JPS6325476B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved radio wave sealing device for a high frequency heating device.

A microwave oven, which is a typical example of a conventional high-frequency heating device, uses a conductive gasket as a means to prevent radio wave leakage from the gap (hereinafter referred to as the radio wave passage) created between the opening of the heating chamber and the door. A contact method, a method using a radio wave absorbing material, a chiyoke method using resonance, etc. have been proposed, and combinations of each have been put into practical use.

Among these methods, the Chi-Yoke method using resonance is considered to be the best method in terms of performance and reliability. However, since this York system uses resonance, it necessarily requires structural dimensions that are related to the wavelength of radio waves that propagate through the radio wave path and are likely to leak.

A conventional chi-yoke system configuration will be explained with reference to FIG. 1A is a configuration diagram, FIG. 1B is an equivalent circuit thereof, and FIG. 1C is a plan view in the y direction of FIG. 1A.

This radio wave seal device is installed on the heating chamber opening flange 1.
It consists of a radio wave passage 3 and a chiyoke cavity 4 formed by an entrance/exit door 2. Radio channel 3 entrance A
By making the length from the entrance B of the chiyoke cavity 1/4 of the wavelength of the leaked radio wave, a wall with zero impedance in terms of radio waves is formed at the entrance A of the radio wave passage, and a radio wave seal is achieved. . However, because of this configuration, the dimension in the Z direction, which is the direction outside the main body of the device, must be at least 1/4 of the wavelength of the leaked radio wave, which has the first drawback that it is difficult to make the dimension in the Z direction compact. An equivalent circuit of such a radio wave sealing device is shown in FIG. 1b. Here, Z _B is the impedance when looking from point B to the chiyoke cavity side, Z _L is the impedance when looking outside the main body from the terminal end C of the radio wave path 3, and l is the dimension from point A to point B.

The impedance when looking at the radio wave seal mechanism from point A is (Z _L + Z _B ) + jtanβl/1+j (Z _L + Z _B ) tanβl
is given by

Here, β=2π/λg, λg is the leakage radio wave wavelength.
Note that each impedance is normalized.

For radio waves that try to leak in the Z direction,
Since λg/4, Z _B = infinity, the impedance when looking at the radio wave seal mechanism from point A becomes almost zero.

However, since this radio wave sealing mechanism does not have a means to restrict the traveling direction of radio waves that are about to leak in the Z direction, it cannot prevent leaked radio waves that are traveling at an arbitrary angle θ to the Z direction as shown in Figure 1 c. It has the following problems.

In other words, since the length l from point A to point B has various dimensions depending on the angle θ, it is impossible to form a wall with zero impedance at point A for radio waves incident from point A at angle θ, and a seal is formed. The disadvantage is that performance deteriorates.

The present invention solves such conventional problems, and aims to provide a novel radio wave sealing device which has a compact configuration and highly performs leakage prevention of radio waves incident on the radio wave sealing device in all directions. .

In order to solve the above-mentioned problems, the radio wave sealing device of the present invention has a configuration based on a novel concept in which transmission lines having short-circuited branch paths are periodically arranged, and the branch paths are loaded with a dielectric material having a predetermined thickness. It consists of the following configuration.

In the present invention, with the above-described configuration, the traveling direction of radio waves that are about to leak is restricted to the direction along the transmission line. Therefore, by optimizing the configuration of the transmission line, leakage of radio waves in all directions can be suppressed. Furthermore, by providing a branch path with an optimal configuration, the longitudinal dimension of the transmission line can be made smaller, and by loading a dielectric material on the branch path,
Since the longitudinal configuration of the branch path can be made smaller, the entire radio wave sealing device can be made smaller.

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 2 is a basic configuration diagram of the radio wave sealing device of the present invention, FIG. 2a is a configuration diagram, and FIG. 2b is an equivalent circuit thereof. The parts in the figure that are compared with FIG. 1 are indicated by the same numbers.

