JPS6325478B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radio wave seal for a consumer high frequency heating device, commonly called a microwave oven, and to a method for loading a dielectric therein.

Microwave ovens are widely used to heat and cook objects using high-frequency energy. However, in microwave ovens, radio waves leak to the outside through a gap between a heating chamber and a door (hereinafter referred to as a radio wave passage). In recent years, society's awareness of radio wave leakage has increased, and in order to suppress the amount of radio wave leakage below an acceptable range, radio wave passages are equipped with radio wave leakage prevention mechanisms.

A well-known radio wave seal is a chiyoke seal.

A chi-yoke seal is a short-circuit at the entrance of the radio wave passage by setting the dimensions from the entrance of the radio wave passage to the radio wave resonant groove and the dimensions of the radio wave resonant groove to be a quarter wavelength of the high frequency generation source used. It becomes equivalent and performs the ideal radio wave seal function.

Furthermore, it is well known that a dielectric material is loaded in the radio wave resonant groove to reduce the size of the radio wave resonant groove and thereby to make it more compact.

In the case of a radio wave seal, it is necessary that both the dimension from the entrance of the radio wave passage to the radio wave resonant groove and the dimension of the radio wave resonant groove be 1/4 wavelength, and there is a limit to how compact the radio wave seal can be made.

In addition, when loading a dielectric material, the wavelength compression rate has the disadvantage that its equivalent permittivity changes due to the influence of the air layer. However, the disadvantage was that it took a long time to design the radio wave seal mechanism.

The present invention theoretically compacts the radio wave sealing mechanism by periodically arranging parallel transmission lines whose radio wave paths are partially short-circuited at T-branches.
By injection molding a method of loading dielectric material into the T-branch section, changes in the permittivity of the dielectric material due to the air layer in this section are prevented, and a microstrip line with periodic arrangement of parallel transmission lines even to the end of the radio wave path is created. The present invention provides a radio wave sealing device for a high frequency heating device, which aims at making the radio wave sealing mechanism more compact and improving the radio wave sealing performance.

To summarize the features of the present invention, one of the three characteristics of the T-branch circuit is ``by short-circuiting one of the three ports of the T-branch circuit at an appropriate position, parallel transmission lines are arranged in a periodic manner. The other 2
Note that no power is transmitted between the two ports, and by arranging parallel transmission lines periodically in a part of the radio wave path as described above, sufficient radio wave sealing performance can be achieved even in complicated radio wave propagation directions.

In addition, when making radio wave stickers more compact,
The impedance at the entrance of the radio wave passage can be reduced by simply making the length from the entrance of the radio wave passage to the radio wave resonant groove and the length of the radio wave resonance groove both 1/4 wavelength (ideally The idea is not to introduce a method of quantitatively analyzing the energy of a radio wave path system that reduces the amount of radio wave leakage itself by replacing all radio wave paths with T-branches with impedance.

This energy quantitative analysis method assumes an impedance Z _L at the end of a radio wave path in which parallel transmission lines are periodically arranged. The reason for introducing this impedance Z _L is the idea that when radio waves leak to the outside space through the radio wave path, energy is consumed at the impedance Z _L. Since the radio wave path has a certain finite gap, the impedance Z _L always has a certain finite value.

Conventionally, this impedance Z _L was considered to be Z _L =0, and the only qualitative approach was to simply reduce the impedance at the entrance of the radio wave path.

By the way, reducing the amount of radio wave leakage based on this energy quantitative analysis method is equivalent to reducing the energy consumed by Z _L. Therefore, the characteristics of the T-branch circuit as described above are used to reduce the energy consumed by Z _L.

Calculation of the impedance of this radio wave path system is derived from the following theoretical formula.

Now, when the reference plane is placed at the radio wave path entrance 6 and the view from there to the T-branch opening 7 is impedance (Z ₁ '), if the total impedance of the T-branch opening 7 is Z _T , then Z ₁ ′=Z ₀ Z _T +jZ ₀ tanβl ₁ /Z ₀ +jZ _T tanβl ₁ (1-1) Here, Z ₀ is the characteristic impedance of the transmission line,
β is the phase constant, l ₁ is. This is the dimension from the radio wave passage entrance 6 to the T-branch opening.

(Sanpo Publishing/Electronic Science Series 21, Microwave Circuit Basic Knowledge P.15) Also, regarding the impedance description of the T-branch opening 7, regarding Z _a to Z _d in Figure 5, refer to the same reference document P.166. There is a relational expression as follows.

Z _a = jB _a Z _b = -jB _b Z _c = -jB _c Z _d = jB _d (1-2) Next, the impedance Z _{2 '} of the T-branch section 4 is determined by the terminal are short-circuited, so Z ₂ ′ = jZ ₀ tanβl ₂ = jZ″ ₂ (1-3), and when combined with Z _b . Z _c . Z _d of T-branch opening 7, Z ₂ = jZ ₂ ′ (B _d −B _c )−1/B _b {Z ₂ ″(B _d −B _c
)−1}+B _c (Z ₂ ″B _d −1)=jW ₁ (1-4) In addition, the impedance Z ₃ from the T-branch opening 7 to the end of the radio wave path is the loss impedance at the end Z _L Then, Z ₃ =Z ₀ Z _L +jZ ₀ tanβl ₃ /Z ₀ +jZ _L tanβl ₃ =W ₂ +jW ₃ (1-5), and the combined impedance with the T-branch 4Z _a is given by equation (1-5). Therefore, Z ₃ = (1/jB _a ) (W ₂ + jW ₃ )/(1/jB _a ) + W ₂ + jW ₃ = W ₄ + jW ₅ (1-6) Furthermore, (1-4), (1- 6).The combined impedance Z _T with the remaining Z _a of the T-branch section 4 is Z _T = (Z ₂ + Z ₃ )・(1/jB _a )/(1/jB _a ) + Z ₂
+Z ₃ =W ₆ +jW ₇ (1-7) Substituting this equation (1-7) into equation (1-1), Z ₁ ′=Z ₀ (W ₆ +jW ₇ )+jZ ₀ tanβl ₁ /Z ₀ +j (W ₆ +jW ₇
)tanβl ₁ =R+jI (1-8) An impedance relational expression is obtained.

