JPH05121167A - Radio wave sealing device - Google Patents

Abstract

PURPOSE:To provide a simple and small-sized radio wave sealing device shielding the radio waves of a high-frequency apparatus such as a microwave oven. CONSTITUTION:In the radio wave sealing device of a high-frequency apparatus constituted of a main body 1 made of a conductor material, having an opening section, and fed with radio waves inside and a door 2 made of a conductor material and openably covering the opening section, a recessed groove 3 is provided at least one of the portions where the main body 1 and the door 2 are faced to each other, and multiple slits 5 are provided on at least one wall face 4 of the recessed groove 3. An edge 7 parallel with the upper face of the upper section of an inside wall and lower than its height is provided at the upper section of the outside wall 4 of the recessed groove 3, and a radio wave absorbing body 6 covering the recessed groove 3 and the edge 7 is provided.

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 high frequency equipment having an openable and closable door such as a microwave oven.

[0002]

2. Description of the Related Art A conventional radio wave sealing device of this type (for example, U.S. Pat. No. 3,182,164) has a structure as shown in FIG. The configuration will be described below.

In the figure, reference numeral 8 denotes a main body of a microwave oven, which covers an opening 9 of the main body 8 so as to be openable and closable, and a handle 10
Is provided with a door 11. A hollow choke portion 13 having a gap portion 12 opened toward the main body 8 side is formed on the peripheral portion of the door 11. The depth L ₁ of the choke portion 13 is designed to be substantially a quarter wavelength of the high frequency wave used. In this case, the door 11
The width of the choke portion 13 must be 1/4 wavelength or more.
That is, since the frequency of the electromagnetic wave used in the conventional microwave oven is 2450 MHz, a quarter wavelength is about 30.
mm. In order to face the choke portion 13 of this length, the thickness L ₂ of the peripheral edge portion 14 formed in the opening 9 of the main body 8
Is larger than a quarter wavelength. Therefore, the effective size of the opening 9 of the main body 8 is reduced by the peripheral portion 14.

As described above, the conventional choke portion 13 is based on the technical idea of attenuating a high frequency with a depth of a quarter wavelength. That is, the characteristic impedance of the choke portion 13 is Z ₀ , the depth thereof is L, and the impedance Z _IN at the opening portion of the choke portion 13 when the termination portion is short-circuited.
Becomes as shown in equation (1).

Z _IN = jZ ₀ tan (2πL / λ ₀ ) ... (1) (λ ₀ is a free space wavelength) The choke type radio wave attenuation means has a depth L of the choke portion 13 which is a quarter. By selecting the wavelength, impedance Z can be obtained as shown in equation (2).
It is based on the principle of achieving _IN with infinity.

| Z _IN | = Z ₀ tan (π / 2) = ∞ (2) The following is a theoretical description with reference to FIG. For convenience of explanation, as shown in FIG. 8, the depth direction of the concave groove 15 is the Z axis, the direction from the inside of the main body 8 to the outside of the main body through the gap of the door 11 is the Y axis, and the longitudinal direction of the concave groove 15. Let's take the X axis.

The choke method is a well-known quarter-wave impedance
It is based on the dance conversion principle. Ie concave
Set the characteristic impedance of the groove 15 to Z_0C, Depth of the concave groove 15
L _CThe characteristics of the leaky waveguide 16 extending from the main body 8 to the concave groove 15 are
Z is the impedance_0P, The length of the leaky waveguide 16 is l_P, Messenger
Assuming that the wavelength for use is λ, the bottom of the concave groove 15 as shown in FIG.
Short circuit impedance Z of C_CIs zero, so the concave groove 1
Impedance Z looking at the bottom C from the opening B of 5_BIs the expression
As shown in (3).

Z _B = jZ _0C tan (2πl _C / λ) (3) Here, by selecting l _C = λ / 4, | Z _B | = ∞ can be converted.

The impedance Z A of the impedance Z _B of the opening _B at the line starting point _A is given by the equation (4).

Z _A = −jZ _0P / tan (2πl _P / λ) (4) Here, by selecting 1 _P = λ / 4, it can be converted to | Z _A | = 0.

The short-circuit state at the bottom C of the concave groove 15 appears at the starting point of the line by utilizing the principle of quarter-wavelength impedance conversion for practical use as a radio wave sealing device.

Dielectric constant ε is applied to leakage waveguide 16 and concave groove 15._rInvitation
The wavelength λ'in the dielectric can be freely set by loading the electric body.
Of spatial wavelength λ (ε_r)^1/2Double the permittivity ε_r, Magnetic permeability
Rate μ _rWavelength in the magnetic body by loading the magnetic body of
λ'is the free space wavelength λ (ε _r× μ_r)^1/2Double
Uses the quarter wavelength (λ '/ 4) impedance principle
The same effect can be obtained by staying. Described in FIG.
And the depth of the concave groove 15 is set to a quarter wavelength in the Z-axis direction.
And the leakage of radio waves in the Y-axis direction can be suppressed.
It Further, conventionally, a slit is provided on the wall surface of the concave groove 15,
There is also a method of reducing the radio wave propagation component in the X direction.

