JP2001208817A - Magnetic field detecting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an electric power consumption in a magnetic field detecting element to which a negative feedback magnetic field and a bias magnetic field are impressed for use. SOLUTION: A common coil C for impressing the bias magnetic field and the negative feedback magnetic field is laid along an element A for detecting an external magnetic field for outputting a modulated wave modulated by the external magnetic field under carrying of an excitation current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic field detecting element, and more particularly to a magnetic field detecting element utilizing a magnetic impedance effect (MI effect).

[0002]

2. Description of the Related Art As an amorphous alloy wire, a zero magnetostrictive or negative magnetostrictive amorphous alloy having 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 alternately separated by domain walls. Wire is being developed. The inductance voltage component in the output voltage across the wire generated when a high-frequency current is applied to the zero-magnetostriction or negative-magnetostriction amorphous magnetic wire is determined by the circumferential magnetic flux generated in the cross section of the wire in the circumferential direction. This is caused by the fact that the easily magnetizable outer shell is magnetized in the circumferential direction. Therefore, the circumferential magnetic permeability μθ depends on the circumferential magnetization of the outer shell. When an external magnetic field is applied to the energized amorphous wire, the magnetic flux acting on the outer shell having the magnetizability in the circumferential direction is obtained by combining the circumferential magnetic flux and the external magnetic flux by the energization. Is deviated from the circumferential direction, so that magnetization in the circumferential direction becomes less likely to occur, and the circumferential magnetic permeability μθ changes. That is, the deviation of the magnetic flux from the circumferential direction when an external magnetic field acts is φ
Then, the circumferential magnetic flux is reduced by a factor of cos φ, and the rotational magnetization reduces μθ. Accordingly, the decrease in μθ reduces the inductance voltage.

Further, when the frequency of the energizing current is on the order of MHz, a high-frequency skin effect appears greatly, and the skin depth δ =
(2ρ / wμθ) ^1/2 (μθ is the circumferential magnetic permeability, ρ is the electrical resistivity, w is the angular frequency, as described above) changes with μθ, and μθ changes with the external magnetic field as described above. Therefore, the resistance voltage in the output voltage across the wire also fluctuates due to the external magnetic field.

Therefore, an external magnetic field is generated 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 called the MI effect). It has been proposed to detect (Japanese Patent Laid-Open No. 7-181239). In the above description, the positive / negative direction of the direction of the external magnetic field causes a positive / negative difference in the circumferential direction φ of the magnetic flux.
cos ± φ does not change, and therefore the degree of decrease of μθ is not changed by the sign of the direction of the external magnetic field. That is, there is no discrimination for the polarity.

As described above, the output appearing at both ends of the MI element under the application of an external magnetic field under the application of a high-frequency current is a modulated wave due to the external magnetic field, and when an external magnetic field signal is detected by detecting the modulated wave. The detection characteristics are symmetric and non-linear as shown in FIG.
Therefore, a non-curve detection characteristic is obtained by applying a negative feedback magnetic field as shown in FIG. Further, in a detection range of an external magnetic field, a bias magnetic field for obtaining an asymmetric detection characteristic as shown in FIG.

FIG. 6 shows a conventional magnetic field detecting device utilizing the magnetic impedance effect, and is a Colpitts oscillation type using the inductance of the MI element as L. In FIG. 6, reference numeral 1 'denotes a Colpitts oscillation circuit including a transistor Tr, an MI element A', and capacitors C1 and C2. Re is inserted to increase the stability of oscillation against temperature changes and to change the sensitivity and the measured magnetic field range. 5 'is a shot key barrier diode D
And 6 ', an amplifier circuit for amplifying the demodulated wave output, and 61', a signal output terminal. 7
1 'is a coil for strong and negative feedback, and 72' is a coil for generating a bias magnetic field. In this Colpitts oscillation type magnetic field detecting device, the amplitude of the oscillating wave is modulated by the fluctuation of L of the MI element A 'due to the external magnetic field, and the modulated wave is demodulated by the detection circuit 5', which is demodulated by the differential amplifier circuit 6 '. Amplified and taken out as a sensor output, a negative feedback circuit and a coil 71 ′ drive negative feedback to the MI element A ′ by this output, and a bias magnetic field is applied to the MI element A ′ by the coil 72 ′. As shown in (c), an asymmetric linear magnetic field detection characteristic is shown.

