WO2018235161A1

WO2018235161A1 - Microwave heating device

Info

Publication number: WO2018235161A1
Application number: PCT/JP2017/022685
Authority: WO
Inventors: 由文河村; 拓海杉谷; 政毅半谷; 山中　宏治
Original assignee: 三菱電機株式会社
Priority date: 2017-06-20
Filing date: 2017-06-20
Publication date: 2018-12-27

Abstract

In this microwave heating device, phase control plates (6, 6a to 6d) are mounted on wall surfaces of an apparatus main body (1), on the heating chamber (2) side thereof. Each of these phase control plates (6, 6a to 6d) comprises unit cells (60, 60-11 to 60-22) arrayed in a plurality of rows and a plurality of columns and uses a meta-material formed from a semiconductor (63). A capacitance value modifying means (8) varies the capacitance values in each of the phase control plates (6, 6a to 6d).

Description

Microwave heating device

The present invention relates to a microwave heating apparatus for heating an object to be heated by microwave irradiation such as a microwave oven.

In a microwave heating apparatus such as a microwave oven, for the purpose of heating the object to be heated efficiently and uniformly, a rotary antenna that radiates microwaves is disposed substantially at the center of the bottom wall surface of the heating chamber. Patent Document 1 proposes that a connecting portion is provided on the right wall surface and the upper wall surface, and a waveguide portion connecting each connecting portion is disposed.

JP, 2009-16149, A

The microwave heating device disclosed in Patent Document 1 performs heating by substantially circulating a part of the microwave energy supplied from the rotary antenna into the heating chamber through the coupling portion between the waveguide and the heating chamber. The amount of microwave energy reflected from the chamber to the magnetron side can be reduced. In addition, since the supply of the microwaves into the heating chamber is also performed from the coupling portion, the microwaves can be supplied from various directions to the object to be heated.
However, even with the microwave heating apparatus configured as described above, there is a problem that high-intensity zones (hot spots) or dead zones of microwaves are generated due to the shape of the heating chamber.

This invention solves the above-mentioned subject, and it aims at obtaining the microwave heating device which suppressed generation | occurrence | production of the hot spot resulting from the shape of a heating chamber.

The microwave heating apparatus according to the present invention is a phase control that is formed of a semiconductor, uses a metamaterial in which unit cells are arranged in a plurality of rows and a plurality of columns, and is mounted on a wall on the heating chamber side of the inner wall in the instrument body A plate and capacitance value changing means for changing the capacitance value of the phase control plate.

According to the present invention, the phase control plate can arbitrarily change the electric field reflection phase on the metal interface which is the inner wall of the instrument body, and can suppress the hot spot due to the shape of the heating chamber surrounded by the inner wall. Uniform heating can be made possible.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows the microwave heating device which concerns on Embodiment 1 of this invention. FIG. 3 is a three-dimensional layout diagram showing a part of phase control plates 6 a to 6 e in the microwave heating device according to Embodiment 1 of the present invention. III-III sectional drawing in FIG. FIG. 7 is an equivalent circuit diagram of a unit cell 60 of phase control plates 6 a to 6 e in the microwave heating apparatus according to Embodiment 1 of the present invention. FIG. 6 is a view showing the relationship between the capacitance value of the variable capacitance element 7 of the unit cell 60 and the reflection phase θ in the phase control plates 6a to 6e in the microwave heating apparatus according to Embodiment 1 of the present invention.

Embodiment 1
A microwave heating apparatus such as a microwave oven is heated by irradiating the object to be heated 100 contained in the heating chamber 2 with microwaves, by the electromagnetic properties of the object to be heated 100, that is, dielectric loss, magnetic loss, etc. Configured to be able to The instrument body 1 has an inner wall 3 and an outer wall 4. The inner wall 3 has a bottom wall 3a made of a metal material that reflects microwaves, a left wall 3b, a right wall 3c, a ceiling wall 3d, and a back wall 3e (not shown). The front surface of the inner wall 3 has an opening serving as an inlet / outlet of the heating object 100, and the opening is closed by a door (not shown). A space surrounded by the bottom wall 3a, the left wall 3b, the right wall 3c, the ceiling wall 3d, and the back wall 3e in the inner wall 3 and the door closing the opening becomes the heating chamber 2. The heating chamber 2 encloses the supplied microwaves therein.

