JPH04294092A - Electric wave sealing device - Google Patents

Abstract

PURPOSE:To accomplish a safe electric wave sealing by furnishing No.1 conductor part at the body of an electric wave heating chamber, allowing this No.1 conductor part to confront No.2 conductor part provided at the door of the heating chamber without electrostatic contacting, and forming a micro-strip line which leads to No.1 conductor wall surface. CONSTITUTION:No.1 conductor part 3 is provided at the body of a heating chamber 16 which has an opening to be fed with electric waves, while No.2 conductor part 4a is furnished at the door covering this opening of the heating chamber body with possibility of opening and closing, wherein the two conductor parts are positioned oppositely without electric connection directly. At least one groove 5a is formed in either or both of these conductor parts 3, 4a. No.2 conductor wall surface 8a where this groove 5a is formed is provided with a notch 10a from the open end, and a plurality of conductor plates 11a are laid in line at a certain pitch in the longitudinal direction of the groove 5a. These conductor plates 11a are contacted electrically with the groove bottom surface 7a to constitute a micro-strip line leading to No.1 conductor wall surface. Therein the shape of conductor plate is selectible any as desired, and therefore, electric waves can be sealed by a structure simple and easy to fabricate.

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 for blocking high frequency radio waves that are at risk of leaking 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.

[0003] Conventionally, a radio wave sealing device for this type of equipment generally had a configuration as shown in FIGS. 7 and 8. The configuration will be explained below.

[0004] As shown in the figure, a heating chamber main body 1 stores food and heats it with high frequency. An opening of the heating chamber main body 1 for taking food in and out is covered with a door 2 so as to be openable and closable. Radio wave sealing measures are taken to prevent high frequency electromagnetic waves inside from leaking outside the heating chamber main body 1 and causing harm to the human body. The first conductor part 3 is provided in the heating chamber main body 1, and the second
The conductor parts 4 are provided on the door 2, and these face each other without direct contact, the second conductor part 4 is provided with a groove 5, and the first conductor wall surface 6 and the groove bottom surface 7 are made of a continuous conductive member. A notch 10 is provided in the second conductor wall surface 8 from the open end 9, and a plurality of conductor strips 11 are arranged in parallel at a constant pitch in the longitudinal direction of the groove 5. The length between depth A and B is set to be a quarter wavelength of the radio waves within the heating chamber main body 1 to attenuate the radio waves. In other words, the characteristic impedance inside the groove 5 (referred to as the choke part) is Z0, and the depth is L.
Then, when the terminal end is short-circuited, the impedance Zin at the choke opening B becomes (Equation 1).

[0005]

[Math 1]

[0006] The choke type radio wave attenuation means has the following characteristics: (
It is based on the principle of achieving equation 2).

[0007]

[Math 2]

Therefore, as shown by the broken line at the tip of the open end 19 in FIG. 8(b), there is a region 12 of infinite impedance.
occurs, and radio waves cannot go out. If the choke part 5 is filled with a dielectric material (relative dielectric constant εr), the wavelength λ' of the radio wave is compressed to (Equation 3). In this case, the depth L' of the choke portion 6 becomes as short as (Equation 4).

[0009]

[Math 3]

0010

[Math 4]

However, L' is still one-fourth of λ', and in the choke method, the depth of the choke portion 5 cannot be made substantially smaller than one-quarter wavelength. However, there is a limit to miniaturization of the choke portion 5 (ie, making the door thinner).

[0012] As a method for making the door thinner in order to reduce the weight of microwave ovens, there is a method described in Japanese Patent Publication No. 62-59438, as shown in FIG.
is composed of the first door conductor 13 and the second door conductor 14, and although the structure of the choke part 5 is complicated, it can attenuate radio waves and realize a depth of less than a quarter wavelength. Met.