[0007]

In the above description, if the exciting current is reduced when no negative feedback is applied to the MI element, distortion occurs in the detection characteristics. However, when negative feedback is applied, linear characteristics without distortion can be obtained. Therefore, it is considered that the negative feedback also contributes to the reduction of the exciting current, that is, the power consumption.

However, in the conventional MI element, an independent bias magnetic field applying coil and a negative feedback magnetic field applying coil are wound, and the mutual coupling of the two magnetic fields occurs due to the electromagnetic coupling between the two coils. The extra power is consumed for compensating for the cancellation, and the battery is quickly consumed, which is disadvantageous.

An object of the present invention is to reduce power consumption in a magnetic field detecting element, particularly an MI element, which is used by applying a negative feedback magnetic field and a bias magnetic field.

[0010]

A magnetic field detecting element according to the present invention comprises a common coil for applying a bias magnetic field and a negative feedback magnetic field to an external magnetic field detecting element for outputting a fluctuating wave fluctuated by an external magnetic field. It is a configuration characterized by being attached, and can be applied not only to the MI element in which the fluctuation due to the external magnetic field is performed by impedance change or inductance change, but also to a magnetoresistive element in which the fluctuation due to the external magnetic field is performed by DC resistance value change. .

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a plan view showing an embodiment of the magnetic field detecting element according to the present invention, FIG. 1B is a cross-sectional view taken along the line I-I of FIG. 1A, and FIG. The sectional views taken along the line C-A in FIG. In FIG. 1, reference numeral 11 denotes an insulating substrate, for example, a ceramic substrate. Reference numerals 12 and 12 denote opposing electrodes provided on the insulating substrate 11, which can be formed by printing and baking a conductive paste. Reference numeral 121 denotes a protrusion provided on the electrode 12. 13 is a lead pin fixed to each electrode 12. A
Is an MI element connected between the protruding portions 121 of the electrodes 12, and can use a zero magnetostrictive or negative magnetostrictive amorphous wire, an amorphous ribbon, a sputtered film, or the like. 14 is a plastic bobbin, C is a coil for applying a negative feedback magnetic field and applying a bias magnetic field wound around the bobbin body, and the above-mentioned MI element mounting board is inserted into the bobbin body.

FIG. 2 shows a case where a magnetic field detecting element according to the present invention is used.
1 shows an example of the configuration of a basic magnetic field detection circuit. FIG.
In the above, 1 is a high-frequency exciting current generating unit. E departure
The magnetic field detecting element according to claim 1, wherein A is the MI element.
And C indicates a coil. 5 is MIele
From the output wave of the
(Referred to as a magnetic field signal).
You. 61 is a detection end of the external magnetic field signal Eout. 8 is outside
Add or decrease the bias magnetic field generation signal to the
And outputs the addition or subtraction output to the coil C.
In the example shown in the figure, the operation circuit is an inverting input terminal.
Operational amplifier with negative feedback
Dance Z ₂, Input side insertion impedance Z₁)
ing.

If the maximum external magnetic field Hex to be detected by the magnetic field detecting device is ± Hmax, a bias magnetic field having an asymmetrical detection characteristic of which polarity can be determined over the entire area can be applied by the coil. various constants _{(Vcc, Z 1, Z 2} , resistance R, coil turns, etc.) are to adjust.

