JPS59230293A - 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 Page 2 Industrial Application Field This invention relates to a radio wave sealing device for shielding high frequency radio waves.

2. Description of the Related Art Conventional Structure and Problems A conventional radio wave sealing device of this type will be described by taking a microwave oven, which cooks food by dielectrically heating it using high frequency waves, as an example. 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.

As a conventional example, US Pat. No. 3,182,164 is shown in FIG. 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. This choke part 6
The depth 7 is designed to be substantially one-fourth of the wavelength of the radio frequency used. In this case, the thickness of the door 4 is also a quarter wavelength. That is, since the frequency of electromagnetic waves conventionally used in microwave ovens is 2450i, the quarter wavelength is approximately 30-. 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, the opening 2 of the heating chamber 1
The effective size of is slightly smaller by the peripheral edge portion 8.

Next, as another conventional example, U.S. Patent No. 2゜5o0,6
No. 76 is shown in Figures 2a 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 storage 11 has a door 14 that covers the opening 13 so as to be openable and closable.
is provided. A groove-shaped choke portion 15 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 15 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 with a depth of 1/4 wavelength.

That is, when the characteristic impedance of the choke part is ZO1 and the depth is L, and the terminal end is short-circuited, the impedance ZN at the opening of the choke part is (λ0 is the free space wavelength).

The choke-type radio wave attenuation means selects the depth L of the choke part to be 1/4 wavelength, so that 1ZIHl=Zo
It is based on the principle of achieving tan(-)=(X).

If five pages of dielectric material (relative dielectric constant εr) are filled in the choke part, the wavelength λ' of the radio wave will be compressed to λ'. In this case, the depth L' of the choke portion becomes very short. However, there is no difference in setting L' = λ'/4, and in the choke method, the depth cannot be made substantially smaller than 1/4 wavelength, and there is a limit to the miniaturization of the choke part. It was something.

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 3Kv, whereas the driving voltage of a solid-state oscillator using a transistor etc. is approximately 4Kv.
It may be less than 0oV, and in reality about 40V6 pages are used. Therefore, since the power supply voltage is low, it is safe for the human body, and even if there is a leak, electric shock accidents are unlikely to occur. Therefore, it becomes possible to create an earthless system, and it is also possible to develop a portable system.

(2) While the lifetime of a magnetron is about 15,000 hours, a solid-state oscillator has a long lifetime, about 10 times longer.

(3) While the oscillation frequency of a magnetron is fixed, the oscillation frequency of a solid-state oscillator can be varied, for example, within the range of 916 and upper and lower 13. Therefore, by automatically tracking the frequency based on the size of the load (food to be cooked), the resonance frequency changes and high efficiency operation can be obtained. According to the experiment, 2450±5
By automatically tracking the frequency within 0M, it was possible to increase the practical load efficiency by about 60 to 80% compared to a fixed frequency.

(4) Solid-state oscillators may become cheaper than magnetrons in the future due to mass production.

Page 7 also shows the ISM frequencies (Industrial) that are currently internationally assigned for high-frequency cooking.

5 scientific, medical) is 5880
1412, 2450■h, 9156.400&, etc., and must not be used in any way. Current magnetrons oscillate at 2450 as described above, but if a solid-state oscillator were used to oscillate at the same frequency as 2450, sufficient output power would not be obtained and the power would be insufficient. Therefore, in order to obtain the desired output power, a lower frequency must necessarily be selected; for example, 915W is appropriate. 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 80 wavelengths. Therefore, if you select 915 as the frequency of the microwave oven,
The thickness of the choke part explained in Figures 1 and 2 exceeds approximately 80 mm, and the effective size of the opening of the heating chamber is extremely small compared to the conventional example, making it extremely difficult to put it into practical use. This has the following disadvantages.

On the other hand, the advantages of changing the oscillation frequency from 245014 to 91511h 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 VPrl and 600 W to bring the center of a piece of meat 12 degrees in diameter to about 50 degrees Celsius, whereas it took less than 5 minutes at 915 rhinoceros and 3 oow.

2. The cause of uneven burning is standing waves, and the standing wave pitch is correlated with wavelength. When using 915W4+1, the standing wave depth is large, and the unevenness in cooking is noticeable.

Therefore, the disadvantage of changing the operating frequency of the microwave oven to 915vPrl is that the radio wave sealing means becomes larger.

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 the wavelength choke part and 9 pages. However, since the dielectric material is expensive, the price of the microwave oven as a whole becomes expensive, and the manufacturing time and cost are high, which hinders its practical use.

The principle of the conventional example will be theoretically explained below.

The choke method is based on the well-known quarter-wavelength impedance conversion principle. That is, when the characteristic impedance of the choke groove is Zoc, the depth of the groove is lC, the characteristic impedance of the leakage path 1 from the heating chamber to the choke groove is Zop, and the length of the leakage path 17 is also the wavelength used, λ. , the short circuit impedance (Zc-0) at the bottom C of the choke groove 18 can be converted to IZBI-(1) by selecting the opening B of the choke groove 18 as shown in FIG. When the impedance ZB of this opening B is viewed at the line starting point A, the impedance ZA is 10. By skillfully utilizing the quarter wavelength impedance conversion principle, the short circuit state at the bottom C of the beige choke groove 18 can be changed to the line starting point. This technology has been put into practical use as a radio wave sealing device.

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

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

Structure of the Invention The present invention is a radio wave seal using a new impedance conversion principle, in which 11 pages of each of the leakage paths and grooves have a characteristic impedance discontinuous configuration.
The shape is smaller than that of a priest who has a wavelength of one-tenth of a wavelength.

DESCRIPTION OF EMBODIMENTS The present invention provides, for example, one or more grooves in at least one of the main body or the door of a microwave oven, and the shape of the groove is such that the characteristic impedance on the short circuit side is larger than that on the open 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.

The characteristic impedance and length phase constant of the groove opening are Zol
, 71!1. Let it be β1. The distance from the open end of the groove to the shorted end (depth of the groove) is l (tot
al), then 1(total)=z1+12.

It can be derived by simple calculation that under the above conditions, the impedance Z at the open end of the groove is (where =Zo2/zo1).

In the conventional example, Zo2-Zol, β1-β2 (i.e. = 1)
This corresponds to Therefore, its impedance Z′
From equation 1 = Zoltan (β1'1+0212) =Z o
1t a n (β1-12 total)...
(2) λ, and the impedance was inverted by setting 1total to -.

On the other hand, according to the configuration of the present invention, since the characteristic impedance satisfies ZO2>ZOl, the value of the characteristic impedance ratio in equation 1 is necessarily larger than 1.

In order to make the impedance Z infinite, the denominator of equation 1 needs to be zero, so 1-Kta
It is sufficient to satisfy nβ1'1・tanβ2'2, and the dimension 11 is equal to the value of characteristic impedance ratio larger than 1.
, 12, the same impedance reversal as in the conventional case can be achieved.

The idea of making the characteristic impedance discontinuous is as follows.

The present invention has a structure in which conductor plates having a width a are arranged in a groove portion of a sealing device with one end serving as a ground conductor and spaced apart by a gap dimension.

In detail, the width on the groove opening side is a1, the gap is b1, the effective dielectric is εoff, the width on the groove shorting side is a2, the gap is β2, and the characteristic impedance ratio K is calculated using the following formula, a2 By making the value of °b1 greater than 1, an attempt is made to make the characteristic impedance discontinuous.

The details of the embodiment will be explained based on the drawings.

FIG. 4 on page 14 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 above.

FIG. 5 shows a sectional view taken along the line A--A in FIG. 4, and FIG. 6 shows a perspective view of FIG.

In FIGS. 5 and 6, a group of conductor pieces forming the groove 32,
26 is a with the tip bent into a U-shape.

Consists of parts b, c, and d. Groove cover 2 covering the groove 32
7 consists of parts e, f, and g. The opening side gutter of the groove 32 is machined,
The bottom groove of the short circuit is indicated by ■.

The open and shorted ends of groove 32 are indicated at 28 and 29, respectively. The punching plate 21 and the door 22 are fastened with screws 31 together with a stopper 3o.

The conductor piece 26 has a pitch P and a portion a, b, a of a width a1 and a width a2.
It consists of a d part of /2. The gap between the a part of the conductor piece of the groove 32 and the door 22 is bl, and the gap between the d part and the door 22 is β2. Therefore, the characteristic impedance ratio in the groove 32 is 15 Bg a2b1, and by making the value of K greater than 1, the depth of the groove (11+12) is made smaller than a quarter wavelength.

FIG. 7 shows a perspective view of only the conductor piece group 26 in FIGS. 5 and 6.

8a and 8b show examples of other shapes of the conductor pieces 27a and 27b. In this example, a cut is made in the conductor plate, leaving a portion of the bottom portion, thereby connecting the bottom portions of the conductor pieces and increasing the strength.

FIG. 9 shows measurement examples in FIGS. 6 and 6. The measurement is 2,450 East and the gap between the main body 23 and the door is 2m.
It is. Dimensions 11 and 13 were kept constant at 7wn and 6mm, respectively. Width a1t a2 is 21mm and 7mm b1 respectively
．． b2. b3 is 14 mm, 7 mm, and 2 mm, respectively, the dielectric cover is made of ABS resin with a thickness of 2 mm, and the dimension T1 of the overlapping portion of the main body 23 and the door is 10 mm. The vertical axis of the graph is the measured leakage value on a logarithmic scale, and the horizontal axis is the depth of the groove, scaled as a ratio to the wavelength used.

As is clear from this characteristic diagram, the depth of the groove is λ/4 compared to the conventional one.
This shows that it can be made shorter than .

FIG. 10 shows the radio wave leakage characteristics when the dimensions of the folded portion 33 are changed. The measurement conditions were almost the same as in the case of Fig. 9 above, and the dimensions (11 and 12) were set to 20 mm.
("-λ/6) and the dimension 13 is used as a variable. The vertical axis of the graph is the measured value of radio wave leakage, and the horizontal axis is the length of 13.

As is clear from this characteristic diagram, the dimension 13 should be at least 3 rrrIn shorter than the depth of the groove. Generally, the folded portion 33 may be made shorter than the tip of the folded portion of the conductor piece.

The above can be said to be the same for various high frequencies, not just the frequencies of 915 koku and 2450 vi+1.

In addition to forming the grooves by bending a metal plate, it is also possible to form the grooves by plating a plastic resin.

Page 17 shows an example in which a rectangular hole is made in the short circuit part of the conductor plate 2 in order to make the characteristic impedance of the short circuit part of the groove smaller than the characteristic impedance of the opening part. The same effect can be obtained by changing the shape of the ground. Further, although an example in which the transmission line is divided into two on the short-circuit portion side has been shown, it goes without saying that the number of transmission lines may be one or more.

Effects of the Invention As is clear from the examples and measured values, in addition to the effect of achieving miniaturization, which is the object of the invention, the following effects are obtained.

(1) The simple structure of just attaching a conductor piece to the door can reduce radio wave leakage and is suitable for cost reduction.

(2) The bent portion of the conductor piece can also be used to hold down the dielectric groove cover.

(3) By lowering the outer circumference of s, the radio wave leakage characteristics against changes in the gap between the door and the main body are improved.

(4) By loading a dielectric material on the opening side of the groove, the phase constant on the opening side can be increased, which can also contribute to reducing the size of the groove.

(5) By lowering the outer periphery of the door, there is no obstacle to opening and closing the door, and the configuration of the oak and hinge sides is facilitated.

(6) Since the bent portion is shorter than the depth of the groove (or there is no bend), less material is required.

