JPS6345792A - Radio frequency heater - Google Patents

Abstract

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

Description

[Detailed description of the invention] Industrial applications The present invention relates to an improvement in the door structure of a high-frequency heating device.

Conventional technology Grooves with different characteristic impedances are provided in the depth direction on the periphery of the door of a high-frequency heating device, and by making the characteristic impedance of the grooves discontinuous in the depth direction, the effective depth is reduced to a quarter of the wavelength used. A proposal was made in JP-A-60-25 that even if the value is smaller than 1, the impedance at the entrance of the groove is maximized, and leakage radio waves can be reduced in the same way as a choke groove.
It is in Publication No. 190. In this conventional example, the shape is quite complicated, such as providing grooves with different widths in the depth direction of the groove and deforming the shape of the peripheral wall of the groove in the depth direction. Furthermore, it is necessary to consider reflection prevention at discontinuous portions of characteristic impedance.

In addition, as shown in FIG. 7, a cavity resonator 12 for preventing radio wave leakage is formed in a curved manner on the outer periphery of the door 5 to form a mouth-shaped cross section.
A structure having an entrance 25 in which the end cut of the protruding surface 11, which is one peripheral wall of the cavity resonator 12, and the other wall surface (first wall surface 8) of the cavity resonator 12 are opposed was developed in 1982. It is shown in Publication No. 795. This conventional example does not describe that the peripheral wall of the cavity resonator 12 is divided into a plurality of conductor pieces. Therefore, higher-order mode radio waves whose propagation direction is not in the yz plane enter the cavity resonator 12, so the cavity resonator 12 goes out of the resonant state and the radio wave leakage prevention effect becomes smaller. If the rising surface 23 and the protruding surface 11 of the cavity resonator 12 in FIG. 7 are aligned in the longitudinal direction (X direction),
It is assumed that the conductor is divided into conductor pieces each having a width smaller than 72. In this case, the cavity resonator 12 can be regarded as a plurality of parallel resonant elements each having an equivalent capacitance C and an equivalent inductance L arranged in the longitudinal direction (X direction) of the door 5. In each parallel resonant element, as shown in equation (2) below, the distance liQM between the entrance 25 of the cavity resonator 12 and the center 0 of the cavity cross section,
The larger the ratio nM/G to the inlet dimension G, the larger the equivalent capacitance C becomes. In the cavity resonator 12 of FIG. 7, Qu/G=1.
0, the equivalent capacitance C is smaller than when AM/G≧1.5 of the present invention, which will be described later. Accordingly, the equivalent inductance L must be increased by that amount according to equation (3), which will be described later, in order to resonate with the frequency of the leaked radio waves. Therefore, as is clear from equation (1) below, the cross section A of the cavity resonator 12
Since it is necessary to increase B, the conventional cavity resonator 1
No. 2 is large in size and is not suitable for downsizing and cost reduction of doors. In addition, FIG. 7 shows each radical system in the drawings of the specification of Utility Model Application Publication No. 61-795 in the same proportion.
Also, the names and numbers of the components corresponding to those of the present invention are the same.

Problems that the invention aims to solve: It is necessary to provide grooves with a complicated shape in the depth direction of the groove, and it takes time and effort to prevent reflections at discontinuous parts of the characteristic impedance, making it unsuitable for miniaturizing doors. This is a point.

Means for solving the problem: A cavity resonator with a square-shaped cross section for preventing leakage radio waves was installed around the door, and a part of the wall of this cavity resonator was formed with a large number of U-shaped conductor pieces. In addition, an entrance for introducing leakage radio waves into the cavity resonator is formed by a part of the U-shaped conductor piece and a part of the other wall surface, and the distance QM between this entrance and the center of area of the cross section of the cavity, and the entrance The ratio Qy/G to the dimension G was set to 1.5 or more, and two capacitance adjusting elements were provided at both ends of the inlet, and the capacitance adjusting element on the other wall side was made larger than the one on one side of the U-shaped conductor. It is something.

Effect: By configuring as described above, radio waves that are about to leak through the U-shaped conductor piece are introduced as TEM waves into the cavity resonator having a square-shaped cross section. This cavity resonator forms a parallel resonant element consisting of an equivalent inductance L proportional to the cross-sectional area of the cavity and an equivalent capacitance C based on the disturbed electric field near the entrance of the cavity as a cylindrical coil with approximately one turn. . If the entrance of the cavity is made smaller and two capacitance adjustment elements are provided, C becomes larger, and L can be made smaller by that amount. That is, the radio wave sealing effect is maximized when each side of the mouth-shaped cross section, which can reduce the cross-sectional area of the cavity, is smaller than one quarter of the wavelength used.

Embodiment The structure and operation of a high-frequency heating device according to an embodiment of the present invention will be explained with reference to the drawings.

In FIGS. 1 and 2, 1 is a heating chamber, 2 is a flange surrounding the opening of the heating chamber 1, and 3 is an outer box.

Reference numeral 4 designates a group of small holes provided in the center of the door 5 as wide as possible to allow viewing into the heating chamber 1. Reference numeral 6 denotes a step surrounding the small hole group 4, and this step 6 prevents the end of the translucent door inner cover 15 fixed to the inner surface of the small hole group 4 from peeling off during cleaning, etc. , flange 2 when door 5 is closed
This improves the flatness of the sealing surface 7 that makes plane contact with the sealing surface 7. Reference numeral 8 denotes a first wall surface bent from the end of the sealing surface 7 at a substantially right angle to the flange 2. Reference numeral 9 denotes a second wall surface extending substantially parallel to the flange 2 from the end of the first wall surface 8. 10 is a large number of double-shaped conductor pieces welded to the second wall surface 9. This U-shaped conductor piece 10 is welded to the second wall surface 9 with a mounting surface 19, a rising surface 23 facing substantially parallel to the first wall surface 8, and an end cut on the first wall surface 8. It consists of three faces, with the overhanging faces 11 facing each other. The width D (X direction) of each U-shaped conductor piece 100 in the longitudinal direction around the door 5 is made smaller than one half of the wavelength used.

A cavity resonator 12 having a cross section surrounded by a first wall surface 8 and a U-shaped conductor piece 10 and having a narrow entrance 25
form. The projection piece 14 protruding from the opaque dielectric cover 13 that blocks the entrance of the cavity resonator 12 is attached to the hole 18 provided on the rising surface 23 of the U-shaped conductor piece 10.
It is designed to be caught on. A protruding piece 17 protruding from a dielectric door frame 24 for holding a translucent door outer cover 16 covering the front surface of the door 5 is hooked onto the outermost peripheral edge 20 of the second wall surface 9. It has become.

Further, as shown in FIG. 5, capacitance adjusting elements 26 and 27 protruding from the dielectric cover 13 are provided near the end of the projecting surface 11 and near the first wall surface 8, respectively, and the capacitance adjustment elements near the first wall surface 8 are provided. The protruding dimension of the element 27 is made larger than the other capacitance adjustment element 26.

Next, the effects of the embodiment configured as described above will be explained. The radio wave sealing effect will be qualitatively explained using a simple equivalent circuit as shown in FIG. 4 with respect to the incident radio waves directed toward the planar contact portion between the flange 2 surrounding the opening of the heating chamber 1 and the sealing surface 7. 21 is a capacitor corresponding to the planar contact portion between the flange 2 and the sealing surface 7, and acts as a type of bypass capacitor. The planar contact portion is considered to be a parallel plate line, and the capacitance of this line is proportional to the gap between the parallel plates, so the capacitance 21 increases as the gap of the planar contact portion decreases, increasing the radio wave sealing effect. Since the width D of 10 (in the X direction in Figure 3) is smaller than half of the wavelength used, the first
The direction of propagation of the radio waves entering the cavity resonator 12 having a square cross section formed by the wall surface 8 and each U-shaped conductor piece 10 is limited within the yz plane of FIG. If there is no overhanging surface 11, the electric field will be distributed as shown in Fig. 6, and the length Q of the parallel plate line will cause parallel resonance at about one quarter of the free space wavelength λ.
The impedance is maximized and radio wave leakage can be prevented, but in the case of a 2450M& high frequency heating device, the Q is 3.
The thickness is 0.6 am, and if it were to be mounted on a door, it would be too thick, which would be disadvantageous both in terms of design and cost.

When the cavity resonator 12 having the protruding surface 11 and having a single-shaped cross section and a narrow entrance 25 is formed as in the present invention, an electric field distribution as shown in FIG. 5 is obtained. In this case, most of the electric lines of force are concentrated between the vicinity of the end cut of the overhanging surface 11 and the first wall surface 8. The cavity resonator 12 is represented in FIG. 4 as a parallel resonant element consisting of an equivalent inductance L and an equivalent capacitance C. The zero equivalent inductance L is approximately a one-turn cylinder with the same cross section as the cavity resonator 12. It acts as a shaped coil, and means isometric inductance as a constant of the coil, and the value per unit length in the cylinder axis direction (X direction) is as shown in equation (1).

Further, one equivalent capacitance C is based on the disturbed electric field near the entrance 25 of the cavity resonator 12, and is approximately increased by 4 according to equation (2).

L=μ, AB...(1)
Here, AB: area μ of the mouth-shaped cross section of the cavity resonator 12. : Permeability e of the medium inside the cavity resonator 12: 2.72 QM: Distance ε between the entrance 25 of the cavity resonator 12 and the area center 0 of the cavity cross section. : To the permittivity of the medium in the cavity resonator 12 : A correction term related to the shape of the vicinity of the inlet 25 G : Gap of the inlet 25 (inlet dimension) The resonant frequency f0 of the cavity resonator 12 can be expressed by equation (3). .

f, = □ (3) 2πV Gotyo - From equation (2), it can be seen that the smaller the gap G of the inlet 25 or the larger QM/G, the larger the equivalent capacitance C becomes. Assuming that the resonance frequency f0 is constant, the larger the equivalent capacitance C, the smaller the equivalent inductance L can be found from equation (3).
In order to make it smaller, the area AB of the mouth-shaped cross section of the cavity resonator 12 can be made smaller according to equation (1). That is, in order to make the cavity resonator 12 smaller, the gap G of the inlet 25 is narrowed to increase the equivalent capacitance C, and the cavity area AB is increased accordingly.
By reducing the equivalent inductance L, parallel resonance is caused at a constant resonance frequency f (heating frequency of the high-frequency heating device C), the impedance at the inlet 25 is maximized, and radio wave leakage is prevented.

