JPS6235232B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to improvement of a radio wave leakage prevention device in a microwave heating device such as a microwave oven. (Background Art) Conventionally, as a means to prevent radio waves from leaking from the gap between the main body and the door of a microwave heating device (for example, a microwave oven), a metal contact method using a shield spring, a chiyoke bonding method, a rubber ferrite, carbon A method using a radio wave absorbing material such as rubber has been proposed. Figure 1 is a cross-sectional view of a conventional radio wave leakage prevention device.
1 is the wall of the main body of the microwave heating device, 2 is the main body 1
A door 3 is attached to the front opening of the refrigerator so that it can be opened and closed freely. The door 2 has a radio wave attenuation groove (hereinafter referred to as a radio wave groove) set to approximately 1/4 of the wavelength of the excited radio waves inside the refrigerator by means of metal partition plates 4 and 5 on the periphery of the surface facing the front opening of the main body 1. ) 6 is provided, and a radio wave absorbing member 7 made of rubber ferrite, carbon rubber, etc. is placed on the outside of the radio wave absorbing member 7 in order to prevent dust from remaining in the radio wave absorbing member 7. A yoke cover 8 which also serves as a presser is attached. The yoke cover 8 is made of a material that does not prevent radio waves from entering the yoke groove 6, for example, a low dielectric constant material such as polypropylene. Reference numeral 9 is a plastic decorative cover, 10 is a glass plate, 11 is a wire mesh, 12 is a mounting screw, 13 is a shield spring attached to the main body 1, and metal contact is made between the main body 1 and the door 2 to prevent leakage of radio waves. If the metal contact becomes incomplete due to deterioration of the elasticity of the shield spring or the formation of a metal oxide film, or if insulating material such as dust gets between the main body and the door, this gap should be removed. However, this leaked radio wave is prevented from leaking to the outside by the electrical suppression by the yoke groove 6 and the radio wave absorption action by the radio wave absorbing member 7. However, it is clear from experience that conventional radio wave leakage prevention devices do not provide sufficient performance despite the fact that the chiyoke groove occupies a large proportion of the volume, and also has a large number of parts, making installation work difficult. Recently, various improvements have been made from the viewpoints of performance, cost, and mass productivity. For example, proposals have been made to construct the yoke cover with a material having a radio wave absorbing function, or to arrange a radio wave absorbing member inside the yoke groove. For example, Tokuko Sho 50-1928, Tokko Sho 51-31982, Jitsugoku Sho 56-
16068 is an example of conventional technology. These methods are impractical because they significantly reduce the chi-yoke function, and because the electric and magnetic field strengths inside the chi-yoke groove are strong, there is a risk of burning out the radio wave absorbing member. (Problems to be solved by the invention) The present invention relates to an improvement of a radio wave leakage prevention device, which improves the conventional drawbacks as described above, and makes the structure of the chi-yoke coupling smaller and achieves a wide band without impairing the function of the chi-yoke. , and by reducing the number of parts, it is possible to provide a device that is inexpensive and highly effective in suppressing radio wave leakage. A feature of the device according to the present invention is that the device has a main body with a closed structure including a door that can be opened and closed, and prevents radio wave leakage from a radio wave leakage path between the main body and the door. , has a structure in which a chiyoke groove is provided in at least one of the main body or the door, and the entrance of the chiyoke groove is closed by a chiyoke cover, and the chiyoke cover is a mixture of a magnetic material and an insulator, and the real number term ε′ of the complex dielectric constant is 15 or less. The radio wave leakage prevention device is made of a certain magnetic material and has a radio wave absorbing portion formed integrally with the radio wave cover from the same material as the radio wave cover on the outside of the radio wave groove. (Structure and operation of the invention) The drawings relate to the present invention, and FIG.
FIG. 2 is a cross-sectional view of a measuring device that uses a step converter 23 to form a four-wavelength channel groove 22 (cavity) and artificially create a narrow radio wave leakage path between the main body and door of the microwave heating device. . d
is the gap thickness of the passage 24 corresponding to the radio wave leakage passage, and 22' indicates the entrance of the choke groove. In addition, a variable short circuit plate 2 is provided so that the length of the chiyoke groove can be adjusted.
