JPH0569276B2 - - 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 one-fourth of the wavelength used. There is a proposal in Japanese Patent Application Laid-Open No. 60-25190 that even if the groove is made smaller, 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, a 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 a projecting 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 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 is 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 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 of FIG. 7, l _M /G=1.0, and the equivalent capacitance C is smaller than l _M /G≧1.5 in the present invention, which will be described later. (3) will be explained later.
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,
Since it is necessary to increase the cross section AB of the cavity resonator 12, the cavity resonator 12 of the conventional example is large.
It is not suitable for making doors smaller and lower in cost.

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 not suitable for miniaturizing the door. This is a 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 a part of the wall of this cavity resonator is formed by 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 l _M. , the ratio l _M /G to the inlet dimension G should be 1.5 or more, and two capacitance adjusting elements are provided at both ends of the inlet, and the capacitance adjusting element on the other wall side is larger than the one on one side of the U-shaped conductor. This is what I did.

Operation With the above configuration, radio waves that are about to leak through the U-shaped conductor piece are guided into the cavity resonator with a square-shaped cross section as a TEM wave 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. . As the entrance of the cavity is made smaller, C becomes larger when two capacitance adjustment elements are provided, 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 square-shaped cross section is smaller than a quarter of the wavelength used.

Embodiment The configuration 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 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 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 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 has a mounting surface 19 welded to the second wall surface 9, a rising surface 23 facing substantially parallel to the first wall surface 8, and an end cut formed on the first wall surface 8.
It consists of three sides, with an overhanging surface 11 facing the opposite side. Each U-shaped conductor piece 10 in the longitudinal direction around the door 5
The width D (in the x direction) of is made smaller than one-half of the wavelength used.

A rectangle-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 . Inlet 25 of this cavity resonator 12
A protruding piece 14 protruding from an opaque dielectric cover 13 that blocks the conductor piece 10 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 16 covering the front surface of the door 5 is hooked on the outermost peripheral edge 20 of the second wall surface 9. It's becoming like that.

In addition, as shown in FIG.
Capacitance adjusting elements 26 and 27 protruding from the capacitance adjusting element 3 are provided, 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.

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 (in the x direction in FIG. 3) of the U-shaped conductor piece 10 is made smaller than half of the wavelength used, a 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 the length l of the parallel plate line will cause parallel resonance at about one quarter of the free space wavelength λ, and the impedance will be maximum, preventing radio wave leakage. 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.

When the cavity resonator 12 is formed by providing the projecting surface 11 and having a rectangular cross section and a narrow entrance 25 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 gathered between the vicinity of the end cut of the overhanging surface 11 and the first wall surface 8. Cavity resonator 12 is represented in FIG. 4 as a parallel resonant element consisting of an equivalent inductance L and an equivalent capacitance C. 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 equivalent inductance as a constant of the coil, and the unit length in the cylindrical axis direction (x direction). The value around is as shown in equation (1). In addition, the equivalent capacitance C is based on the disturbed electric field near the entrance 25 of the cavity resonator 12, and is approximately expressed as (2)
It is given by Eq.

L=μ ₀ AB ...(1) C=(2/πloge√2el _M /G-K)ε ₀ ...(2) where AB: Area of the rectangle-shaped cross section of the cavity resonator 12 μ ₀ : Magnetic permeability e of the medium inside the cavity resonator 12: 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 ₀ : Permittivity of the medium inside the cavity resonator 12 K: Correction term related to the shape of the vicinity of the inlet 25 G: Gap of the inlet 25 (inlet 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. Parallel resonance may be caused at the resonance frequency ₀ (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 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, by narrowing the gap G of the inlet 25 to about 4 to 8 mm and increasing l _M /G to 1.5 or more, the dimensions A and B of the cavity resonator 12 having a rectangular cross section can be respectively reduced. It has become clear that it can be made much smaller than 30.6 mm, which is a quarter of the wavelength λ used.

Dielectric cover 1 that blocks the entrance 25 of the cavity resonator
3, a plurality of capacitance adjustment elements 26 and 27 with different protrusion dimensions are provided in the cavity resonator 12, and the capacitance adjustment element 26 with the shorter protrusion dimension is arranged near the end cut of the protruding surface 11 where the electric field is strong. and the first one with a weak electric field
Since the other longer capacitance adjustment element 27 is arranged near the wall surface 8, the equivalent capacitance of the cavity resonator can be adjusted efficiently.

Further, the equivalent capacitance C is adjusted by the capacitance adjustment elements 26 and 27 to ensure parallel resonance, thereby increasing the radio wave sealing effect. Furthermore, since the capacitance adjustment element 27 near the first wall surface 8 has a longer protruding dimension than the capacitance adjustment element 26 near the end of the projecting surface 11, when the dielectric cover 13 is fitted, the capacitance adjustment element 27 is first inserted along the first wall surface 8;
After being positioned, the capacitive adjustment element 26
Going into 5. Therefore, there is no risk that the capacitance adjustment element 26 will push the projecting surface 11 from the y direction and deform it. Note that the capacitance adjusting element 26 also plays the role of minimizing deformation of the projecting surface 11 against external force in the z direction when the dielectric cover 13 is in a fixed state.

Effects of the Invention As described above, according to the present invention, the population 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 reduced by the overhanging surface of the U-shaped conductor pieces. The end cut and the first wall face each other to make it narrow, and the dimensions are selected such that l _M /G≧1.5. A capacitance adjusting element is provided, with a capacitance adjusting element having a short protruding dimension protruding near the end cut of the protruding surface where the electric field is strong, and the other longer capacitance adjusting element protruding near the first wall surface where the electric field is weak. By efficiently adjusting the equivalent capacitance of the cavity resonator, the cross-sectional dimensions A and B of the cavity resonator can be made smaller than one-fourth of the wavelength λ used, which simplifies the shape of the cavity and makes it possible to We can provide a compact high-frequency heating device that is smaller and thinner and easier to assemble.
There are also significant economic ripple effects.

[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 radio wave seal part, and Figure 6 is a diagram of the electric field distribution of the radio wave seal part of the door 5.
The figure is an electric field distribution diagram of a parallel plate line with the same terminal short-circuited.
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, 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...Entrance, 2
6, 27...capacitance adjustment element, l _M ...cavity resonator 1
2, the distance between the inlet 25 and the center of area O of the cavity cross section,
G...Entrance dimensions.

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.
A second wall surface 9, which is substantially perpendicular to the first wall surface 8, is integrally formed from a single metal plate, and the second wall surface 9 has a wavelength of 2/2 of the wavelength used in the longitudinal direction around the door 5. A large number of U-shaped conductor pieces 10 divided into smaller pieces than 1
A cavity resonator 12 is formed by the first wall surface 8 and the U-shaped conductor piece 10 to form a square-shaped cross section with each side smaller than one-fourth of the wavelength to be used, and has an entrance 25. , and the ratio of the distance l _M between the inlet 25 and the center of area O of the cavity cross section to the inlet dimension G (l _M /G) is 1.5 or more, and the U-shaped conductor piece 10
is integrally formed from a belt-shaped metal plate separately from the door, and has a mounting surface 1 that is fixed to the second wall surface 9.
9, a rising surface 23 facing the first wall surface 8 substantially parallel to the first wall surface 8, and an overhanging surface 11 having an end cut facing the first wall surface 8.
The second inlet 25 is formed by making the end cut of the protruding surface 11 and the first wall surface 8 face each other, and a plurality of inlets having different protruding dimensions are formed from the dielectric cover 13 that blocks the inlet 25 into the cavity resonator 12. Capacitance adjustment elements 26, 27
The capacitance adjusting element 26 with a shorter protruding dimension is placed near the end cut of the overhanging surface 11 where the electric field is strong, and the other capacitance adjusting element 27 is placed near the first wall surface 8 where the electric field is weak. A high-frequency heating device characterized by the following: