JP2006073974A - Magnetic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic sensor which is independent on the strength and polarity of an outside magnet and exhibits a stable output characteristic. <P>SOLUTION: The magnetic sensor is composed of a magnetic line whose end is worked thin, or, a magnetic line which has a soft magnetic magnet at the end. The magnetic sensor is independent on the size and polarity of the outside applying magnetic field and has a stable output voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic sensor.

  In conventional magnetic sensors, it is difficult to show stable output characteristics that do not depend on the strength or polarity of the external magnet. Therefore, a magnetic sensor having a novel structure is desired.

  The magnetic sensor disclosed in the magnetosensitive element (Japanese Patent No. 1238351) is based on the principle of pulse generation in a so-called composite magnetic wire. A composite magnetic wire is a magnetic wire composed of two layers having different coercive forces. By reversing the magnetization direction of the small coercive force portion while keeping the magnetization direction of the large coercive force portion constant, a pulse voltage is induced in the detection coil installed on the outer peripheral portion of the composite magnetic wire. A portion having a large coercive force with a constant magnetization direction is referred to as a fixed magnetization layer, and a portion having a small coercivity that reverses the magnetization direction by an external magnet is referred to as a free magnetization layer.

  The pinned magnetic layer and the free magnetic layer in the composite magnetic line can take two states: a parallel state in which the magnetization directions are the same and an antiparallel state in the opposite direction. The process in which the free magnetic layer shifts from the parallel state to the antiparallel state with respect to the fixed magnetic layer is defined as antiparallel magnetization reversal, and the process in which the free magnetic layer shifts from the antiparallel state to parallel state is defined as parallel magnetization reversal.

  Since the parallel state and antiparallel state are not equivalent to each other, the pulse voltage induced by the antiparallel magnetization reversal is generally unstable compared to the pulse voltage induced by the parallel magnetization reversal and has a small output. It is known that In order to maximize the output accompanying the parallel magnetization reversal, a method called an asymmetric excitation method (Japanese Patent No. 1776963) has been proposed. In this method, it is necessary to make the strengths of a magnet that causes antiparallel magnetization reversal and a magnet that causes parallel magnetization reversal unequal, which is not preferable in practice.

  In the parallel state, the magnetization directions of the fixed magnetization layer and the free magnetization layer are aligned, and a demagnetizing field is generated in the magnetic wire. This demagnetizing field is caused by the presence of positive and negative magnetic poles at both ends of the composite magnetic wire. The demagnetizing field contributes to making the external magnetic field for reversing the composite magnetic wire asymmetric.

  On the other hand, in the antiparallel state, the fixed magnetization layer and the free magnetization layer are magnetostatically coupled. Therefore, it has the function of preventing the reversal of the free magnetic layer by an external magnetic field.

In practical use of a magnetic sensor, it is required that the external magnetic field is smaller and that the magnitudes of positive and negative magnetic fields for inducing parallel and antiparallel magnetization processes are the same. However, the presence of a demagnetizing field and magnetostatic coupling is incompatible with these requirements, and it is desired to realize a magnetic sensor that exhibits stable output characteristics by applying a magnetic field having the same magnitude as positive and negative.
Japanese Patent No. 1238351 Patent No. 1769763

  It is an object of the present invention to provide a magnetic sensor that exhibits stable output characteristics independent of the strength and polarity of an external magnet.

  The present invention provides a magnetic sensor composed of a magnetic wire having a processed end or a soft magnetic magnet at the end.

  To provide a magnetic sensor composed of a magnetic wire having a shape such that the diameter of the end portion is smaller than the diameter of the central portion, or a magnetic wire having a soft magnetic magnet at the end portion.

  Of the both ends of the magnetic wire, the diameter of at least one end is smaller than the diameter of the other portion, or at least one end is provided with a soft magnetic magnet. To provide a magnetic sensor.

  A magnetic sensor that generates a pulse voltage in response to movement of an external magnet or change in an external magnetic field is provided.

  Two magnetic materials with different coercive forces due to different materials and compositions are combined into a magnetic wire with a two-layer structure, or a magnetic wire with a different coercive force at the outer and inner peripheral parts by twisting etc. Called magnetic wire. When the magnetization direction of the part with a large coercive force is kept constant and the magnetization direction of the part with a small coercive force is reversed, a high-speed magnetization reversal accompanied by a so-called large Barkhausen jump occurs. A pulse voltage is induced in the detection coil installed in the. This phenomenon is disclosed in a magnetosensitive element (Japanese Patent No. 1238351), and is practically used as a magnetic sensor for detecting rotation.

  In a composite magnetic wire, a portion with a large coercive force is called a fixed magnetization layer in order to keep the magnetization direction constant without reversing the magnetization, while a portion with a small coercivity that reverses the magnetization direction with an external magnet. This is called a free magnetic layer. The fixed magnetic layer and the free magnetic layer can take two states: a parallel state in which the magnetization directions thereof are the same and an antiparallel state in which the magnetization directions are opposite.

  The process in which the free magnetic layer moves from the antiparallel state to the parallel state with respect to the pinned magnetic layer is called parallel magnetization reversal. In this case, high-speed magnetization reversal accompanied by a large Barkhausen jump occurs, so that the detection coil has a wave. A high pulse output with a high value is induced.

  On the other hand, the pulse voltage induced by the antiparallel magnetization reversal, which is the process in which the free magnetic layer moves from the parallel state to the antiparallel state with respect to the fixed magnetic layer, is generally a pulse voltage induced by the parallel magnetization reversal. It is known that it is unstable and has a small output.

  The output asymmetry in these parallel magnetization reversal and antiparallel magnetization reversal is caused by the demagnetizing field and magnetostatic coupling generated in the magnetic wire. In the parallel state, the magnetization directions of the fixed magnetization layer and the free magnetization layer are aligned, and a demagnetizing field is generated in the magnetic wire. On the other hand, in the antiparallel state, the fixed magnetization layer and the free magnetization layer are magnetostatically coupled.

  Since these demagnetizing field and magnetostatic coupling are both problems that occur locally at the end of the magnetic wire, this problem has been solved by applying some processing and parts to the end of the magnetic wire.

  When the diameter of the end portion of the magnetic wire is made smaller than the diameter of the central portion, the demagnetizing field is distributed to the end portion of the magnetic wire and the portion where the step has a diameter in the parallel magnetization state. Therefore, it is possible to reduce the influence of the demagnetizing field that effectively contributes to the free magnetic layer. It is also clear that magnetostatic coupling in the antiparallel magnetization state is reduced because the ends are not aligned.

  When a soft magnetic magnet is applied to the end of the magnetic wire, the magnetic field applied from the outside concentrates on the soft magnetic magnet, so that the effective magnetic field strength applied to the magnetic wire is reduced. As a result, the externally applied magnetic field is not affected by the demagnetizing field in the parallel magnetization state. In addition, since the soft magnetic magnet absorbs the magnetostatic coupling magnetic field in the antiparallel magnetic field, the influence is reduced.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  In the case where an FeCoV alloy (Bikaloy alloy) is used as a magnetic wire, a two-layer structure having magnetically different properties as shown in FIG. 2 is obtained by performing a twisting process. Here, the outer peripheral portion 13 is a free magnetic layer having a small coercive force, and the inner peripheral portion 14 is a fixed magnetic layer having a large coercive force. FIG. 4A shows a parallel magnetization state, and FIG. 4B shows an antiparallel magnetization state.

  A magnetic wire composed of a plurality of portions having different magnetic properties, so-called composite magnetic wire, can be composed of a wide range of magnetic materials such as NiFe alloy in addition to a twisted FeCoV alloy wire. In addition to the twisting process, the function as a composite magnetic wire can be realized by changing the internal stress distribution, composition, material, and the like.

  Here, the present invention will be described with reference to an example in which a bicalloy alloy wire is adopted as a magnetic wire.

  FIG. 3 (a) shows the demagnetizing field 15 in the parallel magnetization state, while FIG. 3 (b) shows the magnetostatic coupling magnetic field 16 in the antiparallel magnetization state.

  1 and 6 are examples of the configuration of the magnetic wire according to the present invention. The basic element of the magnetic sensor of the present invention is composed of a magnetic wire 12 having a shape such that the diameter of the end in FIG. 1 is smaller than the diameter of the central portion, or soft magnetism at the end in FIG. It is composed of a magnetic wire provided with a magnet 17.

  A magnetic wire having a narrow end as shown in FIG. 1 can be implemented by performing an etching process or a polishing process only on the end.

  As an example, the magnetic wire shown in FIG. 4 has a length of 18 mm and a diameter of 0.25 mm, and the bicalloy alloy magnetic wire 11 is subjected to an etching process over a width of 4 mm from each end. Magnetic wires 12 having a diameter of 15 mm were produced.

  The output characteristics were measured when a sinusoidal alternating current magnetic field having both positive and negative polarities symmetrically applied to a magnetic sensor composed of these magnetic wires. With the magnetic wire 11 in FIG. 4 without the edge etching treatment, the output indicated by the black circle in FIG. 5 was obtained. The output here is a value obtained by converting the peak value of the pulse voltage induced in the detection coil into a voltage per turn. The output on the positive voltage side generated in the parallel magnetization process and the output on the negative voltage side generated in the antiparallel magnetization process are asymmetric. This phenomenon is an unfavorable characteristic that limits the adaptive range of the magnetic sensor in practical use due to the demagnetizing field and magnetostatic coupling existing in the magnetic wire as described above. Further, as the externally applied magnetic field increases, both the positive output and the negative output decrease, which means that the applicable range of the magnetic sensor with respect to the external magnetic field is narrow.

