JPH0875836A - Magnetic field measuring method - Google Patents

Abstract

PURPOSE: To reduce restriction in measuring environment and record magnetic field distribution at an optional time by applying stress to a plate-like magnetic field distribution storage member made of austenitic stainless steel arranged in a magnetic field measuring space. CONSTITUTION: A plate-like magnetic field distribution storage member 1 made of austenitic stainless steel is arranged in a magnetic field measuring space. At an optional time for measuring magnetic field distribution, uniform stress is applied to the storage member 1. For example, the storage member 1 is stretched in the lateral direction by oil hydraulics or pneumatics to apply tensile stress. After applying stress for a specified time, stress is removed. By applying uniform stress, stress-induced transformation is uniformly produced inside the surface, and magnetic domain inside the material is rearranged or enlarged in a direction along the outside magnetic field distribution at this point of time. The magnetic domain with information on magnetic field distribution kept is frozen in the transformation layer. After recording was finished, the storage member 1 is taken out from the measuring space, and the magnetic distribution recorded with a reader such as a magnetic sensor 2 is read out.

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 method for measuring magnetic field distribution.

[0002]

2. Description of the Related Art In recent years, devices such as nuclear fusion, superconducting technology and various actuator technologies that apply magnetic fields have been actively developed, and grasping (measuring) the magnetic field distribution is essential for these developments. is there.

As a method of measuring the magnetic field distribution, conventionally, a magnetic sensor such as a Hall element or a magnetoresistive element is sequentially moved in a magnetic field measurement space to sequentially measure the magnetic field strength at each point in the space. ing.

[0004]

In the above-mentioned conventional magnetic field measuring method, since the strength of the magnetic field at each point in the magnetic measuring space is sequentially measured, the magnetic field distribution in the entire magnetic measuring space is simultaneously measured. I can't. Therefore, when the magnetic field distribution changes, it is impossible to measure the magnetic field distribution at any time.

Further, since the magnetic sensor is arranged and moved in the magnetic measurement space, there are some restrictions due to the measurement environment, and measurement may not be possible. That is, it is impossible to measure a magnetic field in a narrow space where a magnetic sensor cannot be arranged. Moreover, magnetic field measurement is impossible in a severe special environment that humans cannot enter.

The object of the present invention is to solve the above problems,
It is an object of the present invention to provide a magnetic field measuring method which is less restricted by a measurement environment and can record a magnetic field distribution at an arbitrary time and read it out later.

[0007]

DISCLOSURE OF THE INVENTION According to the magnetic field measuring method of the present invention, a plate-like magnetic field distribution preserving member made of austenitic stainless steel is arranged in a magnetic field measuring space, and stress is applied to the magnetic field distribution preserving member. By removing, the magnetic field distribution in the space when stress is applied is frozen in the magnetic field distribution storage member, and the magnetic field distribution frozen in the magnetic field distribution storage member is measured.

In this specification, the "plate" of the plate-shaped magnetic field distribution preservation member includes not only ordinary plates but also members having a shape close to a plate such as thin plates (sheets) and foils.

[0009]

[Operation] When stress is applied to austenitic stainless steel, it undergoes martensitic transformation (transforming from austenite structure, which is a non-magnetic material, to martensite structure, which is a ferromagnetic material, by stress-induced transformation), and becomes a ferromagnetic material. Become. When this transformation is performed in a magnetic field, residual magnetism is generated in the stainless steel, and its magnitude is affected not only by stress but also by the strength of the external magnetic field. Therefore, by applying uniform stress to the plate-shaped magnetic field distribution storage member made of austenitic stainless steel in the magnetic field to be measured and then removing the stress, the residual magnetic distribution corresponding to the distribution of the external magnetic field at the moment of applying the stress Are frozen in the storage member. As described above, the magnetic field distribution frozen in the storage member is hardly affected by the external magnetic field thereafter unless the stress is applied, and the magnetic field distribution at the moment when the stress is applied is recorded in the storage member. In this way, the storage member whose magnetic field distribution is frozen is taken out from the magnetic field measurement space, and the magnetic reader (magnetic force sensor) having a structure similar to, for example, a magnetic force microscope is taken in another place.
By scanning the storage member with the recording medium and measuring the residual magnetic distribution recorded therein as a magnetic force distribution, information corresponding to the magnetic field distribution at the moment when the stress is applied can be obtained.