Therefore, if the impedance Z〓 inside the heating chamber, the impedance Z ₁ ′ outside the heating chamber, and the amount of radio wave radiation from the magnetron are P _IN , then the real parallel circuit of Z〓 and Z ₁ ′ calculates the amount of radio wave leakage _PL . The results showed that the values and the measured values matched. In other words, we discovered that the amount of radio wave leakage can be quantitatively calculated using the relational expression P _L = 1/R/R ² + I ² + 1ZφP _IN .

Therefore, as shown in FIG. 2, the smaller the dimension from the radio wave passage entrance 6 to the T-branch opening 7 is than 1/4 wavelength, the smaller the amount of radio wave leakage. I chose the upper 12mm. (Theoretically, the amount of radio wave leakage is the lowest when l ₁ is 0 mm.) Moreover, according to this energy quantitative analysis method, the distance from the entrance of the radio wave passage to the T-branch opening is one-fourth of the conventional one.
They also discovered that the smaller the wavelength, the smaller the amount of radio wave leakage, making it possible to create a compact radio wave sealing device with excellent radio wave sealing performance.

Now, in FIG. 1, when a dielectric material 8 having a thickness of t is inserted into the T-branch portion 4, some air space 9 will be generated even if the dimensional accuracy is improved. Accordingly, the dielectric constant of the T-branch portion changes based on the following idea. In other words, the dielectric part and the air layer part are regarded as a series capacitor and form an equivalent dielectric constant Eeff. Its general formula can be expressed as Eeff=εr·h/d·t/εo/d+εr/t. Here, h is the T-branch opening dimension, t is the dielectric thickness, d is the air layer thickness,
Er is the permittivity of the dielectric, and Eo is the permittivity of the air layer.

FIG. 2 shows data for inserting a dielectric (Er4.1) t=2.9 mm into the T-branch (opening size 3.1 mm) and calculating the dielectric constant from the wavelength compression ratio.

Calculated from the actual measurement value, Er=3.2, and the theoretical value is also close to Eeff=3.2.

However, in this method of inserting a dielectric, the dielectric constant changes slightly due to the air layer, which is a difficult problem when designing a radio wave sealing mechanism.

Therefore, as in one embodiment of the present invention shown in FIG. 3, a dielectric material 8 is poured into the T-branch portion 4 by injection molding to manufacture the T-branch portion 4 integrally. As a result, only the dielectric material 8 is formed in the T-branch portion 4 narrowed by the parallel transmission line, and no air layer is formed. Therefore, the T-branch portion 4 can also be theoretically made more compact due to the wavelength compression effect solely due to the dielectric constant of the dielectric.

FIG. 4 shows a radio wave seal portion made by injection molding according to the present invention. The length from the entrance 6 of the radio wave path 3 to the opening 7 of the T-branch 4 is shorter than a quarter wavelength, and by loading the T-branch with a dielectric material, this section can be made more compact.

As described above, in the present invention, the radio wave path formed by the heating chamber and the door is periodically arranged with T-branch parallel transmission lines whose ends are short-circuited, and the dimension from the entrance of the radio wave path to the T-branch opening is less than 1/4 wavelength. A compact radio wave sealing device can be realized by loading a dielectric material into the T-branch portion by injection molding, and the following effects can be obtained.

(1) Manufacture is easy because there is no change in dielectric constant due to the air layer.

(2) The dielectric does not shake and does not come off.

(3) The radio wave seal mechanism can be designed theoretically and easily, and the development period can be shortened.

(4) No variation occurs in parallel transmission lines.

(5) The strength of the radio wave seal part can be maintained.

(6) Stable radio wave seal characteristics can be maintained.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the case where a dielectric is inserted into the T-junction, Figure 2 is actual measurement data that shows the equivalent permittivity due to the influence of the air layer in Figure 1, and Figure 3 is the book shown in the book. FIG. 4 is a cross-sectional perspective view of the radio wave seal portion according to the present invention, and FIG. 5 is an equivalent circuit diagram. 1...Heating chamber, 2...Door, 3...Radio wave passage,
4...T branch transmission line, 6...Radio wave passage entrance,
7... T-branch opening, 8... Dielectric material.

Claims (1)

[Claims] 1 It has a heating chamber in which the object to be heated is placed and a door that can be opened and closed to take the object in and out, and a T-branch parallel transmission line with a short-circuited end is connected to the radio wave path formed by the heating chamber and the door around the door. Direction periodic array,
The radio wave sealing device has a structure in which the dimension from the entrance of the radio wave passage to the T-branch opening is smaller than a quarter wavelength, and the T-branch part is loaded with a dielectric material, and the loading method is injection molding.