JPS6372094A - 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 of the groove is complicated, such as by 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. It is also necessary to consider reflection prevention at discontinuities in characteristic impedance.

Problems to be Solved by the Invention It is necessary to provide grooves with complicated shapes in the depth direction of the grooves, and it takes time and effort to prevent reflections at discontinuous portions of characteristic impedance.

Means for Solving the Problems The present invention provides a frame-shaped radio wave attenuation cavity surrounding the door with a plurality of conductor pieces at the outermost peripheral wall, and the tips of the conductor pieces are connected to the entrance of the radio wave attenuation cavity. Extend it out so as to narrow it,
A dielectric cover is provided to cover the projecting surface, and the projecting piece on the back side is fitted and fixed into the conductor piece, the through hole on the projecting surface, and the mounting hole, and the part that constitutes the radio wave attenuation cavity is molded from a single metal plate. This is what I did.

Effect: With the above configuration, radio waves that are about to leak due to the conductor piece are guided to the radio wave attenuation cavity as TEM waves. When the radio wave attenuation cavity is regarded as a parallel resonant circuit of capacitance and inductance, the impedance adjustment section increases the capacitance component at the entrance of the radio wave attenuation cavity, and the inductance component may be reduced accordingly. That is, the depth of the radio wave attenuation cavity can be made smaller than one quarter of the free space wavelength.

Example 1 shows the configuration of a high-frequency heating device according to an embodiment of the present invention.

2 and its operation will be explained with reference to the drawings. Figures 1 and 2
In the figure, 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 as wide as possible in the center of the door 5 in order to look into the inside of 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 adhered 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 which is 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. Numeral conductor pieces 10 are bent at a substantially right angle from the end of the second wall surface 9 toward the flange 2.
0 is provided with an overhanging surface 11 that overhangs toward the heating chamber 1 opening +14'1. Small hole group 41 step part 6. Seal surface7. First wall 8. Second wall9. The conductor piece 10 and the projecting surface 11 are integrally formed from a single metal plate. First wall 8. Second wall9. Conductor piece 10 and overhanging surface 1
1 forms a radio wave attenuation cavity 12. The projection piece 14 protruding from the opaque dielectric cover 13 that blocks the entrance of the radio wave attenuation cavity 12 is hooked into the attachment hole 18 formed in the conductor piece 10 via the through hole 26 formed in the projecting surface 11. There is. A protruding piece 17 protruding from a translucent door outer cover 16 covering the outside of the door 5 is adapted to be caught on the end of a connecting surface 20 that connects the bases of the conductor pieces 10 to each other. A taper 24 that becomes thinner toward the outside is provided on the back surface of the outermost periphery of the dielectric cover 13 to prevent it from riding on the edge of the door outer cover 16 during installation. An impedance adjustment portion 25 that protrudes toward the inside of the radio wave attenuation cavity 12 is provided on the back side of the dielectric cover 13 corresponding to the entrance of the radio wave attenuation cavity 12 . In addition, the conductor piece 10
An opaque sheet 19 is provided on the inner surface of the door outer cover 16 so as to face the door outer cover 16, so that the gap between the conductor pieces 10 is not visible from the outside.

Next, the effects of the embodiment configured as described above will be explained. Heating chamber 1. The radio wave sealing effect will be qualitatively explained using a simple equivalent circuit as shown in FIG. 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 capacity of this line is proportional to the camp of the parallel plates, so the capacitance 21 becomes larger as the gap of the planar contact portion becomes smaller, and the radio wave sealing effect increases. The first wall surface 8 and the conductor piece 10 form a parallel plate line for propagating TEM waves, and it can be considered that the terminal end is short-circuited by the second wall surface 9. in this case,
If there were no overhanging surface 11, the electric field would be distributed as shown in Figure 5, and the length of the parallel plate line would be affected.

