JPH0675030A - Magnetic field measuring apparatus - Google Patents

Abstract

PURPOSE:To provide a magnetic field measuring apparatus employing SQUID for a plurality of channels in which intrusion of heat from normal temperature side into low temperature side is reduced drastically. CONSTITUTION:A glass window 1a is formed at a predetermined position on the side wall of a cryostat 1 and output voltage from each SQUID ring 2 is applied through an amplifier 5 onto a light emitting diode 6. Light emitted from the LED 6 is passed through an optical fiber cable 7a laid on the outside of the glass window 1a and received by a photodiode 7b where the light is converted into an electric signal and fed to an FLL circuit 7c.

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,
More specifically, a superconducting quantum interference device (Super)
conducting Quantum Interf
erenceDevice (hereinafter abbreviated as SQUID)) and a device for measuring a magnetic field using a magnetic flux lock loop circuit.

[0002]

2. Description of the Related Art Conventionally, a magnetic field measuring apparatus using SQUID has been proposed, paying attention to the characteristic that a weak magnetic field can be detected with high sensitivity. Also, in recent years, two Josephson junctions are interposed in a superconducting loop, so-called d
c-SQUID is widely adopted. This dc-SQ
When magnetic field measurement is performed using UID, a magnetic flux lock loop circuit (hereinafter, abbreviated as FLL circuit) is used because it has a characteristic that the output voltage changes periodically according to the fluctuation of the magnetic field. By supplying a feedback current to the feedback coil in order to compensate the fluctuation of the external magnetic field, the SQUID is operated at a predetermined operating point (specifically, voltage-
The external magnetic field measurement result can be obtained by locking at the peak point of the magnetic flux characteristic) and monitoring the output signal from the FLL circuit.

[0003]

In the above conventional magnetic field measuring apparatus, since the SQUID, the input coil, the feedback coil, etc. must be cooled to the superconducting transition temperature or lower, liquid helium, a cryogenic refrigerator, etc. are used. Although it will be cooled to below the superconducting transition temperature by the cryostat, the bias circuit for SQUID, FL
Since the L circuit and the like are arranged in a room temperature atmosphere, electrical wiring for connecting these circuits arranged in a room temperature atmosphere, the SQUID housed inside the cryostat, and the feedback coil is extended from the room temperature atmosphere to the inside of the cryostat. Are provided.

Therefore, heat penetrates into the cryostat from the room temperature side through the electrical wiring and affects the refrigerating capacity. That is, when the SQUID for one channel, the input coil, the feedback coil, etc. are housed inside the cryostat, three pairs of electrical wiring (electrical wiring for bias supply to the SQUID, signal extraction from the SQUID) And electrical wiring for supplying a feedback current to the feedback coil) are required. However, when measuring a biomagnetic field or the like, SQUIDs for a plurality of channels are stored inside the cryostat, Since the input coil, the feedback coil, etc. will be accommodated, the number of electrical wirings will increase in proportion to the number of channels, and the amount of heat entering the cryostat will also increase in proportion to the number of electrical wirings. The number of channels that can be accommodated inside the cryostat will increase. There is a disadvantage that is restricted. Further, if the number of channels is increased, there is a disadvantage in that the cooling capacity of the cryostat has to be remarkably increased.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a magnetic field measuring apparatus capable of increasing the number of channels that can be accommodated without increasing the cooling capacity. .

[0006]

In order to achieve the above object, a magnetic field measuring apparatus according to claim 1 has a plurality of channels of SQUID rings including Josephson junctions, and each SQUID.
Coil for introducing external magnetic flux to D ring and each SQUI
The coil that introduces the magnetic flux that compensates for the change of the external magnetic flux into the D ring is housed in the casing cooled below the superconducting transition temperature, and the SQUID is placed outside the casing.
A bias supply circuit and a magnetic flux lock loop circuit for the ring are arranged, and at least the space between each SQUID ring and the corresponding magnetic flux lock loop circuit is housed inside the casing. Is connected via a signal transmission path including the optical-electrical conversion means arranged in the above and a light transmission member provided at a predetermined position of the casing.

[0007]

According to the magnetic field measuring device of the first aspect, the bias supply circuit and the magnetic flux lock loop circuit arranged on the room temperature side, the SQUID and the feedback coil arranged inside the casing cooled below the superconducting transition temperature. When electrically connecting and, a light transmitting member is provided at a predetermined position of the casing, and an electric
By arranging the optical conversion means and the optical-electrical conversion means directly or indirectly in a facing state, at least each SQUID
Since the signal transmission path between the ring and the corresponding magnetic flux lock loop circuit is configured, there is no intrusion heat amount in the conventional signal transmission path,
The number of channels that can be accommodated can be increased if the cooling capacity is the same as that of the conventional magnetic field measuring device. On the contrary, if the same number of channels as the conventional magnetic field measuring device is required, the cooling capacity can be lowered.

Further, if the present invention is applied between each SQUID ring and the magnetic flux lock loop and between each feedback coil and the magnetic flux lock loop, electric wiring for bias supply can be made common to all channels. Therefore, even if the number of channels increases, the amount of heat entering through the electrical wiring does not change.

[0009]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 1 is an electric circuit diagram showing an essential part of an embodiment of a magnetic field measuring apparatus of the present invention. Inside a cryostat 1 cooled to a temperature below a superconducting transition temperature by a cryogenic refrigerator (not shown), three channels are included. The SQUID ring 2, the input coil 3 and the feedback coil 4 are arranged, and the output voltage of each SQUID ring 2 is applied to the light emitting diode 6 via the amplifier 5.
Then, these light emitting diodes 6 are connected to the cryostat 1.
The side wall is positioned so as to face the glass window 1a formed at a predetermined position. In addition, one end of the optical fiber cable 7a is positioned outside the cryostat 1 at a predetermined position facing each light emitting diode 6, and the other end of each optical fiber cable 7a faces the photodiode 7b. It is positioned. The output signal from each pair of the photodiodes 7b is supplied to the corresponding FLL circuit 7c, and the feedback wiring 7d for supplying the feedback current output from each FLL circuit 7c to the corresponding feedback coil 4 is provided at a predetermined position on the side wall of the cryostat 1. It is arranged via the connector 7e provided in the. In addition, all the SQUID rings 2 are provided by the constant current source 8a disposed outside the cryostat 1.
A pair of bias current supply wirings 8b for supplying a predetermined bias current are arranged via a connector 8c provided at a predetermined position on the side wall of the cryostat 1, and all of the pair of bias current supply wirings 8b are provided. SQUID rings 2 of are connected in parallel with each other. Further, the voltage source 9a
Thus, the amplifier driving power supply wiring 9b for applying a predetermined bias voltage to all the amplifiers 5 is arranged via the connector 9c provided at a predetermined position on the side wall of the cryostat 1. A magnetic field measurement signal is output from each FLL circuit 7c.

The operation of the magnetic field measuring device having the above configuration is as follows. When a predetermined bias current is supplied to all SQUID rings 2 via a pair of bias current supply wirings 8b, the SQUIDs detected by a pickup coil (not shown) and corresponding to the SQUIDs by the input coil 3 are shown.
If the magnetic flux guided to the ring 2 changes, the output voltage from the SQUID ring 2 corresponding to the change in the magnetic flux is applied to the light emitting diode 6 in the state of being amplified by the amplifier 5, so that it corresponds to the output voltage from the SQUID ring 2. The intensity of light is output. This light is transmitted through the glass window 1a and the corresponding optical fiber cable 7a to the photodiode 7
It is guided to b, converted into an electric signal, and supplied to the FLL circuit 7c. Then, a feedback current is output in the FLL circuit 7c in order to compensate for the change in the external magnetic flux and is supplied to the feedback coil 4 via the feedback wiring 7d, so that the change in the external magnetic flux is compensated for and the SQUID.
The magnetic flux introduced into the ring 2 can be kept constant. The external magnetic flux can be measured by monitoring the output signal from the FLL circuit 7c.