Next, another conventional example is shown in FIG. This is the 1/4 wavelength concave groove 17 and the electromagnetic wave absorber 1.
It is a radio wave sealing device in which 8 are combined. However, in this case, the radio wave propagating in the longitudinal direction (X direction) of the choke structure is not regulated and is absorbed by the radio wave absorber 18.

Further, another conventional example (for example, Jitsuko Sho 5)
6-16068), a concave groove 19 is provided as shown in FIG. 10, and a radio wave absorber 20 is provided outside the concave groove 19. This also achieves a quarter wavelength and attenuates radio waves, and the radio wave absorber 20 absorbs radio waves leaking to the outside from the concave groove 19.

[0015]

In the radio wave sealing device of FIG. 7, if the choke portion 13 is made of sheet metal, complicated bending and spot welding are required, and in FIG. 9, considering the propagation of radio waves. Since the component in the X direction is not regulated and is absorbed by the radio wave absorber 18 to suppress radio wave leakage, there is a problem that the load on the radio wave absorber 18 is large.
No. 0 has a concave groove 19, which is also substantially a quarter.
Achieve the wavelength to attenuate the radio wave, and also the radio wave absorber 2
0 is provided outside the concave groove 19 to absorb the electric wave leaking out from the concave groove 19 and suppress the electric wave leaking to the outside. As described above, the radio wave absorber is conventionally used to attenuate the X-direction component or the Y-direction component of the radio wave attenuated by the quarter-wave concave groove, or the radio wave absorber is provided outside the choke portion. Since the electric wave leaked from the concave groove is absorbed in the above, the size of the choke portion requires a space having a quarter wavelength of the electric wave. For example, in the case of 2450 MHz, it becomes about 30.6 mm. Further, even in the case shown in FIGS. 9 and 10, there is a problem that complicated bending and spot welding are required to form the choke portion with the sheet metal.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a radio wave sealing device which is simpler and smaller than conventional ones.

[0017]

In order to achieve the above object, the radio wave sealing device of the present invention is provided with a concave groove in at least one of the portions where the main body and the door face each other, and at least one wall surface of the concave groove. A plurality of slits are provided, an edge portion that is parallel to the upper surface of the inner wall surface and is lower than the height of the outer wall surface of the concave groove is provided, and a radio wave absorber that covers the concave groove and the edge portion is provided. The configuration.

[0018]

According to the present invention, complicated bending and spot welding are not required due to the above-mentioned structure, and the X component of the radio wave propagating in the longitudinal direction of the concave groove can be prevented from propagating, and the concave groove can prevent leakage waves in the Y direction. The depth of the concave groove can be made shorter than a quarter wavelength due to the radio wave compression effect of the radio wave absorber.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.

In these figures, the main body 1 of the microwave oven
Is to be supplied with a radio wave, the door 2 is provided so as to be openable and closable, and the recessed groove 3 is provided in the door 2. A slit portion 5 is provided on an outer wall surface 4 of the concave groove 3 so that the pitch p is larger than the conductor width a in the longitudinal direction of the wall surface. Further, as shown in FIG. 3, an edge portion 7 lower than the height of the inner wall of the opening by l ₁ is provided in the opening of the outer wall of the concave groove 3 in parallel with the door surface. The electromagnetic wave absorber 6 closes the opening of the concave groove 3 at the thickness l ₂ and width k ₁ portion, and extends over the edge portion 7 by the thickness l ₁ and width k ₂ It covers the portion 7 and also serves as a cover for preventing foreign matter from entering the concave groove 3 from the outside.

The effect of the edge portion 7 in the above structure will be described. As shown in (Table 1), the edge portion 7 is provided on the outer wall of the concave groove 3 (No. 2 and No. 3) and no edge portion 7 (N).
It can be seen that the radio wave leakage value is smaller than that of o.1).

[0022]

[Table 1]

Further, as shown in (Table 2), when the edge portion 7 is provided on the outer wall of the concave groove 3 and the edge portion 7 is lowered from the opening surface by l ₁ as in No. 4 and No. 5, The radio wave leakage value is increased compared to No. 3 when it is not lowered, and the concave groove 3
The depth 1 is deeper, but the radio wave leakage value is reduced by extending the radio wave absorber 6 to the edge 7 like No. 6 and No. 7, and the depth 1 does not become deep either. I understand.

[0024]

[Table 2]

If the thickness of the electromagnetic wave absorber 6 is l ₂ , the depth below the electromagnetic wave absorber 6 is l _3, and the depth of the concave groove 3 is l, then l = l ₂ + l ₃ . l ₃ which minimizes the leakage wave when l ₂ is changed
Was measured as shown in (Table 3). No. 3 and No. 9 have a total depth l ₃ of the concave groove as compared with No. 8.
Becomes smaller.

