JP2949965B2 - Radio wave sealing device - Google Patents

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 a high frequency radio wave which may leak from a main body supplying a high frequency radio wave and a door.

[0002]

2. Description of the Related Art In recent years, it has been required to reduce the thickness of a door of a device such as a microwave oven that heats and cooks food by high frequency.

Conventionally, a radio wave sealing device for this type of equipment generally has a configuration as shown in FIGS. Hereinafter, the configuration will be described. As shown in the figure, a heating chamber main body 1 stores food and performs high-frequency heating, and the food chamber opening and closing opening of the heating chamber main body 1 is opened and closed by a door 2. In order to prevent the high frequency electromagnetic wave from leaking out of the heating chamber main body 1 and exerting an adverse effect on the human body, a radio wave sealing measure is taken. As a first method of a conventional radio wave seal, there has been a method using impedance inversion as shown in FIG. 7 when only a conductor portion is shown. FIG.
The radio wave is attenuated by setting the length between the depths A and B of the groove on the door 2 side as the length of a quarter wavelength of the radio wave in the heating chamber main body 1 as shown in FIG. That is, the characteristic impedance (hereinafter referred to as a choke portion) 3 is Z0, the depth is L, and when the terminal portion is short-circuited, the impedance Zin at the choke portion opening B is as follows: Zin = j · Z0 · tan (2 · χ · L / λ0) (λ0 is a free space wavelength). The choke type radio wave attenuating means includes a choke unit 3
Is selected to be a quarter wavelength to achieve | Zin | = Z0 · tan (π / 2) = ∞. Therefore, FIG.
In FIG. 7B in which FIG. 7A is viewed from the α side, an infinite impedance region is generated at the distal end 5 of the open end as shown by a broken line, and radio waves cannot be emitted to the outside. If the choke 3 is filled with a dielectric (relative permittivity εr), the wavelength λ ′ of the radio wave becomes

[0004]

Embedded image

[0005] In this case, the depth L 'of the choke 3 is

[0006]

Embedded image

[0007] However, L 'is λ'4
In the choke method, the depth cannot be substantially reduced to less than a quarter wavelength, and the size of the choke portion 3 can be reduced from the viewpoint of the material (that is, the door may have a smaller size). Thinning) was limited.

FIG. 8 shows a second method of the radio wave seal which has been developed as an attempt to make the door 2 thinner with the reduction in the weight of the microwave oven. FIG.
8A shows the configuration of the conductors of the heating chamber main body 1 and the door 2, and FIG. 8B shows the configuration of the door of FIG. 8A as viewed from the α side. Although the choke structure is complicated, radio waves can be attenuated, and a depth of less than a quarter wavelength can be realized.

In the past, there has been an example in which the microstrip line technology is applied to a radio wave sealing device. This is one that does not satisfy the above-mentioned theory of impedance inversion because one of the main body or the door is considered as the ground plane and the other as the signal line (that is, the impedance ∞ cannot be created because the short side cannot be secured). It could not be used for microwave ovens. (Japanese Patent Laid-Open No. 58
-9400)

[0010]

In such a conventional radio wave sealing device, 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 the radio wave seal, a countermeasure against radio waves as shown in FIG. 8 is taken, and although the door is thin, it cannot be made only by folding one conductor portion (for example, a sheet metal) in manufacturing. The conductor part (b) on the side is composed of the first door conductor 7 and the second door conductor 7.
And the door conductor 8 is spot-welded at the spot point 9, which makes it difficult to manufacture the door conductor 8 and costs high in terms of man-hours and material costs. In addition, there is a variety of problems depending on the method of spot welding, such as the inability to suppress radio wave leakage and the increase in management items even if suppressed.

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems and to provide a safe radio wave sealing performance by suppressing leakage of radio waves to the outside with a simple structure while making the door thin.

[0012]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a first conductor section provided in a heating chamber main body having an opening through which an object to be heated is taken in and out, and into which a radio wave is supplied. And a second conductor provided on a door that opens and closes the opening of the heating chamber body so as to open and close, and at least one groove is formed in at least one of the first conductor and the second conductor. The first conductor wall surface and the groove bottom surface forming the groove are formed of a continuous conductive member, and the second conductor wall surface forming the groove is provided with a cutout from an open end to be constant in the longitudinal direction of the groove. A configuration in which a plurality of conductor strips of pitch are lined up,
Each of the conductor strips is in electrical contact with the bottom of the groove, and constitutes a microstrip line between the conductor strip and the first conductor wall. The conductor strips have two or more different shapes. The configuration for sequentially arranging them is a means for solving the problem.

[0013]

According to the present invention, the medium (air) in the groove is regarded as a substrate material between the conductor plate and the first conductor wall, and is regarded as a microstrip line. Since the shape can be freely selected, impedance inversion not restricted by the conventional method can be realized. That is,
It is only necessary to obtain a quarter wavelength with the combined length in the depth direction and the longitudinal direction of the groove, and the depth itself can be shorter than the quarter wavelength. Further, since two or more types of conductor strips having different shapes are sequentially arranged, a plurality of microstrip lines can be formed within the same pitch, so that radio waves can hardly leak.

