JPS6030078A - Radio wave sealing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a radio wave sealing device for shielding high frequency radio waves.

2. Description of the Related Art Conventional Structures and Problems A conventional radio wave sealing device of this type will be described using, for example, a microwave oven that cooks food by dielectric heating using high frequency waves. A microwave oven is equipped with a heating compartment that stores food and heats it using high-frequency waves, and a door that can be opened and closed to cover the opening of the heating compartment for putting food in and out. At this time, radio wave sealing measures are taken to prevent high-frequency electromagnetic waves inside the heating chamber from leaking outside the chamber and causing harm to the human body.

U.S. Pat. No. 3,182,164 is shown in FIG. 1 as seven conventional examples. In FIG. 1, reference numeral 1 denotes a heating chamber of a microwave oven, and a door 4 having a handle 3 that covers an opening 2 of the heating chamber 1 so as to be openable and closable is provided. A hollow choke part 6 having a gap part 5 opened toward the heating chamber 1 side is formed at the peripheral edge of the door 4. Depth 7 of this choke part 6
is designed to be substantially one-fourth the wavelength of the radio frequency used. In this case, the thickness of the door 4 is also a quarter wavelength. In other words, the frequency of electromagnetic waves conventionally used in microwave ovens is 2460 MHz, so a quarter wavelength is approximately 3
It becomes 0M. In order to face the choke part 6 of this length, the thickness 9 of the peripheral part 8 formed in the opening part 2 of the heating chamber 1 has a value larger than a quarter wavelength. Therefore, heating chamber 1
The effective size of the opening 2 is smaller by 80 minutes at the periphery.

Next, as another conventional example, US Patent No. 2,500,676
The numbers are shown in Figure 2 a and b. This example also shows the configuration of a microwave oven, in which high frequency waves obtained by oscillation of a magnetron 10 are supplied to a heating chamber 11 to heat and cook food 12 by electromagnetic induction. The opening 13 of the heating warehouse 11 is provided with a door 14 that covers the opening 13 so as to be openable and closable. A groove-shaped choke portion 16 is also formed at the peripheral edge of the door 14, and this choke portion 15 prevents high frequency waves from leaking to the outside. The depth 16 of this choke portion 16 is also designed to be a quarter wavelength of the operating frequency. Therefore, the effective size of the opening 13 is slightly smaller than the heating chamber 11, as in FIG.

As mentioned above, the conventional choke section is based on the technical concept of attenuating high frequencies by having a depth of one-quarter wavelength.

That is, the characteristic impedance of the choke part is Zo,
When the depth is L and the terminal end is short-circuited, the impedance ZIN at the opening of the choke part is 2πL ZIN = 4zOtan (,,,) (λ0 is the free space wavelength) 〇The radio wave attenuation means of the choke method is the choke. By selecting the depth L of the part to be a quarter wavelength, 'ZIN l
It is based on the principle of achieving = Zo tan (--) = cxv.

If the choke part is filled with a dielectric material (゛μ electric constant εr), the wavelength λ' of the radio wave will be compressed to λ' - λ0/～'. In this case, the depth L of the choke part will be L' =
It is shortened to L/J acceptable. However, it is still L'-λ'/4, and in the choke method, the depth cannot be made substantially smaller than a quarter wavelength, and there is a limit to the miniaturization of the choke part. In recent years, the development of solid-state oscillators has progressed, and the era of practical use has arrived. Microwave ovens are no exception; traditional magnetron oscillators are being replaced by solid-state oscillators.

The advantages of solid-state oscillators in microwave ovens are as follows.

(1) The driving voltage of a magnetron is approximately 3 kV, whereas the driving voltage of a solid-state oscillator using a transistor or the like may be approximately 400 V or less, and in practice, approximately 40 V is used. Since the power supply voltage is low, it is safe for humans, and even if there is a leak, it is unlikely to cause an electric shock accident. Therefore, it is possible to make it earthless, and it is also possible to develop a portable system.

(2) While the lifespan of a magnetron is about 5,000 hours, a solid-state oscillator has a long life of about 10 times or more.

(3) While the oscillation frequency of a magnetron is fixed, the oscillation frequency of a solid-state oscillator can be varied, for example, within a range of 13 MHz above and below 915 MHz.

