EP3780909A1

EP3780909A1 - High-frequency heating device

Info

Publication number: EP3780909A1
Application number: EP19781210.0A
Authority: EP
Inventors: Kazuki Maeda; Yoshiharu Oomori; Toshiyuki Okajima; Koji Yoshino; Masayuki Kubo; Hiroyuki Uejima; Takanori Hirobe
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2018-04-06
Filing date: 2019-03-29
Publication date: 2021-02-17
Anticipated expiration: 2039-03-29
Also published as: EP3780909A4; WO2019194098A1; EP3780909B1; CN111066375A; CN111066375B

Abstract

A high-frequency heating device includes: a high-frequency power generator configured to generate microwaves; a surface wave line containing a conductive material; a power feeder connected to the high-frequency power generator; and a loop antenna disposed at a front end of the power feeder and facing an end of the surface wave line. In this aspect, a high input impedance can be maintained, and a decrease of radiation resistance can be prevented or reduced. As a result, the size of the power feeder can be reduced, and surface wave heating can be efficiently performed.

Description

TECHNICAL FIELD

The present disclosure relates to a high-frequency heating device including a surface wave transmission line of a periodic structure.

BACKGROUND ART

A high-frequency heating device of this type supplies high-frequency power to a surface wave line through a waveguide to heat a heating target by using surface waves excited on the surface wave line (see, for example, Patent Literature 1). Heating with surface waves will be hereinafter referred to as surface wave heating.
In the field of surface wave heating, Patent Literature 2 discloses a method using a monopole antenna disposed at the front end of a power feeder.

Citation List

Patent Literature

PTL 1: Japanese Patent Application Publication No. S49-16944
PTL 2: Japanese Patent Application Publication No. H06-338387

SUMMARY OF THE INVENTION

In the power supply system including a waveguide, device size increases. In the power supply system including a monopole antenna, device size can be reduced as compared with the power supply system including a waveguide. However, radiation efficiency of the antenna decreases due to the influence of a peripheral object, and it is, therefore, difficult to perform impedance matching with the surface wave line. Consequently, high-frequency power cannot be efficiently supplied, and surface wave heating becomes insufficient.
The present disclosure has been made in order to solve the problems to date, and has an object of providing a small-size high-frequency heating device with high efficiency.
A high-frequency heating device according to an aspect of the present disclosure includes: a high-frequency power generator configured to generate microwaves; a surface wave line containing a conductive material; a power feeder connected to the high-frequency power generator; and a loop antenna disposed at a front end of the power feeder and facing an end of the surface wave line.
According to the present disclosure, the size of the power feeder can be reduced, and surface wave heating can be performed efficiently.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a configuration of a high-frequency heating device according to a first embodiment of the present disclosure.
FIG. 2 is a perspective view illustrating a configuration near a loop antenna according to the first embodiment.
FIG. 3 is a perspective view illustrating an example of a surface wave line.
FIG. 4 is a perspective view illustrating another example of the surface wave line.
FIG. 5 is a schematic view illustrating a configuration of a loop antenna according to a second embodiment of the present disclosure.
FIG. 6 is a perspective view illustrating the configuration of the loop antenna according to the second embodiment of the present disclosure.
FIG. 7 is a schematic view illustrating an example of a high-frequency heating device according to a third embodiment of the present disclosure.
FIG. 8 is a schematic view illustrating another example of the high-frequency heating device of the third embodiment.
FIG. 9 is a schematic view illustrating a configuration near a loop antenna according to a fourth embodiment of the present disclosure.
FIG. 10 is a schematic view illustrating a configuration near a loop antenna according to a fifth embodiment of the present disclosure.
FIG. 11 is a schematic view illustrating a configuration near a loop antenna according to a sixth embodiment of the present disclosure.
FIG. 12 is a schematic view illustrating a configuration of a high-frequency heating device according to a seventh embodiment of the present disclosure.
FIG. 13 is a perspective view illustrating a configuration near a loop antenna according to the embodiment.
FIG. 14 is a schematic view illustrating a configuration of a high-frequency heating device according to an eighth embodiment of the present disclosure.
FIG. 15 is a top view illustrating a configuration near a loop antenna according to a ninth embodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

A high-frequency heating device according to a first aspect of the present disclosure includes: a high-frequency power generator configured to generate microwaves; a surface wave line containing a conductive material; a power feeder connected to the high-frequency power generator; and a loop antenna disposed at a front end of the power feeder and facing an end of the surface wave line.
In the high-frequency heating device according to a second aspect of the present disclosure, in addition to the configuration of the first aspect, the loop antenna has a surface that is parallel to the end of the surface wave line and faces the end of the surface wave line.
In the high-frequency heating device according to a third aspect of the present disclosure, in addition to the configuration of the first aspect, the surface wave line is a periodic structure in which members having a plate or rod shape are periodically arranged on a flat plate and are oriented perpendicularly to the flat plate.
In the high-frequency heating device according to a fourth aspect of the present disclosure, in addition to the configuration of the third aspect, the loop antenna has a height smaller than a height of the members constituting the surface wave line.
In the high-frequency heating device according to a fifth aspect of the present disclosure, in addition to the configuration of the third aspect, the power feeder is disposed near a bottom surface of the surface wave line. The loop antenna extends in parallel with the members constituting the surface wave line and is grounded on a surface on which the power feeder is grounded.
The high-frequency heating device according to a sixth aspect of the present disclosure, in addition to the configuration of the first aspect, further includes a metal plate disposed at a side of the loop antenna opposite to the surface wave line.
In the high-frequency heating device according to a seventh aspect of the present disclosure, in addition to the configuration of the sixth aspect, a position of each of the power feeder and the metal plate is changeable.
The high-frequency heating device according to an eighth aspect of the present disclosure, in addition to the configuration of the first aspect, further includes an antenna cover disposed above the loop antenna and the antenna cover is configured to turn electric power radiated from the loop antenna toward the surface wave line.
In the high-frequency heating device according to a ninth aspect of the present disclosure, in addition to the configuration of the eighth aspect, the antenna covers the loop antenna and a part of the surface wave line.
In the high-frequency heating device according to a tenth aspect of the present disclosure, in addition to the configuration of the eighth aspect, a gap with a predetermined distance is provided between the antenna cover and the surface wave line.
Embodiments of the present disclosure will be described hereinafter with reference to the drawings. In the drawings, the same or like components are denoted by the same reference numerals, and description thereof will not be repeated.

(First Embodiment)

FIG. 1 is a schematic view illustrating a configuration of a high-frequency heating device according to a first embodiment of the present disclosure. FIG. 2 is a perspective view illustrating a configuration near loop antenna 3 according to this embodiment.
As illustrated in FIG. 1, high-frequency power generator 1 generates high-frequency power such as microwaves and supplies high-frequency power to power feeder 2 through a coaxial line. Power feeder 2 includes loop antenna 3 at the front end thereof. Loop antenna 3 emits high-frequency power toward surface wave line 4.
High-frequency power is concentrated in space near surface wave line 4. Heating target 5 is placed on placing table 6 near surface wave line 4, and heated by high-frequency power concentrated near surface wave line 4.
In this embodiment, heating chamber 7 accommodates surface wave line 4 and placing table 6. These components, however, do not need to be disposed in heating chamber 7.
Loop antenna 3 faces an end of surface wave line 4. High-frequency current flows in loop antenna 3 to thereby generate a ring-shaped magnetic field, and an induced current is caused to flow in conductive surface wave line 4 by electromagnetic induction. Accordingly, surface waves are generated and heat heating target 5.
In a known power supply system using a monopole antenna, surface waves are also generated to heat a heating target by the same principle. In this case, however, a near electromagnetic field to a peripheral object is generated so that an input impedance of the antenna decreases. Consequently, radiation efficiency decreases, resulting in insufficient surface wave heating.
In this embodiment, the loop-shaped antenna is used so that the height of the antenna can be reduced, and the length of the antenna can be increased. Accordingly, a packaging volume of the antenna increases so that a high input impedance can be maintained and a decrease in radiation resistor can be prevented or reduced. As a result, the size of the power feeder can be reduced, and surface wave heating can be efficiently performed.
FIG. 3 is a perspective view illustrating an example of surface wave line 4. As illustrated in FIG. 3, surface wave line 4 is a periodic structure in which plate-shaped stubs 9 are periodically arranged at predetermined intervals on a flat plate and are oriented perpendicularly to the flat plate. Stubs 9 are made of a conductive material such as aluminium or copper. This configuration allows surface waves to be transmitted uniformly on surface wave line 4. As a result, heating target 5 can be uniformly heated.
FIG. 4 is a perspective view illustrating another example of surface wave line 4. As illustrated in FIG. 4, surface wave line 4 may be a periodic structure in which rod-shaped stubs 10 are periodically arranged on a flat plate and are oriented perpendicularly to the flat plate. This configuration can ease matching of surface waves radiated from flat loop antenna 8 (see FIGS. 5 and 6) with surface wave line 4. Consequently, surface waves are uniformly transmitted on surface wave line 4 so that heating efficiency thereby increases.