[0014]

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

As shown in the figure, a first conductor portion 10 is provided in a heating chamber main body 1, and the first conductor portion and a second conductor portion 11 provided in a door 2 block a heating chamber space 12. Like that. The second conductor portion 11 is made by simply folding one conductor (sheet metal), and forms a choke portion 16 with the first conductor wall surface 13, the groove bottom surface 14, and the second conductor wall surface 15. I have. In FIG. 1B as viewed from the α side in FIG. 1A, the second conductor wall surface 15 has a notch at the open end, and the conductor plate 1 having a constant pitch in the longitudinal direction of the groove.
When the first conductor wall 13 is considered to be a grind line and the conductor plates 17 and 18 are considered to be signal lines, each of the conductor plates 17 and 18 and the first conductor wall 13 are arranged. It can be considered that a micro-toslip line is formed between them. Here, the second conductor wall 15
Is determined by the shapes of the conductor plates 17 and 18, and this is the most important factor that determines the thickness of the door 2. In the case of the present embodiment, the conductor pieces 17 and 18 are bent rightward from the middle, and the depth L1 is set to a quarter wavelength or less. Therefore, the region of infinite impedance for the radio wave to leak out of the heating chamber appears at a position slightly different from the conventional example in FIG. 7 (at the end portion 19 of the open end. The bending directions are unified on the right side so that infinite impedance appears at regular intervals.

Here, the pitch P of the conductor pieces 17 and 18 will be described. Both the conductor piece plates 17 and 18 are arranged side by side at intervals of the pitch P. , Two types of conductor piece plates 17 and 18 are arranged side by side. That is, since the position of the impedance infinity appears at each of the tip of the conductor plate 17 and the tip of the conductor plate 18, it is double-emphasized and the performance of the radio wave seal can be improved. Although the details are not clear, the pitch P has an optimum value near a quarter wavelength.

Next, the conductor plate 17 will be described with reference to FIG. 2. In order to create a region of infinite impedance, the effective length of the microstrip line is reduced by a quarter.
It is necessary to set the wavelength to the wavelength, but for the signal line having the line width H, since the total of the center lengths is considered to be the actual length, the depth L1 of the second conductor wall surface 15 and the lateral length L
If 2 is used, it must be selected so as to satisfy L1 + L2-H ／ λ / 4. Further, about the pitch interval P (the sum of L2 and the gap S), approximately a quarter wavelength is selected. In the case of a microwave oven, the oscillation frequency is about 2450 MHz and the wavelength is about 120 mm. Calculations are made to find that H = 5 mm, L2 = 20 mm, and S = 10 mm.
mm, L1 ≒ 15 mm, which can be reduced to a half of the conventional 30 mm. Conductor plate 18
The same applies to.

FIG. 3 shows the characteristics of the leakage power of radio waves from the door when L1 and L2 are changed. As is clear from FIG. 3, it is found that there is L1 which gives a minimum value using L2 as a parameter. When L2 is large, L1 that gives the minimum value like characteristic a is reduced (L1
a) It can be seen that when L2 is small, L1 giving the minimum value like characteristic b becomes large (L1b).

FIG. 4 shows characteristics of impedance and radio wave leakage when a microstrip line is used. As shown in FIG. 4A, Zin = j · Z0 · tan (2 · χ · L / λ0) (λ0 is a free space wavelength) | Zin | = Z0 · tan (π / 2) = ∞ On the horizontal axis, the execution length of the signal line (L1 + L
2−H), various impedances can be generated, and when they are replaced with absolute values from the viewpoint of easy passage of radio waves, the results are as shown in FIG. 4B. FIG.
FIG. 4B shows the degree of difficulty in passing radio waves. On the contrary, the amount of leaked power is similar to that shown in FIG.
The characteristic as shown in FIG.

In the case of an actual door configuration, instead of leaving the second conductor 11 bare as shown in FIG.
In many cases, covers 20 and 21 made of resin or glass are used.

[0021]

As is apparent from the above embodiments, according to the present invention, two or more types of conductor pieces having different shapes are used, and a plurality of portions having infinite impedance can be easily formed within a fixed pitch. Therefore, it is possible to realize an extremely safe radio wave seal that is excellent in suppressing radio wave leakage, and because it is based on the concept of microstrip line technology, the shape of the conductor single plate can be freely selected, so the thickness of the door part is thin with a simple configuration. It can be made smaller and lighter.

[Brief description of the drawings]

FIG. 1A is a sectional view of a radio wave sealing device according to an embodiment of the present invention. FIG. 1B is a front view of a second conductor wall surface of the radio wave sealing device.

FIG. 2 is an enlarged front view of a main part of a second conductor wall surface of the radio wave sealing device.

FIG. 3 is a characteristic diagram of the radio wave sealing device.

4A and 4C are characteristic diagrams of impedance inversion based on microstrip line technology.

FIG. 5 is a sectional view of a radio wave seal device according to another embodiment of the present invention.

FIG. 6 is a perspective view of a general microwave oven.

FIG. 7A is a cross-sectional view of an example of a conventional radio wave seal device. FIG. 7B is a front view of a second conductor wall surface of the radio wave seal device.

FIG. 8A is a cross-sectional view of another example of a conventional radio wave seal device. FIG. 8B is a front view of a second conductor wall surface of the radio wave seal device.

[Description of Signs] 10 First conductor portion 11 Second conductor portion 13 First conductor wall surface 14 Groove bottom surface 15 Second conductor wall surface 16 Choke (groove) 17 Conductor plate 18 Conductor plate

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05B 6/76 F24C 7/02 501

Claims (1)

(57) [Claims] 1. A first conductor provided in a heating chamber main body having an opening through which an object to be heated is taken in and out, to which radio waves are supplied, and the opening of the heating chamber main body is openably and closably covered. A second conductor portion provided in the door is opposed to the first conductor portion, and at least one groove is provided in one of the first conductor portion and the second conductor portion; a first conductor wall surface and the groove forming the groove; The bottom surface is made of a continuous conductive member, the second conductor wall surface forming the groove is provided with a cutout from an open end, and a plurality of conductor pieces having a constant pitch are arranged in the longitudinal direction of the groove, and Each of the conductor strips is in electrical contact with the bottom of the groove to form a microstrip line between the conductor strip and the first conductor wall, and the conductor strips are sequentially arranged in two or more different shapes. A radio wave seal device with a configuration.