JP2673284B2 - SQUID magnetometer calibration device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a SQUID (Supercon
ducting Quantum Interference Device: A calibration device for system calibration of a magnetic flux meter such as a SQUID magnetometer or a fluxgate that measures a magnetic field using a superconducting quantum interference device. Where S
A QUID is a DC current as a bias current applied to a SQUID loop, which is a superconducting loop that is maintained in a low temperature state in a heat insulating container (cryostat, Dewar, or the like) by liquid helium, liquid nitrogen, or the like and includes a Josephson junction in the loop. When a magnetic flux from the outside is coupled and applied to this SQUID loop via a pickup coil, an input coil, and the like, a circulating current is induced in the SQUID loop, and a quantum current in the Josephson junction in the loop is generated. This element measures a small change in magnetic flux by utilizing the fact that it operates as a transducer that converts a small change in the applied external magnetic flux into a large change in the output voltage due to the interference effect.

[0002]

2. Description of the Related Art Conventionally, as a calibration device for calibrating the relationship between the magnetic field strength to be measured and the output voltage value of the SQUID magnetometer, the vicinity of the SQUID magnetometer installed near the bottom of a heat insulating container such as Dewar. One circular coil or straight electric wire is installed in this, and a magnetic field is generated by applying a current from the control device to this circular coil or straight electric wire. From the current value at this time and the distance to the SQUID magnetometer, the SQUID magnetometer There is known a device that calculates a theoretical value of the magnetic field strength at a position and calibrates the magnetic field sensitivity of the SQUID magnetometer from the relationship with the output voltage value output from the SQUID magnetometer. The above SQUID magnetometer calibration device requires a calibration control device that applies a current to a circular coil or the like that generates a magnetic field for calibration. This calibration control device mainly uses a current supply source and a generated magnetic field control device. And a communication signal control unit.

[0003]

However, conventionally, all or part of the above-mentioned calibration control device is installed outside the magnetically shielded room (magnetically shielded room), and is different from the calibration device main body in the magnetically shielded room. It was a separate structure. For this reason, there are drawbacks that the configuration of the entire calibration device becomes complicated, and that noise is mixed through a cable or the like that sends a control current to the magnetic field generating coil or the like in the shield room. The present invention has been made to solve the above problems, and an object of the present invention is to provide a calibration device that can accurately calibrate the magnetic field sensitivity of an SQUID magnetometer with a simple configuration and low noise. .

[0004]

In order to solve the above-mentioned problems, a calibration device for an SQUID magnetometer according to a first invention of the present application generates a magnetic field whose installation position is known near the SQUID magnetometer to be calibrated. Means is provided, the output voltage of the SQUID magnetometer is measured when a known current having a known current value is applied to the magnetic field generation means by the current supply means, and the SQUID by the magnetic field generation means to which the known current is applied. The theoretical value of the magnetic field created at the position of the magnetometer is S
A calibration device for an SQUID magnetometer, wherein the SQUID magnetometer is calibrated by an arithmetic means so as to be equal to a measured value of an output voltage of the QUID magnetometer, wherein the SQUID magnetometer, the magnetic field generating means and the current supplying means are installed in a magnetically shielded room Is configured to be. In the above, the current supply unit may include a current supply source and a current control unit that controls a current value applied from the current supply source to the magnetic field generation unit. The SQUID according to the second invention of the present application
The calibration device of the magnetometer is the SQU to be calibrated.
A magnetic field generating means whose installation position is known is installed in the vicinity of the ID magnetometer, and when an electric current is applied to the magnetic field generating means by the current supplying means, the output voltage of the SQUID magnetometer is measured and known by the current supplying means. A SQUID magnetometer calibration device that calibrates by a computing means such that the theoretical value of the magnetic field created at the position of the SQUID magnetometer by the magnetic field generating means to which a current is applied becomes equal to the measured value of the output voltage of the SQUID magnetometer. Therefore, the information including the current value applied to the magnetic field generating means is converted into information regarding the application method of the current applied to the magnetic field generating means, detected by the SQUID magnetometer and sent to the computing means. Is configured as follows. Further, a calibration apparatus for an SQUID magnetometer according to a third invention of the present application installs a magnetic field generating means whose installation position is known in the vicinity of the SQUID magnetometer to be calibrated, and supplies a current to the magnetic field generating means. The output voltage of the SQUID magnetometer is measured and the theoretical value of the magnetic field created at the position of the SQUID magnetometer by the magnetic field generating means to which the known current from the current supply means is applied is the output of the SQUID magnetometer. A calibration device for a SQUID magnetometer, which calibrates by a calculation means so as to be equal to a measured value of a voltage, wherein information including a current value applied to the magnetic field generation means is converted into a magnetic signal by a magnetic communication means. It is configured to be transmitted, detected by the SQUID magnetometer, and transmitted to the computing means. In the above, the magnetic communication means may include communication control means for converting information into an electric signal, and magnetic signal sending means for converting an electric signal from the communication control means into a magnetic signal and sending the magnetic signal.

[0005]

The SQ according to the first invention of the present application having the above-mentioned structure is provided.
According to the calibration device of UID magnetometer, SQ
Since the magnetic field generating means for calibrating the UID magnetometer and the current supply means are magnetically shielded by the magnetic shield room, etc., as in the conventional case, from the current supply source outside the magnetic shield room to the calibration device main body inside the magnetic shield room. There is no need to wire cables, etc., and magnetic noise from the outside is prevented. Further, according to the SQUID magnetometer calibration device according to the second aspect of the present invention having the above-mentioned configuration, the information such as the control information such as the magnetic field generation current value applied to each magnetic field generating means is applied to the magnetic field generating means. SQU
Since it is detected by the ID magnetometer and sent to the calculation means,
Unlike the conventional case, it is not necessary to wire a cable or the like for transmitting a current value for calculation from inside the magnetic shield room to outside the magnetic shield room, and in this respect also, there is no possibility of picking up magnetic noise from the outside. Further, according to the SQUID magnetometer calibration device according to the third invention of the present application having the above-mentioned configuration, information such as control information such as a magnetic field generation current value applied to each magnetic field generation unit is controlled by the magnetic communication unit. Since it is converted into a signal and transmitted, detected by the SQUID magnetometer and sent to the computing means, a cable for transmitting a current value for computation is sent from inside the magnetic shield room to outside the magnetic shield room as in the conventional case. There is no need to wire to, and in this respect also there is no risk of picking up magnetic noise from the outside.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a SQUID magnetometer calibration device according to a first embodiment of the present invention. As shown in the figure, the SQUID magnetometer 1 for calibrating is installed in the dewar 2. The output of the SQUID magnetometer 1 is output from the SQUID output circuit 3 to the computer 4 which is the calculating means, and the output voltage value is monitored and recorded.

The above-mentioned SQUID magnetometer 1 is a SQUID magnetometer.
The magnetic flux input to the loop is converted to the magnetic flux voltage conversion coefficient dV / dΦ
(V: voltage, Φ: magnetic flux) is converted into an electric signal and output as a voltage. This magnetic flux voltage conversion coefficient dV / dΦ is equal to SQUA
The magnetic field sensitivity of the ID magnetometer 1 is shown.

A calibration device 5 is installed near the SQUID magnetometer 1. In the calibration device 5, magnetic field generating coils (circular coils) C1 to CN, which are a plurality of magnetic field generating means, are arranged. It is assumed that the individual coil positions of the magnetic field generating coils C1 to CN (for example, the vector amount from a predetermined origin) are known. The magnetic field generating coils C1 to CN are connected to the calibration control device 10 via cables.

In this embodiment, the calibration control device 10 is built in the calibration device 5, and the calibration control device 1
Calibration device 5 including 0 and SQU
The ID magnetometer 1 is housed in a magnetically shielded room (magnetically shielded room) so as to be magnetically shielded, and the SQUID magnetometer 1 is calibrated.

In the calibration controller 10, a current supply source 6 for supplying a current to each of the magnetic field generating coils C1 to CN,
A generated magnetic field controller 7 for controlling the current to each magnetic field generating coil C1 to CN is provided. Here, the current supply source 6 and the generated magnetic field control unit 7 constitute a current supply means. The generated magnetic field controller 7 corresponds to a current controller.
The current from the generated magnetic field control unit 7 is configured so that the current is sequentially applied to the individual magnetic field generation coils by the switching operation of a changeover switch (not shown).

In the calibration controller 10, control information such as the magnetic field generation current value (current value, frequency, waveform, etc.) applied to each of the magnetic field generation coils C1 to CN is transmitted to the computer 4. A communication signal controller 8 is provided to convert control information such as a magnetic field generation current value into a current value,
The electric signal from the communication signal control unit 8 is sent to the communication coil 9, converted into a magnetic signal, and sent out. This magnetic signal is detected and received by the SQUID magnetometer 1 and sent to the computer 4. Here, the communication signal control unit 8 and the communication coil 9 constitute a magnetic communication unit, the communication signal control unit 8 corresponds to the communication control unit, and the communication coil 9 corresponds to the magnetic signal transmission unit. .

