JP4223124B2 - Magnetic field sensor - Google Patents

Description

BACKGROUND OF THE INVENTION
[0001]
The present invention relates to a magnetic field detection element, for example, a magnetic field sensor using the magnetic impedance effect of an amorphous magnetic material.
[0002]
[Prior art]
As a magnetic field detection element, 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.
The inductance voltage component in the output voltage between both ends of the wire generated when a high frequency current is applied to the zero magnetostrictive or negative magnetostrictive amorphous magnetic wire is easily increased in the circumferential direction by the circumferential magnetic flux generated in the cross section of the wire. It occurs due to the magnetized outer shell being magnetized in the circumferential direction. Therefore, the circumferential magnetic permeability mu _theta depends on the circumferential direction of magnetization of Dosotokara portion.
[0003]
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. direction deviates from the circumferential direction, correspondingly hardly occur magnetization in the circumferential direction, the circumferential permeability mu _theta changes, the inductance voltage content will vary.
[0004]
Further, when the frequency of the energization current is in the order of MHz, the high frequency skin effect cannot be ignored, and the skin depth δ = (2ρ / wμ _θ ) ^1/2 (μ _θ is the circumferential penetration as described above. permeability, [rho is the electrical resistivity, w is the angular frequency) is changed by mu _theta, so changed by this as μθ is the external magnetic field, the resistance voltage of the in wire ends between the output voltage varies with an external magnetic field It becomes like this.
[0005]
Thus, the impedance Z is
Z = ra / (2δ) + jwL ₀ 2δ / a (1)
Given in.
Where a is the radius of the amorphous wire, r is the DC resistance value, L ₀ is the internal inductance of the amorphous wire, δ is the skin depth, and the length of the amorphous wire is I
r = ρ (I / πa ² )
[Equation 3]
L ₀ = μ _θ I / 8π
Given in.
[0006]
Conventionally, the inductance voltage due to the external magnetic field, or the resistance voltage, or both the inductance voltage and the resistance voltage, that is, the fluctuation of the output voltage across the amorphous wire (the fluctuation of the output voltage due to the external magnetic field is a magnetic impedance effect). A method for detecting an external magnetic field has been proposed (for example, JP-A-7-181239).
[0007]
[Problems to be solved by the invention]
The magnetic field detection method using the magnetic impedance effect of the amorphous wire is used for field control of outdoor equipment and equipment in a high temperature environment, such as magnetic field control for industrial robots, magnetic orientation sensors for automobiles, etc. Therefore, it is necessary to plan at least about −30 ° C. to 80 ° C. as the operating temperature range.
Thus, although it is predicted that the impedance changes depending on the temperature, according to the examination result of the present inventors, in the conventional magnetic field sensor using the amorphous wire, the above −30 ° C. to 80 ° C. In the temperature region, the inductance in the impedance changes suddenly with respect to the temperature change at a normal temperature (20 ° C.).
That is, as shown by the dotted line in FIG. 3A, in the temperature change from −30 ° C. → 80 ° C. → −30 ° C., dL / dT is negative between about 20 ° C. and 80 ° C. The dL / dT becomes positive between 20 ° C. and −30 ° C., and the change state of the inductance changes suddenly at about the 20 ° C. boundary.
[0008]
Therefore, the present inventor diligently investigated the cause of this, and presumed that this was caused by thermal stress acting on the amorphous wire due to differences in thermal expansion and contraction coefficient, Young's modulus, and cross-sectional area between the magnetic sensor support substrate and the amorphous wire. Is done.
That is, the temperature when an amorphous wire is connected between electrodes on the substrate is T ₀ , the thermal expansion / contraction coefficient, Young's modulus, and cross-sectional area of the amorphous wire are α ₁ , e _1, and s ₁ , respectively. If the shrinkage coefficient, Young's modulus, and cross-sectional area are α ₂ , e _2, and s ₂ , respectively, the thermal stress δ of the amorphous wire at a certain temperature T is
[Expression 4]
δ = −e ₁ (α ₁ −α ₂ ) (T−T ₀ ) / [1+ (e ₁ s ₁ ) / (e ₂ s ₂ )]
Given cross-sectional area _{s 1} of the amorphous wire with respect to the cross-sectional area _{s 2} of the _substrate, s 1 "because it is _{s 2} Equation 5] In
δ = −e ₁ (α ₁ −α ₂ ) (T−T ₀ )
Is established.
Therefore, the thermal expansion / contraction coefficient α ₁ of the amorphous wire is larger than the thermal expansion / contraction coefficient α ₂ when alumina ceramics is used for the substrate, for example. In the temperature region lower than the normal temperature T ₀ , the amorphous wire A tensile stress acts, and the tensile stress increases as the temperature decreases. In the temperature range higher than the normal temperature T _0, the stress in the equation becomes compressible, but the amorphous wire is slackened by compression in the longitudinal direction, and the compressive force is absorbed by the slack, so the stress of the amorphous wire becomes substantially zero. . Thus, the state in which the inductance decreases with a decrease in temperature starting from 20 ° C., which is a normal temperature, is in good agreement with the state in which the tensile stress increases with a decrease in temperature starting from the same 20 ° C.
[0009]
As is well known, in a magnetic material, as the temperature rises, the magnetic molecules easily rotate and the rotation loss decreases. Therefore, as the temperature rises, the magnetic permeability decreases and the inductance decreases. Also, as the temperature rises, the movement of free electrons becomes violent, so the resistance value increases as the temperature rises.
Thus, the resistance value-temperature characteristic of the amorphous wire is as shown in FIG. 3B, and unlike the case of the inductance, it is estimated that the amorphous wire is not affected by the tensile force.
However, the inductance exhibits a normal change (change in which the inductance decreases as the temperature rises) in the temperature region where the tensile force does not act. However, in the temperature region where the tensile stress acts, the inductance increases as the temperature rises. It is increasing and showing the opposite change from normal.
[0010]
In a magnetic field sensor that detects an external magnetic field using the magnetic impedance effect of an amorphous wire, if the inductance changes suddenly at a certain temperature, the output also changes suddenly. Become.
Therefore, the present inventor examined the inductance-temperature relationship in the temperature range of −30 ° C. to 80 ° C. so as to give sufficient slack to the amorphous wire and not generate a tensile stress on the amorphous wire. It has been found that the temperature decreases with increasing temperature in all temperature ranges and exhibits normal inductance-temperature characteristics.
[0011]
An object of the present invention is to prevent an abrupt change with respect to a temperature change of the inductance of an amorphous wire in a magnetic field sensor that detects an external magnetic field using the magnetic impedance effect of a magnetic field detection element based on the above-described intensive study results. In other words, the external magnetic field can be accurately detected.
[0012]
[Means for Solving the Problems]
The magnetic field sensor according to the present invention is a sensor for detecting an external magnetic field from a change in impedance of the amorphous magnetic body caused by an external magnetic field during energization of the amorphous magnetic body, and between the electrodes of the insulating substrate. The structure is characterized in that the body is connected with slack.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1A is a plan view of the magnetic field sensor according to the present invention, and FIG. 1B is a side view of the same.
In FIG. 1, 1 is an insulating substrate, for example, an alumina ceramic substrate. Reference numerals 2 and 2 denote electrodes fixed to the substrate 1 and have a lead portion 21. Reference numeral 3 denotes a magnetic field detecting element connected between the electrodes 2 and 2, for example, an amorphous wire, which gives a slack (a slack amount in the direction perpendicular to the substrate is y and a slack amount in the horizontal direction is x) 4. And each electrode 2 are joined by welding.
[0014]
The sagging is a size that can give a surplus length ΔI that does not generate a tensile stress to the amorphous wire in a temperature range of −30 ° C. to 80 ° C., for example, and between the welding points of the amorphous wire when the sagging is 0 the length I _{0, 1} the thermal expansion and contraction coefficients of amorphous wire _alpha, thermal expansion and contraction coefficients of the substrate alpha _2, the usual temperature (the temperature when connecting the amorphous wire to the electrode) and T _0,
When α ₁ > α ₂ (when the substrate is a ceramic substrate or a glass epoxy substrate),
[Formula 6]
ΔI> I ₀ (α ₁ −α ₂ ) (T ₀ +30) ( ₂ )
When α ₁ <α ₂ (when the substrate is a paper phenol substrate),
[Expression 7]
ΔI> I ₀ (α ₂ −α ₁ ) (80−T ₀ ) (3)
Given in.
These requirements are as follows if the minimum or maximum temperature in the operating temperature range is T ₁ :
ΔI> | I ₀ (α ₁ −α ₂ ) (T ₁ −T ₀ ) |
It can be expressed as
[0015]
As the magnetic field detection element, for example, an amorphous material having a wire diameter of 100 to 20 μm obtained by a spinning method in a rotating liquid (a method in which a molten alloy is ejected from a circular nozzle and then injected into a high-speed rotating cooling liquid and rapidly solidified). Fine wire can be used. Instead of an amorphous wire, it can be obtained by an amorphous ribbon, for example, a gun method (a method in which an inert gas is blown into a melting furnace, molten metal is blown out from a slit below the melting furnace, and this is struck against a metal slide below and rapidly solidified) Ribbons can also be used.
Further, fine crystalline fine wires and ribbons produced by the same method can be used.
As the amorphous alloy, zero magnetostrictive or negative magnetostrictive iron, cobalt or nickel alloys, for example, FeCoSiB alloys can be used.
[0016]
As the insulating substrate, a ceramic substrate, a glass epoxy substrate, a paper phenol substrate, or the like can be used.
[0017]
In the magnetic field sensor according to the present invention, the magnetic permeability μθ of the magnetic field detection element is changed by an external magnetic field passing through the magnetic field detection element that is energized with a high-frequency current or a pulse current in the axial direction. A phenomenon in which the resistance component or inductance component of the impedance changes, that is, an external magnetic field is detected by utilizing the magnetic impedance effect. For example, an Colpitts oscillation circuit is assembled using an amorphous wire as an inductive element, and the inductance due to the external magnetic field The amplitude of the oscillating wave is modulated by the change in the frequency, the modulated wave is demodulated, the demodulated output is amplified and used as a sensor output, and the output current of the astable multivibrator composed of the C-MOS inverter IC Is applied to the amorphous wire, and the pulse voltage appearing at both ends of the amorphous wire It is possible to use a method of holding a sensor output by holding a diode and a capacitor / resistor parallel circuit.
[0018]
In the magnetic field sensor according to the present invention, for example, even if it is used in a temperature range of −30 ° C. to 80 ° C., the magnetic field detection element is prevented from generating a tensile stress. As can be seen from the measurement results, the inductance change with respect to the temperature change can be made substantially uniform in the entire temperature range, the occurrence of the sudden change point of the inductance can be eliminated, and the external magnetic field can be detected accurately. That is, when a sudden change in inductance occurs, this causes a detection error because the sensor output changes. However, the magnetic field sensor according to the present invention can accurately detect an external magnetic field without any false detection. .
[0019]
It should be noted that since the amount of external magnetic field passing through the axial direction of the magnetic field detection element changes depending on the shape and direction of the deflection of the magnetic field detection element and the sensor output is also affected, it is desirable that the shape and direction of the deflection be uniform. The shape of the slack is not limited to an arc shape. For example, as shown in (a) (plan view) of FIG. 2 and (b) of FIG. 2, the shape of a horizontal line with both end portions raised may be employed.
[0020]
【Example】
〔Example〕
Electrodes are provided on an alumina ceramic substrate having a thickness of 30 mm (thermal expansion / contraction coefficient: 7.0 × 10 ⁻⁶ / ° C.) with an electrode interval of 3 mm, and an amorphous wire having an outer diameter of 30 μmφ (thermal expansion / contraction coefficient 12). 0.0 × 10 ⁻⁶ / ° C.) with a slack. The surplus length was approximately 1.5 times the amount of sag obtained from I ₀ (α ₁ -α ₂ ) (T ₀ +30) in the formula ( ₂ ).
[0021]
[Comparative example]
The example was the same as the example except that the amorphous wire was connected in a straight line without giving a slack.
[0022]
For each of these Examples and Comparative Examples (10 samples each), the inductance and resistance values at a frequency of 100 kHz were measured under a temperature change of −30 ° C. → 80 ° C. → −30 ° C. 3 (average value).
[0023]
As apparent from FIG. 3, in the comparative example (conventional example), the inductance change suddenly changes at a temperature of about 20 ° C., but in the example, there is no sudden change point of the inductance and a uniform change is exhibited as the temperature rises. Yes.
This difference is peculiar to the inductance that is not observed in the resistance value, and it is clear that the sudden change point of the inductance in the comparative example and the generation starting temperature of the tensile stress coincide with each other, which is caused by the tensile stress, In the embodiment in which the generation of the tensile stress is excluded, a sudden change in inductance can be prevented.
[0024]
【The invention's effect】
The magnetic field sensor according to the present invention is a phenomenon in which the magnetic field detection element impedance changes due to a change in the magnetic permeability μθ of the magnetic field detection element due to an external magnetic field passing through the energized magnetic field detection element in the axial direction. In a magnetic field sensor that detects an external magnetic field using the dance effect, even if the ambient temperature changes in the range of −30 ° C. to 80 ° C., it is possible to prevent a sudden change in the inductance due to the temperature change. This is not due to a change in the ambient temperature but due to a sudden change in the external magnetic field, and the external magnetic field can be accurately detected by the magnetic impedance effect of the magnetic field detection element.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a magnetic field sensor according to the present invention.
FIG. 2 is a drawing showing another example of the magnetic field sensor according to the present invention.
FIG. 3 is a diagram showing temperature-impedance characteristics of the magnetic field sensor according to the present invention.
[Explanation of symbols]
1 Insulating substrate 2 Electrode 3 Magnetic field detection element

Claims (3)

This is a sensor that detects the external magnetic field from the change in impedance of the magnetic field detection element due to the external magnetic field when the magnetic field detection element is energized, and connects the magnetic field detection element with slack between the electrodes on the insulating substrate. Magnetic field sensor characterized by that. When the slack of the magnetic field detection element is not slack, the length of the magnetic field detection element when there is no slack is I ₀ , the thermal expansion / contraction coefficient of the magnetic field detection element is α ₁ , the thermal expansion / contraction coefficient of the insulating substrate is α ₂ , and normal temperature To T ₀ The magnetic field sensor according to claim 1, wherein the temperature during use is T ₁ and is not less than | I ₀ (α ₁ −α ₂ ) (T ₁ −T ₀ ) |. When the insulation substrate is a ceramic substrate, the length of the magnetic field detection element due to the slack of the magnetic field detection element is I ₀ , the thermal expansion / contraction coefficient of the magnetic field detection element is α ₁ , and the thermal expansion of the ceramic substrate The magnetic field sensor according to claim 1, wherein the contraction coefficient is α ₂ , the normal temperature is T ₀ , and the value is equal to or greater than I ₀ (α ₁ −α ₂ ) (T ₀ +30).

Images