JP6874296B2 - Magnetic measuring device and geological exploration system using it - Google Patents

Description

The present invention relates to a magnetic measuring device and a geological exploration system using the same.

As a method for exploring underground structures such as geology, there is an electromagnetic exploration method called TEM (Transient ElectroMagnetic) method. A direct current is passed through a loop-shaped cable installed on the ground surface to generate an electromagnetic field, and the state in which the eddy current generated in the ground due to the sudden interruption of the cable current diffuses in the ground is measured by a magnetic field sensor installed on the ground surface. The underground structure is extracted as the distribution of resistivity. Since the specific resistance of the mineral layer containing metal and the aquifer containing water is different from those of the surroundings, it is possible to specify the distribution position. As the magnetic field sensor used in this method, a small and highly sensitive SQUID (Superconducting Quantum Interference Device) sensor is advantageous.

SQUID measures a weak external magnetic field by detecting the superconducting current flowing through the Josephson junction of the superconductor. Therefore, for example, as shown in FIG. 1, a cooling agent such as liquid helium or liquid nitrogen is filled in a low temperature holding container such as a cryostud to hold SQUID at an extremely low temperature. Generally, the SQUID is placed on the bottom surface of the cold storage vessel and the magnetic field sensor is installed on the ground or embedded near the surface of the earth.

As a SQUID storage container that accurately measures the magnetic field without generating a magnetic flux trap, the cylindrical magnetic shield with both ends open is cooled with liquid nitrogen and transferred to the superconducting state, and a magnetic shield space is generated inside the magnetic shield. Is known (see, for example, Patent Document 1). Further, a cooler using liquid nitrogen has been proposed, which is a portable cooler having a fiber aggregate inside which absorbs and retains liquid nitrogen (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 7-321381 Japanese Unexamined Patent Publication No. 2009-473335

The general magnetic sensor used in the TEM method is planned to be used in a situation where there are few artificial noise sources in the surroundings such as a wilderness or a forest. When a conventional magnetic sensor is applied to a metal resource or hydrothermal deposit excavation site or a tunnel excavation site, measurement cannot be performed due to scattering of magnetic noise from metal or magnetic construction equipment or excavation equipment.

The present invention realizes highly sensitive magnetic measurement with reduced external noise in a magnetic measuring device using a superconducting magnetic sensor.

In one embodiment, the magnetic measuring device
With a low temperature holding container,
A magnetic shield arranged in the low temperature holding container, which is a tubular magnetic shield with one end open and the other end closed.
A superconducting magnetic sensor arranged inside the magnetic shield,
At least the coolant filled between the low temperature holding container and the magnetic shield,
Have.

A magnetic measuring device using a superconducting magnetic sensor realizes highly sensitive magnetic measurement with reduced external noise.

It is a schematic diagram of a general magnetic sensor used in geological exploration. It is a schematic block diagram of the magnetic measuring apparatus of an embodiment. It is a figure which shows the structural example of the superconducting magnetic sensor using SQUID. It is a figure which shows the structural example of a magnetic shield. It is a figure which shows the structural example of a magnetic shield. It is a figure which shows the structural example of a magnetic shield. It is a figure which shows the structural example of a magnetic shield. It is a figure which shows the structural example of a magnetic shield. It is a figure which shows the geological exploration system which applied the magnetic measuring apparatus of embodiment to tunnel excavation. It is a figure which shows the geological exploration system which applied the magnetic measuring apparatus of embodiment to underground structure estimation. It is a figure explaining the magnetic flux density created by a transmission current. It is a figure which shows the magnetic flux density at each depth point when the transmission loop diameter and the transmission current are changed variously. It is a figure which shows the appropriate search distance of the aquifer in tunnel excavation.

