JPS6372089A - 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.

Dimensions. 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, higher-order mode radio waves whose propagation direction is not in the yz plane enter the cavity resonator 12, so the cavity resonator 12 goes out of the resonant state and the radio wave leakage prevention effect becomes smaller. 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, as shown in equation (2) below, - is large in the ratio of the distance tM between the entrance 25 of the cavity resonator 12 and the center 0 of the cavity cross section, and the entrance dimension G. The equivalent capacitance C becomes larger. In the cavity resonator 12 of FIG. 7, ZM = t o, and b≧G of the present invention, which will be described later
The equivalent capacitance C is smaller than that of G1.5. For that reason, see (3) below.
According to the formula, the equivalent inductance L must be increased to resonate with the frequency of the leaked radio waves. Therefore, as is clear from equation (1) below, the cavity resonator 12
Since it is necessary to increase the cross section AB of the conventional cavity resonator 12, the conventional cavity resonator 12 becomes large, and is not suitable for downsizing and cost reduction of the door.

2. FIG. 7 shows the dimensions of each part of the drawings in the specification of Japanese Utility Model Application 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 workaround to the problem was to install a cavity resonator with a cross section around the door to prevent leakage radio waves, and form part of the wall of the cavity resonator with a large number of U-shaped conductor pieces. In addition, an entrance for introducing leakage radio waves into the cavity resonator is formed by a part of the U-shaped conductor piece and a part of the other wall surface, and the distance between this entrance and the center of area of the cavity cross section is AM. ,
The M stopper between the entrance dimension G was set to 1.5 or more, and two capacitance adjustment elements were provided at both ends of the entrance, and the capacitance adjustment element on the other wall side was made larger than the one on one side of the U-shaped conductor. It is something.

Operation With the above configuration, radio waves that are about to leak due to the U-shaped conductor piece are guided into the cavity resonator with the square-shaped cross section as TEM 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. . If the entrance of the cavity is made smaller and two capacitance adjustment elements are provided, C becomes larger, and L can be made smaller by that amount. 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 use 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 seven lunges 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 flatness of the sealing surface 7 which makes 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 7 flange 2 . 9 is the first wall surface 8
This is a second wall surface extending substantially parallel to the flange 2 from the end thereof. 10 is a large number of U-shaped conductor pieces welded to the second wall surface 9. This U-shaped conductor piece 10 is connected to the second wall surface 9
It consists of three surfaces: a mounting surface 19 that is welded to the surface, a rising surface 23 that faces the first wall surface 8 in a substantially parallel manner, and an overhanging surface 11 that has an end cut facing the first wall surface 8. door 5
The width D of each U-shaped conductor piece 10 in the longitudinal direction around the
(X direction) is made smaller than half of the wavelength used.

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 projection piece 14 protruding from an opaque dielectric cover 13 that blocks an entrance 25 of this cavity resonator 12 is adapted to be caught in a mounting hole 18 provided in a rising surface 23 of the U-shaped conductor piece 10. A protruding piece 17 protruding from a dielectric door frame 24 for holding a translucent door outer cover 13 covering the front surface of the door 5 is hooked onto the outermost peripheral edge 20 of the second wall surface 9. It has become.

In addition, as shown in FIG.
Capacitance adjusting elements 26 and 27 protruding from the dielectric cover 13 are provided near the first wall surface 8, respectively, and the protruding dimension of the capacitance adjusting element 27 near the first wall surface 8 is made larger than that of the other capacitance adjusting element 26. There is.

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 7 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.

Increases radio wave effect. Width D of U-shaped conductor piece 10 (third
(X direction in the figure) is made smaller than half of the wavelength used, so the cavity resonator 12 with a cross section formed by the first wall surface 8 and each U-shaped conductor piece 10 is The traveling direction of the radio waves that have entered the interior is limited to the yz plane in 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 t is 3 [13 mm] for a 2450 MHz high frequency heating device, and if you try to mount this on a door, it will be thick, which is disadvantageous in terms of design and cost. .

In the case where the cavity resonator 12 having the protruding surface 11 and having a single-shaped cross section and a narrow entrance 25 is formed as in this 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 given by Equation 11. 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=μoAB・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・(1) Here, AB: Area μ0 of the cross-section of the cavity resonator 12: Permeability e of the medium inside the cavity resonator 12: 2.72 tM: Air Distance ε0 between the entrance 25 of the cavity resonator 12 and the center of area O of the cavity cross section: Induction coefficient K of the medium inside the cavity resonator 12: Inlet 2
Correction term G related to the shape around 5: Gap at the entrance 25 (
(inlet dimensions) resonant frequency f of the cavity resonator 12; can be expressed by equation (3).

