JPH04359893A - Electromagnetic wave sealing device - Google Patents

Abstract

PURPOSE:To provide a electromagnetic wave sealing device used in such a door part of an electronic oven, excellent in a electromagnetic wave leakage preventing performance, and reduce the thickness of the door. CONSTITUTION:A groove 4 is provided in a door 14 of an electronic oven. The groove 4 is consisted of a first conductor wall surface 5 comprising a continuous conductive member, a groove bottom face 6, and a second conductor wall surface 7 such that a slitted part being provided from an open end and a plurality of conductor piece plates 8 of a constant pitch along the groove; a microstrip line is constituted between the respective conductor piece plates 8 and the first conductor wall surface 5 while the first conductor wall surface being longer than the second conductor wall surface. This constitution reduces dispersion and enables that positions at which an impedance being infinity, can be easily formed at constant intervals. And simpler constitution reduces the thickness of the door by adapting a microstrip line thechnology.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave sealing device that blocks high frequency radio waves that may leak from between a main body that supplies high frequency radio waves and a door.

0002

2. Description of the Related Art In recent years, there has been a demand for thinner doors of appliances such as microwave ovens that heat and cook food using high frequency waves. Conventionally, a radio wave sealing device for this type of equipment generally had a configuration as shown in FIGS. 8 to 10. The configuration will be explained below. The appearance of the microwave oven is as shown in FIG. 8, and includes a heating chamber main body 13 that stores food and heats it at high frequency, and a door 14 that freely opens and closes the opening for taking food in and out of the heating chamber 13. A radio wave sealing measure is taken to prevent the high frequency electromagnetic waves inside the heating chamber 13 from leaking outside the heating chamber 13 and causing harm to the human body. The first method of conventional radio wave sealing is to utilize impedance inversion as shown in FIG. 9 when only the conductor portion is shown. As shown in FIG. 9(a), the length between the depth A and B of the groove on the door 14 side is set to be a quarter wavelength of the radio waves inside the heating chamber 13, thereby attenuating the radio waves. That is, when the characteristic impedance of the groove interior 4 (also called choke part) is Z0, the depth is L, and the terminal end is short-circuited, the impedance Zin at the choke part opening B is Z
in=j・Z0・tan(2・π・L/λ0) (However, λ
0 is the free space wavelength). The choke-type radio wave attenuation means selects the depth L of the choke portion 4 to be a quarter wavelength, so that |Zin|=Z0・tan(π/2)=∞
It is based on the principle of achieving Therefore, in FIG. 9(b) when FIG. 9(a) is viewed from the α side, the open end tip 15
As shown by the broken line in , an area of infinite impedance occurs, and radio waves cannot escape to the outside. If the choke part 4 is filled with a dielectric material (relative dielectric constant εr), the wavelength λ' of the radio wave is

0003

[Math 1]

It is compressed into [0004]. In this case, the depth of the choke part 4 is L'.

[0005]

[Math 2]

It becomes short as [0006]. However, L' is 4 of λ'
However, in the choke method, the depth cannot be made substantially smaller than a quarter wavelength, and from the viewpoint of materials, the choke part can be made smaller (i.e., the door can be made smaller). There was a limit to how thin it could be.

[0007] A second method of creating a radio wave seal, which was created in an attempt to make the door thinner as microwave ovens were made lighter, was the method shown in FIG. Figure (a) shows the configuration of the heating chamber main body and the conductor part of the door, and figure (b) shows (
a) This is the configuration of the door section shown in the figure viewed from the α side. Although the choke structure is complex, it was able to attenuate radio waves and achieve a depth of less than a quarter wavelength.

There have also been cases in the past where microstrip line technology has been applied to radio wave sealing devices. This is because one side of the main body or door is considered as a ground plane and the other as a signal line, so it does not satisfy the theory of impedance inversion mentioned above (in other words, it is not possible to create impedance ∞ because a short plane cannot be secured). etc., it was very difficult to use. (Unexamined Japanese Patent Publication No. 58-94
(Refer to Publication No. 00)

[0009]

[Problems to be Solved by the Invention] However, with the above-mentioned conventional structure, it has not been possible to realize a simple and easy-to-manufacture structure and to make the door thin. For example, as an example of the second method of radio wave sealing, a radio wave sealing measure as shown in Fig. 10 is taken, and although the door is thin, it cannot be made by simply folding one conductor part (for example, sheet metal), so the door The side conductor portion 2 includes a first door conductor 16 and a second door conductor 17.
It has a complicated structure, such as spot welding at spot point 18, and has the problem of being difficult to manufacture and expensive in terms of man-hours and material costs. In addition, there are various problems such as variations in spot welding methods, which may make it impossible to suppress leakage of radio waves, and even if it can be suppressed, there are many items to be managed.

