JP2005265780A - Non-destructive inspection device using SQUID magnetic sensor - Google Patents

Abstract

There is provided a nondestructive inspection apparatus using a SQUID magnetic sensor capable of performing inspection using a low frequency band without affecting the frequency of an applied AC magnetic field necessary for nondestructive inspection.
The present invention includes an application coil 3 capable of applying an alternating magnetic field from the outside of a sample, and an active magnetic shielding means that shields magnetic noise entering the SQUID magnetic sensor 1 using a compensation coil 4 in real time. A feedback circuit is used that shields the magnetic noise around the SQUID magnetic sensor 1 in real time by feeding back the output due to the magnetic noise that has entered the SQUID magnetic sensor 1 to the compensation coil 4 disposed in the vicinity of the SQUID magnetic sensor 1.
[Selection] Figure 1

Description

  The present invention uses a SQUID magnetic sensor that enables low-noise measurement in a poor magnetic environment in the detection of minute defects and deep defects generated in a structure using a metal material or a conductive composite material. The present invention relates to a destructive inspection apparatus, and more particularly to a SQUID nondestructive inspection apparatus using active magnetic shielding means.

In non-destructive inspection of structures using metal materials or conductive composite materials, eddy current flaw detection methods that detect eddy currents and detect cracks, ultrasonic testing methods that use ultrasonic waves, and X-ray tests that use X-rays A non-destructive inspection method using a SQUID (Superconducting Quantum Interface Device) magnetic sensor has been proposed (see Patent Document 1 below).
Japanese Patent Application Laid-Open No. 07-077516 Japanese Patent Laid-Open No. 10-038854 Y. Hatsukade, et al. , IEEE Trans. Appl. Supercond. , Vol. 13, no. 2, pp. 207-210, 2003. D. F. He, et al. , IEEE Trans. Appl. Supercond. , Vol. 13, no. 2, pp. 200-202, 2003.

  In the conventional eddy current flaw detection method, in order to obtain high sensitivity, it is necessary to induce a high-frequency eddy current, and therefore, there is a problem that inspection can be performed only in a range of about a few millimeters near the sample surface. Further, the sensitivity is insufficient as compared with a SQUID magnetic sensor or the like. The conventional ultrasonic testing method is an excellent inspection method for uniform metal materials, but for composite materials with a complex internal structure, ultrasonic waves are reflected or scattered at the interface. Precise inspection is not possible. The conventional X-ray test method is also an excellent inspection method, but X-rays are generally difficult to handle and require special facilities and qualifications due to the problem of exposure, and are therefore less versatile.

  On the other hand, since the nondestructive inspection method using the SQUID magnetic sensor uses the SQUID magnetic sensor having very high sensitivity even in the low frequency band, it is possible to detect a deeper portion and a minute defect than the eddy current flaw detection method. It has also been proved that it is less susceptible to complex internal structures than ultrasonic testing and can be applied to composite materials. Furthermore, there are few risks like the X-ray test method, and there is no need for special facilities or qualifications.

  However, the nondestructive inspection method using the SQUID magnetic sensor is weak against a strong external magnetic field fluctuation in a low frequency band, and it is difficult to inspect a ferromagnetic material such as iron.

  That is, in the nondestructive inspection method using the SQUID magnetic sensor, a magnetic noise reduction method that shields the magnetic noise by feeding back the noise output to the SQUID magnetic sensor using a compensation coil has been proposed so far. A high-frequency cutoff filter was used. As a result, magnetic noise at low frequencies is shielded, but on the other hand, it cannot be used in the low frequency band, which is the greatest advantage of the SQUID magnetic sensor, and limits the ability to detect deep defects by itself. There were points (see Patent Document 2 and Non-Patent Documents 1 and 2 above).

  In view of the above situation, the present invention reduces the noise from the low frequency to the high frequency without affecting the frequency of the applied AC magnetic field necessary for the nondestructive inspection, and the SQUID that has been difficult until now. An object of the present invention is to provide a nondestructive inspection apparatus using a SQUID magnetic sensor capable of inspecting a wide range while moving the magnetic sensor.

  [1] In a nondestructive inspection apparatus using a SQUID magnetic sensor, an active magnet that has an application coil capable of applying an AC magnetic field from the outside of the sample and shields magnetic noise entering the SQUID magnetic sensor in real time using a compensation coil It has a shielding means.

  [2] In the nondestructive inspection apparatus using the SQUID magnetic sensor as described in [1] above, the magnetic noise around the SQUID magnetic sensor is fed back by feeding back an output due to magnetic noise that has entered the SQUID magnetic sensor to a compensation coil arranged in the vicinity of the SQUID magnetic sensor. An active magnetic shielding means using a feedback circuit that shields noise in real time is provided.

  [3] In the nondestructive inspection apparatus using the SQUID magnetic sensor according to [2], the feedback circuit uses a band cutoff filter that blocks only a narrow band centered on the frequency of the AC magnetic field applied from the application coil. Thus, an externally applied magnetic field having a frequency used for nondestructive inspection is not shielded, but only magnetic noise of other frequencies is shielded.

  [4] In the nondestructive inspection apparatus using the SQUID magnetic sensor according to [1], [2] or [3], the SQUID magnetic sensor is a high temperature superconducting SQUID or a high temperature superconducting SQUID gradiometer. Features.

  [5] The non-destructive inspection apparatus using the SQUID magnetic sensor according to [1], wherein the active magnetic shielding unit is used to apply an external AC magnetic field to the sample and move the sample to perform scanning. It is characterized by doing.

  [6] In the nondestructive inspection apparatus using the SQUID magnetic sensor according to [1], scanning is performed using the active magnetic shielding means, applying an external AC magnetic field to the sample and moving the SQUID magnetic sensor. A mechanism is provided.

  [7] The nondestructive inspection apparatus using the SQUID magnetic sensor according to [6], wherein the active magnetic shielding means is used, an external AC magnetic field is applied to the sample, and the SQUID magnetic sensor is controlled by an arm control mechanism. Scanning is performed while moving three-dimensionally by a scanning arm.

  According to the present invention, by using a band cutoff filter that cuts only a narrow band centered on the frequency of the applied AC magnetic field in the feedback circuit, the frequency of the applied AC magnetic field necessary for nondestructive inspection is not affected at all. Inspection with low magnetic noise becomes possible.

  In addition, since magnetic noise other than the frequency used for inspection can be shielded, high-precision inspection is possible even in a poor magnetic environment, which can greatly contribute to practical use.

  Furthermore, in the conventional method, it was impossible to scan the wide range by moving the SQUID magnetic sensor due to the influence of geomagnetism. However, according to the present invention, the SQUID magnetic sensor can be moved, which is difficult in the past. Practical application to nondestructive inspection of existing large structures becomes possible.

  In a nondestructive inspection apparatus using a SQUID magnetic sensor, an active magnetic shielding means having an application coil capable of applying an AC magnetic field from the outside of the sample and shielding magnetic noise entering the SQUID magnetic sensor in real time using a compensation coil. Provide. Therefore, inspection with low magnetic noise is possible without affecting the frequency of the applied AC magnetic field necessary for nondestructive inspection.

  Embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic view of a nondestructive inspection apparatus showing a first embodiment of the present invention.

  In this figure, 1 is a high-temperature superconducting SQUID magnetic sensor, 2 is a refrigerator for cooling the high-temperature superconducting SQUID magnetic sensor, 3 is an external magnetic field application coil, 4 is a compensation coil, 5 is a band cutoff filter (BEF), Reference numeral 6 denotes an inspection object (sample), 7 denotes a defect of the inspection object (sample) 6, and 8 denotes a sample moving scanning table that moves two-dimensionally in order to scan the inspection object (sample) 6.