In a high-frequency heating device with a heating frequency of 2450 MHz and a high-frequency output of 5°Ow, the gap between the flange 2 and the sealing surface 7 is 211n, and the step between the overhanging surface 11 and the sealing surface 7 is 3.
1m, the width of the U-shaped conductor piece is 15m, and the water is 275mQ.
I heated it and measured the amount of radio wave leakage at a distance of 50 degrees from the periphery of the door 5. As a result, when G=5na, AB=15
．． At 4X15.9mm, QM/G=2.1, the amount of radio wave leakage is less than O,1mw/d, and if G = 8 mm is increased, AB=20 is required to suppress the amount of radio wave leakage to the same level as above. .4X18.4rm, Q M/G=1
．． 75, the area of the mouth-shaped cross section also becomes large. Through such experiments, by narrowing the gap G of the inlet 25 to about 4 to 8 mm and making QM/G 1.5 or more,
It has been found that the dimensions A and B of the cavity resonator 12 having a cross-section can be made considerably smaller than 30.6 mm, which is one-fourth of the working wavelength λ.

In addition, the equivalent capacitance C is adjusted by the capacitance adjustment elements 26 and 27 to ensure parallel resonance, thereby increasing the radio wave sealing effect. Furthermore, since the capacitance adjustment element 27 near the first wall surface 8 has a longer protruding dimension than the capacitance adjustment element 26 near the end of the projecting surface 11, when fitting the dielectric cover 13, the capacitance adjustment element 27 first 1 along the wall surface 8,
After being positioned, the capacitive adjustment element 26 enters the inlet 25. Therefore, the capacitance adjustment element 26
There is no risk of deformation due to pushing from the z force direction. Note that the capacitance adjusting element 26 also plays the role of minimizing deformation of the projecting surface 11 against external forces from two directions when the dielectric cover 13 is in a fixed state.

Effects of the Invention As described above, according to the present invention, the entrance of a cavity resonator having a square cross section surrounded by a large number of U-shaped conductor pieces and the first wall surface is connected to the projecting surface of the U-shaped conductor piece. The end cut and the first wall face each other to make it narrow, and the dimensions are selected such that QM/G≧1.5, and two capacitance adjustment elements are used to more reliably generate parallel resonance. By doing so, the cross-sectional dimensions A and B of the cavity resonator can be made smaller than one quarter of the wavelength used, λ, so the shape of the cavity resonator can be simplified, the door can be made smaller and thinner, and the assembly can be made easier. A simple and compact high-frequency heating device can be provided, and the economic ripple effect is also large.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a main part showing only the metal part of a door 5 of a high-frequency heating device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a main part showing a radio wave seal around the door, and FIG. Figure 4 is a simplified equivalent circuit diagram of the radio wave seal part of the door 5, Figure 5 is an electric field distribution diagram of the radio wave seal part, and Figure 6 is the electric field distribution of the parallel plate line with the same termination short-circuited. FIG. 7 is a configuration explanatory diagram showing a conventional radio wave seal structure, and FIG. 8 is a diagram showing the direction of the electric field.

Claims (1)

[Claims] A sealing surface (7) located at the periphery of the door (5) that opens and closes the opening of the heating chamber (1) and in planar contact with the flange (2) of the opening of the heating chamber (1) when the door (5) is closed; Sealing side (7
) a first wall surface (8) substantially perpendicular to the flange (2) from the end, a second wall surface (9) substantially perpendicular to this first wall surface (8), and this second wall surface ( 9), a rising surface (23) substantially perpendicular to the rising surface (23), and a projecting surface (11) substantially perpendicular to the rising surface (23).
A large number of U-shaped conductor pieces (10
), the first wall surface (8) and the U-shaped conductor piece (10) form a cavity resonator (12) having a square-shaped cross section and an inlet (25); ), the distance (l_M) between the area center (0) of the cavity cross section, and the inlet dimension (G
) with the ratio l_M/G of 1.5 or more, and the first wall surface (8
) of the U-shaped conductor piece (10) protruding from the dielectric cover (13) that blocks the entrance (25) near the end of the projecting surface (11) and near the first wall surface (8), respectively. Capacitance adjusting elements (26) and (27) are provided, and the protruding dimension of the capacitance adjusting element (27) near the first wall surface (8) is made larger than the other capacitance adjusting element (26). High frequency heating equipment.