on installation table 101.
That is, as illustrated in FIG. 4, radio frequency power supplied to surface wave transmission line 106 via radio frequency power supply unit 120 propagates by surface wave near a surface of surface wave transmission line 106. In this context, radio frequency power propagates while forming electric field strength distribution 141 whose electric field strength is strong (dark) near the surface of surface wave transmission line 106 and whose electric field strength becomes weaker (lighter) as radio frequency power becomes away from the surface of surface wave transmission line 106.
Also, as illustrated in FIG. 5, radio frequency power supplied to surface wave transmission line 106 via radio frequency power supply unit 120 propagates by surface wave near the surface of surface wave transmission line 106. In this context, radio frequency power is absorbed into object 102 to be heated from the side of radio frequency power supply unit 120. Accordingly, radio frequency power propagating on surface wave transmission line 106 attenuates in its electric field strength as radio frequency power passes through object 102 to be heated from the side of radio frequency power supply unit 120. This forms electric field strength distribution 142 as illustrated in FIG. 5.
That is, when radio frequency power is supplied to surface wave transmission line 106 having a typical configuration to subject object 102 to be heated placed on installation table 101 to heat treatment, the side of radio frequency power supply unit 120 of object 102 to be heated is heated well. However, as radio frequency power passes through object 102 to be heated, the radio frequency power is absorbed into object 102 to be heated. This gradually attenuates radio frequency power to make radio frequency power for heating object 102 to be heated weak. This generates uneven heating in object 102 to be heated with respect to the propagation direction of radio frequency power of surface wave transmission line 106 in a case of a radio frequency heating device equipped with surface wave transmission line 106.
Next, the heat treatment operation of object 102 to be heated in radio frequency heating device 100 according to the first exemplary embodiment will be described with reference to FIG. 6.
FIG. 6 is a diagram illustrating the heating operation of object 102 to be heated 120 by surface wave transmission line 103 of radio frequency heating device 100 according to the first exemplary embodiment.
Specifically, in FIG. 6, surface wave transmission line 103 is disposed with inclination with respect to the propagation direction of radio frequency power as illustrated in FIG. 3. Radio frequency power generated by radio frequency power generator 110 is supplied to surface wave transmission line 103 disposed with inclination via radio frequency power supply unit 120. A state in this context is illustrated by grayscale where object 102 to be heated placed on installation table 101 is heated with electric field strength distribution 143 formed by radio frequency power propagating on surface wave transmission line 103 by surface wave.
That is, as illustrated in FIG. 6, radio frequency power supplied to surface wave transmission line 103 via radio frequency power supply unit 120 propagates near the surface of surface wave transmission line 103 by surface wave. In this context, radio frequency power is sequentially absorbed into object 102 to be heated from the side of radio frequency power supply unit 120. Accordingly, radio frequency power propagating on surface wave transmission line 103 attenuates in its electric field strength as it passes through object 102 to be heated from the side of radio frequency power supply unit 120.
In this context, for surface wave transmission line 103 according to the first exemplary embodiment, on the side of radio frequency power supply unit 120, object 102 to be heated placed on installation table 101 is away from near the surface of surface wave transmission line 103 as illustrated in FIG. 6. This makes radio frequency power passing through installation table 101 be reduced depending on a distance, preventing object 102 to be heated on installation table 101 from being heated strongly. That is, attenuation of radio frequency power propagating along near the surface of surface wave transmission line 103 also becomes small.
Also, a distance between object 102 to be heated and surface wave transmission line 103 becomes smaller as a position of object 102 to be heated becomes away from the side of radio frequency power supply unit 120. However, even when radio frequency power is attenuated as it propagates on surface wave transmission line 103, radio frequency power passing through installation table 101 becomes large because the distance between with surface wave transmission line 103 becomes small. That is, absorbance of radio frequency power absorbed into object 102 to be heated from surface wave transmission line 103 via installation table 101 becomes large. This enables to balance radio frequency power absorbed into object 102 to be heated to be attenuated with increased absorbance of radio frequency power of object 102 to be heated. Therefore, uniform electric field strength distribution 143 illustrated in FIG. 6 with respect to object 102 to be heated placed on installation table 101 is formed on installation table 101. This enables to uniformly heat object 102 to be heated with respect to the propagation direction of radio frequency power of surface wave transmission line 103 while keeping installation table 101 horizontal.
Note that, in the first exemplary embodiment, although description is made on the basis of an example using surface wave transmission line 103 formed with a single inclination as illustrated in FIG. 3, the example is not limited thereto. For example, in an area of surface wave transmission line 103 that contributes to heat object 102 to be heated (e.g., an area opposed to installation table 101), surface wave transmission line 103 may be inclined with respect to the propagation direction of radio frequency power. That is, it is sufficient that an inclination region of surface wave transmission line 103 is provided such that a distance between surface wave transmission line 103 and installation table 101 becomes large on the side of radio frequency power supply unit 120. Specifically, surface wave transmission line 107 may be used formed by combining horizontal part 107a, horizontal part 107c, and inclination part 107b as illustrated in FIG. 7, for example. In this case, inclination part 107b of surface wave transmission line 107 is disposed to oppose installation table 101 on which object 102 to be heated is placed. This enables to obtain the same effect as that in the first exemplary embodiment.

