JPH0311863Y2 - - Google Patents

Description

[Detailed description of the invention] "Field of industrial application" This invention relates to an electromagnet used in, for example, a YIG oscillator.

``Prior art'' The YIG oscillator is an oscillator that utilizes the resonance phenomenon of magnetic spheres made of single-crystal ferrite. This oscillator is equipped with an electromagnet, and the oscillation frequency can be changed by changing the magnetic field applied to the magnetic sphere by the electromagnet. Therefore, by changing the excitation magnetic field in a sawtooth waveform, a frequency sweep signal can be obtained. Because of these characteristics, it is generally used as a local oscillator for spectrum analyzers.

Figure 4 shows the structure of an electromagnet used in a conventional YIG oscillator. In the figure, 301 indicates a cup-shaped magnetic case made of a highly magnetic material such as permalloy. This cup-shaped magnetic case 30
A rod-shaped magnetic core 302 is provided at one axis. The magnetic core 302 and the cup-shaped magnetic case 301 are generally made of the same magnetic material.

The opening surface of the cup-shaped magnetic case 301 is covered with a lid 303 made of a similar magnetic material, and the screw 30
4. An excitation coil 305 is wound around the rod-shaped magnetic core 302, and the rod-shaped magnetic core 302 and the lid 3
03, a magnetic gap 306 is formed between the two.

A magnetic ball 307 is supported in the magnetic gap 306,
The magnetic field given to this magnetic ball 307 causes the excitation coil 30
It is controlled to change depending on the excitation current given to 5.

"Problem that the invention attempts to solve" In the structure shown in Fig. 3, the excitation coil 305
Heat is generated in the excitation coil 305 by passing an excitation current through the excitation coil 305 . The temperature of the excitation coil 305 is approximately +20° C. higher than room temperature.

As the temperature of the excitation coil 305 rises, the rod-shaped magnetic core 302 thermally expands, and the gap length of the magnetic gap 306 changes. As the gap length of the magnetic air gap 306 changes, the magnetic field applied to the magnetic sphere 307 changes, resulting in a drawback that the oscillation frequency of the YIG oscillator fluctuates due to changes in temperature. For example, the void length is
Even if it changes by about 0.01 micron, the oscillation frequency of the YIG oscillator will change by about several 100 Hz compared to the 8 GHz oscillation frequency. The oscillation frequency fluctuates greatly immediately after the power is turned on, and the oscillation frequency stabilizes after a certain period of time, for example, 3 to 4 hours has passed.

It has been known that such drawbacks exist. As a countermeasure to this problem, a method is generally adopted in which an automatic frequency control circuit is attached to the YIG oscillator to prevent the oscillation frequency from changing.

However, when an automatic frequency control circuit is added, another disadvantage arises in that the cost increases.

``Purpose of the invention'' This invention provides a highly stable electromagnet that can reduce fluctuations in oscillation frequency without providing an automatic frequency control circuit.

"Means for solving the problem" In this invention, a negative resistance element is provided so as to detect the temperature change of the rod-shaped magnetic core 302, and this negative resistance element is connected in parallel to the excitation coil. It is configured to reduce the current flowing through the excitation coil in accordance with the rise in temperature of the core 302.

(Function) According to this configuration, when the rod-shaped magnetic core 302 expands due to thermal expansion, the gap length of the magnetic gap 306 becomes narrower, and the magnetic field in the magnetic gap 306 changes to become stronger, the negative resistance element The resistance value of the negative resistance element decreases, and the current flowing through the negative resistance element increases. As a result, the value of the excitation current flowing through the excitation coil is corrected in a decreasing direction, thereby operating to suppress the rise in the magnetic field.

Therefore, even if the magnetic core expands due to thermal expansion, the magnetic field within the magnetic gap 306 can be maintained at a substantially constant value.

``Example'' Figure 1 shows an example of this invention. 4th in the diagram
Portions corresponding to those in the figure are designated by the same reference numerals. The characteristic structure of this invention is that a negative resistance element 100 is provided thermally coupled to a rod-shaped magnetic core 302, and this negative resistance element 100 is connected in parallel with an exciting coil 305 as shown in FIG. be.

