JP2726218B2 - 3D magnetic field detection coil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field detecting coil used as a pick-up coil or the like in a device for measuring a very weak magnetic field such as a SQUID magnetometer, and more particularly to a measurement of a cerebral magnetic field induced by a stimulus or the like in biomagnetic measurement. The present invention relates to a magnetic field detection coil suitable for, for example, the present invention.

[0002]

2. Description of the Related Art In a SQUID magnetometer for measuring an extremely weak magnetic field, a magnetic field to be measured is not picked up by a SQUID ring, but is called a magnetic flux transformer or the like which is a superconducting closed loop including a pickup coil and an input coil. It is often used to pick up through an input circuit.

As a pickup coil in such an input circuit, a monocoil (magnetometer) illustrated in FIG. 5A, a first-order differential coil (gradiometer) illustrated in FIG. 2 shown in (C)
There are secondary differential coils (secondary gradiometers) and the like.
The primary differential coil has two windings wound in opposite directions, and the secondary differential coil has two pairs of reverse windings, ie, front coil F, in the order of +,-,-, +.
A total of 4 of the 2-turn mid coil M and the rear coil R
It has a structure in which a wound coil is wound. A differential coil has a high effect of canceling noise, and the effect increases as the order of differentiation increases.

[0004] Of the above coils, monocoils and first-order differential coils are shown in FIG. 5 (A) or (B).
The three-dimensional detection type in which such coils are arranged around axes orthogonal to each other has been put to practical use, but the coil of the second derivative type has conventionally been provided with a vertical component (FIG. 5).
In most cases, only the one-dimensional type that measures only the direction of φ _in (C) is not practically used. This may cause a problem of crosstalk with respect to the horizontal component, or the winding of the wire may be difficult. However, in the case of the differential type coil, the measured object is generally placed on the front coil F as illustrated in FIG. This is because the idea of measuring in the direction of the baseline is the mainstream, and other measurement methods are not considered.

[0005]

However, the three-dimensional pickup coil of the first-order differential type and the second-order type of the pickup coil measuring only in the vertical direction have the effect of eliminating the noise as described above, thereby reducing the S signal of the detection signal. Although / N is good, there is a problem that it is difficult to specify the number and position of a plurality of current dipoles such as induced brain magnetic fields.

That is, as exemplified in FIG.
When a single current dipole is placed in the vertical measurement direction using a second-order differential coil, the detection signal becomes 0 immediately above the current dipole, and the position can be specified. As shown in FIG.
When two current dipoles are placed, the detection signal is the sum of those signals, and it is extremely difficult to specify the number and each position.

The present invention has been made in view of such circumstances, and provides a pickup coil capable of specifying the number and the position of each current dipole with high accuracy even if a plurality of current dipoles exist. It is an object.

[0008]

A structure for achieving the above object will be described with reference to FIGS. 1 to 3 which are drawings of an embodiment. The three-dimensional magnetic field detecting coil of the present invention has a low temperature resistance. Three axes Bγ, Bθ, B passing through the center of the bobbin 1 and orthogonal to each other are provided on the outer periphery of the bobbin 1 made of a material.
For each of φ, four grooves 11γ to 14γ, 11θ to 14θ, 11φ to 14φ are engraved in a loop shape around each axis Bγ, Bθ, Bφ and parallel to each other. And each of the grooves 11γ to 14γ, 1
Superconducting wires 2γ, 2θ, and 2φ are wound in four turns in the order of +,-,-, + for each axis, respectively, using 1θ to 14θ and 11φ to 14φ as guides. Attached.

[0009]

The structure of the present invention is a so-called three-dimensional secondary differential type in which coils of the secondary differential type are arranged not only in the vertical direction (Bγ axis direction) but also in the horizontal two axis directions (Bθ and Bφ axis directions). When a magnetic field is detected by arranging an object to be measured in the Bγ-axis direction using such a coil, FIG.
As shown in the example, the signal from each coil in two horizontal directions (Bθ axis direction, Bφ axis direction) has a characteristic that the signal level becomes maximum or minimum immediately above the current dipole.

Therefore, even if a plurality of current dipoles exist in the Bγ direction as shown in FIG. 1B or FIG. 1C, by focusing on the signals from the coils in the Bθ and Bφ axis directions, The number and each position can be specified.

[0011]

FIG. 1 is a perspective view showing the entire structure of an embodiment of the present invention, and FIG. 2 is a partially enlarged sectional view of the vicinity of the surface of a bobbin 1. As shown in FIG.

On the outer periphery of the bobbin 1 having a rectangular parallelepiped shape,
Four grooves 11γ to 14γ, 11θ to 14θ, and 11φ to 14φ parallel to each other are formed around three axes Bγ, Bθ, and Bφ passing through the center of the bobbin 1 and orthogonal to each other. Have been.

The grooves 11γ to 14γ, 11θ to 14
θ and 11φ to 14φ are shown in FIG.
As shown in the enlarged sectional view taking θ as an example,
And each of the grooves 11γ to 14
Along each of γ, 11θ to 14θ, and 11φ to 14φ, a superconducting wire 2 made of Nb-Ti is provided.
It is wound so that γ, 2θ, and 2φ are embedded.

The winding directions of the superconducting wires 2γ, 2θ, and 2φ are in the order of +,-,-, + from one end of each of the axes Bγ, Bθ, and Bφ.
Thus, a two-dimensional differential coil is formed along the outer circumference of the bobbin 1 in the directions of the axes Bγ, Bθ, and Bφ.

In this embodiment, since the Bγ direction is important in terms of the magnetic signal level, a bobbin shape is adopted such that the base line of the coil in the Bγ direction can be made longer than the other directions. 30mm x 30 depth x height
mm × 60 mm. In addition, each of the grooves 11γ to 14γ and 11θ to have a baseline of 28.6 mm in the Bγ direction and 14.0 mm in the Bθ and Bφ directions.
14θ and 11φ to 14φ are formed.

Here, the material of the bobbin 1 is a ceramic material which has good workability, withstands the liquid helium temperature at which the superconductivity of the superconducting wire used can be obtained, and has little deformation even at such a low temperature. For example, the product name is McCall). Preferably, the bobbin 1 is provided with, for example, about four mounting holes to reduce the heat capacity of the bobbin itself, absorb distortion due to low temperature, and the like.

The way of winding the superconducting wire corresponding to the mid-coil in each of the axes Bγ, Bθ and Bφ directions is as shown in FIG. The above-mentioned winding direction is obtained.

The use of the embodiment of the present invention described above will be described. Both ends of the coils in the directions of the axes Bγ, Bθ and Bφ are not shown, but superconducting coils provided corresponding to the respective axes are provided. It is connected to both ends of a body input coil. Then, the magnetic signal picked up by the coil in each axis direction is transmitted to the SQUID provided for each axis through each superconducting closed loop, and a magnetic measurement signal in each axis direction is obtained from each SQUID.

By using the magnetic measuring apparatus according to the embodiment of the present invention as described above, when performing high-sensitivity magnetic field measurement including cerebral magnetic field, for example, the right wrist and the right thumb
Even if a plurality of current dipoles are generated as in the case of an induced brain magnetic field for one stimulus, the number and positions of the current dipoles can be easily specified.

FIG. 4 is a graph showing the magnetic field detection characteristics of the Bθ and Bφ direction coils when a current dipole exists in the Bγ direction according to the embodiment of the present invention. The signal level will be maximum or minimum accordingly, and the number and location of the current dipole can be determined.

The measuring method using the three-dimensional second-order differential detection coil of the present invention utilizes the know-how for specifying the position and number of not only SQUID magnetometers but also fluxgate magnetometers. It is also effective for fields such as exploration of underground buried objects.

The shape of the bobbin in the three-dimensional secondary differential magnetic field detecting coil of the present invention is not limited to a rectangular parallelepiped as in the above-described embodiment, but may be a cube or a sphere.

[0023]

As described above, according to the present invention,
Since the secondary differential coil is applied in all three orthogonal directions, the signal from the horizontal two-axis coil which is not perpendicular to the magnetic field to be measured is focused on in the presence of a plurality of current dipoles. It is possible to easily specify the number and each position, especially in the measurement field such as induced brain magnetic field,
It has been confirmed that the method is effective for analyzing measured data of evoked magnetoencephalograms for two stimuli.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the overall configuration of an embodiment of the present invention.

FIG. 2 is a partially enlarged sectional view of the vicinity of the surface of the bobbin 1.

FIG. 3 is an enlarged view of a main part of the embodiment of the present invention.

FIG. 4 is a graph showing an example of a magnetic field detection characteristic of a coil in two horizontal axis directions according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram of each type of a magnetic field detection coil for SQUID.

FIG. 6 is a graph showing an example of a magnetic field detection characteristic of a conventional one-dimensional secondary differential coil.

[Explanation of symbols]

1 bobbins 11γ to 14γ, 11θ to 14θ, 11φ to
14φ groove 2γ, 2θ, 2φ superconducting wire Bγ, Bθ, Bφ orthogonal 3 axes

Claims (1)

(57) [Claims] 1. A second-order differential pickup in which a superconducting wire is wound in each direction in the order of +,-,-, + with a predetermined baseline, wherein a superconducting wire is wound around a bobbin made of a low temperature resistant material. Each axis is centered on each of three axes passing through the center of the bobbin and orthogonal to each other .
Four grooves are formed in a loop shape and are parallel to each other , and the superconducting wire is wound inside each of the four grooves for each axis in the above order using each groove as a guide. A three-dimensional magnetic field detection coil, characterized in that it is made.