If the detection sensitivity when no negative feedback is applied is α and the feedback ratio is β, then αβ≫1 according to the negative feedback theory.
Set to

Eout = Hex / β−K (1) (where K is a constant determined by the bias current), if the number of turns of the coil is n, the coil length is 1 and the negative feedback resistance is R, β = nZ ₁ / (lRZ ₂ ),

The detection characteristic is set to be linear by satisfying Eout = Z ₂ lRHex / Z ₁ n−K (2)

In order to detect an external magnetic field using the magnetic field detecting device, the MI element A of the magnetic field detecting device is exposed to the action field of the external magnetic field Hex, and an exciting current is supplied to the MI element A. Thus, magnetization rotation occurs due to the MI element axial component Hex of the external magnetic field, and the aforementioned μθ decreases. Then, the impedance of the MI element under a high frequency where the skin effect appears strongly is (wμθ)
^Since it is proportional to ^1/2 , the signal output Eout changes due to the decrease of μθ with the increase of Hex. Since this signal output is based on the impedance change of the MI element, it appears as an amplitude modulated wave of the current flowing through the MI element A. Therefore, the output signal is taken out by demodulation by the detection circuit 5 to obtain the external magnetic field signal Eout.

In the above, when the negative feedback and the bias magnetic field are not applied, the detection characteristics become symmetrical. However, since the bias magnetic field is superimposed, the external magnetic field having the same magnetic field strength which is asymmetrical and has a different sign is discriminated. Can be detected. Further, since the negative feedback is applied and the relationship of the above equation 2 can be satisfied, the external magnetic field signal can be stably detected in a linear form.

In the above-mentioned magnetic field detecting element, an exciting current in a frequency band where a skin effect appears is used to make use of the magnetic impedance effect. , That is, the magnetic inductance effect can be used.

In the above-described magnetic field detecting device, the source of the exciting current of the MI element A is a piezoelectric effect type oscillator which is less affected by the ambient temperature (an oscillator utilizing the piezoelectric effect, a typical one is a crystal oscillator). However, it is advantageous to use a ceramic oscillator), and it is preferable to use a triangular wave obtained by integrating the rectangular oscillation output of the oscillator as the exciting current. This triangular wave includes all so-called sawtooth waves as long as it includes a repetition of a rising slope portion and a falling slope portion that hardly includes a horizontal portion. Although a demodulation circuit using a diode can be used as the detection circuit 5, the signal output (external magnetic field detection value) varies depending on the ambient temperature due to the unstable temperature characteristics of the diode. Therefore, it is desirable to use a demodulation circuit using an ideal diode. Further, the demodulated signal is usually 0.63
When the signal is used as an output of a control circuit or a display, it is desirable to amplify the signal by an amplifier because the signal is very small, about ^10-3 V / A / m.

FIG. 3 shows an example of a magnetic field detecting circuit using the magnetic field detecting element according to the present invention. In FIG. 3, the OS
C is a crystal oscillator, and its oscillation output is a rectangular wave.
c 'is a DC cut capacitor, and 2 is an integrating circuit, which forms a rectangular wave into a triangular wave. 3 is a triangular wave amplifier circuit, and 31 is an amplification input controller. E denotes a magnetic field detecting element according to the present invention, A denotes an MI element, and C denotes a coil. 5 is a Schottky barrier diode as a detector, and 61 is a signal output terminal. An operational amplifier 8 receives an external magnetic field signal and a bias magnetic field generation signal, amplifies the signal with a predetermined amplification factor, and inputs the amplified signal to the coil C.

