JPH04370693A - Radio wave sealing device and its manufacture - Google Patents

Abstract

PURPOSE:To shield high frequency radio waves of a microwave oven, etc., using a compact, easy-to-fabricate sealing device, wherein no complicated folding or welding process is involved and the part with a groove provided in a door, etc., has not a greater thickness than in a conventional arrangement. CONSTITUTION:An opening provided in the body for supplying radio waves to the inside is enclosed with a door 3 with possibility of being opened, and a groove 4 is furnished in either or both of the mating parts of the body and door 3. Wall surfaces 8 are formed so that at least one wall surface of this groove 4 has a pitch in longitudinal direction greater than the conductor width, and a wave absorbent 10 is furnished in this groove 4. The groove 4 is embodied in multi-layer structure of resin 5 and electroconductivce body 6 having the wall surfaces 8, and the electroconductive body 6 is adhered by an adhesive 9 to the inner surface of the resin 5 formed concavely, and with this groove 4 a choke part is formed to shield electric waves.

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 from a device having a door that can be opened and closed, such as a microwave oven, and a method for manufacturing the same.

0002

2. Description of the Related Art Conventionally, this type of radio wave sealing device (for example, the specification and drawings of US Pat. No. 3,182,164) has been constructed as shown in FIG. The configuration will be explained below.

As shown in the figure, reference numeral 21 denotes a heating chamber of the main body of the microwave oven, and a door 24 having a handle 23 is provided to cover an opening 22 of the heating chamber 21 so as to be openable and closable. A hollow choke portion 26 having a gap portion 25 opened toward the heating chamber 21 is formed at the peripheral edge of the door 24 . The depth L1 of the choke portion 26 is designed to be substantially one-fourth of the wavelength of the high frequency wave used. In this case, the width of the choke portion 26 of the door 24 needs to be equal to or more than 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 mm. In order to face the choke part 26 of this length, the opening 2 of the heating chamber 21 is
The thickness L2 of the peripheral edge portion 27 formed at 2 has a value larger than a quarter wavelength. Therefore, the opening 2 of the heating chamber 21
The effective size of 2 is slightly smaller due to the peripheral edge 27.

As described above, the conventional choke section 26 is based on the technical concept of attenuating high frequencies by having a depth of one-quarter wavelength. That is, assuming that the characteristic impedance of the choke part 26 is Z0 and the depth is L, the impedance Z at the opening of the choke part 26 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 has a depth L of the choke part 26 of 4
It is based on the principle that impedance ZIN can be made infinite by selecting a fraction of the wavelength, as shown in equation (2).

|ZIN|=Z0 tan(π/2)=∞
(2) A theoretical explanation will be given below using FIG. 14. For convenience of explanation, the concave groove 28 is shown in FIG.
The depth direction of the heating chamber 21 is taken as the Z axis, the direction from inside the heating chamber 21 to the outside of the chamber through the gap between the doors 24 is taken as the Y axis, and the longitudinal direction of the concave groove 28 is taken as the X axis.

The choke method is based on the well-known quarter-wavelength impedance conversion principle. That is, the characteristic impedance of the concave groove 28 is Z0C, the depth of the concave groove 28 is lC, the characteristic impedance of the leakage path 29 from the heating chamber 21 to the concave groove 28 is Z0P, the length of the leakage path 29 is 1P, and the wavelength used is λ, the short-circuit impedance ZC at the bottom C of the concave groove 28 is zero as shown in FIG. It comes to show.

[0008] ZB =jZ0Ctan(2πlC/λ)
………………(3) Here, by choosing lC = λ/4, it can be converted to |ZB |=∞.

The impedance ZB of this opening B when viewed at the starting point A of the line is expressed by the formula (4
).

ZA =-jZ0P/tan(2πlP/λ
) ...... (4) Here, by choosing lP = λ/4, it can be converted to |ZA |=0.

The short-circuit condition at the bottom C of the concave groove 28 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.

By loading the leakage path 29 and the concave groove 28 with a dielectric having a dielectric constant εr, the wavelength λ' in the dielectric becomes 1/2 (εr) times the free space wavelength λ, and the dielectric constant ε
By loading a magnetic body with magnetic permeability μr and magnetic permeability μr, the wavelength λ′ in the magnetic body is equal to (εr × μr
), but the same effect can be obtained by using the quarter wavelength (λ'/4) impedance principle. To explain with reference to FIG. 14, if the depth of the concave groove 28 in the Z-axis direction is set to 1/4 wavelength, leakage of radio waves in the Y-axis direction can be suppressed.

Next, as another conventional example, FIG.
There is one shown in (b). This is a radio wave sealing device that combines a quarter wavelength concave groove 30 and a radio wave absorber 31. However, in this case, the longitudinal direction (X
Radio waves propagating in the direction) are not regulated and are absorbed by the radio wave absorber 31.

[0014] Furthermore, another conventional example (for example,
6-16068), there is one in which a concave groove 32 is provided and a radio wave absorber 33 is provided on the outside of the concave groove 32, as shown in FIG. This also achieves a quarter wavelength to attenuate the radio waves, and the radio wave absorber 33 absorbs the radio waves leaking to the outside from the concave groove 32.

As mentioned above, theoretically, a quarter wavelength,
In other words, radio waves can be shielded by providing a concave groove of approximately 30 mm around the periphery of the door, but if applied to the door as is, the thickness of the door would be over 30 mm. As shown in 16,
The concave grooves were turned sideways to reduce the thickness of the door. Also,
The radio wave shielding structure as described above has conventionally been formed of metal.

[0016]

[Problems to be Solved by the Invention] Such conventional radio wave sealing devices require complicated bending structures and welding on the sheet metal parts, which requires many manufacturing steps and is difficult to manufacture.Furthermore, a simple bending structure results in concave shapes. There was a problem that the groove part became thicker.

[0017] The present invention solves the above-mentioned problems, and the thickness of the concave groove provided in a door etc. does not become larger than before, and there is no need for complicated bending or welding, making it easy to manufacture and compact. The purpose is to provide a radio wave sealing device.

[0018]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a main body having an opening and into which radio waves are supplied, a door that covers the opening of the main body so as to be openable and closable, and the main body. a concave groove provided in at least one of the portions where the concave groove and the door face each other; a wall surface group in which at least one wall surface of the concave groove has a pitch larger than the conductor width in the longitudinal direction; and a wall surface group provided in the concave groove. A first aspect of the present invention is that the concave groove has a multilayer structure of a conductor having at least a resin body and the wall group, and the conductor is bonded to the inner surface of the concave resin body with an adhesive. It is used as a means of solving problems.

[0019] Furthermore, the concave grooves of the first problem solving means can be formed by bonding a multilayer transfer sheet having a support, a release member, a conductor, and an adhesive onto the inner surface of the resin body using the adhesive. The second problem-solving means is that the support is formed by being peeled off from the peeling body.

[0020]

[Operation] The present invention has the above-mentioned first problem solving means.
The concave groove can form a choke part and seal radio waves, and it is easy to make without the need for complicated bending or welding.
A compact radio wave sealing device can be obtained.

Furthermore, according to the second problem-solving means, a radio wave sealing device can be obtained in which the conductor can be easily bonded to the inner surface of the resin body and the quality is stable.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

As shown in the figure, a microwave oven main body 1 has a heating chamber 2, into which radio waves are supplied, and a door 3 is provided opposite the main body 1 so as to be openable and closable. This door 3 is provided with a concave groove 4, and the door 3 including this concave groove 4 is
is composed of a multilayer structure of a resin body 5 and a conductor 6,
This conductor 6 has a slit portion 7 on the outer wall surface of the concave groove 4, and is configured to have a wall group 8 in the longitudinal direction of the wall surface with a pitch P larger than the conductor width a. A conductor 6 is bonded to the inner surface of the resin body 5, which is formed into a concave shape, by an adhesive 9. Therefore, the concave groove 4 can form a choke portion. The radio wave absorber 10 has a concave groove 4
It is positioned to close the opening of the concave groove 4, and also serves as a cover to prevent foreign matter from entering the concave groove 4 from the outside.