Transmission line groups 5a, 5b, and 5c are periodically arranged facing the heating chamber opening flange 1 and extending outward from the main body. This transmission line is arranged with a gap S between adjacent transmission lines, and its convergence dimension is W.

Providing a gap between adjacent transmission lines suppresses the propagation of radio waves incident at an angle θ with respect to the Z direction shown in FIG. 1c.

The configuration and operation of this transmission line in the Z direction will be explained below based on the transmission line 5a as a representative of the transmission line group.

The transmission line 5a has a dimension l ₁ from the input end A of the radio wave path 3 to the point where the branch path 6 is formed, a depth dimension of the branch path is l ₂ , and a dimension from the branch path to the terminal end C of the radio wave path. is composed of l ₃ .

The equivalent circuit of such a transmission line is shown in FIG. 2b, as is well known in microwave engineering.

The major difference here from Figure 1b is that since the width of the transmission heat path is specified, the radio wave path and branch path can be positioned as a transmission line, so inductive and capacitive parameters can be interposed at the branch point. It becomes possible to express an equivalent circuit. In addition, when calculating these parameter values, please refer to the "Waveguide Handbook" MI
It is explained in detail on T.Radiation Laboratory P.337.

Impedance Z _A viewed from point A toward the radio wave sealing device side is related using each parameter of equivalent circuit b. This obtained impedance Z _A is
If Z _A = R + jX and the impedance seen from point A toward the heating chamber is Z _pv , the microwave power P _L leaking out of the main body from point C is as follows for the microwave power P _io incident on the radio wave sealing device: The present inventors have experimentally confirmed that they are related by the formula.

_{R L} ∝R・Z _{pv /} (Z _{pv +} R) ^{2 +} The results showed that the leakage of microwave power P _L is smaller as the amount of leakage increases. To prove this, we actually measured the attenuation characteristics of the radio wave seal device for l ₁ dimensions of 30 mm and 12 mm, and the result was that the amount of radio wave leakage was 1/2 to 1/3 lower when l ₁ = 12 mm than when l ₁ = 30 mm. I got it. The main structural dimensions at the time of actual measurement are as follows. When the gap between the heating chamber opening flange and the radio wave seal device is 1 mm and 4 mm, the opposing dimension of the branch passage is 8 mm, and the depth of the branch passage is l ₂ = 32 mm, l ₁ = 12 mm, l ₃ = 10 mm, l ₁ = 30.
When mm, l ₃ = 12 mm, transmission line width W = 10 mm, gap S = 10 mm.

In calculations, the smaller the _l1 dimension, the better the results.
In order to prevent the θ-direction transmission of radio waves incident at an angle θ with respect to the Z-direction of the radio wave sealing device, the l ₁ dimension should be a considerable size to face the heating chamber opening flange. Considering the actual configuration, l ₁
= 12 mm is considered to be approximately the minimum dimension of l ₁ .

As a result, the fact that the dimension from the entrance of radio waves to the Chiyork cavity in the Chiyork system, which has been used as a well-known fact in the past, is 1/4 wavelength corresponds to the Chiyork cavity, as shown in the basic configuration of the present invention. By adopting a radio wave sealing device configuration in which transmission lines with branch paths are arranged periodically with gaps S in between, the length up to the branch path can be configured to be sufficiently smaller than 1/4 wavelength. It has been shown that the radio wave seal device can be made more compact in size in the z-direction compared to the conventional chi-yoke method.

With this radio wave sealing device, the depth of the branching path can be set to approximately 1/4 of the leakage radio wave wavelength.
The origin of the present invention is to compress the leakage radio wave wavelength in the branch path by interposing a dielectric material in the branch path, thereby reducing the actual size of the branch path (dimension in the y direction in Figure 2 a). .

FIG. 3 is a conceptual diagram of the radio wave sealing device of the present invention.