  As described above, the high-temperature superconducting SQUID magnetic sensor 1 is cooled by the refrigerator 2, and the external magnetic field applying coil 3 and the compensation coil 4 are disposed around the high-temperature superconducting SQUID magnetic sensor 1. Then, the inspection object (sample) 6 is arranged on the scanning table 8, and an eddy current is induced in the sample 6 by applying a current to the external magnetic field application coil 3. If the sample 6 has a defect 7, the defect 7 disturbs the flow of eddy current, and the magnetic field generated by the disturbed current is detected by the high-temperature superconducting SQUID magnetic sensor 1 cooled by the refrigerator 2. The output of the high-temperature superconducting SQUID magnetic sensor 1 passes through the BEF 5, and components other than the frequency of the externally applied magnetic field are fed back to the compensation coil 4. As a result, the compensation coil 4 cancels out magnetic noise other than the frequency of the externally applied magnetic field without generating any influence on the externally applied magnetic field, thereby generating a magnetic field and enabling defect inspection with low noise.

  According to such a configuration, even if the sample 6 is a ferromagnetic material such as iron that always generates a strong magnetic field, a magnetic field having a frequency that is not necessary for the inspection that occurs when the sample 6 passes through the SQUID magnetic sensor 1. Since it can be shielded, it is possible to perform highly accurate nondestructive inspection that eliminates noise for conductive materials regardless of whether they are nonmagnetic or magnetic.

FIG. 2 shows a result of actually manufacturing a SQUID nondestructive inspection apparatus having the configuration shown in FIG. 1 and measuring SQUID output noise. In FIG. 2, the horizontal axis represents frequency [Hz] and the vertical axis represents magnetic noise [mφ ₀ / Hz ^1/2 ].

  Here, a band cutoff filter that cuts off a band centering on 50 Hz is used. For comparison, the noise B in the state where the active magnetic shielding function is not operated is also measured with respect to the noise A in the state where the active magnetic shielding function is operated, and is shown in FIG.

  As shown in FIG. 2, by applying the active magnetic shielding according to the present invention, compared with the state where the active magnetic shielding function is not operated, the environmental magnetic noise is nearly an order of magnitude in all frequency bands except around 50 Hz. Was able to be reduced.

  FIG. 3 is a schematic view of a nondestructive inspection apparatus showing a second embodiment according to the present invention.

  In this embodiment, a high-temperature superconducting SQUID magnetic sensor 11, a refrigerator 12 for cooling the high-temperature superconducting SQUID magnetic sensor 11, an external magnetic field applying coil 13, a compensation coil 14, a band-shielding filter (BEF) 15, and a test object The scanning mechanism 16 for moving the sensor moves the high-temperature superconducting SQUID magnetic sensor 11 to scan the object (sample) 17.

  In such a configuration, the sample 17 is disposed below the nondestructive inspection apparatus, and an eddy current is induced in the sample 17 by applying a current to the external magnetic field application coil 13. If the sample 17 has a defect 18, the defect 18 disturbs the flow of eddy current, and a magnetic field generated by the disturbed current is detected by the high-temperature superconducting SQUID magnetic sensor 11 cooled by the refrigerator 12. The output of the high-temperature superconducting SQUID magnetic sensor 11 passes through the BEF 15, and components other than the frequency of the externally applied magnetic field generated by the external magnetic field applying coil 13 are fed back to the compensation coil 14. Thus, the compensation coil 14 is used for magnetic noise having a frequency other than the applied magnetic field interlinked with the high-temperature superconducting SQUID magnetic sensor 11 by moving in the geomagnetism without affecting the externally applied magnetic field. Counteracts and generates a magnetic field. Thereby, the defect inspection while moving the high-temperature superconducting SQUID magnetic sensor 11 becomes possible.

  According to such a structure, even if it is a large structure in which the sample 17 cannot be moved easily, a highly accurate nondestructive inspection over a wide range is possible. Actually, a SQUID nondestructive inspection apparatus having the configuration shown in FIG. 3 was manufactured, and the high-temperature superconducting SQUID magnetic sensor 11 was moved and the SQUID output noise during the movement was measured. Table 1 shows the measurement results of SQUID output noise when the high-temperature superconducting SQUID magnetic sensor 11 is fixed, when the sensor is moved without active magnetic shielding, and when the sensor is moved by operating the active magnetic shielding. . Table 2 shows the results when a higher performance superconducting SQUID gradiometer was used.

このとき、５０ＨｚのＢＥＦを用いた。表１に示すように、アクティブ磁気遮蔽を適用していない状態ではＳＱＵＩＤ磁気センサを移動させることは不可能であったが、本発明によるアクティブ磁気遮蔽の適用により、８ｍｍ／ｓの速度でＳＱＵＩＤ磁気センサを低雑音の状態で移動させることが可能となった。移動速度を３２ｍｍ／ｓに増加しても、ＳＱＵＩＤのロックは外れず、８ｍｍ／ｓの移動と同じレベルの出力雑音が得られた。

At this time, 50 Hz BEF was used. As shown in Table 1, it was impossible to move the SQUID magnetic sensor in a state where the active magnetic shielding was not applied. However, by applying the active magnetic shielding according to the present invention, the SQUID magnetic sensor could be moved at a speed of 8 mm / s. The sensor can be moved with low noise. Even when the moving speed was increased to 32 mm / s, the lock of the SQUID was not released, and the output noise of the same level as the moving of 8 mm / s was obtained.

  FIG. 4 is a schematic view of a nondestructive inspection apparatus showing a third embodiment of the present invention.

  In this embodiment, a high-temperature superconducting SQUID magnetic sensor 21, a refrigerator 22 for cooling the high-temperature superconducting SQUID magnetic sensor 21, an external magnetic field applying coil 23, a compensation coil 24, a band cutoff filter (BEF) 25, a refrigerator 22 Each of them includes a sensor moving robot arm (scanning arm) 26, an arm control mechanism 27, and wheels 28 that move the high-temperature superconducting SQUID magnetic sensor 21.

  In such a configuration, as in the second embodiment, the compensation coil 24 cancels the magnetic field having a frequency other than the applied magnetic field interlinked with the high-temperature superconducting SQUID magnetic sensor 21 by moving in the geomagnetism. By generating the defect inspection, it is possible to inspect the defect while moving the high-temperature superconducting SQUID magnetic sensor 21.

  According to such a configuration, various operational versatility is generated by the sensor moving robot arm (scanning arm) 26, and nondestructive inspection by automatic piloting is possible regardless of the inspection place and the size of the inspection target. .

  Actually, a SQUID nondestructive inspection apparatus having the configuration shown in FIG. 4 was manufactured, and the movement of the high-temperature superconducting SQUID magnetic sensor and the measurement of the SQUID output noise during the movement were performed. A result equivalent to that obtained was obtained. That is, it was impossible to move the SQUID magnetic sensor before the application of the active magnetic shielding, but the high temperature superconducting SQUID magnetic sensor can be moved at a speed of 32 mm / s by applying the active magnetic shielding according to the present invention. Became possible. In addition, regarding the SQUID output noise during the movement of the high-temperature superconducting SQUID magnetic sensor, it was possible to maintain a substantially equivalent noise level as compared with the state in which it was not moved.

  The following are suitable as the SQUID magnetic sensor used in the present invention.

(1) High temperature superconducting SQUID
As the high-temperature superconducting SQUID, an SQUID having a high superconducting transition temperature using an oxide high-temperature superconductor as a thin film material, or as an oxide high-temperature superconductor, mainly an yttrium (Y) -based oxide material (YBa Those using ₂ Cu ₃ O _7-x ) are preferred. However, as for Y, other group IIIA elements such as Yb and Er may be used.

(2) High-temperature superconducting SQUID gradiometer As the high-temperature superconducting SQUID gradiometer, in the high-temperature superconducting SQUID of the above (1), one using a differential coil as a detection coil for detecting magnetic flux is preferable. By using this differential detection coil, environmental magnetic noise having a spatially uniform gradient can be reduced. In this case, depending on the shape of the detection coil, the range from the primary differential type gradiometer having the primary differential type detection coil 31 shown in FIG. 5 to the high-order differential type gradiometers such as secondary and tertiary is included.

  In addition, this invention is not limited to the said Example, Based on the meaning of this invention, a various deformation | transformation is possible and these are not excluded from the scope of the present invention.

  The nondestructive inspection apparatus using the SQUID magnetic sensor of the present invention realizes low noise in the nondestructive inspection of conductive materials in a poor magnetic environment such as a manufacturing factory or a power plant, or a large size such as an aircraft, a rocket, a ship, etc. Suitable for precise wide-range nondestructive inspection equipment for structures.

It is a schematic diagram of the nondestructive inspection apparatus which shows 1st Example of this invention. It is a figure which shows the measurement result of the SQUID output noise of the nondestructive inspection apparatus of 1st Example of this invention. It is a schematic diagram of the nondestructive inspection apparatus which shows 2nd Example by this invention. It is a schematic diagram of the nondestructive inspection apparatus which shows 3rd Example of this invention. It is a schematic diagram of the primary differential detection coil of the primary differential gradiometer according to the present invention.

Explanation of symbols

1,11,21 High-temperature superconducting SQUID magnetic sensor 2,12,22 Refrigerator 3,13,23 External magnetic field application coil 4,14,24 Compensation coil 5,15,25 Band cut filter (BEF)
6,17 Inspection object (sample)
7, 18 Defect of inspection object (sample) 8 Scan table for moving sample 16 Scan table for moving sensor 26 Robot arm for moving sensor (scan arm)
27 Arm control mechanism 28 Wheel 31 Primary differential detection coil

Claims (7)

  A SQUID magnetic sensor having an application coil capable of applying an AC magnetic field from the outside of a sample and having an active magnetic shielding means for shielding magnetic noise entering the SQUID magnetic sensor in real time using a compensation coil is used. Nondestructive inspection equipment.   2. The nondestructive inspection apparatus using the SQUID magnetic sensor according to claim 1, wherein the magnetic noise intruding into the SQUID magnetic sensor is fed back to a compensation coil arranged in the vicinity of the SQUID magnetic sensor, and the magnetic noise around the SQUID magnetic sensor is real-time. A nondestructive inspection apparatus using a SQUID magnetic sensor, comprising active magnetic shielding means using a feedback circuit for shielding.   3. The nondestructive inspection apparatus using the SQUID magnetic sensor according to claim 2, wherein the feedback circuit uses a band cutoff filter that blocks only a narrow band centered on the frequency of the alternating magnetic field applied from the application coil. A nondestructive inspection apparatus using a SQUID magnetic sensor characterized in that an externally applied magnetic field having a frequency used for destructive inspection is not shielded but only magnetic noise of other frequencies is shielded.   4. The non-destructive inspection apparatus using the SQUID magnetic sensor according to claim 1, wherein the SQUID magnetic sensor is a high temperature superconducting SQUID or a high temperature superconducting SQUID gradiometer. Nondestructive inspection equipment.   2. The nondestructive inspection apparatus using the SQUID magnetic sensor according to claim 1, further comprising a mechanism for scanning by applying an external alternating magnetic field to the sample and moving the sample using the active magnetic shielding means. A nondestructive inspection apparatus using a SQUID magnetic sensor.   2. The nondestructive inspection apparatus using the SQUID magnetic sensor according to claim 1, further comprising a mechanism for performing scanning while applying an external AC magnetic field to the sample and moving the SQUID magnetic sensor using the active magnetic shielding means. A nondestructive inspection apparatus using a SQUID magnetic sensor.   7. The nondestructive inspection apparatus using the SQUID magnetic sensor according to claim 6, wherein the active magnetic shielding means is used, an external AC magnetic field is applied to the sample, and the SQUID magnetic sensor is controlled by a scanning arm controlled by an arm control mechanism. A nondestructive inspection apparatus using a SQUID magnetic sensor, which performs scanning while moving three-dimensionally.

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