JPS62249386A - 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 The door or main body of a high-frequency heating device has a groove, and by making the characteristic impedance of the groove discontinuous in the depth direction, even if the actual depth is smaller than one quarter of the wavelength used, There is a proposal in Japanese Patent Laid-Open No. 60-25190 that the impedance at the entrance of the groove is maximum, and the amount of radio wave leakage can be reduced similarly to the choke groove.

In this conventional example, it is well known that the larger the difference in characteristic impedance at the discontinuous portion in the depth direction of the groove, the greater the reflection at the discontinuous portion.

Therefore, in the conventional example, in order to reduce this reflection and efficiently introduce the leaked radio waves to the short-circuited surface of the groove, and to obtain a sufficient radio wave sealing effect, and to prevent the adverse effects of discontinuities, cuts are made in the groove wall surface. It was set up.

Problems to be Solved by the Invention Since the reflection by the characteristic impedance discontinuity in the depth direction of the groove has a negative effect on the radio wave sealing effect, it takes time and effort to adjust the shape and dimensions of the cut on the groove wall surface, 5 harmonics are not sufficiently blocked, interfering with satellite broadcasting,
Another problem is that the configuration is complicated and it takes time to assemble.

Means for Solving the Problems The present invention provides a leakage radio wave path between a door and a flange that surrounds the opening of the heating chamber, which has a sealing surface that makes plane contact with the flange, and a protruding surface whose tip protrudes outward. A large number of conductor pieces are provided approximately at right angles to the flange to simplify the door structure, the door body is integrally molded from a single metal plate, and the gap between the conductor pieces is set to 1/2 wavelength of the fifth harmonic. The dimensions are as follows.

The planar contact between the working flange and the sealing surface is used as a type of bypass capacitor, and the conductor piece facing the flange is made to act as a series resonant element to block leakage radio waves including the fifth harmonic.

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 FIG. 1, 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, 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 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 approximately at right angles from the end of the second wall surface 9 toward the flange 2;
0 is provided with a protruding surface 11 that protrudes outward with a step relative to the sealing surface 7. Small hole group 4, step 6, sealing surface 7
, the first wall surface 8, the second wall surface 9, the conductor piece 1o, and the projecting surface 11 are integrally formed from one metal plate. Conductor piece 1
The protrusion piece 14 protruding from the opaque dielectric cover 13 that closes the gap 12 between the door 5 and the first wall surface 8 and the protrusion piece 17 protruding from the translucent door outer cover 16 forming the exterior of the door 5 are hooked and fixed. For this purpose, mounting holes 18 are provided in some of the large number of conductor pieces 1o.

The length Q1+122 of the entire conductor piece 10 including the overhanging surface 11 is set to approximately one quarter of the wavelength used as an electrical length, taking into account the wavelength shortening effect of the dielectric cover 13. The gap W between the conductor pieces 10 has a dimension of 1/2 wavelength or less of the fifth harmonic, that is, about 1.5 cm when the wavelength used is about 12c++.
It is set at 2 am or less.

Further, an opaque sheet 19 is provided on the inner surface of the door outer cover 16, facing the conductor piece 10.

FIG. 2 is a perspective view of the main body of the door 5, which is integrally molded from a single metal plate, showing the zero step part 6, the sealing surface 7. First wall surface 8, second wall surface 9. The mechanical strength of the door 5 is maintained by not providing a slit in the connecting surface 20 that connects the bases of the conductor pieces 10 to each other.

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 seven 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 increases as the gap of the planar contact portion becomes smaller, increasing the radio wave sealing effect. is the stepped portion 6 and the other is the sealing surface 7
Since the first wall surface 8 is bent approximately at right angles to the first wall surface 8, the flatness of the sealing surface 7 can be improved, and the mechanical strength can be increased, and the effect as the bypass capacitor can be improved. This effect can be maintained for a long time.

22 indicates that the entire conductor piece 10 including the projecting surface 11 acts as a series resonant element. That is, when the series resonant element 22 is in a series resonant state, the impedance becomes 0.
Therefore, it is completely reflected and leakage of radio waves can be prevented. This can be done by installing a metal post with a length of about one-fourth of the free space wavelength inside the waveguide.

It is an application of the well-known principle that it acts as a series resonant element and the transmitted energy is completely reflected at its posts. Each conductor piece 10 serves as the metal post.

In addition, in a parallel plate line as shown in Fig. 4, the parallel capacitance C between the parallel plates per unit length and the series connection along the longitudinal direction of the parallel plates are as follows, where ε is the permittivity of the medium and μ is the magnetic permeability. ,
It is known that it can be expressed approximately by the following equation.

C=t-...(1) L=μm...(2) Considering equations (1) and (2), assuming that the width a of the conductor piece 10 is constant in FIG. , the dimension d1 of the gap 12 between the conductor piece 10 and the first wall surface 8 is made sufficiently larger than the distance between the flange 2 and the overhanging surface 11 when the door 5 is sealed, that is, the step d2 between the sealing surface 7 and the overhanging surface 11. In this case, it can be considered that the portion of the conductor piece 10 having a length Ql mainly acts as an inductance, and the portion of the overhanging surface 11 having a length 0□ mainly acts as a capacitance between it and the flange 2. Therefore, the series resonant element 22 has dimensions a and d8 without considering the basic shape.
, d2, Ω0, and Q2, it is possible to cause series resonance with the heating frequency and prevent radio wave leakage, including the element of the fifth harmonic due to the dimension of the gap W.

The door 5 that prevents radio wave leakage in this manner has a simple bending structure as shown in FIG. 2, so it can be integrally formed from a single metal plate, which is advantageous in terms of structure.

Effects of the Invention As described above, according to the present invention, the flange and the sealing surface are brought into planar contact to act as a kind of bypass capacitor, and a large number of conductor pieces each having an overhanging surface with the tip extending outward are connected to the flange. Since they are opposed to each other at approximately right angles and act as a series resonant element, radio wave leakage is prevented, the door structure is simple, and it can be integrally molded from a single metal plate. Furthermore, since the gap between the conductor pieces is limited, it does not interfere with satellite broadcasting.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a main part of the radio wave seal part of a door 5 of a high-frequency heating device according to an embodiment of the present invention, FIG. 2 is a perspective view showing only the metal part of the door 5, and FIG. FIG. 4 is a simplified equivalent circuit diagram of the radio wave seal portion between the door 5 and the flange 2 around the heating chamber 1, and FIG. 4 is an explanatory diagram of the same general parallel plate line. 1... Heating chamber 2... Flange 4... Small hole group 5... Door 6... Step portion 7... Sealing surface 8... First wall surface 9... Second wall surface 10... Conductor piece 1
1... Overhanging surface W... Gap

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 to the second wall surface (9);
) A large number of conductor pieces (10) bent at a substantially right angle from the ends of the flange (2) toward the flange (2), and the conductor pieces (10)
and a projecting surface (11) projecting outward with a step with respect to the sealing surface (7) are integrally molded from one metal plate, and the gap between the conductor pieces (10), (10) is W) as the fifth
A high-frequency heating device characterized by having dimensions of 1/2 wavelength or less of harmonics.