JP2014216067A - High-frequency wave heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To emit a microwave power generated by a magnetron at the maximum in a heating chamber without loss by efficiently coupling the microwave power with a rotation antenna.SOLUTION: A high-frequency wave heating device comprises: a heated object placement plate provided on a bottom face of a heating chamber; a high-frequency supply chamber provided at a substantially central part on the bottom face of the heating chamber, below the heated object placement plate; a magnetron; a waveguide to which the magnetron is attached; a coupling hole provided at the central part on a bottom face of the high-frequency supply chamber; an inner conductor provided to penetrate through the coupling hole and to face the inside of the high-frequency supply chamber substantially vertically; a metal rotation antenna having a spacial structure, substantially horizontally coupled in the high-frequency supply chamber at one end of the inner conductor; a dielectric body shaft coupled in the waveguide of the inner conductor; and a drive part rotating and driving the dielectric body shaft. The rotation antenna is configured by a square plane part, and a downward vertical wall part provided at an outer periphery of one side of the plane part and two sides sandwiching it.

Description

  The present invention relates to a high-frequency heating apparatus that uses a rotating antenna to radiate microwave energy into a heating chamber to heat food and the like.

  The high-frequency heating device of Patent Document 1 includes a mounting base made of a dielectric material fixed to the bottom surface of a heating chamber, and a rotating antenna made of a horn-shaped radiation path at an excitation port portion of a waveguide provided in the central portion of the conductor surface. The microwave energy guided by the waveguide is coupled to the rotating antenna, and then radiated into the heating chamber from the horn-shaped opening of the rotating antenna to heat the food placed on the mounting table at a high frequency. is there.

JP 2010-199209 A

  In Patent Document 1, one end of an inner conductor that passes through a coupling hole provided in a conductor surface, faces substantially vertically into the conductor surface and is coupled to a rotating antenna is projected into a waveguide, and the conductor Rotation consisting of a horn-shaped radiating path with a narrow upper surface on the lower base and two lower edges connecting the upper base with a long side at the upper and lower bases of the planar wide surface. After the microwave generated by the magnetron and transmitted through the waveguide is coupled to the antenna, the microwave is radiated into the heating chamber from the top end of the rotating antenna where the narrow surface is not installed. ing. In addition, a short-circuit surface is provided at the narrow surface end of the rotating antenna at the narrow surface end so as to face the conductive surface at a right angle to the narrow surface end. To prevent leakage.

  However, the microwave leaking from the gap between the narrow surface and the conductor surface cannot be sufficiently suppressed only by providing the flat short-circuit surface, and it is difficult to improve the directivity and the degree of coupling. In particular, if there is a large amount of microwaves leaking from the gap between the lower bottom side narrow surface end facing the upper bottom side where the narrow surface portion is not provided in the trapezoidal wide surface and the conductor surface, the upper base side of the wide surface There is a problem that the directivity of the radiating microwave is weakened and the degree of coupling is significantly reduced.

  The present invention has been made to solve the above-described problem, and includes a heating chamber that accommodates an object to be heated, a heated object mounting plate made of a dielectric provided on the bottom surface of the heating chamber, and the heated object. A high-frequency supply chamber that is a conductor surface provided at a substantially central portion of the bottom surface of the heating chamber below the object placement plate, a magnetron that generates microwave energy, a waveguide for mounting the magnetron, and a bottom surface of the high-frequency supply chamber A coupling hole provided in the center, an inner conductor provided through the coupling hole and facing the high-frequency supply chamber substantially vertically, and a metal made of metal that is housed in the high-frequency supply chamber and connected to one end of the inner conductor In a high-frequency heating apparatus including a rotating antenna, a dielectric shaft connected in the waveguide of the inner conductor, and a drive unit that rotationally drives the dielectric shaft, the rotating antenna is connected to the inner conductor. A substantially horizontal and polygonal plane And a vertical wall portion provided so as to hang down on a part of the outer periphery of the planar portion, and faces a side of the outer periphery of the planar portion where the vertical wall portion is not provided. The vertical wall portion provided on the side is provided with a choke structure that suppresses leakage of electromagnetic waves.

