JPH04366319A - Electromagnetic wave sealing device - Google Patents

Abstract

PURPOSE:To present an electromagnetic wave sealing device which seals high frequency electromagnetic waves such as used in a microwave oven, etc., and combines a choke groove with slit construction and an electromagnetic wave absorbing body and is smaller than conventional devices and easy to be constructed. CONSTITUTION:An magnetic wave sealing device consists of the main body 1 that has an open port section 7 and heating chamber 6 into which electromagnetic waves are supplied, door 2 that is free to be opened or closed and covers the open port section 7 of the main body 1, and recessed groove 3 that is provided on the side of the door in the section where the main body 1 and said door 2 oppose each other. Many slits are provided periodically along the wall face of one of the recessed grooves 3 and, further, above the recessed groove 3 an electromagnetic wave absorbing body is provided. With this constitution electromagnetic wave leakage is reduced and at the same time the choke section is easy to be constituted.

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 shielding high frequency radio waves, and more particularly to a radio wave sealing device for equipment having a door that can be opened and closed, such as a microwave oven.

0002

2. Description of the Related Art An example of a conventional radio wave sealing device of this type is shown in FIG. Reference numeral 6 denotes a heating chamber of a microwave oven, and a door 9 has a handle 8 that covers the opening 7 of the heating chamber 6 so as to be openable and closable.
is provided. A hollow choke part 11 having a gap part 10 opened toward the heating chamber 6 is formed at the peripheral edge of the door 9 . Depth 12 of this choke part 11
is designed to be substantially one-fourth the wavelength of the radio frequency used. In this case, the thickness of the door 9 is also a quarter wavelength. That is, since the frequency of electromagnetic waves conventionally used in microwave ovens is 2450 MHz, a quarter wavelength is approximately 30 cm. In order to face the choke part 11 of this length, the thickness d0 of the peripheral part 13 formed at the opening 7 of the heating chamber 6 has a value larger than a quarter wavelength. Therefore, the effective size of the opening 7 of the heating chamber 6 is the peripheral area 1
3 is slightly smaller (for example, U.S. Patent No. 318
2164 specification).

[0003] As mentioned above, the conventional choke part is one-quarter
It is based on the technical concept of attenuating high frequencies as the depth of the wavelength increases.

That is, when the characteristic impedance of the choke part is Z0 and the depth corresponding to the depth is L, the impedance Z at the opening of the choke part when the terminal end is short-circuited is
IN is as shown in equation (1).

[0005] ZIN=jZ0 tan(2πL/λ0)
(1) (λ0 is the free space wavelength) The choke-type radio wave attenuation means can increase the impedance ZIN to infinity by selecting the depth L of the choke part to be a quarter wavelength, as shown in equation (2). It is based on the principle of achieving

|ZIN|=Z0 tan(π/2)=∞
(2) Theoretical explanation will be given below using FIG. 9. For convenience of explanation, as shown in Figure 9, the Z-axis is the depth direction of the choke groove, the Y-axis is the direction from inside the refrigerator to the outside of the refrigerator through the door gap, and the X-axis is the longitudinal direction of the groove. shall be.

The choke method is based on the well-known quarter-wavelength impedance conversion principle. That is, when the characteristic impedance of the choke groove is Zoc, the depth of the groove is 1c, the characteristic impedance of the leakage path 15 from the heating chamber to the choke groove is ZDP, the length of the leakage path 15 is 1P, and the wavelength used is λ. , the bottom C of the choke groove 16 as shown in FIG.
Since the short-circuit impedance ZC is zero, the impedance ZB when looking from the opening B of the choke groove 16 to the bottom C is as shown in equation (3).

[0008] ZD =jZ0Ctan(2π1C/λ)
(3) 17 is a heating chamber of the microwave oven, and 18 is a door. By selecting equation (4) here, it can be converted to equation (5).

1C = λ/4
(4)
｜ZB ｜=∞
(5)
When the impedance Zn of this opening B is viewed at the line starting point A, the impedance ZA is expressed by equation (6).

ZA =-jZOP/tan(2π1P/λ)
(6) Here, by selecting equation (7), it can be converted to equation (8).

[0011] 1P = λ/4
(7)
|ZA |=0
(8)
The short-circuit condition at the bottom C of the choke groove 18 appears at the starting point of the line by skillfully utilizing the quarter-wavelength impedance conversion principle, thereby making it practical as a radio wave sealing device.

The leakage path 15 and the choke groove 16 have a dielectric constant εr.
By loading the dielectric with the wavelength λ′ in the dielectric
is (εr) 1/2 times the free space wavelength λ, and by loading a magnetic material with permittivity εr and magnetic permeability μr, the wavelength λ' in the magnetic body becomes (εr μr) times the free space wavelength λ.
) A similar effect can be obtained by using the quarter wavelength (λ'/4) impedance principle.

