GB2313918A

GB2313918A - Linear magnetic field sensor

Info

Publication number: GB2313918A
Application number: GB9711812A
Authority: GB
Inventors: Kaneo Mohri; Kazumi Toyoda; Masaki Minabe
Original assignee: Uchihashi Estec Co Ltd
Current assignee: Uchihashi Estec Co Ltd
Priority date: 1996-06-07
Filing date: 1997-06-06
Publication date: 1997-12-10
Anticipated expiration: 2017-06-06
Also published as: GB2313918B; JP3607447B2; GB9711812D0; JPH1054870A; GB2313918A8

Abstract

In a magnetic field sensor, an external magnetic field detecting element (3) e.g. an amorphous magnetic alloy wire or magnetoresistor is disposed between electrodes (2a,2b), and a current flows through the element (3). An external magnetic field to be detected Hex is detected in the axial direction of the element (3) by superimposing a biasing magnetic field Hb with the external field resulting in a change of a voltage V 0 across the ends of the amorphous magnetic element (3). Magnetized materials are used as the electrodes (2a, 2b) and a static magnetic field generated thereby functions as the biasing magnetic field Hb to linearize the sensor response.

Description

LINEAR MAGNETIC FIELD SENSOR The invention relates to a linear magnetic field sensor using an amorphous magnetic element.

As an amorphous alloy wire, an amorphous alloy wire of zero or negative magnetostriction, such as CoZ0.5BI5SilOFe4 has been developed. Such a developed amorphous alloy wire has an outer shell where magnetic domains which are opposite to each other in spontaneous magnetization direction along the circumference of the wire are alternatingly arranged with being separated by magnetic domain walls.

The inductance voltage component of a voltage generated across the ends of the wire when a high-frequency current flows through such an amorphous magnetic wire of zero or negative magnetostriction is due to the phenomenon that the outer shell where the axis of easy magnetization elongates along the circumference is magnetized in the circumferential direction by magnetic fluxes in the circumferential direction which are generated in a cross section of the wire. Therefore, also the circumferential permeability pO depends on the circumferential magnetization of the outer shell.

When an external magnetic field in the axial direction of the amorphous wire is applied to the amorphous wire while the current flows therethrough, the circumferential magnetic fluxes due to the current flow are Synthesized with the external magnetic fluxes. This causes the magnetic fluxes acting on the outer shell where the axis of easy magnetization elongates along the circumEerence, to be deviated from the circumferential direction, whereby the magnetization is hardly caused in the circumferential direction. As a result, the circumferential permeability 8 is changed, and the inductance voltage component is varied.

Unexamined Japanese Patent Publication No. HEI6283344 has been proposed a technique for detecting an external magnetic field by using this phenomenon. In the proposed technique, such an amorphous wire is incorporated into one arm of a bridge circuit, a resistance voltage component of the output voltage (consisting of the voltage drop due to a resistance and the above-mentioned voltage drop due to an inductance) across the ends of the wire is canceled by balancing the bridge circuit, and only the inductance component is detected. The external magnetic field in the axial direction of the wire is detected on the basis of a variation of the detection voltage with respect to the external magnetic field.

When the frequency of the current flowing through the wire is raised to the order of MHz, the high-frequency skin effect cannot be neglected, and the skin depth 6 = (2p/ (where > 0 is indicates the circumferential permeability as defined above, p indicates the electric resistivity, and X indicates the angular frequency) is changed depending on e.

As described above, e is changed by the external magnetic field. Consequently, also the resistance voltage component of the output voltage across the ends of the wire is varied by the external magnetic field.

Therefore, a technique for detecting an external magnetic by using both the inductance and resistance voltage components due to the external magnetic field, i.e., a variation of the output voltage across the ends of the wire (hereinafter, a variation of the output voltage due to the external magnetic field is referred to as "impedance effect," and a variation of the inductance component as "inductance effect") is proposed (Unexamined Japanese Patent Publication No. HEI7-181239).

According to the external magnetic field detection method using the impedance or inductance effect, a magnetic field detection resolution of 1/105 Oe can be ensured in an AC magnetic field even if the wire has a very small size or a length of about 1 mm.

Unlike the wound induction detection, according to the external magnetic field detection method using the impedance or inductance effect, a sensor does not require a winding head, can be miniaturized, and is highly sensitive.

Consequently, a sensor based on this detection method is expected to be practically used in the fields of an audio tape recorder, a video tape recorder, a computer, a rotary encoder, and the like, in place of a magnetic reproducing fread of the wound induction detection type.

The impedance effect of an amorphous alloy wire of zero or negative magnetostriction depends on the following phenomena. The magnetic domains of an outer shell where magnetic domains of the positive spontaneous magnetization direction, and those of the negative spontaneous magnetization direction are alternatingly arranged are rotated by the circumferential AC magnetic field deviated by a certain angle (a") by the external magnetic field, thereby causing the circumferential permeability > 0 to be changed by the external magnetic field. Further, the skin depth is varied by the circumferential permeability > 8 changed by an external magnetic field. The sign of the deviation angle (aO) generates no difference. Consequently, no difference of the output arises in accordance with the sign of the external magnetic field in the axial direction of the wire or +Hex and -Hex, and parameters are symmetrically changed.

In a known technique, therefore, a biasing magnetic field is generated so as to attain linear characteristics.

However, this technique inevitably complicates the structure of a sensor device.

It is an object of the invention to provide a magnetic field sensor which uses the impedance or inductance effect of an amorphous magnetic wire of zero or negative magnetostriction, and in which the output can be made linear while ensuring simplicity of the structure of the sensor.

A linear magnetic field sensor according to the present invention comprises: a plurality of electrodes each comprising an permanent magnet; and an external magnetic field detecting element disposed between the electrodes; wherein an external magnetic field is detected by superposing a static magnetic field generated by the permanent magnets as a biasing magnetic field on the external magnetic field.

In the accompanying drawings: Fig. 1 is a plan view showing the linear magnetic field sensor of the invention; Fig. 2A is a view showing the use state of the linear magnetic field sensor of the invention; Fig. 2B is a partial enlarged view of the linear magnetic field sensor of the invention; Fig. 3A is a graph showing sensitivity characteristics of an example of the invention; and Fig. 3B is a graph showing sensitivity characteristics of a comparison example.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

Fig. 1 is a view showing an example of the linear magnetic field sensor of the invention.

In Figs. 1, reference numeral 1 designates an insulation substrate such as a glass-epoxy resin substrate or a ceramics substrate in which both the length and width are 10 mm or less. Reference numerals 2a and 2b designate a pair of bar-like electrodes each consisting of a magnetized material. Incidentally, the magnetized material in the present invention includes a permanent magnet, magnetized metal, magnetized alloy and the like. The electrodes are arranged in parallel and their tip end portions are fixed on one face of the insulation substrate 1. The rear end portions of the bar-like electrodes 2a and 2b are drawn out from the insulation substrate 1. The tip end portion of one of the bar-like electrodes, i.e., the electrode 2a is formed into a hook-like shape. The bar-like electrodes Ra and 2b are magnetized so that a static magnetic field is generated between the hook-shaped tip end 21a and the tip end 21b of the other bar-like electrode 2b. The reference numeral 3 designates an amorphous magnetic wire which is provided between the tip ends 21a and 21b of the bar-like electrodes by means of soldering or welding and which functions as the amorphous magnetic element. In order to widen the detection range for a localized magnetic-field, preferably, one end portion 31 of the wire is projected from the tip end 21a of the one electrode as shown in Fig. 2B.

Further, in this embodiment, although the electrodes 2a and 2b projects from the substrate, it is not always necessary to project therefrom. If the sensor has a shape like a chip part, it is not necessary to project therefrom.

Accordingly, the shape of the electrode can be changed in accordance with its use.

In the sensor shown in Fig. 1, although the thickness of a portion of the electrode which projects from the substrate is made thicker, this is not a specific feature of the present invention. This shape is useful so that the sensor is coupled with a connector or the like. Further, if this portion is too thin, it is easy to be broken. If this portion is too thick, it is difficult to couple with the connector and the sensor becomes large. Accordingly, the shape and the size of this portion can be variously changed in accordance with its use.

As the amorphous magnetic wire 3, used is an amorphous alloy wire of zero or negative magnetostriction having an outer shell where magnetic domains which are opposite to each other in spontaneous magnetization direction along the circumference of the wire are alternatingly arranged with being separated by magnetic domain walls.

Fig. 2A shows the use state of the linear magnetic field sensor of the invention.

In Fig. 2A, Hex indicates the external magnetic field to be detected, and Hb indicates the static magnetic field generated by the tip end 21a and 21b.

In order to detect the external magnetic field to be detected Hex, a high-frequency power source 4 is connected between the electrodes 2a and 2b so as to supply a highfrequency current to the amorphous magnetic wire 3, and an output voltage V0 across the ends of the wire is measured.

Fig. 3A shows an example of the output voltage characteristics according to the present invention with respect to the external magnetic field in the case where the biasing magnetic field is applied. The output voltage characteristic is linear.

Fig. 3B shows an example of the output voltage characteristics of a conventional one with respect to the external magnetic field in the case where the biasing magnetic field is zero. The output voltage characteristics have a symmetrical shape.

As described above, the output voltage is varied by the external magnetic field because of the following reasons.

That is, magnetic domains of an outer shell of an amorphous magnetic wire where magnetic domains of the positive spontaneous magnetization direction and those of the negative spontaneous magnetization direction are alternatingly arranged are rotated by the circumferential AC magnetic field deviated by a certain angle (O) by the external magnetic field, thereby causing the circumferential permeability gO to be changed by the external magnetic field. Furthermore, the skin depth is varied by the circumferential permeability gE changed by the external magnetic field. When there is only a difference of the sign of the deviation angle a", a difference is not generated in the output voltage.

Therefore, linear characteristics cannot be attained.

By contrast, when the biasing magnetic field Hb is applied, the output voltage value with respect to the external magnetic field (Hb+Hex) is different from that with respect to the external magnetic field (Hb-Hex). Therefore, the output voltage with respect to the external magnetic field to be detected -Hex can be made different from that with respect to the external magnetic field to be detected +Hex. Hence, it is possible to judge the polarity of the external magnetic field to be detected. When the biasing magnetic field Hb is appropriately set, linear characteristics can be attained as apparent from an example described below.

In this way, linear characteristics can be attained only by magnetizing the electrodes so as to form the electrodes as magnetized material. Consequently, it is not required to add special members for attaining linear characteristics, and the structure can be simplified.

As the electrodes of the magnetic field sensor of the invention, a material which stably exhibits electromagnetic characteristics even when heat is applied in soldering or welding of the amorphous magnetic wire and which has a sufficiently large coercive force is used. For example, a magnetized material which mainly contains Fe and to which Ni, Co, and the like are added may be used.

In the magnetic field sensor of the invention, an amorphous magnetic thin film (thickness: 0.001 to 5 zm) formed by conducting vacuum deposition or ion sputtering on a substrate may be used as the amorphous magnetic element in place of the amorphous magnetic wire.

The magnetized materials useful in the invention include also a semi-hard magnetic material.

The magnetic field sensor of the invention may be incorporated into a magnetic field sensor device while connecting a filter, an amplifier and the like to the output terminals of the sensor.

For example, a Colpitts oscillator is assembled by using the magnetic field sensor of the invention as an inductive element, and a demodulator which demodulates the amplitude modulation of the oscillator due to the external magnetic field is connected to the oscillator, whereby a magnetic field sensor device can be configured.

The inductance voltage component of the output voltage of the magnetic field sensor of the invention rises more sharply than the resistance voltage component.

Therefore, the output may be passed through a filter and only the inductance voltage component may be taken out so that this inductance voltage component is output.

In the case where the skin effect is so weak that the resistance voltage component is less varied with respect to the external magnetic field and the resistance voltage component is substantially constant, a bridge circuit may be configured so as to take out only the inductance voltage component, and the external magnetic field may be detected on the basis of a variation of the inductance voltage component.

In all the cases, according to the linear magnetic field sensor of the invention, a biasing means is incorporated into the element itself by configuring the electrodes as magnetized materials. Therefore, a circuit for generating a bias is not required, and the sensor device can be miniaturized as a whole.

The invention may be applied also to an MR magnetic field sensor using the magnetoresistance effect, in place of the amorphous magnetic element.

EXAMPLE Referring to Fig. 2A, a ceramics plate having a thickness of 1.0 mm was used as the insulation substrate 1, and a semi-hard magnetic material shown in Table 1 of JIS SK4 having a thickness of 0.1 mm (C: 0.90 to 1.00 wt%, Si: 0.35 or less wt%, Mn: 0.50 or less wt%, P: 0.03 or less wt%, S: 0.03 or less wt%, Cu: 0.03 or less wt%, Ni: 0.25 or less wt%, Cr: 0.20 or less wt%, and the remainder is Fe) was used as the electrodes 2a and 2b. The dimensions were set as follows: a = 5.0 mm, b = 6.0 mm, c = 10.30 mm, d = 0.5 mm, e = 0.3 mm, f = 0.3 mm, g = 0.5 mm, and h = 2.3 mm.

A Co705Bl5Sil0Fe4 amorphous wire having an outer diameter of 50 iim was used as the amorphous magnetic wire, and the electrodes were magnetized so that the static magnetic field of about 0.50 Oe was generated.

While a current of about 10 mA and about 40 MHz was supplied to the amorphous wire and the external magnetic field to be detected Hex was changed in the range of about 0.8 to +0.8 Oe, the output voltage across the ends of the wire was measured. As a result, excellent linear characteristics were obtained as shown in Fig. 3A (in Fig. 3, 100 mA corresponds to 0.16 Oe).

COMPARATIVE EXAMPLE A sensor configured in the same manner as the Example except that the electrodes were not magnetized was produced.

Measurement results of the output voltage across the ends of the wire are shown in Fig. 3B and exhibit symmetrical characteristics.

According to the linear magnetic field sensor of the invention, in the case where an external magnetic field detecting element is disposed between electrodes, a current flows through a wire, and the external magnetic field to be detected in the axial direction of the wire is Ji.nearly detected on the basis of a change of a voltage between the electrodes under application of a biasing magnetic field on the external magnetic field, the electrodes can be configured by magnets. Therefore, the structure is very simple and the sensor can be miniaturized as a whole.

Claims

1. A linear magnetic field sensor comprising: a a plurality of electrodes each comprising a magnetized material such as a permanent magnet, a magnetized metal and a magnetized alloy; and an external magnetic field detecting element disposed between said electrodes; wherein an external magnetic field is detected by superposing a static magnetic field generated by said magnetized materials as a biasing magnetic field on the external magnetic field.

2. The linear magnetic sensor according to claim 1, wherein said external magnetic field detecting element is an amorphous magnetic element.

3. The linear magnetic sensor according to claim 2, wherein a current flows through said amorphous magnetic element, and the external magnetic field is detected based on a variation of a voltage across ends of said amorphous magnetic element under superposing a biasing magnetic field on the external magnetic field.

4. The linear magnetic sensor according to claim 2, wherein a current flows through said amorphous magnetic element, and the external magnetic field is detected based on a variation of an inductance component of a voltage across ends of said amorphous magnetic element under superposing a biasing magnetic field on the external magnetic field.

5. The linear magnetic sensor according to claims 2, 3 or 4, wherein a tip end portion of said amorphous magnetic element is projected from at least one end of said electrode.

6. The linear magnetic sensor according to claim 1, 2, 3, 4 or 5, wherein the ends of said electrodes remote from the magnetic field detecting element project from said substrate.

7. The linear magnetic sensor according to claim 6, wherein the projecting ends of the electrodes have a width wider than said electrodes on said substrate.

8. The linear magnetic sensor according to claim 1, 2, 3, 4, 5, 6 or 7, wherein said electrodes are formed from a magnetized material comprising Fe, Ni and Co.

9. A linear magnetic sensor substantially as described with reference to Figures 1, 2 and 3A of the accompanying drawings.