JPS6345795A - 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 is reduced to a quarter of the wavelength used. A proposal was made in JP-A-60-25 that even if the value is smaller than 1, the impedance at the entrance of the groove is maximized, and leakage radio waves can be reduced in the same way as a choke groove.
It is in Publication No. 190. 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 prevention of reflection at discontinuous portions of characteristic impedance.

In addition, 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. In this conventional example, there is no description that the peripheral wall of the cavity resonator 12 is divided into a plurality of conductor pieces.Therefore, inside the cavity resonator 12, the traveling direction shown in FIG. Since the generated higher-order mode radio waves enter, the cavity resonator 12 is removed from the resonant state, and the radio wave leakage prevention effect is reduced. Assuming that the cavity resonator 1 in Fig. 7
It is assumed that the rising surface 23 and the overhanging surface 11 of 2 are divided in the longitudinal direction (X direction) into conductor pieces each having a width smaller than 172, which is the wavelength used. 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 distance QM between the entrance 25 of the cavity resonator 12 and the area center 0 of the cavity cross section is
The larger the ratio Qy/G between
becomes larger. In the cavity resonator 12 of FIG. 7, QM/G=
When QM/G is 1.0, the equivalent capacitance C is smaller than when QM/G≧1.5 of the present invention, which will be described later. Accordingly, the equivalent inductance L must be increased by that amount according to equation (3), which will be described later, in order to resonate with the frequency of the leaked radio waves. 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

In addition, FIG. 7 shows each radical in the drawings of the specification of Utility Model Publication No. 61-795 in the same proportion, and the names and numbers of the constituent elements correspond to those in this example. It's the same.

Problems to be Solved by the Invention It is necessary to provide a groove with a complicated shape in the depth direction of the groove, and it takes time and effort to prevent reflections at discontinuous parts of the characteristic impedance, and it is not suitable for downsizing the door. It is a point.

Means for solving the problem A cavity resonator with a cross-section shaped like a cross section for preventing leakage radio waves is provided around the door, and three of the four sides of this cavity resonator are provided in the longitudinal direction around the door. The cavity resonator is formed of a large number of U-shaped conductor pieces, and the remaining wall surface and the end cut of the U-shaped conductor pieces are opposed to each other to serve as an entrance for introducing leakage radio waves into the cavity resonator, and this entrance is connected to the cavity. The ratio mm/G of the distance QM between the area center of the cross section of the body and the inlet dimension G is set to 1.5 or more, and a dielectric cover that blocks the inlet and a plurality of capacitance adjustment elements protruding from it are provided, and these are It is located at the same location.

Effect: By configuring as described above, radio waves that are about to leak through the U-shaped conductor piece are introduced as TEM waves into the cavity resonator having a square-shaped cross section. 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 radio wave sealing effect is maximized when each side of the 0-shaped test section is smaller than one quarter of the wavelength used, which allows the cross-sectional area of the cavity to be reduced.

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 FIGS. 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 surrounding the small hole group 4, and this stepped portion 6 prevents the end portion of the translucent door inner cover 15 fixed to the inner surface of the small hole group 4 from peeling off during cleaning, etc. Flange 2 when door 5 is closed
This improves the flatness of the sealing surface 7 that makes plane contact with the sealing surface 7. 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. Reference numeral 9 denotes a second wall surface extending substantially parallel to the flange 2 from the end of the first wall surface 8. 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 23 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. The width D (X direction in FIG. 3) of each U-shaped conductor piece 10 in the longitudinal direction around the door 5 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 1o so as to be caught in the hole 18. A protruding 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 peripheral edge 20 of the second wall surface 9. It has become.

In addition, as shown in FIG.
At least one of 7 is disposed near the cut end of the projecting surface 11 to prevent the U-shaped conductor piece 10 from being deformed (in the direction in which the inlet 25 becomes smaller) when an impact is applied from the outside.

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 the capacitance of this line is proportional to the gap between the parallel plates, so the capacitance 21 becomes larger as the gap of the planar contact portion is smaller, and the radio wave sealing effect increases. Since the width D (in the X direction in FIG. 3) 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 the length Q of the parallel plate line will cause parallel resonance at about one quarter of the free space wavelength λ.
The impedance is maximized and it is possible to prevent radio wave leakage, but in a 2450MHz high frequency heating device, a is 30.6on+, and if you try to mount this on a door, it will be thick, which is disadvantageous both in terms of design and cost. .

When the cavity resonator 12 is formed by providing the projecting surface 11 and having a cross-section with a narrow inlet 25 as in this embodiment, an electric field distribution as shown in FIG. 5 is obtained. 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. The cavity resonator 12 is represented in FIG. 4 as a parallel resonant element consisting of an equivalent inductance L and an equivalent capacitance C.
acts 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 the inductance per unit length in the cylinder axis direction (X direction). The value is as shown in equation (1). Also, the equivalent capacitance C
is based on the turbulent electric field near the entrance 25 of the cavity resonator 12, and can be approximated by equation (2): % 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 ΩM: Distance between the entrance 25 of the cavity resonator 12 and the center of area 0 of the cavity cross section εll: Dielectricity of the medium inside the cavity resonator 12 Rate: Entrance 25
Correction term G related to the shape of the vicinity: gap of the inlet 25 (inlet dimension) The resonant frequency f0 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 or the larger Qy/G, the larger the equivalent capacitance C becomes. If the resonant frequency f0 is kept constant, it can be seen from equation (3) that the larger the 1-equivalent capacitance C is, the smaller the equivalent inductance L is. equivalent inductance L
In order to make it smaller, the area AB of the mouth-shaped cross section of the cavity resonator 12 can be made smaller according to 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 cavity area AB is increased accordingly.
It is sufficient to reduce the equivalent inductance L and cause parallel resonance at a constant resonance frequency f0 (heating frequency of the high-frequency heating device) to maximize the impedance at the inlet 25 and prevent radio wave leakage.

In a high-frequency heating device with a heating frequency of 2450 MHz and a high-frequency output of 500 W, the gap between the flange 2 and the sealing surface 7 is 2I, and the step between the overhanging surface 11 and the sealing surface 7 is 3II.
W11, the width of the U-shaped conductor piece is 15 nm+, water 27
I heated 5mQ and measured the amount of radio wave leakage at a distance of 5 marks from around door 5. As a result, when G=5nn, AB
= 15.4X15.9mm, 12M/G = 2.1, the amount of radio wave leakage is less than O,1mw/d, and if G = 8nm is increased, in order to suppress the amount of radio wave leakage to the same level as above, AB =20.4X18.4mm, QM/G=1
．． 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 about 4 to 8I and making QM/G 1.5 or more. It has become clear that each wavelength can be made considerably smaller than 30.6 nm, which is a quarter of the wavelength λ used.

In addition, the plurality of capacitance adjustment elements 26 and 27 have an equivalent capacitance C of m
In addition, since it is also arranged at the cut end of the overhanging surface 11, it helps to prevent deformation of the U-shaped conductor piece 10 and prevents it from deforming over a long period of time. A stable radio wave seal effect can be maintained.

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. Since the end cut and the first wall face each other to make it narrow, and the dimensions are selected such that 12M/G≧1.5, the cross-sectional dimensions A and B of the cavity are set to the wavelength λ used. The shape of the cavity resonator can be simplified, the door can be made smaller and thinner, and at least one of the capacitance adjustment elements can be arranged near the end cut of the projecting surface. Therefore, the external force on the U-shaped conductor piece (
This prevents deformation in two directions) and increases the stability of the radio wave seal effect.

[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.

Claims (1)

[Claims] A sealing surface (7) located at the periphery of the door (5) that opens and closes the opening of the heating chamber (1) and in planar contact with the flange (2) of the opening of the heating chamber (1) when the door (5) is closed; Sealing side (7
) and a second wall (8) extending substantially perpendicularly to the flange (2) from the end of the first wall (8), and a second wall extending substantially parallel to the flange (2) from the end of the first wall (8). The wall surface (9) of
A rising surface (23) approximately perpendicular to this second wall surface (9)
and an overhanging surface (11) that is approximately perpendicular to this rising surface (23).
), the second wall surface (9
) with a large number of U-shaped conductor pieces (10) whose end surfaces are in contact with each other,
The first wall surface (8) and the U-shaped conductor piece (10) form a cavity resonator (12) having a square cross section and an inlet (25), and the inlet (25) and the cavity The ratio l_M/G of the distance (l_M) between the center of area (O) of the body cross section and the entrance dimension (G) is 1.5 or more, and the dielectric cover (13) that blocks the entrance (25) and the cavity Resonator (12
) a plurality of capacitance adjusting elements (26), (27
), and at least one of them is a U-shaped conductor piece (
10) A high-frequency heating device characterized in that it is disposed near an end cut of a projecting surface (11) projecting toward a first wall surface (8).