In the embodiment, in order to prevent external noise in a magnetic measuring device using SQUID, the SQUID sensor is arranged in a magnetic shield of a superconductor having an opening only in the direction of a useful magnetic signal source. The magnetic shield is closed except for the opening facing the direction of arrival of the target signal to prevent the intrusion of external noise. In addition, the configuration can be used in any posture such as horizontal (horizontal direction) or vertical (vertical direction) regardless of the direction of the incoming signal.

FIG. 2 is a schematic configuration diagram of the magnetic measuring device 1 of the embodiment. The magnetic measuring device 1 includes a low temperature holding container 2, a magnetic shield 20 arranged in the low temperature holding container 2, a superconducting magnetic sensor 10 arranged in the magnetic shield 20, and a low temperature holding container 2 and a magnetic shield 20. It has a coolant 8 to be filled in between. The low temperature holding container 2 is an adiabatic vacuum container, and the inside can be kept in an extremely low temperature environment. For example, it has a double structure of a resin container and a glass (quartz) dewar, and a vacuum is maintained between the outer resin container and the inner glass dewar. In the embodiment, SQUID of an oxide-based high-temperature superconductor operating at a temperature of liquid nitrogen (77K) is used, and the inside of the low temperature holding container 2 is maintained at least at the temperature of liquid nitrogen.

The magnetic shield 20 has a tubular main body 21 having an opening 22 in a single direction, and the superconducting magnetic sensor 10 is arranged inside the main body 21 in the vicinity of the opening 22. The cross-sectional shape of the tubular main body 21 is an arbitrary shape that can accommodate the superconducting magnetic sensor 10 inside, and is a cross-sectional shape such as a circle, an ellipse, or a polygon. The main body 21 of the magnetic shield 20 is formed of a bismuth (Bi) -based or yttrium (Y) -based oxide superconducting material. As an example, BiSrCaCuO, YBaCuO and the like can be used. It is desirable that the opening 22 is formed in only one direction in order to block magnetic signals other than the target signal.

The coolant 8 is formed of, for example, a liquid nitrogen absorber so that the coolant does not leak regardless of the angle at which the magnetic measuring device 1 is used. The liquid nitrogen absorber is a foam that does not freeze or shrink at the temperature of liquid nitrogen, such as foamed metal having open cells, glass fiber, and melamine foam, and retains liquid nitrogen in the bubbles. The coolant 8 may be filled in at least a part of the internal space of the magnetic shield 20. The use of a liquid nitrogen absorber is not essential, and the inside of the low temperature holding container 2 may be filled.

The superconducting magnetic sensor 10 has a superconducting loop for detecting magnetism and a SQUID having one or two Josephson junctions. The lead wire 9 extending from the superconducting magnetic sensor 10 penetrates the lid 3 with the pressure release valve, is drawn out to the outside of the magnetic measuring device 1, and is connected to the FLL (Flux Locked Loop) 4. The output voltage of the FLL 4 is filtered by the ASP (Analog Signal Processor) 5 and recorded in the data recorder 6. In the configuration example of FIG. 2, the magnetic measuring device 1 is arranged in the direction in which the opening 22 of the magnetic shield 20 is desired to be measured.

FIG. 3 shows a configuration example of the superconducting magnetic sensor 10 used in the embodiment. In this example, the superconducting magnetic sensor 10 is a SQUID magnetometer using a single coil (pickup coil) 11. The superconducting magnetic sensor 10 includes a pickup coil 11, an input coil 14, a SQUID ring 13, and a feedback coil 15. Although drawn as a planar circuit for convenience of illustration, the pickup coil 11, the input coil 14, and the feedback coil 15 may be formed in a layer different from the SQUID ring 13 via an insulating film.

The input coil 14 transmits the magnetic flux captured by the pickup coil 11 to the SQUID ring 13. The SQUID ring 13 has two Josephson junctions 131 in the configuration example of FIG. A Josephson junction refers to a configuration in which two superconductors are weakly bonded via a barrier layer of a thin insulator or a normal conductor, for example, several nanometers. A bias current near the critical current value of the Josephson junction is passed through the SQUID ring 13, and superconducting electron pairs tunnel the barrier layer so that a superconducting current flows between the two superconductors. When an external magnetic field is applied to the SQUID, a superconducting current flows in the direction of canceling the magnetic field, and a voltage proportional to the magnetic field is generated at both ends of the Josephson junction 131. Since the relationship between the magnetic flux change and the output voltage is not linear, negative feedback is performed by the external FLL4. The FLL 4 integrates the output voltage of the SQUID ring 13 and outputs the integrated voltage to the ASP 5, and returns the integrated voltage to the SQUID ring 13 as a feedback magnetic flux via the feedback coil 15. As a result, the interlinkage magnetic flux of the SQUID ring 13 is locked to zero, and the output voltage of the FLL 4 is proportional to the detected signal magnetic flux.

The superconducting magnetic sensor 10 may be formed as one SQUID chip and arranged in the magnetic shield 20. The SQUID chip can be manufactured in any configuration by any method. For example, a loop (washer) pattern of a superconductor and a Josephson junction 131 are formed on the surface of a magnesium oxide (MgO) substrate having a thickness of 10 mm to 15 mm and a thickness of 0.5 mm. The Josephson junction 131 is made of a metal-based superconductor or an oxide-based superconductor. Metal-based superconductors are highly sensitive, but Josephson junctions of oxide-based superconductors can be used at liquid nitrogen temperatures, and are excellent in operability and cost.

In the embodiment, oxide high temperature superconductors such as YBCO-based materials (for example, YBa ₂ Cu ₃ O ₇ ) and BSCCO-based materials (for example, Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ ) are used, but the present invention is not limited to this example. .. The SQUID ring 13 having the Josephson junction 131 may be formed of a metal-based superconductor such as Nb, Pb, NbTi, and liquid helium may be used as the coolant 8.

The Josephson junction 131 may be formed on a slope or step formed on the substrate (step edge junction). Alternatively, the lower superconductor layer deposited on the MgO substrate may be processed in a step shape, and the upper superconductor layer may be deposited there (ramp edge bonding). When an oxide-based superconducting material is used, the grain boundaries formed at the interface of the superconducting material can be used as the barrier layer for the Josephson junction. An insulating film is formed on the SQUID ring 13, and a pickup coil 11, an input coil 14, a feedback coil 15, and other necessary wiring are formed on the insulating film.

In the example of FIG. 3, a single-coil magnetometer is formed, but instead of the pickup coil 11, a pair of coils wound in opposite phases (differentiately configured) are used to form a SQUID gradiometer. It may be produced. Also in the case of the SQUID gradiometer, it is arranged near the opening 22 inside the main body 21 of the magnetic shield 20. By arranging the opening 22 of the magnetic shield 20 close to the ground to be measured or the wall surface of the tunnel, a large amount of noise magnetic signals from construction equipment (a mass of metal or magnetic material) or the like can be blocked.

4 to 8 show a configuration example of the magnetic shield 20. The magnetic shield 20A of FIG. 4 has a plastic (resin) or non-magnetic metal pedestal 23 that is not damaged by the temperature of liquid nitrogen inside a tubular main body 21 that opens only at one end. The superconducting magnetic sensor 10 is fixed to the exposed surface 23s of the pedestal 23 with a resin adhesive or the like. The inside of the pedestal 23 may be hollow, or may be filled with foamed metal or glass fiber impregnated with liquid nitrogen. Alternatively, the inside of the pedestal 23 may be filled with liquid nitrogen itself.

The fixed position of the superconducting magnetic sensor 10 can be appropriately determined from the solid angle of the target signal incident on the superconducting magnetic sensor 10. The lead wire 19 extending from the superconducting magnetic sensor 10 is led out to the outside of the magnetic shield 20.

The main body 21 of the magnetic shield 20A may be formed by processing a bulk of BiCaCuO or YBaCuO into a tubular shape, or may be molded from a Bi-based or Y-based material and fired. Bi-based or Y-based materials are superconducting at liquid nitrogen temperature and have a high magnetic shielding effect due to complete antimagnetism. By arranging the superconducting magnetic sensor 10 in the magnetic shield 20A having one side opening as shown in FIG. 4, it is possible to selectively capture the magnetic signal from the target direction.

FIG. 5 shows a magnetic shield 20B as a modified example. The magnetic shield 20B has a high magnetic permeability shield 27 arranged outside the magnetic shield 20A of the high-temperature superconductor of FIG. The shield 27 having a high magnetic permeability is a magnetic shield 20A in which a shield material having a high magnetic permeability is arranged in one to three layers. The high magnetic permeability material is, for example, mu metal. By arranging the shield 27 having a high magnetic permeability, the external magnetic field is captured by the outer shield 27, and the intrusion of the magnetic field inside is blocked.

FIG. 6 shows the magnetic shield 20C as another modification. The magnetic shield 20C has a sintered body 25 of a superconducting material arranged inside the main body 21 of the tubular high-temperature superconductor. The sintered body 25 is formed of a Bi-based oxide superconductor (BiCaCuO) or a Y-based oxide superconductor. The sintered body 25 has a cavity 26, and the superconducting magnetic sensor 10 is fixed to the bottom surface of the cavity 26. The opening of the cavity 26 becomes the opening 22 of the magnetic shield 20C, and the lead wire 19 extending from the superconducting magnetic sensor 10 is pulled out of the cavity 26.

FIG. 7 shows the magnetic shield 20D as yet another modification. The main body 21 of the magnetic shield 20D has a cavity 28 formed in a bulk of BiCaCuO or YBaCuO, and a superconducting magnetic sensor 10 is fixed to the bottom surface of the cavity 28.

FIG. 8 shows the magnetic shield 20E as yet another modification. The magnetic shield 20E has a liquid nitrogen absorber 24 inside a tubular main body 21 made of a superconducting material. The liquid nitrogen absorber 24 is a foamed metal having open cells, glass fiber, melamine foam, or the like, and retains liquid nitrogen in the bubbles. The superconducting magnetic sensor 10 is fixed to the exposed surface 24s of the liquid nitrogen absorber 24, and the lead wire 19 extending from the superconducting magnetic sensor 10 is drawn out from the opening 22 to the outside of the magnetic shield 20E.

In any of the configurations of FIGS. 4 to 8, by arranging the superconducting magnetic sensor 10 in the magnetic shield of the opening on one side, it is possible to block external noise and selectively capture the magnetic signal from the target direction. it can. A shield 27 having a high magnetic permeability as shown in FIG. 5 may be arranged outside the magnetic shields 20C to 20E of FIGS. 6 to 8. In this case, the effect of blocking external noise is further improved.

FIG. 9 shows a geological exploration system 101 to which the magnetic measuring device 1 of the embodiment is applied. 9 (a) is a side view, and FIG. 9 (b) is a front view of the installation position of the magnetic measuring device 1. The geological exploration system 101 is used to detect a spring or aquifer at a tunnel excavation site. At the tunnel excavation site, it is meaningful to determine whether or not there is an aquifer in front of the excavation position.

At the time of measurement, a loop-shaped conductive wire or a cable 40 is installed on or near the surface of the excavation surface 30, and the magnetic measuring device 1 is arranged at the center of the cable 40. The magnetic measuring device 1 has a superconducting magnetic sensor 10 arranged inside the magnetic shield 20, and the opening 22 (see FIGS. 4 to 8) of the magnetic shield 20 faces the excavation surface 30.

The cable 40 forms a loop with radius a. The loop does not necessarily have to be a circular loop and may form a rectangular loop. A direct current is passed from the current supply source 41 to the loop-shaped cable 40 to generate an artificial electromagnetic field F. By cutting off the cable current abruptly, the magnetic flux (magnetic signal) from the eddy current generated inside the bedrock is measured. The cable current is interrupted periodically, and the state of attenuation of the magnetic field at the time of interruption is observed. From the observation results of the magnetic field, the resistivity value at each time after the current is cut at each point in the bedrock is obtained, and the presence or absence of the aquifer is judged from the distribution of the resistivity.