Therefore, by automatically tracking the frequency based on the size of the load (food to be cooked), the resonance frequency changes and highly efficient operation can be obtained. According to the experiment, 245o±50M&
By automatically tracking the frequency within the system, it was possible to improve the practical load efficiency by about 60 to 80% compared to a fixed frequency.

(4) Will solid-state oscillators be mass produced? ＋、In the future, magnetrons may also become cheaper.

In addition, the ISM frequency (Industrial) is currently allocated internationally for high-frequency cooking.

5 scientific, medical) is 58
80MHz.

2450 MH2, 915 MHz, 400 MH2, etc., and must not be used outside of this range. As mentioned above, current magnetrons oscillate at 92450 MHz, but if a solid-state oscillator were used to oscillate at the same frequency of 2450 MHz, sufficient output power could not be obtained and the power would be insufficient. Therefore, in order to obtain the desired output power, it is necessary to select a lower frequency, for example, 91
sMHz is suitable. However, since this frequency is about 1/2.7 of the conventional frequency, the wavelength is, on the contrary, about 2.7 times, and the quarter wavelength is about 8 owL. Therefore, the frequency of the microwave oven is 915
If M& is selected, the thickness of the choke part explained in Figures 1 and 2 will exceed approximately 8 (IIIZ), and the effective size of the opening of the heating chamber will be extremely small compared to the conventional example. However, it has the disadvantage that it is extremely difficult to put it into practical use.

On the other hand, the advantages of changing the oscillation frequency from 2460 MHz to 916 MHz are as follows.

1. Because the wavelength has become longer, radio waves can penetrate deep into the food, making it possible to speed up the cooking time. For example, it took more than 60 minutes at 2450 MHz and EOOW to bring the center of a meat block with a diameter of 120 to about 60 degrees Celsius, but it took less than 50 minutes at 916 MHz and 300 W.

2. The cause of uneven burning is standing waves, and the standing wave pitch is correlated with wavelength. When 915MH2 is used, the pitch of the standing waves is large, and uneven cooking is less noticeable on the food.

Therefore, the disadvantage of changing the operating frequency of the microwave oven to 916 MHz is that the radio wave sealing means becomes thicker.

Note that as one means for reducing the thickness of the choke portion, there is a configuration in which the choke portion is filled with a dielectric material. According to this configuration, the dielectric constant of the choke part increases, so the choke part can be made smaller than a quarter wavelength, and moreover, the choke part can be made smaller than a quarter wavelength.
It has the same effect as a wavelength choke section. However, since the dielectric material is expensive, the price of the entire microwave oven is also expensive, and the manufacturing time and cost are high, which hinders its practical application. Explain.

The choke method is based on the well-known quarter-wavelength impedance conversion principle. That is, the characteristic impedance of the choke groove is Zoc 1 and the depth of the groove is °Cc,
When the characteristic impedance of the leakage path 1 from the heating chamber to the choke groove is ZOp1, the length of the leakage path 17 is ℃p, and the wavelength used is λ, the short circuit impedance of the bottom C of the choke groove 18 (Zc= O) becomes ZB-jZoctan-7-11° at the opening B of the choke groove 18. 19 is a heating chamber of the microwave oven, and 2o is a door. Here 1. c.
By choosing =A, it can be converted to IzBl-■0 When the impedance zB of this opening B is viewed at the line starting point A, the impedance ZA becomes λ. Here, by choosing 2p=-, 1ZAl=
It can be converted to o. 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, and has been put into practical use as a radio wave sealing device.

By loading a dielectric material with a permittivity ε into the leakage path 17 and the choke groove 18, the wavelength λ' becomes λ/11 of the free space wavelength λ, but the quarter wavelength (λ'/4) impedance principle A similar effect can be obtained by using it.

OBJECTS OF THE INVENTION The present invention provides a radio wave seal device in which the size of the choke portion does not increase even if the oscillation frequency is lowered.

Structure of the Invention This invention is a radio wave seal that uses a new impedance conversion principle, and by having each of the leakage path and the groove have a characteristic impedance discontinuity configuration, it has a shape that is smaller than the size equivalent to a quarter wavelength. This is what I did.

DESCRIPTION OF EMBODIMENTS The present invention provides, for example, at least two grooves in at least one of the main body or the door of a microwave oven, and the shape of the grooves is larger than that of the characteristic impedance on the short circuit side and the fully open hole side. , is characterized in that the groove depth from the open end to the shorted end is less than a quarter wavelength.

The basic idea that makes miniaturization possible is as follows.
It is a cage.

