JPS6335518Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Technical Field) The present invention relates to an improvement of a radio wave leakage prevention device in a microwave heating device such as a microwave oven. Conventionally, as means to prevent radio waves from leaking through the gap between the main body and the door of a microwave heating device, a metal contact method using a shield spring, a tie-yoke coupling method, or a method using radio wave absorbing materials such as rubber ferrite or carbon rubber have been proposed. ing. Figure 1 is a cross-sectional view of a conventional radio wave leakage prevention device.
1 is the main body of the microwave heating device, 2 is a door attached to the front opening of the main body 1 so as to be openable and closable, and 3 is the inside of the refrigerator. 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. 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 have sufficient performance despite the fact that the chiyoke groove occupies a large proportion.
In addition, since the number of parts is large, the installation workability is poor, so recently various methods of improvement have been made from the viewpoints of performance, cost, and mass productivity. For example, proposals have been made to construct the radio wave cover with a material that has a radio wave absorbing function, or to place a radio wave absorbing member inside the radio wave groove, but these methods significantly reduce the radio wave function and cause the radio wave absorption function to deteriorate. Due to the strong electric and magnetic fields inside, there is a risk of burning out the radio wave absorbing member, making it unsuitable for practical use. For example, Tokuko Sho 50-1928, Tokko Sho 50-31982,
Utility Model Publication No. 56-16068 is an example of the conventional technology. (Problems with the invention) The present invention improves the conventional drawbacks as described above, and provides a device that is compact and has a reduced number of parts without impairing the radio wave function, and is inexpensive and highly effective in preventing radio wave leakage. It is something to do. (Structure and operation of the invention) FIGS. 4A and 4B are cross-sectional views of the radio wave leakage prevention device of the invention, and since the reference numerals are the same as those in FIG. 1, explanations of the same reference numerals will be omitted. The yoke cover 14 is made of a mixture of ferrite powder and an insulator such as rubber or plastic, and one end 14a thereof is formed into a key shape so as to engage with the metal partition plate 5.
The other end 14b closes the entrance of the chiyoke groove, extends outward, and is fixed at the end of the decorative cover 9. The surface of the chiyoke cover is a plane parallel to the opposing wall 1' of the main body 1, and the back surface has a protrusion ₁₄₁ that projects inward of the chiyoke groove 6, and a metal partition plate 4 on the outside of the chiyoke groove 6. A radio wave absorbing member 14 ₂ inserted into a narrow space surrounded by 15 is integrally formed. As shown in Table 1, there are two types of materials for the cheese yoke cover 9: Mn-Zn ferrite rubber, which has a large dielectric constant and large magnetic loss, and Ni-Mg-Zn ferrite rubber, which has a relatively small dielectric constant and large magnetic loss. Complex permittivity (ε′=ε′−jε″) and complex magnetic permeability (μ=
We made seven kinds of cheese covers made of different materials and placed them at the entrance of a cheese groove formed in a part of the waveguide to measure the attenuation of radio waves.The measurement results are shown in Table 2. Figures 2 and 3 summarize the relationship between permittivity and characteristics. From this, it can be seen that when ε' is approximately 15 or less, the characteristics are sufficient for practical use, although the minimum transmission amount is slightly worse than the minimum transmission amount of the chi yoke alone. A characteristic of 25 dB or more can be obtained, and a sufficient bandwidth of 240 MHz or more can be obtained.
From FIGS. 2 and 3, it can be seen that the characteristics deteriorate sharply when ε' reaches around 15. It has been found that when the real value ε' of the complex permittivity is 15 or more, radio waves are reflected a lot, and the penetration of radio waves into the inside of the chi-yoke groove is significantly obstructed, impairing the chi-yoke function. This is because the electric field strength is at its maximum near the entrance of the chiyoke groove, so if a chiyoke cover with a large dielectric constant is placed near this region, radio waves will be reflected more on its surface. Therefore, the yoke cover needs to be made of a material with ε' of 15 or less. Incidentally, as the imaginary value μ'' of the complex magnetic permeability becomes larger, the magnetic loss becomes larger and the radio wave focusing effect becomes larger, so that the radio wave absorption effect of the chiyoke cover itself becomes larger.

【table】

【table】

[Table] As shown in Figure 4B, one example of the chiyoke cover is a substantially rectangular integrally molded product with elongated sides in the shape of a picture frame, or four elongated pieces (or two or three pieces) on each side. It is attached to the opposing peripheral surface of the main body or door. The protrusions 14 ₁ are provided at predetermined intervals or in a continuous manner. The radio wave absorbing member 14 ₂ extends vertically and horizontally along the sides. The yoke cover 14, the protrusion 14 ₁ and the radio wave absorbing member 14 ₂ are integrally molded from a magnetic material. The radio wave absorbing member ₁₄₂ , which is integrally molded with the tee yoke cover 14, is a relatively large-volume member that extends perpendicularly to the cover, and has the effect of absorbing the leakage radio waves suppressed by the tee yoke groove through the electromagnetic loss of the material itself. This minimizes radio wave leakage to the outside. If the mixing ratio of ferrite powder is increased to increase the effect of radio wave absorption, ε' becomes too large, so the mixing ratio is selected so that ε' becomes 15 or less. There is a protrusion 1 on the back side of the yoke cover 14.
4 ₁ is integrally formed, but this protrusion 14 ₁
is a so-called antenna effect, and is provided to improve the penetration of radio waves into the inside of the chiyoke groove. As for the shape of the protruding portion 14 ₁ , it is desirable that the protruding portion 14 1 protrudes in a stepwise or projecting shape toward the inside of the chiyoke groove. Various modifications or modifications to each of the above embodiments are possible. FIGS. 5a and 5b show examples of fixing structures for the yoke cover 14, in which a is a structure in which the yoke cover 14 is held down at the end of the decorative cover 9. FIGS. At this time, the radio wave absorbing member 14 ₂ may be supported by being pressed against the wall of the empty room. FIG. 5b shows a structure in which a snap-action pin 5a is erected on the partition plate 5, a corresponding hole is provided in the cheese yoke cover 14, and the cheese yoke cover 14 is fixed by the pin. Note that a pin may be provided in the chain yoke cover and fixed by a snap operation through a hole provided in the partition plate. Figure 5c shows the protrusion 14
₁ , three shapes (trapezoid, cylinder, triangular pyramid) are shown.
Further, the material of the yoke cover may be a mixture of ferrite and rubber, or a mixture of ferrite and synthetic resin. (Effects of the invention) As described above, the present invention consists of a chiyoke cover made of a material that has a radio wave absorption function.
Since a certain amount of radio waves can be absorbed by the chiyoke cover itself, the wavelength inside the chiyoke groove is shortened, and the length of the chiyoke groove is shortened, allowing for miniaturization. Furthermore, the chi-yoke function is compensated by the antenna effect of the protrusion ₁₄₁ ,
In addition, the radio wave absorbing member 14 ₂ makes the effect of preventing radio wave leakage more complete, and the reduction in the number of parts simplifies the installation work, lowers the price, and improves the performance of preventing radio wave leakage. .

[Brief explanation of the drawing]

Fig. 1 is an example of the structure of a conventional radio wave leakage prevention device, Figs. 2 and 3 are diagrams showing the relationship between the dielectric constant and the characteristics of the yoke cover, and Figs. 4A and B are diagrams of the radio wave leakage prevention device according to the present invention. Structural examples, FIGS. 5a to 5c show various modifications of the present invention. 6; Chi yoke groove, 14; Chi yoke cover, 14
₁ ; Projection; 14 ₂ ; Radio wave absorbing member.

Claims (1)

[Scope of utility model registration request] In a device that 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, a chiyoke groove is provided in at least one of the main body and the door facing the radio wave leakage path. is provided, and has a structure in which 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 has a real value ε' of a complex permittivity of 15.
The cover is made of a material with a uniform thickness of: A radio wave leakage prevention device characterized in that a radio wave absorbing member disposed on the outside of the radio wave leakage groove and the radio wave absorbing member are integrally formed of the same material as the radio wave cover.