JPS6372092A - 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 surrounding 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 on the outermost peripheral wall of a frame-shaped radio wave attenuation cavity surrounding the door, and the tips of these conductor pieces narrow the entrance of the radio wave attenuation cavity. A dielectric cover is provided to cover the projecting surface, a tapered impedance adjustment section is protruded from the back surface of the dielectric cover, and the portion constituting the radio wave attenuation cavity is molded from a single metal plate.

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 the 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 tapered impedance adjustment part.
The inductance component can 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.

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 FIGS. 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. 6. This step part 6 surrounds the small hole group 4 of the cigarette, and this step part 6 prevents the end 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 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.
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 49 steps 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. The conductor piece 10 and the projecting surface 11 form a radio wave attenuation cavity 12 . The projection piece 14 protruding from the opaque dielectric cover 16 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 23 formed in the projecting surface 11. There is. Therefore, the dielectric cover 13 can be easily attached without using tools. 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 . Also, conductor piece 1
An opaque sheet 19 is provided on the inner surface of the door outer cover 16 so as to face the outer door cover 16, and is thinned 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. 3 with respect to the incident radio waves toward the planar contact portion between the flange 2 surrounding the opening 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 FIG. 5, and the length of the parallel plate line will be t.

That is, when the depth of the radio wave attenuation cavity 12 is approximately 1/4 of the free space wavelength λ, parallel resonance occurs 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 overhanging surface 11, the protrusion surface 11 is formed as shown in FIG. This results in electric field distribution. 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 even if the capacitance component in the radio wave attenuation cavity 12 population in FIG. 4 becomes large and the inductance component is reduced by that amount, resonance can be achieved at a specific frequency. That is, even if the depth t 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 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 t 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 section 25 is selected in accordance with the density of the electric lines of force, thereby increasing the effect of increasing the capacitance component with a small amount of material.

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) having different characteristic impedances.

A protruding surface is provided at the tip of the conductor piece that corresponds to the outermost peripheral wall of the radio wave attenuation cavity, and this is covered with a dielectric cover, and an impedance adjustment section is protruded to reduce the depth of the radio wave attenuation cavity to one-fourth of the free space wavelength. It can be made smaller, the door can be made thinner, and a compact high-frequency heating device can be provided.

Furthermore, since the impedance adjustment section has a specific shape, the capacitance component can be increased with less material.

Yet again. Since the door can be integrally molded from a single metal plate and the dielectric cover can be easily attached, 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. 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...First wall surface, 9...Second wall surface. 10... Conductor piece, 11... Projection surface. 13... Dielectric cover, 14... Protrusion piece. 18...Mounting hole, 23...Through hole.

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 (
a dielectric cover (11) that protrudes from the tip of the heating chamber (1) toward the opening side of the heating chamber (10), and blocks a gap between the tip of the protruding surface (11) and the first wall (8); The impedance adjustment section 4 is protruded from the back surface of the impedance adjustment section 4 (13), and the cross-sectional shape of the impedance adjustment section (25) is aligned with the projecting surface (11).
The tip of the hole approaches the first wall (8), and the small holes (4), the step (6), the sealing surface (7), and the first wall (8) are thickened.
), second wall surface (9), conductor piece (10) and overhanging surface (
11) is formed from a single metal plate.