JPS6345791A - 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. ``Even if the impedance 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.'' was proposed in JP-A-1988-
It is in Publication No. 25190. In this conventional example, the shape is quite complicated, as grooves with different widths are provided in the depth direction of the groove, and the shape of the peripheral wall of the groove is deformed in the depth direction. Furthermore, it is necessary to consider reflection prevention 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. 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 that the cavity resonator 12 goes out of its resonant state.

The effect of preventing radio wave leakage will be reduced. Assume that the rising surface 23 and the projecting surface 11 of the cavity resonator 12 shown in FIG. 7 are divided into conductor pieces having a width smaller than 1/2 of the wavelength used in the longitudinal direction (X direction). In this case, the cavity resonator 12 has an equivalent capacity 'l1
It can be considered that a plurality of parallel resonant elements consisting of kC and equivalent inductance L are arranged in the longitudinal direction (X direction) of the door 5. In each parallel resonant element, as shown in equation (2) below, the larger the ratio CM7G of the distance mQps between the inlet 25 of the cavity resonator 12 and the area center 0 of the cavity cross section to the inlet dimension G is, the greater the equivalent capacitance. C becomes larger. Cavity resonator 1 in Figure 7
2, QM/G=1.0, and QM/G of the present invention described later
The equivalent capacitance c becomes smaller than when ≧1.5. 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.
The cavity resonator 12 of the conventional example is large, and the door is made smaller.
It is not suitable for cost reduction. In addition, Figure 7 shows the
Each radical in the drawings of the specification of Publication No. 1-795 is shown in the same proportion, and the names and numbers of the constituent elements corresponding to those in this embodiment are the same.

Problems that the invention aims to solve: 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 reflection of characteristic impedance at discontinuous parts, making it unsuitable for miniaturizing doors. This is a point.

Means for solving the problem: A cavity resonator with a square-shaped cross section for preventing leakage radio waves was installed around the door, and a part of the wall of this cavity resonator was formed with a large number of U-shaped conductor pieces. , and the cavity resonator is provided with an entrance for introducing leakage radio waves, and the ratio QM/G between the distance AM between the entrance of the bracket and the center of area of the cavity cross section and the entrance dimension G is 1.5 or more,
A plurality of capacitance adjustment elements are provided at the inlet.

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. . If the entrance of the cavity is made smaller and a capacitance adjustment element is provided, C becomes larger, and L can be made smaller by that amount. That is, the radio wave sealing effect is maximized when each side of the single-shaped cross section, which can reduce the cross-sectional area of the cavity, is smaller than one-fourth 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. 6 is a step surrounding this small hole group 4.

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, and also serves as a sealing surface that makes plane contact with the flange 2 when the door 5 is closed. 7 improves the flatness. 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 attached to the second wall surface 9 by welding to the surface 19.
and a rising surface 2 facing substantially parallel to the first wall surface 8.
3, and an overhanging surface 11 whose end cut faces the first wall surface 8.
It consists of three sides. The width D (X direction) of each U-shaped conductor piece 10 in the longitudinal direction of the periphery of the door 5 is made smaller than one-half of the wavelength used.

The opening-shaped cross section surrounded by the first wall surface 8 and the U-shaped conductor piece 1o forms a cavity resonator 12 having a narrow entrance 25. A projection piece 14 protruding from the opaque dielectric cover 13 that blocks the entrance 25 of the cavity resonator 12 is attached to a hole 18 provided on the rising surface 23 of the U-shaped conductor piece 10. . A protruding piece 17 protruding from the dielectric door frame 24 for holding the light-transmitting door external force 16 covering the front surface of the door 5 is hooked on the outermost peripheral edge 2o of the second wall surface 9. It has become.

Further, as shown in FIG. 5, a plurality of capacitance adjustment elements 26 and 27 are protruded from the back surface of the dielectric cover 13 that blocks the entrance 25 toward the inside of the blank resonator 12.

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 capacity corresponding to the planar contact portion between the flange 2 and the sealing surface 7;

It acts as a kind 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 increases as the gap of the planar contact portion becomes smaller, increasing the radio wave sealing effect.
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 width D of the U-shaped conductor piece 10 is The direction of propagation of the radio waves entering the cavity resonator 12 having a cross-section is limited to the yz plane of FIG. 3. If there is no overhanging surface 11, the electric field will be distributed as shown in Figure 6, and the length Q of the parallel plate line will cause parallel resonance at about one-fourth of the free space wavelength λ, and the impedance will be maximum, preventing radio wave leakage. You can, but
2 is 30.6mm for a 2450MHz high frequency heating device
If you try to implement 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 equivalent inductance as a constant of the coil, and the value per unit length in the cylinder axis direction (X direction) is expressed as equation (1). Also, the equivalent capacitance C
is based on the turbulent electric field near the entrance 25 of the cavity resonator 12, and is approximated by Permeability e of the medium in the cavity resonator 12: 2.72 ΩM: Distance ε between the entrance 25 of the cavity resonator 12 and the center of area O of the cavity cross section: Permittivity of the medium inside the cavity resonator 12: Near the entrance 25 Correction term G related to the shape of: 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 QM/G, the larger the equivalent capacitance C becomes. Keep the resonance frequency f0 constant.

Then, the larger the 1-equivalent capacitance C is, the smaller the equivalent inductance L is required to be. From equation (3), it is found that in order to reduce the zero-equivalent inductance L, the shape of the cavity resonator 12 is determined from equation (1). In other words, in order to make the cavity resonator 12 smaller, the cross-sectional area AB can be made smaller.In order to make the cavity resonator 12 smaller, the gap G of the inlet 25 can be narrowed to increase the equivalent capacitance C, and the cavity area AB can be made smaller accordingly. and the equivalent inductance L
, and cause parallel resonance at a constant resonance frequency f, (heating frequency of the high-frequency heating device) to maximize 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 2 nm, and the step between the overhanging surface 11 and the sealing surface 7 is 3 m.
, the width of the U-shaped conductor piece is 15 mm, and the water is 275 m.
Q was heated and the amount of radio wave leakage was measured at a distance of 5a++ from around the door 5. As a result, when G=5mn+, A
When B=15.4X15.91a and QM/G=2.1, the amount of radio wave leakage is less than O,1mw/d, and if G=8m is increased, in order to suppress the amount of radio wave leakage to the same level as above, AB=20.4Xl, 8.4mm, 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 8 m and making QM/G 1.5 or more. It has become clear that each can be made considerably smaller than 30.6n*n, which is one quarter of the used wavelength λ.

In addition, since a plurality of capacitance adjustment elements 26 and 27 protrude from the back surface of the dielectric cover 13 toward the inside of the cavity resonator 12, the mutual positional relationship of the capacitance adjustment elements 26 and 27 and the dimensions of the protrusion are By adjusting, the equivalent capacitance C can be made larger. Therefore, the equivalent inductance L can be reduced, that is, the cavity cross-sectional dimensions A and B can be further reduced, and the door 5 can be made smaller and thinner.

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.

In addition, the dimensions were selected such that QM/G≧1.5, and a plurality of capacitance adjustment elements were made to protrude from the dielectric cover toward the inside of the cavity resonator, so that the cross-sectional dimension of the cavity resonator was A.
and B can be made smaller than one-fourth of the used wavelength λ, the shape of the cavity resonator can be simplified, the door can be made smaller and thinner, a compact high-frequency heating device can be provided, and economic ripple effects can be achieved. There is also something big.

[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. FIG. 7 is an explanatory diagram of the structure of a conventional radio cable 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
), a first wall surface (8) substantially perpendicular to the flange (2), a second wall surface (9) substantially perpendicular to the first wall surface (8), and a second wall surface (9) substantially perpendicular to the first wall surface (8); (9), a rising surface (23) substantially perpendicular to the rising surface (23), and a projecting surface (11) substantially perpendicular to the high-frequency heating device, the end surface of which is in contact with the second wall surface (9). Many U-shaped conductor pieces (1
0), and the first wall surface (8) and the U-shaped conductor piece (10)
A cavity resonator (12) having a square-shaped cross section and an entrance (25) is formed by the above, and the distance (l_M) between the entrance (25) and the center of area (O) of the cavity cross section, and the entrance dimension (
G), the ratio l_M/G is 1.5 or more, and the entrance (25)
The cavity resonator (
12) a plurality of capacitance adjustment elements (26) toward the inside;
(27) A high-frequency heating device characterized by protruding.