5 inside. FIG. 3 shows the installed state of the member 26 that is located in the radio wave leakage passage 24 and closes the entrance 22' of the chiyoke groove 6. The flat member 26 (thickness: 2.5 mm, length: 15 mm)
is located within the passage 24 and blocks the entrance 22', and
It extends slightly in the direction of leaked radio waves, and also serves as a radio wave absorbing member. As the flat plate-like member, materials with different ε′ shown in Table 1 were used. In Table 1, Samples Nos. 1 to 3 are rubber ferrites made of a mixture of Ni-Mg-Zn ferrite powder, a material with a relatively low dielectric constant and large magnetic loss, and chloroprene rubber; 7 is a rubber ferrite made of a mixture of Mn--Zn ferrite, a material with a high dielectric constant and large magnetic loss, and powdered chloroprene rubber. The transmittance characteristics of the case where the cheese cover made of various samples Nos. 1 to 7 shown in Table 1 are attached to the cheese yoke inlet 22' will be compared and evaluated. The measurement method is frequency
Sweeping the range from 2200 to 2660MHz, log-converting the output level, and calibrating it, observed the waveform with an oscilloscope, and evaluated its characteristics from the waveform and value.

【table】

[Table] Figure 4 shows the characteristics (curve) when the entrance of the chi yoke is closed with a metal plate, that is, without the chi yoke, the characteristics (curve) of the chi yoke only, and the characteristics (curve) of the chi yoke, as shown in Figure 2. .1
Characteristics (curves ~) when the chiyoke inlet is closed with a flat chiyoke cover made of material 26 (thickness: 2.5 mm, dimension in the direction of radio wave propagation, ie, length: 15 mm) of ~7 are shown. The materials of sample Nos. 1 to 7 have dielectric constants ε' varied from 4.5 to 41.4.
In the case of no chain yoke, the amount of transmission is as shown in the curve.
It is almost constant and is set as 0dB standard. In the case of only a chi yoke, the amount of transmission is 40 dB at 2450 MHz as shown in the curve, and most of the leaked radio waves are attenuated at this frequency.
Only 1/10,000 of the power is transmitted (leaked) of the amount of power transmitted without a choke. From the characteristic curves when the entrance of the chi yoke is blocked with radio wave absorbing material samples Nos. 1 to 7, the characteristics have a peak value in Nos. 1 to 4 where ε' is relatively small 15 or less, and the characteristics of the chi yoke only. It has a wide band compared to . However, the value of the minimum transmission amount will be slightly larger, and the frequency at that time will be
It can be seen that it is moving downward from 2450MHz. Further, in No. 5 to No. 7, where ε' is large and is 20 or more, the characteristics show almost no peak value, and although some attenuation due to the influence of the yoke is observed, the attenuation is almost flat. In particular, sample No. 7ε′
In the material of =41.4, there is no effect of the chi yoke, and the characteristic is only the transmission attenuation of magnetic material No. 7.
This is considered to be because when ε' is large, the reflection from the sample itself is large and the radio waves do not enter the inside of the yoke. Next, as shown in Figure 4, depending on the material, the minimum transmission amount point shifts toward lower frequencies, but by shortening the length of the chi yoke, the frequency characteristics due to the chi yoke can be returned to that state, and 2450MHz The variable short circuit plate 2 in Figure 2 is promoted when the minimum amount of transmission is obtained.
By adjusting the yoke size (reducing the yoke size) using 5, the center frequency is 2450MHz.
The characteristics were measured when the magnetic material was placed at the entrance of the chi yoke by moving the point of minimum permeation amount (by about 0.5 mm to 10 mm). As a result, the characteristics shown in FIG. 5 were obtained. As can be seen from FIG. 5, it was found that in samples Nos. 1 to 4 in which ε' was about 15 or less, the function of the chi yoke was utilized, and a broader range of characteristics could be obtained compared to the characteristics of the chi yoke alone. Furthermore, ε′ is
In samples Nos. 5 to 7 of 20 or more, the reflection is still large and the radio waves do not enter the inside of the chiyoke sufficiently, so the chiyoke characteristics are not utilized and it is not possible to obtain a sufficiently small amount of transmission. From the results shown in Figure 5, it was found that the influence of ε' is large, so the ε' value of samples No. 1 to 7, the minimum transmission amount, the region (bandwidth) where the transmission amount is less than 20 dB, and the material Table 2 summarizes the transmission attenuation values. Further, the relationship between ε' and characteristic values is shown in FIGS. 6 and 7. FIG. 6 shows the relationship between ε' and the minimum attenuation value, and FIG. 7 shows the relationship between ε' and the bandwidth. From this, when ε′ is approximately 15 or less, although it is slightly worse than the minimum transmission amount of the chi yoke alone, a practically sufficient characteristic of 25 dB or more can be obtained, and the bandwidth is also sufficient with a bandwidth of 240 MHz or more. is obtained. From FIGS. 6 and 7, it can be seen that when ε' reaches around 15, the characteristics deteriorate rapidly.

[Table] Radio wave absorption properties are also utilized in this case, and as shown in Table 1, the materials of sample Nos. 1 to 7 have a transmission attenuation of 2 dB/cm or more, so the attenuation effect is has been fully utilized and the bandwidth has become wider. Moreover, even if the dimension d in FIG. 2 becomes large and the yoke function deteriorates, the radio wave leakage prevention effect is exhibited due to the attenuation characteristics of the material. Samples No. 3 and No. 4 in Table 1
Comparing the tan δμ of 1.79 and 0.70, there is a large difference in transmission attenuation between 9.42 dB/cm and 7.27 dB/cm. In other words, the transmission attenuation varies greatly depending on the ferrite material, but tan δμ (μ''/μ'), which greatly contributes to the transmission attenuation, is the same for the samples in Table 1.
When tanδμ of No. 1 is 0.48, transmission attenuation α (dB/
cm) is 2.37dB/cm, so in order to obtain 3dB, which attenuates at least half of the radio waves, approximately
Requires 0.5 or higher. Generally, when the purpose is to attenuate power, there are situations in which it cannot be said that the attenuation effect has been achieved unless the power is reduced to 1/2 or less of the original power.
The attenuation effect is such that the first 3dB can be compared to the subsequent 1000dB. i.e. for example 100mV
If the power of
Even 1000dB is still insufficient. In this sense, "3dB attenuation (half reduction)" has a symbolic meaning regarding attenuation. The shape of the cover is such that the surface facing the radio wave leakage path is flat.
By protruding toward the inside of the cheese yoke, it is possible to improve the penetration of radio waves into the inside of the yoke due to a kind of antenna effect, and it can be said that the characteristics can be improved without impairing the yoke function. FIG. 9 shows the characteristics when sample No. 3 is used and the mounting state in which the entrance 22' of the cavity 22 in FIG. 2 is closed as shown in FIGS. Fig. 8A shows a flat plate, Fig. 8B shows a convex shape, and Fig. 8C shows an even larger convex shape that protrudes into the cavity. In either case, a wide band can be obtained without significantly impairing the characteristic. As described above, according to the present invention, the structure of the yoke can be made smaller without significantly impairing the function of the yoke, and it also has a function of absorbing radio waves while preventing dust from entering the inside of the yoke, thereby preventing radio wave leakage. The prevention effect can be further increased. Furthermore, by reducing the number of parts, an inexpensive device can be provided. Examples of the present invention are shown below. Example 1 FIG. 10 shows a cross-sectional view of the radio wave leakage prevention device of Example 1. Since the reference numerals are the same as those in FIG. 1, explanations of the same reference numerals will be omitted. Reference numeral 14 denotes a cheese cover made of mixture sample No. 3 of ferrite powder and an insulating material such as rubber or plastic, one end 14a of which is formed into a hook shape to engage with a metal partition plate 25, and the other end 14b. closes the entrance of the chiyoke groove and extends outward, and is fixed at the end of the decorative cover 9. In other words, the surface of the chiyoke cover is made substantially parallel to the opposing wall 1' of the main body 1, and is attached so as to close the entrance of the chiyoke groove and the entrance portion of the adjacent chamber 6'. Embodiment 2 FIGS. 11A and 11B show cross-sectional views of a radio wave leakage prevention device of Embodiment 2. 14 is a chiyoke cover,
It is made of a mixture of ferrite powder and an insulator such as rubber or plastic, and one end is connected to a metal partition plate 2.
