JPH0748429B2 - Variable inductance device and magnetic field strength measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a variable inductance device which changes the current flowing through a magnetic core of a coil having a superconductor as a magnetic core to change the inductance of the coil, and a known current. The present invention relates to a magnetic field strength measuring device for measuring magnetic field strength by measuring the inductance of a coil having a superconductor supplied as a magnetic core.

<Prior Art> Conventionally, there is a variable inductance device for changing the inductance of a coil as shown in FIG. This variable inductance device has a relative magnetic permeability μ of 1 in the coil 31.
A coil is obtained by inserting a larger magnetic piece 32 and mechanically moving the magnetic piece 32 in the coil 31 in the axial direction.
It changes the inductance as seen from the terminals 33 and 34 of 31.

<Problems to be Solved by the Invention> However, the above-mentioned conventional variable inductance device is
Since the magnetic piece 32 inserted in the coil 31 is mechanically moved in order to change the inductance viewed from the terminals 33 and 34 of the coil 31, it is difficult to move the magnetic piece 32 at high speed. Is. Therefore, there is a problem that the inductance cannot be changed at high speed. Further, there is a problem that it is difficult to move the magnetic piece 32 from a distance, and the inductance cannot be changed from a distance.

Therefore, an object of the present invention is to provide a variable inductance device that is easy to operate and that can change the inductance at high speed.

<Means for Solving the Problems> In order to achieve the above object, the variable inductance device of the present invention includes a coil having a superconductor as a magnetic core, and a current changing unit for changing a current flowing through the superconductor, It is characterized in that the inductance of the coil is changed by changing the current.

Further, the magnetic field strength measuring device of the present invention includes a coil having a superconductor to which a known current is supplied from the outside as a magnetic core, and an inductance measuring unit for measuring the inductance of the coil, and measures the inductance of the coil. This is characterized by measuring the strength of the external magnetic field.

<Operation> In the variable inductance device of the present invention, when the current flowing through the superconductor is changed by the current changing means, the magnetic characteristics of the superconductor change according to the change in the current flowing through the superconductor. Then, since the superconductor forms the magnetic core of the coil, the magnetic characteristics of the magnetic core of the coil itself change and the inductance of the coil changes. Therefore, the inductance of the coil can be changed by changing the current passed through the superconductor.

Further, in the magnetic field strength measuring device of the present invention, when the external magnetic field strength is changed while supplying a known current from the outside to the magnetic core made of a superconductor, the magnetic characteristics of the superconductor change. Then, since the superconductor serves as the magnetic core of the coil, the inductance of the coil changes according to the change in the magnetic characteristics of the superconductor. Therefore, the strength of the external magnetic field can be measured by measuring the inductance of the coil with the inductance measuring means.

<Example> Hereinafter, the present invention will be described in detail with reference to illustrated examples.

This invention utilizes the diamagnetic property of superconductors (that is, the Meissner effect).

First, the superconducting state will be described with reference to FIG. The superconducting state and range are curved surfaces connecting the three critical values of the critical temperature Tc, the critical magnetic field Hc, and the critical current Jc (hereinafter, TH-J
It is limited by the critical surface). In other words, this T-
The superconducting state is abruptly extinguished beyond the HJ critical plane, and the superconducting state is realized within the THJ critical plane. In the T-H-J critical plane,
As is well known, superconductors have zero electric resistance and exhibit the property of complete diamagnetism (Meissner effect). Further, the superconductor is broken in the superconducting state outside the TH-J critical plane and does not show perfect diamagnetism.

FIG. 1 shows an embodiment of the variable inductance device of the present invention. In this variable inductance device, a coil 2 is wound with a superconductor 1 as a magnetic core, and liquid nitrogen is used as a critical temperature.
It is cooled below Tc. In this state, the inductance between the terminals 3-4 of the variable inductance device
Measure L ₁ . Next, when measuring the inductance L ₃ between the terminals 3-4 in a state where the external magnetic field was applied to the magnetic core 1, between the two inductance relationship of L ₁ <L _3. This is
As shown in FIG. 11, the temperature of the superconductor 1 was fixed to the temperature TN by being cooled by liquefied nitrogen, and the superconductor 1 was in the superconducting state. It is considered that the magnetic properties of the superconductor 1 which is the magnetic core of the coil 2 reach the T-H-J critical surface and lose the Meissner effect, that is, diamagnetism.

2 (a) is an external magnetic field B for the superconductor 1 of FIG.
And the inductance L between the terminals 3-4 are shown. The change in the inductance L due to the external magnetic field B is divided into regions I, II and III as shown in FIG. Inductance L changes according to external magnetic field B II
The area of can be widened or narrowed depending on the material, structure, preparation conditions, etc. of the superconductor 1. Therefore, what characteristics should be used may be determined depending on the application. For example, when the inductance L is changed in an analog manner with respect to the change in the external magnetic field B, the area II is preferably wide. In the case of a ceramic superconductor, the THJ critical surface has a certain thickness. Therefore, when a ceramic superconductor is used as the magnetic core, a variable inductance device having a wide range II can be obtained.
Further, when judging whether the value of the inductance is L ₁ or L ₃ depending on whether the strength of the external magnetic field B is larger or smaller than a certain value, the region II may be narrow.

