JPS63246688A - Magnetic flux detector - Google Patents

Abstract

PURPOSE:To eliminate wear otherwise caused by contact with a non-contact measurement, by using a superconducting interference element magnetic flux meter as magnetic flux detecting section of a magnetic flux detector to enhance sensitivity of detection. CONSTITUTION:A sensor coil 3 in a low-temperature container 2 and a superconducting quantum interferometer SQUID 4 are set in proximity to a medium 1 to be inspected to detect a magnetic field. Here, the medium 1 being inspected is moved at a fixed speed or the sensor coil 3 is moved. A signal detected with the SQUID 4 is fetched outside with a magnetic flux meter circuit 5 and an inspection circuit 6 evaluates uniformity of the medium 1 being inspected by magnetic characteristic. This enables non-contact reading of a magnetic signal written into a magnetic recording medium 1 thereby avoiding problems such as poor reading and breakage of a medium due to a foreign matter as caused when a sensor is brought into contact with the medium to read out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic flux detection device, and particularly to a highly sensitive magnetic flux detection device suitable for inspecting objects that emit magnetism, such as magnetic recording media, or measuring magnetic flux.

[Conventional technology]

Conventionally, the detection section of magnetic flux detection devices was developed by I.E.
E.E., Transaction On Magnetic SCM Age-15, Number 6゜ (1979) No. 162
Pages 5 to 1627 (IEEE, Trans, M
agnetics, MAG 15, Na 6 (1
979) pp. 1625-1627).

[Problem that the invention seeks to solve]

In the above conventional technology, the detection sensitivity of the magnetic flux detection part is low, so it is necessary to contact the detection part with the magnetic recording medium, and there is no consideration given to the wear of the detection part and the wear of the magnetic recording medium. There were problems with poor reading and poor inspection. Furthermore, when inspecting uniform media other than magnetic recording media, there are problems in that contact cannot be made or the sensitivity is insufficient, making inspection difficult. Furthermore, a highly sensitive magnetic flux detection device is required to measure the magnetic flux of not only magnetic recording media but also magnetic objects.

An object of the present invention is to obtain a highly sensitive magnetic flux detection device, and when used in an inspection device, to provide a magnetic flux detection device that can increase detection sensitivity and enable non-contact measurement.

[Means for solving problems]

The above object is achieved by using a superconducting interference device (SQUI'D) magnetometer as a magnetic flux detection section of a magnetic flux detection device.

[Effect]

A magnetometer using a 5QUID element has high sensitivity and can read recorded signals without the sensor coil coming into contact with the magnetic recording medium, so there is no wear due to contact, and no reading or inspection failures occur.

〔Example〕

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

(Example 1) FIG. 1 is a schematic diagram of Example 1 of the present invention. A sensor coil 3 and a superconducting quantum interferometer (SQUID) 4 housed in a low-temperature container 2 are installed close to the medium 1 to be inspected (detected), thereby detecting a magnetic field. The medium 1 to be inspected moves at a constant speed. Conversely, inspection can be performed by moving the sensor coil 3 and keeping the medium 1 to be inspected stationary. Furthermore, 5Q
Since the UID flux meter can detect DC magnetic fields, the medium to be inspected 1
It is possible to inspect even if both the sensor coil 3 and the sensor coil 3 are stationary.

The signal detected by the 5QUID 4 is taken out to the outside by the magnetometer circuit 5 and processed by the circuit under test 6. The test circuit 6 evaluates the uniformity of the medium 1 to be tested using magnetic properties, and has the effect that the uniformity can be evaluated based on fluctuations from a certain level. Furthermore, in the case of the present invention, the magnetic signals written on the magnetic recording medium 1 can be read without contact, which eliminates problems such as poor reading and damage to the medium due to foreign objects when reading by touching the sensor. It has the effect of being able to be avoided. In this embodiment, since the axis of the sensor coil 3 is parallel to the medium to be inspected 1, the magnetic flux generated in parallel from the medium to be inspected 1 can be detected, and this has the effect that it can also be used for reading ordinary magnetic recording media. . In addition, it can be used to inspect the thickness, defects, and impurities of magnetic materials such as steel plates, and since it is a non-contact inspection, it has the effect of being able to inspect even when the medium to be inspected is at a high temperature, such as at the exit of a rolling mill. moreover.