Furthermore, in terms of dispersion, FIGS. 9 and 1
0, if the length of the first conductor wall surface and the second conductor wall surface are the same in the depth direction, there is a problem that the characteristics will change significantly when the length of either becomes longer. there were.

[0011] The present invention is intended to solve the above-mentioned problems, and aims to suppress the leakage of radio waves to the outside with a simple structure while making the door thin, and to provide safe radio wave sealing performance. .

0012

[Means for Solving the Problems] In order to achieve the above-mentioned object, the radio wave sealing device of the present invention has a first part provided in the main body of the heating chamber, which has an opening through which the object to be heated is taken in and taken out, and into which radio waves are supplied. A conductor part and a second conductor part provided on a door that covers the opening of the heating chamber main body in an openable and closable manner are arranged to face each other, and at least one conductor part is attached to at least one of the first conductor part and the second conductor part. A groove is provided, and the first conductor wall surface and groove bottom surface forming the groove are made of a continuous conductive member, and the second conductor wall surface forming the groove is provided with a cut portion from the open end to extend in the longitudinal direction of the groove. a plurality of conductor strips arranged at a constant pitch, and each of the conductor strips is in electrical contact with the groove bottom surface to form a microstrip line between the first conductor wall surface and the first conductor wall surface; The length of the groove in the depth direction is made longer on the first conductor wall surface than on the second conductor wall surface.

[0013]

[Operation] According to the above structure, the present invention allows the shape of the conductor plate to be freely changed between the conductor plate and the first conductor wall by considering the medium (air) in the groove as the substrate material and treating it as a microstrip line. Impedance inversion can be achieved without being restricted by conventional methods. That is, it is sufficient to obtain a quarter wavelength by the combined growth in the depth direction and the longitudinal direction of the groove, and the depth itself has the effect of being shorter than a quarter wavelength.

Furthermore, according to the present invention, the length of the groove in the depth direction is configured such that the first conductor wall surface is longer than the second conductor wall surface, so that even if variations are taken into account, the microstrip line can be It has an effect that can be achieved stably.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a door seal for a microwave oven will be described below with reference to the drawings.

As shown in FIG. 1(a), the first conductor part 1 of the microwave oven body and the second conductor part 2 of the door are shaped to block the heating chamber space 3. The conductor part 2 of the door is made by simply folding one conductor (sheet metal), and the groove (choke part)
4 is composed of a first conductor wall surface 5, a groove bottom surface 6, and a second conductor wall surface 7. Further, in FIG. 1(b), the second conductor wall surface 7 has a notch from the open end, and has a structure in which a plurality of conductor strips 8 are lined up at a constant pitch in the longitudinal direction of the groove.
Considering that the conductor wall surface 5 is a ground line and the conductor strip 8 is a signal line, it can be considered that a microstrip line is formed between each conductor strip 8 and the first conductor wall surface 5. Here, the depth L1 of the second conductor wall surface is the conductor piece plate 8
This is the most important factor in determining the thickness of the door itself. In this embodiment, the conductor strip 8 is bent to the right from the middle, and L1 is 1/4
The depth is less than the wavelength. Therefore, a region of infinite impedance for radio waves that are about to leak out of the heating chamber appears at a slightly different position (tip 9 of the open end) from the conventional example shown in FIG. At this time, the direction in which the conductor strip 8 is bent is unified on the right side so that the impedance ∞ appears at regular intervals.

Further, the depth L2 of the first conductor wall surface is longer than the depth L1 of the second conductor wall surface, and the difference in length L2
-L1 is made larger than R of the folded portion 10 of the first conductor wall surface 5 of the conductor portion 2 of the door.

Further, in the figure, G is the distance between the first conductor part 1 and the second conductor part 2 (hereinafter referred to as a gap), which changes depending on how the door is attached.

In FIG. 2, the structure of the conductor strip 8 will be further explained. In order to create a region with infinite impedance, it is necessary to make the effective length of the microstrip line a quarter wavelength, but for a signal line with line width H,
Since the total length of the center length can be considered as the actual length,
When using the depth L1 and the lateral length L3 of the second conductor wall surface, they must be selected so that L1+L3-H≈λ/4 is satisfied.

Additionally, the pitch interval P is also selected to be approximately 1/4 wavelength. In the case of a microwave oven, the oscillation frequency is approximately 2450MHz, and the wavelength is approximately 1
If you calculate it considering that it will be 20mm, H = 5mm
, L3=20mm, S=10mm, then L1≒15m
m, which is half the depth of the conventional 30 mm.

FIG. 3 shows the characteristics of the leakage power of radio waves from the door when the shape is actually changed. It can be seen that there is an L1 that gives a minimum value using L3 as a parameter. L3
When is large, L1 that gives the minimum value is made small as shown by curve a. (Lla), and when L3 is small, L1, which gives the minimum value like curve b, becomes large (Llb
).

FIGS. 4 and 5 will be explained. Regarding the relationship between L1 and L2 mentioned above, when L1 and L2 are equal as shown in FIG. 4, the optimum value of L1 due to the gap G is different, so it is not possible to stably suppress the leakage power, whereas as shown in FIG. <
If L2 is used, Ll will stably lower the leakage power regardless of G.
It is experimentally known that c. Next, FIG. 6 shows the impedance and radio wave leakage characteristics when using a microstrip line. As shown in FIG. 6(a), Zin=j
・Z0・tan(2・π・L/λ0) (λ0 is the free space wavelength), |Zin|=Z0・tan(π/2)=∞, the horizontal axis shows the effective length of the signal line (L1+L3 −
By taking the length of H), various impedances can be generated, and when converted to absolute values from the viewpoint of ease of passage of radio waves, the result is as shown in FIG. 6(b). Figure 6(b) shows how difficult it is for radio waves to pass through, and conversely, the leakage power is shown in Figure 6 as shown in Figures 3 to 5.
The characteristics shown in (c) are obtained. Further, in the case of an actual door configuration, the second conductor portion 2 of the door is not left exposed as shown in FIG. 7, but is often covered with resin 11, 12 or the like.

[0023]

[Effects of the Invention] As explained above, the radio wave sealing device of the present invention has the following effects. (1) The seal structure using microstrip line technology is stable because the positions of impedance ∞ can be easily created at regular intervals and because the depth of the first conductor wall is longer than the depth of the second conductor wall. In this respect, it is possible to realize an extremely safe radio wave seal that is excellent in suppressing radio wave leakage. (2) Since the conductor part is formed by punching out sheet metal and then bending it, there is no need for spot welding, making it simple and easy to manufacture, and the cost can be reduced. (3) Since it is based on the concept of microstrip line technology, the shape of the conductor plate can be freely selected, so the thickness of the door part can be made thinner with a simple structure, making it possible to reduce the size and weight.

[Brief explanation of drawings]

[Fig. 1] A cross-sectional view of a radio wave sealing device according to an embodiment of the present invention and a front view of a second conductor wall surface.

[Figure 2] Enlarged front view of the second conductor wall of the radio wave sealing device

[Figure 3] Characteristic diagram of the radio wave seal device

[Figure 4] Characteristic diagram of the radio wave seal device

[Figure 5] Characteristic diagram of the radio wave seal device

[Figure 6] Characteristic diagram of impedance inversion based on microstrip line technology

FIG. 7 is a sectional view of a radio wave sealing device according to another embodiment of the present invention.

[Figure 8] Perspective view of a conventional microwave oven

[Fig. 9] A cross-sectional view of a conventional radio wave sealing device and a front view of the second conductor wall surface.

[Fig. 10] A cross-sectional view of a conventional radio wave sealing device and a front view of the second conductor wall surface.

[Explanation of symbols]

1 First conductor part 2 Second conductor part 4 Groove (choke part) 5 First conductor wall surface 6 Groove bottom surface 7 Second conductor wall surface 8 Conductor single plate

Claims (1)

[Claims] 1. A first conductor part provided in a heating chamber main body that has an opening for taking in and out the heated object and into which radio waves are supplied, and a first conductor part that covers the opening of the heating chamber main body so as to be openable and closable. A first conductor wall face and a groove bottom face that face a second conductor part provided on the door, and at least one groove is provided in at least one of the first conductor part and the second conductor part, and the groove is formed by a first conductor wall surface and a groove bottom surface. is made of a continuous conductive member, the second conductor wall surface forming the groove has a cut portion from the open end, and a plurality of conductor strips are arranged at a constant pitch in the longitudinal direction of the groove,
Each of the conductor strips is in electrical contact with the bottom surface of the groove and forms a microstrip line between the conductor wall surface and the first conductor wall surface, and the length of the groove in the depth direction is equal to that of the first conductor. A radio wave sealing device in which the wall surface is longer than the second conductor wall surface.