When the resin body 5 and the conductor 6 are constructed in a multilayer structure, as shown in FIG.
Apply the adhesive 9 on the continuous sheet 14 provided with the conductor 6 formed in the pattern 13 as shown in FIG.
It is adhered to the inner surface of a resin body 5 molded into a shape having a concave groove 4 on the peripheral edge. Thereafter, the support body 11 is peeled off using a peeling body 12, and a multilayer structure of the resin body 5 and the conductor 6 is obtained. The peeling body 12 has the function of holding the conductor 6 on the support body 11 and peeling off the conductor 6 after it is adhered to the resin body 5 by the adhesive body 9. Note that the pattern 13 is formed on the continuous sheet 14, and the hole 15 is a hole to be used as a peephole for the door 3, and is not necessary if the conductor 6 is transparent. Even if the conductor 6 and the resin body 5 are not transparent, the inside can be seen through the door 3 by providing the hole 15 in the conductor 6 and the resin body 5. Furthermore, by changing the pattern 13 of the conductor 6, one continuous sheet can be applied to doors of various shapes.

The conductor 6 may be any material as long as it has a conductivity sufficient to reflect radio waves and has a thickness greater than the skin thickness for radio waves. For example, when copper is used as the conductor 6, the skin thickness is about 1.4 μm for a 2.45 GHz radio wave, so it is sufficient to have a thickness of about 2 μm or more. Therefore, the conductor portion can be made thinner than conventional sheet metal, and the overall weight can be reduced.

To explain the operation in the above configuration, let the thickness of the radio wave absorber 10 be l1, the depth below the radio wave absorber 10 be l2, and the depth of the concave groove 4 be l, then l=
It becomes l1 + l2. Here, when l2 at which the leakage is minimized when l1 is changed is measured, the results are 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%. (Table 1
), it can be seen that the total depth l of the concave grooves 4 can be reduced by increasing the thickness of the radio wave absorber 10. This is due to the radio wave compression effect due to the dielectricity and magnetic permeability of the radio wave absorber 10, and if the thickness is further increased, l can be made even smaller. The permittivity of the radio wave absorber 10 is εr, the magnetic permeability is μr, and the radio wave absorber 10
Let λ' be the wavelength of the radio wave in , and λ be the wavelength of the radio wave in free space, then λ' = λ/(εr × μr ) 1/2...
…………………(5). Therefore, equation (6
) holds, and as shown in Table 1, εr×μr can be found. From equation (6), l can be made smaller if a radio wave absorber with a larger dielectric constant εr or larger magnetic permeability μr is used.

[0029] l1 × (εr × μr ) 1/2 + l2
=λ/4 (6) FIG. 6 is a diagram in which slits 7 (2 mm, 10 mm) were formed in the outer wall of the concave groove 4, and the radio wave leakage value was measured when the pitch was varied. When the pitch is 300 mm, it corresponds to when there is no slit portion 7. Even if the size of the slit part 7 is changed, the pitch is still 30.
The leakage value is the minimum when it is about mm.

In order to see the effect of the slit section 7, FIG. 7 compares how the radio wave leakage value changes depending on the presence or absence of the slit section 7. Vertical axis is leakage value, horizontal axis is door 3
This is the gap between the main body 1 and the main body 1. As can be seen from FIG. 7, the leakage value is about one digit lower when the slit portion 7 is present than when it is not present.

Furthermore, in order to see the effect of the radio wave absorber 10, FIG. 8 compares how the radio wave leakage value changes depending on the presence or absence of the radio wave absorber 10. The vertical axis is the leakage value, and the horizontal axis is the gap between the door 3 and the main body 1. Figure 8
As can be seen, the leakage value is about one order of magnitude lower when the radio wave absorber 10 is present than when it is not present.

As described above, it can be seen that even if only the slit portion 7 is not provided, and even if only the radio wave absorber 10 is not provided, the leakage of waves is large. In other words, it can be seen that the slit portion 7 and the radio wave absorber 10 interact with each other and have the effect of reducing leakage waves.

FIG. 9 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 described above, according to this embodiment, the thickness of the groove portion provided in the door 3 etc. does not become larger than before, and the radio wave seal device is easy to manufacture without requiring complicated bending or welding. It can be done. Furthermore, since the door 3 can be integrally molded by bonding the resin body 5 and the conductor 6, there is an advantage that the number of manufacturing steps can be reduced. In this embodiment, the door 3 is made of resin, but as shown in FIG.
, 17' may be used as the door.

