JPH0251244B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a variable capacitor, and particularly to a variable capacitor suitable for high frequencies.

[Background of the invention]

High-frequency variable capacitors are used as impedance matching resonance circuits and output waveform shaping bandpass filters in high-frequency heating devices and the like. High-frequency variable capacitors work as energy storage tanks, so they have high current resistance characteristics, have low high-frequency energy loss (high allowable current value) over a wide frequency band, have a wide variable capacitance range, and have a wide usable frequency band. (high internal resonance frequency) is desirable.

Here, FIG. 1 shows an outline of a high frequency heating device in which a high frequency variable capacitor is used. 1st
As shown in the figure, the high-frequency heating device uses a heated object 13
This is a device for resonant heating of an ion cyclotron, and includes a source oscillator 1, a pulse generator 2, a human power resonance circuit 3, a high frequency amplification section 4, an output resonance circuit 5, a coaxial switch 6, an impedance matching device 8, a transmission line 10, It consists of an antenna 11 and a dummy load 7. The source oscillator 1 is a device for oscillating high frequency waves for resonantly heating the object 13 to be heated.
The pulse generator 2 determines the time and timing for heating the object to be heated 13, processes the high frequency oscillated by the source oscillator 1 according to the heating time and timing, and generates the human power resonance circuit 3, the high frequency amplifier 4, and the output resonance circuit 5. This is a device for transmitting signals to a high frequency amplifier consisting of. The high-frequency amplifier composed of the human power resonator 3, the high-frequency amplification section 4, and the output resonator 5 is a device for amplifying the high-frequency energy emitted from the source oscillator 1 in order to sufficiently resonantly heat the object to be heated 10. . Here, the human power resonator 3 is a device for matching the output impedance of the pulse generator 2 and the human power impedance of the high frequency amplification section 4. Further, the output resonator 5 is a device for matching the output impedance of the high frequency amplification section 4 and the characteristic impedance of the transmission line 10 and for reducing harmonic distortion generated in the high frequency amplification section 4. The impedance matching device 8 is a device for effectively transmitting the output of the high frequency amplifier to devices including the antenna 11 and the transmission line 10. The transmitter 10 is a device for efficiently transmitting the output of the high frequency amplifier to the antenna 11. The dummy load 7 is a device for checking the output of the high frequency amplifier. The coaxial switch 6 is an output switch for switching the output of the high frequency amplifier to the dummy load 7 or the transmission line 10. The heating container 8 is a device for holding the object 13 to be heated. The DC cut transmission line 9 is provided in the transmission line 10 and is a protection device for preventing direct current from flowing into the high frequency amplifier when the potential of the heating container 8 becomes higher than the ground potential of the high frequency amplifier. . In these high-frequency heating devices, the high-frequency variable capacitor 14 is used in the human power resonant circuit 3, the output resonant circuit 5, and the impedance matching device 8.

Next, the high frequency variable capacitor will be explained. Generally, in high-frequency variable capacitors, the withstand voltage characteristics are obtained by making the inside of the capacitor a vacuum and providing a vacuum gap in order to improve the withstand voltage. Furthermore, in order to widen the variable range of capacitance, multiple layers of electrodes are provided in a circular shape to obtain a large capacitance.

Here, FIG. 2 shows a sectional view of a high frequency variable capacitor. In FIG. 2, the fixed electrode side connecting flange 24 is a flange attached to the high potential side. A movable electrode connecting flange 25 is attached to the low potential side.
Install. The variable capacitor section has a fixed electrode 18
The fixed electrode 18 and the movable electrode 20 are arranged to form a concentric cylindrical capacitor. The fixed electrode short-circuit plate 19 short-circuits the fixed electrodes 18 together, and short-circuits the fixed electrode side connecting flange 24 and the fixed electrode 18. The movable electrode shorting plate 21 short-circuits the movable electrodes 20 together. The bellows 22 is a movable electrode shorting plate 21
Then, the movable electrode connecting flange 25 is short-circuited, and the movable electrode 20 is positioned. In order to seal the insulator 26, a manifold is composed of a fixed electrode short circuit plate 19, a fixed electrode short circuit plate support 15, an insulator 16, a movable electrode connection flange support 17, a movable electrode connection flange 25, a bellows 22, and a movable electrode short circuit plate 21. are doing. The shaft 23 is rotated to slide the movable electrode via the feed screw 29, thereby changing the capacitance of the capacitor. The insulator 16 has the withstand voltage characteristics of the fixed electrode 18 and the movable electrode 20.

In this way, as shown in FIG. 2, conventional high frequency variable capacitors have a circular structure consisting of a fixed electrode 18 and a movable electrode 20 in order to equivalently increase the electrode area (increase capacitor capacity). The core cylindrical capacitor is constructed in multiple layers or extended in the longitudinal direction. In addition, in order to improve the withstand voltage characteristics, ultra-high vacuum is used as the insulator 26,
Required characteristics are obtained by maintaining the distance between the fixed electrode 18 and the movable electrode 20. Such a capacitor is generally called a vacuum variable capacitor.

However, the conventional structure described above has the disadvantage that the external dimensions become large because concentric cylindrical capacitors are formed in multiple layers in order to increase the capacitor capacity. Furthermore, since ultra-high vacuum is used as the insulator, there is a drawback that the withstand voltage characteristics deteriorate due to gas released from the electrodes. Furthermore, since the gap between the fixed electrode 18 and the movable electrode 20 is affected by welding deformation that occurs when attaching a bellows or the like, there is a problem in that the capacitance varies between products. In addition, the bellows 22 is made of a very thin metal plate such as stainless steel in order to maintain the required strength and improve its mobility. The disadvantage is that the heat causes high temperatures, which limits the current flow. Furthermore, since the bellows 22 is a thin metal film as described above, it has a relatively short lifespan, and has a fatal drawback that it no longer functions as a capacitor if it fails due to fatigue. Furthermore, the mechanical natural frequency and electrode resonance frequency of the capacitor are determined by the fixed electrode 18 and the movable electrode 20 located at the outermost periphery, but as the capacitance increases, the dimensions of the electrode increase, and Since the structure is a support structure with a one-sided structure, it is prone to vibration, lowering the natural frequency and resonant frequency, and deteriorating the frequency characteristics.

[Object of the Invention] An object of the present invention is to provide a variable capacitance capacitor that can be made smaller in size, has a larger capacity, and has good characteristics.

[Summary of the invention]

In order to achieve the above object, the variable capacitor according to the present invention includes a plurality of electrically short-circuited cylindrical conductors assembled to form a honeycomb cross section to form an outer electrode, and each of the cylindrical conductors The present invention is characterized in that an inner electrode is provided in which a plurality of electrically short-circuited conductors are fitted with a solid dielectric interposed within the conductor, and one of the electrodes is movable in the axial direction thereof.

[Embodiments of the invention]

Next, an embodiment of a variable capacitor according to the present invention will be described based on the drawings.

FIG. 3 shows a cross-sectional view of the variable capacitor of the present invention, and FIG. 4 shows an example of the structure of the capacitor section in a cutaway perspective view. Note that parts that may be the same as those in FIG. 2 are given the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 3, a plurality of cylindrical conductors 30 electrically short-circuited by a fixed electrode connecting flange 24 are assembled in the same direction and have a honeycomb cross-section (a fourth
A fixed electrode 31 is formed which extends from the fixed electrode fitting flange 24 and serves as an outer electrode. The surface of each cylindrical conductor 30 is covered with a solid insulator (dielectric) 35 such as ceramics, and a conductor 33 of a movable electrode (inner electrode) 32, which will be described later, is fitted inside each cylinder. A possible recess 34 is formed in each case. On the other hand, similarly, the movable electrode 32 is also placed in each recess 34 of the insulator 35 with a
1, a conductor 33 is formed extending from the movable electrode shorting plate 21 as a base so that the conductor 33 can be fitted in a corresponding manner.
The position of the movable electrode 20 can be changed in the axial direction by rotation of the shaft 23, since the feed screw 29 at the tip thereof is screwed into the current conductor guide. The current conductor guide 28 transmits the current from the movable electrode 32 to the variable fitting flange 25 and also functions as a support member that supports the movable electrode 32.

Although the cross-sectional shape of the cylindrical conductor 30 is a hexagonal honeycomb shape in FIG. 4, various shapes such as circular or rectangular can be used.
The spring 27 serves as a spring washer and is biased so as to act as a reaction force in the direction of pulling out the current conductor guide 29.

The cylindrical conductor 30 of the fixed electrode 31 can be formed into a cylindrical shape in advance by preparing an insulator such as ceramic with a groove corresponding to the cylindrical conductor, and fitting the conductor 30 into the groove to integrate the cylindrical conductor 30, or by other methods. As a method, a vapor deposition method or the like may be used. The conductor 33 of the movable electrode 32 may also be hollow as long as the strength is ensured.

Next, the operation will be briefly explained. First, by rotating the shaft 23, the current introduction guide 28
The movable electrode 21 moves forward and backward through the conductor 33.
The penetration depth of the fixed electrode 31 into the recess of the cylindrical conductor 30 changes, and as a result, the facing area of the conductors 30 and 33 changes, so that the capacitance can be changed. When the movable electrode 21 moves forward and backward, the conductor 30
Since the insulator 26 having a constant thickness is interposed between the conductors 30 and 33, the facing distance between the conductors 30 and 33 is always maintained constant, thereby suppressing product variations.

The above configuration has the following advantages. First, a fixed electrode 31 is formed of a plurality of cylindrical conductors 30 with a honeycomb cross section, and each conductor 33 of a movable electrode 32 is inserted inside this through an insulator (an insulator in a solid state rather than a vacuum). By making this possible, the distance between the electrodes facing each other can be reduced, so the capacitance can be increased, and the external size can be reduced. Second, since the insulator 26 is interposed between them, it is possible to prevent the movable electrode 32 from wobbling, and as a result, it is possible to manufacture products with stable quality, and the mechanical strength can be improved. It becomes possible. Thirdly, by downsizing the shape per unit of each conductor 30, it is possible to suppress a decrease in the mechanical natural frequency and the electrical resonance frequency, or conversely, it is possible to raise the resonance point, and the frequency Characteristics can be improved. Also,
Since there is no need to provide an ultra-high vacuum by providing a bellows 22 (Fig. 2) as in the conventional case, current restriction by the bellows 22 does not occur, and the bellows 2
There is no problem such as loss of airtightness due to damage to the capacitor 2, which makes the entire capacitor unusable, and therefore reliability can be improved.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a variable capacitor that can have a smaller external size, a larger capacitance, and has good characteristics.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an outline of a high frequency heating device, Fig. 2 is a sectional view showing the structure of a conventional high frequency variable capacitor, and Fig. 3 is a sectional view showing the structure of a variable capacitor according to the present invention. FIG. 4 is a partially cutaway perspective view showing the main structure of the present invention. 14...Variable capacitor for high frequency, 15...Fixed electrode connection flange support, 16...Insulator,
24... Fixed electrode mounting flange, 25... Movable electrode mounting flange, 28... Current conductor guide, 29
...Feed screw, 30 ... Cylindrical conductor, 31 ... Fixed electrode (outer electrode), 32 ... Movable electrode, 33 ...
Conductor, 35... Insulator.

Claims (1)

[Claims] 1. A solid dielectric is provided between an outer electrode formed in a honeycomb cross-section by a plurality of electrically short-circuited cylindrical conductors gathered in the same direction, and the inner circumferential surface of each cylindrical conductor. and inner electrodes made of a plurality of electrically short-circuited conductors that are fitted individually through the body, and one of the electrodes is movable in its axial direction. Variable capacitor.