  In the rotating antenna of the high-frequency heating device of the present invention, the microwave leaking from the gap between the vertical wall end and the bottom of the high-frequency supply chamber can be blocked by arranging the choke outside the vertical wall with the rotating antenna. . As a result, the microwave coupled to the rotating antenna forms a radiation path that is transmitted to a radiation port without a vertical wall portion serving as an opening surface, thereby improving directivity and degree of coupling.

1 is a longitudinal sectional view of a main part of a high-frequency heating device according to Embodiment 1. FIG. 1 is a perspective view of a rotary antenna according to Embodiment 1. FIG. FIG. 3 is an enlarged perspective view of a choke portion of the rotating antenna according to the first embodiment. Sectional drawing in the aa surface of the rotating antenna of Example 1. FIG. The analysis result of the return loss of the rotating antenna of Example 1. FIG. 3 is an equivalent transmission path of the choke of the rotating antenna according to the first embodiment. FIG. 3 is an equivalent circuit of a choke for the rotating antenna according to the first embodiment. The leakage microwave electric field distribution analysis result of the rotating antenna choke of Example 1. Near field pattern analysis result indicating directivity of the rotating antenna of the first embodiment FIG. 6 is a perspective view of a rotating antenna according to a second embodiment. FIG. 6 is an enlarged perspective view of a choke portion according to a third embodiment. FIG. 10 is a perspective view of a rotating antenna according to a fifth embodiment. It is a perspective view when the rotation antenna of Example 1 is manufactured by integral molding in the perspective view of the rotation antenna of Example 6. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  1 is a longitudinal sectional view of a main part of the high-frequency heating apparatus according to the first embodiment, FIG. 2 is a perspective view of a rotating antenna, FIG. 3 is an enlarged perspective view of a choke portion of the rotating antenna of FIG. FIG. 5 shows an equivalent transmission path of the rotating antenna choke. FIG. 6 is an equivalent circuit of the choke of the rotating antenna, and FIG. 7 is an aa cross section of the rotating antenna. FIG. 8 shows the leakage microwave electric field distribution analysis result of the rotating antenna choke, and FIG. 9 shows the near field pattern analysis result indicating the directivity of the rotating antenna.

  As shown in the cross-sectional view of the main part of FIG. 1, the high-frequency heating device of the present embodiment is mounted on a heated object 1 made of a heating chamber 1 that houses a heated object 12 and a dielectric provided on the bottom surface of the heated chamber 1. A mounting plate 2, a high-frequency supply chamber 3 provided below the heated object mounting plate 2, a magnetron 4 that generates microwave energy, a waveguide 5 to which the magnetron 4 is attached, and a waveguide 5. In order to radiate the guided microwave energy to the high-frequency supply chamber 3, the coupling hole 6 provided in the center of the bottom surface of the high-frequency supply chamber 3 and the coupling hole 6 penetrate into the high-frequency supply chamber 3 substantially vertically. Are connected in a waveguide 5 of the inner conductor 7, the metal three-dimensional rotating antenna 8 connected substantially horizontally in the high-frequency supply chamber 3 at one end of the inner conductor 7, and the inner conductor 7. A dielectric shaft 9 and a drive unit 10 that rotationally drives the dielectric shaft 9. In the rotating antenna 8, the microwave energy generated in the magnetron 4 whose rotation is controlled by the driving unit 10 is guided to the waveguide 5 and propagated to the rotating antenna 8 by coaxial mode coupling with the inner conductor 7 penetrating the coupling hole 6. Then, it is radiated into the heating chamber 1 through the high-frequency supply chamber 3 and the heated object placing plate 2.

