JPS59218971A - Measuring device of magnetic field - Google Patents

Abstract

PURPOSE:To improve the sensitivity of magnetic field intensity and to measure the magnetic field accutately by arranging a ferromagnetic material magneto- optics conversion part having light reflectors on both the ends between a polarizer and an analyser and arranging a magneto-optics conversion part in the magnetic field. CONSTITUTION:The ferromagnetic material magneto-optics element 1 having light reflectors 4 on both the ends is arranged between the polarizer 2 and the analyser 3 of which transmitted polarized-light directions are different each other. A photodetecting means 10 detecting an output obtained after light from a light source 9 has been transmitted through the magneto-optics element 1 is provided. If the magneto-optics element 1 is arranged in the magnetic field, the magnetic field intensity is detected by the photodetecting means 10. When the thickness of the magneto-optics element 1 is reduced, the linear property and reproducibility of Farady effect are improved, but Radady's turning angle is reduced in proportion to the thickness and the sensitivity is reduced. Consequently, the effect efficiently increasing the thickness of the element is obtained by reflecting and reicprocating light in the magneto-optics element many times, so that high sensitivity, high linear property and high reproducibility are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic field measuring device for observing the Faraday effect due to the magnetic field of an optical element and measuring its (differential intensity).

Conventional Structure and Problems Recently, a method has been proposed that utilizes the Faraday effect, which is one of the magneto-optical effects, in place of the conventionally well-known Hall element and the like for measuring magnetic fields. Since it uses light as a medium, it has characteristics such as good insulation and is not susceptible to electromagnetic induction noise, and can be applied to high-voltage large-scale commercial measurements in power transmission equipment and first-class measurements of welding machines.

Figure 1 shows a principle diagram of a magnetic field measurement method using the Faraday effect. Figure 1 shows a principle diagram of a magnetic field measurement method using the Faraday effect. Element 1 is arranged.

Light that has been linearly polarized by a polarizer 2 (indicated by an arrow) is passed through this magneto-optical element 1-. Due to the Faraday effect, the 4m optical surface undergoes rotation in proportion to the magnetic field strength. Its rotation angle is indicated by θ.

The rotated polarized light passes through an analyzer 3 whose transmission polarization direction is different from that of the polarized light f2, and at step 1117, the magnitude of the angle θ is converted into a change in the amount of light. For example, when the transmitted polarization directions of the polarizer 2 and the analyzer 3 are different by 45 degrees, the change in the amount of light after passing through the analyzer 3 is expressed by the following equation.

△■= sin 2θ ・・・・・・・・・
...(1) Here, θ-VHg, △ is the amount of change in light intensity, is a proportionality constant, θ is the Faraday rotation angle [degrees], and ■ is the Weerde constant, and the unit is [n'tyn-○]. e〕
, which represents the sensitivity of the magneto-optical element.

Conventionally, lead glass and paramagnetic glass are often used as magneto-optical elements, but the Werde constant is small. It is well known that ferromagnetic materials, represented by Y3Fe5O12, have a large Faraday effect and are highly sensitive. However, Y3Fe5O12 is a ferromagnetic material,
There are domains (magnetic domains) with uniform magnetization. The Faraday effect of such a substance is explained in FIG.

Figure 2 shows the case of a strongly monolithic magneto-optical element with striped magnetic domains, and the magnetization S of adjacent magnetic domains is
is facing the opposite direction. When there is no magnetic field H as shown in FIG. 2(a), the magnetization cancels each other out and the Faraday effect does not occur. When an external magnetic field H is applied as shown in FIG. 2(b), the magnetization tends to align in the direction of the magnetic field. Therefore, the magnetization in the direction of the magnetic field increases, and the difference causes the Faraday effect. However, as shown in Figure 2, when the number of magnetic domains (rll d ) included in the diameter φ of the incident light beam L is small, the linearity and reproducibility of the 7-Araghi effect deteriorate. Figure 3 shows an example of the measurement. This is a measurement of the Faraday effect when the polarizer and analyzer are arranged at an angle of 45 degrees with respect to the change in light amount ΔI. The magneto-optical element is made of Ys Fe5012 and has a thickness of 4 mm. Here, the case is when a DC magnetic field is applied, and the change in light intensity is not proportional to the magnetic field strength, and the change in light intensity when increasing the magnetic field strength does not match that when decreasing it. .

This clearly shows that the linearity and reproducibility are poor.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide a compact magnetic field measuring device that is highly sensitive and has excellent linearity and reproducibility of measurement output.

The present invention provides a magneto-optical converter in which a ferromagnetic magneto-optical element having light reflecting mirrors at both ends is arranged between a polarizer and an analyzer whose transmission polarization directions are different from each other; an optical transmission path provided at both ends of the magnetic optical conversion section, a light generation means for drawing light to the optical transmission path, and a detection means for detecting the output after the incident light passes through the magneto-optic conversion section fjq. Towo・
By placing it in the magneto-optical magneto-optical conversion section, the magnetic field strength is detected by the detection section, preferably a ferromagnetic magneto-optic element, for example. It is represented by the general formula (TbxYl-x)3Fe5O12, and one in which X is (0, 1≦X≦03) is used.

Example It is known that the magnetic domain width of a ferromagnetic material has a shape effect, and if the thickness of the ferromagnetic material shown in FIG. By doing so, the reproducibility of the Faraday effect is reduced to the same level as above, but as shown in equation (1), the Faraday rotation angle θ becomes smaller in proportion to the thickness, and the measurement sensitivity becomes smaller. According to the present invention, reflection and reciprocation are performed multiple times in the magneto-optical element, effectively increasing the J speed, achieving high sensitivity, and improving linearity and reproducibility. A good one can be obtained.

An la magnetic field measuring device according to an embodiment of the present invention will be explained below.

One embodiment of the present invention will be described in FIG.

In the drawing, 1 is (Tb0.19 Yo, 81)3
A ferromagnetic magnetic element represented by Fe5o12,
Both sides are parallel polished so that the thickness a is 200 μm. Furthermore, the light incident and light emitting portions are polished and tilted by an angle φ. Reference numeral 4 denotes a light reflecting mirror made of an aluminum vapor-deposited film, which is attached to both sides of the magneto-optical element 1 which are parallel to each other and polished. 2 is a polarizer attached to the entrance portion of the magneto-optical element 1. 3 is magneto-optical element 1
The analyzer is attached to the light emitting part of the analyzer and is installed so that the transmitted polarization direction is inclined by 45 degrees with respect to the polarizer 2.

As the polarizer 2 and the analyzer 3, polarization separation plates made of T102 crystal, which have good temperature characteristics, excellent mechanical strength, and good polarization characteristics, were used. Magneto-optical element 1, light reflecting mirror 4
．． Polarizer 2. A magneto-optical converter consisting of the analyzer 3 is placed in the magnetic field H. Reference numerals 6 and 6 are selfoc lenses, respectively. The lens 6 converts the light incident on the magneto-optic converter into parallel rays, and the lens 6 collects the light that has passed through the magneto-optic converter. 7 and 8 are optical fibers forming an optical transmission path. 9 is a fiber, a light ray that enters 7, and the wavelength of the light is (T
bO,19YO,81)3 Among the wavelength range of 1.0 μm to 1.6 μm, which has good transmittance to the Fe5O12 crystal, a wavelength of 1.27 μm was used. Reference numeral 10 denotes a light detection means for detecting the light output transmitted through the magneto-optic converter, and converts it into an electric signal according to the light intensity detected here.

In the magneto-optical element of this example, the number of light reflections is 20.
times, the sensitivity is 20 times the sensitivity of 0.01 mm Oe when it passes once through a magneto-optical element with a thickness 2 of 200 μm, that is, 0.
It is 2°10e. An example of the magnetic field measurement results according to this example is shown in FIG.

Compared to the conventional array, the amplitude word difference, which represents linearity, was 11% or less, and the reproducibility was also good, at 11% or less.

In this embodiment, an aluminum vapor deposited film is used for the light reflecting mirror 4, but a reflecting mirror made of a dielectric multilayer film may also be used.

Further, a Tl 02 polarization splitting plate may be used for the polarizer 2 and the analyzer 3, or a polarization splitting plate made of CaCO3, a polarization beam sinter using a dielectric multilayer film, a Glan-Thompson prism, or the like may be used.

As the element 1, a ferromagnetic magneto-optical element having magnetic domains can be used, for example, Y a F el 50.
There are rare earth garnate crystals represented by 12. Among them, the general formula (TbxYlx)3 Fe5012 (o, 1≦
X≦0.3) is desirable.

Effects of the Invention As is clear from the above description, the magnetic field measuring device of the present invention can measure magnetic field strength with high sensitivity and accuracy, is relatively small, and has high industrial value.

[Brief explanation of the drawing]

Figure 3 is a diagram showing the results of measuring the linearity and reproducibility of the Faraday effect of an optical element with a large magnetic domain width, and Figure 4 is a diagram for explaining the magnetic domains of the body and the Faraday effect. A diagram for explaining a magnetic field measuring device in one embodiment,
FIG. 5 is a diagram showing the results of the actual milling of the present invention. 1...Magneto-optical element, 2...Polarizer, 3
...Analyzer, 4...Light anti-H theory, 5+ 6
...Self 2. Cleanse, 7, 8...
・Optical Fino Q1・・・9 light sources, 10・
...Light detection means. Name of agent: Patent attorney Toshio Nakao and 1 other person39 Figure 1 Figure 2 Figure 3 Figure 4

Claims (2)

[Claims] (1) A magneto-optic converter in which a ferromagnetic magneto-optical element having light reflecting mirrors at both ends is arranged between a polarizer and an analyzer with different transmission polarization directions, and +) rj magneto-optic conversion. an optical transmission path provided at both ends of the section; a light generating means for inputting light into the optical transmission path; means and II
f! ? Furthermore, a magnetic field measurement device characterized in that the magnetic field strength is detected by the detection unit by arranging the magneto-optical conversion unit in a magnetic field. (2) As a ferromagnetic magneto-optical element, the general formula (TbxYl
-x )3 Fe5O12, and the value of X is (0,
1. The magnetic field measuring device according to claim 1, wherein the magnetic field measuring device satisfies the following: 1≦X≦0.3.