JPH0569274B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention 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. There is a proposal in Japanese Patent Laid-Open No. 60-25190 that even if the diameter 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 the chiyoke groove. 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.

Further, as shown in FIG. 7, the cavity resonator 12 for preventing radio wave leakage is bent on the outer periphery of the door 5 to have a rectangle-shaped cross section, and the protruding surface 11 that is one peripheral wall of the cavity resonator 12 is bent. A structure having an inlet 25 in which the end cut and the other wall surface (first wall surface 8) of the cavity resonator 12 are opposed to each other is shown in Japanese Utility Model Application Publication No. 61-795.
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 that occur in a direction other than the yz plane as shown in FIG. 8 enter the cavity resonator 12, so the cavity resonator 12 comes out of the resonant state, preventing radio wave leakage. The effect becomes smaller. 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 each having a width smaller than 1/2 of 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, the ratio l _M /G between the distance l _M between the entrance 25 of the cavity resonator 12 and the center of area O of the cavity cross section and the entrance dimension G is The larger the value, the larger the equivalent capacitance C becomes.

In the cavity resonator 12 in FIG. 7, l _M /G=1.0,
The equivalent capacitance C is smaller than l _M /G≧1.5 in the present invention, which will be described later. Accordingly, the equivalent inductance L must be increased by that amount according to equation (3) described later, so that it resonates 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 is large, which leads to a smaller door and lower cost. It is not suitable for

In addition, FIG. 7 shows the dimensions of each part in the drawing of the specification of Utility Model Application Publication No. 61-795 in the same proportion, and the names and numbers of the components are the same for the parts corresponding to the present invention. There is.

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 difficult to miniaturize the door. This is an unsuitable point.

Measures to solve the problem A cavity resonator with a rectangle-shaped cross section for preventing leakage radio waves is installed around the door, and three of the four sides of this cavity resonator are installed around the door in the longitudinal direction. The remaining surface and the end cut of the U-shaped conductor piece are made to face each other and serve as an entrance for introducing leakage radio waves into the cavity resonator, and this entrance and the cavity Ratio of the distance l _M between the center of the resonator area and the entrance dimension G
l _M /G is 1.5 or more.

Operation With the above configuration, radio waves that are about to leak through the U-shaped conductor piece are introduced into the cavity resonator with a square-shaped cross section as TEM waves with the shortest wavelength among the propagation modes. 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 square-shaped cross section is smaller than a 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;
is the outer box. Reference numeral 4 designates a group of small holes provided in the center of the door 5 as widely as possible in order to look inside the heating chamber 1 at any time. 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. This improves the flatness of the sealing surface 7 that makes plane contact with the flange 2 when the door 5 is opened. 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. 23 is a rising surface bent at a substantially right angle from the end of the second wall surface 9 toward the flange surface 2. 11
is a projecting surface that projects from the end of the rising surface 23 to face the first wall surface 8 . Sealing surface 7, first
The five surfaces of the wall surface 8, the second wall surface 9, the rising surface 23, and the projecting surface 11 are integrally formed from one metal plate. Both the projecting surface 11 and the rising surface 23 are provided with notches in the longitudinal direction around the door 5 at intervals smaller than one-half of the wavelength used. 1
0 is the second wall surface 9, the rising surface 23, and the overhanging surface 1
It is a U-shaped conductor piece consisting of three sides. The width D (x direction in FIG. 3) of the shaped conductor piece 10 is 2 times the wavelength used.
It is smaller than 1/1. Further, a square-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 the entrance of the cavity resonator 12 is adapted to be hooked into a mounting hole 18 provided in a rising surface 23 of the U-shaped conductor piece 10. 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 adapted to be caught around the mounting hole 18.

Next, the effects of the embodiment configured as described above will be explained. Flange 2 surrounding heating chamber 1 opening
The radio wave sealing effect will be qualitatively explained using a simple equivalent circuit as shown in FIG. 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 since the capacity of this line is inversely proportional to the parallel gap, 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 (x direction in FIG. 3) of the U-shaped conductor piece 10 is 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 rectangle-shaped 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 parallel resonance will occur when the length l of the parallel plate line is about 1/4 of the free space wavelength λ, impedance will be maximum, and radio wave leakage will be prevented. However, in the case of a 2450MHz high-frequency heating device, l is 30.6mm, and if you try to mount this on a door, it will be thick, which is disadvantageous both in terms of design and cost.

As in the present invention, a cavity resonator 1 is provided with an overhanging surface 11, has a square-shaped cross section, and has a narrow entrance 25.
2, the electric field distribution will be as shown in FIG. In this case, most of the electric lines of force are gathered 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. equivalent inductance L
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 is the value per unit length in the cylindrical axis direction (x direction). becomes as shown in equation (1). In addition, the equivalent capacitance C is the inlet 2 of the cavity resonator 12.
It is based on the turbulent electric field around 5, and is approximately given by equation (2).