A is a diagram in which the branch path 6 is composed of only an air layer 7, and the depth l ₂ of the branch path is approximately 1/4 of the wavelength of the leaked radio wave. For example, if the inside of this branch path is filled with a dielectric layer 8 with a relative dielectric constant of 4, the wavelength propagating inside the branch path will be compressed to 1/2, so the depth l ₄ of the branch path will be in the configuration shown in figure a. In comparison, 1/2 would be sufficient. This is shown in Figure 3b.

In addition, in FIG. 3, parts that are compared with FIG. 2 are indicated by the same numbers.

By the way, the mechanism for inserting a dielectric material into this branch path to reduce the actual size while keeping the effective length of the branch path for radio waves the same is theoretically simple and clear, as shown in Figure 3, but it is difficult to implement in actual design. However, the following difficulties arise.

During assembly in which a formed dielectric material is inserted and loaded into a branch path, a considerable gap (air layer) is created between the conductor and the dielectric material forming the branch path.

Further, even in a molding configuration in which resin is poured into a branch path conductor as a mold, due to resin contraction, a considerable gap may occur between the conductor as a mold and the contracted resin (dielectric material).

The influence of this gap (air layer) will be explained with reference to FIGS. 4 and 5.

FIG. 4 is a diagram illustrating the influence of an air layer on the branch path of the radio wave sealing device of the present invention, and FIG. 5 shows the effective permittivity characteristics in the branch path when the dielectric layer and the air layer are combined. This shows that.

FIG. 4a shows the electric field distribution in the radio wave sealing device of the present invention.

The high frequency input from A is propagated into the branch path 6 as shown in the figure. In this figure, the line conductor is 9 and the ground conductor is 10. FIG. 4b is an enlarged view of the part surrounded by a circle 11 in the branch road.

In FIG. 4b, the ground conductor 10 and the line conductor 9
is a dielectric layer 12 having a thickness h and having a desired dielectric constant.
and are separated by an interval d with an air layer 13 having a thickness g interposed therebetween. Arrows in the figure indicate the direction of the electric field.

In order to know the effective wavelength of leakage radio waves in a branch path having such a two-layer structure, it is necessary to know the effective permittivity of the branch path in which the dielectric layer 12 and the air layer 13 are combined. This effective permittivity ε _eff is the fourth
As shown in FIG. 4B, the equivalent circuit of FIG. 4B is obtained from the combined capacitance of the series connection of the dielectric layer capacitance c ₁ and the air layer capacitance c ₂ . That is, c ₁ = ε ₀ · ε _r · s/h, c ₂ = ε ₀ s/g ε ₀ · ε _eff · s/d = 1/1/C ₁ +1/C ₂ ε ₀ is the permittivity of vacuum, From the unit facing area, s is given by ε _eff =d/h/εr+g (1). Note that the dielectric constant of the air layer was 1. FIG. 5 shows the characteristics of g and ε _eff when h=3 mm and ε _r =4 from equation (1).

What can be seen from Figure 5 is that when inserting a dielectric material molded with a thickness of 3 mm and a relative dielectric constant of 4 into a branch path, the gap between this dielectric material and the branch path conductor (line conductor or ground conductor) is 0.2 mm. If it is hot, the effective dielectric constant of the branch will be approximately 3.4, and the wavelength of leakage radio waves propagating through the branch will be approximately 10% longer than when the gap is zero.

The effect of increasing the wavelength by 10% will be explained using a radio wave attenuation characteristic diagram with respect to the branch path length l ₂ of the radio wave sealing device of the present invention shown in FIG.

The curve indicated by 14 in the figure is a theoretical curve when the branch path is composed of only an air layer, and the black circles are actual measured values.
The frequency used was 2450MHz.

The theoretical curve when this branch path is completely filled with a dielectric material having a relative dielectric constant of 4 is 15. Air layer now 0.2
If mm exists, the wavelength will become longer by about 10%, and the attenuation of the radio wave sealing device will deteriorate by more than 10 dB. For this reason, the method of completely filling and inserting dielectric material into the branch path in order to substantially minimize the actual depth of the branch path has the disadvantage that highly accurate control is required in the actual design and performance variation tends to be large. play.

The present invention takes advantage of the influence of this air layer.

FIG. 7 is a block diagram of a radio wave sealing device showing one embodiment of the present invention. Portions in the figure that match those in FIG. 2 are designated by the same numbers.

The ground conductor 10 of the branch path 6 and the line conductor 9 are separated by two layers: a dielectric layer 12 with a thickness of h (mm) and an air layer 13 with a thickness of g (mm) that has been actively provided in advance. Further, the ground conductor 10 and the line conductor 10 are short-circuited at the end of the branch path.

As an example, the thickness h of a dielectric layer with a relative permittivity of 4
If is 3 mm and the thickness g of the air layer is 1.5 mm, then
Ideally, the effective dielectric constant ε _eff is 2, and the radio wave attenuation characteristic becomes the curve shown at 16 in FIG.

Assuming that the thickness g of the air layer varies by ±0.2 mm,
The effective dielectric constant ε _eff is 1.9 to 2.1. As a result, the amount of attenuation deteriorates by only 3 dB at most, making it possible to provide a high-performance and compact radio wave sealing device that sufficiently absorbs manufacturing variations.

In the above explanation, the relative permittivity of the dielectric material is 4 as a representative example in order to make the numerical values clear, but the effectiveness of the present invention is enhanced as the dielectric material has a higher relative permittivity.For example, if alumina is used, The effectiveness of the present invention is further enhanced and the size of the branch path can be made more compact.

As described above, the present invention provides a radio wave sealing device for a high-frequency heating device in which a transmission line having a short-circuit terminated branch path is periodically arranged in the direction outside the main body of the device in a radio wave path created by the heating chamber opening periphery and the entrance/exit door. provides a radio wave sealing device having a configuration in which a line conductor and a ground conductor are separated by two layers: a dielectric layer of a predetermined thickness having a desired relative permittivity and an air layer of a predetermined thickness; The dielectric layer of the circuit makes it easy to understand the effectiveness and facilitate design and manufacturing management.

(2) The mechanism can be made more compact by loading dielectric material.

(3) Manufacturing variations in dielectric materials and branch path materials can be absorbed by a combination of the two.

It has the following effects.

[Brief explanation of the drawing]

Fig. 1 shows a conventional radio wave sealing device, a is a block diagram, b is its equivalent circuit, c is a plan view in the y direction of Fig. a, and Fig. 2 is a basic configuration diagram of the radio wave sealing device of the present invention. is a block diagram, b is its equivalent circuit, FIG. 3 is a conceptual block diagram of the radio wave sealing device of the present invention, FIG. 4 is a diagram explaining the influence of an air layer on the branch path of the radio wave sealing device of the present invention, and The figure is an effective permittivity characteristic diagram for the air layer in the branch path, FIG. 6 is a radio wave attenuation characteristic diagram for the branch path length of the radio wave sealing device of the present invention, and FIG. 7 is a diagram of the radio wave seal device showing an embodiment of the present invention. FIG. 1... Heating chamber opening flange (heating chamber opening periphery), 2... Access door, 3... Radio wave passage, 5a,
5b, 5c...Transmission line, 6...Short-terminated branch path, 9...Line conductor, 10...Grounding conductor, 1
2...Dielectric layer, 13...Air layer.

Claims (1)

[Claims] 1. A transmission line having a branch path short-circuited toward the outside of the device main body of the radio wave path created by the heating chamber opening periphery and the entrance/exit door is arranged periodically, and the branch path is formed of a dielectric layer having a predetermined thickness. A radio wave sealing device in which a line conductor and a ground conductor are separated by two air layers having a predetermined thickness.