[0026]

[Table 3]

Here, the measurement was performed using a radio wave absorber 6 in which ferrite was dispersed in resin and the absorption rate was about 80%. The total groove depth l can be made small by changing the thickness. This is due to the radio wave compression effect of the radio wave absorber 6, and if the thickness is further increased, l can be made smaller. When ε _r × μ _r is calculated from the radio wave leakage value, the values that should be the same are 42 to 112, which are scattered. It is considered that this is due to other shape effects such as the width of the edge portion and the concave groove. Although the value varies, l becomes smaller as l ₂ becomes larger.

In FIG. 4, the slit portion 5 is formed on the outer wall of the concave groove 3.
It is a figure which measured the leakage value when (2 mm, 10 mm) was put and the pitch was changed. The case where the pitch is 300 mm corresponds to the case where there is no slit portion 5. Slit part 5
The leakage value is the smallest when the pitch is about 30 mm.

To see the effect of the slit portion 5, FIG. 5 compares how the radio wave leakage value changes depending on the presence or absence of the slit portion 5. The vertical axis is the leakage value, the horizontal axis is the door 2
And a gap between the main body 1 and the main body 1. From FIG. 5, it can be seen that the leakage value of about one digit is lower when the slit portion 5 is provided and when the slit portion 5 is not provided.

In order to see the effect of the electromagnetic wave absorber 6,
FIG. 6 compares how the radio wave leakage value changes depending on the presence or absence of the radio wave absorber 6. The vertical axis represents the leakage value, and the horizontal axis represents the gap between the door 2 and the main body 1. From FIG. 6, it is 1 when compared with the case where the electromagnetic wave absorber 6 is not provided.
It can be seen that the leakage value around the digit is low.

As described above, it can be seen that the leakage wave is large without the slit portion 5 and the radio wave absorber 6. That is, it can be seen that the slit portion 5 and the radio wave absorber 6 have an effect on each other to reduce a leak wave.

Next, conductive potassium titanate whiskers are dispersed in a resin, the absorption rate is about 50% and the dielectric constant is about 40.
When measured using the radio wave absorber 6 of No. 6, the result is as shown in (Table 4).

[0033]

[Table 4]

Even when this radio wave absorber 6 was placed in the concave groove 3 for measurement, the same effect as that obtained by dispersing ferrite in resin was obtained.

The radio wave sealing device of this embodiment is shown in FIGS.
As shown in FIG. 2, the structure is simpler and more compact than the conventional one because the structure has the slits and the wave absorber is bent without complicated bending or spot welding of the sheet metal as in the related art.

Although the door is provided with the concave groove and the edge portion and the radio wave absorber is provided so as to cover both of them in the embodiment, the same effect can be obtained even if the front portion of the main body has the same configuration. was gotten.

[0037]

As is apparent from the above embodiments, according to the present invention, a concave groove is provided in at least one of the portions where the main body and the door face each other, and a plurality of slit portions are formed on at least one wall surface of the concave groove. By providing an edge portion that is parallel to the upper surface of the upper portion of the inner wall surface and lower than the height of the outer wall surface of the concave groove, and a radio wave absorber that covers the concave groove and the edge portion is provided. , Complicated bending and spot welding are not required, and the X component of the radio wave propagating in the longitudinal direction of the concave groove can be prevented from propagating, the leaky wave in the Y direction can be attenuated, and the radio wave compression effect of the radio wave absorber can be reduced. Since the depth of the concave groove can be made shorter than 1/4 wavelength, a simpler and smaller radio wave sealing device than the conventional one can be obtained.

[Brief description of drawings]

FIG. 1 is a cutaway perspective view of essential parts of a radio wave sealing device according to an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of a microwave oven equipped with the same radio wave sealing device.

FIG. 3 is an enlarged cross-sectional view of the main part of the radio wave sealing device.

FIG. 4 is a characteristic diagram of radio wave leakage with respect to a slit pitch in the radio wave sealing device.

FIG. 5 is a characteristic diagram of radio wave leakage with respect to the gap between the main body and the door in the radio wave sealing device.

FIG. 6 is a characteristic diagram of radio wave leakage with and without a radio wave absorber for the gap between the main body and the door in the radio wave sealing device.

FIG. 7 is a sectional view of a main part of a microwave oven equipped with a conventional radio wave sealing device.

FIG. 8 is an enlarged cross-sectional view of the main part of the radio wave sealing device.

FIG. 9A is a cross-sectional view of a main part of another conventional radio wave sealing device, and FIG. 9B is a perspective view of a main part of the same radio wave sealing device.

FIG. 10 is a sectional view of a main part of another conventional radio wave sealing device.

[Explanation of symbols]

 1 main body 2 door 3 concave groove 4 wall surface 5 slit portion 6 radio wave absorber 7 edge portion

Claims (1)

[Claims] 1. A radio wave sealing device for high-frequency equipment, comprising: a main body of a conductor material into which radio waves are supplied and having an opening; and a door of a conductor material that covers the opening so as to be openable and closable. Is provided in at least one of the portions facing each other, and a plurality of slits is provided in at least one wall surface of the concave groove, and the upper part of the outer wall surface of the concave groove is parallel to the upper surface of the upper part of the inner wall surface and its height is higher. A radio wave sealing device, wherein an edge portion lower than the height is provided, and an electric wave absorber that covers the concave groove and the edge portion is provided.