JP2015014494A - Optical probe current sensor using magnetic substance having shape magnetic anisotropy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the following problem: when an optical probe current sensor which applies magnetic anisotropy in an in-plane direction of a magnetic substance with induction magnetic anisotropy or crystal magnetic anisotropy to obtain sensor sensitivity, is disposed inside a vehicle or in an environment at about 200°C, magnetic moment direction of the magnetic substance is changed, thereby changing sensor sensitivity.SOLUTION: An optical probe current sensor includes: a magnetic substance which is arranged near a conductor where a current to be measured flows, has shape magnetic anisotropy, and is configured so that a length of a part along an axis of easy magnetization is longer than a part along an axis of difficult magnetization; a light source which irradiates the magnetic substance with light; a magnetic field detection unit which detects a magnetic field applied to the magnetic substance, on the basis of polarization state of reflected light reflected by the magnetic substance; and a current calculation unit which calculates the current flowing in the conductor, on the basis of the magnetic field detected by the magnetic field detection unit.

Description

  The present invention relates to an optical probe current sensor, and more particularly to an optical probe current sensor provided with a magnetic body having shape magnetic anisotropy.

  Current sensors for observing the amount of current are widely used in various electronic devices such as home appliances and electric / hybrid vehicles. Particularly in recent years, the influence of electromagnetic noise propagating from the outside or noise generated from the device itself on the measurement current has been regarded as a problem, and a highly accurate current sensor with a good S / N ratio is required.

  However, a current sensor using a Hall element that has been conventionally used has a problem that current cannot be measured with high accuracy because noise is induced in a conductive wire (wire harness) connected to the sensor. Therefore, an optical probe current sensor using a magnetic Kerr effect in a magnetic material applying the magneto-optical disk technology has been reported (for example, Patent Document 1). This is because light that is not affected by electromagnetic noise is used as a probe, so that highly accurate current detection is possible even in a poor electromagnetic noise environment.

FIG. 1 shows a configuration of a conventional optical probe current sensor. FIG. 1A shows a state in which no current flows through the conductor, and FIG. 1B shows a state in which current flows through the conductor. As shown in FIG. 1A, a magnetic body 100 is disposed in the vicinity of the conductor 2 to detect a magnetic field generated by a current flowing through the conductor 2. The magnetic body 100 has magnetic anisotropy, and the initial magnetic moment direction mp ₀ is made to coincide with the direction of the current flowing through the conductor 2. The magnetic body 100 is provided with magnetic anisotropy using, for example, induced magnetic anisotropy or crystal magnetic anisotropy.

The magnetic body 100 is irradiated with incident light L _i including linearly polarized light through the polarization prism 12 from the light source 11. Incident light L _i is reflected by the surface of the magnetic body 100 and emitted to the magnetic field detector 20 as reflected light L _r . In the magnetic field detection unit 20, the reflected light L _r is azimuthally adjusted by the half-wave plate or the quarter-wave plate 13 and then incident on the polarization beam splitter 14 and separated into S-polarized light L _s and P-polarized light L _p. The The S-polarized light L _s and the P-polarized light L _p are respectively incident on the first light receiving element 15 and the second light receiving element 16, and the respective output voltages are input to the inverting input terminal and the non-inverting input terminal of the operational amplifier 17, and the difference between the two is detected. Is done. Since the output voltage of the operational amplifier 17 has a correlation with the current flowing through the conductor 2, the current calculation unit 30 can calculate the current flowing through the conductor 2 based on the output voltage of the operational amplifier 17.

Here, when no current flows through the conductor 2, the reflected light L _r remains linearly polarized light, and the light passing through the half-wave plate or the quarter-wave plate 13 shows circularly polarized light. Accordingly, the P-polarized light L _p and the S-polarized light L _s have the same magnitude, and no current is detected.

On the other hand, as shown in FIG. 1B, when the current I flows through the conductor 2, the direction of the magnetic moment of the magnetic body 100 changes from mp ₀ to mp by the magnetic field m generated by the current I. FIG. 2 shows how the magnetic body 100 is irradiated with light. It is assumed that the magnetic body 100 is disposed on the conductor 2 and a current I flows through the conductor 2 in the direction of the arrow y. The magnetic body 100 is assumed to have a width w ₀ , a length l _o , and a thickness t ₀ . The length l _o and the width w ₀ is sufficiently larger than the irradiation region 10 of the incident light L _i. Light L _i emitted from the light source 11 is incident from the direction of arrow d _i, is reflected as reflected light L _r is reflected by the illuminated area 10 on the surface of the magnetic body 100 in the direction of arrow d _r. At this time, since the direction of the magnetic moment of the magnetic body 100 is changed from mp ₀ to mp in the irradiation region 10, the reflected light L _r becomes elliptically polarized light. The phenomenon that the reflected light becomes elliptically polarized light when the surface of the magnetized magnetic material is irradiated with linearly polarized light is called “magnetic Kerr effect”.

When the reflected light L _r becomes elliptically polarized light, a difference occurs between the magnitudes of the P-polarized light L _p and the S-polarized light L _s , and a current proportional to the difference is detected. In this way, since the current can be detected using light, the current can be accurately detected even in an environment where noise such as electromagnetic waves exists.

  Current sensors are required to be used in various environments. Especially when used in electric / hybrid vehicles, sensor sensitivity and characteristics do not change even when the ambient temperature reaches as high as 200 ° C. Is required.

JP 2012-193981 A

  However, in the conventional optical probe current sensor, magnetic anisotropy is imparted in the in-plane direction of the magnetic material by using induced magnetic anisotropy or crystal magnetic anisotropy to obtain sensor sensitivity. When placed in an environment of about 200 ° C., such as inside, the direction of the magnetic moment of the magnetic material changes, causing a problem that the sensor sensitivity is lowered.

  The optical probe current sensor of the present invention is disposed in the vicinity of the conductor through which the current to be measured flows, has shape magnetic anisotropy, and the length of the portion along the easy magnetization axis direction is along the hard magnetization axis direction A magnetic material longer than the length of the part, a light source for irradiating the magnetic material with light, a magnetic field detector for detecting a magnetic field applied to the magnetic material based on a polarization state of reflected light reflected by the magnetic material, and magnetic field detection And a current calculation unit that calculates a current flowing through the conductor based on the magnetic field detected by the unit.

  According to the optical probe current sensor of the present invention, the magnetic anisotropy is imparted to the magnetic body by utilizing the shape magnetic anisotropy, and therefore the magnetic anisotropy that affects the sensor sensitivity even if the ambient temperature changes. There is an effect that an optical probe current sensor having good temperature characteristics can be configured.

It is a figure which shows the structure of the conventional optical probe current sensor. It is a perspective view of the magnetic body used for the conventional optical probe current sensor. It is a figure which shows the structure of the optical probe current sensor which concerns on Example 1 of this invention. It is the perspective view and sectional drawing of a magnetic body used for the optical probe current sensor which concerns on Example 1 of this invention. It is a flowchart for demonstrating the operation | movement procedure of the optical probe current sensor which concerns on Example 1 of this invention. It is a figure which shows the relationship between the size of the magnetic body which comprises the optical probe current sensor which concerns on Example 1 of this invention, and a demagnetizing-field coefficient. It is a graph which shows the temperature characteristic of the optical probe current sensor which concerns on Example 1 of this invention. It is the perspective view and sectional drawing of a magnetic body used for the optical probe current sensor which concerns on Example 2 of this invention. It is the perspective view and sectional drawing of a magnetic body which are used for the optical probe current sensor which concerns on Example 3 of this invention.

  Hereinafter, an optical probe current sensor according to the present invention will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

[Example 1]
An optical probe current sensor according to Example 1 of the present invention will be described. FIG. 3 shows the configuration of the optical probe current sensor according to the first embodiment of the present invention. FIG. 3A shows a state where no current flows through the conductor 2, and FIG. 3B shows a state where current flows through the conductor 2. FIG. 4 shows a perspective view and a cross-sectional view of a magnetic body used in the optical probe current sensor according to the first embodiment of the present invention. The optical probe current sensor according to Example 1 of the present invention is a magnetic body disposed in the vicinity of a conductor 2 through which a current I to be measured flows, has a shape magnetic anisotropy, and has an easy magnetization axis direction Ae. portion and the magnetic body 1 is longer than the length w _s of along the length l _m is the magnetization hard axis Ah of along the portion, a light source 11 for irradiating light L _i in the magnetic body 1, is reflected by the magnetic substance 1 The magnetic field detection unit 20 that detects the magnetic field applied to the magnetic body 1 based on the polarization state of the reflected light L _r , and the current that calculates the current I that flows through the conductor 2 based on the magnetic field detected by the magnetic field detection unit 20 And a calculation unit 30.

  The light source 11 is a light source that outputs light including linearly polarized light. For example, a laser light source that outputs laser light such as a gas laser such as a He—Ne laser or a semiconductor laser can be used. The light output from the light source 11 has a diameter of about 100 μm, for example.

The light output from the light source 11 enters the polarizer 12, and the polarizer 12 polarizes the light emitted from the light source 11 into linearly polarized light having a predetermined polarization axis direction. Since the linearly polarized light is incident on the magnetic body 1, it referred to as the incident light L _i this. As the polarizer 12, for example, a Glan-Thompson polarizing prism or a Grand Taylor polarizing prism can be used.

FIGS. 4A and 4B are a perspective view and a cross-sectional view, respectively, of a magnetic body used in the optical probe current sensor according to the first embodiment of the present invention. The cross-sectional view of FIG. 4B is a cross-sectional view taken in the direction perpendicular to the horizontal plane of the conductor 2 in AA of FIG. Although the magnetic body 1 is disposed in the vicinity of the conductor 2 through which the current to be measured flows, it is not necessary to be in contact therewith. The magnetic body 1 may be disposed directly on the conductor 2, but an interlayer insulating film (not shown) such as a SiO ₂ film may be provided between the magnetic body 1 and the conductor 2.

The magnetic body 1 has shape magnetic anisotropy, and has a so-called strip shape. The magnetic body 1 is a soft magnetic body containing at least one of Fe, Co, Ni, and Gd, and is, for example, a yttrium-iron-garnet (YIG: Yttrium-Iron-Garnet) ferrite single crystal. A magnetic body having shape magnetic anisotropy has an easy magnetization axis direction and a hard magnetization axis direction, but the “strip shape” means the length l _m of the magnetic body 1 along the easy magnetization axis direction Ae. Means longer than the length w _{s of the} portion along the hard axis direction Ah. By processing the magnetic material into a strip shape, the shape magnetic anisotropy that is hardly affected by the ambient temperature with respect to the crystal magnetic anisotropy or the like becomes dominant. As a result, the temperature characteristic of the anisotropic magnetic field (sensor sensitivity) of the magnetic material is improved.

As shown in FIG. 3A, the direction mp ₁ of the magnetic moment of the magnetic body 1 in the state where no current flows through the conductor 2, that is, the state where no magnetic field is applied to the magnetic body 1, is the easy axis direction Ae. Is consistent with When the thickness of the magnetic substance 1 and t _m, t _m may be thicker to such an extent that the incident light L _i is not transmitted, it is sufficient for example 0.1μm about.

The magnetic substance 1, the incident light L _i is incident from the direction of d _i, is reflected in the direction of d _r in the irradiation region 10 as reflected light L _r. For all of the incident light L _i is reflected by the surface of the magnetic substance 1, the length w _s hard axis magnetic Ah of the magnetic body 1, may be at greater than width of the irradiation region 10. That is, the length w _s of the magnetic material along the hard axis direction Ah is preferably larger than the length in the hard axis direction in the region where the light from the light source is irradiated onto the magnetic material 1. For example, the incident light Li is incident at an angle θ with respect to the magnetic substance 1, if the diameter of the circular incident light L _i is phi, may be determined to w _s to satisfy w _s ≧ φ / sinθ .

The magnetic field detector 20 detects the magnetic field strength of the external magnetic field applied to the magnetic body 1 using the magnetic Kerr effect. The magnetic field detection unit 20 includes a half-wave plate or quarter-wave plate 13, a polarizing beam splitter 14, a first light receiving element 15, a second light receiving element 16, and an operational amplifier 17. The half-wave plate or the quarter-wave plate 13 finely adjusts the polarization direction of the reflected light L _r . The polarization beam splitter 14 splits the reflected light L _r into S-polarized light L _s and P-polarized light L _p . S-polarized light L _s is received by the first light receiving element 15, and P-polarized light L _p is received by the second light receiving element 16. As the first light receiving element 15 and the second light receiving element 16, for example, a photodiode, a phototransistor, or a CCD sensor can be used. The first light receiving element 15 and the second light receiving element 16 output photoelectrically converted signals to the inverting input terminal and the non-inverting input terminal of the operational amplifier 17, respectively. The current calculation unit 30 calculates the current flowing through the conductor 2 based on the difference value that is the output result of the operational amplifier 17.

  Next, the operation of the optical probe current sensor according to the first embodiment of the present invention will be described with reference to the flowchart of FIG. First, in order to adjust the optical probe current sensor in a state where no external magnetic field is applied to the magnetic body 1, a state in which no current flows through the conductor 2 (I = 0 [A]) is set (S101).

Next, in step S <b> 102, the intensity of the P / S polarized light is made uniform by the ¼ wavelength plate (or ½ wavelength plate) 13. Specifically, the adjustment is performed as follows. When no current flows through the conductor 2, that is, when the magnetic field applied to the magnetic body 1 is zero, the two polarization components L _s and L _p separated by the polarization beam splitter 14 are equal in intensity. The angle of the slow axis of the half-wave plate or quarter-wave plate 13 is adjusted. Specifically, by tilting 45 degrees relative to the polarization plane of the incident light L _i slow axis 1/2-wave plate or a quarter-wave plate 13, the two polarization components separated by the polarization beam splitter 14 The light intensities of L _s and L _p are made almost equal. By adjusting in this way, the magnitude of the magnetic field in the magnetic body 1 can be detected by detecting the difference in intensity between L _s and L _p . In a state where no current flows through the conductor 2, the differential output V of the operational amplifier 17 is 0 [V] (S103).

Next, in step S104, a current I is passed through the conductor 2 (I = I [A]). The direction of the current I flowing through the conductor 2 is the direction of the arrow y, which coincides with the easy magnetization axis direction Ae of the magnetic body 1, that is, the longitudinal direction of the strip-shaped magnetic body 1. As shown in FIG. 3B, when the current I flows through the conductor 2 in the direction of the arrow y, a magnetic field m is generated around the conductor 2. As a result, the magnetic moment of the magnetic body 1 is changed in the direction of mp _2. In this state, is irradiated with incident light L _i in the magnetic body 1, the polarization plane rotates incident light L _i is subjected to the magnetic Kerr effect by the magnetization vector mp ₂ of the magnetic body 1, the reflected light L _r is the elliptically polarized light (S105). As a result, an intensity difference is generated between the two polarization components L _s and L _p according to the magnitude of the optical rotation angle, and the differential output V = Vo [V] is detected from the intensity difference between the P and S polarizations. (S106). Next, in step S107, the current calculation unit 30 calculates the current I flowing through the conductor 2 from the differential output Vo.

Next, a method for designing the shape of the magnetic material used for the optical probe current sensor according to the first embodiment of the present invention will be described. The shape of the magnetic body can be designed based on the anisotropic magnetic field Hk generated in the magnetic body. When the demagnetizing field Hd due to the shape magnetic anisotropy is dominant, the anisotropic magnetic field Hk substantially coincides with Hd. When the magnetic body 1 is processed into a strip shape as shown in FIG. 4A, the demagnetizing field Hd is expressed by the following equation.
Hd = NMs (1)
Here, N is the demagnetizing field coefficient, and Ms is the saturation magnetization of the magnetic material. Since the saturation magnetization Ms is a value inherent to the magnetic material, the relationship between the shape of the magnetic material and the demagnetizing factor N is important. The demagnetizing factor N is expressed by the following equation (where l _m >> w _s ≥t _m ).

上式を用いることにより、一例として以下のような組み合わせが得られる。

By using the above formula, the following combinations are obtained as an example.

この場合、反磁界係数ＮはＮ ＝ ０．００９９と算出される。
式（１）より反磁界Ｈｄは
Hd = 0.0099 × 2.15 × 10⁴ ≒ 213 [Oe] = 16.9 [kA/m] （純鉄の場合）
と求められる。

In this case, the demagnetizing field coefficient N is calculated as N = 0.0099.
From equation (1), the demagnetizing field Hd is
Hd = 0.0099 × 2.15 × 10 ⁴ ≒ 213 [Oe] = 16.9 [kA / m] (in the case of pure iron)
Is required.

By using Equation (2), the shape of the magnetic body 1 can be determined from the demagnetizing factor N. For example, FIG. 6 shows the relationship between the demagnetizing factor N and the length w _s of the magnetic body 1 in the hard axis direction when the length 1 _m of the magnetic body 1 in the easy axis direction is used as a parameter. Here, the thickness t _m of the magnetic body 1 is set to 0.1 [μm]. Demagnetizing factor N is decreased monotonically with increasing w _s, if l _m is 5 or 10 [[mu] m], it appears may increase with increasing w _s. From this result, the length in the longitudinal direction of the strip-shaped magnetic body 1, i.e., the length l _m of the easy magnetization axis direction is said to be greater than 10 [μm].

  FIG. 7 shows a graph of temperature characteristics of a magnetic material used in the optical probe current sensor according to the first embodiment. This figure shows the relationship between the applied magnetic field strength H [Oe] and the magnetization 4πM [kG] when the temperature of the environment in which the magnetic material is arranged is changed from 25 ° C. to 150 ° C. Even if the temperature is changed from 25 ° C. to 150 ° C., there is no significant change in the magnetic characteristics. Therefore, by using the magnetic material used in the optical probe current sensor according to Example 1, the environmental temperature is reduced to at least 150 ° C. It can be seen that the magnetic properties do not change even when the temperature is raised. From this result, shape magnetic anisotropy is imparted so that the length of the portion along the easy magnetization axis direction is longer than the length of the portion along the hard magnetization axis direction as in the present invention. Thus, it can be seen that the magnetic field can be accurately measured even in a high-temperature environment, and thus accurate current measurement is possible.

[Example 2]
Next, an optical probe current sensor according to Example 2 of the present invention will be described. Since the measurement system and the measurement procedure are the same as those in the first embodiment, detailed description thereof is omitted. The optical probe current sensor according to the second embodiment is different from the optical probe current sensor according to the first embodiment in that the magnetic body has one or a plurality of grooves along the easy magnetization axis direction. FIG. 8 shows a perspective view and a cross-sectional view of a magnetic body used in the optical probe current sensor according to the second embodiment of the present invention. FIG. 8B is a cross-sectional view taken along the line BB in FIG. 8A in a direction perpendicular to the horizontal plane of the conductor 2. The magnetic body 1 ′ is provided with a groove 1 a along the easy axis direction Ae. The groove 1a is formed so as to penetrate in the thickness (t _m ) direction of the magnetic body 1 ′. The groove 1a does not need to be formed over the entire region in the easy magnetization axis direction Ae of the magnetic body 1 ′, but is preferably long enough to exhibit shape magnetic anisotropy. When the groove 1a is formed over the entire region in the easy axis direction Ae of the magnetic body 1 ′, the state is the same as when two magnetic bodies are arranged in parallel.

8A and 8B show an example in which only one groove 1a is formed. However, the present invention is not limited to this, and a plurality of grooves may be provided. Further, in the figure, an example is shown in which the formed so as to overlap the groove 1a and the reflection region 10 of the incident light L _i, this not limited, than the length of the hard magnetization axis direction of the reflection regions 10 and w _s May be sufficiently large to be provided outside the reflective region 10.

  According to the optical probe current sensor according to the second embodiment, one or more grooves are provided in a magnetic body having shape magnetic anisotropy, so that the shape magnetic anisotropy is greater than when no groove is formed. Sex can be made to appear strongly. In addition, since the level of shape magnetic anisotropy of the magnetic material is determined by the ratio of the length in the easy axis direction and the length in the hard axis direction, providing a groove reduces the effective length in the hard axis direction. Since it can be shortened and the length in the easy axis direction can be shortened, the size of the magnetic body can be reduced.

Example 3
Next, an optical probe current sensor according to Example 3 of the present invention will be described. Since the measurement system and the measurement procedure are the same as those in the first embodiment, detailed description thereof is omitted. The optical probe current sensor according to the third embodiment is different from the optical probe current sensor according to the first embodiment in that the magnetic body has one or a plurality of grooves along the easy axis of magnetization. The depth d of at least one of the grooves is that it is not more than the thickness t _m of the magnetic material. FIG. 9 shows a perspective view and a cross-sectional view of a magnetic body used in the optical probe current sensor according to Embodiment 3 of the present invention. FIG. 9B is a cross-sectional view taken along a line CC in FIG. 9A in a direction perpendicular to the horizontal plane of the conductor 2. The magnetic body 1 ″ is provided with a groove 1b along the easy axis direction Ae. The groove 1b is formed in the thickness direction of the magnetic body 1 ″, but does not penetrate therethrough. The groove 1b does not have to be formed over the entire region in the easy magnetization axis direction Ae of the magnetic body 1 ″, but it is preferable that the groove 1b has such a length that the shape magnetic anisotropy sufficiently appears.

9A and 9B show an example in which only one groove 1b is formed. However, the present invention is not limited to this, and a plurality of grooves may be provided. In the case where a plurality of grooves are provided, a groove that penetrates in the thickness direction of the magnetic material (d = t _m ) and a groove that does not penetrate (d <t _m ) may be mixed. . Further, in the figure, an example of forming such a groove 1b overlapping with the reflective area 10 of the incident light L _i, this not limited, reflecting the length w _s of the hard magnetization axis direction of the magnetic material The groove 1b may be provided outside the reflective region 10 by making it sufficiently larger than the size of the region 10.

According to the optical probe current sensor according to the third embodiment, one or a plurality of grooves are provided in the magnetic body having shape magnetic anisotropy, so that the shape magnetic anisotropy is compared with the case where no groove is formed. Sex can be made to appear strongly. Further, by so as not to penetrate the grooves in the thickness direction of the magnetic body, it is possible to incident light L _i is prevented from leaking from the magnetic body.

  As described above, as a method for imparting shape magnetic anisotropy to a magnetic material, the configuration in which the magnetic material is formed in an elongated strip shape has been described. However, a needle-like crystal structure elongated in one direction in the plane of the magnetic material You may make it have.

  Moreover, although the example which applied the magnetic body to the optical probe current sensor was demonstrated in the above Example, it is not restricted to this, It can apply also to the other use which detects a magnetic field using the magnetic body mentioned above. .

DESCRIPTION OF SYMBOLS 1 Magnetic body 2 Conductor 11 Light source 12 Polarizer 13 1/2 wavelength plate or 1/4 wavelength plate 14 Polarizing beam splitter 15 1st light receiving element 16 2nd light receiving element 17 Operational amplifier 20 Magnetic field detection part 30 Current calculation part

Claims (5)

A magnetic body that is disposed in the vicinity of a conductor through which a current to be measured flows, has shape magnetic anisotropy, and a length of a portion along the easy magnetization axis direction is longer than a length of a portion along the hard magnetization axis direction;
A light source for irradiating the magnetic material with light;
A magnetic field detector that detects a magnetic field applied to the magnetic body based on a polarization state of reflected light reflected by the magnetic body;
A current calculation unit that calculates a current flowing through the conductor based on the magnetic field detected by the magnetic field detection unit;
An optical probe current sensor comprising:   2. The optical probe according to claim 1, wherein a length of a portion of the magnetic body along a hard axis direction is larger than a length of a hard axis direction in a region irradiated with light from the light source on the magnetic body. Current sensor.   The optical probe current sensor according to claim 1, wherein the magnetic body has one or a plurality of grooves along the easy axis direction.   The optical probe current sensor according to claim 3, wherein a depth of at least one of the one or more grooves is equal to or less than a thickness of the magnetic body.   The optical probe current sensor according to any one of claims 1 to 4, wherein a direction of a current flowing through the conductor coincides with an easy axis direction of magnetization of the magnetic body.

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