JPH06273500A - Magnetic measurement device using SQUID - Google Patents

Abstract

PURPOSE:To provide a magnetic measuring apparatus which can easily magnetically shield a SQUID element without influence to magnetism to be measured with excellent operability of measuring the magnetism even if a multichannel is employed. CONSTITUTION:A pickup coil 2 is inserted into a cryostat 4 provided separately from a cryostat 3 for cooling a SQUID element, and the coil 2 is connected to an input coil of the element 1 by a superconducting cable 6 passing through a tube 5 containing refrigerant to communicate the cryostat 3 with the cryostat 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field measuring device using an SQUID, which is suitable as a minute magnetic field measuring device for biomagnetic field measurement such as brain magnetic field measurement and cardiac magnetic field measurement.

[0002]

2. Description of the Related Art In a magnetic measurement device using an SQUID, generally, the magnetic flux to be measured is not directly picked up by the SQUID ring, but an input coil magnetically coupled to the SQUID and a superconducting connection with the input coil. An input circuit called a magnetic flux transformer, which is a superconducting closed loop composed of a pickup, is used, and the measured magnetic flux picked up by the pickup coil is SQU'ed through the input coil.
Transmission to the ID ring is often used.

As described above, the input coil is SQUI
Since it needs to be magnetically coupled to the D ring, it is usually formed on the same substrate as the SQUID ring and is connected to a separately provided pickup coil by a superconducting cable.

In such a measuring device, conventionally, as shown in the sectional view of FIG. 4, SQUI is formed on one substrate.
A SQUID element 41 having a D ring, an input coil and the like formed on a substrate, and a pickup coil 42 wound around a cylindrical bobbin and the like are placed in one common cryostat (usually a Dewar bottle) 43. It is arranged to cool them down to the superconducting temperature.

[0005]

By the way, in recent years, for example, in the measurement of a brain magnetic field, there is a strong demand for so-called multi-channels, in which a large number of combinations of such SQUID elements and pickup coils are provided. In such a case, a cryostat such as a Dewar bottle becomes large in size, which causes a problem that operability of magnetic measurement is limited.

Further, in order to reduce magnetic noise due to environmental magnetism other than the magnetism to be measured entering the SQUID ring, it is necessary to provide a magnetic shield to the SQUID element. Shielding distorts the magnetic field near the pickup coil,
There is also a problem that correct measurement cannot be performed.

The present invention has been made in view of such a situation, and even if the number of channels is increased, the operability of the magnetic measurement is good, and the S to be measured is easily exerted without affecting the measured magnetic field.
SQU capable of magnetically shielding the QUID element
The purpose is to provide a magnetic measurement device using an ID.

[0008]

In order to achieve the above object, in a magnetic measurement apparatus using an SQUID of the present invention, as shown in FIG. 1 which is an embodiment drawing, a pickup coil 2 is connected to an SQUID ring and an input. Coil (SQ
The UID element 1) is inserted into a cryostat 4 provided separately from the cryostat 3 for cooling, and the pickup coil 2 and the input coil thereof communicate with the respective cryostats 3 and 4 for cooling them, respectively. The structure is such that they are connected to each other by a superconducting cable 6 that passes through a tube 5 in which the refrigerant is stored.

[0009]

The SQUID element 1, the pickup coil 2, and the superconducting cable 6 are respectively provided with a cryostat 3 and
It is cooled to the superconducting temperature individually by the cryostat 4 and the tube 5. Then, the measured magnetic flux detected by the pickup coil 2 in the cryostat 4 is transmitted to the input coil of the SQUID element 1 in the cryostat 3 via the superconducting cable 6 in the tube 5.

The cryostat 4 for cooling the pickup coil 2 is reduced in size and weight as much as the SQUID element 1 need not be housed, resulting in improved operability of magnetic measurement. Further, as a result of the SQUID element 1 and the pickup coil 2 being separated, even if the SQUID element 1 and the superconducting cable 6 are magnetically shielded, the influence on the magnetic field in the vicinity of the pickup coil 2 can be eliminated. , The desired purpose can be achieved.

[0011]

1 is a schematic sectional view showing the structure of a basic embodiment of the present invention. In this basic example, one channel is shown to simplify the description.

The SQUID element 1 in which the SQUID ring, the input coil, and the feedback coil are laminated on the substrate is placed in a Dewar bottle 3 containing a coolant such as liquid helium while being supported by an appropriate support. Inserted and measured by superconducting cable 8 (not shown)
It is connected to the.

On the other hand, a pickup coil 2 formed by winding a superconducting cable around a bobbin is inserted in another Dewar bottle 4 which also contains a refrigerant. And this pickup coil 2 has two Dewar bottles 3
A tube 5 that connects between 4 and 4 and contains a refrigerant inside
With the superconducting cable 6 inserted inside, SQUID
It is connected to the input coil on the element 1.