From equation (2), it can be seen that the smaller the gap G of the inlet 25 is, the more this is true. Assuming that the resonant frequency fo 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 (from equation 11, the area AB of the mouth-shaped cross section of the cavity resonator 12 should be made smaller; 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 cavity area AB is correspondingly decreased to decrease the equivalent inductance L.
Parallel resonance may be caused at a certain resonance frequency to (heating frequency of the high-frequency heating device) to maximize the impedance at the inlet 25 and prevent radio wave leakage.

Heating frequency is 2.450 MHz, high frequency output is 50 MHz
In a 0W high frequency heating device, 7 langes 2 and sealing surface 7
The gap between
I heated it and measured the amount of radio wave leakage at a distance of 50 degrees from the periphery of the door 5. As a result, when G = 5mmy-1, AB = 15.4 x 15.9mm, -2,1
Therefore, the amount of radio wave leakage is less than 0.1 mW//cA,
If we assume that G = Bwm, in order to suppress the amount of radio wave leakage to the same level as above, AB = 20.4 x 18
．． The area of the kuji-shaped cross section also becomes larger, as in the case of 4 kakus, mu = 1.75. Through these actual experiments, the dimensions A and B of the cavity resonator 12 with a single-shaped cross section can be respectively reduced by narrowing the gap G of the inlet 25 to 4 m8 and making the gap t5 or more. It has become clear that the wavelength can be made considerably smaller than 30.6 m, which is one quarter of the wavelength λ used.

Further, the equivalent capacitance C is adjusted by the capacitance adjustment elements 26 and 27 to ensure parallel resonance and increase the radio wave sealing effect. Furthermore, the capacitance adjustment element 2 near the first wall surface 8
7 has a longer protruding dimension than the capacitance adjustment element 26 near the end of the projecting surface 11, so when the dielectric cover 15 is fitted, the capacitance adjustment element 27 is first inserted along the first wall surface 8 and the 9 positioning is performed. After the capacitance adjustment element 26 is connected to the inlet 25
going into. Therefore, the capacitance adjustment element 26
There is no risk of deformation by pushing 1 from the y direction. Note that the capacitance adjustment element 26 has a Z value when the dielectric cover 13 is fixed.
It also plays the role of minimizing deformation of the projecting surface 11 against external forces from directions.

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 overhanging surface of the U-shaped conductor piece. The end cut and the first wall face each other and are narrow.

By selecting the dimensions such that e≧i, 5, and ensuring that parallel resonance is generated by the two capacitance adjustment elements, the cross-sectional dimensions A and B of the cavity resonator can be reduced to a quarter of the wavelength λ used. Because it can be made smaller than.

The shape of the resonant cavity is simplified, making the door more compact.

It is possible to provide a compact high-frequency heating device that is thin, easy to assemble, and has a large economic impact.

[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 termination short-circuited. 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. DESCRIPTION OF SYMBOLS 1... Heating chamber 2... Flange 4... Small hole group 5... Door 6... Step part 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 19 ... Mounting surface 23 ... Rising surface 25 ... Inlet 26
, 27...Capacitance adjustment element AM...Cavity resonator 12
Distance G between the inlet 25 and the center of area O of the cavity cross section...Inlet dimension

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 (
7), a first wall surface (8) substantially perpendicular to the flange (2), a second wall surface (9) substantially perpendicular to this first wall surface (8), and a second wall surface (9) substantially perpendicular to this first wall surface (8); In a high-frequency heating device including a rising surface (23) substantially perpendicular to the wall surface (9) and an overhanging surface (11) substantially perpendicular to the rising surface (26),
A large number of U-shaped conductor pieces (
10), and the first wall surface (8) and the U-shaped conductor piece (10
) forms a cavity resonator (12) having a square-shaped cross section and an inlet (25), and the distance lM between the inlet (25) and the center of area O of the cavity cross section and the inlet dimension G comparison
M/G is 1.5 or more, and near the end of the projecting surface (11) of the U-shaped conductor piece (10) projecting toward the first wall surface (8) and near the first wall surface (8), respectively. Entrance (25
) are provided with capacitance adjustment elements (26) and (27) protruding from the dielectric cover (13) that blocks the first wall (8).
) The protruding dimension of the capacitance adjustment element (27) near the other capacitance adjustment element (26) is made larger than that of the other capacitance adjustment element (26), and the U-shaped conductor piece (
10) is the mounting surface (19) in contact with the second wall surface (9)
It consists of three surfaces: a rising surface (23) facing substantially parallel to the first wall surface (8), and an overhanging surface (11) with an end cut facing the first wall surface (8). Body resonator (12
) The inlet (25) of the high-frequency heating device is characterized in that the end cut of the projecting surface (11) and the first wall surface (8) are opposed to each other.