L=μ ₀ AB ...(1) C=(2/πlog e√2elm/G-K)ε _p ...(2) where AB: Area of the rectangle-shaped cross section of the cavity resonator 12 μ ₀ : Magnetic permeability of the medium inside the cavity resonator 12 e: 2.72 l _M : Distance between the entrance 25 of the cavity resonator 12 and the center of area O of the cavity cross section _{ε p} : Permittivity of the medium inside the cavity resonator 12 K: Correction term related to the shape of the vicinity of the entrance 25 G: Gap of the entrance 25 (entrance dimension) The resonance frequency ₀ of the cavity resonator 12 can be expressed by equation (3).

₀ = 1/2π√LC ...(3) From equation (2), the smaller the gap G of the inlet 25, the more
Alternatively, it can be seen that as l _M /G increases, the equivalent capacitance C increases. Assuming that the resonance frequency ₀ 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 rectangle-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 between the entrances 25 is narrowed to increase the equivalent capacitance C, and the cavity area AB is correspondingly reduced to reduce the equivalent inductance L, which is constant. Resonant frequency ₀ (heating frequency of high frequency heating device)
Parallel resonance may be caused in the inlet 25 to maximize the impedance at the inlet 25 to prevent radio wave leakage.

In a high-frequency heating device with a heating frequency of 2450MHz and a high-frequency output of 500W, the flange 2 and the sealing surface 7
The gap between
I heated 275ml and measured the amount of radio wave leakage at a distance of 5cm from around Door 5. As a result, G=5mm
When AB = 15.4 x 15.9 mm, l _M /G = 2.1, the amount of radio wave leakage is 0.1 mw/cm ² or less, and if G = 8 mm, it is necessary to suppress the amount of radio wave leakage to the same level as above. The area of the square cross section is also large, as AB = 20.4 x 18.4 mm and l _M /G = 1.75. Through such experiments, the gap G of the inlet 25 was set to 4 to 8 mm.
By making l _M /G 1.5 or more, the dimensions A and B of the cavity resonator 12 with a rectangular cross section are each one-fourth of the wavelength λ used.
It has become clear that it can be made much smaller than 30.6mm.

Furthermore, since the door 5 and the U-shaped conductor piece 10 are integrally formed from one metal plate, the number of parts is small, which is advantageous in terms of cost.

Effects of the Invention As described above, according to the present invention, the entrance of a cavity resonator having a rectangle-shaped cross section surrounded by a large number of U-shaped conductor pieces and the first wall surface is connected to the end cut of the U-shaped conductor piece. and the first wall facing each other to make it narrow, and
l Since the dimensions were selected such that _M /G≧1.5, the cross-sectional dimensions A and B of the cavity can be made smaller than a quarter of the wavelength λ used, which simplifies the shape of the resonant cavity and makes it possible to It can be made smaller and thinner to provide a compact high-frequency heating device, and since the door and the U-shaped conductor piece are integrally formed from a single metal plate, it also has a large economic ripple effect. There is.

[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;
The figure is a sectional view of the main part showing the radio wave seal part around the door, Figure 3 is a diagram showing the xyz direction in Figure 1,
Figure 4 is a simplified equivalent circuit diagram of the radio wave seal part of the door 5.
Figure 5 is an electric field distribution diagram of the same radio wave seal part, Figure 6 is an electric field distribution diagram of the parallel plate line with the same termination short-circuited, and Figure 7 is an electric field distribution diagram of the same radio wave seal part.
The figure 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, 7... Sealing surface, 8
...first wall surface, 9 ... second wall surface, 10 ... U-shaped conductor piece, 11 ... overhanging surface, 12 ... U-shaped conductor piece, 23 ... rising surface, 25 ... entrance, l _M
... Distance between the entrance 25 of the cavity resonator 12 and the center of area O of the cavity cross section, G ... Inlet dimension.

Claims (1)

[Claims] 1 In a high-frequency heating device in which a cavity resonator 12 for preventing leakage radio waves is provided at the periphery of a door 5 that opens and closes the opening of the heating chamber 1, the cavity resonator 12 is located at the periphery of the door 5 and when the opening of the heating chamber 1 is closed. A sealing surface 7 that is in planar contact with the flange 2, and a first wall surface 8 that is bent from the end of the sealing surface 7 at a substantially right angle to the flange 2.
and a second wall surface 9 that is approximately perpendicular to this first wall surface 8.
and a rising surface 23 bent at a substantially right angle from the end of the second wall surface 9 toward the flange surface 2, and a rising surface 23 extending from the end of the rising surface 23 opposite to the first wall surface 8. A projecting surface 11 is integrally formed from one metal plate, and both the projecting surface 11 and the rising surface 23 are cut out in the longitudinal direction around the door 5 at intervals smaller than one-half of the wavelength used. , and the second wall surface 9 and the rising surface 2
A U-shaped conductor piece 1 consisting of three sides, 3 and an overhanging surface 11
0 and the first wall surface 8 form a cavity resonator 12 having a rectangle-shaped cross section each side of which is smaller than a quarter of the wavelength used, and having an inlet 25;
And the distance between the inlet 25 and the center of area O of the cavity cross section l _M
A high-frequency heating device characterized in that the ratio (l _M /G) of the distance between this and the inlet dimension G is 1.5 or more.