  As shown in FIG. 2, the rotating antenna 8 has a substantially polygonal (quadrangle in this embodiment) plane portion 11 that contacts the inner conductor 7, and a direction substantially perpendicular to the direction of the high-frequency supply chamber bottom surface 3 provided on the plane portion 11. The vertical wall portions 8a, 8b, and 8c that hang down, and the vertical wall portions 8a, 8b, and 8c provided on a total of three sides, that is, the one side 8a of the plane portion 11 and the two sides 8b and 8c sandwiching the one side 8a, A rectangular bowl-shaped radiation path having an opening at one end is formed. The width of the side 8d where the vertical wall portion is not provided in the flat portion 11 and the vertical wall portion 8a facing the side 8d is longer than 1 / 2λ (λ is the wavelength of the microwave) and shorter than λ, and the vertical wall Is a radiation path having the same shape as the waveguide 5 shorter than 1 / 2λ and 1 / 25λ, and the total length of the rotating antenna 8 is 3 / 2λ. A choke 13 that suppresses leakage of electromagnetic waves is disposed outside the vertical wall portion 8a facing the side 8d where no vertical wall portion is provided. As shown in FIG. 3, the choke 13 forms a rectangular parallelepiped cavity 13-1 in which a rectangular plane is bent in a square shape, and the rectangular parallelepiped cavity surface 13-2 facing the bottom surface of the high-frequency supply chamber 3 has the above-mentioned vertical shape. The notch 13-3 is provided along the end of the vertical wall 8d on the wall 8a side. The length L from the choke entrance point A of the choke 13 to the choke short-circuit point B is selected to be ¼ wavelength. For example, in a home high-frequency heating device (microwave oven) using a frequency of 2450 ± 50 MHz, the wavelength λ is 125 to 120 mm. Therefore, the choke length L is about 30 mm. Further, since the size of the high-frequency supply chamber 3 that houses the rotating antenna 8 of this embodiment is 5 / 3λ in width, 4 / 3λ in depth, and 1 / 6λ in depth, the width 3 / 2λ in which the choke 13 is arranged, The rotating antenna 8 having a depth of 3 / 4λ and a depth of 1 / 25λ can be sufficiently accommodated.

In the rotating antenna 8 of the present embodiment, the vertical portion 8a, 8b, 8c is provided on the three sides of the flat portion 11 and the outer periphery of the flat portion 11, and the vertical wall portion is provided in the flat portion. The width of the non-side 8d and the vertical wall portion 8a facing the side 8d is longer than 1 / 2λ (λ is the wavelength of the microwave) and shorter than λ, and the height is selected as a radiation path shorter than 1 / 2λ. . As a result, the electric field disappears in the height direction, so that the same TE ₁₀ mode fundamental wave as that of the waveguide 5 can be coupled to the rotating antenna 8 without generating higher-order mode microwaves. Therefore, the reflection is small and the degree of coupling is high, and the microwave energy generated by the magnetron 4 can be efficiently transmitted to the rotating antenna 8.

  FIG. 4 shows the return loss analysis results when the radiation path of the rotating antenna 8 has the conventional horn shape described in Patent Document 1 (FIG. 7) and the waveguide shape of this embodiment. The rotating antenna 8 having a waveguide-shaped radiation path according to the present embodiment can suppress a -3 dB retard loss at a use frequency of 2460 MHz, and can efficiently couple the microwave energy generated by the magnetron 4 to the rotating antenna 8 with little reflection. You can see that The degree of coupling is evaluated from the value of the reflection coefficient, and the degree of coupling increases as the reflection coefficient decreases. Note that the return loss is a logarithm of the reflection coefficient, and the reflection increases as it approaches 0 dB, and it can be seen that the return loss of this embodiment is reduced as shown in FIG.

  Microwave energy generated in the magnetron 4 is guided to the waveguide 5 and propagated to the rotating antenna 8 by coaxial mode coupling with the inner conductor 7 penetrating the coupling hole 6, and the high frequency wave supply chamber 3, the object to be heated is mounted. It is emitted into the heating chamber 1 through the mounting plate 2. At this time, the microwave energy coupled to the rotating antenna 8 is reflected by the vertical wall portions 8a, 8b and 8c, and the microwave is radiated into the heating chamber 1 from the opening surface of the side 8d where the vertical wall is not installed. Generally, when there is a gap between the high-frequency wave supply chambers 3 facing the end of the vertical wall, microwaves leak through the gap and the directivity and coupling degree are lowered. In particular, leakage from the gap between the vertical wall 8a (referred to as a back plunger) facing the opening surface and the bottom surface of the high-frequency supply chamber 3 is likely to occur, and blocking and suppressing this microwave improves the directivity and coupling degree of the rotating antenna. Connected.

  In the rotating antenna 8 of the present embodiment, by arranging the choke 13 outside the vertical wall portion 8a, the microwave leaking from the gap between the vertical wall 8a and the bottom surface of the high-frequency supply chamber 3 can be suppressed. The degree of coupling is improved. The reason for this will be described with reference to FIGS.

  As described above, the choke 13 forms the choke short-circuit point B from the choke entrance point A of the choke 13 obtained by bending a rectangular plane into a square shape, and the rectangular parallelepiped cavity surface 13-2 facing the high-frequency supply chamber bottom surface 3 is formed. The notch 13-3 is provided along the end of the vertical wall 8a on the vertical wall 8a side. The length L of the choke 13 from the choke entrance point A to the choke short-circuit point B is selected to be ¼ wavelength, and here it is about 30 mm.

The choke 13 which is this three-dimensional circuit is represented by an equivalent transmission line having a characteristic impedance Z _o when the load impedance Z _L at the end of the line length L shown in FIG. 5 is short-circuited (Z _L = 0). In addition, the choke 13 is a circuit in which an L and C parallel resonant circuit is connected in series to the circuit as shown in FIG.

Here, the input impedance Z _in viewed from the choke entrance point A to the choke short-circuit point B is assumed that the line is lossless.

It is expressed. Where L is the line length of the choke 13 and β is the phase constant.

It is.

Since the line length L from the choke entrance point A to the choke short-circuit point B of the choke 13 is designed to be λ / 4, the input impedance Z _in at the choke entrance A point becomes infinite from Equation 1. When the input impedance Z _in becomes infinite at the point A, the parallel resonant circuit of L and C in FIG. 6 resonates, thereby opening the circuit, so that the current is cut off and perpendicular to the bottom surface of the high-frequency supply chamber 3. Microwaves leaking from the wall portion 8a are blocked. As shown in FIG. 6, the choke 13 is a circuit in which L and C parallel resonant circuits are connected in series to the circuit, and the leakage microwave causes parallel resonance at the point A so that the circuit is open. The current is cut off and the microwave does not leak. Such a phenomenon of resonance in parallel and in series every λ / 4 is referred to as impedance reversal action. The choke 13 is a microwave three-dimensional circuit that uses this impedance reversal action to suppress leakage microwaves.

  FIG. 8 and FIG. 9 show the results of comparison of leakage wave suppression and directivity improvement effect by microwave analysis when the choke 13 is provided. FIG. 8 shows the electric field intensity distribution of the leakage wave when the conventional short-circuit surface described in Patent Document 1 (FIG. 7) is provided on the vertical wall 8a of the rotating antenna 8 and when the choke 13 of this embodiment is provided. Show. In FIG. 8, the upper diagram is based on the flange method, and the lower diagram is based on the choke method in this embodiment. In the flange method, a leaky wave is seen from the inside of the radiation path of the rotating antenna 8, but in the choke method in this embodiment, no leaky wave is seen, and it can be seen that the leakage wave is blocked by providing the choke 13. Further, FIG. 9 shows the near field (Near Field Pattern) of the flange type and the choke type. It can be seen that the choke method has a large electric field strength of about 10 kV / m and superior directivity than the flange method. The directivity is evaluated from the value of the electric field intensity in the antenna radiation direction, and the directivity becomes sharper as the electric field intensity increases.

  In the rotating antenna of the high-frequency heating apparatus of the present embodiment described above, the microwave leaking from the gap between the vertical wall end and the bottom of the high-frequency supply chamber can be obtained by arranging the choke outside the vertical wall with the rotating antenna. Can be blocked. As a result, the microwave coupled to the rotating antenna forms a radiation path that is transmitted to a radiation port without a vertical wall portion serving as an opening surface, thereby improving directivity and degree of coupling.

In addition, when the width of the radiation path is set to 1 / 2λ to λ or less and the height is set to 1 / 2λ or less, the same microwave as the waveguide is transmitted without generating a high-order mode microwave. It can be coupled to the rotating antenna in the form of the fundamental wave of the TE ₁₀ mode, which is the fundamental mode. Therefore, there is little reflection of the radiation path, and the microwave energy generated by the magnetron can be efficiently coupled to the rotating antenna. Further, the improvement in the degree of coupling has the effect of suppressing leakage microwaves from between the vertical wall end and the bottom surface of the high-frequency supply chamber facing it.

  A perspective view of the rotating antenna 8 of the second embodiment is shown in FIG. In addition, a present Example is another structural example of the rotating antenna accommodated in FIG. 1 of Example 1, and abbreviate | omits description which is common in Example 1 below.

  The rotating antenna 8 according to the second embodiment includes a rectangular flat portion 11 and downward vertical wall portions 8a, 8b, and 8c on three sides of the flat portion 11, and the vertical wall portion is disposed in a rectangular bowl-shaped radiation path. A vertical wall portion 8e extending downward (toward the bottom surface of the high-frequency supply chamber 3) on the outer periphery of the two sides excluding the trapezoidal flat portion 11a and its upper base 8g and lower base 8d in accordance with the opening surface on the side 8d not provided. , 8f is a rotating antenna that connects horn-shaped radiation paths.

  Thereby, in addition to the effect of Example 1, since a microwave is radiated | emitted widely from a rotating antenna in a heating chamber, there exists an effect which can suppress a heating nonuniformity.

  FIG. 11 shows an enlargement of the choke 13 portion of the rotating antenna 8 of the third embodiment. Note that description of points in common with the other embodiments is omitted.

  In Example 3, a rectangular parallelepiped cavity surface 13-2 provided with a notch 13-3 by the choke 13 of Example 1, and a rectangular parallelepiped cavity surface 13-2 bent at right angles to the rectangular parallelepiped cavity surface 13-2 are slit. 13-4 is provided to form an L-shaped corrugated piece 13-5. The length L from the choke entrance point A to the choke short-circuit point B of the choke 13 is set to a quarter wavelength as in the choke 13 of the first embodiment. Thus, in Example 3, by forming the plurality of L-shaped corrugated pieces 13-5, the choke can be reduced in size and a stable leakage suppressing effect can be obtained.

  That is, according to the configuration of the present embodiment, by providing the slit 13-4 on the rectangular parallelepiped cavity surface 13-2, the wall surface current flowing through the choke is aligned along the L-shaped corrugated piece 13-5 and has a high density. As a result, a strong electric field is generated between the tip of the corrugated piece 13-5 and the wall surface facing the corrugated piece 13-5, and the leakage wave coupled to the choke becomes stronger, and the microwave leaking to the outside can be suppressed.

  The rotating antenna 8 of Example 4 is shown in FIG. Note that description of points in common with the other embodiments is omitted.

In the description of the rotating antenna 8 of the present embodiment, a choke formed with the L-shaped corrugated piece 13-5 of the fourth embodiment is used. In the first embodiment, the choke is provided outside the vertical wall 8a on the back plunger side. However, in this embodiment, the rotating antenna 8 has three sides on the outer periphery of the plane portion 11 and the sides of the plane portion 11. Rotating antenna having a radiation path structure in which chokes 13a, 13b, 13c are arranged in a U-shape by welding to the vertical wall portions 8a, 8b, 8c at right angles to the outer sides of the vertical wall portions 8a, 8b, 8c provided downward In this way, the microwave leaking from the gap between the other two vertical walls 8b and 8c and the bottom surface of the high-frequency supply chamber 3 can be cut off and suppressed in addition to the vertical wall 8a on the back plunger side. it can. The provision of the chokes 13a, 13b, and 13c is the same as the rectangular transmission waveguide in terms of structure and radio wave, and the TE ₁₀ mode, which is the fundamental mode when microwaves are transmitted through the waveguide, is coupled. Will be transmitted. For this reason, there is almost no reflection loss and insertion loss, and the number of microwaves transmitted to the microwave radiation port side opposite to the vertical wall portion 8a is increased, and the directivity and coupling degree are further improved. Note that the lengths of the chokes 13b and 13c provided by welding on the vertical walls 8b and 8c are not required from the vertical wall portion 8a to the side 8d, and if they are at least ¼ wavelength or more, the directivity and the degree of coupling are further improved. is there.

  A rotating antenna 8 of Example 5 is shown in FIG. Note that description of points in common with the other embodiments is omitted.

  In the fifth embodiment, the choke 13 is formed by integral molding with the flat portion 11 of the rotating antenna 8 of the first embodiment, and the manufacturing cost is taken into consideration. In order to manufacture the choke 13 by integral molding, a bowl-shaped concave portion 14 is formed on the outer side of the vertical wall portion 8 a by using the flat surface portion 11, and the choke 13 is configured outside the concave portion 14. . By providing the bowl-shaped recess 14 between the vertical wall 8a and the choke 13, it is considered that the plate thickness of the vertical wall 8a is apparently increased. This has the effect of preventing sparks and abnormal heating in the gap between the bottom surfaces of the high-frequency supply chamber 3 facing the 8a.

  In addition, when the rotary antenna of Example 5 is integrally molded, the vertical wall portions 8b and 8c have a structure of integrally molded choke similar to that of Example 6. In the first, fifth, and sixth embodiments, the rotating antenna 8 has the choke 13 disposed outside the vertical wall as a radiation path having the same shape as the waveguide 5, but the shape of the radiation path is not limited to this. The radiation path of the rotating antenna 8 may be provided with a choke as a conventional horn-shaped radiation path. In this case, the effect of the degree of coupling and directivity is inferior to that of the waveguide-shaped radiation path. However, since the choke contributes to the improvement of the degree of coupling and directivity, it does not matter that the effect is not extremely reduced.

DESCRIPTION OF SYMBOLS 1 Heating chamber 2 To-be-heated object mounting board 3 High frequency supply chamber 4 Magnetron 5 Waveguide 6 Coupling hole 7 Inner conductor 8 Rotating antenna 8a Vertical wall part (back plunger)
8b, 8c, 8e, 8f Vertical wall portion 9 Dielectric shaft 10 Drive portion 11 Plane portion 12 Object to be heated 13 Choke 13-1 Cuboid cavity 13-2 13-3 Cuboid cavity surface 13-3 Notch 13-4 Slit 13-5 Corrugated piece 14 Recess

Claims (7)

A heating chamber for storing an object to be heated;
A heated object mounting plate made of a dielectric provided on the bottom surface of the heating chamber;
A high-frequency supply chamber provided at a substantially central portion of the bottom surface of the heating chamber below the heated object placing plate;
A magnetron that generates microwave energy;
A waveguide for mounting the magnetron;
A coupling hole provided in the center of the bottom surface of the high-frequency supply chamber;
An inner conductor that passes through the coupling hole and faces the high-frequency supply chamber substantially vertically;
A metal rotating antenna housed in the high-frequency supply chamber and connected to one end of the inner conductor;
A dielectric shaft connected in the waveguide of the inner conductor, and a drive unit that rotationally drives the dielectric shaft,
The rotating antenna is
A substantially horizontal and polygonal plane portion connected to the inner conductor;
A vertical wall provided to hang down from a part of the outer periphery of the flat part;
Have
A choke structure that suppresses leakage of electromagnetic waves is provided on a vertical wall provided on a side opposite to a side on which the vertical wall is not provided in the outer periphery of the flat part. High frequency heating device. In the high frequency heating apparatus according to claim 1,
The planar portion of the rotating antenna is square;
A vertical wall portion provided on a total of three sides, one side of the plane portion and two sides sandwiching it, constitutes a rectangular bowl-shaped radiation path with one end opened,
2. A high-frequency heating apparatus according to claim 1, wherein a choke is disposed outside the vertical wall portion opposite to the side where the vertical wall portion is not provided. In the high frequency heating apparatus according to claim 2,
A high-frequency heating apparatus, wherein a horn-type radiation path provided with the vertical wall portion is connected to an opening surface of a rotating antenna not provided with the vertical wall portion. In the high frequency heating device according to claim 2 or 3,
The choke is a rectangular parallelepiped cavity having a notch on one side, and the notch is provided on the vertical wall portion side of the rectangular cavity surface facing the bottom surface of the high-frequency supply chamber. A high-frequency heating device characterized by In the high frequency heating cooking appliance as described in any one of Claim 2 to 4,
A high frequency heating apparatus, wherein a plurality of slits are provided in the rectangular parallelepiped cavity of the choke provided in the rotating antenna to form a plurality of L-shaped corrugated pieces. In the high frequency heating cooking appliance according to any one of claims 2 to 5,
A high-frequency heating apparatus, wherein the choke is provided outside the plurality of vertical walls of the rotating antenna. In the high frequency heating cooking appliance as described in any one of Claim 2 to 6,
In the antenna forming the radiation path, the width of the vertical wall portion provided facing the opening surface is reduced from 1 / 2λ (λ is the wavelength of the microwave) to λ or less, and the height is reduced to 1 / 2λ or less. A high-frequency heating device.