(Second exemplary embodiment)

Hereinafter, radio frequency heating device 200 according to a second exemplary embodiment will be described with reference to FIG. 8.
In radio frequency heating device 200 according to the second exemplary embodiment, the same reference numeral is used for the same element having the same function as the function of radio frequency heating device 100 according to the first exemplary embodiment, and description thereof will be omitted. Contents having the same operation as the operation of radio frequency heating device 100 according to the first exemplary embodiment will be also omitted.
FIG. 8 is a block diagram illustrating a basic configuration of radio frequency heating device 200 according to the second exemplary embodiment.
As illustrated in FIG. 8, radio frequency heating device 200 differs from radio frequency heating device 100 according to the first exemplary embodiment illustrated in FIG. 1 in that surface wave transmission line 203 is included instead of surface wave transmission line 103, radio frequency power generator 210 is included instead of radio frequency power generator 110, and two radio frequency power supply units 220 formed of first radio frequency power supply unit 220a and second radio frequency power supply unit 220b are included instead of radio frequency power supply unit 120. Hereinafter, in a case of collectively describing first radio frequency power supply unit 220a and second radio frequency power supply unit 220b, they are described as radio frequency power supply units 220.
In radio frequency heating device 200 of FIG. 8, although an example is illustrated including one surface wave transmission line 203, one radio frequency power generator 210, and two radio frequency power supply units 220, the example is not limited thereto. Numbers of surface wave transmission line, radio frequency power generator, and radio frequency power supply unit are not limited to the above-mentioned numbers.
Above-mentioned radio frequency heating device 200 operates as described below.
First, radio frequency heating device 200 generates radio frequency power by radio frequency power generator 210. The generated radio frequency power is divided into two, and supplied to both ends of surface wave transmission line 203 via respective first radio frequency power supply unit 220a and second radio frequency power supply unit 220b. This makes radio frequency power be supplied to the both ends of surface wave transmission line 203. Radio frequency power supplied is propagated near a surface from the both ends of surface wave transmission line 203 toward a middle by surface wave, or radiated from near the surface. This heats object 102 to be heated placed on installation table 101.
Note that a configuration of radio frequency power supply unit 210 and a configuration of first radio frequency power supply unit 220a and second radio frequency power supply units 220b are the same as the configuration of radio frequency power generator 110 and the configuration of radio frequency power supply unit 120 described in the first exemplary embodiment, respectively, so that description thereof is omitted.
Radio frequency heating device 200 according to the second exemplary embodiment is configured and operated as described above.
Next, a shape of surface wave transmission line 203 according to the second exemplary embodiment will be described with reference to FIG. 9.
FIG. 9 is a diagram illustrating an example of the shape of surface wave transmission line 203 according to the second exemplary embodiment.
As illustrated in FIG. 9, surface wave transmission line 203 is formed in, for example, a mountain shape inclined at constant inclination angles 205a and 205b (e.g., about 10°) with respect to installation table 101 near installation table 101 disposed in a horizontal state illustrated in FIG. 8. That is, surface wave transmission line 203 is formed in a mountain shape having constant inclination angle 205a and inclination angle 205b with respect to installation table 101 in transmission direction 204a and transmission direction 204b of radio frequency power respectively supplied from the both ends of surface wave transmission line 203.
Specifically, as illustrated in FIG. 8, surface wave transmission line 203 is disposed with respect to installation table 101 such that distance d201 on a side of first radio frequency power supply unit 220a between surface wave transmission line 203 and installation table 101 and distance d202 on a side of second radio frequency power supply unit 220b between surface wave transmission line 203 and installation table 101 become larger than distance d203 between highest part 203a of surface wave transmission line 203 having a mountain shape and installation table 101. Note that highest part 203a of surface wave transmission line 203 corresponds to a position most away from each of first radio frequency power supply unit 220a and second radio frequency power supply unit 220b.
Radio frequency heating device 200 according to the second exemplary embodiment having the above-mentioned configuration supplies radio frequency power generated by radio frequency power generator 210 from the both ends of surface wave transmission line 203 via respective first radio frequency power supply unit 220a and second radio frequency power supply unit 220b. This makes object 102 to be heated placed on installation table 101 disposed near a surface of surface wave transmission line 203 be subjected to heat treatment.
Also, surface wave transmission line 203 is disposed near installation table 101 such that distance d201 and distance d202 between respective portions near the both ends of surface wave transmission line 203 and respective ends 101a, 101b of installation table 101 become larger than distance d203 between highest part 203a of surface wave transmission line 203 and installation table 101. Accordingly, absorbance of radio frequency power propagating from the both ends of surface wave transmission line 203 absorbed into object 102 to be heated via installation table 101 becomes larger as a position becomes away from sides of both ends 101a, 101b of surface wave transmission line 203 supplying radio frequency power. This enables to uniformly heat object 102 to be heated even when a plurality of objects 102 to be heated are aligned and installed or even when object 102 to be heated having a long length size is installed with respect to the propagation direction of radio frequency power of surface wave transmission line 203.