  On the other hand, in the magnetic wire 12 in FIG. 4 subjected to the edge etching process, the output indicated by the white circle in FIG. 5 was obtained. The positive output and the negative output are approximately the same value and are symmetric. That is, it does not depend on the polarity of the external magnetic field. This sensor characteristic is practically desirable when processing an output signal in an electronic circuit. In addition, the negative output had a very small voltage value in the magnetic wire without etching, but the output value increased in the magnetic wire subjected to the etching treatment. Further, as the externally applied magnetic field increases, a sufficiently large output for both positive output and negative output is secured, and it is clear that a magnetic sensor that secures a wider adaptive range with respect to the external magnetic field has been realized.

  From the knowledge that the demagnetizing field at the end of the magnetic wire and magnetostatic coupling are caused by the deterioration of the magnetic sensor characteristics, it is also effective to solve the problem by applying an external magnetic field only to the central part of the magnetic wire. is there. Therefore, FIG. 7 shows the effect of providing the soft magnetic magnets 17 at both ends like the magnetic wire 11 in FIG. The figure shows the result of measuring the magnetic field strength applied to each part of the magnetic wire with a micro coil when a uniform magnetic field of 20 Oersted (Oe) is applied to the entire magnetic wire from the outside. It was confirmed that the applied magnetic field intensity was almost zero at both ends of the magnetic wire. That is, the magnetic field is not applied to the end portion of the magnetic wire where the influence of the demagnetizing field exists. Further, since the magnetic flux of the magnetostatic coupling magnetic field is concentrated on the soft magnetic magnet, it is possible to avoid deterioration of sensor characteristics.

  Furthermore, it can be seen that in the magnetic wire provided with the soft magnetic magnet, a magnetic field of about 38 Oersted, which is larger than 20 Oersted of the external magnetic field, is applied to the central portion of the magnetic wire. This has an effect of increasing the magnetic field by the soft magnetic magnet, and realizes an improvement in sensitivity of the magnetic sensor.

  When the output characteristics of the magnetic sensor composed of the magnetic wire 17 provided with the soft magnetic magnet in FIG. 6 were measured, it was the same as that of the magnetic sensor composed of the magnetic wire having the end indicated by the white circle in FIG. 5 etched. The effect was confirmed. That is, the positive and negative outputs are symmetric, and a stable output can be obtained over a wide range of the external magnetic field.

Industrial applicability

  The magnetic sensor according to the present invention exhibits stable output characteristics over a wide range of the external magnetic field and does not depend on the polarity of the magnetic field. Therefore, for example, when used in a magnetic sensor for detecting rotation, there is little demand for the size and strength of the magnet installed in the rotating part, and a high output independent of the polarity of the magnet can be secured. A magnetic sensor having such properties is highly convenient in detecting rotation, speed, etc. in various devices and devices. It is obvious that these advantages are due to the processing of the end of the magnetic wire or the provision of a soft magnetic magnet, and the effects of the present invention are wide-ranging in industrial applications.

It is a figure which shows the structure of the magnetic wire which concerns on one Example of this invention. It is a figure which shows the structure in which the magnetization free layer and magnetization fixed layer in a magnetic wire are in a parallel state, respectively, and the structure in an antiparallel state. It is a figure which shows the demagnetizing field which arises when the magnetization free layer and magnetization fixed layer in a magnetic wire are in a parallel state, respectively, and the magnetostatic coupling which arises when it is in an antiparallel state. It is a figure which shows the structure of the magnetic wire which concerns on one Example of this invention. It is a figure which shows the output voltage of the magnetic sensor which concerns on one Example of this invention. It is a figure which shows the structure of the magnetic wire which concerns on one Example of this invention. It is a figure which shows the magnetic field strength applied to the magnetic wire which concerns on one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Magnetic wire 12 Magnetic wire 13 whose diameter of both ends is narrower than the diameter of the central portion 13 Free magnetic layer 14 Fixed magnetic layer 15 Demagnetizing field 16 in parallel magnetization state 16 Magnetostatic coupling 17 in antiparallel magnetization state Soft magnetic magnet

Claims (3)

  A magnetic sensor comprising a magnetic wire having a shape in which the diameter of the end portion is thinner than the diameter of the central portion, or a magnetic wire having a soft magnetic magnet at the end portion.   2. The magnetic wire according to claim 1, wherein at least one of the two ends of the magnetic wire has a diameter that is smaller than the diameter of the other portion, or at least one of the ends has a soft magnetic magnet. A magnetic sensor.   3. The magnetic sensor according to claim 1, wherein a pulse voltage is generated in response to a movement of an external magnet or a change in an external magnetic field.

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