JP2009180596A - Magnetic field probe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic field probe precisely detecting the intensity and the direction of the magnetic field in a frequency band between static magnetic field and MHz with a miniaturized, inexpensive, and simple circuit. <P>SOLUTION: The magnetic field probe detecting the intensity and the direction of the magnetic field in space includes: a sensor equipped with a substrate where a plurality of anisotropic magnetic resistance elements are formed and a permanent magnet; and a sensor fixing substrate equipped with a wiring part covered with a high conductive material for fixing the sensor. The sensor forms four regions in the positions of the same distance from the origin on X-axis and Y-axis with the magnetic center of the magnetic pole face of the permanent magnet as an origin on the substrate parallel to the magnetic pole face of the permanent magnet. For respective regions, two anisotropic magnetic resistance elements the angle of which respective extension directions form is normal extended at the angle of 45° (or 135°) with the axis line are adjacently formed so that it is constituted with totally eight anisotropic magnetic resistance elements. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic field probe for detecting the strength and direction of a magnetic field such as a permanent magnet, residual magnetism of a metal material, and a magnetic field in a space generated from a coil.

Magnetic field probes exist as devices for eliminating the influence of an electric field and detecting only a magnetic field. The electromagnetic field generated by the generation source includes components of an electrostatic magnetic field and an induction electromagnetic field in addition to the radiated electromagnetic field. These also affect electromagnetic noise in the vicinity of the source. The magnetic field probe is mainly used for the purpose of measuring electromagnetic noise due to a radiated electromagnetic field at a distance of about 1/6 wavelength or more from a generation source and for the purpose of specifying the generation source. The types of magnetic field probes include those using a loop antenna having a coiled loop (Patent Documents 1 and 2), a Hall probe as a technique for measuring electromagnetic noise in the vicinity of the source, and an anisotropic magnetoresistance. There is a magnetic field probe (Patent Document 3) in which an element and a loop antenna are combined.
JP 2002-156430 A JP 2004-085465 A JP 2001-289893 A

In the case of the magnetic field probe using the loop antenna described in Patent Documents 1 and 2, since the output from the coil is a differential waveform, that is, the induced voltage depends on the frequency of the magnetic field, a low frequency magnetic field of 100 kHz or less. Then, it is necessary to increase the sensitivity depending on whether the effective area of the loop is increased or the number of turns is increased. Therefore, there is a problem that the shape becomes large and it is difficult to measure a local magnetic field.
Although not described in detail, V ₀ = 2πfnSB ₀ is between the maximum value V ₀ of the induced voltage and the maximum value B _{0 of the} magnetic field applied to the coil at the number of turns n of the coil, the cross-sectional area S of the coil, and the frequency f. A relationship is established. For example, when f = 100 Hz, B ₀ = 0.002T, and n = 10, in order to obtain 0.098V as the maximum value V ₀ of the induced voltage, the radius of the coil must be about 5 cm. End up.

In the case of a Hall probe as a technique for measuring electromagnetic noise in the vicinity of the generation source, since a Hall element is used as a detection unit, detection is possible from a static magnetic field such as a permanent magnet to a low-frequency magnetic field of 10 kHz. The magnetic field range can be several hundred mT and is wide. However, there is a problem that it is difficult to detect a magnetic field in a frequency band of 10 kHz or more. In addition, the Hall element has a problem that it is difficult to have a magnetic field resolution of 0.05 mT or less.
That is, the magnetic field probe and the hall probe using the loop antenna have a problem in that it is difficult to perform efficient measurement covering the entire frequency range of 100 kHz or less with respect to electromagnetic noise near the generation source.

On the other hand, in a magnetic field probe that combines an anisotropic magnetoresistive element and a loop antenna as described in Patent Document 3, a magnetic field in a low frequency band of 100 kHz or less from a static magnetic field is generated by an anisotropic magnetoresistive element. Since a magnetic field having a frequency of 100 kHz or higher is measured by the loop antenna, magnetic field detection corresponding to a wide range of frequencies is possible. In general, an anisotropic magnetoresistive element is formed of a thin film of an alloy mainly composed of a ferromagnetic metal such as Ni, Fe, or Co, and the resistance value changes according to the direction of the magnetic field strength. The response of the ferromagnetic thin film metal is measured as ΔR / R ₀ (ΔR = change in resistance of the ferromagnetic thin film metal, R ₀ = nominal resistance of the ferromagnetic thin film metal).
As shown in FIGS. 9A and 9B, the relationship between the strength (H) of the magnetic field perpendicular to the direction of the current and ΔR / R ₀ is the bell shape (ΔR / R ₀ is H ^2). It is a graph of (decrease substantially in proportion to).

  The problem of the magnetic field probe combining this anisotropic magnetoresistive element and the loop antenna is that the operating point is a zero magnetic field as shown in FIG. Even if the width is examined and the sensitivity is increased, in some cases, it is difficult to obtain a magnetic field resolution of 0.01 mT. Further, FIG. 9C is an enlarged view of the vicinity of the zero magnetic field in FIG. 9B. However, as shown in FIG. 9C, hysteresis always occurs when the operating point is a zero magnetic field. There is a problem that accurate detection cannot be performed, or a processing circuit for obtaining a result excluding the influence of hysteresis is required, and the configuration becomes complicated.

  The present invention has been made in view of the above problems, and provides a magnetic field probe that can detect the strength and direction of a magnetic field with high accuracy in a frequency band from a static magnetic field to MHz and can be realized with a small, inexpensive, and simple circuit. It is for the purpose.

  Claim 1 of the present invention is a magnetic field probe for detecting the strength and direction of a magnetic field in a space, comprising a substrate having a plurality of anisotropic magnetoresistive elements formed thereon and a permanent magnet, and a high conductivity. A magnetic field probe comprising: a sensor fixing substrate for fixing the sensor having a wiring portion covered with a material.

  According to a second aspect of the present invention, in addition to the first aspect, the sensor includes an X axis and a Y axis on a substrate parallel to the magnetic pole surface of the permanent magnet, with the magnetic center of the magnetic pole surface of the permanent magnet as an origin. Four regions are formed at the same distance from the upper origin, and an anisotropic magnetoresistive element is formed by extending each region in a direction that forms an angle of 45 ° (or 135 °) with the axis. A magnetic field probe comprising a total of four anisotropic magnetoresistive elements.

  According to a third aspect of the present invention, in addition to the first aspect, the sensor includes an X axis and a Y axis on a substrate parallel to the magnetic pole surface of the permanent magnet, with the magnetic center of the magnetic pole surface of the permanent magnet as an origin. Four regions are formed at the same distance from the upper origin, and the direction in which the extending directions of each region are perpendicular to each other, and the direction that forms an angle of 45 ° (or 135 °) with the axis The magnetic field probe is characterized in that two anisotropic magnetoresistive elements extending in the direction are formed adjacent to each other, and is composed of a total of eight anisotropic magnetoresistive elements.

  According to a fourth aspect of the present invention, in addition to the first to third aspects, the substrate on which a plurality of the anisotropic magnetoresistive elements are formed has a low magnetic permeability and is an insulator. .

  According to the first aspect of the present invention, since the magnetic field probe is configured by the sensor including the substrate on which a plurality of anisotropic magnetoresistive elements are formed and the permanent magnet, the bias from the permanent magnet is applied to the anisotropic magnetoresistive element. By applying a magnetic field, hysteresis is improved and magnetic field resolution is improved. Moreover, it is possible to eliminate the influence of the electric field by covering the wiring part with a material having high conductivity.

  According to a second aspect of the present invention, the sensor is the same on the substrate parallel to the magnetic pole surface of the permanent magnet from the origin on the X axis and the Y axis with the magnetic center of the magnetic pole surface of the permanent magnet as the origin. Four regions are formed at the position of the distance, and anisotropic magnetoresistive elements extending in a direction forming an angle of 45 ° (or 135 °) with the axis are formed for each region, and a total of 4 regions are formed. Since it is composed of two anisotropic magnetoresistive elements, the direction of the magnetic field can be detected with high accuracy.

  According to a third aspect of the present invention, the sensor is the same on the substrate parallel to the magnetic pole surface of the permanent magnet from the origin on the X axis and the Y axis with the magnetic center of the magnetic pole surface of the permanent magnet as the origin. Four regions are formed at distance positions, and for each of the two regions, the angle formed by the direction in which the layers extend is perpendicular to each other, and the two extending in the direction that forms an angle of 45 ° (or 135 °) with the axis Since the anisotropic magnetoresistive elements are formed adjacent to each other so as to be composed of a total of eight anisotropic magnetoresistive elements, the output can be obtained by configuring the eight anisotropic magnetoresistive elements in a Wheatstone bridge configuration. The second harmonic component is canceled out and the output linear range is expanded.

  According to a fourth aspect of the present invention, a substrate on which a plurality of the anisotropic magnetoresistive elements are formed is formed of a material having a low magnetic permeability and an insulator, for example, a ceramic or glass material, thereby providing a high frequency band. The eddy current generated by the magnetic field probe itself can be suppressed.

  A magnetic field probe according to the present invention is a magnetic field probe for detecting the intensity and direction of a magnetic field in a space, and includes a sensor having a substrate on which a plurality of anisotropic magnetoresistive elements are formed and a permanent magnet, and a material having high conductivity. A sensor fixing substrate for fixing the sensor provided with the wiring portion covered by the sensor, wherein the sensor is disposed on the substrate parallel to the magnetic pole surface of the permanent magnet. Four regions are formed at the same distance from the origin on the X-axis and the Y-axis with the magnetic center of the magnetic pole surface of the permanent magnet as the origin, and the angle formed by the extending direction of each region is relative to each region. Two anisotropic magnetoresistive elements that are perpendicular to each other and extend in a direction that forms an angle of 45 ° (or 135 °) with the axis are formed adjacent to each other, and are composed of a total of eight anisotropic magnetoresistive elements. It is characterized by. Hereinafter, a detailed description will be given based on the drawings.

  Embodiments of the present invention will be described. FIG. 1A is a perspective view showing a configuration of a magnetic field probe 10 of the present invention, and FIG. 1B is a side view. A sensor having a sensor 11 having a permanent magnet 13 on a substrate 12 on which a plurality of anisotropic magnetoresistive elements are formed, and a wiring portion 15 covered with a shield film 18 made of a material having high conductivity. It is composed of a fixed substrate 14. The sensor 11 and the sensor fixing substrate 14 are electrically connected by wire bonding between the wiring end 16 and the sensor 11 with a gold wire 17. Although not shown in the drawing, each wiring end 16 and the wiring 15 are electrically connected. Although illustration in this figure is omitted, the sensor 11 is protected by a single layer or multiple layers of silicon, epoxy, or urethane resin, which are general electronic component materials. The sensor fixing substrate 14 is made of a glass epoxy material or FPC (flexible printed circuit board), the wiring portion 15 is made of a Cu material, and the wiring end portion 16 is plated with Ni and Au. The shield film 18 is made of, for example, a copper thin film, and the shield film 18 and the wiring portion 15 are insulated. Since the wiring portion 15 is covered with a material having high conductivity, it is possible to eliminate the influence of the electric field.

  In FIG. 1, the sensor 11 is formed by arranging the permanent magnet 13 on the substrate 12. However, as shown in FIG. 2A or 2B, holes are formed in the front or back of the sensor fixing substrate 14. Further, the one in which the permanent magnet 13 is embedded can be cited as another embodiment of the present invention.

  FIG. 3A is a first embodiment relating to the configuration of the anisotropic magnetoresistive element of the sensor 11 in FIG. is there. The substrate 12 on which the anisotropic magnetoresistive element is formed is disposed so that it is parallel to the magnetic pole surface of the permanent magnet 13 and the center of the substrate 12 coincides with the center of the magnetic pole of the permanent magnet 13. Anisotropic magnetoresistive element 19 extended in a direction forming an angle of 45 ° (135 °) with respect to the axis in four regions on the substrate 12 at the same distance from the center (origin) on the X and Y axes. , 20, 21 and 22 are formed respectively. The anisotropic magnetoresistive elements (19 to 22) are connected on the substrate 12 as shown in FIG.

  FIG. 4A is a second embodiment relating to the configuration of the anisotropic magnetoresistive element of the sensor 11 in FIG. 1, and is a diagram showing the positional relationship between the permanent magnet 13 and the anisotropic magnetoresistive element in the sensor 11. is there. The substrate 12 on which the anisotropic magnetoresistive element is formed is arranged so that it is parallel to the magnetic pole surface of the permanent magnet 13 and the center of the substrate 12 coincides with the center of the magnetic pole of the permanent magnet 13. In each of the four regions on the substrate 12 at the same distance from the center (origin) on the X-axis and the Y-axis, the angle formed by the extending direction of each other is vertical and an angle of 45 ° (135 °) with respect to the axis Two adjacent anisotropic magnetoresistive elements extending in the direction of forming are formed, and a total of eight anisotropic magnetoresistive elements 23a, 23b, 24a, 24b, 25a, 25b, 26a, 26b are formed. The anisotropic magnetoresistive elements (23a to 26a and 23b to 26b) are connected to form a Wheatstone bridge on the substrate 12, as shown in FIG. 4B.

Next, the principle of improving the characteristics by constantly applying a bias magnetic field to the anisotropic magnetoresistive element will be described. In the resistance change of the anisotropic magnetoresistive element shown in FIG. 9A, a method for improving the characteristics by constantly applying a bias magnetic field is known as a known technique (for example, Japanese Patent Laid-Open No. 58-016580). It has been.
That is, by applying a bias magnetic field in the Y direction of the anisotropic magnetoresistive element shown in FIG. 9A, the hysteresis in FIG. 9C is eliminated, and the anisotropic magnetism shown in FIG. By applying a bias magnetic field in the X direction of the resistance element, the operating point moves from a 0 (zero) magnetic field to a P point magnetic field as shown in FIG.

  The detection signal indicating the resistance change of the anisotropic magnetoresistive element when the magnetic field generated from the generation source is an input magnetic field changes as shown in FIG. 6A when the operating point is a zero magnetic field. When moved to the point P, the change is as shown in FIG. As can be seen from FIG. 6, in FIG. 6 (b), the operating point has moved to a highly sensitive linear portion of the bell-shaped waveform (secondary curve waveform) rather than FIG. 6 (a). Accordingly, it can be understood that the magnetic field resolution is improved because the change width of the resistance value is increased even with the same magnetic field change. As a result, measurement is possible even in a magnetic field of 0.01 mT or less.

  In addition, a permanent magnet as means for applying a bias magnetic field according to the present invention will be described. FIG. 7 is a schematic diagram showing the magnetic vector of the permanent magnet 13, where (a) is a perspective view and (b) is a bottom view. As shown in FIGS. 7A and 7B, the magnetic vector of the permanent magnet 13 is generated radially from the magnetic pole surface. At this time, since the sensor 11 is configured by superimposing the magnetic pole surface of the permanent magnet 13 and the center of the substrate 12, all the anisotropic magnetoresistive elements shown in FIG. 3A or FIG. Is applied with a bias magnetic field in a direction of 45 ° with respect to the stretching direction. That is, the bias magnetic field is simultaneously applied in the X direction and the Y direction in FIG. 9A described above. Therefore, hysteresis is improved and magnetic field resolution is improved.

FIG. 8 is a schematic diagram showing a case where a magnetic field from a generation source is input to the magnetic field probe 10 of the present invention. The magnetic field probe 10 shown in FIG. 8 is a top view of what is shown in FIG. 1, with the X-axis and Y-axis in FIGS. 3 and 4 added, and the wiring and shields omitted from the drawing.
When the input magnetic field is applied from the directions of A, B, and C, respectively, the change in the resistance value of the anisotropic magnetoresistive element formed in the X axis direction and the resistance of the anisotropic magnetoresistive element formed in the Y axis direction The following relationship holds for the value change.
B: Resistance value change in the X-axis direction> Resistance value change in the Y-axis direction
B: Resistance value change in the X-axis direction = Resistance value change in the Y-axis direction
C: Resistance value change in the X-axis direction <Resistance value change in the Y-axis direction

  That is, by forming an anisotropic magnetoresistive element on the substrate 12 as shown in Example 1 or Example 2, the direction of the input magnetic field can be known. The magnitude of the amplitude representing the strength of the input magnetic field is proportional to the amplitude of the resistance value change. Since the second embodiment has a Wheatstone bridge configuration, the output is twice that of the first embodiment, the second harmonic component is canceled, and the linear range of the output is expanded. It can also be understood from FIG. 6B that the resistance value changes at the same frequency as the frequency of the input magnetic field.

  Further, by forming the substrate 12 from a ceramic or glass material that has a low magnetic permeability and is an insulator, eddy currents generated by the magnetic field probe 10 itself in a high frequency band can be suppressed.

According to the magnetic field probe of the present invention described above, it is possible to cope with a wide range from a static magnetic field to a frequency band of MHz, and it is possible to detect the strength and direction of the magnetic field with high accuracy while being small.
When the magnetic field probe of the present invention is actually constructed, the substrate 12 on which the anisotropic magnetoresistive element is formed has a size of about 2 mm × 2 mm, and the sintered ferrite material as the bias magnet 13 has a diameter of about 1.5 mm × 0.35 mm. Unlike the conventional loop coil described above, there is an advantage that the size can be reduced without depending on the frequency. There is also an advantage that the whole can be configured at a low cost.

(A) is a perspective view showing the structure of the magnetic field probe 10 of this invention, (b) is a side view. (A) And (b) is the schematic diagram showing the other Example of the sensor 11 in FIG. (A) is Example 1 regarding the structure of the anisotropic magnetoresistive element of the sensor 11 in FIG. 1, (b) is a circuit diagram showing the connection of the anisotropic magnetoresistive element. (A) is Example 2 regarding the structure of the anisotropic magnetoresistive element of the sensor 11 in FIG. 1, (b) is a circuit diagram showing the connection of the anisotropic magnetoresistive element. It is explanatory drawing showing the movement of the operating point of the anisotropic magnetoresistive element at the time of applying a bias magnetic field. It is a schematic diagram showing the resistance change of the anisotropic magnetoresistive element when the magnetic field generated from the generation source is the input magnetic field, (a) is a case where the operating point is a zero magnetic field, (b) This is a case where the operating point moves to point P. It is the schematic diagram showing the magnetic vector of the permanent magnet 13, (a) is a perspective view, (b) is a bottom view. It is the schematic diagram showing the case where the magnetic field from a generation source is input into the magnetic field probe 10 of this invention. (A) thru | or (c) are explanatory drawings explaining the general property of resistance value change of an anisotropic magnetoresistive element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Magnetic field probe, 11 ... Sensor, 12 ... Board | substrate, 13 ... Permanent magnet, 14 ... Sensor fixed board | substrate, 15 ... Wiring, 16 ... Wiring edge part, 17 ... Gold wire, 18 ... Shielding film, 19-22 ... Anisotropic Magnetoresistive elements, 23a to 26a and 23b to 26b, anisotropic magnetoresistive elements.

Claims (4)

  A magnetic field probe for detecting the strength and direction of a magnetic field in a space, comprising a substrate having a plurality of anisotropic magnetoresistive elements formed thereon and a permanent magnet, and a wiring portion covered with a material having high conductivity And a sensor fixing substrate for fixing the sensor.   The sensor forms four regions on the substrate parallel to the magnetic pole surface of the permanent magnet, with the magnetic center of the magnetic pole surface of the permanent magnet as the origin and at the same distance from the origin on the X and Y axes. The anisotropic magnetoresistive element extended in a direction forming an angle of 45 ° (or 135 °) with the axis is formed for each of these regions, and is composed of a total of four anisotropic magnetoresistive elements. The magnetic field probe according to claim 1.   The sensor forms four regions on the substrate parallel to the magnetic pole surface of the permanent magnet, with the magnetic center of the magnetic pole surface of the permanent magnet as the origin and at the same distance from the origin on the X and Y axes. Two anisotropic magnetoresistive elements extending in a direction in which the extending direction of each other is perpendicular to each of the regions and extending at an angle of 45 ° (or 135 °) with the axis are adjacent to each other. 2. The magnetic field probe according to claim 1, wherein the magnetic field probe is formed of a total of eight anisotropic magnetoresistive elements.   4. The magnetic field probe according to claim 1, wherein the substrate on which the plurality of anisotropic magnetoresistive elements are formed is an insulator with a low magnetic permeability.

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