JP3291858B2 - Magnetic detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called multi-channel magnetism detecting device for detecting a magnetic field to be measured at a plurality of points using a plurality of SQUIDs, and for example, to measure weak magnetism such as biomagnetism with high accuracy. The present invention relates to a magnetic detection device suitable for the field.

[0002]

2. Description of the Related Art In the measurement of a brain magnetic field in biomagnetic measurement, it is necessary to detect a weak magnetic field from the brain at a plurality of points. In such a case, a multi-channel magnetic field using a plurality of SQUIDs is usually used. A detection device is used.

In such a measurement, it is necessary to remove the influence of a magnetic field from an external magnetic noise source in addition to the magnetic field to be measured. In this type of conventional device, one or more reference detecting units are provided in addition to a plurality of detecting units used for actual measurement to measure a magnetic noise component.

[0004] That is, as shown in FIG. 4 as an example of a configuration diagram of a detection unit of a conventional device, measurement pickup coils 41 for detecting a magnetic field to be measured are provided in the vicinity of an object W to be measured. The magnetism picked up by each of these S
In addition to measuring the magnetism at each point by guiding to a QUID ring (not shown), reference pickup coils 42 and 42 are provided separately from these, and the magnetism picked up by these is similarly guided to each SQUID ring. It measures external magnetic noise components. The magnetic noise component is removed by subtracting the magnetic data measured via the reference pickup coils 42 from the magnetic data measured via the measurement pickup coils 41.

[0005]

According to the above conventional apparatus, a reference detecting unit for measuring the magnetism from an external magnetic noise source is required, which not only complicates the apparatus, but also increases the complexity of the apparatus. However, when an external magnetic noise source is present near the magnetic field to be measured, the magnetic field from the noise source has a value in the space where the measurement detection unit is located and a value in the space where the reference detection unit is located. In some cases, the external magnetic noise elimination was incomplete.

The present invention has been made in view of such circumstances, and it is not necessary to particularly provide a detecting unit for reference, and even if the position of the magnetic noise source is closer than before, the adverse effect due to the magnetic noise component is present. It is an object of the present invention to provide a magnetic detection device capable of avoiding the problem.

[0007]

In order to achieve the above-mentioned object, a magnetic detecting apparatus according to the present invention includes a plurality of SQUIDs for measuring a magnetic field to be measured, each of which has a detection axis parallel to each other. And each SQUID
Calculating means for inputting a detection signal equally affected by the external magnetic noise detected by D and calculating an average value thereof;
It is characterized by having a correction means for subtracting the average value as a reference signal from the detection signal of each SQUID.

[0008]

The result of the magnetic detection by the measuring unit for measuring the magnetic field to be measured includes both the magnetic field to be measured and the magnetic field from the magnetic noise source. By arranging them in parallel, each detection unit is equally affected by the magnetic field from the magnetic noise source. Therefore, by averaging the magnetic detection results of the detectors arranged in this way and subtracting the value from the magnetic detection results of the detectors, the adverse effect from the magnetic noise component is canceled out, and only the contribution of the measured magnetic field is obtained. Can be extracted.

[0009]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of the present invention. Each of the plurality of magnetic measurement channels has a SQUID
It is composed of an element 10, a driving circuit 11 thereof, and a pickup coil 12.

[0010] Each SQUID element 10a.
In addition to the UID ring, an input coil magnetically coupled to the UID ring, a feedback coil connected to the drive circuit 11, and the like are provided.

Each of the pickup coils 12a.
For example, a first-order differential type gradiometer, each SQUA
A superconducting loop is formed together with the input coils in the ID elements 10a... 10n, and the input magnetic field is transmitted to the corresponding SQUID rings in the SQUID elements 10a. Each of these pickup coils 12a
.. 12n are arranged close to the measured object W whose generated magnetic field is to be measured, and their respective coil axes, that is, the detection axes are arranged in parallel with each other.

The drive circuits 11a... 11n are known circuits called magnetic flux lock circuits. For example, an AC current from an AF oscillator is fed through a feedback coil to apply an AC magnetic flux to the SQUID ring. The output of the pickup coil 12 is amplified and phase-detected in comparison with the reference signal from the AF oscillator, and is fed back to the SQUID ring via an integrating amplifier and a feedback coil.
It is possible to output an electric signal corresponding to the magnitude of the input magnetism to a..12n. Each drive circuit 11a... 11n
Are output from the A / D converters 13a,.
After being digitized by n, it is taken into the computer 14.

FIG. 2 is a flowchart showing the outline of the contents of the data processing in the computer 14, as shown in FIG.
Once stores in memory each of the driving circuits 11a the magnetic detection data elaborate taken from ·· 11n D _a ·· D _n, calculates the average value D _ave of the magnetic detection data D _a ·· D _n. Then, the average value D _ave is subtracted from each of the magnetic detection data D _a ... D _n , and the resulting values d _a ... D _n are stored as the magnetic measurement data for each channel.

The magnetic measurement data d _a ... D _n obtained as described above are, as described below, data of only the contribution from the DUT W in which the influence of the external magnetic noise has been offset. Become.

That is, each pickup coil 12a.
The magnetic field from the DUT at the 12n arrangement position is shown in FIG.
Assuming that the magnetic field has a distribution as shown in FIG. 3A, the magnetic field actually detected through each of the pickup coils 12a... 12n is changed as shown in FIG. It will be. Here, the pickup coils 12a... 12n are equally affected by extraneous magnetic noise because their detection axes are parallel to each other, and the magnetic field detected via each pickup coil 12a. A certain level of external magnetic noise is superimposed on the magnetic field from the measurement object W.

[0016] Thus, the value d _a · · d _n by subtracting the average value D _ave from the magnetic detection data D _a ·· D _n is 3
As shown in FIG. 3C, although the average value is slightly different from the actual magnetic field from the DUT shown in FIG. 3A, even if the contribution of extraneous magnetic noise is large, the average value is canceled out. Only the contribution of the measured object W is obtained.

Here, according to such a configuration and data processing, magnetic noise is substantially detected by the pickup coils 12a... 12n for measurement. In other words, magnetic noise is detected in the space to be measured. As a result, even if the magnetic noise source is somewhat close to the space to be measured, the effect can be eliminated.

In the above embodiment, the pickup coils 12a,..., 12n, which are primary differential gradiometers, are used as the magnetic detectors. However, the pickup coils may employ higher-order differential gradiometers. Alternatively, a magnetometer may be used, and the magnetism may be directly picked up by the SQUID ring itself without using a pickup coil.

[0019]

As described above, according to the present invention,
A plurality of SQUID detectors for detecting a magnetic field to be measured are arranged so that their detection axes are parallel to each other, and magnetic data equally affected by extraneous magnetic noise detected via the respective detectors. Are averaged, and the average value is subtracted from each magnetic data, so that there is no need to separately provide a reference SQUID and its detection unit as in the related art, and the apparatus is simplified,
Even if a magnetic noise source exists to some extent close to the space to be measured, since the magnetic noise is substantially detected in the space to be measured, it is possible to remove the influence of the magnetic noise.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a flowchart illustrating the contents of data processing by the computer 14;

FIG. 3 is a diagram illustrating the operation of the embodiment of the present invention.

FIG. 4 is a configuration diagram of a detection unit of a conventional multi-channel magnetometer.

[Explanation of symbols]

 10a..10n SQUID element 11a..11n Drive circuit 12a..12n Pickup coil 13a..13n A / D converter 14 Computer

Claims (1)

(57) [Claims] 1. A multi-channel magnetic detecting device for detecting a magnetic field to be measured at a plurality of points using a plurality of SQUIDs, wherein said detecting units of said SQUIDs are arranged with their respective detection axes parallel to each other. Calculating means for inputting a detection signal equally affected by the external magnetic noise detected by each SQUID and calculating an average value thereof; and using the average value as a reference signal for each of the above SQUIDs.
A magnetic detection device comprising a correction means for subtracting from a D detection signal.