That is, the depth of the radio wave attenuation cavity 12 causes parallel resonance at approximately one quarter of the free space wavelength λ, and the impedance becomes maximum. In practice, the thickness of the peripheral wall of the radio wave attenuation cavity 12 is sufficiently smaller than the free space wavelength λ, so it will be ignored in the description. In FIG. 3, which shows a simple equivalent circuit, it can be expressed as a parallel resonant circuit 22 in which a capacitance and an inductance are connected in parallel.

As in this embodiment, when the tip of the conductor piece 10 that is on the outermost peripheral wall of the radio wave attenuation cavity 12 is bent to narrow the entrance of the radio wave attenuation cavity 12 to form the projecting surface 11, as shown in FIG. The electric field distribution will be as follows. in this case.

The lines of electric force between the end of the overhanging surface 11 and the first wall surface 8 are as follows:
It is much easier to crowd than in Figure 5. This means that even if the capacitance component in the radio wave attenuation cavity 12 shown in FIG. 4 is small, even if the inductance component is reduced by that much, resonance can be achieved at a specific frequency. That is, even if the depth 2 of the radio wave attenuation cavity 12 is made smaller than one-fourth of the free space wavelength λ, the maximum impedance can be obtained and leakage radio waves can be kept small.

Note that the impedance adjustment section 25 has the effect of further increasing the capacitance component at the entrance of the radio wave attenuation cavity 12 in proportion to its dielectric constant, and further reduces the depth l of the radio wave attenuation cavity 12. be.

Furthermore, the cross-sectional shape of the impedance adjustment portion 25 is made thicker as it approaches the first wall surface 8 from the tip of the projecting surface 11. That is, as shown in FIG. 4, the cross-sectional shape of the impedance adjustment part 25 is selected in accordance with the density of the electric lines of force, and the effect of increasing the capacitance component with a slightly thicker material is achieved.

Furthermore, the dielectric cover 13 has a projection piece 14 and a through hole 23.
, and are securely fixed by the action of the mounting hole 18.

Effects of the Invention As described above, according to the present invention, an overhanging surface can be provided at the tip of the conductor piece that contacts the outermost peripheral wall of the radio wave attenuation cavity without providing a plurality of parallel plate lines (grooves) with different characteristic impedances. ,
Furthermore, a dielectric cover was provided to cover the protruding surface, and the protruding pieces were fitted into the through holes and mounting holes, so the depth of the radio wave attenuation cavity could be reduced to less than one-fourth of the free space wavelength by simple means.
The door can be made thinner, and a compact high-frequency heating device can be provided.

Further, since the door can be integrally molded from a single metal plate, the number of assembly steps can be reduced, and the economic ripple effect is also significant.

[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. 6 is a simplified equivalent circuit diagram of the radio wave seal portion of the door 5, FIG. 4 is an electric field distribution diagram of the radio wave seal portion, and FIG. 5 is an electric field distribution diagram of the parallel plate line with its terminal ends short-circuited. 1... Heating chamber, 2... Furanone. 4... Small hole group, 5... Door. 6... Stepped portion, 7... Sealing surface. 8...First wall surface, 9...Second wall surface. 10... Conductor piece, 11... Projection surface. 16... Dielectric cover, 25... Impedance adjustment section.

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 (
A first wall surface (8) extends from the end of the first wall surface (8) substantially perpendicular to the flange (2), and a first wall surface (8) extends substantially parallel to the flange (2) from the end of the first wall surface (8). 2 wall surface (9), a large number of conductor pieces (10) approximately perpendicular to the flange (2) from the end of this second wall surface (9), and this conductor piece (
10) is provided with an overhanging surface (11) that overhangs from the tip of the heating chamber (1) toward the opening side, and is provided in the conductor piece (10) through a through hole (23) provided in the overhanging surface (11). The dielectric cover (13) is fixed to the door (5) by hooking the projection piece (14) provided on the back side of the dielectric cover (13) into the mounting hole (18), 6), the sealing surface (7), the first wall surface (8), the second wall surface (9), the conductor piece (10) and the projecting surface (11) are formed from a single metal plate. High frequency heating device.