5QUID is also highly sensitive when inspecting non-magnetic metals, so it has the advantage of being able to inspect minute amounts of impurities and defects. The present invention has the advantage that various types of non-magnetic media, such as sheets of synthetic resin, can be inspected in the same way.

(Example 2) In Example 2 shown in FIG. 2, the axis of the sensor coil 3 is installed perpendicular to the medium 1 to be inspected, and the magnetic field generated perpendicularly from the medium 1 can be detected.

This embodiment is effective in reading signals from perpendicular magnetic recording media. Furthermore, in the case of inspecting magnetic metal media, there is an effect that the thickness of the medium, impurities, and defects can be inspected with high sensitivity.

(Embodiment 3) In Embodiment 3 shown in FIG. 3, the sensor coil 13 is a second-order differential coil, and DC magnetic fields and gradient magnetic fields other than signals can be removed. This has the effect that reading and inspection can be performed by detecting a signal magnetic field smaller than the noise magnetic field. In particular, there is an effect that non-magnetic metals and non-metals can be inspected with high sensitivity.

(Embodiment 4) In Embodiment 4 shown in FIG. 4, the sensor coil 23 is an asymmetrical second-order differential coil, and the coil at the tip of the sensor coil 23 is made smaller to improve the positional resolution of inspection. be. This has the effect that defects and impurities in minute parts can be inspected.

(Embodiment 5) Embodiment 3 shown in FIG. 5 is a multi-channel reading and inspection device in which minute sensor coils 33 are arranged in a straight line and one SOUTD 4 is attached to each of them. The signals of each channel are extracted by a multichannel magnetometer circuit 15. In the case of reading from the magnetic recording medium 1, signals for each track on the medium can be read in each channel and taken out from the magnetometer circuit 15. In the case of an inspection device, the inspection circuit 16 performs comparison with a predetermined level value,
It is possible to determine whether the signal is good or bad by comparing it with the signal pattern stored in the memory circuit 7. This embodiment has the advantage that signals can be read efficiently and with high sensitivity from a magnetic recording medium. Further, by setting the axis of the sensor coil 33 perpendicular or parallel to the medium, there is an effect that various recording methods can be supported.

(Embodiment 6) In Embodiment 6 shown in FIG. 6, the sensor coil 43 is divided into minute parts and arranged so that the polarities of the coils of the minute parts are always opposite to each other. Since such a coil operates as a differential coil in a two-dimensional direction, no output is produced if the medium to be inspected is uniform, but an output appears if defects or impurities are present. This is taken out by the magnetometer circuit 5.

Processed by the inspection circuit 6. The inspection circuit 6 compares the output ID number with the data stored in the memory circuit 7 to determine whether it is good or bad. This embodiment has the advantage that the medium 1 to be inspected can be inspected with high positional resolution and in a short time.

(Embodiment 7) In Embodiment 7 shown in FIG. 7, the outer shape of the sensor coil 53 is made into a disk shape as shown in FIG. They are arranged so that they have opposite polarities. Such a coil is 2
Since it operates as a differential coil in the dimensional direction, no output will be generated if the medium to be inspected is uniform, but if there are defects or impurities, an output will appear in the magnetometer circuit 5, so the memory circuit 7
The inspection circuit 6 compares the data with the data stored in the memory and determines whether it is good or bad. This embodiment has the advantage that the medium to be inspected 1 can be inspected in a short time. Furthermore, in the case of testing magnetic recording media, changing the polarity of minute portions in accordance with pre-recorded bit patterns has the effect of allowing testing to be performed by selecting only a specific bit pattern.

(Embodiment 8) In the actual tM,@ in FIG. 9, a sensor head 63 is used instead of the sensor coil. This is a 5QUI sensor coil wrapped around a magnetic head made of low-temperature permalloy material.
Connected to D4. This makes it possible to read magnetic recording media with narrow track widths.

This has the effect of being able to read magnetic recording media with high recording density.

(Example 9) In this example, even if the magnetic flux detection device is placed in a gradient magnetic field where the generated magnetic field is non-uniform, such as when placed in an environment surrounded by electromagnets, a minute magnetic flux is detected. Improvements were made to enable detection. For this purpose, the detection coil of the detection unit is shielded with a suitable electromagnetic shield.

By shielding the detection coil with an electromagnetic shield, even if the detection unit is installed in a non-uniform magnetic field, the shield can make only the magnetic field around the detection coil uniform, making direct current magnetic fields and gradient magnetic fields more efficient. Can be removed easily. Thereby, a minute signal magnetic field can be measured without the influence of unnecessary DC magnetic fields or gradient magnetic fields.

This embodiment will be explained with reference to the drawings.

In FIG. 10, a detection coil (sensor coil) 102 of a highly sensitive magnetic flux detection device is placed in an electromagnetic shield 101.

Reference numeral 103 indicates a superconducting shield case that shields the 5QUID 4 shown in FIG. ``C1! The magnetic shield case 101 is made of a thin, good conductor such as aluminum or copper. In this way, the skin effect of the good conductor blocks AC signals above a certain frequency. Therefore, a low-pass filter is inserted in the detection coil 102. The cutoff frequency of the filter is determined by the thickness and material of the shielding case 101.For a normal good conductor 1, such as copper, the skin depth (the depth at which the magnetic field can penetrate) due to the skin effect is 70 μm at I MHz. The 70μm thick copper shield case is LM
IIz's (i is attenuated to 1/Q, and the attenuation rate is 1/, /
It becomes a low-pass filter proportional to 7, which has the effect of reducing noise. When the upper limit f of the target signal frequency is given, and the cut-off frequency of the low-pass filter is f, the thickness required for the shielding case is expressed as follows. σ is electrical conductivity, μ is magnetic permeability, and ω is angular frequency, which in this case is 2πf. Since σ and μ are values specific to the substance, t can be found by substituting the σ and μ of the material used into the above equation. When the material is extremely thin or thin, the optimal structure can be obtained by changing the material. Furthermore, when the detection coil is made of superconducting wire and the shield case 101 is made of superconductor, the magnetic field penetration depth λ is 1 μm.
Since it is as follows, there is an advantage that four extremely thin superelectric bodies can be used to obtain the same effect as in the above embodiment. Furthermore, in this case, since the attenuation extends to the DC region, it is also effective against DC noise. Furthermore, shield case 1
01 itself can also be made smaller.

When the external magnetic field is large, a material with a high critical magnetic field (I(c) (for example, NbTi, NbaGa, etc.) can be used as the material for the shield cases 1 and 01. In this embodiment, in a large magnetic field, It also has the effect of shielding and attenuating noise.

FIG. 11 is a diagram showing only the shield case 111 for noise removal. This shield case 111 has slits on the side and bottom surfaces. The noise attenuation characteristic of the shield case 111 is obtained by using the shield case 111 shown in FIG. 11 in place of the shield case 101 shown in FIG.

That is, the characteristics can be changed as a low-pass filter. In this case, since the slit is provided in the axial direction of the shield case 111, the attenuation rate is small for the magnetic field in the axial direction, and the attenuation rate is large for the magnetic field in other directions.

FIG. 12 shows the directivity characteristics of the magnetic field attenuation rate in this embodiment using the shield case 111.

Usually, the object to be measured is in the Z direction. In the Z direction, the signal attenuation is the most iJ-. Noise magnetic fields entering from directions other than the Z direction are greatly attenuated, improving the S/N ratio. Therefore, the direction of the attenuation characteristic can be controlled by the direction of the slit.

This has the effect of improving the S/N ratio. moreover.

Providing an opening other than a slit has the effect of realizing complex attenuation characteristics.

According to this embodiment, since the attenuation characteristics can be controlled by the material and shape of the shielding case, there is an effect that noise magnetic fields having a complicated distribution can be efficiently removed.

(Example 10) Regarding the sensor coil for measuring minute magnetic fields of the magnetic flux measuring device, IE, Transaction on Magnetics, MG-19, Nα3. (1983
2003), pages 835 to 844. A three-dimensional second-order differential coil is used as the sensor coil in order to remove DC noise other than the signal and noise of the gradient magnetic field.

However, the above-mentioned conventional technology does not take into account multi-channel design, and when multi-channel technology is used, there are problems such as the shape of the sensor coil becomes large and the fine adjustment mechanism of the coil becomes complicated.

The purpose of this embodiment is to provide a sensor coil that is advantageous for multi-channel use.

To achieve this objective, in this embodiment, the sensor coil is flattened.

Planar coils have a smaller shape than conventional sensor coils, and can be used to create multiple channels by arranging multiple coils.Also, fine adjustment of sensor coils can be easily performed by trimming during coil manufacturing. So,
Problems such as slight adjustment deviations do not occur.

This will be explained below with reference to the drawings.

FIG. 13 is a schematic diagram of the sensor coil of this embodiment. Two sets of gear-shaped coils 201 on a flat board (solid line)
and coil 202 (dashed line) are shifted by one gear tooth and overlap. This coil stack 204 is connected in series at the external terminal portion to form a first-order differential coil. This embodiment has the effect that the characteristics as a first-order differential coil can be changed by the deviation between the inner diameter rl of the gear-shaped coil and the outer diameter rZ and 2'm of the coil. Furthermore, uniformity of the directionality of the coil characteristics can be easily achieved by increasing the number of gear-shaped teeth.

In FIG. 14, two sets of coils are connected in parallel and have the same effect as the sensor coil in FIG. 1.

FIG. 15 shows an embodiment in which a circular coil is further superimposed on two sets of gear-shaped coils to form a second-order differential coil. The balance conditions at this time are that the area and inductance of the coil 201 are Ss and Ll, and for the coil 202, St
, Lx, and Ss and La for the coil 203, the following conditions are required: 5s--8t 5x=0.

FIG. 16 shows a stacked body 205 in which three coils are stacked and connected in series at external terminals.

There is an effect similar to that of the first embodiment shown in FIG.

In addition to the above combinations, the characteristics of a second-order differential coil or a third-order differential coil can be realized by stacking gear-shaped coils in three or four layers, or by combining them with a circular coil.

In FIG. 17, 16 coil stacks 205 are lined up at the bottom of a cryogenic container 206, and an i6ch magnetometer is used to measure ttl'? FIG. In this embodiment, since the sensor coil is thin and small, even if 16 channels are lined up, it can be stored in a normal cryogenic container.

Since the sensor coil according to this embodiment is a thin film coil,
Fine adjustments to balance the sensor coil can be easily made by removing part of the coil with a laser trimmer, or by providing trimming wiring and removing the wiring as necessary. There is.

According to this embodiment, the sensor coil for measuring minute magnetic fields can be flattened, which is advantageous for multi-channel design.
There is also the advantage that fine adjustments only need to be made initially by trimming a portion of the coil.

(Example 11) An example of applying the present invention to biomagnetic measurement is shown in the 18th example.
As shown in the figure. Conventionally, when measuring brain magnetic waves from the back of the head,
Since the sensor coil is installed at the bottom of the cryogenic container,
The test subject was forced to lie face down. In this embodiment, since the sensor coil 301 is made of a high-temperature superconductor, it can be installed above the SQυID 302, so there is an effect that the test subject does not have to take an unreasonable posture. Furthermore, if a low-temperature container is placed above the test subject as in the past, the test subject may be at risk due to breakage of the container, but if it is placed below the test subject as in this example. You can avoid danger. Furthermore, in this embodiment, safety is enhanced by inserting a non-magnetic protective plate 303 between the subject and the cryogenic container. The protective plate 303 is made of heat insulating plastic, and has the effect of increasing the safety of the test subject by placing it in a low-temperature container with the test subject, even with respect to conventional testing equipment.

In all the embodiments described so far, the sensor coil and 5QUID are made of Ba, Cu, Sc, Y.

Forming the superconductor using a high temperature superconductor made of an oxide containing a rare earth element or Hf has the effect of simplifying the equipment required for cooling.

〔Effect of the invention〕

According to the present invention, it is possible to read magnetic recording media and detect the magnetic flux of uniform media with high sensitivity, so it is possible to inspect materials that cannot be inspected with conventional sensors (such as metal impurities in synthetic resin), and in a short period of time. The effect is that it can be done in a short amount of time.

Furthermore, it is possible to prevent the influence of noise magnetic fields having a complicated distribution and to detect minute magnetic fluxes.

Moreover, it is possible to provide a magnetic flux detection device that can accommodate multiple channels.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for explaining Example 1 of the present invention,
FIG. 2 is a schematic diagram for explaining Example 2 of the present invention,
FIG. 3 is a schematic diagram for explaining Embodiment 3 of the present invention,
FIG. 4 is a schematic diagram for explaining Embodiment 4 of the present invention,
FIG. 5 is a schematic diagram for explaining Example 5 of the present invention,
FIG. 6 is a schematic diagram for explaining Example 6 of the present invention,
7 and 8 are schematic diagrams for explaining Example 7 of the present invention, FIG. 9 is a schematic diagram for explaining Example 8 of the present invention, and FIGS. 10, 11, and FIG. 12 is a schematic diagram for explaining Embodiment 9 of the present invention, and FIGS. 13, 14, 15, 16, and 17 are schematic diagrams for explaining Embodiment 10 of the present invention. A schematic diagram, FIG. 18 is a schematic diagram for explaining Example 11. 1... Medium to be detected, 2... Low temperature container, 3, 13, 2
3゜33.43.53...Sensor coil, 4...5
QUIo, 5.15... Magnetometer circuit, 6.16...
Inspection circuit, 7... Memory circuit, 63... Sensor head, 101° 111... In air shield case, 10
2...Detection coil, 103...Superconducting shield case, 104...Magnetic flux 3f control circuit, 201, 202,
203-... Coil, 204-. 205...Coil laminate, 206...Cryogenic container. Figure 1 Figure ZZ Figure 5 Figure Kuzu 2 Figure 7 Figure Figure 3 Figure 9 Kutomi /θ Figure % 11 Figure Certain lz Figure 13
Ku Atsushi 74 Fig. Tomomi 15 Fig. 16 Fig.'fJ13 Fig.

Claims (1)

[Claims] 1. A magnetic flux detection device characterized in that a superconducting quantum interferometer type magnetometer is connected to a sensor coil. 2. The magnetic flux detection device according to claim 1, wherein the sensor coil scans a magnetic recording medium in a non-contact manner. 3. The magnetic flux detection device according to claim 1, wherein the sensor coil is provided within an electromagnetic shielding case. 4. The magnetic flux detection device according to claim 1, wherein the sensor coil is of a planar type. 5. In the magnetic flux detection device according to claim 1, the sensor coil and the superconducting quantum interferometer type magnetometer are formed of Ba, Cu, and oxides containing Sc, Y, rare earth elements, and Hf. A magnetic flux detection device featuring: