JPS59230292A - 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 Structure and Problems A conventional radio wave sealing device of this type will be described by taking as an example an electric two-page microwave oven that cooks food by dielectrically heating it 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.

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 6 opened toward the heating chamber 1 is formed at the peripheral edge of the door 4. The depth 7 of this choke portion 6 is designed to be substantially one-fourth of the wavelength of the high frequency wave 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 2450M, so a quarter wavelength is approximately 3
It becomes 0van. In order to face the choke part 6 of this length, the thickness 9 of the peripheral part 8 formed in three pages at the opening 2 of the heating chamber 1 has a value larger than the 1/4 waveform. Therefore, the effective size of the opening 2 of the heating chamber 1 is slightly smaller by the peripheral edge 8.

Next, as another conventional example, U.S. Patent No. 2,50q67
No. 6 is 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 1o are supplied to a heating chamber 11 to heat and cook food 12 by electromagnetic induction. This heating warehouse 11
The opening 13 is provided with a door 1 that covers the opening 13 so that it can be opened and closed freely.
4 is provided.

A groove-shaped choke portion 16 is also formed at the peripheral edge of the door 14, and this choke portion 16 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 part is based on the technical concept of JP-A-59-2 which attenuates high frequencies by having a depth of 1/4 wavelength.
3 (based on J292(2)).

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 becomes 2πLZIN=jZotan(,,) (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.
It is based on the principle of achieving l = Zotan (-1 (3).

If the choke part is filled with a dielectric material (relative dielectric constant ε), the wavelength λ' of the radio wave is compressed to λI mark 04. In this case, the depth L' of the choke part is L'
It is shortened to ト／T. However, there are many changes to L'-λ'/4, and in the choke method, the depth of 5 pages cannot be made substantially smaller than a quarter wavelength, and it is difficult to miniaturize the choke part. It had its limits.

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.

0) The driving voltage of a magnetron is approximately 3W, whereas the driving voltage of a solid-state oscillator using a transistor etc. is approximately 40W.
The voltage may be 0V or less, and in reality, about 40V is 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 5000 hours, a solid-state oscillator has a long lifetime, about 10 times longer.

(3) Although the oscillation frequency of the magnetron is fixed, the oscillation frequency of the solid-state oscillator is variable, and can be varied within a range of 13 up or down compared to 9161, for example. 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, 2460
By automatically tracking the frequency within ±60 degrees, it was possible to improve the practical load efficiency by approximately 60 to 80 degrees compared to a fixed frequency.

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

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

5 scientific, medical) is 6ss
oJ 2460 stones.

9115J 40011h, etc., and must not be used in a manner that deviates from this. Current magnetrons oscillate at 2450M as described above, but if a solid-state oscillator were used to oscillate at the same frequency of 246011, sufficient output power would 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 by 71.
16 horses is appropriate. However, this frequency is about 1/2.7 compared to the conventional frequency, so the wavelength is about 2.7 times, and a quarter wavelength is about 80+++++++
It becomes. Therefore, if 916 stones are selected as the frequency of the microwave oven, Fig. 1.

The thickness of the choke part explained in Fig. 2 exceeds approximately 80 mm, and the effective size of the opening of the heating chamber is extremely small compared to the conventional example, which has the disadvantage of making it extremely difficult to put it to practical use. It is something.

On the other hand, the advantages of changing the oscillation frequency from 246C1& to 916 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 process. For example, it took more than 50 minutes with the 245011h and aoow to bring the center of a meat block with a diameter of 121 m to about 60°C, but it took less than 60 minutes with the 915J 300W.

2 The cause of uneven burning is standing waves, and the standing wave pitch is correlated with wavelength. When using 9161, the pitch of the standing waves is large, making it difficult to notice uneven cooking on the food.

Therefore, the disadvantage of changing the operating frequency of the microwave oven to 916 Hz 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 a wavelength choke section. 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, the characteristic impedance of the choke groove is Zoc, the depth of the groove is to, and the characteristic impedance of the leakage path 1 from the heating chamber to the choke groove is Z.
op, when the length 91·-2 of the leakage path 17 is 1p and the wavelength used is λ, the short-circuit impedance (Zc=O) at the bottom C of the choke groove 18 is equal to the opening of the choke groove 18 as shown in FIG. In part B, Z B = j Zo ct
It becomes an-7-7c. 19 is the heating chamber of the microwave oven, 2
o is a door. Here t. -7 by choosing IZ
It can be converted as BI=■. The impedance ZB of this opening B can be converted to 1ZAl=o by selecting the impedance ZA when viewed at the line starting point A as 1ZAl=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, thereby making it practical 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 equal to the free space wavelength λ)47F.
However, a similar effect can be obtained by using the quarter wavelength (λ'/4) impedance principle.

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 each of the leakage path and groove has a characteristic impedance discontinuity configuration, resulting in a shape smaller than the size equivalent to a quarter wavelength. It is something.

DESCRIPTION OF EMBODIMENTS The present invention provides 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 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.

11 The characteristic impedance and length phase constant of the Beige groove opening are Zol
, t, , β1. The characteristic impedance and length phase constant of the groove short-circuit part are zo2. t2. The distance from the open end of the groove to the shorted end (depth of the groove), which is β2, is t (total
) then Z (t o t a l ) −71”
It becomes Z2.

It can be derived by simple calculation that under the above conditions, the impedance Z at the open end of the groove is (-2o2/Z01).

In the conventional example, Zo2-Zol, β1-β2 (i.e. -1)
This corresponds to Therefore, its impedance Z′
From equation 1, -Zo, tan (β1t1+β21.,) = Zol
tan (β1-Zotal)...
(2) The impedance was inverted by setting lt o t a 1 as the ward.

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 characteristic impedances in equation 1 is necessarily larger than 1.

In order to make impedance Z infinite, the denominator of equation 1 needs to be zero, so 1-Ktanβ111・tanβ2
12, and set the value of characteristic impedance ratio to 1.
Even if the dimension 11.12 is made smaller by the increased amount, the same impedance inversion 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 al, the gap is bl, and the effective dielectric is ε. ff, and the width on the groove short circuit side is 82, and the gap is β2.
With this configuration, the characteristic impedance ratio K is calculated using the following formula, and by setting the value of K to be greater than 1, an attempt is made to make the characteristic 13 page impedance discontinuous.

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

FIG. 4 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. FIG. The main body is provided with an operation panel 24 and a door handle 26.
is attached to the door above.

6 shows a sectional view taken along the line A-A in FIG. 4, and FIG. 6 shows a perspective view of FIG. 5. In Figures 5 and 6, the first
The conductor plate 26 that partitions the groove 34 and the second groove 35 is bent into a rectangular wave shape.

It consists of parts d and e, which are installed parallel to the longitudinal direction of the groove. The groove cover 27 that covers the first groove 34 and the second groove 36 consists of parts f+q and h. 1st ° 2nd groove 34
．． 35, the opening side groove is I, II [, the short circuit side groove is I
I, indicated by ■.

The open end and short-circuit end of the first and second grooves 34 and 35 are each 28
, 29, 30.31. The punching plate 21 and the door 22 are fastened together with a stopper 32 and a screw 33.

The conductive plate 26 is composed of parts a and d having a width a1 and parts b14 and d and 0 having a width a2/2. Therefore, the characteristic impedance ratio of the matching groove is 2, and by making K larger than 1, the groove depth can be reduced to 1/4 of 11 + 11°) and (121)'22.
It is configured to be smaller than the wavelength.

FIG. 7 shows a perspective view of only the conductor plate 26 in FIGS.

FIG. 8 shows another shape of the conductor plate 26a. This is done by partially bending the conductor plate at the opening end of the groove.

As shown in FIG. 9 al b, c, the conductor plate 26b.

Various shapes can be considered for the periodic bending structure in the longitudinal direction of the grooves of 26C and 2ed.

It goes without saying that what has been described above applies not only when the frequency is 916, but also when the frequency is 245011k and other frequencies. There are 16 pages of methods for constructing the grooves, including by bending a metal plate or by plating a plastic resin.

In order to make the characteristic impedance of the short circuit part of the groove smaller than the characteristic impedance of the opening part, we have shown an example in which a rectangular hole is made in the short circuit part of the conductor plate 27. The same effect can be obtained in the form of In addition, an example was shown in which the transmission line was divided into two on the short-circuit side, but
Of course, it goes without saying that there may be more than one.

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. Strength is increased and accuracy is stabilized by bending the conductor piece.

2. The hole at the bottom of the conductor piece can also be used as a dielectric cover holder.

3. Suitable for cost reduction due to the simple structure of attaching a conductor piece to the door.

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.