(Second Embodiment)

FIG. 5 is a schematic view illustrating a configuration near loop antenna 3 according to a second embodiment of the present disclosure. FIG. 6 is a perspective view illustrating a configuration near loop antenna 3.
As illustrated in FIGS. 5 and 6, loop antenna 3 according to this embodiment is flat loop antenna 8. Flat loop antenna 8 has a surface that is parallel to an end of surface wave line 4 and faces the end of surface wave line 4.
Power feeder 2 is connected to high-frequency power generator 1. Power feeder 2 is disposed on a surface on which the bottom surface of surface wave line 4 is placed. An end of flat loop antenna 8 is connected to power feeder 2. The other end of flat loop antenna 8 is grounded on the surface on which the bottom surface of surface wave line 4 is placed.
This configuration can ease attachment of power feeder 2 and enables size reduction of power feeder 2. In this case, flat loop antenna 8 has a rectangular shape, and has a surface that is parallel to the end of surface wave line 4 and faces the end of surface wave line 4.
With this configuration, the area of a magnetic field generated by a flow of a high-frequency current in flat loop antenna 8 can be made large relative to surface wave line 4. Thus, electromagnetic waves radiated from flat loop antenna 8 can easily match with surface wave line 4. As a result, efficiency in conversion to surface waves increases, and thus, heating efficiency is enhanced.

(Third Embodiment)

FIG. 7 is a schematic view illustrating an example of a high-frequency heating device according to a third embodiment of the present disclosure. As illustrated in FIG. 7, a height of flat loop antenna 8 according to this embodiment is lower than a height of stubs 9 constituting surface wave line 4.
This configuration allows placing table 6 to be disposed closer to surface wave line 4. Thus, even in a case where placing table 6 is expanded to a place above flat loop antenna 8, heating target 5 can be placed closer to surface wave line 4. As a result, heating efficiency increases.
FIG. 8 is a schematic view illustrating another example of the high-frequency heating device of this embodiment. As illustrated in FIG. 8, in a case where placing table 6 is large, power feeder 2 and flat loop antenna 8 may be disposed at both ends of surface wave line 4.

(Fourth Embodiment)

FIG. 9 is a schematic view illustrating a configuration near flat loop antenna 8 according to a fourth embodiment of the present disclosure.
As illustrated in FIG. 9, supposing a height of stubs 9 constituting a periodic structure of surface wave line 4 is La, and a distance between two adjacent stubs 9 is Lb, if a distance from the upper surface of one stub 9 to the upper surface of its adjacent stub 9 by way of the surfaces of stubs 9 (i.e., 2La + Lb) is 1/2 of the wavelength of radiant power, a surface concentration degree of resultant surface waves increases so that heating efficiency thereby increases.
In other words, the wavelength of radiant power is varied such that the length corresponding to 1/2 of the wavelength of radiant power is equal to the distance from the upper surface of one stub 9 to its adjacent stub 9 by way of the surfaces of stubs 9 (i.e., 2La + Lb). Accordingly, the surface concentration degree of surface waves is increased so that heating efficiency can be thereby increased.
Supposing the thickness of each stub 9 is Lc, a distance between upper surfaces of two stubs 9 sandwiching one stub 9 is 2La + 2Lb + Lc. Application of electric power of a wavelength corresponding to 2La + 2Lb + Lc can vary the surface concentration degree of surface waves.
That is, by adjusting the wavelength of radiant power from high-frequency power generator 1, the surface concentration degree of surface waves can be controlled. Accordingly, optimum and efficient heating can be performed in accordance with the thickness and width of an object to be cooked.

(Fifth Embodiment)

FIG. 10 is a schematic view illustrating a configuration near flat loop antenna 8 according to a fifth embodiment of the present disclosure. As illustrated in FIG. 10, metal plate 11 is disposed at a side of flat loop antenna 8 opposite to surface wave line 4. With this configuration, metal plate 11 reflects high-frequency power radiated from flat loop antenna 8 to a direction opposite to surface wave line 4 and turns the direction of the high-frequency power toward surface wave line 4.
With this configuration, when a distance from the center of flat loop antenna 8 to metal plate 11 is set at a length of 1/4 of the wavelength of radiant power, the phase of electromagnetic waves radiated from flat loop antenna 8 toward surface wave line 4 coincides with the phase of electromagnetic waves reflected on metal plate 11. Accordingly, two electromagnetic waves interfere with each other to enhance each other, resulting in generation of standing waves. Consequently, stronger energy enters the surface wave line so that heating can be performed more efficiently.

(Sixth Embodiment)

FIG. 11 is a schematic view illustrating a configuration near flat loop antenna 8 according to a sixth embodiment of the present disclosure. As illustrated in FIG. 11, a high-frequency heating device according to this embodiment includes antenna base 8a.
Antenna base 8a is used for fixing power feeder 2 and grounding flat loop antenna 8. Antenna base 8a is electrically connected to surface wave line 4 and metal plate 11 through position adjuster 13 such as a cable. The position of antenna base 8a can be changed freely. Coaxial line 12 connects high-frequency power generator 1 to power feeder 2.
In this embodiment, a relative position of surface wave line 4 and flat loop antenna 8 and a relative position of metal plate 11 and flat loop antenna 8 are variable. Accordingly, it is possible to cope with the magnitude of the magnetic field in accordance with the frequency of radiant power so that impedance matching can be easily performed. As a result, efficiency in converting to surface waves is enhanced, and heating efficiency increases.

(Seventh Embodiment)

FIG. 12 is a schematic view illustrating a configuration of a high-frequency heating device according to a seventh embodiment of the present disclosure. FIG. 13 is a perspective view illustrating a configuration near flat loop antenna 8 according to this embodiment.
As illustrated in FIGS. 12 and 13, the high-frequency heating device according to this embodiment includes antenna cover 14 disposed at a predetermined distance from flat loop antenna 8 ahead of and above flat loop antenna 8 in FIG. 13. Antenna cover 14 is made of a metal member.
Flat loop antenna 8 radiates electric power mainly forward, rearward, and upward in FIG. 13. Antenna cover 14 reflects electric power radiated forward and upward from flat loop antenna 8 and turns the reflected electric power toward surface wave line 4. As a result, heating target 5 can be efficiently heated.
In this embodiment, flat loop antenna 8 has a rectangular shape. The present disclosure, however, is not limited to this example. Flat loop antenna 8 may have a circular shape or a square shape, for example.

(Eighth Embodiment)

FIG. 14 is a schematic view illustrating a configuration of a high-frequency heating device according to an eighth embodiment of the present disclosure. As illustrated in FIG. 14, in this embodiment, antenna cover 14 is disposed to cover not only flat loop antenna 8 but also at least some of stubs 9 included in surface wave line 4. That is, antenna cover 14 covers flat loop antenna 8 and a part of surface wave line 4.
In FIG. 14, dot-dash lines represent magnetic fields directly radiated from flat loop antenna 8. Broken lines represent magnetic fields generated by reflection on antenna cover 14. Dotted lines represent electric fields generated at this time.
An optimum length Ld of a portion of antenna cover 14 covering surface wave line 4 varies depending on the size of flat loop antenna 8 and the size of a periodic structure constituting surface wave line 4, and needs to be adjusted in accordance with electromagnetic field distribution.
As illustrated in FIG. 14, when high-frequency power is supplied, an electric field is generated perpendicularly from the upper surface of flat loop antenna 8 toward antenna cover 14. Accordingly, a magnetic field generated upward is reflected on antenna cover 14 and turned toward surface wave line 4. Stubs 9 generate surface waves in response to the reflected magnetic field. The thus-generated strong surface waves can efficiently heat heating target 5.

(Ninth Embodiment)

In a ninth embodiment, in the configuration illustrated in FIG. 14, a perpendicular distance between the upper surface of surface wave line 4 and antenna cover 14 is set at a predetermined distance (distance Le). That is, a gap with the predetermined distance is provided between antenna cover 14 and surface wave line 4.
In this configuration, when distance Le is varied, an impedance around flat loop antenna 8 varies, and a resonance frequency varies. For example, when distance Le is reduced so that flat loop antenna 8 and antenna cover 14 approach each other, the resonance frequency decreases. Thus, an electromagnetic field radiated from flat loop antenna 8 easily matches with an electromagnetic field reflected on antenna cover 14. As a result, surface wave heating can be performed efficiently.
FIG. 15 is a top view illustrating a configuration near flat loop antenna 8 according to the ninth embodiment. Broken lines and dot-dash lines in FIG. 15 represent magnetic fields generated when high-frequency power generator 1 operates. The dot-dash lines represent magnetic fields in the absence of antenna cover 14, and the broken lines represent magnetic fields in the presence of antenna cover 14.
When an electric field is generated from flat loop antenna 8 toward antenna cover 14, a magnetic field is generated around the electric field, and this electric field further generates an electric field. When an orientation of the thus-generated magnetic field (broken line) is matched with an orientation of a magnetic field (dot-dash line) generated irrespective of the presence of antenna cover 14, a magnetic field surrounding stubs 9 of surface wave line 4 becomes strong. Accordingly, induced current increases. As a result, electric power transmitted as surface waves increases so that heating target 5 can be efficiently heated.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to household or industrial high-frequency heating devices.

DESCRIPTION OF REFERENCE CHARACTERS

1: high-frequency power generator
2: power feeder
3: loop antenna
4: surface wave line
5: heating target
6: placing table
7: heating chamber
8: flat loop antenna
8a: antenna base
9, 10: stub
11: metal plate
12: coaxial line
13: position adjuster
14: antenna cover

Claims

A high-frequency heating device comprising:
a high-frequency power generator configured to generate microwaves;

a surface wave line containing a conductive material;

a power feeder connected to the high-frequency power generator; and

a loop antenna disposed at a front end of the power feeder and facing an end of the surface wave line.
The high-frequency heating device according to claim 1, wherein the loop antenna has a surface that is parallel to the end of the surface wave line and faces the end of the surface wave line.
The high-frequency heating device according to claim 1, wherein the surface wave line is a periodic structure in which members having a plate or rod shape are periodically arranged on a flat plate and are oriented perpendicularly to the flat plate.
The high-frequency heating device according to claim 3, wherein the loop antenna has a height smaller than a height of the members constituting the surface wave line.
The high-frequency heating device according to claim 3, wherein the power feeder is disposed near a bottom surface of the surface wave line, and
the loop antenna extends in parallel with the members constituting the surface wave line and is grounded on a surface on which the power feeder is placed.
The high-frequency heating device according to claim 1, further comprising a metal plate disposed at a side of the loop antenna opposite to the surface wave line.
The high-frequency heating device according to claim 6, wherein a position of each of the power feeder and the metal plate is changeable.
The high-frequency heating device according to claim 1, further comprising an antenna cover disposed above the loop antenna, the antenna cover being configured to turn electric power radiated from the loop antenna toward the surface wave line.
The high-frequency heating device according to claim 8, wherein the antenna cover covers the loop antenna and a part of the surface wave line.
The high-frequency heating device according to claim 8, wherein a gap with a predetermined distance is provided between the antenna cover and the surface wave line.