JP3634281B2 - Magneto-impedance effect sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic field sensor using a magnetoimpedance effect element.
[0002]
[Prior art]
As an amorphous alloy wire, an amorphous alloy wire having zero magnetostriction or negative magnetostriction has been developed, which has an outer shell portion in which magnetic domains whose spontaneous magnetization directions are opposite to each other in the circumferential direction of the wire are separated by a domain wall. Yes.
[0003]
The inductance voltage component in the output voltage between both ends of the wire generated when a high-frequency current is applied to an amorphous magnetic wire having zero magnetostriction or negative magnetostriction is generated by the circumferential magnetic flux generated in the cross section of the wire. This occurs because the easily magnetizable outer shell is magnetized in the circumferential direction. Accordingly, the circumferential magnetic permeability μθ depends on the circumferential magnetization of the outer shell.
Therefore, when an external magnetic field is applied to the energized amorphous wire, the magnetic flux acting on the outer shell portion having the easily magnetizable property in the circumferential direction is obtained by synthesizing the circumferential magnetic flux and the external magnetic flux by the energization. Is deviated from the circumferential direction and magnetization in the circumferential direction is less likely to occur, and the circumferential magnetic permeability μθ changes. That is, if the deviation of the magnetic flux from the circumferential direction when an external magnetic field is applied is φ, the circumferential magnetic flux is reduced by cos φ and the μθ is reduced by this rotational magnetization. Therefore, the inductance voltage is reduced by the decrease in μθ.
[0004]
Further, when the frequency of the energization current is in the order of MHz, a high-frequency skin effect appears greatly, and the skin depth δ = (2ρ / wμθ) ^1/2 (μθ is the circumferential permeability, as described above, and ρ is The electrical resistivity, w is an angular frequency) changes with μθ, and this μθ changes with the external magnetic field as described above. Therefore, the resistance voltage component in the output voltage between both ends of the wire also changes with the external magnetic field.
[0005]
Therefore, the external magnetic field is detected from both the inductance voltage and the resistance voltage due to the external magnetic field, that is, the fluctuation of the output voltage between both ends of the wire (the fluctuation of the output voltage due to the external magnetic field is referred to as the magneto-impedance effect). Has been proposed (Japanese Patent Laid-Open No. 7-181239).
The characteristics of the magneto-impedance effect element itself are symmetric and non-linear.
[0006]
As shown in FIG. 2, the magnetic field detection apparatus using the magneto-impedance effect element basically oscillates for supplying a high-frequency current or a pulse current to the magneto-impedance effect element 13 ′ and the magneto-impedance effect element 13 ′. A circuit unit 1 ′, a detection unit 2 ′ and a measurement unit 3 ′ for detecting an external magnetic field by demodulating a modulation wave based on an impedance change between both ends of the magnetoimpedance effect element due to the external magnetic field Hex applied to the magnetoimpedance effect element 13 ′ The negative feedback magnetic field generating coil 2a ′ applies negative feedback, and the detection output Eo is given by
Eo≈Hex × lR / N (1)
The detection output Eo is linear (where l is the length of the negative feedback magnetic field generating coil, N is the number of turns, and R is the ground resistance), and a polarity is applied by applying a DC bias magnetic field by the bias magnetic field generating coil 2b ′. The external magnetic field can be detected regardless of whether or not.
[0007]
[Problems to be solved by the invention]
As the magneto-impedance effect element with a coil, a substrate having a magneto-impedance effect element disposed on one side is inserted into a bobbin or tube, and a negative feedback magnetic field generating coil and a bias magnetic field generating coil are wound around the bobbin or tube. (Hereinafter referred to as a bobbin type), or a negative feedback magnetic field generating coil and a bias magnetic field generating coil printed on the other side of a substrate having a magneto-impedance effect element disposed on one side (hereinafter referred to as a printed type). Are known.
However, the bobbin type is disadvantageous in high-density mounting on a wiring board due to an increase in dimensions and an increase in planar dimensions, and the distance between the magneto-impedance effect element and the magnetic field detection object is reduced due to the intervention of the coil. Therefore, it must be enlarged, and it is disadvantageous in terms of detection sensitivity.
On the other hand, the printed type has a disadvantage in terms of high-density mounting on a wiring board because of the flatness of the printed coil due to the flatness of the printed coil.
[0008]
An object of the present invention is to provide a magneto-impedance effect sensor that can reduce the plane size and can be detected close to a detection object with high sensitivity.
[Means for Solving the Problems]
A magneto-impedance effect sensor according to the present invention includes a magneto-impedance effect element disposed on one side of a substrate, and a coil in which a negative feedback magnetic field generating coil and a bias magnetic field generating coil are wound around an iron core. The iron core and the magneto-impedance effect element are arranged so as to form a magnetic circuit. A C-shaped iron core is used for the iron core, and a split type can be used.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1A is a side view showing an embodiment of the magneto-impedance effect sensor according to the present invention, FIG. 1B is a bottom view, and FIG. 1C is a cross-sectional view of FIG. -A cross-sectional view.
In FIG. 1, reference numeral 11 denotes an insulating substrate, and for example, a ceramic plate can be used. Reference numerals 12 and 12 denote electrodes provided on one side of the insulating substrate, and each include an element connecting protrusion 121. This electrode can be provided by printing and baking a conductive paste, for example, a silver paste. A magneto-impedance effect element 13 is connected between the protrusions 121 and 121 of the electrodes 12 and 12 by soldering or welding. Usually, zero magnetostrictive or negative magnetostrictive amorphous wires, amorphous ribbons, sputtered films, etc. are used. . Reference numeral 14 denotes a pin conductor attached to each electrode 12 by soldering or welding. In No. 2, a negative feedback magnetic field generating coil 2a and a bias magnetic field generating coil 2b are wound around a C-shaped iron core 21 (both are usually enameled wires made by baking an insulating paint on a copper wire). Both ends of the C-shaped iron core 21 are fixed to the other surface of the substrate 11 with an adhesive or the like so that the magnetic impedance effect element 13 and the C-shaped iron core 21 constitute a magnetic circuit.
The iron core material may be a magnetic material. Examples thereof include permalloy, ferrite, iron, amorphous magnetic alloy, magnetic powder mixed plastic, and the like.
[0010]
In the above, if the length of the C-shaped iron core 21 is la, the cross-sectional area is Sa, and the magnetic permeability is μa, the magnetic resistance Ra of the C-shaped iron core is
Ra = la / (Saμa) (2)
In addition, if the length of the magneto-impedance effect element portion that is a component of the magnetic circuit is lb, the cross-sectional area is Sb, and the magnetic permeability is μb, the magneto-resistance Rb of the magneto-impedance effect element portion is ]
Rb = lb / (Sbμb) (3)
Furthermore, if the magnetic resistance between the both ends of the C-shaped iron core and the magneto-impedance effect element is Rc, the magnetic resistance Rm of the magnetic circuit is given by
Rm = Ra + Rb + Rc (4)
Given in
Therefore, the self-inductance L1 of the negative feedback magnetic field generating coil 2a is expressed as follows:
L1 = N1 ² / Rm (5)
The self-inductance L2 of the bias magnetic field generating coil 2b is expressed by the following equation (6).
L2 = N2 ² / Rm (5)
Given in.
[0011]
Thus, the length of the C-shaped iron core 21 can be reduced by reducing the thickness of the substrate 11 so that Rc can be reduced and the height of the legs of the C-shaped iron core 21 is made slightly higher than the diameter of the winding. Therefore, the magnetic resistance Rm of the magnetic circuit can be made sufficiently low, and the number of turns N of each coil can be reduced accordingly. As a result, the coil 2 itself can be reduced in size.
[0012]
A magneto-impedance effect sensor according to the present invention is a substrate in which a negative feedback magnetic field generating coil and a bias magnetic field generating coil are wound around a C-shaped iron core, and a magnetic impedance effect element is arranged on one side. It can be manufactured by fixing the C-shaped iron core leg of the coil to the other surface with an adhesive.
Further, the C-shaped iron core is divided into a leg portion and a horizontal portion, the leg portion is fixed to the other surface of the substrate, and a negative feedback magnetic field generating coil and a bias magnetic field generating coil are provided on the C-shaped iron core horizontal portion. It can also be manufactured by joining both ends of the coiled horizontal part to the leg part by soldering or welding.
[0013]
【The invention's effect】
In the magneto-impedance effect sensor according to the present invention, a coil in which a negative feedback magnetic field generating coil and a bias magnetic field generating coil are wound around a C-shaped iron core is provided on the back surface of the base substrate of the magneto-impedance effect element. And the magneto-impedance effect element are fixed so as to form a magnetic circuit, and the outline of the magneto-impedance effect sensor can be confined to the outline of the base substrate. In addition, since the magnetic resistance of the magnetic circuit of the coil can be reduced, a predetermined inductance can be obtained with a smaller number of coil turns, and the height of the coil can be sufficiently reduced.
Furthermore, the magneto-impedance effect element surface can be brought close to the detection object.
Therefore, according to the present invention, it is possible to provide a negative feedback magnetic field generating coil and a magneto-impedance effect element with a bias magnetic field generating coil that are small and capable of high sensitivity detection.
[Brief description of the drawings]
FIG. 1 shows a magneto-impedance effect sensor according to the present invention.
FIG. 2 is a circuit diagram showing a normal magnetic field detection device using a magneto-impedance effect element.
[Explanation of symbols]
11 Substrate 13 Magneto-impedance Effect Element 2 Coil 21 C-shaped Iron Core 2a Negative Feedback Magnetic Field Generating Coil 2b Bias Magnetic Field Generating Coil

Claims (3)

A magneto-impedance effect element is disposed on one side of the substrate, and a coil in which a negative feedback magnetic field generating coil and a bias magnetic field generating coil are wound around an iron core is provided on the other side of the substrate. A magneto-impedance effect sensor, which is arranged so as to constitute a magnetic circuit. 2. The magneto-impedance effect sensor according to claim 1, wherein the iron core is a C-shaped iron core. 3. The magneto-impedance effect sensor according to claim 1, wherein the iron core is a split type.

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