JPS599895A - Radio wave sealing device - 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 The present invention relates to an improved radio wave sealing device for a high frequency heating device.

A microwave oven, which is a typical example of a conventional high-frequency heating device, uses a conductive gasket as a means to prevent radio wave leakage from the gap (hereinafter referred to as the radio wave passage) created between the heating chamber opening and the entrance/exit door. Contact methods, methods using radio wave absorbing materials, and choke methods using resonance have been proposed, and combinations of each have been put into practical use.

Among these methods, the choke method using resonance is considered to be the best method in terms of performance and reliability.

However, since this choke method uses resonance, it necessarily requires structural dimensions that are related to the wavelength of radio waves that propagate through the radio wave path and are likely to leak.

A conventional choke system configuration will be explained with reference to FIG.

Figure 1 (2L) is a configuration diagram, (b) its equivalent circuit, (0
) is a plan view in the y direction of figure (a).

This radio wave sealing device has a configuration in which a choke cavity 4 is arranged starting from the entrance A of a radio wave passage 30 formed by the heating chamber opening flange 1 and the entrance/exit door 2 at a point B at the dead length of the leakage radio wave wavelength. The first drawback is that the dimensions in two directions, which are the outward directions of the device main body, require at least a falsification of the leakage radio wave wavelength, making it difficult to make it compact.

Also, if the load impedance seen from the terminal C of the radio wave path 3 outside the body is zL, and the impedance seen from B to the choke cavity side is zB, then the radio wave sealing mechanism shown in figure (a) is the equivalent circuit shown in figure Φ). indicated, i.e. Z'B >
In the case of Zb, the radio wave sole mechanism having the configuration shown in FIG.

However, the main reason why theoretical analysis is difficult in such a radio wave seal mechanism is that even though the entrance of the radio wave passage (represented by point A) is the same, as shown in Figure (C), the directions in which the radio waves travel are two directions. Any θ in two directions without being restricted by
One example of this is that there are leakage radio waves that travel at certain angles.

With respect to such leakage radio waves, there is a drawback that if the value of zB becomes smaller than the value of zB at θ-0, the radio wave/-sill mechanism attenuation characteristics deteriorate.

In view of these circumstances, the present invention introduces a parallel transmission line used for transmitting radio waves into a radio wave seal mechanism, provides a branch path in the transmission line, provides a new and compact mechanism, and has a compact mechanism configuration. The main objective is to provide a radio wave sealing device that achieves stable performance and improved reliability.

The present invention will be explained below with reference to the drawings.

FIG. 2 is a basic configuration diagram of the radio wave sealing device of the present invention,
(&) is the configuration diagram, and ■) is its equivalent circuit.

The parts in the figure that are compared with FIG. 1 are indicated by the same numbers.

A transmission line group 5+L, 5b, 50 is formed facing the heating chamber opening flange 1 and extending outward from the apparatus main body and having a width W and arranged with a gap S from adjacent transmission lines. The following explanation will be given based on the transmission line 5a as a representative of this transmission line group. The transmission line 5a has a branch path 6 at a length B of 11 from the input end of the radio wave path 3,
The depth 12 is approximately the depth of the leakage radio wave wavelength λg. Further, the length from the branch path to the terminal end C of the radio wave path is 43.

The equivalent circuit of such a transmission line is expressed as shown in the diagram Φ, as is well known in microwave engineering.

The big difference here from Fig. 1 (1)) is that the width of the transmission line is limited to W, so there is inductivity at the branch point.

There is a capacitive parameter involved.

Taking this incidental parameter into consideration, and calculating the impedance 2m as seen from the terminal A-m' with the depth of the branch path 6 as % wavelength, we obtained a result that the shorter l, the closer 2m is to zero. This indicates that the shorter 11 is, the higher the radio wave attenuation characteristic of the radio wave sealing device shown in the basic configuration of the present invention is. To prove this, l+ is 3Q1nm and 1
When the attenuation characteristics were actually measured with a diameter of 2 mm, β:127 nm yielded a shamefully low radio wave leakage result compared to 11=30 mm, and the characteristics of the radio wave sealing device of the basic configuration of the present invention were theoretically and experimentally verified. We were able to.

As a result, the fact that the dimension from the entrance of the radio wave to the choke cavity in the choke system, which has been used as a well-known fact in the past, is the % wavelength has been changed from the fact that the branching path corresponding to the choke cavity, as shown in the basic configuration of the present invention, By adopting a configuration of a radio wave sealing device in which transmission lines having a wavelength of It has been shown that the radio wave seal device can be made more compact in size compared to the conventional choke method.

In this radio wave sealing device, since the depth of the branch path should be set to t'A of the leakage radio wave wavelength, a dielectric material is interposed in the branch path to compress the leakage radio wave wavelength in the branch path. Actual dimensions of the branch road (dimensions in the y direction in Figure 2 (2L))
The origin of the present invention is to make it more compact.

FIG. 3 is a conceptual diagram of the radio wave sealing device of the present invention.

(a) is a diagram in which the branch path 6 is composed of only an air layer 7,
The depth 12 of the branch path is approximately A of the leakage radio wave wavelength.

A dielectric layer 8 with a relative dielectric constant of 4 is taken as an example inside this branch path.
If it is satisfied, the wavelength propagating in the branch path is greatly compressed, so the depth p4 of the branch path can be equal to the depth p4 compared to the (+L) diagram configuration. This is shown in FIG. 3(b).

In addition, in FIG. 3, parts that are compared with FIG. 2 are indicated by the same numbers.

By the way, the mechanism for inserting a dielectric material into this branch path to reduce its actual size while keeping the effective length of the branch path for radio waves the same is as follows.
As shown in FIG. 3, although theoretically it is simple and clear, the following difficulties arise in actual design.

In the assembly process in which the formed dielectric material is inserted and loaded into the branch path, a considerable gap (air layer) is created between the conductor and the dielectric material forming the branch path.

Even in a molding configuration in which resin is poured using a branch path conductor as a mold, a considerable gap may occur between the conductor as a mold and the contracted resin (dielectric material) due to resin contraction.

The influence of this gap (air layer) will be explained with reference to FIGS. 4 and 5.

FIG. 4 is a diagram illustrating the influence of an air layer on the branch path of the radio wave sealing device of the present invention, and FIG. 5 shows the effective permittivity characteristics in the branch path when a dielectric layer and an air layer are combined. It is something that shows.

FIG. 4(a) shows the electric field distribution in the radio wave sealing device of the present invention. High frequency waves input by a person are propagated into the branch path 6 as shown in the figure. In this figure, the line conductor is 9 and the ground conductor is 10. An enlarged view of the part surrounded by a circle 11 in the branch path is shown in FIG. 4).

In FIG. 4(b), the ground conductor 10 and the line conductor 9 are separated by a distance d through a dielectric layer 12 having a desired dielectric constant and a thickness h and an air layer 13 having a certain thickness. There is. Arrows in the figure indicate the direction of the electric field.

In order to know the effective wavelength of leakage radio waves in a branch path having such a two-layer structure, it is necessary to know the effective permittivity of the branch path in which the dielectric layer 12 and the air layer 13 are combined. This effective permittivity εeff is shown in Fig. 4(C) and Fig. 4(b).
As shown in the equinodal circuit shown in FIG. That is, C1-εo·εr"H+'2-60g ε0 is the permittivity of vacuum, and S is given by the unit facing area. Note that the dielectric constant of the air layer is 1.

FIG. 5 shows the characteristics of g and εeff when h :=:3 mJ tr=4 from equation (1).

What can be seen from Figure 5 is that when inserting a dielectric material molded to a thickness of 3 mm and a dielectric constant of 4 into a branch path, the gap between this dielectric material and the branch conductor (line conductor or ground conductor) is 0.
If it is 2 mm, the effective permittivity of the branch path is approximately 3.4.
Therefore, the wavelength of the leakage radio wave propagating through the branch path becomes about 10 times longer than when the gap is zero.

The effect of increasing the wavelength by 10% will be explained using the radio wave attenuation amount characteristic diagram with respect to the branch path length 12 of the radio wave sealing device of the present invention shown in FIG.

The curve indicated by 14 in the figure is a theoretical curve when the branch path is composed of only an air layer, and the black circles are actual measured values.

The frequency used was 24s□MHz.

The theoretical curve when this branch path is completely filled with a dielectric material having a relative dielectric constant of 4 is 15. If an air layer of 0.2 mm exists, the wavelength will become longer by about 10%, and the attenuation of the radio wave sole device will deteriorate by more than 10 dB. For this reason, the method of completely filling and inserting dielectric material into the branch path in order to substantially minimize the actual depth of the branch path has the disadvantage that highly accurate control is required in the actual design and performance variation tends to be large. play.

The present invention takes advantage of the influence of this air layer.

FIG. 7 is a block diagram of a radio wave sealing device showing one embodiment of the present invention. Portions in the figure that correspond to those in FIG. 2 are designated by the same numbers.

The thickness of the ground conductor 1o of the branch path 6 and the line conductor 9 is h −)
The dielectric layer 12 and the thickness g Qnr actively provided in advance
The ground conductor 1o and the line conductor 1o are further short-circuited at the end of the branch path.

As an example, if the thickness h of the dielectric layer with a relative dielectric constant of 4 is 3 mm, and the thickness g of the air layer is 1.5 mm, then ideally the effective permittivity εeff is 2, and the radio wave attenuation characteristic is This results in a curve indicated by 16 in FIG.

Assuming that the thickness g of the air layer varies by -Q, 21RIIL, the effective dielectric constant εeff will be 1.9 to 2.1. As a result, the deterioration is only 3 dB at most, and it is possible to provide a high-performance and compact radio wave control device that sufficiently absorbs manufacturing variations.

In the above description, 4 was used as a representative example as the relative dielectric constant of the dielectric material in order to clarify the numerical values. However, if a dielectric material with a high relative dielectric constant is used, the effect of the present invention will be enhanced.For example, if alumina is used, the effect of the present invention will be further enhanced and the size of the branch path can be made more compact. In a radio wave sealing device for a high frequency heating device in which a transmission line having a terminated branch path is arranged periodically in the direction outside the device main body of the radio wave path created by the heating chamber opening periphery and the entrance/exit door, the branch path has a desired dielectric constant. The present invention provides a radio wave sealing device having a configuration in which a line conductor and a ground conductor are separated by two layers: a dielectric layer of a predetermined thickness and an air layer of a predetermined thickness, and (1) by the dielectric layer of the branch path. It is easy to design and manage manufacturing to ensure effectiveness.

Shun) By loading dielectric material, the mechanism can be made more compact.

(3) Manufacturing variations in the dielectric material and branch path material can be absorbed by a combination of the two. , 1 with special effects,

[Brief explanation of the drawing]

Fig. 1 shows a conventional radio wave seal device, (a) is a block diagram, (b) is its equivalent circuit, (C) is a plan view in the y direction of Fig. (a), and Fig. 2 is a radio wave sole of the present invention. 3 is a conceptual diagram of the radio wave sealing device of the present invention, and FIG. 4 is a branching path of the radio wave sealing device of the present invention. FIG. 6 is an effective permittivity characteristic diagram for the air layer in the branch path, FIG. 6 is a radio wave attenuation characteristic diagram with respect to the branch path length of the radio wave sealing device of the present invention, and FIG. FIG. 1 is a configuration diagram of a radio wave sealing device showing an embodiment of the present invention. 1... Heating chamber opening flange (heating chamber opening periphery p, 2... Access door, 3... Radio wave passage, 5a, 5b, 50...・Transmission line, 6...
... Short circuit terminated branch path, 9 ... Line conductor, 10 ... Ground conductor, 12 ... Dielectric layer, 13 ... Air layer. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 (OJ) (b) Figure 4 Figure 5 Figure 6 Figure 1/! e summer mml Figure 7

Claims (1)

[Claims] A transmission line having a branch path short-circuited toward the outside of the device main body of the radio wave path created by the heating chamber opening periphery and the entrance/exit door is periodically arranged, and the branch path is formed by connecting a dielectric layer having a predetermined thickness and a predetermined thickness. A radio wave sealing device 1) in which a line conductor and a ground conductor are separated by two layers of air having a thickness of