The antennas 5a to 5c are mounted on the ceiling wall 3d of the inner wall 3 of the instrument body 1, and are supplied from the microwave source (not shown) and transmitted through the waveguide to the heating chamber 2 Do. The microwave source and the waveguide are disposed in a space 1 a formed between the inner wall 3 and the outer wall 4 of the tool body 1. In the first embodiment, three antennas 5a to 5c are mounted on the ceiling wall 3d of the inner wall 3. However, one antenna may be used, or the bottom wall 3a, the left wall 3b, the right wall 3c, One or more may be attached to at least one wall of the ceiling wall 3d and the back wall 3e.

The phase control plate includes a phase control plate 6a attached to the bottom wall 3a of the inner wall 3 by adhesion or screwing, a phase control plate 6b attached to the left wall 3b by adhesion or screwing, and the right wall 3c. A phase control plate 6c attached by adhesion or screwing, a phase control plate 6d attached by adhesion or screwing to the ceiling wall 3d, and a phase control plate attached by adhesion or screwing to the back wall 3e 6e (not shown). In each of the phase control plates 6a to 6e, a large number of unit cells 60 are arranged in a plurality of rows and a plurality of columns, and is formed of a metamaterial (Meta-material) formed of a semiconductor. In other words, each of the phase control plates 6a to 6e has a metamaterial structure in which unit cells 60 are periodically arranged in the vertical and horizontal directions in a two-dimensional area on the surface of the insulating substrate 61. Note that the periodic arrangement means that a plurality of identical structures are arranged at a constant period, that is, at equal intervals. A table (not shown) made of a low dielectric loss material on which the object to be heated 100 is mounted is disposed on the phase control plate 6a mounted on the bottom wall 3a.

Each of the phase control plates 6a to 6e functions as an electromagnetic field distribution adjusting unit, in which the surface on the heating chamber 2 side is a metal interface, and the reflection phase of the electric field at the metal interface is arbitrarily changed. When the phase control plates 6a to 6e are not attached to the bottom wall 3a, the left wall 3b, the right wall 3c, the ceiling wall 3d, and the back wall 3e in the inner wall 3, the bottom wall 3a, the left wall 3b, the right wall 3c, and the ceiling The reflection phase of the electric field at the metal interface, which is the wall surface of the wall 3d and the back wall 3e, is always 180 °. On the other hand, the phase control plates 6a to 6e are attached to the wall surfaces of the bottom wall 3a, the left wall 3b, the right wall 3c, the ceiling wall 3d, and the back wall 3e in the inner wall 3 to form the bottom wall 3a and the left wall 3b. , And the reflection phase of the electric field on the wall surfaces of the right wall 3c, the ceiling wall 3d, and the back wall 3e can be made arbitrary.

Next, each of the phase control plates 6a to 6e which is a unique configuration of the microwave heating apparatus according to the first embodiment will be described with reference to FIGS. Each of the phase control plates 6a to 6e is disposed on the entire wall surface of the bottom wall 3a, the left wall 3b, the right wall 3c, the ceiling wall 3d, and the back wall 3e of the inner wall 3 to be attached. , And only the number of rows and the number of columns of unit cells 60 arranged are different, and the structure is otherwise the same including the structure of unit cells 60.
Therefore, in the following description of FIGS. 2 to 4, the phase control plates 6 a to 6 e will be representatively described as the phase control plate 6.

FIG. 2 is a three-dimensional layout diagram showing a portion of the phase control plate 6 in which unit cells 60-11 to 60-22 are arranged in two rows and two columns. FIG. 3 is a cross-sectional view taken along the line iii-iii of FIG. In practice, the unit cells 60 are periodically arranged in a large number in the right direction and a large number in the lower direction in FIG.
Each of the unit cells 60-11 to 60-22 includes a ground conductor 62 formed on the surface of the insulating substrate 61, a semiconductor 63, and an electrode portion 64 having a cross-shaped plane. The phase control plate 6 is mounted with the back surface of the insulating substrate 61 facing the wall surface of the inner wall 3. The ground conductor 62 is a ground conductor layer 620 formed of an aluminum (Al) layer vapor-deposited on the surface of the insulating substrate 61, and is located in the formation region of the unit cells 60-11 to 60-22. The ground conductor layer 620 is set to the ground potential.

The semiconductor 63 is a large band gap gallium nitride (GaN) layer 630 formed on the surface of the ground conductor layer 620. Each electrode portion 64 is formed of an aluminum (Al) layer vapor-deposited on the surface of the GaN layer 630, and is located in the formation region of unit cells 60-11 to 60-22. Each of the electrode portions 64 serves as one electrode of the variable capacitance element 7 which is a varactor diode in each of the unit cells 60-11 to 60-22. Each of the varactor diodes which are the variable capacitance elements 7 is formed in the GaN layer 630 located between the opposing tips in the cross shape of the adjacent electrode parts 64. The varactor diode changes its capacitance value by adjusting the PN junction depletion region, and when the reverse voltage applied between the anode and the cathode increases, the capacitance value decreases and the reverse voltage decreases. Capacity value increases.

