JPH02198107A - Inductance variable superconducting inductor - Google Patents

Abstract

PURPOSE:To vary inductance in regard to a very small external magnetic field Hex by disposing a spiral coil on a flat plane of a core material made of the second superconductor formed in the form of a thin plate via an insulating film on an inductance variable superconducting inductor. CONSTITUTION:An inductance variable superconducting inductor includes a spiral coil disposed on a flat plane made of the second superconductor formed in the form of a thin plate via an insulating film. Therefore, even if an external magnetic source or an external magnetic field Hex applied by a coil is small, an effective magnetic field Heff inside a superconductor can be made larger than a lower section critical magnetic field Hc1. As a result, inductance can be made variable by a very small external magnetic field Hex. Since the rate of change of inductance to the change in the external magnetic field Hex can be increased, the inductance variable superconducting inductor can be made highly sensitive.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable inductance superconducting inductor whose inductance can be changed reversibly electromagnetically. The variable inductance superconducting inductor of the present invention includes, for example,
In addition to being applicable to high-sensitivity, wide-frequency-band magnetic sensors and various modulators, it can also be applied to detecting the superconducting state of superconductors. This magnetic sensor can be applied to a high-speed response sensor for detecting discharge current, which is difficult to detect with conventional magnetic sensors using amorphous, permalloy, or ferrite.

[Prior art] As a superconductor, its internal effective magnetic field
becomes completely diamagnetic and superconducting below the lower critical magnetic field Hc1, and when the upper critical magnetic field 1 is larger than the lower critical magnetic field Hc1,
A type 2 superconductor is known that becomes incompletely diamagnetic (mixed state) and superconducting under −IC2IX, and becomes paramagnetic and paraconductive at an upper critical magnetic field of 802 or more.

Proceedings of the 1986 Tokai Branch Conference of Electrical Associations,
Page 274, "Inductance of Ceramic Superconducting Core" by Nachi, Tetari et al., states that an inductor is constructed by winding a coil around a rod-shaped core material made of a second type superconductor, and a lower critical magnetic field 101 is connected to an upper critical magnetic field Hc2. The effective magnetic field He
It is described that when 1'f is changed, the inductance changes continuously.

[Problem to be solved by the invention] The above-mentioned effective magnetism! By using the correlation between 1IliLHeff and inductance, it is possible to estimate the effective magnetic field Heff, external magnetic field Hex, and superconducting state from changes in inductance. Further, by detecting the above inductance change, a magnetic sensor can be obtained, and in addition, a modulator can be obtained that modulates the alternating current signal current passed through the coil by the above inductance change.

However, if such a variable inductance element (hereinafter referred to as a variable inductance superconducting inductor) is considered ideally, ignoring its hysteresis characteristics,
Since the inductance change occurs only in the range where the effective magnetic field Heff is greater than or equal to the lower critical magnetic field Hc1 and less than the upper critical magnetic field HC2, the applied external magnetic field 1-1ex is small and the effective magnetic field Heff induced inside the core material by the external magnetic field HeX is There is a drawback that it cannot be used when the lower critical magnetic field H01 is smaller than the lower critical magnetic field H01.

The present invention was made in view of these problems, and an object of the present invention is to provide a highly sensitive variable-inductance superconducting inductor that can change its inductance in response to a minute external magnetic field HeX.

[Means for Solving the Problems] The variable inductance superconducting inductor of the present invention has a spiral coil disposed on the flat surface of a core material made of a second type superconductor formed into a thin plate via an insulating film. It is characterized by

This variable inductance superconducting inductor is mainly used in a lower critical magnetic field Hc1 or higher and an upper critical magnetic field IC2 or lower. The inductance of the variable inductance superconducting inductor is ideally O in the lower critical magnetic field 1-fcl, but in reality there is a leakage inductance LO. Also, the inductance is the upper critical magnetic field Hc2
In the vicinity, the saturation inductance LS (inductance of an air-core coil) in the normal conduction state of the core material is approximately reached.

Generally, LS is several times larger than LO, and the inductance changes continuously between LO and LS, ignoring hysteresis.

The core material can be formed by firing a thin plate of unfired material, or it may be formed by applying a paste to an insulating substrate and firing it.

In addition, PVD methods such as RF sputtering method and CVD
It can be formed by a method such as a method or a screen printing method. The thickness of the core material is preferably as thin as possible, and is preferably 1 mm or less, preferably several tens of μm or less. Type 2 superconductors include Y-Ba-Cu-0, [3i, la,
A T-based oxide superconductor may also be used.

The spiral coil is preferably carved from metal foil or a metal film by photolithography, but a thin metal wire or a superconducting wire can also be used.

The insulating film may be provided on the flat surface of the core material, or may be provided on the surface of the spiral coil.

[Effect] External magnetic field Hex magnetically or electromagnetically applied to the core material
As a result, an effective magnetic field Heff is generated inside the core material. When the effective magnetic field I-1e f is greater than or equal to the lower critical magnetic field HC1 and less than the upper critical magnetic field IC2, the inductance increases or decreases as the effective magnetic field Ieff increases or decreases.

This inductance change is caused by an increase in the ratio of the normal conductive part of the core material due to an increase in the effective magnetic field Heff, and an increase in the effective magnetic field Heff.
This is because the ratio of the superconducting portion of the core material increases as ff decreases.

The effective magnetic field 1-1eff generated in the core material depends not only on the external magnetic field Hex described above, but also on the demagnetizing field coefficient [)m based on the shape of the core material, and the larger the demagnetizing field coefficient Dm, the more the effective magnetic field 1-1eff 1eff becomes larger than the external magnetic field 1-(ex.

For example, B is the magnetic flux density inside the core material, μO is the magnetic permeability of the core material, Hdem is the demagnetizing field inside the core material, Heff is the effective magnetic field inside the core material, l-1ex is the external magnetic field applied to the core material, [
) If m is the demagnetizing field coefficient of the core material, the lower critical magnetic field HC
Near I, B= (μOHdem/Dm)+/fOHeff'=0
, Heff=Hex-1-1dem. Again, Heff+Hex/ (1-Dm> (1)).

From the above formula (1), the inventors have found that the closer the demagnetizing field coefficient Dm of the core material is to 1, the greater the effective magnetic field Heff can be compared to the external magnetic field Hex. Electromagnetically applied external magnetic field Hex
It has been found that even if the magnetic field is very small, the effective magnetic field 1-1eff can be sufficiently made equal to or higher than the lower critical magnetic field H01, and the inductance can be changed.

The demagnetizing field coefficient [)m is a coefficient larger than O and smaller than 1, and the thinner the core material is, the closer the demagnetizing field coefficient [)m is to 1, but the thinner the core material is, the more the effect on the core material is. Winding the coil becomes difficult and requires multiple winding of the coil. Multiple winding of the coil increases the gap between the coil and the core material, and an increase in the gap causes a decrease in the rate of change in inductance due to an increase in leakage inductance LO, which is not preferable.

The spiral coil used in the present invention is arranged on the flat surface of the core material with a thin insulating film interposed therebetween, and a sufficient number of turns can be ensured regardless of the thickness of the core material. Moreover, since the coil is in close contact with the flat surface of the core material through a thin insulating layer over the entire length of the coil, the leakage inductance L○ is reduced.

Furthermore, as can be seen from the above equation, as the demagnetizing field coefficient Dm approaches 1, the change in the effective magnetic field 1-1eff with respect to the change in the external magnetic field 1-(ex increases, and as a result, the rate of change in inductance increases. .

[Example] Example 1 An example of a variable inductance type superconducting inductor of the present invention will be explained with reference to FIGS. 1 and 2.

This inductor has a thin film-like core material 2 disposed on a flat surface of an insulating substrate 1, and a spiral coil 4 bonded to the flat surface of the core material 2 via an insulating film 3. A protective insulating film 5 is provided thereon.

The insulating substrate 1 is a magnesia substrate with a negative side of 2 cm and a thickness of 200 μm.

Core material 2 is YBa2 CU30 with a thickness of 2um? -Y thin film, and is formed by RF sputtering in a mixed gas of oxygen and argon at a substrate temperature of about 670°C.

The insulating film 3 is a silicon oxide film with a thickness of about 1 μm deposited on the flat surface of the core material 2 by plasma CVD.

The spiral coil 4 is an aluminum coil having approximately 250 turns with a line width of 5 μm, a thickness of 1 μm, and a pitch between adjacent lines of 20 μm, and is formed by photolithography from an aluminum film deposited by vacuum evaporation. . An output electrode portion 4 of approximately 100 square μm is provided at both ends of the spiral coil 4.
0.41 is provided by the same process as the spiral coil 4.

The protective insulating film 5 has a thickness of about 3μ and is deposited by CVD method.
The protective insulating film 5 on the output electrode portion 40.41 is opened and a gold wire 50.5 for output extraction is formed.
1 is wire bonded.

According to this embodiment, since the thickness of the core material 2 is small and the demagnetizing field coefficient [)m is large, the rate of change in inductance with respect to the external magnetic field 1-1 e x becomes high. Furthermore, since the spiral coil 4 is arranged by photolithography, the number of coils can be increased and the leakage inductance LO can be decreased, and the sensitivity of the negative layer can be increased.

Example 2 A variable inductance superconducting inductor according to another example is shown in FIG. However, the same components as in Example 1 are given the same reference numerals.

In this inductor, a spiral coil 4 made of tungsten is disposed on a flat surface of an insulating substrate 1 by photolithography, and an insulating film 5 made of a silicon oxide film is placed on the insulating substrate 1 so as to cover the surface of the spiral coil 4. is deposited on a flat surface.

A core material 2 is formed on the surface of the insulating film 5 by screen printing to surround the spiral coil 4. After firing the core material 2, a protective insulating film 7 made of silicon oxide is provided on the surface of the core material 2. The central part of the core material 2 is opened, and the insulating film 5 and protective insulating film 7 above this opening are opened using a photolithography method, and an aluminum bonding pad 8 is formed.
is provided by vacuum evaporation and photolithography. Similarly, a bonding pad (not shown) is also provided at the outer end of the spiral coil 4 (not shown).
Bonding wires 5 are attached to these bonding pads 8.
0 is crimped.

In this embodiment as well, the same effects as in the first embodiment can be achieved.

In addition to the above-mentioned embodiments, spiral coils 4 can be provided on both sides of the substrate 1 and connected using through-holes, each of which insulates a plurality of core members 2 each having a spiral coil 4. They may be stacked with the film 5 interposed therebetween. The spiral coil 4 can be formed into a rectangular coil shape, for example, in addition to a spiral shape, and a plurality of spiral coils can be arranged concentrically and used as a primary coil and a secondary coil.

The insulating substrate 1 is preferably made of a material having a relatively large coefficient of linear expansion, such as strontium titanate or zirconia.

(Application Example) A magnetic sensor using the variable inductance type superconducting inductor described above will be explained with reference to FIG. 4, which is a block diagram thereof.

One end of the signal line led out from the inductor 10 of Example 1 is grounded, and the other end is connected to the oscillation circuit 11 and the sense amplifier 1.
Connected to 2.

] The dragon circuit 11 has its predetermined internal output impedance Z
A minute current of 5 Mk to IZ is applied to the inductor 10 through the inductor 10. Its inductance is determined depending on the external magnetic field Hex. Then, a signal voltage is output to the sense amplifier 12 according to the ratio between the reactance X of the inductor 10, which is proportional to this inductance, and the internal output impedance Z, and the sense amplifier 12 amplifies and outputs the signal voltage. After the signal voltage amplified by the sense amplifier 12 is detected,
The data is transmitted to a predetermined processing circuit (not shown).

FIG. 5 shows a transformer type magnetic sensor.

In this magnetic sensor, an oscillation circuit 11 passes a minute high-frequency current to the primary coil of an inductor 13, and
The signal voltage output from the secondary coil of sense amplifier 1
It is amplified by 2.

[Effects of the Invention] As explained above, the variable inductance superconducting inductor of the present invention includes a spiral coil disposed on a flat surface of a second type superconductor having a die plate shape with an insulating film interposed therebetween. Therefore, even if the external magnetic field 1-1ex applied by the external magnetic source or coil is small, the effective magnetic field (-1eff) inside the superconductor can be made larger than the lower critical magnetic field HCI, and as a result, the minute external magnetic field Magnetic field Hex
The inductance can be made variable by
Since it is possible to increase the rate of change in inductance with respect to a change in the external magnetic field (external magnetic field) 1ex, it is possible to increase the sensitivity of the variable inductance type superconducting inductor.

Furthermore, even though the core material is made into a thin plate in order to increase the demagnetizing field coefficient [)m, it is possible to increase the number of turns of the coil and increase the inductance. The rate of change in inductance can be increased by reducing the leakage inductance LO through the insulating layer.

As a result of the above results, a highly sensitive variable inductance superconducting inductor can be realized.

When this variable inductance type superconducting inductor is used in a magnetic sensor, it is possible to detect a much smaller magnetic field than when a coil is wound around the outer circumference of the core material, and when used in a modulator, the inductance change rate with respect to the coil current can be detected. can be increased.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing the principle of the variable inductance superconducting inductor of the present invention, and FIGS. 2 and 3 are schematic cross-sectional views showing each embodiment of the variable inductance superconducting inductor of the present invention. FIGS. 4 and 5 are block diagrams of magnetic sensors using these variable inductance superconducting inductors, respectively. 1... Insulating substrate 2... Core material 3... Insulating film 4... Spiral coil 5... Protective insulating film

Claims (2)

[Claims] (1) A variable inductance superconducting inductor characterized in that a spiral coil is disposed on the flat surface of a core material made of a second type superconductor formed into a thin plate shape with an insulating film interposed therebetween. (2) A magnetic sensor comprising the variable inductance superconducting inductor according to claim 1 and a sense amplifier connected to both ends of the coil to detect an external magnetic field applied to the core material.