The change in the inductance due to the change in the external magnetic field is changed by the current (hereinafter referred to as the magnetic core current) passed through the superconductor 1 as shown in FIG. FIG. 2A shows the relationship between the external magnetic field B and the inductance L when the magnetic core current I is used as a parameter. The larger the magnetic core current I is, the lower the magnetic field B is and the inductance L is changed. It is considered that this is because as the magnetic core current I increases, the action point of temperature-magnetic field-current moves to the outside of the T-H-J critical surface with a smaller magnetic field B.
FIG. 2B shows the relationship between the magnetic core current I and the inductance L when the magnetic field B is used as a parameter. The change in the inductance L with respect to the magnetic core current I shows almost the same tendency as the change in the inductance L with respect to the external magnetic field B.

From the above characteristics, the coil 2 having the superconductor 1 as the magnetic core is
The inductance can be changed by changing the magnitude of the external magnetic field B applied to the coil 2 and the magnetic core current I flowing through the magnetic core of the superconductor 1. In FIG. 2 (a) or 2 (b), the external magnetic field B and the current I are changed at the same time, but it is possible to change only one of them.

In the variable inductance device having the above configuration, the terminal 3-
Due to the current flowing between the four, a current that cancels this current flows in the superconductor 1. In order to prevent the current flowing through the superconductor 1, the structure of the magnetic core of the coil 2 may be set as follows. That is, the magnetic core shown in FIG.
Are formed in a plate shape, and the surfaces thereof are bonded together while being insulated from each other. In this case, since the amount of change in the inductance L with respect to the amount of change in the external magnetic field B changes depending on the direction of the external magnetic field B, a variable inductance device having a strong directivity can be obtained. The magnetic core shown in FIG.
A plurality of rod-shaped superconductors 22 are insulated and bundled. The magnetic core of this structure may be formed by forming an insulator layer on the surface of the rod-shaped superconductor 22 and solidifying the rod-shaped superconductor 22 having the insulator layer with an insulating substance. . Further, the magnetic core shown in FIG. 5 is obtained by winding a band-shaped superconductor 23 to insulate the layers. However, all the magnetic cores do not have to be formed in this way, and may be solid columnar ones or pipe-like ones depending on the application.

As described above, the coil having the superconductor according to the present invention as the magnetic core is a circuit element whose inductance can be changed by the external magnetic field B and the magnetic core current I as shown in FIG. The core current I may be direct current or may change with time). That is, as shown in FIG. 7, the coil 5 having the superconductor 7 as a magnetic core is attached to the magnet 6
The inductance L (B) changes as is approached. Moreover, the changing magnetic field B can be controlled by the magnetic core current I. Therefore, the inductance L (B) can be changed by the change of the magnetic field strength due to the change of the position or direction of the magnet 6. The inductance L (B) is the magnetic core current I.
It can also be changed by changing.

FIG. 8 (a) is an embodiment different from the above embodiment, in which an external magnetic field is generated by the coil 13. The coil 12 of the variable inductance device uses the superconductor 11 as a magnetic core as in the case of FIG. 1 and is cooled to a critical temperature Tc or lower with, for example, liquefied nitrogen. The power supply 14 is a power supply for generating an external magnetic field, and the coil 13 generates an external magnetic field B that changes according to the voltage from the power supply 14. Then, the inductance L (B) between the terminals of the coil 1 changes according to the change in the magnetic field strength of the coil 13. Therefore, the inductance can be changed according to the voltage from the power supply 14.

In the embodiment shown in FIG. 8B, the inductance L (I) is changed by changing the magnetic core current I flowing through the magnetic core of the superconductor. That is, the magnetic core current I is changed based on the signal from the power source 24, and the inductance L (I) between the terminals of the coil 12 is changed according to the magnetic core current I.

Here, the power source 14 in the embodiments of FIGS. 8 (a) and 8 (b) described above may be a direct current, a power source that changes with time, or a power source in which both are superposed. Further, FIG. 8 (a) and FIG. 8 (b)
The embodiments may be combined to change the external magnetic field B and the magnetic core current I at the same time to change the inductance.

The variable inductance device can change the inductance according to the changes in the external magnetic field and the magnetic core current as described above. This means that the strength of the external magnetic field can be measured by measuring the inductance of the coil of the variable inductance device under a known magnetic core current.