The other end closes the entrance of the yoke groove and extends outward, and is fixed at the end of the decorative cover 9. The front surface of the yoke cover is a plane substantially parallel to the opposing wall 1' of the main body 1, and a protrusion ₁₄₁ projecting inward of the yoke groove 6 is integrally formed on the back surface. As shown in FIG. 11B, a plurality of protrusions are provided around the door at appropriate intervals. This protrusion functions as an antenna and emits radio waves into the chiyoke groove, thereby improving radio wave absorption characteristics. Embodiment 3 FIG. 12 is a sectional view of a radio wave leakage prevention device according to Embodiment 3. Reference numeral 14 denotes a cheese yoke cover, which is made of a mixture of ferrite powder and an insulating material such as rubber or plastic. The radio wave absorber 14 is inserted into a narrow space surrounded by metal partition plates 4 and 15.
₂ are integrally formed. This radio wave absorber 14
₂ is provided around almost the entire circumference of the door as shown in FIG. 12B. Embodiment 4 FIG. 13 is a sectional view of A and B, a radio wave leakage prevention device of Embodiment 4. 14 is a chiyoke cover,
The surface of the yoke cover is made of a mixture of ferrite powder and an insulator such as rubber or plastic.
A projecting portion 14 ₁ that is parallel to the opposing wall 1 ′ of the main body 1 and projects inwardly of the chiyoke groove 6 on the back surface.
and metal partition plates 4 and 1 on the outside of the yoke groove 6.
A radio wave absorbing member ₁₄₂ inserted into a narrow space surrounded by 5 is integrally formed (FIG. 13B). In all of Examples 1 to 4, it may be attached to the periphery of the door in a frame-like manner, or it may be attached so as to surround the periphery of the door using several rod-shaped objects. Various modifications or modifications to each of the above embodiments are possible. FIGS. 14a and 14b show examples of fixing structures for the yoke cover 14, in which a is a structure in which the yoke cover 14 is held at the end of the decorative cover 9. FIGS. At this time, in embodiments in which the radio wave absorbing member ₁₄₂ is present, this member may be supported by being held down by the wall of the empty room. In FIG. 14b, a snap-action pin 5a is set up on the splitting plate 5, a corresponding hole is made in the yoke cover 14, and the yoke cover 14 is inserted into the yoke cover 14 with the pin.
This shows the structure for fixing the . Note that a pin may be provided in the chain yoke cover and fixed by a snap operation through a hole provided in the dividing plate. FIG. 14c shows a structure in which the empty chambers have been removed, and in the case of FIGS. 10 and 11, the empty chambers may be removed. FIG. 14d shows three shapes (trapezoid, cylinder, triangular pyramid) of the protrusion ₁₄₁ in FIGS. 11A, B and 13A, B. FIG. Further, the material of the yoke cover may be a mixture of ferrite and rubber, or a mixture of ferrite and synthetic resin. The chiyoke cover has a rectangular picture frame shape consisting of four elongated sides, and the four sides can be integrated, or the four sides can be constructed separately and fixed to the wall of the chiyoke groove. It is. (Effects of the Invention) As described above, according to the present invention, by constructing the chiyoke cover with a magnetic material, a radio wave leakage prevention device having a wide band, a simple structure, and excellent absorption characteristics can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a conventional radio wave leakage prevention device, Fig. 2 is a cross-sectional view of the main part of the measuring device, Fig. 3 is a diagram of the state in which the yoke cover is attached, and Figs. 4 and 5 are yoke cover sample No. 1. - Frequency characteristics diagrams with and without a chi yoke when using No. 7, Figures 6 and 7 are transmission amount and bandwidth characteristics diagrams depending on the difference in ε', and Figure 8 A, B, and C. 9 is a diagram of the state in which various shapes of the yoke covers are attached, FIG. 9 is a frequency characteristic diagram when using sample No. 3 having the shapes shown in FIG. 8 A, B, and C, FIGS. 10 and 11 A and B. , FIGS. 12A and B, and FIGS. 13A and B are structural examples according to the present invention, and FIGS. 14 a to 14 d are various modified examples of the present invention. (Explanation of symbols; Fig. 12A), 6: Chi yoke groove, 14: Chi yoke cover, 14 ₂ : Radio wave absorbing portion.

Claims (1)

[Claims] 1. In a device that has a main body with a closed structure including an openable/closable door and prevents radio wave leakage from a radio wave leakage path between the main body and the door, at least one of the main body or the door on the side facing the radio wave leakage path. It has a structure in which a chiyoke groove is provided in the chiyoke groove, and the entrance of the chiyoke groove is closed by a chiyoke cover.
15 or less, and further comprising a radio wave absorbing portion integrally formed of the same material as the chi yoke cover on the outside of the chi yoke groove.