When the ground conductor layer 620 is viewed from above, the opening 621 is formed at a position including the opposing tip of the cross shape of the adjacent electrode portion 64. That is, after an Al layer is formed on the surface of the insulating substrate 61 by vapor deposition, openings 621 are formed on the vertical and horizontal matrixes by etching. As a result, the ground conductor layer 620 remains in the formation region of the unit cells 60-11 to 60-22, and the ground conductor layer 620 in the remaining portion becomes the ground conductor 62 of each unit cell 60-11 to 60-22.

Each of the electrode portions 64 is electrically connected by a ground conductor 62 and a contact 65, the center of the cross shape being positioned immediately below the cross shape. The electrode portion 64 and the contact 65 are formed as follows. That is, in the GaN layer 630, the contact holes 63a are formed at respective central positions in the formation regions of the unit cells 60-11 to 60-22. In this state, an Al layer is formed on the surface of the GaN layer 630 by vapor deposition. At this time, Al is buried in contact hole 63a, electrically connected to corresponding ground conductor 62 in ground conductor layer 620, and also electrically connected to the Al layer formed on the surface of GaN layer 630. Contacts 65 are formed. Thereafter, the Al layer is etched to form a plurality of cross-shaped electrode portions 64 formed on the surface of the GaN layer 630 in a plurality of rows and a plurality of columns.

The four cross-shaped tips of each of the electrode portions 64 are electrically connected to wiring contacts 66a to 66d electrically connected to corresponding wiring layers (not shown) formed on the back surface of the insulating substrate 61. Ru. The wiring contacts 66a to 66d are formed simultaneously with the electrode portion 64 and the contact 65. That is, through holes are formed in the GaN layer 630 and the insulating substrate 61 at the positions where the cross-shaped four tips of the electrode portion 64 are located. In this state, when an Al layer is formed on the surface of the GaN layer 630 by vapor deposition, Al is embedded in the through holes and electrically connected to the corresponding wiring layer formed on the back surface of the insulating substrate 61. A plurality of wiring contacts 66 electrically connected also to the Al layer formed on the surface of 630 are formed.

The variable voltage source 8 is connected between the facing end portions of the adjacent electrode portions 64 via the wiring contacts 66a to 66d and the wiring layer. Each of the variable voltage sources 8 is a DC power supply capable of automatically, continuously and temporally changing the voltage value. The variable voltage source 8 in which the plus electrode is connected to the wiring contact 66a is a wire to which the tip portion of the adjacent electrode portion 64 is connected, whose minus electrode faces the tip portion of the electrode portion 64 to which the brass electrode is connected. It is connected to the contact 66b. The variable voltage source 8 in which the plus electrode is connected to the wiring contact 66c is a wire to which the tip portion of the adjacent electrode portion 64 is connected such that the minus electrode faces the tip portion of the electrode portion 64 to which the brass electrode is connected. It is connected to the contact 66d.

When the voltage value of the variable voltage source 8 is automatically, continuously and temporally changed, the variable capacitance element 7 formed between the facing tips of the adjacent electrode parts 64 connected to the variable voltage source 8 The volume values also change automatically, continuously and temporally. As a result, the reflection phase of the electric field on the surface of the phase control plate 6 facing the inside changes, and the impedance on the surface facing the inside of the heating chamber 2 changes, and the electromagnetic field distribution (the standing wave distribution) ) Changes. Therefore, when microwaves are supplied into the heating chamber 2 from the antennas 5a to 5c, the distribution of the temperature rise of the object to be heated 100 is also changed by the change of the electromagnetic field distribution, and the entire object to be heated 100 is It can be uniformly heated.
The variable voltage source 8 serves as capacitance value changing means for changing the capacitance value of the phase control plates 6a to 6e.

FIG. 4 shows an equivalent circuit diagram of the unit cell 60 of the phase control plates 6a to 6e, and there are variable capacitance elements 7 extended in four directions from the equivalent circuit formation surface to be the common node 9. An inductive element 10 is present between the common node 9 and the ground conductor 62. Further, the wall surfaces of the bottom wall 3a, the left wall 3b, the right wall 3c, the ceiling wall 3d, and the back wall 3e in the inner wall 3 to which the phase control plates 6a to 6e are attached become the periodic boundary 11.