[Brief Description of the Drawings] 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. 6. 6 is a sectional view of a radio wave sealing device according to an embodiment of the present invention, FIG. 6 is a perspective view of FIG. 5, and FIG. 7 is a perspective view of FIG.
Figure 6 is a perspective view of the conductor piece group, Figures 8a and b are side views showing examples of other shapes of the conductor piece group, Figures 9 and 1
FIG. 0 is a characteristic diagram of an embodiment of the radio wave seal of the present invention. 21...Door, 23...Body, 26...
...Conductor piece, 32...Groove, 33...
- Folded part, 34... bottom plate part. Name of agent: Patent attorney Toshio Nakao and 1 other person Compilation 1
Fig. 8 Figure 2 α // Fig. 3 ( Fig. 5 Fig. 6 Fig. 7 Mouth Fig. 8 (S(b) Fig. 9 + J constant frequency fatigue number tough flea Ut Nano 2) Fig. 10 1 Constant frequency 0 6 IQ 1
5 2673 (yrcm) Procedural amendment July 17, 1980 1 Indication of the case 1988 Patent Application No. 103100 2 Name of the invention Radio wave seal device 3 Person making the amendment Relationship with the case Patent application Nominated office 1006 Bold Kadoma, Kadoma City, Osaka Name (582) Representative of Matsushita Electric Industrial Co., Ltd.
Toshihiko Yamashita 4th Agent 571 Address 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 5 Subject of Amendment 2 - Noro, Contents of Amendment (1) Page 13, Line 5 of the Specification Insert the following sentence after "It is measured.""The present invention performs impedance inversion using less than 274 lines, rather than the λ/4 line historically used in the field of radio wave seals. To make this principle easier to understand, we will present the analysis results. A part of the transmission line is shown in Fig. 4. Fig. 4 shows a part of the transmission line with the A end as the excitation source and the D end open.
A groove having an opening B whose tip C is short-circuited is provided. 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 lT is changed, the electric field in the transmission line changes as aSb, c, and D
The radio wave does not reach the end in case b, that is, when the groove depth 7T is about 80 inches, which is a quarter wavelength (less than λ/4 line), and even if it is longer or shorter than that, (For cases a and C), radio waves leak more than in case b. This is /1=/
2=lT/2=λ/10.2, K=b2/b1=2
By substituting 1 #K tanB711 and tanβ12, 3 pages can be confirmed. j (2) On page 13, line 19 of the same page, insert the following sentence after "I'm trying to do something." [In actual application, the groove cover space (TO
Pl) and a bending reinforcement space (AXl) 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 set to 2rran and l! X1 to 6
An example of a case where the number of staff is set to ~6 is shown below. FIG. 5 is a study example of a 915 MHz sealing device, and shows the relationship in which the groove depth AT changes with the dimension of TOPl. When the dimension of TOPl is set to 1 to 3 mm, l! T becomes deeper by 1 to 6 m. FIG. 6 is a study example of a 2450 MHz sealing device, and shows the relationship in which TOP1 is fixed at 2 mm and the groove depth 1T changes in the reinforcement space (4×1). By setting the space/X1 to 2 to 6wn, the groove depth/T becomes 1 to 3 degrees deeper. 4be/゛(3) Change "Figure 4" in the first and fifth lines of page 14 to "
Corrected to Figure 7. (4) Page 14, line 6, line 6, line 7, line 1
Correct "Figure 5" in lines 7 and 13 of page 6 to "Figure 8." (5) "Figure 6" on page 14, lines 5 and 7, and page 15, lines 7 and 13, will be corrected to "Figure 9." (6) "Figure 7" on page 16, line 7 of the same page has been changed to "Figure 10"
will be corrected. (7) "Figure 8" on page 16, line 9 of the same page has been changed to "Figure 11"
will be corrected. (8) "Figure 9" on page 15, line 13 will be corrected to "Figure 12." (9) Correct ``14 cylinder. (10) Change “Figure 10” in line 6 of page 16 to “Figure 13”.
Correct it to "Figure". (11) The statement "Figure 4 is a characteristic diagram" in lines 8 to 14 of page 18 will be corrected as follows. [Figures 4a, b, and c are electric field analysis diagrams of the groove portion in the present invention; Figures 5a, b, and c are sectional views, side views, and characteristic diagrams of the device at 915 MHz; Figures 6a, b, and C is 2450M
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 piece group in Figures 8 and 9, Figures 11a and b are side views showing an example of the shape of the conductor piece group, Figures 12 and 13. 1 is a characteristic diagram of an embodiment of the radio wave seal of the present invention. (12) The drawing numbers of Figures 4, 5, 6, 7, 8, 9, and 10 are indicated in red on the attached sheet. Figures 10, 11, 12, and 13 have been corrected, and Figures 4, 5, and 6 have been added as shown in the attached sheet. ? 4. Fig. 4. Fig. 5 (0-) (b Knob Ashi set pa 09 Shimai Tsukage-kari number phase rule! Liquid length (〕 (f)? Fig. 5 (a-) (C) \ \ a' t, o \ 緘 \ t BiPI・2 ' TOP1=0 , . ?) 1972-230293 (12) Figure 6 (a) " \ ) / " 0.1 °゛\. X,,''! = Δlt

Claims (2)

[Claims] (1) A main body having an opening and into which radio waves are supplied, and a door that covers the opening so as to be openable and closable are configured on at least one of opposing parts, and an outer peripheral edge side is provided on the opposing part of the main body and the field. A conductor piece with a stepped surface is provided so that the gap is widened, and the tip of the conductor piece is bent into a U-shape on the side with the wide gap (bottom plate) and the bottom is thinner than the opening. A radio wave sealing device in which the grooves are arranged periodically in the longitudinal direction in a direction in which the grooves are narrow in opening and wide in the bottom, and the characteristic impedance of the opening of the groove is smaller than the characteristic impedance of the bottom. (2) A folded portion is provided on the outer periphery of the conductor piece by bending the outer peripheral edge of the bottom plate portion of the groove, and this folded portion is
The radio wave sealing device according to claim 1, wherein the depth of the groove is shorter than the depth of the groove.