JPS62268088A - Radio frequency heater - Google Patents

Abstract

(57) [Summary] 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 impedances are provided in the door or main body of a high-frequency heating device in the depth direction, and by making the characteristic impedance of the grooves discontinuous in the depth direction, the effective depth is reduced to 4 minutes of the wavelength used. JP-A No. 1983-1999 proposed that even if the impedance at the entrance of the groove is made 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.
It is in Publication No. 25190. In this conventional example, grooves having different widths in the depth direction of one groove are provided, and the shape of the circumferential wall of the groove is deformed in the entire binding direction, resulting in a rather complicated shape.

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 thereof, and the ends of the conductor pieces are connected to the entrance of the radio wave attenuation cavity. It was bent to narrow it.

The radio wave attenuation cavity, which introduces radio waves that are about to leak through the working conductor piece as TEM waves, constitutes a parallel resonant circuit of capacitance and inductance, but the capacitance component at the entrance of the radio wave attenuation cavity is larger due to the overhanging surface. Therefore, the inductance component can be reduced accordingly, and the depth of the radio wave attenuation cavity can be 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 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 stepped portion surrounding the small hole group 4. This stepped portion 6 prevents the edge of the translucent door inner cover 15 adhered 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. 9 is the first wall surface 8
This is a second wall surface extending substantially parallel to the flange 2 from the end thereof. 10 is the flange 2 from the end of the second wall surface 9.
A large number of conductor pieces 10 are bent approximately at right angles toward the heating chamber 1, and a protruding surface 11 is provided at the tip end of the conductor piece 10, which protrudes toward the opening side 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. 1st
wall 8. Second wall? , conductor piece 10 and overhanging surface 11
(This forms a radio wave attenuation cavity 12. The protrusion piece 14 protruding from the opaque dielectric cover 13 that blocks the entrance of the radio wave attenuation cavity 12 passes through the through hole 23 provided in the projecting surface 11 to the conductor piece 10. A projection piece 17 protruding from a light-transmitting door outer cover 16 that covers the outside of the door 5 is attached to an 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 at a portion of the dielectric cover 13 that corresponds to the entrance of the radio wave attenuation cavity 12 . Also, 4 body pieces 1
An opaque sheet 19 is provided on the inner surface of the door outer cover 16 opposite to the outer door 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. For 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, a simple method as shown in FIG. Let us qualitatively explain the radio wave sealing effect using an equivalent circuit.21 is the capacitance corresponding to the planar contact between the flange L- and the sealing surface 7, and acts as a type of bypass capacitor.The planar contact is considered to be a parallel plate line. Since the capacitance of this line is proportional to the cap of the parallel plate, the capacitance 21 becomes larger as the gap between the planar contact portions becomes smaller, and the radio wave sealing effect increases.The first wall surface 8 and the conductor piece 10 transmit TEM waves. It can be considered that a propagating parallel plate line is formed and 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.
The length of the parallel plate line is t.

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 the simplified equivalent circuit of FIG. 6, it can be expressed as a parallel resonant circuit 22 in which a capacitance and an inductance are connected in parallel.

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 12 to form the overhanging surface 11.

The electric field distribution will be as shown in Figure 4. In this case, the overhanging surface 11
The lines of electric force between the end of and the first wall surface 8 are .

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 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 is a radio wave attenuation cavity 12
This has the effect of further increasing the capacitance component at the entrance of the radio wave attenuation cavity 12, and further reduces the depth t of the radio wave attenuation cavity 12.

Effects of the Invention 7 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. The depth of the radio wave attenuation cavity can be made smaller than one-fourth of the free space wavelength λ.

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

[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, FIG. 2 is a sectional view of a main part showing a radio wave seal around the door, and FIG. The figure is a simple equivalent circuit diagram of the radio wave seal part of the door 5, FIG. 4 is an electric field distribution diagram of the radio wave seal part, and FIG. 5 is an electric field distribution diagram of the parallel plate line with the terminal ends short-circuited. 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.

Claims (1)

[Claims] In the door (5) for opening and closing the opening of the heating chamber (1), a group of small holes (4) for looking into the inside of the heating chamber (1), a stepped portion (6) surrounding the group of small holes (4), This step (6)
a sealing surface (7) that surrounds the door (5) and comes into planar contact with the flange (2) of the opening of the heating chamber (1) when the door (5) is closed;
A first wall surface (8) bent from the end of this sealing surface (7) at a substantially right angle to the flange (2), and a first wall surface (8) bent from the end of this first wall surface (8) to the flange (2). a second wall surface (9) extending substantially parallel; a large number of conductor pieces (10) bent at a substantially right angle from the end of the second wall surface (9) toward the flange (2); and the conductor pieces. An overhanging surface (11) that overhangs from the tip of (10) toward the opening of the heating chamber (1)
A high-frequency heating device characterized by comprising: