JP5019196B2 - High frequency magnetic field measuring device - Google Patents

Description

  The present invention is a magnetic field strength measuring device, and in particular, by providing a magnetic field sensor head with frequency selection characteristics, a high frequency magnetic field measuring device that can selectively detect a frequency component and a direction component of a high frequency magnetic field can be selectively detected. The present invention relates to a high-frequency magnetic field measuring apparatus.

  In the vicinity of the source of the high-frequency electromagnetic field, it is known that the electromagnetic wave has a complicated electric field distribution and magnetic field distribution because radiation by high-order multipoles is not attenuated. Further, since the wave impedance is not a constant value in the immediate vicinity of the measurement target (wave source), the magnetic field distribution cannot be obtained only from the electric field measurement. For this reason, it is required to measure the high-frequency magnetic field distribution.

  FIG. 4 is a diagram showing the configuration of the optical element of the magneto-optical probe described in Non-Patent Document 1. In this magneto-optic probe, a Bi-YIG magneto-optic (MO) crystal placed in a magnetic field to be measured is irradiated with laser light, and light subjected to the Faraday effect is measured as reflected light. Further, this Non-Patent Document 1 describes the frequency characteristics of the response to the high frequency magnetic field in the arrangement of FIG. 5A, and this is shown in FIG. FIG. 5B also shows frequency characteristics when a static magnetic field from a permanent magnet is applied to the position of the laser beam spot on the magneto-optical crystal. Thus, it can be seen that when the static magnetic field is used, the output of the magneto-optic probe is lowered, but the frequency bandwidth in which the output is constant is expanded.

  Patent Document 1 describes a minute magnetic field detection element using the Faraday effect of a magneto-optical crystal as shown in FIG. Here, an apparatus for detecting a magnetic field component in a specific direction by changing the arrangement of crystals is described.

  When performing frequency analysis of a high-frequency magnetic field using a conventional device, it is necessary to analyze the detected signal using a spectrum analyzer, which has the disadvantage that the device is complicated and expensive. In addition, when performing a three-dimensional analysis of a high-frequency magnetic field component, it is necessary to detect the magnetic field component in each direction. For this purpose, a magnetic field probe with a sensor head using a magneto-optic crystal is mechanically rotated. Therefore, it is necessary to change the direction of the magnetic field probe or to use a magnetic field probe using magneto-optic crystals with different orientations, which has the disadvantage that the apparatus becomes complicated and the measurement time increases.

JP 2005-315697 A Ikegame "Measurement of high-frequency current waveform of magnetic head with magneto-optic probe", IDEMA Japan News No.53 pp.1-6, Joint Subcommittee (2002.11)

  When performing measurement analysis of a high-frequency magnetic field, an operation of picking up a specific frequency component from a magnetic field signal detected using a spectrum analyzer is required, but there is a drawback that the apparatus is complicated and expensive.

  In order to measure magnetic field components with different orientations, it is necessary to mechanically rotate the direction of the probe containing the magneto-optic crystal or use another probe having a magneto-optic crystal with a different orientation, which complicates the apparatus. In addition, there was a drawback that the measurement took time.

  In a conventional magnetic field intensity measuring device using a magneto-optic crystal, a spectrum analyzer needs to be used when obtaining a spectrum distribution of a high-frequency magnetic field, but according to the present invention, a specific frequency component can be obtained without using a spectrum analyzer. It becomes possible to detect selectively, and the configuration of the apparatus becomes simple. Further, in the conventional apparatus, the probe must be mechanically rotated or replaced with another probe. However, according to the present invention, the detection direction can be changed only by electrically controlling the direction of the external magnetic field. Therefore, measurement in a short time can be realized.

  According to the finding of the inventor of this application, in the high frequency magnetic field measurement using the magnetic Kerr effect or the Faraday effect of the magneto-optic crystal, the output characteristic of the high frequency magnetic field sensor head includes the static magnetic field as the frequency selective characteristic of the high frequency magnetic field. Alternatively, some have quasi-static magnetic field dependency. For example, a BLIG (Bismuth-doped lutetium iron garnet) crystal, which is a magnetic garnet material shown in FIG. 1, has a sharp peak at the high frequency end of the output characteristics. Further, when a static magnetic field is applied thereto, the peak position moves according to the magnetic field strength. The present invention uses this phenomenon, and proposes a high-frequency magnetic field measuring apparatus having frequency selection characteristics and capable of freely changing the selection characteristics by a static magnetic field or a quasi-static magnetic field.

Accordingly, the present invention provides a measuring apparatus for measuring the strength of a high-frequency magnetic field to be measured using the magnetic Kerr effect or Faraday effect exhibited by a magneto-optic crystal in a high-frequency magnetic field having frequency selectivity in a static magnetic field or a quasi-static magnetic field Because
Polarization measuring means for measuring the rotation angle of the polarization plane of the light irradiated on the magneto- optic crystal;
Auxiliary magnetic field generating means for applying a direct current or low frequency auxiliary magnetic field capable of changing the frequency selectivity of the magneto- optical crystal;
Display means for displaying the output of the polarization measuring means as a function of the intensity or direction of the auxiliary magnetic field;
Is provided.

The auxiliary magnetic field is generated by a plurality of independent permanent magnets or electromagnets, and at least one of the permanent magnets or electromagnets has auxiliary magnetic field adjusting means for changing the magnetic field at the light irradiation point of the magneto- optic crystal. It is to prepare.

  The magneto-optical crystal may be used as a magnetic probe by being fixed to the tip of an optical path using an optical fiber.

  In addition, the magneto-optical crystal is distributed on the surface of the measurement sample, and at least a part of the distributed magneto-optical crystal is irradiated with light from the polarization measuring unit, and a measurement position adjusting unit that selects a measurement position is provided. It may be provided.

  In addition, the direction of application of a direct current or low frequency auxiliary magnetic field is fixed, polarization measurement is performed in a plane, and the measurement result of the polarization measurement means is displayed, stored, or transmitted as two-dimensional data. Distribution of high frequency magnetic field strength can be obtained.

  Further, the direction of application of the direct current or low frequency auxiliary magnetic field is changed to a plurality of predetermined directions, the polarization measurement is performed in a planar shape, and the measurement result of the polarization measurement means is displayed and stored as two-dimensional data. Alternatively, by transmitting, it is possible to obtain a two-dimensional distribution of high-frequency magnetic field strength without being masked by a direct current or a low-frequency auxiliary magnetic field directed in a specific direction.

  In addition, the magneto-optical crystal is provided distributed on the surface of the measurement sample, and light from the polarization measuring unit is irradiated to a plurality of points of the distributed magneto-optical crystal, and the plurality of points of the polarization measuring unit are applied. Display means for displaying the output as a function of the intensity or direction of the auxiliary magnetic field.

  Further, when the auxiliary magnetic field generating means is an auxiliary magnetic field generating means for synchronous detection that generates an auxiliary magnetic field including an auxiliary magnetic field that varies periodically, the polarization measuring means is synchronized with the fluctuation period of the auxiliary magnetic field. Can be detected with high sensitivity.

  As the magneto-optic crystal, a magnetic garnet material such as BLIG (Bismuth-doped lutetium iron garnet) can be used.

Other magneto-optic crystals include C, Y (yttrium), Bi (bismuth), Lu (lutetium), Ga (gadolinium), Sm (samarium), Yb (ytterbium), Eu (europium), or Pr (praseodymium). ) And the like, and elements A and D each include a metal element such as iron, Ga (gallium), Al (aluminum), or Ge (germanium). A magneto-optic crystal having a composition formula of C ₃ A ₂ D ₃ O ₁₂ when O is oxygen can be used.

  The intensity of the auxiliary magnetic field is desirably higher than the saturation magnetic field of the magneto-optical crystal.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, devices having the same function or similar functions are denoted by the same reference numerals unless there is a special reason.

  First, as described above, according to the finding of the inventor of this application, the output characteristics of a high-frequency magnetic field sensor head using the Faraday effect of a magneto-optic crystal include a static magnetic field or a quasi Some have static magnetic field dependence. For example, in a BLIG (Bismuth-doped lutetium iron garnet) crystal (110) shown in FIG. When a magnetic field is applied, the peak position moves according to the magnetic field strength. As can be seen from FIG. 1, the frequency selection characteristic can be set in a frequency band of 10 GHz or more. Further, the example shown in FIG. 7 is a measurement example under an auxiliary magnetic field of 1 kOe or less, which is an example of a saturation magnetic field or less. In this case, a selection characteristic appears at the high frequency end. The present invention uses such a phenomenon, and relates to a high-frequency magnetic field measuring apparatus that can freely change its frequency selection characteristic by a static magnetic field or a quasi-static magnetic field.

  FIG. 2 shows a high-frequency magnetic field measuring apparatus that obtains a spectrum of a high-frequency magnetic field by measuring the Faraday effect of the magneto-optical crystal 3 provided on the measurement sample 2 that is a high-frequency magnetic field generation source. In the magneto-optical crystal, a reflecting mirror made of a multilayer dielectric film is formed in order to reflect light back. The magneto-optical crystal is, for example, BLIG. In order to measure the Faraday effect, pulsed light or continuous light from the laser light source 6 is input to the galvano scanner 5. The reason why the circulator 7 is used in the middle is to measure the returned light. As is well known, the galvano scanner is for specifying a point on the XY plane by using two movable mirrors, and can perform a sweep measurement to display a two-dimensional display of a measurement result. it can. The light from the galvano scanner 5 is converged on the magneto-optical crystal 3 by the converging optical system 4, and the light that has received the Faraday effect is reflected by the reflecting mirror and traces the optical path in the reverse direction to converge the optical system 4 and the galvano scanner. 5 to the circulator 7. Next, by passing the wave plate 8 and the polarizer 9, the change in the polarization of the return light that changes according to the high-frequency magnetic field strength is measured, and converted into an electrical signal using the photoelectric converter 10, and the computer 11 To enter. The computer 11 also performs analog-digital conversion, and the output of the photoelectric converter 10 is displayed on the display 12, stored in a storage device, or transmitted to another electronic device. The computer 11 sets the movable mirror of the galvano scanner 5 and sets the external magnetic field controller 13 to apply a static magnetic field or a low-frequency quasi-static magnetic field to the measurement sample 2. By changing the strength of the magnetic field, the peak frequency position of the output characteristics of FIG. 1 can be changed. Therefore, the spectral distribution can be measured by scanning the strength of the static magnetic field.

  Further, since the direction of the magnetic field can be set arbitrarily, the detection direction of the high-frequency magnetic field can be set. In FIG. 2, three coils are used as the external magnetic field generator. However, the number of coils is not necessarily limited to this, and it is possible to acquire orientation dependency by setting a plurality of coils to positions adjusted according to measurement. Is clear. Moreover, even if the external magnetic field generator uses a permanent magnet or has a variable magnetic field strength, it is clear that there is no problem even if such an external magnetic field generator is used.

As other materials of the magneto-optical crystal, C may be Y (yttrium), Bi (bismuth), Lu (lutetium), Ga (gadolinium), Sm (samarium), Yb (ytterbium), Eu (europium). Or a rare earth element such as Pr (praseodymium) as an element containing one or more elements, and A and D are each a single metal element such as iron, Ga (gallium), Al (aluminum), or Ge (germanium). Alternatively, it may be an element including a plurality of elements, and when O is oxygen, it may have a composition formula of C ₃ A ₂ D ₃ O ₁₂ . Incidentally, the composition formula of BLIG used in the above embodiment is (BiLu) ₃ (FeGa) ₅ O ₁₂ , and A and D are equal to FeGa.

  The thickness of the magneto-optic crystal is appropriately determined depending on the balance between the above-described material and the optical loss of the wavelength of light used for detecting the magneto-optic effect and the required sensitivity. Usually, the thickness is about 1 to 20 microns due to limitations such as light loss in the crystal. However, if the light loss at the light wavelength to be used is small, the thickness may be larger. In addition, when an auxiliary magnetic field equal to or higher than the saturation magnetic field is used, the crystal orientation dependency is reduced, so that a polycrystalline film or a coating film in which minute magneto-optical crystals are dispersed can be used.

  FIGS. 8 (a) and 8 (b) are measurements in the measurement system of FIG. 2, and a magneto-optic crystal film is provided on the strip line on the integrated circuit, and a static magnetic field is applied so as to be orthogonal or parallel to the strip line. FIG. 6 is an image of data obtained by performing sweep measurement on a measurement position. A high-frequency current flows through the strip line indicated by the dotted line. In FIGS. 8A and 8B, the high-frequency magnetic field strength is large on the side surface or top surface of the stripline. In the case of the arrangement shown in FIG. 8B, since a larger magneto-optical effect than that shown in FIG. 8A is obtained, measurement is performed with a lower sensitivity range. For this reason, in FIG.8 (b), the high frequency magnetic field intensity by the side of a stripline is displayed relatively weakly. Thus, it can be seen that the direction of the magnetic field to be measured can be selected by selecting the direction of the applied static magnetic field. That is, two-dimensional distribution measurement with a specific magnetic field component masked can be performed by fixing the static magnetic field direction and sweeping the high-frequency magnetic field in a planar shape. Conversely, when obtaining a high-frequency magnetic field intensity distribution without masking a specific magnetic field component, it is desirable to perform high-frequency magnetic field measurements performed in a plurality of static magnetic field directions by sweeping in a planar shape. At this time, it is obvious that the direction of the static magnetic field may be changed during the sweep, or the high-frequency magnetic field measurement may be performed by sweeping the static magnetic field in each direction in a planar shape.

  FIG. 3 is a diagram showing a high-frequency magnetic field measuring apparatus in which a magnetic field sensor head 15 using a magneto-optic crystal is installed at the tip of an optical fiber optical path and the position thereof is freely set by an XY stage 14. In measurement, the magnetic field sensor head 15 is often provided close to the measurement sample 2. The advantage of using the magnetic field sensor head 15 in this way is that there is no reflectance dependency due to a difference in position and no position dependency of the state of the magneto-optical crystal. A three-dimensional distribution can be obtained by performing a three-dimensional sweep measurement.

  In the above high-frequency magnetic field measuring apparatus, a magnetic field including an auxiliary magnetic field that varies periodically is generated. For this purpose, in addition to the current component for scanning the magnetic field, a periodic current for generating an auxiliary magnetic field that varies periodically is supplied to the coil for the external magnetic field generator. As a result, a fluctuating output is obtained from the photoelectric converter, and this output is synchronously detected with a periodic current for generating an auxiliary magnetic field. By this synchronous detection, high-sensitivity high-frequency magnetic field measurement can be performed.

It is a figure which shows the static magnetic field strength dependence of the high frequency magnetic field sensor head which is the principle of this invention. It is a figure which shows the 1st Example of this invention. It is a figure which shows the 2nd Example of this invention. It is a figure which shows the structure of the optical element of the magneto-optical probe described in the nonpatent literature 1. It is a figure which shows the frequency characteristic at the time of applying the static magnetic field of the magneto-optical probe described in the nonpatent literature 1. It is a figure which shows the structure of the magnetic field detection element described in patent document 1. FIG. It is a figure which shows the static magnetic field strength dependence below the saturation magnetic field strength of the high frequency magnetic field sensor head which is the principle of this invention. It is a figure which shows the example which changes the direction of a static magnetic field with respect to a high frequency current direction, and selects the direction of the magnetic field to measure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b, 1c External magnetic field generator 2 Measurement sample 3 Magneto-optic crystal 4 Converging optical system 5 Galvano scanner 6 Laser light source 7 Circulator 8 Wavelength plate 9 Polarizer 10 Photoelectric converter 11 Computer 12 Display 13 External magnetic field controller 14 X- Y stage 15 magnetic field sensor head

Claims (12)

A measuring device that measures the strength of a high-frequency magnetic field to be measured using a magnetic Kerr effect or a Faraday effect exhibited by a magneto-optic crystal in a high-frequency magnetic field,
Polarization measuring means for measuring the rotation angle of the polarization plane of the light irradiated on the magneto- optic crystal;
Auxiliary magnetic field generating means for applying a direct current or low frequency auxiliary magnetic field capable of changing the frequency selectivity of the magneto- optical crystal;
Display means for displaying the output of the polarization measuring means as a function of the strength of the auxiliary magnetic field;
A high-frequency magnetic field measuring apparatus comprising: The auxiliary magnetic field is generated by a plurality of independent permanent magnets or electromagnets, and at least one of the permanent magnets or electromagnets includes auxiliary magnetic field adjusting means for changing the magnetic field at the light irradiation point of the magneto- optical crystal. The high-frequency magnetic field measuring apparatus according to claim 1.   2. The high-frequency magnetic field measuring apparatus according to claim 1, wherein the magneto-optical crystal is fixed to a tip of an optical path using an optical fiber.   The magneto-optical crystal is provided distributed on the surface of the measurement sample, and includes a measurement position adjusting unit that irradiates at least a part of the distributed magneto-optical crystal with light from the polarization measurement unit and selects a measurement position. The high-frequency magnetic field measuring apparatus according to claim 1, wherein A measuring device that measures the strength of a high-frequency magnetic field to be measured using a magnetic Kerr effect or a Faraday effect exhibited by a magneto-optic crystal in a high-frequency magnetic field,
Polarization measuring means for measuring the rotation angle of the polarization plane of the light irradiated on the magneto- optic crystal;
Auxiliary magnetic field generating means for applying a direct current or low frequency auxiliary magnetic field capable of changing the frequency selectivity of the magneto- optical crystal;
A polarization measurement means for fixing the direction of application of a direct current or low frequency auxiliary magnetic field and performing polarization measurement in a plane;
Display means for displaying the measurement result of the polarization measurement means as two-dimensional data, storage means for storage, or transmission means for transmission;
A high-frequency magnetic field measuring apparatus comprising: A measuring device that measures the strength of a high-frequency magnetic field to be measured using a magnetic Kerr effect or a Faraday effect exhibited by a magneto-optic crystal in a high-frequency magnetic field,
Polarization measuring means for measuring the rotation angle of the polarization plane of the light irradiated on the magneto- optic crystal;
Auxiliary magnetic field generating means for applying a direct current or low frequency auxiliary magnetic field capable of changing the frequency selectivity of the magneto- optical crystal;
Polarization measuring means for changing the direction of application of a direct current or low frequency auxiliary magnetic field to a plurality of predetermined directions and performing polarization measurement in a plane,
Display means for displaying the measurement result of the polarization measurement means as two-dimensional data, storage means for storage, or transmission means for transmission;
A high-frequency magnetic field measuring apparatus comprising: The polarization measurement unit is a polarization measurement unit that irradiates a plurality of points with light from the polarization measurement unit and measures rotation angles of polarization planes of the light at the plurality of points irradiated on the magnetic crystal,
The magneto-optical crystal is distributed on the surface of the measurement sample, and the light from the polarization measuring means is irradiated to a plurality of points of the distributed magneto-optical crystal, and the output from the plurality of points of the polarization measuring means is output. 2. The high-frequency magnetic field measuring apparatus according to claim 1, further comprising display means for displaying as a function of the intensity or direction of the auxiliary magnetic field.   The magneto-optical crystal is provided distributed on the surface of the measurement sample, and includes a measurement position adjustment unit that selects a measurement position by irradiating a part of the distributed magneto-optical crystal with light from the polarization measurement unit. The high-frequency magnetic field measuring apparatus according to claim 1, wherein   The auxiliary magnetic field generation means is a synchronous detection auxiliary magnetic field generation means for generating a magnetic field including a periodically changing auxiliary magnetic field, and synchronizes the output of the polarization measuring means in synchronization with the fluctuation period of the auxiliary magnetic field. 2. The high-frequency magnetic field measuring apparatus according to claim 1, wherein the high-frequency magnetic field measuring apparatus performs detection and outputs.   10. The high frequency magnetic field measuring apparatus according to claim 1, wherein the magneto-optic crystal is a magnetic garnet material. C is a single rare earth element such as Y (yttrium), Bi (bismuth), Lu (lutetium), Ga (gadolinium), Sm (samarium), Yb (ytterbium), Eu (europium), or Pr (praseodymium). An element containing multiple elements,
Each of A and D is an element containing one or more elements such as iron, Ga (gallium), Al (aluminum), or Ge (germanium),
When O is oxygen
10. The high-frequency magnetic field measuring apparatus according to claim 1, wherein the magneto-optical crystal has a composition formula of C ₃ A ₂ D ₃ O ₁₂ .   The high-frequency magnetic field measuring apparatus according to claim 1, wherein the intensity of the auxiliary magnetic field exceeds the saturation magnetic field of the magnetization of the magneto-optical crystal.

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