Next, another embodiment of the present invention will be described with reference to FIGS. 11 and 12. Components having the same configuration as those in the above embodiment are given the same reference numerals and explanations will be omitted.

As shown in the figure, the door 3 is made by cutting a continuous sheet 19 in which a conductor 6 is provided on a heat-fusible resin body 18 into a pattern 13 shown in FIG. It is heat-sealed to the inner surface of a resin body 5 molded into a shape having grooves 4. This case also has the same effect as the previous embodiment. Furthermore, since a support and an adhesive body as in the above-mentioned embodiments are not required, it becomes easier to manufacture.

[0037]

As is clear from the above embodiments, according to the present invention, a concave 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 concave groove extend in the longitudinal direction. The concave groove includes a wall group having a pitch larger than the conductor width, and a radio wave absorber provided in the concave groove. Since the conductor is bonded to the inner surface of the resin body using an adhesive layer, there is no need for complicated bending or welding, making it possible to provide an easy-to-manufacture and compact radio wave sealing device, allowing the door to be integrated with the resin body. It is also possible to mold it, and it can be made lighter.

Further, the concave groove is adhered to the inner surface of a resin body in which a multilayer transfer sheet having a support layer, a release layer, a conductor, and an adhesive layer is formed in a concave shape, using the adhesive layer;
Since the support layer is formed by being peeled off from the release layer, the conductor can be easily adhered to the inner surface of the resin body,
A radio wave sealing device with stable quality can be obtained.

[Brief explanation of the drawing]

[Fig. 1] A perspective view of the main parts of a radio wave sealing device according to an embodiment of the present invention.

[Figure 2] Cross-sectional view of a microwave oven equipped with the same radio wave sealing device

[Figure 3] Cross-sectional view of the main parts of the radio wave seal device

[Figure 4] Cross-sectional view of the transfer sheet used in the radio wave sealing device

[Fig. 5] A diagram showing the pattern of the transfer sheet used in the radio wave sealing device.

[Figure 6] Diagram showing the influence of the slit pitch of the radio wave sealing device

[Figure 7] Diagram showing the effect of the slit in the radio wave sealing device

[
Figure 8: Diagram showing the effect of the radio wave absorber of the radio wave sealing device

[
Figure 9: Diagram showing the effect of the presence or absence of a radio wave absorber and the thickness of the radio wave sealing device

FIG. 10 is a sectional view of a microwave oven equipped with a radio wave sealing device according to another embodiment of the present invention.

FIG. 11 is a perspective view of a main part of a radio wave sealing device according to another embodiment of the present invention.

[Figure 12] Cross-sectional view of a continuous sheet used in the radio wave sealing device

[Figure 13] Partial cross-sectional view of a microwave oven equipped with a conventional radio wave sealing device

[Figure 14] Enlarged cross-sectional view of the main parts of the radio wave seal device

[Figure 15
] (a) A sectional view of the main parts of another conventional radio wave sealing device (b) A perspective view of the main parts of the same radio wave sealing device

[Fig. 16] A sectional view of the main part of another conventional example of a radio wave sealing device.

[Explanation of symbols]

1 Main body 3 Door 4 Concave groove 5 Resin body 6 Conductor 7 Slit part 8 Wall group 9 Adhesive body 10 Radio wave absorber

Claims (3)

[Claims] Claim 1: A main body having an opening and into which radio waves are supplied; a door that covers the opening of the main body so as to be openable and closable; and a door provided on at least one of the parts where the main body and the door face each other. A concave groove, a wall group in which at least one wall surface of the concave groove has a pitch larger than a conductor width in the longitudinal direction, and a radio wave absorber provided in the concave groove, and the concave groove is made of at least resin. What is claimed is: 1. A radio wave sealing device comprising a multilayer structure of a conductor having a body and the wall group, and the conductor is adhered to the inner surface of a resin body formed in a concave shape using an adhesive. 2. The radio wave sealing device according to claim 1, wherein the conductor is heat-sealed to the inner surface of the resin body using a heat-fusible resin body instead of the adhesive body. 3. A multilayer transfer sheet having a support, a release member, a conductor, and an adhesive is bonded to the inner surface of the resin body using the adhesive to form the concave groove, and then the support is peeled off from the release member. 2. The method of manufacturing a radio wave seal device according to claim 1, wherein the radio wave seal device is formed by: