JPS6132989A - High 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 Field of the Invention The present invention relates to an improvement in the radio wave leakage prevention structure of a door provided at the entrance of a heating chamber of a high frequency heating device so as to be openable and closable.

Conventional technology A radio maze is installed around the door of the high-frequency heating device.

There is a proposal in Japanese Utility Model Application Publication No. 54-130642 (Figure 6) to provide a slit in the partition plate that constitutes this radio maze (choke), but in this conventional example, the slit (width 2m±1
Since it cannot be said that the radio wave sealing effect is sufficient with only a pitch of 5 mm and a pitch of 10 mm or less, a radio wave absorbing material is added to the outer wall of the partition plate. Note that the explanations of the symbols in Figure 2 are the same as those described later.

Problems to be solved by the invention include an increase in the number of parts, a complicated structure, poor assembly performance, an increase in the external dimensions of the door, and a poor space factor.

Means for Solving the Problem A part of the peripheral wall of the radio maze is constructed from a plurality of metal pieces spaced sufficiently apart and bent into an L-shape.

The action leakage radio waves are absorbed by the U-shaped microstrip line,
The remaining minute amount is reflected at the entrance of another microstrip line 15 and does not leak to the outside.

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 is a heating chamber into which an object to be heated is placed; 2 is a flange surrounding the entire opening of the heating chamber 1; Reference numeral 6 denotes an outer box that houses the heating chamber 1, and the front periphery of the outer box B serves as a sash 5 that extends the metal plate constituting the outer box 6 and encloses the door 4.

A door rear plate 6 is in planar contact with the flange 2, and a radio wave maze 8 is formed by joining a door front plate 7 to the door rear plate B. Heating chamber flange 2/sash 5. The door rear plate 6 and the door front plate 7 are each made of a metal plate.

Reference numeral 9 denotes a door cover made of a radio wave transparent dielectric material that covers the entrance 10 of the radio wave maze 8 and the outer periphery of the door front plate 7. 11
12 is a transparent window cover provided on the heating chamber 1 side of the viewing window 11. 1 Lo is a plurality of L-shaped bent metal pieces protruding from the outermost edge of the door front plate 7, with the - side 14 facing the sash 5, and the section indicated by the dotted arrow as a narrow microstrip line 1.
5, and the other surface 16 protrudes into the inside of the radio maze 8, so that the radio wave propagation path of the radio maze 8 is a U-shaped microstrip line 17 as shown by the solid arrow.

Next, the operation and effect of the above embodiment will be explained. Door rear plate 6
Most of the leakage radio waves that try to go out through the radio wave passage between the
These are several types of higher-order modes at MH2±50MHz). The wavelength perpendicular to the traveling direction of the higher-order mode, the so-called cutoff wavelength (λC), is the free space wavelength (λ0).
wavelength in the direction of travel.

The so-called guide wavelength (λg) is also longer than λ0. There is a property that the inner wavelength (λg) of a higher-order mode becomes longer as the order becomes higher. In general choke grooves, radio wave propagation is difficult for higher-order modes having λg larger than λ0 as described above, so the radio wave propagation path is too short and the radio wave sealing effect is degraded. Furthermore, the order of the higher-order mode changes depending on various factors such as the type and position of the load stored in the heating chamber 1, variations in the oscillation frequency of the high-frequency oscillator, and the dimensions of the heating chamber, making the radio wave sealing effect unstable. It is.

On the other hand, in the configuration shown in FIG.
and a U-shaped microstrip line 1 formed between the metal wall surfaces of the door rear plate 6 and the door front plate 7 facing thereto.
When leakage radio waves enter 7, they propagate as TEM waves due to the well-known characteristics of microstrip lines. The propagation of the TEM wave in the traveling direction is the same as the free space wavelength λ0. Therefore, a microwave sealing effect can be obtained. Also,
A small amount of the leaked radio waves passes through the population 10 of the radio wave maze 8 and directly enters the narrow microstrip line 15 formed between the one surface 14 of the metal piece 16 and the sash 5.

Since the entrance 10 of the radio wave maze 8 has approximately infinite impedance, it is estimated that the characteristic impedance of the radio wave path for leakage radio waves passing through this population 10 is extremely large. When the width W of the metal piece 16 is larger than the gap between the metal piece 16 and the sash 5.

The characteristic impedance 2 of the microstrip line 15 is approximately expressed as 120π(-) in 2. In reality, since the door cover 9 is made of dielectric material, the characteristic impedance 2 of the micronutri tube line 15 is much smaller than the value calculated using the above equation. Therefore, due to the large difference between the above-mentioned extremely large characteristic impedance for leakage radio waves and the characteristic impedance 2 of the microstrip line 15, the reflection at the entrance 18 of the microstrip line 15 becomes large, and the waves that pass through the microstrip line 15 to the outside. The amount of radio waves radiated to the area will be significantly reduced.

From a structural point of view, the radio wave propagation path of the radio wave maze 8 is U-shaped, and the population 10 faces the Satsushi-5, so the dimension T in the thickness direction of the door 4 and the external dimension of the door 4 are reduced. In addition, the dimension S, which is desirable to be as small as possible in order to enlarge the viewing window 11, and the ratio of the effective volume of the heating chamber 1 to the volume of the entire high-frequency heating device, that is, the space-saving space between the left and right doors 4 and the flange) 2. Each opposing length can be made smaller. Therefore, according to the present invention, the door 4 can be made thinner and smaller.

The viewing window 11 is large so that the inside of the heating chamber 1 can be easily seen, and the space factor can be improved.

Effects of the Invention As described above, according to the present invention, the outermost edge of the door front plate that forms the wall of the radio maze is composed of a plurality of metal pieces, the metal pieces are bent into an L shape, and the surface is A plurality of narrow microstrip lines are formed facing each other, and the other side protrudes into the inside of the radio wave maze, making the radio wave propagation path of the radio wave maze a U-shaped microstrip line, thereby preventing significant leakage of radio waves. In addition to reducing the number of parts, the structure is simple and easy to assemble, and the door is thinner.

It can be made smaller, and the heating chamber is easy to see because there is no obstruction to prying eyes.
It is possible to provide a high-frequency heating device with a good space factor, and the effects of implementation are significant.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the main part of a high-frequency heating device according to an embodiment of the present invention, FIG. 2 is a perspective view of the main part showing the shape of the metal piece, and FIG. 6 is a main part of a conventional high-frequency heating device. FIG. 1...Heating chamber, 2...Flange. 420. Door, 5...Satush? 6...
・Door rear board, 7...Door front board. 8...Radio maze, 16...Metal piece. 14... One side of a metal piece, 15... Microstrip line. 16...Another side of the metal piece, 17...Micros) JL Tsubu railway.

Claims (1)

[Claims] A flange (2) surrounding the entire opening of the heating chamber (1), a sash (5) made of a metal plate protruding in front of the flange (2), and a door rear plate (2) that is in plane contact with the flange (2). 6) and a radio labyrinth (8) formed by joining a door front plate (7) whose outermost edge is made of a plurality of metal pieces (13). one side (14) is opposed to the sash (5) to form a plurality of narrow microstrip lines (15), and the other side (16) is protruded into the radio maze (8). A high-frequency heating device characterized in that the radio wave propagation path of the radio maze (8) is a U-shaped microstrip line (17).