[0013]

[Problems to be Solved by the Invention] However, with the above-mentioned conventional radio wave sealing device, it has not been possible to realize a simple and easy-to-manufacture structure and to make the door 2 thin. For example, as a second example of a radio wave seal, in the radio wave seal device shown in FIG.
The conductor portion 4 includes a first door conductor 13 and a second door conductor 14.
It has a complicated structure, such as spot welding at spot points 15, and has the problem of being difficult to manufacture and resulting in high costs 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.

The present invention has been made 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 improve the safe radio wave sealing performance.

[0015]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a first conductor portion provided in a heating chamber body having an opening and into which radio waves are supplied, and a first conductor portion provided in a heating chamber body having an opening and into which radio waves are supplied. A second conductor portion provided on a door that can be opened and closed to cover the opening is opposed to each other without direct electrical contact, and at least one groove is formed in at least one of the first conductor portion and the second conductor portion. The first conductor wall surface forming the groove and the groove bottom surface 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 and is constant in the longitudinal direction of the groove. The problem is solved by having a structure in which a plurality of conductor strips are lined up at different pitches, each of the conductor strips is in electrical contact with the groove bottom surface, and a microstrip line is formed between the conductor strip and the first conductor wall surface. It is used as a means.

[0016]

[Operation] By the above-mentioned problem solving means, the present invention can construct a microstrip line between the conductor strip and the first conductor wall using the medium (air) in the groove as the substrate material, and the shape of the conductor strip can be changed. As long as it is kept parallel to the first conductor wall surface, it can be freely selected and impedance inversion can be achieved. In other words, the combined growth in the depth direction and the longitudinal direction of the groove is 4
This means that the depth itself can be made shorter than a quarter wavelength.

[0017]

Embodiment An embodiment of the present invention will be described below with reference to FIG. Note that components having the same configuration as those of the conventional example are given the same reference numerals, and description thereof will be omitted.

As shown in the figure, the first conductor section 3 is shaped to close off the heating chamber space 16 together with the second conductor section 4a provided on the door. The second conductor portion 4a is one conductor (
The groove (choke part) 5a is made up of a first conductor wall surface 6a, a groove bottom surface 7a, and a second conductor wall surface 8a. The second conductor wall surface 8a is provided with a cut portion 10a from the open end 9a, and a plurality of conductor strips 11a are arranged in parallel at a constant pitch in the longitudinal direction of the groove 5a. The first conductor wall surface 6a is the ground line and the conductor piece plate 11
Considering that a is a signal line, each conductor piece plate 11a and the first conductor wall surface 6a form a microstrip line with the groove bottom surface 7a as a short point in terms of impedance. Here, the depth L1 of the groove 5a is determined by the shape of the conductor strip 11a, which is the most important factor in determining the thickness of the door itself. In the case of this embodiment, the conductor single plate 11
a is bent to the right from the middle, and the depth of the groove 5a is L1.
to a depth of less than a quarter wavelength. Therefore, a region 12a of infinite impedance for radio waves that are about to leak out of the heating chamber appears at a slightly different position (at the tip of the open end) than in the conventional example shown in FIG.

To further explain the structure of the conductor strip 11a with reference to FIG. 2, in order to create a region of infinite impedance, the running length of the microstrip line must be reduced to a quarter wavelength, but the line width H Regarding the signal line, the total center length is considered to be the actual length, so using the vertical length (groove depth) L1 and the horizontal length L2, the line can be selected to satisfy (Equation 5). There must be.

[0020]

[Math 5]

However, it has been experimentally found that the above formula holds true when the fold is changed from the vertical direction to the horizontal direction by cutting diagonally as shown in FIG.

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 2450 MHz and the wavelength is approximately 120 mm.
=5mm, 12=20mm, S=10mm, then L1
The depth is approximately 15 mm, which is half the depth of the conventional 30 mm.

The characteristics of the leakage power of radio waves from the door section when the shape of the second conductive wall surface 8a is changed are as shown in FIG.
It turns out that there is 1. When L2 is large, characteristic a
Reduce L1 that gives the minimum value as (L1a)
It can be seen that when L2 is small, L1 that gives the minimum value becomes large (L1b) as in characteristic b. As another example, in FIG. 4, H=5 mm, 12=25
mm, S=5 mm, and L1≈10 mm.