As shown in the schematic enlarged sectional views (A) and (B) in the axial direction and the radial direction in FIG. 2, the tube 5 has two flexible tubes 51 and 52 made of, for example, a bellows tube made of stainless steel. The structure is such that the refrigerant and the superconducting cable 6 are accommodated in the inner flexible tube 51 and the vacuum heat insulating layer V surrounded by the flexible tube 52 is provided in the inner side of the flexible tube 51. It has a structure that minimizes the evaporation of the refrigerant.

The injection of the refrigerant into the tube 5 is performed by, for example, disposing the Dewar bottle 3 at a higher position than the Dewar bottle 4,
The refrigerant in the Dewar bottle 3 is caused to flow down to the Dewar bottle 4 through the tube 5 and equilibrated at an appropriate liquid level.
Alternatively, a refrigerant may be supplied from one of the Dewar bottles to the other side by a pump or the like to equilibrate the refrigerant at an appropriate position.

According to the structure of the embodiment of the present invention described above, only the Dewar bottle 4 accommodating the pickup coil 2 needs to be arranged close to the object to be measured W, which improves the operability and accommodates the SQUID element 1. In order to reduce the influence of environmental noise and the like on the entire Dewar bottle 3 and tube 5, even if a magnetic shield is applied by, for example, depositing a superconducting material on the inner wall of the refrigerant layer, the magnetic field around the pickup coil 2 is distorted. Never.

Here, a large number of SQUID elements 1 and pickup coils 2 are housed in the Dewar bottles 3 and 4, respectively, and each of them is connected by an individual superconducting coil 6, so that there are multiple channels and operability. Also, a magnetic measuring device having a good noise shielding property can be obtained.

The structure of the tube 5 is shown in FIG.
If the structures shown in (A) and (B) are schematic cross-sectional views in the axial direction and the radial direction, the evaporation of the refrigerant can be further suppressed.

That is, in this example, the flexible tubes 51, 52 and 53 have a three-layer structure, the superconducting cable 6 and the refrigerant are accommodated on the innermost side, the vacuum heat insulating layer V is formed on the outermost side, and in the middle thereof, Since the refrigerant gas layer G in which the evaporated gas of the refrigerant generated from the pickup coil 2 or the SQUID element 1 side flows is interposed, the amount of heat transferred from the outside to the innermost refrigerant is extremely small, and the evaporation amount of the refrigerant is minimized. be able to.

[0020]

As described above, according to the present invention,
The SQUID element and the pickup coil are housed in separate cryostats so that the pickup coil and the SQUID
The input coil of the ID element has a structure in which both cryostats are connected to each other and is connected by a superconducting cable arranged in a tube capable of containing a refrigerant therein. The cryostat for cooling the coil can be made smaller and lighter than the conventional one, and it is possible to prevent the measurement unit from becoming large even if the number of channels is increased.
The cryostat on the SQUID element side can be placed at any position, increasing the degree of freedom in layout and greatly improving the operability of measurement.

Since the SQUID element and the pickup coil are separated, the SQUID element, and
Even if a magnetic shield is applied to the superconducting cable that connects the pickup coil and the input coil, there is less risk of distorting the magnetic field around the pickup coil, so it is possible to provide a more sufficient magnetic shield than before. Therefore, it is possible to realize a minute magnetic measurement with less noise.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the configuration of a basic embodiment of the present invention.

FIG. 2 shows the detailed structure of the tube 5 in the axial direction (A).
And a schematic enlarged sectional view in the radial direction (B)

FIG. 3 is an explanatory view of the structure of a tube 5 according to another embodiment of the present invention, which is a schematic cross-sectional view in the axial direction (A) and the radial direction (B).

FIG. 4 is a cross-sectional view showing a configuration example of a conventional magnetic measurement device using SQUID.

[Explanation of symbols]

 1 SQUID element 2 Pickup coil 3,4 Dewar bottle 5 Tube 6 Superconducting cable 51,52,53 Flexible tube V Vacuum heat insulation layer G Refrigerant gas layer

Claims (1)

[Claims] 1. A magnetic measurement device comprising a SQUID ring and an input coil formed on a substrate, and a pickup coil for detecting a magnetic field to be measured is connected to the input coil, wherein the pickup coil has the SQUID. It is inserted into a cryostat that is provided separately from the cryostat that cools the ring and the input coil, and the pickup coil and the input coil pass through a tube that communicates with both the cryostats and that contains a refrigerant inside. A magnetic measurement device using SQUID, which is connected to each other by a conductive cable.