FIG. 9 shows a tank circuit using the variable inductance device as described above. The resonance frequency f (B) at the external magnetic field strength B and the magnetic core current I of this tank circuit is f
It is given by (B) = / (2π L (B) · C). Therefore, when such a tank circuit is applied to an oscillation circuit, if the coil of the oscillation circuit is placed at the magnetic field strength B and a magnetic core current I is passed through the magnetic core, this oscillation circuit responds to the magnetic core current I. It oscillates at a predetermined frequency f (B) (the magnetic core current I at this time may be zero). That is, from the oscillation frequency f (B) of this oscillation circuit, the magnetic field strength B at that location
Can know. Since the configuration of the above-mentioned oscillation circuit may be the same as that of the conventional technique, its details are omitted.
Here, in the case of detecting the change of the external magnetic field B in an analog manner by the change of the inductance L, II in FIG.
It is needless to say that the region of II may be narrow when the strength of the external magnetic field B is larger or smaller than a certain value. Further, by changing the value of the magnetic core current I, the measurement range of the magnetic field B can be freely selected. In this case, the magnetic core current I does not have to be direct current and may change with time.

Conventionally, when measuring the magnetic field strength, using a Hall element,
Since the measurement was performed by measuring the resistance value, only a low-precision measurement value was obtained. However, according to this method, since the change in the magnetic field strength can be measured as the change in the inductance, the magnetic field strength can be measured with high accuracy.

The oscillation circuit can process the oscillation signal as a digital signal by shaping the oscillation signal into a pulse. Also, by selecting an appropriate value for the oscillation frequency, an oscillation signal of oscillation frequency f (B) is radiated into the air by a simple antenna of the transmitter 15 and received by the wireless receiver 16 as shown in FIG. It is also possible.

A variable inductance device for generating an external magnetic field by a coil as shown in FIG. 8 (a) and a variable inductance device for changing magnetic core current as shown in FIG. 8 (b) are provided.
An oscillator is configured as the inductance L of the tank circuit. Then, the voltage signal of the power supply 14 can be FM-modulated. Further, in the wireless receiver in which the variable inductor device for generating an external magnetic field by the coil is the inductance L of the tank circuit, the receiving frequency can be freely controlled by the voltage of the power supply 14. Moreover, the measurable magnetic field range can be selected by the core current. Therefore, it is possible to detect a radio signal having an unknown frequency.

Further, by using the variable inductance device as a part of the filter circuit, the characteristics of the filter circuit can be easily controlled.

<Effects of the Invention> As is apparent from the above, in the variable inductance device of the present invention, the magnetic core of the coil is made of a superconductor, and the current changing means changes the current flowing through the superconductor to change the magnetic properties of the magnetic core itself. Since the inductance of the coil is changed by changing the characteristic, the operation is simple and the inductance can be changed at high speed.

Further, the magnetic field strength measuring device of the present invention includes a coil having a superconductor to which a known current is supplied from the outside as a magnetic core, and an inductance measuring unit for measuring the inductance of the coil, and measures the inductance of the coil. By doing so, the strength of the external magnetic field is measured, so that the magnetic field strength can be measured from a distance with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic view of a variable inductance device of the present invention,
2 (a) is a diagram showing the relationship between the external magnetic field strength and the inductors when the magnetic core current in the above embodiment is used as a parameter, and FIG. 2 (b) is the magnetic core when the external magnetic field is used as a parameter. Figure 3 showing the relationship between current and inductance
FIGS. 4, 5 and 5 are views showing an example of the structure of the magnetic core in the above embodiment, FIG. 6 is an explanatory view of the change of the inductance due to the change of the external magnetic field in the above embodiment, and FIG. 7 is the above embodiment. Showing an example of a method of changing the external magnetic field in
FIG. 8 (a) is a schematic view of an embodiment different from the above embodiment,
FIG. 8 (b) is a schematic view of a further different embodiment, FIG. 9 is a schematic view of a tank circuit using the variable inductance device, and FIG. 10 is an embodiment in which the tank circuit of FIG. 9 is incorporated in a transmitter. Fig. 11 is an explanatory view of the THJ critical surface,
FIG. 12 is a schematic diagram of a conventional variable inductance device. 1,7,11,21,22,23 …… Superconductor, 2,5,12,13 …… Coil, 3,4 …… Terminal, 6 …… Magnet, 14,24 …… Power supply, 15 …… Transmit Machine, 16 …… receiver.

Claims (2)

[Claims] 1. A coil comprising a superconductor as a magnetic core, and current changing means for changing a current flowing through the superconductor. The inductance of the coil is changed by changing the current. Variable inductance device. 2. A coil having a magnetic core of a superconductor to which a known current is supplied from the outside, and an inductance measuring means for measuring the inductance of the coil are provided, and the inductance of the coil is measured to measure the external magnetic field. A magnetic field strength measuring device characterized by measuring strength.