To explain this with reference to FIG. 9, if the depth of the groove in the Z-axis direction is set to 1/4 wavelength, leakage of radio waves in the Y-axis direction can be suppressed.

[0014] Furthermore, there has conventionally been a method of providing a slit on the outer wall surface of the choke groove to reduce the radio wave propagation component in the X direction.

Next, as another conventional example (conventional example 2),
There are those shown in FIGS. 10(a) and 10(b). This is a door seal device that combines a quarter wavelength choke groove 19 and a radio wave absorber 20. However, in this case, radio waves propagating in the longitudinal direction (X direction) of the choke structure are not regulated and are absorbed by the radio wave absorber.

As another conventional example (Conventional Example 4), as shown in FIG. 11, a choke groove 21 is provided, and a radio wave absorber 22 is provided on the outside of the choke groove 21. This also achieves a quarter wavelength to attenuate the radio waves, and the radio wave absorber 22 absorbs the radio waves leaking to the outside from the groove 21. (For example, Jikko Sho 56-160
No. 68)

[0017]

[Problems to be Solved by the Invention] However, in the conventional configurations shown in FIGS. 10(a) and 10(b), when considering the propagation of radio waves, the component in the X direction is not regulated and is absorbed by the radio wave absorber. Since radio wave leakage is suppressed, the load on the radio wave absorber is large.

Further, in the conventional configuration shown in FIG. 11, a choke groove 21 is provided, which also substantially achieves a quarter wavelength and attenuates the radio wave. Furthermore, the radio wave absorber 22
is provided outside the groove 21 to absorb radio waves leaking outside from the groove 21 and suppressing radio waves leaking to the outside of the microwave oven.

As described above, conventionally, the radio wave absorber is used to attenuate the X-direction component or the Y-direction component of the radio wave, which is attenuated by a quarter wavelength choke groove, or the radio wave absorber is used to Because it is placed outside the structure and absorbs radio waves leaking from the choke groove, the choke structure requires a space that is one-fourth the wavelength of the radio waves. For example, 24
In the case of 50 MHz, it is approximately 30.6 mm.

[0020] In addition, conventional Fig. 10(a), Fig. 10(b),
As shown in FIG. 11, there was a problem in that complicated bending and spot welding were required to achieve the choke structure using sheet metal.

[0021] The present invention solves the above-mentioned problems, and aims to provide a radio wave sealing device that is smaller and has a simpler structure than the conventional one.

[0022]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a radio wave sealing device having a heating chamber having an opening through which heated objects are taken in and taken out, and into which radio waves are supplied. a main body, a door provided on the front surface of the main body that covers the opening face in an openable and closable manner, a recessed groove provided in at least one of the parts where the main body and the door face each other, and at least one wall surface of the recessed groove. A radio wave absorber is provided in a concave portion of the groove in a group of slits provided periodically along the wall surface.

[0023]

[Operation] With the above configuration, the present invention can suppress radio wave leakage.

Since the groove is composed of a group of slits provided along the wall surface on at least one wall surface, the X component of the radio wave propagating in the longitudinal direction of the groove is prevented from propagating, and the choke groove prevents the radio wave from propagating in the Y direction. leakage waves are attenuated. Furthermore, the depth of the groove is made shorter than a quarter wavelength due to the radio wave compression effect due to the dielectricity and magnetic permeability of the radio wave absorber provided in the choke groove, and the leakage radio waves are further reduced due to the radio wave attenuation effect of the radio wave absorber.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the accompanying drawings. In FIGS. 1, 2, and 3, reference numeral 1 denotes a microwave oven body, and a concave choke groove 3 is provided in a door 2 facing the microwave oven body, and a slit portion 5 is provided on the wall surface outside the groove 3. , a wall group consisting of a line group in which the pitch P is larger than the conductor width a in the longitudinal direction of the wall surface, that is, a group of slits having a width p-a provided along the wall surface. The radio wave absorber 4 is located at a position that closes the opening of the concave choke groove.
It also serves as a cover to prevent foreign matter from entering. The thickness is 11, the depth under the radio wave absorber 4 is 12,
If the depth of the groove is 1, then equation (9) is obtained.

1=11 +12
(9) When 12 was measured to minimize the leakage when changing 11, the results were as shown in Table 1.

[0027]

[Table 1]

[0028] Here, ferrite is dispersed in resin.
Measurements were made using a radio wave absorber with an absorption rate of approximately 80%. By changing the thickness, the total groove depth 1 can be reduced. This is due to the radio wave compression effect due to the dielectricity and magnetic permeability of the radio wave absorber, and if the thickness is further increased, 1 can be made even smaller.

The permittivity of the radio wave absorber is εr, and the magnetic permeability μr
If the wavelength of the radio wave in the radio wave absorber is λ', and the wavelength of the radio wave in free space is λ, then Equation (10) is obtained.