Also, installation table 101 is disposed to keep a horizontal state as illustrated in FIG. 8. This enables to prevent occurrence of a malfunction that object 102 to be heated placed on installation table 101 is rolled and moved for example. This enables to more surely prevent occurrence of uneven heating associated with movement of object 102 to be heated.
Radio frequency power is supplied to surface wave transmission line 203 from the both ends of surface wave transmission line 203. This enables to more uniformly heat object 102 to be heated with respect to the propagation direction of radio frequency power of surface wave transmission line 203.
Next, a heat treatment operation of object 102 to be heated in radio frequency heating device 200 equipped with the above-mentioned configuration will be described in more detail with reference to FIG. 10 and FIG. 11.
First, a heat treatment operation of object 102 to be heated in a typical radio frequency heating device for heating an object to be heated by radio frequency power supplied from both ends of surface wave transmission line 203 will be described with reference to FIG. 10.
FIG. 10 is a diagram illustrating a heating operation of object 102 to be heated by surface wave transmission line 206 of a typical radio frequency heating device.
Specifically, FIG. 10 illustrates by grayscale a state of electric field strength distribution 241 formed by radio frequency power propagating on surface wave transmission line 206 by surface wave and heating object 102 to be heated when radio frequency power is supplied from the both ends of surface wave transmission line 206 in a state where object 102 to be heated is placed on installation table 101.
That is, radio frequency power is supplied to the both ends of surface wave transmission line 206 via first radio frequency power supply unit 220a and second radio frequency power supply unit 220b as illustrated in FIG. 10. The radio frequency power supplied propagates near the surface of surface wave transmission line 206 by surface wave, and is absorbed into object 102 to be heated from both sides of object 102 to be heated via installation table 101. Accordingly, radio frequency power propagating on surface wave transmission line 206 is absorbed as the radio frequency power passes through object 102 to be heated, and its electric field strength is attenuated. This forms electric field strength distribution 241 as illustrated in FIG. 10.
That is, when radio frequency power is supplied to surface wave transmission line 206 having the typical configuration to subject object 102 to be heated placed on installation table 101 to heat treatment, the both sides of object 102 to be heated are heated well. However, radio frequency power is absorbed into object 102 to be heated as radio frequency power comes close to a middle of surface wave transmission line 206. This gradually attenuates radio frequency power to make radio frequency power for heating object 102 to be heated weak. This generates uneven heating in object 102 to be heated with respect to the propagation direction of radio frequency power of surface wave transmission line 206 in a case of a radio frequency heating device equipped with surface wave transmission line 206.
Next, the heat treatment operation of object 102 to be heated in radio frequency heating device 200 according to the second exemplary embodiment will be described with reference to FIG. 11.
FIG. 11 is a diagram illustrating a heating operation for object 102 to be heated by surface wave transmission line 203 of radio frequency heating device 200 according to the second exemplary embodiment.
Specifically, FIG. 11 illustrates the heating operation for object 102 to be heated in a following state.
First, in FIG. 11, radio frequency power generated by radio frequency power generator 210 is supplied to the both ends of surface wave transmission line 203 formed in a mountain shape illustrated by FIG. 9 via respective first radio frequency power supply unit 220a and second radio frequency power supply unit 220b. A state in this context is illustrated by grayscale where object 102 to be heated placed on installation table 101 is heated with electric field strength distribution 242 formed by radio frequency power propagating on surface wave transmission line 203 by surface wave.
That is, as illustrated in FIG. 11, radio frequency power supplied to the both ends of surface wave transmission line 203 via first radio frequency power supply unit 220a and second radio frequency power supply unit 220b propagates near the surface of surface wave transmission line 203 by surface wave. In this context, radio frequency power is sequentially absorbed from both end sides of object 102 to be heated. Accordingly, radio frequency power propagating on surface wave transmission line 203 attenuates in electric field strength as radio frequency power passes through object 102 to be heated. This forms electric field strength distribution 242 as illustrated in FIG. 11 to heat object 102 to be heated on installation table 101.
In this context, as illustrated in FIG. 11, in a case of surface wave transmission line 203 formed to incline with respect to the propagation direction of radio frequency power, both end sides of object 102 to be heated placed on installation table 101 is away from near the surface of surface wave transmission line 203. This makes radio frequency power passing through installation table 101 be reduced depending on a distance, preventing object 102 to be heated on installation table 101 from being heated strongly. That is, attenuation of radio frequency power propagating along near the surface of surface wave transmission line 203 becomes also small.