The characteristic impedance and length phase constant of the groove opening are Zol
, rl, β1. The characteristic impedance and length phase constant of the groove short circuit part are set as Zo2. μ2. β2 is the distance from the open end of the groove to the shorted end (groove depth) as 2 (total)
Then, it becomes 12(total)-4+122.

Under the above conditions, the impedance z at the open end of the groove is (however,
K −Zo2 /Zo + ) can be derived by simple calculation.

In the conventional example, it corresponds to Z02"ZO+ +β1-β2 (that is, -1). Therefore, the impedance Z' is expressed by the following formula:
1tan (β1-E total)--...
・(2) Impedance was inverted by setting Rtotal f knee.

On the other hand, according to the configuration of the present invention, the characteristic impedance is Zo2) zol according to the configuration requirements, so the value of the ratio of the characteristic impedances in Equation 1 is necessarily larger than 1. In order to make impedance 2 infinite, the denominator of equation 1 needs to be zero, so 1=Ktanβ1 equivalent・tanβ
2"2, and even if the characteristic impedance ratio is increased by 1, the same impedance reversal as before can be achieved even if λ2 is decreased.0 Concept of making the characteristic impedance discontinuous is as follows.

The present invention consists of a groove part of a sealing device having a configuration in which one side is a ground conductor and a conductor plate having a width dimension a is arranged with a gap dimension apart. Specifically, the width of the groove part side is eat, the gap is bl, and an effective dielectric ε. Calculate the characteristic impedance ratio K using the following formula in a configuration where the width on the groove short-circuit side is β2 and the gap is b2, and by setting the value of K to be greater than 1, the characteristic impedance is made discontinuous. We are trying to make it happen.

The details of the embodiment will be explained based on the drawings.〇Figure 4 i This is a perspective view of a microwave oven, in which a door 22 having a patching plate 21 is attached to a main body covered with a main body cover 23. The main body is provided with an operation panel 24, and a door handle 25 is attached to the door.

5 shows a sectional view taken along the line shown in FIG. 4, FIG. 6 shows a perspective view of FIG. 6, and FIG. 7 shows a perspective view of only a group of conductor pieces. In FIGS. 6 and 6, the conductor plate groups 26 that partition the first groove 34 and the second groove 3 and the second groove 35 and the third groove 36 are a, b, and c.

Consists of part d. The groove cover 27 that covers the first groove 34, the second groove 36, and the third groove 36 has a structure to prevent removal and is composed of e+f+q+)l+1 parts.

1st. Second. The opening side grooves of the third groove 34, 36, 36 are indicated by Z, a, V, and the shorting side grooves are indicated by II, JV, W □.

1st. Second. The open ends and shorted ends of the third grooves 34, 36.36 are indicated by 28, 29, 30, 31132.33, respectively. The punching plate 21 and the door 22 are fastened together with a stopper 37 and screws 38. The conductor plate 26 has a pitch P
It is composed of portions a and d of width a1 and portions a and c of width a2 (see Fig. 7). The ratio of characteristic impedance in the first groove 34 is 1 to 2, the value in the second groove is 2, the value in the third groove is 3, and both are 1. 2. By making 3 larger than 1, the depths of the grooves Lh+ +42) r(z+ +n22) and (Ils+ + n52) are made smaller than a quarter wavelength.

Although the explanation has been made using the group of conductor pieces shown in Fig. 7,
32a, 32b in Figure 8 a, b, c, d.

The same can be said of other construction methods such as 32c, 32d, 328 in FIG. 9, and 32f in FIG. 10. In addition, the same effect can be obtained even if the conductor piece that partitions the first groove and the second groove and the conductor piece that partitions the second groove and the third groove are not the same shape, and the spacing between the grooves is also not constant. It's fine.

In order to make the characteristic impedance of the opening part of the groove smaller than the characteristic impedance of the short-circuit part, a rectangular hole is used on the short-circuit part side of the conductor piece that makes up the groove. A similar effect can be obtained with a semicircular shape or the like. Further, although an example has been shown in which the conductor piece of the short-circuit portion is composed of two lines, it may be one or three or more lines.

FIG. 11a shows the amount of radio wave leakage when the resonant frequency of each groove is shifted, and FIG. 11S shows the amount of radio wave leakage when the resonant frequency of each groove is matched.

The above naturally holds true not only when the frequency is 915 MHz but also when the frequency is 2450 MHz.

Moreover, the conductor piece group can be constructed by plating plastic resin instead of being constructed from sheet metal.

Effects of the invention In addition to the effect of achieving miniaturization, which is the purpose of the invention, the following effects are obtained.

(1) Downsizing requires increasing the dimensional accuracy of the seal structure, but by slightly shifting the resonance frequency characteristics of two or more grooves, accuracy management can be simplified (No. 11) Diagram a).

(20 By matching the resonant frequencies of two or more grooves, the sealing performance is improved compared to a single groove (No. 11)
Figure b).

(3) A plurality of grooves can be formed by simply bending a single plate.

[Brief explanation of the drawing]

Fig. 1, Fig. 2 a, b, and Fig. 3 are respectively sectional views of the conventional radio wave sealing device, Fig. 4 is a perspective view of a general microwave oven, and Fig. 5 is a sectional view of a conventional radio wave sealing device. A cross-sectional view of the radio wave seal device, FIG. 6 is a perspective view of FIG. 6, FIG. 7 is a perspective view of the conductor part, FIGS. 8 a, b, c, d, and FIGS. Cross-sectional view, perspective view, and FIG. 11a of another embodiment of
, b are radio wave leakage characteristics diagrams due to three grooves. 21...Door, 23...Body, 26...
...Conductor piece, 34...First groove, 36...
...Second groove, 36...Third groove. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2// /4 /, 5 Figure 3 Figure 5 Figure 6 Figure 7 Figure 8 a-b c z Figure 10 Figure 1 Liquid Chief Procedures Amendment 1 Case Indication 1988 Patent Application No. 103108 2 Name of the invention Radio wave seal device 3 Person making the amendment (Relationship with 'l Patent application Person address 1006 Bold Kadoma, Kadoma City, Osaka Prefecture Name 'l+: (582)
Matsushita Electric Industrial Co., Ltd. Representative name: Toshihiko Yamashita 4 Agent Address: 6, Kamiya Matsushita Electric Industrial Co., Ltd., 1006 Bold Kadoma, Kadoma City, Osaka Prefecture Contents of amendment (1) Amendment of the scope of claims in the specification Correct the terms as shown in the attached sheet. (2) On page 13, line 6, insert the legal text next to "It is measured.""The present invention performs impedance inversion using a less than λ/4 line, rather than the λ/4 line historically used in the field of radio wave seals. To make this principle easier to understand, we will analyze it. A part of the results is shown in Figure 4. In Figure 4, a groove with an opening B whose tip C is short-circuited is provided in a part of the transmission line with the A end as the excitation source and the D end open. The width of the groove on the short-circuit side is twice that on the open-hole side.When point A is excited under the same conditions and the groove depth 4T is varied, the electric field in the transmission line is 8,b, Changes like c, D
The radio wave does not reach the end in case b, that is, when the groove depth IT is about 80% of a quarter wavelength (less than λ/4 line), and even if it is longer than that, the armor Even if (cases a and C), radio waves leak more than in case b. This is 41=1
This can be confirmed by substituting 2=lT/2=λ/10.2 and =b2/b1=2 into 1 # K tanβ11-'tanβ12. ” (3) “I am trying my best” on page 13, line 20.
Insert the legal text after . [In actual application, the groove cover space (TO
Pl) and a bending reinforcement space (lX1) are often provided. In these cases, compared to the case where the principle is explained, the radio waves are disturbed and the calculated dimensions are slightly deviated. The details of the deviation are shown below. When the dimension of ToPl is 2 sieves and l! X1 6-6m
An example is shown in which m is set. FIG. 5 is a study example of a 915 MHz Nour device and shows the relationship in which the groove depth lT changes with the dimension of TOPl. 10210
When the dimensions are set to 1 to 3 WIn, AT becomes deeper by 1 to 6 mm. Figure 6 is an example of a 24soMHz sealing device.
The relationship is shown in which the groove depth JT changes depending on the reinforcement space (lxl) with P1 = 2rrnn fixed. Space 7! By setting x1 to 2~(Stan, the groove depth lT is 1~smm
It gets deeper. ” (4) Change “Figure 4” in the second and sixth lines of page 14 to “
Corrected to Figure 7. (6) "Figure 6" in lines 6, 7, and 8 of page 14 will be corrected to "Figure 8." (6) Change “Figure 6” in lines 6 and 8 of page 14 to “
Corrected to Figure 9. (7) Page 14, line 7, page 15, line 2, line 17
Correct "Figure 7" in the row to "Figure 10". (8) "Figure 8" on page 15, line 18 will be corrected to "Figure 11." (9) "Figure 9" on page 16, line 19 of the same page is corrected to "Figure 12." (1o) Page 15, line 19 [Figure 10 j is “1st
Corrected to Figure 3. (11) "Figure 11" on page 16, lines 12 and 13, and page 17, lines 7 and 11, will be corrected to "Figure 14." (12) From page 17, line 16 to page 18, line 2, “
FIG. 4 is a characteristic diagram. ' will be corrected as follows. [Figures 4a, b, and c are electric field analysis diagrams of the groove portion in the present invention; Figures 6a and b1c are cross-sectional views, side views, and characteristic diagrams of the device at 915 MHz; Figures 6a, b, and C are 2450 M
7 is a perspective view of a general microwave oven, FIG. 8 is a sectional view of a radio wave sealing device according to an embodiment of the present invention, and FIG. Figure 10 is a perspective view of the conductor part, Figure 11a,
12 and 13 are cross-sectional views and perspective views of other embodiments of the conductor piece group, and FIG. 14 aSb is a radio wave leakage characteristic diagram due to three grooves. (13) The drawing numbers of Figures 4, 5, 6, 7, and 8 are attached to the attached red stamps.
We have corrected Figures 10 and 11 and added Figures 4, 5, and 6 in the attached sheet. 2. Claims (1) A main body having an opening and into which radio waves are supplied is provided, a door is provided to cover the opening of the main body so as to be openable and closable, and a portion where the main body and the door face each other is provided. at least two grooves are provided in at least one of the grooves parallel to the peripheral direction, these grooves are separated by at least one conductor piece, and each conductor piece is installed continuously at intervals in the longitudinal direction of the groove. the group of conductor pieces that partition the at least two grooves is constructed by bending one plate into a U-shape, and the width of each conductor piece is wider at the opening of the groove than at the short-circuited part; A radio wave sole device in which the characteristic impedance of the opening is smaller than the characteristic impedance of the short-circuit part (1), and the depth of each groove is shorter than λ/4 when the wavelength used is λ. (2) The radio wave sealing device according to claim 1, wherein the conductor width ratios of the opening portion and the short-circuit portion are approximately the same in at least two grooves.しFig. 4 也; fig./l No. @P12I α b, c 〆/3 No. shi'1 1 gay, 袢语子んしIREMI Long wavelength FIG. Figure (Sr. Procedural amendment September 3-1980 Director-General of the Japan Patent Office, Indication of 1.A.11, 4 affixed) 1989 Patent Application No. 103108 2. Name of the invention Radio wave seal device 3. Person making the amendment 4. Representative Person: 571 Address: Matsushita Electric Industrial Co., Ltd., 1006 Kadoma, Kadoma City, Osaka Prefecture, Japan 6 Amendment Order, Daily Report of Written Amendment dated July 17, 1988, Contents of Amendment Column 7, Contents of Amendment July 1982 No. 16 of Amendment 1 of Procedures dated May 17th
(13) Supplementary JEL to Figures 4 to 11 of the drawings.'' is first corrected as follows. (13) The drawing numbers of Figures 4, 5, 6, 7, 8, 9, 10, and 11 are shown in red on the attached sheet. Figures 9, 10, 11, 12, 13, and 14 have been corrected, and j

Claims (2)

[Claims] (1) A main body having an opening and into which radio waves are supplied is provided, a door is provided to cover the opening of the main body so as to be openable and closable, and at least one of the parts where the main body and the door face each other is provided in a peripheral direction. at least two grooves are provided parallel to the grooves, these grooves are separated by at least one conductor piece, and each conductor piece is successively installed at intervals in the longitudinal direction of the groove; The group of conductor pieces that separate the two grooves is constructed by bending a single plate into a U-shape, and the width of each conductor piece is made wider at the opening of the groove than at the short-circuit part, and A radio wave sealing device in which the characteristic impedance is smaller than the characteristic impedance of a short circuit part, and the depth of each groove is shorter than λ/4 when the wavelength used is λ. (2) The radio wave sealing device according to claim 1, wherein the conductor single width ratios of the opening portion and the short circuit portion are made almost the same in at least two grooves.