JPH08226959A - Magnetic detector - Google Patents

Abstract

PURPOSE: To provide a multichannel type magnetic detector in which the influence of a magnetic noise source can be effectively removed even if the position of the source is relatively near to a space to be measured without particularly using a high-order differential gradiometer and without providing a reference SQUID. CONSTITUTION: The detection signals of at least three SQUIDs of SQUID detectors 12(1) to 12(n) for measuring with known position and direction are used, and hence the magnetic vector components of the spaces in which they are disposed can be calculated by calculating means 14b. The vector components corresponding to the positions and the directions of the detectors 12(1) to 12(n) of the SQUIDs can be calculated from the calculated results. The results are subtracted from the signals of the SQUIDs by correction calculating means 14c, thereby removing the magnetic noise components.

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 magnetic detection device for detecting a magnetic field to be measured at a plurality of points by using a plurality of SQUIDs, for example, for measuring weak magnetism such as biomagnetism with high accuracy. The present invention relates to a magnetic detection device suitable for a field.

[0002]

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

By the way, in such 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. As a countermeasure against this, in a conventional device of this type, a higher-order differential gradiometer is used as a pickup coil which is a detection unit of each SQUID, or a plurality of SQUIDs used for actual measurement are used.
In addition to D, one or more SQUIDs for reference are provided to measure the magnetic noise component, and the measurement result is subtracted from the output of each SQUID used for actual measurement to remove the magnetic noise component. ing.

[0004]

Among the conventional countermeasures for removing magnetic noise as described above, the former method using a high-order differential gradiometer has a drawback that the apparatus becomes more complicated. In addition, the latter method of separately providing the reference SQUID requires not only an additional reference device but also a measurement SQUID when the magnetic noise source exists near the magnetic field to be measured. There is a case where the influence from the noise source is greatly different between the space in which the detection unit is located and the space in which the reference SQUID detection unit is located, resulting in incomplete removal of external magnetic noise.

The present invention has been made in view of the above circumstances, and in particular, the position of the magnetic noise source is relatively high without using a high-order differential type gradiometer and without providing an SQUID for reference. It is an object of the present invention to provide a magnetic detection device capable of reliably removing the influence even when it is close to the space to be measured.

[0006]

In order to achieve the above-mentioned object, the magnetic detection device of the present invention is arranged so that the detection units 12 (1) ... 12 (n) of each SQUID for measurement are respectively arranged at respective positions. The direction of the detection axis is arranged in a known state, and each S
Each of the SQUIDs is calculated by using the calculation means 14b that calculates the vector component of the detected magnetism from the detection signals of at least three SQUIDs among the QUIDs and the calculation result.
The magnetic vector components corresponding to the positions and directions of the individual detectors 12 (1) ... 12 (n) of are calculated, and the calculation results are subtracted from the individual detection signals of each SQUID to obtain the magnetic noise components. It is characterized by having a correction calculation means 14c for removing the.

[0007]

[Operation] Detection unit 12 (1) ... 12 of each SQUID for measurement
The magnetism detected by (n) includes both magnetism from the magnetic source to be measured and magnetism from the magnetic noise source.
(1) ... 12 (n) are farther away, so it is considered that each of these detectors 12 (1) ... 12 (n) receives a substantially equal magnetic field from the magnetic noise source. be able to.

Therefore, at least 3 positions and directions are known.
When the vector component of the detected magnetism is calculated using the detection signals from the one detector, the result of the calculation is the average magnetic field present in the space where three or more detectors used for the calculation are placed. It is data that represents the size and direction. From this data, magnetic vector components corresponding to the positions and directions of the individual detection units 12 (1) ... 12 (n) are calculated, and the calculation result is subtracted from the detection result by each SQUID, The influence of the magnetic noise component is removed, and only the contribution of the magnetic field to be measured can be extracted.

[0009]

FIG. 1 is a schematic diagram showing the structure of an embodiment of the present invention.
An example in which the present invention is applied to an n-channel first-order differential magnetometer is shown.

Each of the plurality of magnetic measurement channels is S
It is composed of a QUID element 10, a drive circuit 11 for the QUID element 10, and a pickup coil 12. Each SQUID
The elements 10 (1) ... 10 (n) are, in addition to the SQUID ring, an input coil magnetically coupled to the SQUID ring and a feedback coil connected to the drive circuits 11 (1) ... 11 (n). And so on.

Each pickup coil 12 (1) ... 12 (n)
Is, for example, a first-order differential type gradiometer, and each S
SQUIDs in the SQUID elements 10 (1) ... 10 (n) that form a superconducting closed loop with the input coils in the QUID elements 10 (1) ... 10 (n) Communicate to the ring. These pickup coils 12 (1) ... 12 (n) are arranged close to the object to be measured W (magnetic source to be measured), and their positions and the direction of the coil axis (detection axis) are Each is known.

The drive circuits 11 (1) ... 11 (n) are known circuits called magnetic flux lock circuits. For example, an AC current from an AF oscillator is passed through a feedback coil to cause SQUID.
An AC magnetic flux is applied to the ring, the output of the SQUID ring in that state is amplified, phase detection is performed in comparison with the reference signal from the AF oscillator, and this is further fed back to the SQUID ring via an integrating amplifier and a feedback coil. With such a configuration, it is possible to output an electric signal corresponding to the magnitude of input magnetism to the corresponding pickup coils 12 (1) ... 12 (n). Each drive circuit 11
The output signals from (1) ... 11 (n) are digitized by the AD converters 13 (1) ... 13 (n), respectively, and then taken into the computer 14.

The computer 14, as shown in the block diagram of its function in FIG.
The magnetic vector D _mx ′ in the measurement space is calculated by the memory 14a for storing the magnetic detection data D ₁ ... D _n from the UID and the calculation described later using the contents of the memory 14a.
An arithmetic unit 14b for calculating D _my ′, D _mz ′ and the individual pickup coils 12 (1) ... 12 (n) based on the arithmetic result.
Output data D ₁ ′ ·· D _n ′ corresponding to the position and direction of
Is calculated, and each value is calculated as the individual actual magnetic detection data D ₁
..Correction calculation unit 1 that removes noise components by subtracting from D _n
4c.

FIG. 2 is a flow chart showing the outline of the contents of data processing by the computer 14. The operation of the embodiment of the present invention will be described below with reference to this figure. First, each A
The magnetic detection data D ₁ ... D _n by each SQUID of ₁ to n channels digitized by the -D converters 13 (1) ... 13 (n) are sampled and stored in the memory 14a such as a RAM. . Next, from the data in the memory 14a, 1
For each of the channels n to n, magnetic vectors are calculated near the positions where the pickup coils 12 (1) ... 12 (n) are arranged. That is, for example, the SQUI of the m-th channel
When the magnetic detection data by D is D _m, and the channels having pickup coils near the m-th channel pickup coil 12 (m) are m + 1, m + 2, m + 3 ..., SQUI of at least three channels.
From the magnetic detection data D _{m + 1,} D _{m + 2,} D _{m + 3} ··· _by D, an approximate magnetic vector component D _mx existing near the arrangement position of the m-th channel pickup coil 12 (m) ′, D
It is possible to calculate _my ′ and D _mz . The vector components D _mx ′ _, D _my ′ _, D _mz ′ are m + 1 and m described above.
The data represents the average magnitude and direction of the magnetic field existing in the space where the pickup coils of channels +2, m + 3 ...

Next, the vector components D _mx ′ _, D _my ′ _,
D _mz ′ to m-th channel pickup coil 12
The magnetic component D _m ′ in the position and direction of (m) is calculated. Then, the value of D _m ′ is subtracted from the actual detection data D _m by the SQUID of the mth channel. The value d _m after this subtraction is the m-th channel pickup coil.
It is the difference between the actual magnetic data picked up by (m) and the detection data obtained by virtually detecting the magnetism that exists evenly in the space near the pickup coil 12 (m) at the same position and direction. , This is equivalent to a software implementation of a higher-order differential gradiometer in which the contribution of extraneous magnetic noise is smaller.

The above processing is applied to all data of the first to n-th channels. That from the measured data D ₁ to D _n for each channel, we obtain the value d ₁ to d _n by subtracting the respective virtual detection data D ₁ '~D _n' calculated as above, the respective values Sequentially stored as magnetic detection data.

In the space near the channel of interest,
Vector component of magnetic field D_mx′_,D _my′_,D_mzFor ′
In order to do this, at least three
Channel output required, 4 channels or more
To find this vector from the output above,
The channel is the output of the channel m of interest,
Good.

Further, in the above embodiments, the first-order differential type gradiometer is used as the detection unit (pickup coil) of each SQUID, but a higher-order differential type gradiometer may be adopted as the pickup coil. However, it may be a magnetometer, and further, the SQUID ring itself may directly pick up the magnetism without using a pickup coil.

[0019]

As described above, according to the present invention,
A plurality of SQUID detectors are arranged with their positions and directions being known, and each SQUID
An average magnetic vector component of the measurement space is calculated from the magnetic signal detected by, and the vector component is used to calculate a component corresponding to the position and direction of the detection unit of each SQUID detection unit. However, since the calculation result is subtracted from the actual detection result by each SQUID to correct the external magnetic noise, it is not necessary to use a complicated higher-order differential gradiometer as in the conventional case. Further, it is not necessary to provide a dedicated SQUID for reference, and the device configuration is simplified. Moreover, since the magnetic noise to be corrected is substantially averagely measured in the measured space, even if the magnetic noise source is close to the measured space to some extent, compared to the case where the conventional reference SQUID is provided. Thus, the magnetic noise can be removed with higher accuracy.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing an outline of the contents of data processing by the computer 14.

[Explanation of symbols]

 10 (1) ・ ・ ・ 10 (n) SQUID element 11 (1) ・ ・ ・ 11 (n) Drive circuit 12 (1) ・ ・ ・ 12 (n) Pickup coil 13 (1) ・ ・ ・ 13 (n) A / D converter 14 Computer 14a Memory 14b Calculation unit 14c Correction calculation unit

Claims (1)

[Claims] 1. A multi-channel magnetic detection device for detecting a magnetic field to be measured at a plurality of points by using a plurality of SQUIDs, wherein the detectors of the respective SQUIDs are arranged with their positions and directions of detection axes known. And each of the SQUIDs has at least three SQUIDs
From the detection signal by the ID, the calculation means for calculating the detected magnetic vector component and the calculation result are used to calculate the magnetic vector component corresponding to the position and direction of the individual detecting portion of each SQUID, The calculation result is used for each SQ
A magnetic detection device comprising: a correction calculation unit that removes a magnetic noise component by subtracting from each detection signal of a UID.