Furthermore, a distance between object 102 to be heated and surface wave transmission line 203 becomes small as a portion of surface wave transmission line 203 becomes away from the side of first radio frequency power supply unit 220a and the side of second radio frequency power supply unit 220b disposed at both ends toward highest part 203a. However, even when radio frequency power is attenuated as it propagates from the both ends of surface wave transmission line 203 toward highest part 203a, radio frequency power passing through installation table 101 becomes large because a distance between with surface wave transmission line 203 becomes small. That is, absorbance of radio frequency power absorbed into object 102 to be heated from surface wave transmission line 203 via installation table 101 becomes large. This enables to balance radio frequency power absorbed into object 102 to be heated to be attenuated with increased absorbance of radio frequency power of object 102 to be heated. Therefore, uniform electric field strength distribution 242 illustrated in FIG. 11 is formed on installation table 101 with respect to object 102 to be heated placed on installation table 101. This enables to uniformly heat object 102 to be heated with respect to the propagation direction of radio frequency power of surface wave transmission line 203 while keeping installation table 101 horizontal.
Note that, in the second exemplary embodiment, although description is made on the basis of an example using surface wave transmission line 203 formed by a single mountain-shaped inclination as illustrated in FIG. 9, surface wave transmission line 203 is not limited thereto. For example, in an area of surface wave transmission line 103 that contributes to heat object 102 to be heated (e.g., an area opposed to installation table 101), a surface wave transmission line may be formed to incline in a mountain shape with respect to the propagation direction of radio frequency power. That is, it is sufficient that at least an inclination area of surface wave transmission line 203 is provided such that a distance between surface wave transmission line 203 and installation table 101 become large on the sides of first radio frequency power supply unit 220a and second radio frequency power supply unit 220b. Specifically, surface wave transmission line 207 formed by combining horizontal part 207a, horizontal part 207c, and inclination part 207b illustrated in FIG. 12 may be used, for example. In this case, inclination part 207b of surface wave transmission line 207 is disposed to oppose installation table 101 on which object 102 to be heated is placed. This enables to obtain the same effect as that in the second exemplary embodiment.
The radio frequency heating device according to the present invention is described above on the basis of each exemplary embodiment. However, the present invention is not limited to the exemplary embodiments. Exemplary embodiments variously modified from the present exemplary embodiments by those skill in the art, and exemplary embodiments constructed by combining constituent elements of different exemplary embodiments are also included in the scopes of the present invention as long as they do not depart from the gist of the present invention.
As described above, the present invention is of a radio frequency heating device that subjects an object to be heated placed on an installation table to heat treatment. The radio frequency heating device includes at least one surface wave transmission line provided near the installation table, at least one radio frequency power generator that generates radio frequency power, and at least one radio frequency power supply unit that directly supplies radio frequency power to the surface wave transmission line. The surface wave transmission line is installed to incline with respect to the propagation direction of radio frequency power such that a distance between the surface wave transmission line and the installation table becomes large on the side of the radio frequency power supply unit.
This configuration makes the distance between the installation table and the surface wave transmission line shorter as a position becomes away from the side of supplying radio frequency power of the surface wave transmission line without moving the installation table. In this context, absorbance of radio frequency power propagating on the surface wave transmission line into the object to be heated becomes larger as radio frequency power becomes away from the side from which radio frequency power of the surface wave transmission line is supplied. This enables to uniformly heat the object to be heated with respect to the propagation direction of radio frequency power of the surface wave transmission line even when a plurality of objects to be heated are aligned and installed or even when an object to be heated having a long length is installed with respect to the propagation direction of radio frequency power of the surface wave transmission line. This also enables to keep the installation table horizontal, making it possible to more surely prevent occurrence of a malfunction such as rolling of the object to be heated placed on the installation table.
A radio frequency heating cooker according to the present invention may have a configuration in which radio frequency supplying units are disposed at both ends of the surface wave transmission line, and the surface wave transmission line has a mountain-shaped inclination to substantially have a highest part in a middle with respect to the propagation direction of the radio frequency power.
This configuration enables to supply radio frequency power from the both ends of the surface wave transmission line. This also enables to make the distance between the installation table and the surface wave transmission line shorter as a position becomes away from the side of supplying radio frequency power of the surface wave transmission line without moving the installation table. This enables to more uniformly heat the object to be heated with respect to the propagation direction of radio frequency power of the surface wave transmission line even when a plurality of objects to be heated are aligned and installed or even when an object to be heated having a long length is installed with respect to the propagation direction of radio frequency power of the surface wave transmission line. This also enables to keep the installation table horizontal, making it possible to prevent occurrence of a malfunction such as rolling of the object to be heated placed on the installation table.

INDUSTRIAL APPLICABILITY

The present invention enables to efficiently heat an object to be heated without uneven heating in a radio frequency heating device that subject the object to be heated to heat treatment by a surface wave transmission line. Accordingly, the present invention is useful as a cooking appliance such as a microwave heater.

REFERENCE MARKS IN THE DRAWINGS

100, 200 radio frequency heating device
101 installation table
101a, 101b end
102 object to be heated
103, 106, 107, 203, 206, 207 surface wave transmission line
104, 204a, 204b transmission direction
105, 205a, 205b inclination angle
107a, 107c, 207a, 207c horizontal part
107b, 207b inclination part
110, 210 radio frequency power generator
111 magnetron
120, 220 radio frequency power supply unit
203a highest part
220a first radio frequency power supply unit (radio frequency power supply unit)
220b second radio frequency power supply unit (radio frequency power supply unit)
121 rectangular waveguide
141, 142, 143, 241, 242 electric field strength distribution
d101, d102, d201, d202, d203 distance

Claims

A radio frequency heating device that heats an object to be heated placed on an installation table, the device comprising:
at least one surface wave transmission line provided near the installation table;

at least one radio frequency power generator that generates radio frequency power; and

at least one radio frequency power supply unit that directly supplies the radio frequency power to the surface wave transmission line, wherein

the surface wave transmission line is formed to have an inclination with respect to a propagation direction of the radio frequency power to make a distance between the surface wave transmission line and the installation table larger on a side of the radio frequency power supply unit, the surface wave transmission line being installed on the surface wave transmission line.
The radio frequency heating device according to claim 1, wherein
the radio frequency power supply unit is disposed on both ends of the surface wave transmission line, and
the surface wave transmission line is formed to have a mountain-shaped inclination to substantially have a highest part in a middle with respect to the propagation directions of the radio frequency power.
The radio frequency heating device according to claim 1 or claim 2, wherein the inclination of the surface wave transmission line is disposed in at least an area opposing the installation table.