[Brief explanation of drawings]

Fig. 1, Fig. 2 a, b, and Fig. 3 are respectively sectional views of conventional radio wave sealing devices, Fig. 4 is a perspective view of a general microwave oven, and Fig. 5 is a diagram of an embodiment of the present invention. 6 is a perspective view of FIG. 6, FIG. 7 is a perspective view of the conductor plate in FIGS. 5 and 6, and FIGS. 8 and 9 a, b, and c are conductors. This is an example of another shape of the plate. 21...Door, 23...Body, 26...
...Conductor plate, 34...First groove, 36.Old...Second groove, 36.River/hole. Name of agent: Patent attorney Toshio Nakao, 1 person, 1 person
Figure 2 α l /4 16 Figure 3? 4 Figure 5 Figure 7 Figure 9 Procedural amendment document July 1980 Noah Day 1 Indication of case 1988 Patent Application No. 103094 2 Name of invention Radio wave seal device 3 Person making amendment Relationship with case Patent Application Colonel Address 1006 Kadoma, Kadoma City, Osaka Prefecture Name
(582) Matsushita Electric Industrial Co., Ltd. Representative Yama
Toshihiko Shimo 4 Agent 571 Address 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 6 Subject of amendment 6 Contents of amendment (1) Please refer to the appendix for the claims of the specification. I will correct it. (2) Insert the written sentence next to "It is measured" on the 8th line of page 12. rThe present invention performs impedance inversion using a sub-λ/4 line instead of the λ/4 line historically used in the field of radio wave seals. In order to make this principle easier to understand, part of the analysis results are shown in FIG. In FIG. 4, a groove having an opening B with a short-circuited tip C is provided in a part of a transmission line with the A end as an 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 7T is changed, the electric field in the transmission line changes as a, b, c, and D
The radio wave does not reach the end in case b, that is, when the groove depth/T is about 8096, which is one-quarter wavelength (less than λ/4 line), and even if it is longer or shorter than that, (In cases a and c), radio waves leak more than in case b. This is 11-
6 =llT/2=λ/10.2, K=b2/b1
This can be confirmed by substituting =2 into 1'-rKtclnβ11·tanB12. ” (3) “Figure 4” in the 3rd and 7th lines of page 13 is changed to “
Correct it to "Figure 5" and cut it out. (4) Page 13, line 7, line 8 (2 locations), 1
Correct "Fig. 6 j" in the 8th line of page 4 to "Fig. 6". (5) "Figure 6" on page 13, lines 7 and 8, and page 14, line 8, will be corrected to "Figure 7." (6) "Figure 7" on page 14, line 8 will be corrected to "Figure 8." (7) "Figure 8" on page 14, line 10 of the same page has been changed to "Figure 9."
will be corrected. (8) Correct “Figure 9” on page 14, line 13 of the same page to “Figure 1o.” (9) Page 16, lines 3 to 8 [Figure 4 is ~]. ' will be corrected as follows. "Figures 4 a, b, and c are electric field analysis diagrams of the groove portion in the present invention, Figure 6 is a perspective view of a general microwave oven, and Figure 6 is a sectional view of a radio wave sealing device in an embodiment of the present invention, Figure 7 is a perspective view of Figure 6, Figure 8 is a perspective view of the conductor plate in Figures 6 and 7, Figures 9 and 10 a, b, and c are of other shapes of the conductor plate. (1o) The drawing numbers of Figures 4, 6, 6, 7, 8, and 9 are shown in the attached document.
Figures 7, 8, 9, and 10 have been corrected, and Figure 4 has been added as shown in the attached sheet. 1 B-7 2. Scope of Claims 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 the main body and the door face each other. Two or more grooves partitioned by a conductor plate are provided in at least one of the parts, and the conductor plate is bent so that the first groove width and the second groove width are periodically changed in the longitudinal direction of the groove, A radio wave sealing device in which holes are periodically provided at the bottom of the conductor plate, and the characteristic impedance of the opening of the groove is smaller than the characteristic impedance of the bottom. 5 Kyoto map

Claims (1)

[Claims] 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 conductive plate is provided on at least one of the parts where the main body and the field face each other. The conductor plate is bent so that the first groove width and the second groove width are periodically changed in the longitudinal direction of the groove, and a hole is formed in the bottom of the conductor plate. A radio wave seal device that is provided periodically so that the characteristic impedance of the opening of the groove is smaller than the characteristic impedance of the bottom.