As is clear from the above description, SQUI
Since the middle of the path for transmitting the output voltage of the D ring 2 to the FLL circuit 7c is composed of the optical signal transmission path that optically couples through the glass window 1a of the cryostat 1, the electrical wiring is connected to the side wall of the cryostat 1. Since there is no invasion of heat due to the penetration of the magnetic field, the amount of heat entering the inside of the cryostat through the electrical wiring can be significantly reduced in the entire magnetic field measuring apparatus. Specifically, if the number of electrical wirings that cause heat from the room temperature side is (4n
+4) (however, n is the number of channels)
The number was reduced to (n + 4). As a result, the number of channels that can be accommodated can be increased without increasing the refrigeration capacity. On the contrary, if it is not necessary to increase the number of channels, the refrigerating capacity can be reduced.

Further, in the cryostat 1 using the cryogenic refrigerator, a plurality of cooling stages are provided so that the cryogenic temperatures are sequentially generated from the low temperature. Therefore, as shown in FIG. Position corresponding to a relatively high temperature cooling stage, and further, the light emitting diode 6 is arranged on the radiation shield 6a, and the radiation shield 6a is attached to the thermal anchor 6 with respect to the corresponding cooling stage.
It is preferable to perform thermal coupling by b, and the disadvantage caused by forming the glass window 1a can be eliminated. Further, by providing the filter 1b as shown by the broken line in FIG. 2 to prevent the invasion of light having an unnecessary wavelength, it is possible to more reliably eliminate the inconvenience caused by forming the glass window 1a.

The present invention is not limited to the above embodiment, and the light emitting diode 6 and the photodiode 7b can be directly opposed to each other through the glass window 1a without interposing an optical fiber cable. In addition to the above, it is possible to apply a configuration in which the light emitting diode and the photodiode are directly opposed to each other to the feedback wiring 7d directly or indirectly via the glass window 1a, and the scope of the present invention is not changed. It is possible to make various design changes within.

[0014]

As described above, according to the first aspect of the invention, the number of electric wirings that cause heat to enter from the room temperature side to the region below the superconducting transition temperature can be significantly reduced, and the refrigerating capacity can be increased. There is a unique effect that the number of channels can be increased without performing the operation, and conversely, the refrigerating capacity can be reduced without reducing the number of channels.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a main part of an embodiment of a magnetic field measuring apparatus of the present invention.

FIG. 2 is a vertical cross-sectional side view showing the relationship between a light emitting diode and a glass window in detail.

[Explanation of symbols]

 1 Cryostat 1a Glass Window 2 SQUID Ring 3 Input Coil 4 Feedback Coil 5 Amplifier 6 Light Emitting Diode 7b Photodiode 7c FLL Circuit 8a Constant Current Source

Claims (1)

[Claims] 1. A SQUID ring (2) for a plurality of channels including a Josephson junction, a coil (3) for introducing an external magnetic flux into each SQUID ring (2), and each SQ.
A coil (4) for introducing a magnetic flux that compensates for a change in the external magnetic flux into the UID ring (2) is housed in the casing (1) cooled to a temperature below the superconducting transition temperature, and also outside the casing (1). A bias supply circuit (8a) and a magnetic flux lock loop circuit (7c) for the SQUID ring (2) are arranged, and a casing is provided at least between each SQUID ring (2) and the corresponding magnetic flux lock loop circuit (7c). An amplifying means (5) and an electro-optical converting means (6) housed inside (1), and an opto-electric converting means (7b) arranged outside the casing (1),
A light transmitting member (1) provided at a predetermined position of the casing (1).
A magnetic field measuring device characterized in that it is connected via a signal transmission path including a).