λ′=λ/(εr×μr)1/2
(10) Therefore, equation (11) holds true (Table 1)
As shown in , εr×μr can be found. From equation (11), if an absorber with a larger dielectric constant εr or larger magnetic permeability μr is used, 1 can be made even smaller.

11×(εr×μr)1/2 +12 =λ/4
(11) Figure 4 shows a slit (
It is a figure in which the leakage value was measured when the pitch was changed by inserting a wire with a width of 2 mm or a width of 10 mm. pitch 300
When it is mm, it corresponds to when there is no slit. Even if the size of the slits is changed, the leakage value is minimum when the pitch is about 30 mm.

In order to see the effect of the slits, FIG. 5 compares how the radio wave leakage value changes depending on the presence or absence of the slits. The vertical axis is the leakage value, and the horizontal axis is the gap between the door and the main body. As can be seen from FIG. 5, the leakage value is about one digit lower when there are slits than when there are no slits.

Furthermore, in order to see the effect of the radio wave absorber, FIG. 6 compares how the radio wave leakage value changes depending on the presence or absence of the radio wave absorber. The vertical axis is the leakage value, and the horizontal axis is the gap between the door and the main body. As can be seen from Figure 6, the case with the radio wave absorber is 1 higher than the case without it.
It can be seen that the leakage value around the digits is low.

As mentioned above, even if there is no slit,
It can be seen that the leakage is large even without the absorber. In other words, it can be seen that the slit and the radio wave absorber interact with each other and have the effect of reducing leakage waves.

FIG. 7 is a diagram showing the presence or absence of a ferrite resin body and changes in thickness. It can be seen that the leakage value is smaller when there is a ferrite resin body than when there is no ferrite resin body. It can also be seen that the larger the thickness, the smaller the leakage value.

As shown in FIG. 1, the structure is made by bending the sheet metal without complicated bending or spot welding as in the conventional structure, so it is easy to manufacture because it requires fewer manufacturing steps.

Next, measurements were made using a radio wave absorber having an absorption rate of about 50% and a dielectric constant of about 40, in which conductive potassium titanate whiskers were dispersed in a resin, and the results were as shown in Table 2.

[0038]

[Table 2]

In this case, if equations (10) and (11) are replaced by equation (12), the same equation holds true.

μr =1
(12) Even when this radio wave absorber was installed in a concave choke groove and measured, the same effect as in the case of the ferrite resin body was obtained.

[0041] Although the above description has been made regarding the case where the slit is provided on one surface of the concave groove, the slit may be provided on other surfaces, and even if it is provided on two or three surfaces at the same time, the same radio wave will be generated. A shielding effect can be obtained.

[0042]

[Effects of the Invention] As described above, according to the radio wave sealing device of the present invention, the following effects can be obtained. (1) At least one wall surface of a concave choke groove is made up of a line group with a pitch larger than the conductor width in the longitudinal direction, and a radio wave absorber is provided in the concave groove to leak radio waves. It is possible to provide a radio wave sealing device that reduces (2) Unlike conventional structures, the structure does not involve complicated bending or spot welding of sheet metal, but instead is a structure in which sheet metal is bent, so it is easy to manufacture because it requires fewer manufacturing steps.

[Brief explanation of drawings]

[Fig. 1] A cross-sectional view showing an outline of an embodiment of the present invention.

[Figure 2] Cross-sectional view of the main parts of Figure 1 above

[Fig. 3] A cross-sectional perspective view of the main part of the concave groove shown in Fig. 1 above.

[Figure 4]
A diagram showing the influence of the slit pitch in the embodiment shown in FIG. 1 above.

[Fig. 5] A diagram showing the effect of the slit in the embodiment shown in Fig. 1 above.

[Fig. 6] A diagram showing the effect of the radio wave absorber in the embodiment shown in Fig. 1 above.

[Fig. 7] A diagram showing the effect of the presence or absence of a radio wave absorber and its thickness in the embodiment shown in Fig. 1 above.

[Fig. 8] Cross-sectional view showing an outline of conventional example 1

[Fig. 9] Cross-sectional view showing the outline of the door part of Conventional Example 1

FIG. 10 (a) A sectional view showing an outline of the choke part of the door of Conventional Example 2 (b
) Cross-sectional perspective view showing the outline of the choke part of the door of Conventional Example 2

[Fig. 11] Cross-sectional view showing the outline of the door part of Conventional Example 3

[Explanation of symbols]

1 Main body 2 Door 3 Concave groove 4 Radio wave absorber 5 Slit part 6 Heating chamber 7 Opening

Claims (1)

[Claims] Claims: 1. A main body having a heating chamber having an opening for putting in and taking out a heated object and into which radio waves are supplied; a door provided on the front surface of the main body to cover the opening face in an openable and closable manner; A radio wave comprising a concave groove provided in at least one of the portions facing the door, a group of slits provided along the wall surface on at least one wall surface of the concave groove, and a radio wave absorber provided in the concave groove. sealing device.