FIG. 4 shows another example of a magnetic field detecting circuit using the magnetic field detecting element according to the present invention. In FIG. 4, reference numeral 1 denotes a rectangular wave oscillation circuit, which uses a low-power CMOS-IC as an oscillation unit, and has a crystal oscillator P arranged in parallel for stabilizing the oscillation frequency. Reference numeral 2 denotes an integration circuit for forming a triangular wave, and reference numeral 3 denotes an amplification circuit. E is a magnetic field detecting element according to the present invention, and A is M
I element and C indicate a coil. 5
Reference numeral denotes a detection circuit which uses an inversion type ideal diode in which a Schottky barrier diode and an operational amplifier are combined to prevent fluctuation of demodulation output due to ambient temperature. 51 is a peak hold circuit for demodulated signals, 6 is an output signal amplifier, 62 is a zero point adjuster, and 61 is a signal output terminal. An operational amplifier 8 receives an external magnetic field signal and a bias magnetic field generation signal, amplifies the signal with a predetermined amplification factor, and inputs the amplified signal to the coil C.

In the above magnetic field detection circuit, an operational amplifier circuit is used as an arithmetic circuit for adding or subtracting a bias signal for the external magnetic field to or from the external magnetic field signal and inputting the bias signal superimposed negative feedback signal to the coil. However, a differential amplifier circuit can be used, and further, an isolation amplifier, a photocoupler and the like can be used.

In the above-described magnetic field detecting device, the rectangular wave oscillation output of a crystal oscillator that is less affected by the ambient temperature or the rectangular wave oscillation output of a CMOS IC oscillator whose oscillation frequency is stabilized by a crystal oscillator is obtained by integration. Since a triangular wave is used for the excitation current, the external magnetic field can be detected while suppressing the influence of the ambient temperature. In addition, in the magnetic field detection device shown in FIG. 4, the ideal diode circuit is used for the detection circuit. There is an advantage that the external magnetic field signal amplitude-modulated by the current can be detected while sufficiently suppressing the influence of the ambient temperature.

The present invention can be applied to a magnetic field detecting element other than the MI type magnetic field detecting element, for example, an MR magnetic field detecting element. For example, in a magnetic detection device that detects the output of a magnetoresistive element that fluctuates based on a change in DC resistance value due to an external magnetic field and detects an external magnetic field signal, a coil is electromagnetically coupled to the magnetoresistive element, The external magnetic field can be detected by providing an arithmetic circuit for adding or subtracting a bias signal to the external magnetic field to the signal and inputting the bias signal superimposed negative feedback signal to the coil.

[0024]

According to the present invention, in a magnetic field detecting element used by applying a negative feedback magnetic field and a bias magnetic field, a single coil is used for applying both magnetic fields. In this case, the mutual cancellation of the magnetic fields can be eliminated, and the consumption of the battery as the magnetic field generating power source can be reduced accordingly, which is advantageous for portable use.

[Brief description of the drawings]

FIG. 1 is a drawing showing an example of a magnetic field detecting element according to the present invention.

FIG. 2 is a basic circuit diagram of a magnetic field detecting device using the magnetic field detecting element according to the present invention.

FIG. 3 is a drawing showing an example of a magnetic field detecting device using a magnetic field detecting element according to the present invention.

FIG. 4 is a drawing showing another example of a magnetic field detecting device using the magnetic field detecting element according to the present invention.

FIG. 5 is a drawing for showing detection characteristics of a magnetic field detection device using an MI element.

FIG. 6 is a diagram showing a conventional magnetic field detection device.

[Explanation of symbols]

 11 Substrate A Magnetic sensing element C Coil

Claims (5)

[Claims] 1. A magnetic field detecting element, wherein a common coil for applying a bias magnetic field and a negative feedback magnetic field is attached to an external magnetic field detecting element for outputting a fluctuating wave fluctuated by an external magnetic field. 2. The magnetic field detecting element according to claim 1, wherein the fluctuation due to the external magnetic field is performed by an impedance change. 3. The magnetic field detecting element according to claim 1, wherein the fluctuation due to the external magnetic field is performed by a change in inductance. 4. The magnetic field detecting element according to claim 1, wherein the fluctuation due to the external magnetic field is performed by a change in a DC resistance value. 5. A substrate on which a magnetic amorphous element is mounted is inserted into the body of a coil winding bobbin.
Or the magnetic field detecting element according to 3.