Next, FIG. 5 shows the impedance and radio wave leakage characteristics when using a microstrip line, and as shown in FIG. 6(a), as shown in (Equation 1) and (Equation 2),
The horizontal axis represents the effective length of the signal line (in the present invention, the length of (Equation 5))
If we take , various impedances can be generated, and if we convert it to an absolute value from the point of view of ease of passage of radio waves, we get the result shown in Fig. 5(b). FIG. 5(b) shows the difficulty in passing radio waves, and conversely, the leaked power has characteristics as shown in FIG. 5(c), similar to FIG. 3.

Furthermore, in the case of an actual door configuration, instead of leaving the first conductor portion 3a bare as shown in FIG.
It is often covered with resin members 17, 18, etc.

Although the groove 5a is provided in the second conductor portion 4a in the above embodiment, the same operation and effect can be obtained even if the groove 5a is provided in the first conductor portion 3.

[0027]

As is clear from the above embodiments, according to the present invention, each of the conductor strips on the second conductor wall is in electrical contact with the bottom of the groove, and there is a microstructure between the conductor plate and the first conductor wall. Since the strip line is configured, the shape of the conductor plate can be freely selected, so the thickness of the door part can be reduced with a simple configuration. Since it can be made by punching sheet metal and then bent in one step using a mold, it is easy to make and can be realized at a low cost. Furthermore, since there is no need for spot welding and variations in the seal structure are less likely to occur, extremely low-cost performance in suppressing radio wave leakage can be achieved.

[Brief explanation of drawings]

FIG. 1 (a) A cross-sectional view of a radio wave sealing device according to an embodiment of the present invention. (b) A side view of a second conductor wall surface of the radio wave sealing device.

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

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

FIG. 4 (a) A cross-sectional view of a radio wave sealing device according to another embodiment of the present invention. (b) A side view of a second conductor wall surface of the same radio wave sealing device.

[Figure 5] (a) to (c) Characteristic diagrams of impedance inversion based on the microstrip theory of the radio wave sealing device

[Figure 6]
A sectional view of a radio wave sealing device according to another embodiment of the present invention

[Figure 7]
Perspective view of a general microwave oven

[Fig. 8] (a) Cross-sectional view of an example of a conventional radio wave seal device (
b) Side view of the second conductor wall of the radio wave sealing device

[Figure 9
] (a) Cross-sectional view of another example of the conventional radio wave seal device (b)
Side view of the second conductor wall of the radio wave sealing device

[Explanation of symbols]

3 First conductor part 4a Second conductor part 5a Groove 6a First conductor wall surface 7a Groove bottom surface 8a Second conductor wall surface 10a Notch part 11a Conductor single plate

Claims (4)

[Claims] 1. A first conductor provided in a heating chamber main body having an opening and into which radio waves are supplied, and a second conductor provided in a door that covers the opening of the heating chamber main body so as to be openable and closable. A first conductor wall surface and a groove bottom surface that face the conductor portion without direct electrical contact, and provide at least one groove in at least one of the first conductor portion and the second conductor portion, and form the groove. is made of a continuous conductive member, and the second conductor wall surface forming the groove has a cut portion from the open end so that a plurality of conductor strips are arranged at a constant pitch in the longitudinal direction of the groove, and each of the above-mentioned A radio wave sealing device, wherein each of the conductor strips is in electrical contact with the groove bottom surface, and a microstrip line is formed between the conductor strips and the first conductor wall surface. 2. The radio wave sealing device according to claim 1, wherein each conductor strip is parallel to the first conductor wall surface and bent at least once. 3. The radio wave sealing device according to claim 1, wherein each conductor strip extends a certain length (L1) in the vertical direction from the bottom of the groove, and then bends at a right angle and extends for a certain length (L2) in the horizontal direction. 4. The radio wave sealing device according to claim 3, wherein each of the conductor strips has a structure in which bent portions are cut.