Various excavating machines exist in the tunnel, and unnecessary magnetic field signals also reach the magnetic measuring device 1, but the superconducting magnetic sensor 10 having SQUID is arranged inside the closed magnetic shield 20 except for the opening 22. Has been done. In order to capture the magnetic flux from the excavated surface in the loop, it is desirable that the superconducting magnetic sensor 10 is arranged relatively close to the opening 22 of the magnetic shield 20. The superconducting magnetic sensor 10 detects only the magnetic signal included in the solid angle of the opening 22 as seen from SQUID. By arranging the opening 22 of the magnetic shield 20 close to the excavation surface 30, it is possible to reduce the incident of reflected electromagnetic waves from the ceiling or floor of the tunnel. When a liquid nitrogen absorber is used as the coolant 8, liquid leakage can be prevented even when the magnetic measuring device 1 is used sideways (horizontally).

FIG. 10 shows another application example of the magnetic measuring device 1 of the embodiment. In FIG. 10, the magnetic measuring device 1 is used for geological exploration in the plain. In FIG. 10A, the cable 40 is arranged in a loop on the ground surface. One side of the loop is, for example, 100 m to 200 m. The cable 40 is connected to the transmitter 50. The magnetic measuring device 1 connected to the receiver 60 is arranged in the center of the loop.

As shown in FIG. 10B, the current flowing through the cable 40 at the transmitter is periodically interrupted. The sweep current by the transmitter 50 has, for example, pulse waveforms of three amplitude levels. The cable 40 serves as an artificial signal source, and electromagnetic waves generated near the surface of the earth permeate underground, and an induced current (eddy current) is generated in the ground. The magnetic flux generated by the eddy current is detected by the magnetic measuring device 1, and the detection signal is received by the receiver 60. The magnetic measuring device 1 captures magnetic signals from each depth. The received waveform has a transient response (dotted circle) as shown in the lower part of FIG. 10B. From this response characteristic, the non-resistance in each layer is obtained and the underground structure is estimated. The presence of metal resources-containing layers and groundwater is estimated from the resistivity value.

FIG. 11 is a diagram for explaining the magnetic flux density created by the transmission current. _{The magnetic flux density B p} of the magnetic field generated at the point P at the depth Z [m] in the ground when the transmission current I [A] is passed through the transmission loop having the radius a [m] is expressed by the equation (1). Will be done.

^{_{B p = μ 0 Ia 2/}} 2 (a 2 + Z 2) 3/2 (1)
Here, μ ₀ is the magnetic permeability in vacuum.

When Z = 0 is substituted into equation (1), that is, the magnetic flux density at the origin O is
_BO = μ ₀ I / 2a (2)
Is.

The transmission loop diameter (radius) a and the transmission current I are variously changed, and the magnetic flux density at each depth is calculated by the SQUID arranged at the origin O. The transmission loop diameter a for metal resource exploration is 100 meters, the transmission loop radius at the tunnel excavation site is 3 meters, and the reference loop radius is 25 meters. The transmission current I of the loop having a radius of 100 m is changed to 10A, 20A, and 40A. The transmission current I of the loop having a radius of 3 m is changed to 10A, 1A, and 0.5A. The transmission current I in the reference loop is 15A.

FIG. 12 is a diagram showing a calculation result of FIG. The curves A to C of the broken line are the calculation results in the loop with a radius of 100 m, the curves D to F of the solid line are the calculation results in the loop with a radius of 3 m, and the curves R of the thick broken line are the calculation results in the reference loop. From FIG. 12, it is not appropriate to pass 10A through a loop with a radius of 3m because it exceeds the reference value on the ground surface (Z = 0), but it is possible to pass a current of 1A through a loop with a radius of 3m.

When a current of 1 A is passed through a loop with a radius of 3 m (curve E), the accuracy is about the same as the detection result of magnetic flux from a depth of 800 m by the reference loop (R) within a depth range of about 100 m from the ground surface. can get.

FIG. 13 is a diagram showing an appropriate search distance for the aquifer when a loop having a radius of 3 m is used in tunnel excavation. Similar to FIG. 12, the magnetic flux density detected at a depth of 800 meters underground by the reference loop R is used as a reference. Further, the magnetic flux density detected at a depth of 1000 meters when a current of 20 A is passed through a loop having a radius of 100 m is used as a second reference.

In order to pass a current of 1A through a loop with a radius of 3m and obtain the same accuracy as the magnetic flux density observed at a depth of 800m underground in the reference loop R, a depth of 80m from the ground surface is appropriate. .. Comparing the case where a current of 1 A is passed through a loop with a radius of 3 m and the case where a current of 20 A is passed through a loop with a radius of 100 m, it is the same as the magnetic flux density observed at a depth of 1000 meters from the ground surface in a loop with a radius of 100 m. Degree values are obtained at a depth of 30 m from the ground surface in a loop with a radius of 3 m.

From this result, when confirming the existence of the aquifer at the tunnel excavation site using the loop having a radius of 3 m and the magnetic measuring device 1 of the embodiment, good measurement results can be obtained in the range of 30 m to 80 m from the excavation surface. You can see that. If the presence of aquifer is detected, measures such as changing the excavation direction of the tunnel can be taken.

The magnetic measuring device 1 of the embodiment uses a magnetic shield 20 having a single opening 22, and by arranging the openings toward the arrival direction of a desired signal, external noise is blocked and a minute magnetic signal is detected. can do.

The magnetic measuring device of the embodiment is suitably used for magnetic field measurement in a noisy environment, and is applied to exploration of metal resources, petroleum resources, water resources hydrothermal deposits, and the like. It is also applied to the exploration of water veins and aquifers at tunnel excavation sites. Furthermore, it can be applied to the exploration of underground structures in urban areas.

In response to the above explanation, the following additional notes are presented.
(Appendix 1)
With a low temperature holding container,
A magnetic shield arranged in the low temperature holding container, which is a tubular magnetic shield with one end open and the other end closed.
A superconducting magnetic sensor arranged inside the magnetic shield,
At least the coolant filled between the low temperature holding container and the magnetic shield,
Magnetic measuring device having.
(Appendix 2)
The magnetic shield has a tubular main body made of a superconducting material and a pedestal arranged inside the main body, and the superconducting magnetic sensor is fixed to the surface of the pedestal. The magnetic measuring device according to Appendix 1.
(Appendix 3)
The magnetic measuring apparatus according to Appendix 2, wherein the pedestal is made of a non-magnetic metal or a resin material that does not freeze or break at the operating temperature of the superconducting magnetic sensor.
(Appendix 4)
The magnetic measuring device according to Appendix 2 or 3, wherein the inside of the pedestal is filled with a cavity or a liquid nitrogen absorber.
(Appendix 5)
The magnetic shield has a tubular main body made of a superconducting material and a sintered body of the superconducting material arranged inside the main body.
The magnetic measuring device according to Appendix 1, wherein the superconducting magnetic sensor is fixed to the bottom surface of a cavity formed in the sintered body.
(Appendix 6)
The magnetic shield has a body having a cavity formed on one end side of a columnar bulk of superconducting material.
The magnetic measuring device according to Appendix 1, wherein the superconducting magnetic sensor is fixed to the bottom surface of the cavity.
(Appendix 7)
The magnetic shield has a tubular body made of a superconducting material and a liquid nitrogen absorber arranged inside the body.
The magnetic measuring device according to Appendix 1, wherein the superconducting magnetic sensor is fixed to the liquid nitrogen absorber.
(Appendix 8)
The magnetic measuring device according to any one of Supplementary note 2 to 7, wherein the magnetic shield further has a shield of a high magnetic permeability material arranged outside the main body.
(Appendix 9)
The low temperature holding container has a lid for drawing out a lead wire extending from the superconducting magnetic sensor to the outside.
The magnetic measuring device according to any one of Supplementary note 1 to 8, wherein the opening of the magnetic shield is arranged at an end opposite to the lid.
(Appendix 10)
The superconducting magnetic sensor has a superconducting quantum interference element formed of a high-temperature superconducting material.
The magnetic measuring apparatus according to any one of Supplementary note 1 to 9, wherein the coolant is a liquid nitrogen absorber that absorbs and retains liquid nitrogen.
(Appendix 11)
Conductive wires that form loops and
A current supply source that supplies current to the conductive wire and
The magnetic measuring device according to any one of Supplementary note 1 to 10 arranged at the center of the loop.
A geological exploration system characterized by having.
(Appendix 12)
The geological exploration system according to Appendix 11, wherein the loop is formed perpendicular to the surface of the earth.

1 Magnetic measuring device 2 Low temperature holding container 3 Lid 4 FLL
5 ASP
6 Data recorder 8 Cooling material 9, 19 Lead wire 10 Superconducting magnetic sensor 20, 20A to 20E Magnetic shield 21 Main body 22 Opening 23 Pedestal 24 Liquid nitrogen absorber 25 Sintered body 26, 28 Cavity 27 Shield 40 Cable (conductive wire) )
41 Current source 50 Transmitter 60 Receiver 101, 102 Geological survey system

Claims (6)

With a low temperature holding container,
A magnetic shield arranged in the low temperature holding container, which is a tubular magnetic shield with one end open and the other end closed.
A superconducting magnetic sensor arranged inside the magnetic shield,
At least the coolant filled between the low temperature holding container and the magnetic shield,
Have,
The magnetic shield has a tubular main body made of a superconducting material and a pedestal arranged inside the main body, and the superconducting magnetic sensor is fixed to the surface of the pedestal. Magnetic measuring device. With a low temperature holding container,
A magnetic shield arranged in the low temperature holding container, which is a tubular magnetic shield with one end open and the other end closed.
A superconducting magnetic sensor arranged inside the magnetic shield,
At least the coolant filled between the low temperature holding container and the magnetic shield,
Have,
The magnetic shield has a tubular main body made of a superconducting material and a sintered body of the superconducting material arranged inside the main body.
The superconducting magnetic sensor is a magnetic measuring device characterized in that it is fixed to the bottom surface of a cavity formed in the sintered body. With a low temperature holding container,
A magnetic shield arranged in the low temperature holding container, which is a tubular magnetic shield with one end open and the other end closed.
A superconducting magnetic sensor arranged inside the magnetic shield,
At least the coolant filled between the low temperature holding container and the magnetic shield,
Have,
The magnetic shield has a body having a cavity formed on one end side of a columnar bulk of superconducting material.
The superconducting magnetic sensor is a magnetic measuring device characterized in that it is fixed to the bottom surface of the cavity. With a low temperature holding container,
A magnetic shield arranged in the low temperature holding container, which is a tubular magnetic shield with one end open and the other end closed.
A superconducting magnetic sensor arranged inside the magnetic shield,
At least the coolant filled between the low temperature holding container and the magnetic shield,
Have,
The magnetic shield has a tubular body made of a superconducting material and a liquid nitrogen absorber arranged inside the body.
The superconducting magnetic sensor is a magnetic measuring device characterized in that it is fixed to the liquid nitrogen absorber. The magnetic measuring device according to claim 1, 2, or 4, wherein the magnetic shield further includes a shield of a high magnetic permeability material arranged outside the main body. Conductive wires that form loops and
A current supply source that supplies current to the conductive wire and
The magnetic measuring device according to any one of claims 1 to 5 , which is arranged at the center of the loop.
A geological exploration system characterized by having.

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