According to the magnetic field measuring method of the present invention, as described above, stress is applied to the storage member arranged in the magnetic field measurement space at any time, and the magnetic field distribution at that moment is recorded in the storage member. Then, the magnetic field distribution recorded at the storage member can be measured at another place later to measure the magnetic field distribution at the arbitrary time.

Further, since it suffices to dispose a plate-shaped storage member in the magnetic field measurement space and apply stress thereto, there are few restrictions due to the measurement environment. For example, a narrow space or a special environment where humans cannot enter. Also in, magnetic field measurement becomes possible.

[0012]

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

FIG. 1 shows an example of the procedure of the magnetic field measuring method according to the present invention.

In FIG. 1, first, a plate-shaped magnetic field distribution storage member (1) made of austenitic stainless steel is prepared and placed in a magnetic field measurement space (see FIG. 1 (a)). Then, uniform stress is applied to the storage member (1) at an arbitrary time when the magnetic field distribution should be measured (see FIG. 1 (b)). For example, by a suitable means such as hydraulic pressure, pneumatic pressure or electromagnetic force, the storage member (1) is pulled in the lateral direction as shown by an arrow in the drawing to apply a tensile stress. If the stress is applied for a predetermined time, the stress is removed. By applying uniform stress to the stainless steel, stress-induced transformation occurs uniformly in the plane of the material, and at the same time the magnetic domains in the material rearrange or expand in the direction along the external magnetic field distribution at that time. These magnetic domains are fixed in the material while keeping the information of the external magnetic field distribution, and even if the external magnetic field is removed, the residual magnetic field distribution of the magnetic domains is frozen in the transformation layer. Thus, the magnetic field distribution frozen in the storage member (1) is hardly affected by the external magnetic field thereafter, and the magnetic field distribution at the moment when the stress is applied is recorded in the storage member (1). When the recording of the magnetic field distribution is completed, the storage member (1) is taken out of the magnetic field measurement space, and the storage member (1) is read using a magnetic reader such as a magnetic force sensor (2).
Read the magnetic field distribution recorded in and measure the magnetic field distribution at the moment when stress is applied (see Fig. 1 (c)).

FIG. 2 shows an example of a magnetic reading device for reading the magnetic field distribution recorded in the storage member (1), and FIG. 3 shows the details of the main part thereof. This magnetic reader (10)
The magnetic reader is similar to the magnetic reader disclosed in Japanese Patent Laid-Open No. 5-334602 proposed by the present inventors, and has the following configuration.

In FIG. 2, the support is placed on a horizontal base (11).
(12) is fixed vertically. An XY table (13) is provided on the base (11), and a sample table is placed on the table (13).
(14) is fixed and can be moved in the horizontal plane by driving the table (13). A beam support (15) is attached to the column (12) so that the beam support (15) can move up and down.
A displacement gauge support (16) is attached to 5) so that it can be moved up and down.

On the sample table (14), the above-mentioned storage member (1) is placed.
Can be placed.

The base end of a horizontal cantilever beam (18) made of an elastic material is fixed to the lower part of the beam support (15), and the horizontal reflecting mirror (19) is attached to the free end of this beam (18). It is fixed. Beam (18)
Is composed of, for example, two thin glass fibers parallel to each other. The reflecting mirror (19) is made of, for example, aluminum foil. At the center of the bottom surface of the reflector (19),
The permanent magnet probe (20) is fixed vertically downward.

An optical displacement gauge (21) is provided on the lower surface of the front end of the displacement gauge support (16) as follows. That is,
A triangular notch (22) is formed on the lower surface of the support (16), and a light emitter (23) is provided on one inclined surface of the notch (22) so as to face the reflecting mirror (19). , Reflecting mirror on the other inclined surface (19)
A semiconductor type one-dimensional position sensor (24) is provided so as to face. Here, the position sensor means a position detecting element, for example, a light spot position sensor to which a photodiode is applied.

Displacement gauge support (16) with respect to beam support (15)
By moving up and down, the vertical distance between the reflecting mirror (19) of the beam (18) and the displacement gauge (21) is adjusted. Displacement meter (21) light emitter (2
The light emitted from 3) is reflected by the reflecting mirror (19) and reaches the position sensor (24). When elastic deformation occurs in the beam (18),
The position and angle of the reflecting mirror (19) change, and the arrival point of the light reflected by the reflecting mirror (19) to the position sensor (24) moves. Then, the movement of this reaching point is detected by the position sensor (24).
The elastic deformation amount of the beam (18) can be obtained by detecting with.

Although not shown in the drawing, the magnetic reader (10) processes the output of the displacement gauge (21) to store the storage member.
A computer and a display device for obtaining the two-dimensional distribution of the magnetic field recorded in (1) are provided.

By moving the beam support (15) up and down with respect to the column (12), the vertical distance between the storage member (1) and the probe (20) is adjusted. Further, by driving the table (13), the surface of the storage member (1) is scanned by the probe (20). At each point on the surface of the storage member (1), an external magnetic field is applied to the storage member (1) by the probe (20) made of a permanent magnet, and acts between the probe (20) and the storage member (1). Elastic deformation occurs in the beam (18) corresponding to the vertical component of the magnetic force. This beam (1
The amount of elastic deformation of 8) is detected by the displacement meter (21) as described above,
The output of the displacement meter (21) is input to a computer via an AD converter (not shown), and the computer obtains a two-dimensional distribution of elastic displacement of the beam (18). Further, in the computer, this displacement amount is converted into a magnetic force from the relationship between the displacement amount and the force obtained in advance, and is displayed on the display device as the magnetic force recorded in the storage member (1), that is, the two-dimensional distribution of the magnetic field. It FIG. 4 shows an example of the two-dimensional distribution of the magnetic field recorded in the storage member (1) thus obtained.

According to the above magnetic field measuring method, stress is applied to the storage member (1) arranged in the magnetic field measurement space at an arbitrary time, and the magnetic field distribution at that moment is recorded in the storage member (1). Then, the magnetic field distribution recorded at the storage member (1) can be measured at another place later to measure the magnetic field distribution at the arbitrary time.

In order to confirm the above effects, various experiments were conducted in which a tensile stress in a uniform direction was applied to the storage member in an external magnetic field and the magnetic field remained in the transformation layer of the storage member. I tried to clarify.

A. Confirmation of freezing phenomenon of magnetic field under uniform stress b. Relationship between magnetic force distribution due to frozen magnetic field and original magnetic force distribution due to external magnetic field c. Grasp of Fracture Strength of Frozen Magnetic Field with respect to Subsequent External Magnetic Field Next, with reference to FIGS. 4 to 11, an experimental example regarding recording and reading of this magnetic field will be described.

The shape and dimensions of the storage member used in the experiment and the configuration of the tension device are as follows.

The shape and dimensions of the test piece of the storage member are shown in FIG.
0 is shown. The shape of the test piece (30) is JIS Z 2201.
The No. 7 test piece of (Metallic material tensile test piece) was used as a reference, and the shape was made suitable for a tensioning device. The material of the test piece (30) includes
SUS3, which is a representative austenitic stainless steel
04 was used.

FIG. 11 shows an outline of a tensioning device that was prototyped. The pulling device (31) is a manual hydraulic pump (P-1C-0, manufactured by Riken Kikai Co., Ltd.), a mini cylinder, not shown.
(32) and roller guide type slide table (33). One end side of the tensile test piece (30) is fixed to the fixed part (35) on the base (34) and the other end side is fixed to the moving part (36) on the slide table (33). Then, by pressing the moving part (36) with the hydraulically operated mini cylinder (32), the test piece (30)
Is pulled. The pull rate is about 150 N / sec.

As the external magnetic field, a magnetic field generated by passing a current through a coil formed by winding a copper wire having a diameter of 0.1 mm on a pure iron wire having a diameter of 0.5 mm was used. The number of turns of the copper wire is 30 times x 4
I made it heavy. Since a tensile force is generated between the transformation layer of the storage member generated by the zero magnetic field and the probe (20) of the displacement gauge (21) of the magnetic reader (10), the residual magnetic field is observed. For the sake of simplicity, a current was passed in the direction in which the magnetic pole of the frozen magnetic field was the same as that of the probe (20). That is, a repulsive force is generated between the probe (20) and the residual magnetic field, which is displayed on the upper side in the magnetic field distribution chart.

First, in order to apply an external magnetic field to the storage member (test piece), the coil was fixed so that the front end surface of the coil was in the center of the storage member. The clearance between the surface of the storage member and the end surface of the coil was 0.3 mm. Next, the value of the current flowing through the coil is increased to generate a magnetic field, and after that, about 150N
The tensile force was applied to the storage member at a rate of / sec. The tensile load is a value at which plastic deformation is small and magnetic force can be measured, that is, 3000 N (tensile stress 400MP
The value was set to a), and after holding this value for 10 seconds, the tensile force was removed. After unloading, the current value of the coil was slowly decreased to zero the generated magnetic field. And the above-mentioned magnetic reader
According to (10), the magnetic field frozen in the storage member was measured.

FIG. 4 is an example of a magnetic force distribution diagram obtained by measuring the surface of the storage member on the side where the external magnetic field was generated by a magnetic reader. FIG. 4 clearly shows that a part of the magnetic field generated in the coil in the uniform stress field is frozen in the transformation layer of the storage member.
The freezing phenomenon of the magnetic field, which is the first examination item, was confirmed.

Next, the relationship between the external magnetic field and the freezing magnetic field, which is the second examination item, was investigated. FIG. 5 shows a magnetic force distribution diagram of the external magnetic field generated from the coil. The distribution of the intensity of this external magnetic field cannot be measured due to the problem of the resolution of the Gauss meter, but when measured with a Gauss meter at a point 0.3 mm above the coil tip surface, the maximum strength was 1 Gauss. In addition, since the surface shape of the Hall element of the Gauss meter is larger than the coil tip surface, the actual value is larger than this value. The strength of the magnetic field of the coil described below includes the above error.
The strength of the external magnetic field used in the experiment for obtaining the frozen magnetic field shown in FIG. 4 exceeds the measurement range of the magnetic force sensor.
Therefore, in practice, an external magnetic field weaker than the external magnetic field used in the experiment for obtaining the freezing magnetic field is generated to obtain the magnetic force distribution map as shown in Fig. 5, and the external magnetic field used in the experiment for obtaining the freezing magnetic field is obtained. The magnetic force distribution of the magnetic field was considered to be proportional to the distribution shown in FIG. The strength of the external magnetic field used in the experiment for obtaining the freezing magnetic field shown in FIG. 4 is 12 times larger than the strength of the magnetic field generated from the coil in the experiment for obtaining the magnetic force distribution shown in FIG. .

In order to examine the similarity between the magnetic force distribution due to the external magnetic field (hereinafter referred to as the external distribution) and the magnetic force distribution due to the frozen magnetic field (hereinafter referred to as the frozen distribution), the respective distributions are examined. The distribution was compared with the same maximum height. The result is shown in FIG. In FIG.
(a) shows the external distribution and (b) shows the frozen distribution. As is clear from FIG. 6, the distribution shapes of the two show fairly good agreement, but the external distribution has a nearly perfect axisymmetric distribution, while the frozen distribution is slightly stretched in the tensile stress direction. It is distributed. The maximum value of both magnetic forces and the distribution curve before and after that are shown in FIG. 7, and when the half width of each was measured, the results of the following Table 1 were obtained.

Table 1 Half width of external distribution and freezing distribution (mm) External distribution Freezing distribution Half width of distribution curve a of magnetic force 2.37 2.42 Half width of distribution curve b of maximum value of magnetic force 2.41 2.39 Half-value width of distribution curve c of magnetic force 2.40 2.35 Both have almost the same half-value width, and the effect of tensile stress is not seen. However, in the distribution curve of Fig. 7, there is a slight difference in the degree of spread between the two, and it seems that appropriate measures such as correction are necessary when the original external magnetic field is strictly estimated from the frozen distribution. Be done.

Next, an attempt was made to compare the absolute values of the strengths of the external magnetic field and the frozen magnetic field. From the measurement results shown in FIG. 6, it is expected that the strength of the frozen magnetic field is much smaller than that of the external magnetic field. Under the experimental conditions of FIG. 4, it is difficult to measure the strength of the frozen magnetic field with a normal magnetic field measuring device. Therefore, as an external magnetic field given at the time of freezing, as shown in FIG.
I decided to give a much larger external magnetic field than that of.

The external magnetic field is a ferrite magnet (2500 Gaus
s) was used, and in a state where it was brought into close contact with the storage member, a tensile stress of 440 MPa was applied to freeze the magnetic field. A cracks gate meter (WAL), which is a magnetic field measuring device with a much higher sensitivity than the Gauss meter, for the strength of this frozen magnetic field.
It was 9.0 * 10 < ^-3 > Gauss when it measured using KER Scientific make, FGM-3D1).

From the above results, it is understood that the strength of the frozen magnetic field is extremely low, which is 3.6 × 10 ⁻⁶ times that of the external magnetic field.

Finally, the third study item, the breaking strength of the freezing magnetic field against the external magnetic field, was examined. If the breaking strength of the freezing magnetic field is sufficiently high, applying stress to the storage member will lead to identification of the measurement time in the magnetic field measurement. That is,
The application of stress can be used as a trigger when measuring a time-varying magnetic field.

When the method according to the invention is used to measure the magnetic field, there is a risk that the frozen magnetic field will be exposed to other external magnetic fields when the storage element with the frozen magnetic field is removed from the magnetic field measuring space. Also, even after taking out from the magnetic field measurement space,
There is a risk that the freezing magnetic field will be exposed to other external magnetic fields before the freezing magnetic field is measured.

Therefore, the influence of such an external magnetic field was investigated. First, the external magnetic field generated by the coil was frozen in the storage member, and the frozen distribution was measured. At this time, the maximum strength of the external magnetic field was 12 Gauss and the tensile stress was 400 MPa.
Next, in a state where the stress was zero, an external magnetic field stronger than the external magnetic field previously applied was applied for 10 seconds. Then, the frozen distribution was measured, and if there was no change compared with the initially measured frozen distribution, a stronger external magnetic field was applied in the same manner, and the external magnetic field was strengthened until the frozen magnetic field was destroyed. The freeze distribution map thus obtained is shown in FIG. In FIG. 8, (a) shows an external magnetic field of 12 Gauss and a tensile stress of 400MP.
Freezing distribution of the magnetic field frozen in a (first freezing distribution),
(b) is the frozen distribution after applying the external magnetic field of 32 Gauss to the frozen distribution, (c) is the frozen distribution after applying the external magnetic field of 52 Gauss to the frozen distribution, and (d) is the frozen distribution after applying the external magnetic field of 57 Gauss Frozen distribution, (e) shows a frozen distribution with an external magnetic field of 73 Gaus
The freezing distribution after giving s, (f) is the external magnetic field 8
The freezing distribution after giving 2 Gauss is shown respectively.
In order to study the fracture strength, the maximum value of each magnetic force is obtained from each distribution chart in FIG. 8, the horizontal axis shows the increase rate of the external magnetic field, and the vertical axis shows the increase rate of the maximum magnetic force of the freezing magnetic field. (Less than,
It is called the increase rate of the maximum magnetic force. ), The result is as shown in FIG. The rate of increase of the external magnetic field and the rate of increase of the maximum magnetic force are defined by the following equations (1) and (2).

The rate of increase in the external magnetic field [%] = _{[(B n -B o) / B} o ] × 100 ...... (1) the rate of increase in the maximum magnetic force (%) = [(F _n -F _o) / F _o ] × 100 (2) where B _o is an external magnetic field given to freeze [Gaus
s], B _n is an external magnetic field [Gauss] given to destroy the frozen magnetic field, F _o is the maximum magnetic force [μN] of the frozen distribution obtained by freezing the magnetic field, and F _n is the frozen It is the maximum value [μN] of the magnetic force of the frozen distribution after applying an external magnetic field to destroy the generated magnetic field.

Assuming that the increase rate of the maximum magnetic force is not affected by the external magnetic field up to 10% or less, the frozen magnetic field is stored without being affected by the increase rate of the external magnetic field up to about 400% from FIG. Has been done.

From the above, the stress acts as a trigger, and the magnetic field can be frozen in the storage member. The frozen magnetic field, as long as the external stress is removed,
In the above example, the strength of about 5 times the strength of the frozen magnetic field is stored without being affected, so that it is possible to estimate the magnetic field distribution at any time by applying the transformation phenomenon.

[0044]

As described above, according to the magnetic field measuring method of the present invention, the restriction due to the measuring environment is small, and the magnetic field distribution at any time can be recorded and read out later.

[Brief description of drawings]

FIG. 1 is an explanatory diagram sequentially showing an example of a magnetic field measuring method according to the method of the present invention.

FIG. 2 is a perspective view showing an example of a magnetic reader used for measuring a magnetic field distribution frozen in a storage member in the magnetic field measuring method of the present invention.

FIG. 3 is an enlarged side view showing a main part of the magnetic reader of FIG.

FIG. 4 is an explanatory diagram showing an example of magnetic force distribution of a magnetic field frozen in a storage member.

FIG. 5: 1 of magnetic force distribution of external magnetic field generated from coil
It is explanatory drawing which shows an example.

FIG. 6 is an explanatory diagram showing an example of a magnetic force distribution due to an external magnetic field and a magnetic force distribution due to a frozen magnetic field.

FIG. 7 is an explanatory diagram showing an example of a magnetic force distribution curve due to an external magnetic field and its half width, and a magnetic force distribution curve due to a frozen magnetic field and its half width.

FIG. 8 is an explanatory diagram showing an example of a change in magnetic force distribution due to a frozen magnetic field due to an external magnetic field.

FIG. 9 is a graph showing the relationship between the external magnetic field and the increase rate of the maximum magnetic force.

FIG. 10 is a drawing showing the shape and dimensions of the test piece of the storage member used in the experiment.

FIG. 11 is a perspective view schematically showing a pulling device used in an experiment.

[Explanation of symbols]

 (1) Plate-shaped magnetic field distribution preservation member (2) Magnetic force sensor (10) Magnetic reader

Claims (1)

[Claims] 1. A magnetic field measurement when a stress is applied by arranging a plate-shaped magnetic field distribution storage member made of austenitic stainless steel in a magnetic field measurement space, applying stress to the magnetic field distribution storage member, and then removing the stress. A magnetic field measuring method characterized by freezing a magnetic field distribution of a space in a magnetic field distribution storage member and measuring the magnetic field distribution frozen in the magnetic field distribution storage member.