In the example shown in FIGS. 1 and 2, a negative resistance element 100 such as a thermistor is attached to the rod-shaped magnetic core 302, and the temperature of the rod-shaped magnetic core 302 is measured by the negative resistance element 100.
The case where the structure is given directly is shown. The negative resistance element 100 is connected in series with a current adjusting variable resistor 201, and the series circuit is connected in parallel with an exciting coil 305 as shown in FIG. Note that R shown in FIG. 2 represents the DC resistance of the excitation coil 305.

200 indicates an excitation current source. Here, a case is shown in which a current source that generates a current that changes in a sawtooth waveform is connected. It is assumed that this excitation current source 200 supplies a constant current I ₀ that changes in a sawtooth shape to the excitation coil 305 .

(Explanation of operation of the embodiment) According to this implementation structure, the current I ₀ given from the excitation current source 200 is divided into the excitation coil 305 and the negative resistance element 100 and operates while maintaining the relationship I ₀ =I _L +I _s .

As shown in FIG. 3, the temperature T of the excitation coil 305
When the temperature rises over time and the rod-shaped magnetic core 302 thermally expands, the negative resistance element 100
02's temperature rise is sensed, and its resistance value decreases. Therefore, the current I _S increases, and the excitation current I _L decreases by the amount that the current I _S increases, suppressing the increase in the excitation magnetic field. The current I _S that flows into the negative resistance element 100 can be adjusted by changing the resistance value of the variable resistor 101. Therefore, immediately after startup, the magnetic gap 3
Adjustment can be easily made so that the magnetic field within 06 does not change significantly. Note that the resistance value of the negative resistance element 100 and the DC resistance R of the excitation coil 305
If the value of is appropriate, the variable resistor 201 can be omitted. It is also conceivable to perform adjustment using a variable resistor and then connect a fixed resistor matching the resistance value in place of the variable resistor 201.

In addition, in the above description, the negative resistance element 100 is
Although the case where the negative resistance element 100 is attached directly to the excitation coil 305 has been described, it is also possible to configure the negative resistance element 100 to be attached to the excitation coil 305 and to know the temperature of the rod-shaped magnetic core 302 from the temperature of the excitation coil.

"Effect of the invention" As mentioned above, the electromagnet of this invention has a bar-shaped magnetic core 3
Even if the temperature T°C of 02 increases and the gap length of the magnetic gap 306 narrows due to thermal expansion and the magnetic field becomes stronger, the resistance value of the negative resistance element 100 decreases due to the temperature increase of the rod-shaped magnetic core 302. Due to this decrease in resistance value, the current I _S flowing through the negative resistance element 100 increases, and the current flowing through the excitation coil 305 decreases.
As the excitation current decreases, the excitation magnetic field becomes weaker and the magnetic field within the magnetic air gap 306 is held at a constant value.

Therefore, according to this invention, it is possible to obtain a highly stable electromagnet that can maintain the magnetic field within the magnetic gap constant against temperature changes. By using an electromagnet, for example, a YIG oscillator with less fluctuation in oscillation frequency can be constructed.

[Detailed description of the invention] Fig. 1 is a sectional view for explaining an embodiment of this invention, Fig. 2 is a connection diagram for explaining the electrical connection structure of this invention, and Fig. 3 is a sectional view for explaining an embodiment of this invention. A graph for explaining the operation of the invention, and FIG. 4 is a cross-sectional view for explaining the conventional electromagnet.

100: Negative resistance element, 200: Excitation current source,
301: Magnetic case, 302: Rod-shaped magnetic core, 30
3: Lid, 306: Magnetic air gap.

Claims (1)

[Scope of utility model registration request] In an electromagnet having an excitation coil and a magnetic air gap, a temperature sensing element is provided to detect the temperature of the magnetic core around which the excitation coil is wound, and this temperature sensing element is connected in parallel to the excitation coil to prevent temperature rise of the magnetic core. A highly stable electromagnet configured to follow the excitation coil and reduce the value of the excitation current flowing through the excitation coil.