JPS6372096A - Radio frequency heater - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an improvement in the door structure of a high-frequency heating device.

Conventional technology Grooves with different characteristic impedances are provided in the depth direction on the periphery of the door of a high-frequency heating device, and by making the characteristic impedance of the grooves discontinuous in the depth direction, the effective depth can be reduced to one-fourth of the wavelength used. Even if it is made smaller, the impedance at the entrance of the groove is maximum.

There is a proposal in Japanese Patent Laid-Open No. 60-25190 that it is possible to reduce leakage radio waves in the same way as choke grooves. In this conventional example, the shape is quite complicated, such as providing grooves with different widths in the depth direction of the groove and deforming the shape of the peripheral wall of the groove in the depth direction. Furthermore, it is necessary to consider reflection prevention at discontinuous portions of characteristic impedance.

Still, as shown in FIG. 7, a cavity resonator 12 for preventing radio wave leakage is formed in a curved manner on the outer periphery of the door 5 to form a mouth-shaped cross section.
A structure having an entrance 25 in which the end cut of the protruding surface 11, which is one peripheral wall of the cavity resonator 12, and the other wall surface (first wall surface 8) of the cavity resonator 12 are opposed was developed in 1982. It is shown in Publication No. 795. This conventional example does not describe that the peripheral wall of the cavity resonator 12 is divided into a plurality of conductor pieces. Therefore, high-order mode radio waves whose propagation direction shown in FIG. 8 is generated outside the yz plane enter the cavity resonator 12.

The cavity resonator 12 goes out of the resonant state, and the radio wave leakage prevention effect becomes small. It is assumed that the rising surface 23 and the projecting surface 11 of the cavity resonator 12 shown in FIG. 7 are divided into conductor pieces each having a width smaller than the wavelength used in the longitudinal direction (X direction). In this case, the cavity resonator 12 can be regarded as a plurality of parallel resonant elements each having an equivalent capacitance C and an equivalent inductance L arranged in the longitudinal direction (X direction) of the door 5. In each parallel resonant element, the cavity resonator 12
The equivalent inductance L must be increased by the ratio of the distance tM between the inlet 25 and the center of area O of the cavity cross section and the inlet dimension G according to the equation (3) described later, so that it resonates at the frequency of the leaked radio wave. It won't happen. Therefore, as is clear from equation (1) below, it is necessary to increase the cross section AB of the cavity resonator 12, so the cavity resonator 12 of the conventional example has a large size, resulting in a smaller door and lower cost. It is not suitable for

Incidentally, FIG. 7 shows the dimensions of each part of the drawings in the specification of Japanese Utility Model Publication No. 61-795 in the same proportions.

Also, the names and numbers of the components corresponding to those of the present invention are the same.

Problems to be solved by the invention It is necessary to provide grooves with complicated shapes in the depth direction of the groove, and it takes time and effort to prevent reflections at discontinuous portions of characteristic impedance, making it unsuitable for miniaturizing doors. This is a point.

A solution to the problem is to provide a cavity resonator with a cross-section shaped like a cross section around the door to prevent leakage radio waves, and six of the four sides of this cavity resonator are provided in the longitudinal direction around the door. a large number of U-shaped conductor pieces, with the remaining surface and the end cut of the U-shaped conductor pieces facing each other to serve as an entrance for introducing leakage radio waves into the cavity resonator;
In addition, the ratio between the distance AM between this entrance and the center of area 0 of the cavity cross section and the entrance dimension Gt is 1.5 or more, and a dielectric cover is provided to block the entrance, and a protrusion piece is provided on the inner surface of the outermost periphery. is fixed in the mounting hole of the U-shaped conductor piece.

Operation With the configuration as described above, radio waves that are about to leak from the U-shaped conductor piece are guided into the cavity resonator having a square-shaped cross section as T and EM waves.

This cavity resonator forms a parallel resonant element consisting of an equivalent inductance L proportional to the cross-sectional area of the cavity and an equivalent capacitance C based on the disturbed electric field near the entrance of the cavity as a cylindrical coil with approximately one turn. do. The smaller the entrance of the cavity, the larger C becomes, and L can be made smaller accordingly. In other words, the cross-sectional area of the cavity can be reduced. The radio wave sealing effect is maximized when each side of the cross-section is smaller than one quarter of the wavelength used.

Embodiment The structure and operation of a high-frequency heating device according to an embodiment of the present invention will be explained with reference to the drawings.

In Figures 1 and 2, 1 is a heating chamber.

2 is a flange surrounding the opening of the heating chamber 1, and 3 is an outer box. Reference numeral 4 designates a group of small holes provided in the center of the door 5 as wide as possible to allow viewing into the heating chamber 1. Reference numeral 6 denotes a stepped portion that surrounds the small hole group 4. This stepped portion 6 prevents the edge of the translucent door inner cover 15 fixed to the inner surface of the small hole group 4 from peeling off during cleaning, etc. 5. This improves the plane deformation of the sealing surface 7 which comes into plane contact with the flange 2 when closed. Reference numeral 8 denotes a first wall surface bent from the end of the sealing surface 7 at a substantially right angle to the flange 2. 9 is a second wall extending from the end of the first wall surface 8 substantially parallel to the flange 2;
It is the wall of. 10 is a large number of U-shaped conductor pieces welded to the second wall surface 9. This U-shaped conductor piece 10 is welded to the second wall surface 9 with a mounting surface 19, a rising surface 26 facing substantially parallel to the first wall surface 8, and an end cut on the first wall surface 8. It consists of three faces, with the overhanging faces 11 facing each other. Width D of each U-shaped conductor piece 10 in the longitudinal direction around the door 5
(X direction in FIG. 3) is made smaller than one-half of the wavelength used.

Further, the opening-shaped cross section surrounded by the first wall surface 8 and the U-shaped conductor piece 10 forms a cavity resonator 12 having a narrow entrance 25. A protruding piece 1 protruding from the outermost inner surface of the opaque dielectric cover 13 that blocks the entrance 25 of the cavity resonator 12
4 is attached to the rising surface 23 of the U-shaped conductor piece 10 so as to be caught in the hole 18. A projection piece 17 protruding from a dielectric door frame 24 for holding a translucent door outer cover 16 covering the front surface of the door 5 is hooked onto the outermost edge of the second wall surface 9. It has become.

Next, the effects of the embodiment configured as described above will be explained. The radio wave sealing effect will be qualitatively explained using a simple equivalent circuit as shown in FIG. 4 with respect to the incident radio waves directed toward the planar contact portion between the flange 2 surrounding the opening of the heating chamber 1 and the sealing surface 7. 21 is a capacitor corresponding to the planar contact portion between the flange 2 and the sealing surface 7, and acts as a type of bypass capacitor. The planar contact portion is considered to be a parallel plate line, and since the capacitance of this line is proportional to the cap of the parallel plate, the capacitance 21 becomes larger as the cap of the planar contact portion is smaller, and the radio wave sealing effect increases. Since the width D (in the X direction in FIG. 6) of the U-shaped conductor piece 10 is made smaller than half of the wavelength used, the first
The direction of propagation of the radio waves entering the cavity resonator 12 having a square cross section formed by the wall surface 8 and each U-shaped conductor piece 10 is limited within the yz plane of FIG. If there is no overhanging surface 11, the electric field will be distributed as shown in Fig. 6, and parallel resonance will occur when the length t of the parallel plate line is approximately one-fourth of the free space wavelength λ.
Impedance is maximized and radio wave leakage can be prevented, but with a 2450MHz high frequency heating device
az is 30.6+mn, and if it were to be mounted on a door, it would be thick, which would be disadvantageous both in terms of design and cost.

When the cavity resonator 12 is formed by providing an overhanging surface 11 and having a single-shaped cross section and a narrow entrance 25 as in the wooden embodiment, the electric field distribution will be as shown in FIG.

In this case, most of the electric lines of force are concentrated between the vicinity of the end cut of the overhanging surface 11 and the first wall surface 8. Cavity resonator 1
2 is equivalent inductance L and equivalent capacitance C in Figure 4.
It is expressed as a parallel resonant element consisting of. The equivalent inductance L works as a one-turn cylindrical coil with approximately the same cross section as the cavity resonator 12, and means the isometric inductance as a constant of the coil, and is expressed in the cylindrical axis direction (X
The value per unit length of (direction) is as shown in equation (11). Also, the 1-equivalent capacitance C is based on the disturbed electric field near the entrance 25 of the cavity resonator 12, and is approximately given by equation (2). .

L=μ. AB・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・(11 Here.

AB: Area μ of the mouth-shaped cross section of the cavity resonator 12. : Permeability e of the medium inside the cavity resonator 12: 2.72 tM: Distance ε0 between the entrance 25 of the cavity resonator 12 and the center of area O of the cavity cross section ε0: Dielectricity of the medium inside the cavity resonator 12 Rate K: Entrance 2
Correction term G related to the shape around 5: Gap at the entrance 25 (
(inlet dimensions) resonance frequency f of the cavity resonator 12; can be expressed by equation (3).

From formula (2), the smaller the gap G of the inlet 25, the more
It can be seen that as M or −d− increases, the equivalent capacitance C increases. Resonant frequency f. Assuming that is constant.

It can be seen from equation (3) that the larger the equivalent capacitance C is, the smaller the equivalent inductance L is. In order to reduce the equivalent inductance L, the area AB of the mouth-shaped cross section of the cavity resonator 12 can be reduced from equation (1). That is, in order to make the cavity resonator 12 smaller, the gap G of the inlet 25 is narrowed to increase the equivalent capacitance C, and the cross-sectional area AB of the cavity is correspondingly decreased to decrease the equivalent inductance L. , constant resonant frequency f. (heating frequency of the high-frequency heating device) to cause parallel co-grinding to maximize the impedance at the inlet 25 and prevent radio wave leakage.

Heating frequency is 2,450MH2, high frequency output is 500W
In the high-frequency heating device trap, the gap between the flange 2 and the sealing surface 7 is set to 2 degrees, the step between the projecting surface 11 and the sealing surface 7 is set to 3 degrees, and the width of the U-shaped conductor piece is set to 15 degrees. I heated water 275- and measured the amount of radio wave leakage at a distance of 5 cm from around the door 5. As a result, when G = 5mm and 7M, AB = 15.4 x 15.9 cabinets = 2.1,
The amount of radio wave leakage is 0.1 mW/- or less, G = 811
If it is increased to 1+++, the amount of radio wave leakage can be suppressed to the same level as above.
．． 75, the area of the mouth-shaped cross section also becomes large. Through such experiments, the dimensions A and B of the cavity resonator 12 with a single-shaped cross section can be reduced by narrowing the gap G of the inlet 25 to 4 to 8 pores and making the gap 1.5 or more. It has become clear that each can be made considerably smaller than 3 0.6 van, which is a quarter of the wavelength λ used.

Further, the dielectric cover 13 connects the projection piece 14 to the U-shaped conductor piece 1.
0 can be easily fixed to the door 5 by hooking it into the hole 18, so the installation work is easy.

Effects of the Invention As described above, according to the present invention, the entrance of a cavity resonator having a square cross section surrounded by a large number of U-shaped conductor pieces and the first wall surface is connected to the projecting surface of the U-shaped conductor piece. The end cut and the first wall face each other and are narrow.

Since the dimensions were selected such that 7M and 1"≧1.5, the cross-sectional dimensions A and B of the cavity resonator can be made smaller than a quarter of the wavelength λ used, and the shape of the resonant cavity can be simplified. , the door can be made smaller and thinner, and the installation of the dielectric cover that blocks the entrance is easier to install, and one end surface of the U-shaped conductor piece is attached to the second
The structure is such that it makes contact with the wall surface, which has the effect of simplifying installation.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a main part showing only the metal part of a door 5 of a high-frequency heating device according to an embodiment of the present invention, and FIG. 2 is a sectional view of a main part showing a radio wave seal part around the door. Fig. 3 is a diagram showing the direction of the electric field, Fig. 4 is a simplified equivalent circuit diagram of the radio wave seal part of the door 5, Fig. 5 is an electric field distribution diagram of the radio wave seal part, and Fig. 6 is a parallel diagram with the same terminal shorted. An electric field distribution diagram of a board line, FIG. 7 is a configuration explanatory diagram showing a conventional radio wave seal structure, and FIG. 8 is a diagram showing the direction of the electric field. 1... Heating chamber, 2... Flange, 4... Small hole group. 5... Door, 6... Step portion, 7... Sealing surface. 8... First wall surface, 9... Second wall surface. 10... U-shaped conductor piece, 11... Overhanging surface. 12... Cavity resonator, 13... Dielectric cover. 14... Projection piece, 18... Mounting is on the surface, 19...
Mounting is on the surface. 26...Rising surface, 25...Entrance. tM: Distance between the entrance 25 of the cavity resonator 12 and the center of area O of the cavity cross section. G...Entrance dimensions.

Claims (1)

[Claims] a sealing surface (7) located at the periphery of a door (5) that opens and closes the opening of the heating chamber (1), and which makes plane contact with the flange (2) of the opening of the heating chamber (1) when the door (5) is closed; This sealing surface (
A first wall surface (8) extends from the end of the first wall surface (8) substantially perpendicular to the flange (2), and a first wall surface (8) extends substantially parallel to the flange (2) from the end of the first wall surface (8). 2 wall surface (9) and a rising surface (23
) and an overhanging surface (1) approximately perpendicular to this rising surface (23).
1) In the high-frequency heating device equipped with the second wall surface (
9) is provided with a large number of U-shaped conductor pieces (10) whose end surfaces are in contact with each other, and a square-shaped cross section is formed by the first wall surface (8) and the U-shaped conductor pieces (10), and the entrance (25) A cavity resonator (12) is formed with The above, and the cavity resonator (1
2) is provided with a dielectric cover (13) that blocks the entrance (25), and the protrusion piece (14) provided on the outermost inner surface of the dielectric cover (13) is hooked into the mounting hole (18) of the U-shaped conductor piece (10) from the outside direction. the dielectric cover (13) is fixed to the door (5), and the U-shaped conductor piece (10) is attached to the mounting surface (19) that is in contact with the second wall surface (9) and approximately to the first wall surface (8). The parallel opposing rising surfaces (23) and the end cut are the first wall surface (8).
The entrance (25) of the cavity resonator (12) consists of three surfaces, the end cut of the projecting surface (11) and the first wall surface (8) facing each other. A high frequency heating device characterized by the following: