JP2005164562A - Flux gate magnetic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flux gate magnetic sensor having a structure which can suppress outside leakage in a magnetic field so as to be low, and has high sensitivity and is suitable for detecting the local magnetic field. <P>SOLUTION: In the flux gate magnetic sensor, two amorphous ribbons with each of which has a sharp tip suitable for detecting the local magnetic field being arranged in parallel so as to slightly shift their tips, and a pair of exciting coils which generate magnetic fields in opposite directions, are wound on the ribbons from their edges, and magnetic field detecting coils are wound on respective center sections of the two amorphous ribbons and are connected so as to cancel a wide-area external magnetic field, whereby only the local magnetic field can be detected. Therefore, the influence of the wide-area external magnetic field, such as the terrestrial magnetism or the like, can be made less by this flux gate magnetic sensor, without using two sets of magnetic sensors. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

Detailed Description of the Invention

  The present invention is a new type of high-sensitivity magnetic sensor of the fluxgate type. In addition to detection of a wide magnetic field such as geomagnetism, non-destructive testing by magnetism, reading of magnetic ink of banknotes, observation of biomagnetism, etc. are weak. It is used in many fields where local magnetic field detection is required.

  The fluxgate magnetic sensor is a highly sensitive magnetic sensor that has been widely used for detecting weak magnetic fields such as geomagnetism. The magnetic sensor itself generates a magnetic field in order to put the magnetic material in a supersaturated state by applying alternating current to the exciting coil. When this generated magnetic field is applied to an object to be measured such as a magnetic body or a living body, the characteristics of the object to be measured may be affected. Therefore, the fluxgate magnetic sensor cannot be used for magnetic measurement of the object in such a case.

  As a structure with relatively little leakage magnetic flux to the outside, for example, a case where an excitation coil and a detection coil are formed on a toroidal high permeability magnetic material as shown in FIG. However, this shape is suitable for detecting a wide magnetic field such as geomagnetism, but is not structurally suitable for detecting a near magnetic field. In order to detect a near magnetic field with a fluxgate magnetic sensor, it is desirable to form an excitation coil and a detection coil on a rod-like high permeability magnetic body. However, in this structure, a large amount of leakage magnetic flux leaks to the outside, which may affect the characteristics of the measured object situation.

  In addition, when a fluxgate magnetic sensor is used for nondestructive testing, the increase in residual stress inside the material is measured. In this case, the detected magnetic field is smaller than that of various external magnetic fields generated by geomagnetism and electrical equipment. A small amount of crab. Furthermore, in non-destructive testing, it is difficult to shield an external magnetic field due to location restrictions, so in general, an attempt is made to take a difference using two sets of magnetic sensors, but the device becomes complicated. There is.

Problems to be solved by the invention

An object of the present invention is to provide a fluxgate magnetic sensor having a structure that can suppress a leakage magnetic field to the outside to a small extent and is highly sensitive and suitable for detecting a local magnetic field.
Furthermore, it is to provide a fluxgate magnetic sensor having a structure capable of suppressing the influence of the external magnetic field to a small extent without using two sets of magnetic sensors.

Means for solving the problem

  In order to achieve the above object, we use a rod-shaped magnetic material as a shape with a high permeability magnetic body, and in order to make the area of the tip portion sufficiently narrower than the cross-sectional area of the rod, the tip is conical, etc. The thing of the shape to be used was used. The shape of the bar is not necessarily a columnar shape, and may be a rectangle or other shapes, and the tip may take any shape according to the shape.

  As a material of the high magnetic permeability magnetic material, a rod-shaped amorphous magnetic material (hereinafter referred to as an amorphous ribbon) that is a soft magnetic material was used. Actually, it is possible to use not only an amorphous ribbon but also other rod-like high magnetic permeability magnetic bodies, but here, a case where an amorphous ribbon is used will be described.

  Further, in order to cancel the magnetic field that goes out, a set of modulation exciting coils including a first exciting coil and a second exciting coil that generate magnetic fields in opposite directions are used.

  The set of excitation coils for modulation is wound in opposite directions from both sides of the amorphous ribbon so as to be targeted with respect to the center of the amorphous ribbon. The terminals at both ends are respectively connected to an AC power source, and form a series closed loop as a whole to excite the amorphous ribbon.

  As a result, magnetic field symmetry is obtained around the amorphous ribbon. The modulation of the magnetic field is obtained in each of the set of excitation coils for modulation, and the magnetization is saturated in a sufficiently wide region. The overall magnetoresistance is greater than the zero field. A detection coil is separately wound around the central portion of the amorphous ribbon, thereby enabling detection of an external magnetic field introduced into the ribbon.

  First

The method of connecting the one set of excitation coil and AC power source described in the above is to connect an AC power source between the two terminals at the center of the amorphous ribbon, and connect the terminals at both ends of the amorphous ribbon to form a series closed loop. But the effect is the same.

  The one set of modulation exciting coils is wound in the same direction, and an AC power source is connected to the end side of the first exciting coil and the central side of the second exciting coil. The same effect can be obtained by connecting the center side and the end side of the second exciting coil.

  With the above method, a fluxgate magnetic sensor that suppresses the leakage magnetic field to the outside can be provided, but in addition to this, the local magnetic field is not affected by the wide-area external magnetic field generated by geomagnetism or electrical equipment. Provided is a fluxgate magnetic sensor capable of detecting only.

In order to achieve the above objective, we used two amorphous ribbons arranged in parallel. The configuration method is described below.
The two amorphous ribbons are bundled so that one protrudes slightly before the other. The two amorphous ribbons have a set of modulation exciting coils integrated with the two amorphous ribbons so that the two amorphous ribbons are opposed to each other so as to be directed to the center of the two amorphous ribbons from both sides. Two terminals on the center side of the two amorphous ribbons are connected to each other, and terminals on both ends of the amorphous ribbon are connected to an AC power source, forming a series closed loop as a whole.

  In the central part of the two amorphous ribbons, a detection coil is separately wound around the two amorphous ribbons. These coils are wound in such a direction as to extinguish the external magnetic field, and the terminals on one side are connected to each other. The remaining two terminals that are not connected serve as output terminals. An external magnetic field such as geomagnetism is equally input to the two amorphous ribbons, but a near magnetic field is input only to the amorphous ribbon that is in front.

  Previous

,

The method of connecting the two sets of modulation exciting coils and the AC power source described in the section of

Of course, this also applies to the following inventions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on examples with reference to the drawings.
FIG. 2 is a structural diagram of a fluxgate magnetic sensor of a type that suppresses the leakage magnetic field to the outside. In one amorphous ribbon, two first exciting coils and three second exciting coils are opposite to each other. It is wound to generate a magnetic field. Further, the center side terminals of the second first exciting coil and the third second exciting coil are respectively connected. Four AC power supplies are applied to the end side terminals of the first excitation coil 2 and the second excitation coil 3 to excite the amorphous ribbon.

Five detection coils are wound around the center of the amorphous ribbon, and a waveform of the detection magnetic field appears at both ends of the coil. FIG. 4 shows the waveform, 13 is the waveform I (t) of the AC power source applied to the excitation coils 2 and 3, and 13 is the output waveform R _M (t) of the detection coil. As is clear from the figure, the tip of the amorphous ribbon has a pointed shape suitable for detection of a local magnetic field.

  FIG. 3 is a structural diagram of a fluxgate magnetic sensor of a type that suppresses the leakage magnetic field to the outside and further reduces the influence from a wide-range external magnetic field such as geomagnetism. The amorphous ribbons of 6 and 7 are bundled in a state where 6 further protrudes slightly before 7 in a parallel state. Eight first exciting coils and nine second exciting coils are wound around the entire amorphous ribbon parallel to the two to generate magnetic fields in opposite directions. Furthermore, the center side terminals of the 8 first exciting coils and the 9 second exciting coils are respectively connected. Ten AC power supplies are applied to the end terminals of the first excitation coil 8 and the second excitation coil 9 to excite the amorphous ribbon.

  11 and 12 are detection coils, 11 is wound on an amorphous ribbon 6 and 12 is wound on an amorphous ribbon 7 in a direction to cancel a wide-area external magnetic field such as geomagnetism, and one end of 11 and 12 is connected. Yes. The two unconnected terminals 11 and 12 are output terminals, and the detected signals are output.

  FIG. 4 is a waveform diagram of a signal, 13 is a waveform of a modulation signal for excitation, and 14 is an output waveform of a detected signal. It can be seen that the output waveform of 14 detected signals has a frequency 13 that is twice the frequency of the excitation modulation signal waveform. 14, the point where the amplitude R (t) becomes 0 is observed, and the magnitude of the external magnetic field is measured.

The invention's effect

  By using the present invention, the fluxgate magnetic sensor can be used also in fields such as biomagnetism measurement that has been difficult to use because magnetic flux leaks to the outside and affects the measurement object. In addition, the influence of the wide-area magnetic field generated by geomagnetism and electrical equipment, which is a problem when detecting weak local magnetic fields, can be handled without complicated processing such as using two magnetic shields and sensors. It becomes possible to measure.

A configuration example of a conventional fluxgate magnetic sensor Configuration diagram of a fluxgate magnetic sensor that reduces the leakage magnetic field to the outside. Configuration diagram of a fluxgate magnetic sensor that suppresses leakage magnetic field to the outside and is less affected by a wide-area magnetic field Waveform diagram of fluxgate magnetic sensor in the present invention

Claims (3)

  A first modulation exciting coil wound in the center direction from one end of the rod-like high permeability magnetic body, and a second coil wound in the middle direction from the opposite end of the high permeability magnetic body. A modulation excitation coil, and the first modulation excitation coil and the second modulation are arranged so that the magnetic fields generated by the first modulation excitation coil and the second modulation excitation coil are in opposite directions, respectively. One end of each excitation coil is connected, and a modulation AC power source is connected to the other terminals of the first modulation excitation coil and the second modulation excitation coil to form a series circuit. By forming a detection coil in an intermediate portion of the rod-like high permeability magnetic body around which the first modulation excitation coil and the second excitation coil are wound, a leakage magnetic field from the device to the outside can be reduced. Fluxgate magnetism characterized by low holding Sensor.   The fluxgate magnetic sensor having the first and second exciting coils according to claim 1, wherein two rod-like high magnetic permeability magnetic bodies are arranged in parallel, and one of the rod-like magnetic bodies is more than the other of the rod-like magnetic bodies. The first modulation excitation coil, the second modulation excitation coil, and the AC power supply are connected to the first modulation excitation coil and the second modulation in the same manner as in claim 1. A series circuit is formed by connecting so that the magnetic field generated by the excitation coil is in the opposite direction, and two detection coils are provided in the middle portion between the first excitation coil and the second excitation coil. A fluxgate magnetic sensor, wherein the two magnetic rods are wound separately in such a manner as to cancel an external magnetic field and then connected in series so that only a local magnetic field can be detected by canceling a wide-area magnetic field. In the rod-like high permeability magnetic body according to claim 1 and claim, by making the tip portion conical or the like, the area of the tip portion is sufficiently narrower than the cross-sectional area of the rod, and the spatial resolution is improved. A fluxgate magnetic sensor using a soft magnetic material such as an amorphous magnetic material.

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