Next, the operation of the microwave heating apparatus according to the first embodiment will be described with reference to FIGS. 1 to 4. The operating frequency of the microwave supplied from the antennas 5a to 5c into the heating chamber 2 is f0, and the wavelength of the operating frequency is λ.
When the microwave generation source is operated, the microwaves transmitted through the waveguide are supplied from the antennas 5a to 5c into the heating chamber 2 by the solid line arrows A1 to A3 and the dotted line arrow B1 shown in FIG. As a result, heat loss occurs and the object to be heated 100 is heated.

The heating action on the object to be heated 100 is dominated by the dielectric loss of the object to be heated 100 generated by the irradiation of the microwaves. Therefore, the following description will be given focusing on only the electric field components generated from the antennas 5a to 5c.
First, microwaves directly incident on the object to be heated 100 from the antennas 5a to 5c, and microwaves indicated by solid arrows A1 to A3 in FIG. 1 will be described. The electric field component E1 of the microwave A1 output from the antenna 5a, the electric field component E2 of the microwave A2 output from the antenna 5b, and the electric field component E3 of the microwave A3 output from the antenna 5c. At this time, each of the electric field components E1 to E3 has an arbitrary amplitude and phase at the momentary time, and can be expressed by the following equations (1) to (3) as electric field components at the momentary time.

E1 = | E1 | exp (-γ * z1 + j * ωt) (1)
E2 = | E2 | exp (-γ * z2 + j * ωt) (2)
E3 = | E3 | exp (-γ * z3 + j * ωt) (3)
Here, γ is a propagation constant at the operating frequency f0, ω is an angular frequency derived from the operating frequency f0, t is an arbitrary time, z1, z2 and z3 are arbitrary positions of the respective antennas 5a to 5c and the object 100 to be heated And the distance.

At this time, the electric field strength at an arbitrary position of the object to be heated 100 is a combined electric field Etotal of the three electric field components, and can be expressed by the following equation (4).
Etotal = E1 + E2 + E3
= | E1 | exp (-γ * z1 + j * ωt)
+ | E2 | exp (-γ * z2 + j * ωt)
+ | E3 | exp (-γ * z3 + j * ωt) (4)
As understood from the equation (4), since the distances z1, z2 and z3 are different at each position where the microwaves A1 to A3 are incident from the antennas 5a to 5c in the object to be heated 100, the microwaves A1 to A3 are obtained. The combined electric field Etotal at the position where the light is incident is also different. As a result, the electric field strength varies depending on the position of the object 100 to be heated. The variation in electric field strength causes uneven heating to the object to be heated 100.

However, the microwaves incident on the object to be heated 100 are not only the microwaves A1 to A3 directly incident from the antennas 5a to 5c, but also the bottom wall 3a, the left wall 3b, and the right wall of the inner wall 3 of the tool body 1 The microwaves incident on the phase control plates 6a to 6e mounted on the wall surfaces of the ceiling wall 3d and the back wall 3e are also incident on the object to be heated 100.
There are many microwaves that are incident on the phase control plates 6a to 6e from the antennas 5a to 5c, reflected, and incident on the object to be heated 100, but the idea is the same, so the incident on the phase control plate 6b from the antenna 5a The description will be added regarding the reflected and reflected microwaves and the microwaves indicated by dotted line B1 in FIG.

The microwave B1 incident from the antenna 5a is taken as the electric field component E1r of the reflected wave reflected by the phase control plate 6b. At this time, the electric field component E1r has an arbitrary amplitude and phase at the momentary time, and can be formulated as the momentary electric field component according to the following equation (5).
E1r = | E1 | exp (-γ * z1r + j * ωt + j * θ) (5)
Here, z1r is the sum of the distance between the antenna 5a and the reflection point of the phase control plate 6b and the distance between this reflection point and an arbitrary position of the object 100, and θ is the microwave B1 by the phase control plate 6b. It is a reflection phase when it is reflected.

On the other hand, the relationship between the capacitance value of the variable capacitance element 7 of the phase control plate 6b and the reflection phase θ is as shown in FIG. In FIG. 5, the horizontal axis represents the capacitance value of the variable capacitance element 7, and the vertical axis represents the reflection phase θ. As understood from FIG. 5, when the capacitance value of the variable capacitance element 7 is changed from 1.4 pF to 2.0 pF and at least 1.6 pF to 1.8 pF, the reflection phase is changed from -150 ° to 130 °. .
Therefore, when the voltage value of the variable voltage source 8 is automatically, continuously and temporally changed, the capacitance value of the variable capacitance element 7 connected to the variable voltage source 8 is also automatically, continuously and temporally changed. Do. That is, the reflection phase θ can be made variable by continuously controlling the capacitance value of the variable capacitance element 7 by the variable voltage source 8.

As a result, the reflection phase θ of the electric field at the surface of the phase control plate 6 b facing the inside of the heating chamber 2 changes, and the impedance at the surface of the heating chamber 2 facing the inside changes. Distribution) changes. That is, the electric field component E1r of the reflected wave also changes.
Therefore, the dispersion of the combined electric field Etotal at the incident position due to the microwave directly incident on the object to be heated 100 from the antennas 5a to 5c is incident on the phase control plates 6a to 6e from the antennas 5a to 5c and reflected. This can be suppressed by the microwave B incident on the object to be heated 100. As a result, the variation in the electric field strength can be suppressed depending on the position of the object to be heated 100, the heating unevenness to the object to be heated 100 can be suppressed, and uniform heating can be realized.

In short, in the microwave heating apparatus according to the first embodiment, the phases mounted on the bottom wall 3a, the left wall 3b, the right wall 3c, the ceiling wall 3d, and the back wall 3e in the inner wall 3 of the instrument body 1 By electronically operating the reflection characteristics of the microwaves on the wall surface of the inner wall 3 on the heating chamber 2 side using the control plates 6a to 6e, it is possible to suppress hot spots due to the shape of the heating chamber 2. The whole of the article to be heated 100 can be uniformly heated, and uniform heating of the article to be heated 100 can be realized.

In the scope of the present invention, free combination of each embodiment, or modification of any component of each embodiment, or omission of any component in each embodiment is possible within the scope of the invention. .

DESCRIPTION OF SYMBOLS 1 Apparatus main body, 2 heating chamber, 3 inner wall, 3a bottom wall, 3b left wall, 3c right wall, 3d ceiling wall, 4 outer wall, 5a to 5c antenna, 6, 6a to 6d phase control plate, 7 variable capacitance element, 8 Variable voltage source, 60, 60-11 to 60-22 unit cells, 62 ground conductors, 63 semiconductors, 64 electrode parts, 65 contacts, 100 heated objects, 620 ground conductor layers, 630 GaN layers, 640 electrode layers.

Claims

An instrument body having a heating chamber in which the object to be heated is accommodated;
An antenna for supplying microwaves into the heating chamber;
A phase control plate formed of a semiconductor and using a metamaterial in which unit cells are arranged in a plurality of rows and a plurality of columns and mounted on a wall surface on the heating chamber side of the device body,
Capacitance value changing means for changing the capacitance value of the phase control plate,
Microwave heating device.
The device body has an inner wall and an outer wall, and the inner wall has a bottom wall, a left wall, a right wall, a ceiling wall, and a back wall made of a metal material that reflects microwaves, Have an opening closed by the door
The micro-device according to claim 1, wherein the wall of the inner wall of the device body on which the phase control plate is mounted is the bottom wall, the left wall, the right wall, the ceiling wall, and the back wall. Wave heating device.
The metamaterial has a variable capacitance element,
The microwave heating apparatus according to claim 1 or 2, wherein the capacitance value changing means is a variable voltage source which temporally changes the capacitance value of the variable capacitance element of the metamaterial.
An instrument body having a heating chamber in which the object to be heated is accommodated;
An antenna for supplying microwaves into the heating chamber;
An insulating substrate, a ground conductor layer formed on the surface of the insulating substrate, a gallium nitride layer formed on the surface of the ground conductor layer, and a plurality of rows and columns arranged on the surface of the gallium nitride layer An electrode layer which has a plurality of cross-shaped electrode parts and which constitutes a variable capacitance element between adjacent electrode parts, and electrically connects the center of the electrode parts corresponding to the electrode layer and the ground conductor layer And a plurality of contacts connected to the phase control plate mounted on the wall surface of the tool body on the heating chamber side,
A variable voltage source connected to the tips of adjacent electrode parts in this phase control plate and applying a voltage between the connected tips,
Microwave heating device.
The device body has an inner wall and an outer wall, and the inner wall has a bottom wall, a left wall, a right wall, a ceiling wall, and a back wall made of a metal material that reflects microwaves, Have an opening closed by the door
The micro-device according to claim 4, wherein the wall of the inner wall of the device body on which the phase control plate is mounted is the bottom wall, the left wall, the right wall, the ceiling wall, and the back wall. Wave heating device.
6. The variable voltage source according to claim 4, wherein the voltage applied between the connected tips of adjacent electrode portions of the phase control plate is continuously and temporally changed. Microwave heating device.