JPS6343291A - 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. A proposal was made in JP-A-60-25 that even if the value 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.
In the conventional example disclosed in Japanese Patent No. 190, 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.

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 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. It sticks out like this,
This projecting surface is covered with a tapered dielectric cover.

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 considering a radio wave attenuation cavity as a parallel resonant circuit of capacitance and inductance, the capacitance component at the entrance of the radio wave attenuation cavity becomes larger due to the dielectric cover, and the inductance component only needs to be smaller by that much, that is, the radio wave attenuation cavity acts as a choke groove with a depth of less than a quarter 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.

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. Reference numeral 6 denotes a step surrounding the small hole group 4;
This prevents the end of the translucent door inner cover 15 adhered to the inner surface of the door from peeling off during cleaning, etc., and improves the flatness of the sealing surface 7 that makes plane contact with the flange 2 when the door 5 is closed. be. 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. Numerous conductor pieces 10 are bent at a substantially right angle from the end of the second wall surface 9 toward the flange 2, and each of the conductor pieces 10 has a projecting surface 11 extending toward the opening of the heating chamber 1 at the tip thereof. It is set up. Small hole group 4, stepped portion 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 integrally formed from a single metal plate.

First wall 8. A radio wave attenuation cavity 12 is formed by the second wall surface 9, the conductor piece 10, and the projecting surface 11. The projection piece 14 protruding from the opaque dielectric cover 13 that blocks the entrance of the radio wave attenuation cavity 12 is connected to a through hole 23 provided in the projecting surface 11.
It is adapted to be hooked into a mounting hole 18 provided in the conductor piece 10 via the conductor piece 10. A protruding piece 17 protruding from a translucent door outer cover 16 covering the outside of the door 5 is hooked onto an end of a connecting surface 2o 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 protruding 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 Jljl12. Further, an opaque sheet 19 is placed on the door outer cover 1 facing the conductor piece 10.
6, 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. 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 capacitance of this line is proportional to the gap between the parallel plates, so the capacitance 21 becomes larger as the gap of the planar contact portion is 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 is no overhanging surface 11, the electric field will be distributed as shown in Figure 5, and the length Q of the parallel plate line, that is, the depth of the radio wave attenuation cavity 12, will cause parallel resonance at about one-fourth of the free space wavelength λ. , the impedance is maximum. In practical terms, the thickness of the peripheral wall of the radio wave attenuating space J5i12 is sufficiently smaller than the free space wavelength λ, so it is ignored in the explanation. Figure 3, which shows a simple equivalent circuit, shows a parallel resonant circuit 22 in which capacitance and inductance are connected in parallel.
It can be expressed as

When, as in the present invention, the tip of the conductor piece 10 that is the outermost peripheral wall of the radio wave attenuation cavity 12 is bent to narrow the entrance of the radio wave attenuation cavity Jlq12 to form the overhanging surface 11, the electric field distribution as shown in FIG. 4 is obtained. becomes. In this case, the lines of electric force between the end of the projecting surface 11 and the first wall surface 8 are much more likely to be concentrated than in FIG. 5.

This means that the capacitance component at the entrance of the radio wave attenuation cavity 12 shown in FIG. 4 becomes large, and even if the inductance component is reduced by that much, resonance can be achieved at a specific frequency. That is, even if the depth Q of the radio wave attenuation cavity 12 is made smaller than one quarter of the free space wavelength λ, the maximum impedance can be obtained and leakage radio waves can be suppressed to a small level.

Note that the impedance adjustment section 25 is a radio wave attenuation cavity 12
This has the effect of further increasing the capacitive component at the entrance of the radio wave attenuating cavity 12, and further reducing the depth of the radio wave attenuation cavity 12.

Effects of the Invention As described above, according to the present invention, an overhanging surface is provided at the tip of the conductor piece that contacts the outermost peripheral wall of the radio wave attenuation cavity, without the need to provide a plurality of parallel plate lines (grooves) having different characteristic impedances.
In addition, since 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. Furthermore, since the tapered dielectric cover is provided, the door can be made thinner and fit better with the door outer cover.

[Brief explanation of drawings]

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, FIG. 2 is a cross-sectional view of a main part showing a radio wave seal around the door, and FIG. FIG. 4 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 the terminal ends short-circuited. DESCRIPTION OF SYMBOLS 1... Heating chamber 2... Flange 4... Small hole group 5... Door 6... Step part 7... Sealing surface 8... First wall surface 9... Second wall surface 10...
・Conductor piece 11...Protruding surface 13...Dielectric cover 16...Door outer cover 24...Taper

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
) and a second wall (8) extending substantially perpendicularly to the flange (2) from the end of the first wall (8), and a second wall extending substantially parallel to the flange (2) from the end of the first wall (8). The wall surface (9) of
A large number of conductor pieces (10) extending from the end of the second wall surface (9) to the flange (2) are substantially perpendicular to the flange (2).
A dielectric cover (13) is provided, which has a projecting surface (11) projecting from the tip of the heating chamber (1) toward the opening side of the heating chamber (1), and covers the projecting surface (11). The back surface of the outermost periphery is tapered (24) that becomes thinner toward the outside, and at the tip of this taper (24), the door outer cover (16) is formed.
A high frequency heating device characterized by being integrated with.