With the above configuration, the SQU
The current supply source of the magnetic field generating coil for calibrating the ID magnetometer and the generated magnetic field controller can be built in the calibration device 5, and all of them and the SQUID magnetometer 1 can be housed in the magnetic shield room. , It is not necessary to wire a cable or the like from the current supply source outside the magnetic shield room to the calibration device main body inside the magnetic shield room, and the mixing of magnetic noise from the outside is prevented. Further, information such as control information such as a magnetic field generation current value applied to each magnetic field generation coil is converted into a magnetic signal by the communication signal control unit 8 and the communication coil 9 and transmitted.
Since it is detected by the D magnetometer 1 and sent to the computer 4, a cable or the like for transmitting control information such as a magnetic field generation current value applied to each magnetic field generation coil C1 to CN is provided in the magnetic shield room as in the conventional case. There is no need to wire from the outside to the magnetic shield room, and in this respect also there is no risk of picking up magnetic noise from the outside.

In this embodiment, the SQU is made by the following method.
The computer 4 estimates the parameters of the magnetometer position of the ID magnetometer 1 (for example, a vector amount from a predetermined origin), the detected magnetic field direction (for example, a unit vector in a predetermined direction), and the magnetic field sensitivity (scalar value). Do it.

First, the above N magnetic field generating coils C1 ...
The magnetic field generating coil Cj of CN is the SQUID magnetometer 1
The theoretical value of the magnetic field created at the position is calculated by the Biot-Savart law. Then, the theoretical value Vtheory of the output voltage of the SQUID magnetometer 1 is calculated from the theoretical value of the magnetic field generated by the magnetic field generating coil Cj at the position of the SQUID magnetometer 1.

Next, the theoretical value Vtheory of the output voltage of the SQUID magnetometer 1 and the measured output voltage of the SQUID magnetometer 1 actually output by the SQUID magnetometer 1 by the magnetic field generating coil Cj to which the current is applied are monitored by the computer 4. If the computer 4 calibrates Vpj to be equal, the actual magnetic field strength and the output voltage of the SQUID magnetometer 1 will correspond exactly. However, since the measured values actually vary, each parameter is searched using the numerical solution method such as the least square method.

Next, FIG. 2 shows a magnetic communication method in the calibration apparatus for the SQUID magnetometer, which is the second embodiment of the present invention. In the second embodiment, magnetic communication means such as the communication signal controller 8 and the communication coil 9 in the first embodiment is not provided. Instead, it is converted into information by a combination of magnetic field generation currents applied to the magnetic field generation coils C1 to CN, for example, time series information of magnetic field generation currents applied to the magnetic field generation coils C1 to CN, and the like. Control information such as a magnetic field generation current value (current value, frequency, waveform, etc.) applied to C1 to CN is transmitted to the computer 4. The example shown in FIG. 2 is a method of informing the computer 4 that a current is applied to the magnetic field generating coil C1 after the current is applied to the magnetic field generating coil C1 after the current is applied to the magnetic field generating coil C1. is there. In addition to this, the control information is converted into information on the current application method by changing the length of the rest period, the time interval of the current application to each magnetic field generation coil, the order, etc. to change the control information to the magnetic field generation coil. Magnetic communication can be performed using C1 to CN and SQUID1.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the claims of the present invention, and any device having the same function and effect can be realized by the present invention. It is included in the technical scope of the invention.

For example, although a plurality of circular coils are used as the magnetic field generating means in the above embodiment, the magnetic field generating means is not limited to this, and may be linear electric wires, or may be arranged in an array.

In the above embodiment, the information is converted into the information transmitted by the communication signal controller 8 and the communication coil 9, or the time series information of the magnetic field generating currents applied to the magnetic field generating coils C1 to CN. An example in which the information is control information such as a magnetic field generation current value (current value, frequency, waveform, etc.) applied to each magnetic field generation coil C1 to CN has been described, but the present invention is not limited to this, and other magnetic field measurement related It may be additional information.

[0020]

As described above, according to the calibration device of the SQUID magnetometer having the above-described structure according to the first invention of the present application, the magnetic field generating means and the current supplying means for calibrating the SQUID magnetometer are magnetic. Since it is magnetically shielded by the shield room etc., there is no need to connect cables etc. from the current supply source outside the magnetic shield room to the calibration device main body inside the magnetic shield room as in the past, and magnetic noise from the outside is mixed. Is prevented.
The SQU according to the second invention of the present application having the above configuration
According to the calibration device of the ID magnetometer, the information such as the control information such as the magnetic field generation current value applied to each magnetic field generation unit is converted into the information about the application method of the current applied to the magnetic field generation unit, and the SQUID magnetic flux. Since it is detected by the meter and sent to the calculation means, there is no need to wire a cable for transmitting the current value for calculation etc. from inside the magnetic shield room to outside the magnetic shield room as in the conventional case. There is no danger of picking up magnetic noise from the outside. Further, the S according to the third invention of the present application having the above configuration
According to the calibration device of the QUID magnetometer, information such as control information such as the magnetic field generation current value applied to each magnetic field generator is converted into a magnetic signal by the magnetic communication unit and transmitted, and detected by the SQUID magnetometer. It is not necessary to wire a cable or the like for transmitting a current value for calculation from inside the magnetic shield room to outside the magnetic shield room as in the conventional case, since it is sent to the calculating means. There is an advantage that magnetic noise is not picked up. Therefore, there is an advantage that the calibration device can be downsized, noise can be reduced, and operability can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a calibration apparatus for an SQUID magnetometer according to the present invention.

FIG. 2 is a diagram illustrating a magnetic communication method in a second embodiment of the calibration device for the SQUID magnetometer according to the present invention.

[Explanation of symbols]

 1 SQUID magnetometer 2 Dewar 3 SQUID output circuit 4 Computer 5 Calibration device 6 Current supply source 7 Generated magnetic field control unit 8 Communication signal control unit 9 Communication coil 10 Calibration control device C1 to CN Magnetic field generation coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takanori Komuro 2-1200 Takenishi Gakuendai, Inzai-cho, Inba-gun, Chiba Inside Superconducting Sensor Laboratory Co., Ltd. (72) Hisashi Kado 1-chome, Umezono, Tsukuba, Ibaraki No. 4 Naoki Nakatsuka, Examiner, Electronic Technology Research Institute, AIST

Claims (5)

(57) [Claims] 1. The SQUID magnetic flux when a magnetic field generating means whose installation position is known is installed in the vicinity of the SQUID magnetometer to be calibrated and a known current whose current value is known is applied to the magnetic field generating means by the current supplying means. Measure the output voltage of the meter,
The SQ by the magnetic field generating means to which the known current is applied
The theoretical value of the magnetic field created at the position of the UID magnetometer is the SQUI
A calibration device for a SQUID magnetometer, which is calibrated by an arithmetic means so as to be equal to a measured value of an output voltage of a D magnetometer, wherein the SQUID magnetometer, the magnetic field generating means, and the current supplying means are installed in a magnetically shielded room. S that is characterized by
Calibration device for QUID magnetometer. 2. The current supply means comprises a current supply source and a current control means for controlling a current value applied from the current supply source to the magnetic field generation means. SQUID magnetometer calibration device. 3. A magnetic field generating means having a known installation position is installed near the SQUID magnetometer to be calibrated, and the SQ is applied when a current is applied to the magnetic field generating means by a current supplying means.
Measure the output voltage of the UID magnetometer and use it for the current supply means.
The SQ by the magnetic field generating means known current is applied by
The theoretical value of the magnetic field created at the position of the UID magnetometer is the SQUI
A calibration device for a SQUID magnetometer, which calibrates by an arithmetic means so as to be equal to a measured value of an output voltage of a D magnetometer, wherein information including a current value applied to the magnetic field generator is stored in the magnetic field generator. A calibration device for an SQUID magnetometer, which is converted into information on an application method of an applied current, detected by the SQUID magnetometer, and sent to the arithmetic means. 4. A magnetic field generating means having a known installation position is installed near the SQUID magnetometer to be calibrated, and the SQ is applied when a current is applied to the magnetic field generating means by a current supply means.
The output voltage of the UID magnetometer is measured, and the SQ is generated by the magnetic field generation means to which the known current is applied by the current supply means.
The theoretical value of the magnetic field created at the position of the UID magnetometer is the SQUI
A calibration device for a SQUID magnetometer, which calibrates by an operating means so as to be equal to a measured value of an output voltage of a D magnetometer, wherein information including a current value applied to the magnetic field generating means is magnetic by a magnetic communication means. A calibration device for an SQUID magnetometer, which is converted into a signal, transmitted, detected by the SQUID magnetometer, and transmitted to the computing means. 5. The magnetic communication means includes communication control means for converting information into an electric signal, and magnetic signal sending means for converting an electric signal from the communication control means into a magnetic signal and sending the magnetic signal. The SQ according to claim 4, characterized in that
Calibration device for UID magnetometer.