JPS6372091A - 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 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. 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 a groove having a complicated shape in the depth direction of the groove, and it takes time and effort to prevent reflection at discontinuous portions of characteristic impedance.

Means for Solving the Problems The present invention uses a plurality of conductor pieces at the outermost peripheral wall of a frame-shaped radio wave attenuation cavity surrounding the door, and narrows the entrance of the radio wave attenuation cavity at the tips of these conductor pieces. Therefore, the overhang
This projecting surface is covered with a tapered dielectric cover 2, and those parts constituting the radio wave attenuation cavity are molded from a single metal plate.

Operation With the above configuration, radio waves that are about to leak through the conductor piece are guided to the wave attenuation cavity as TEM waves. When the radio wave attenuation cavity is regarded as a parallel resonant circuit of capacitance and inductance, the dielectric cover increases the capacitance component at the entrance of the radio wave attenuation cavity, and the inductance component may be reduced accordingly. That is, the radio wave attenuation cavity acts as a choke groove when its depth is smaller than one-fourth of the free space wavelength.

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. 1 and 2, 1 is a heating chamber, and 2 is a 7 that surrounds the opening of the heating chamber.
In the lunge, 3 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 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 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 7 flange 2 from the end of the second wall surface 8. Numeral conductor pieces 10 are bent approximately at right angles from the end of the second wall surface 9 toward the flange 2;
A projecting surface '11 projecting toward the opening of the heating chamber 1 is provided at the tip of the heating chamber 1. Small hole group 42 steps 6. Seal surface 7
．． ) Wall surface 8. Second wall? , the conductor piece 10 and the projecting surface 11 are integrally molded from a single metal plate. ) Wall surface 8. Second wall9. The conductor piece 10 and the projecting surface 11 form a radio wave attenuation cavity 12 . This radio wave attenuation cavity 12
A projection piece 14 protruding from an opaque dielectric cover 13 that blocks the entrance of the conductor piece 10 is hooked into a mounting hole 18 formed in the conductor piece 10 via a through hole 23 formed in the projecting surface 11. Translucent door outer cover 16 that covers the outside of the door 5
The projection piece 17 protruding from the conductor piece 10 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 16 to prevent it from riding on the edge of the door outer cover 16 during installation. On the back side of the dielectric cover 13 corresponding to the entrance of the radio wave attenuation cavity 12,
An impedance adjustment section 25 is provided that protrudes toward the inside of the radio wave attenuation cavity 12. Further, an opaque sheet 19 is provided on the inner surface of the door outer cover 16 so as to face the conductor piece 10, 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. The radio wave sealing effect will be qualitatively explained using a simple equivalent circuit as shown in FIG. 3 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. 22 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 since the capacitance of this line is proportional to the gap between the parallel plates, the capacitance 21 becomes smaller as the gap of the planar contact portion is smaller, and the radio wave sealing effect increases. The second 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 is no overhanging surface 11, the electric field will be distributed as shown in FIG. occurs, and the impedance becomes maximum. In practice, the thickness of the four walls of the radio wave attenuation cavity 12 is sufficiently smaller than the free space wavelength λ, so it is ignored in the explanation. 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 1), as shown in FIG. This results in an electric field distribution. in this case.

The lines of electric force between the end of the overhanging surface 1) and the wall surface 8) tend to be much more concentrated than in FIG. 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. In other words, the depth t of the radio wave attenuation cavity 12 is set to one quarter of the free space wavelength λ.
Even if it is made smaller, maximum impedance can be obtained and leakage radio waves can be suppressed.

Note that the impedance adjustment section 25 has the effect of further increasing the capacitance component at the entrance to the radio wave attenuation cavity, and further reduces the depth t of the radio wave attenuation cavity 12.

Effects of the Invention As described above, according to the present invention, there is no need to provide a plurality of parallel plate lines (grooves) with different characteristic impedances, and only an overhanging surface is provided at the tip of the conductor piece that contacts the outermost peripheral wall of the radio wave attenuation cavity. Therefore, the depth of the radio wave attenuation cavity can be made smaller than one quarter of the free space wavelength.

The door can be made thinner, and a high-frequency heating device with a simple structure can be provided.

In addition, the door can be integrally molded from a single metal plate, and by providing a taper on the back surface of the outermost periphery of the dielectric cover, it improves the fit with the outer door cover, reducing the number of assembly steps. There are also 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, and FIG. 2 is a sectional view of a main part showing a radio wave seal part around the door. FIG. 3 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...Flange. 4... Small hole group, 5... Door. 6...Stepped portion, 7...-Sealing surface. 8...The second wall surface, 9...The second wall surface. 10... Conductor piece, 11... Projection surface. 13...Dielectric cover 16...Door outer cover 24.
··taper.

Claims (1)

[Claims] Located at the periphery of the door (5) that opens and closes the heating chamber 1 opening,
When the door (5) is closed, the heating chamber (1) opening flange (
2) and a sealing surface (7) that makes plane contact with the sealing surface (7).
a first wall surface (8) extending substantially perpendicularly to the flange (2) from the end thereof, and a second wall surface (8) extending substantially parallel to the flange (2) from the end of the first wall surface (8). a 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 (
A dielectric cover (13) is provided, which has a projecting surface (11) projecting from the tip of the heating chamber (10) toward the opening side of the heating chamber (1), and covers the projecting surface (11). Taper that becomes thinner outward on the back surface of the outermost periphery (24)
The tip of this taper (24) connects the door outer cover (
16), the small hole group (4), the stepped part (6), and the sealing surface (
7), first wall surface (8), second wall surface (9), conductor piece (
10) and an overhanging surface (11) are formed from a single metal plate.