JP2008164310A - Magnetic impedance effect sensor head, sensor and magnetic inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve detection sensitivity and broaden the detection area of the magnetic impedance effect sensor. <P>SOLUTION: The magnetic impedance effect element 1 is provided with an iron core 103 so as to form a magnetic loop. A plurality of magnetic impedance effect elements 1 wound with negative feed back coil 6 and bias magnetic field coil 7 on the iron core are serially arranged as magnetic impedance effects (1, 1), and moreover the mutual interval between the magnetic impedance effect elements 1 in the magnetic sensitive axis direction is made shorter than the length of the magnetic impedance effect element 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sensor using a magneto-impedance effect element, a sensor head thereof, and a magnetic inspection method using the sensor.

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.
The inductance voltage component in the output voltage between both ends of the wire generated when a high-frequency current is passed through an amorphous magnetic wire having zero magnetostriction or negative magnetostriction is caused 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, the circumferential permeability μθ is changed, and the inductance voltage is changed.
Thus, this fluctuation phenomenon is called a magnetic inductance effect, and an amorphous wire or the like that exhibits this effect is called a magnetic inductance effect element.

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 indicates the angular frequency, respectively) varies with μθ, and this μθ varies with the external magnetic field as described above, so that the resistance voltage component in the output voltage across the wire also varies with the external magnetic field. Become.
Thus, this fluctuation phenomenon is called a magnetoimpedance effect, and an amorphous wire or the like that exhibits this effect is called a magnetoimpedance effect element.

  Therefore, an external magnetic field detection method using the magneto-impedance effect element (see, for example, Patent Document 1) and an external magnetic field detection method using the magnetic inductance effect (see, for example, Patent Document 2) have been proposed.

  In the above, the positive and negative of the external magnetic field causes the circumferential shift φ of the magnetic field to be positive or negative, but the reduction factor cos (± φ) of the circumferential magnetic field does not change, so the degree of decrease in μθ is positive or negative in the direction of the external magnetic field. Does not change. Accordingly, the external magnetic field-output characteristics are substantially symmetrical with respect to the y axis as shown in FIG. 4A when the magnetic field is taken on the x axis and the output is taken on the y axis. In addition, as shown in FIG.

The magnetic field detection circuit using this magneto-impedance effect element basically has (1) a high-frequency current source 2 ′ for applying a high-frequency excitation current to the magneto-impedance effect element 1 ′, as shown in FIG. (2) a magneto-impedance effect element 1 ′, (3) a detection circuit 3 ′ that demodulates a modulated wave obtained by modulating the high-frequency excitation current (carrier wave) with an external magnetic field Hex applied to the magneto-impedance effect element, and (4) demodulation. It comprises an amplifier 4 'for amplifying a wave and (5) a detection output terminal 5'.
In FIG. 5B, (a) shows a detected magnetic field (external magnetic field) Hex applied to the magneto-impedance effect element, (b) shows a high-frequency excitation current wave (carrier wave) Ic passed through the magneto-impedance effect element, and (c). Represents a modulated wave as an output of the magneto-impedance effect element, and (d) represents a demodulated wave.

It can be expressed as in FIG. 4 from the left and right symmetry and nonlinearity and illustrates the relationship between the amplitude of the output E _out the amplitude Hex of the detection magnetic field (B).
Therefore, in the circuit of FIG. 5-1, a negative feedback coil indicated by 6 'is subjected to negative feedback to linearize the characteristics as shown in FIG.
Further, as shown in FIG. 4C, the characteristics shown in FIG. 4B can be moved in the direction of the arrow by a bias magnetic field as shown in FIG. It has been broken.
In FIG. 5A, reference numeral 7 'denotes a bias magnetic field coil.

6 (a) and 6 (b) show a known magneto-impedance effect element with a coil in the magneto-impedance effect sensor. In the case shown in FIG. 6 (a), a negative feedback coil is added to the magneto-impedance effect element 1 '. 6 'and a bias magnetic field coil 7' are wound. In the case shown in FIG. 6B, the magneto-impedance effect element 1 'is disposed on one surface of the substrate 100', and the iron core is disposed on the other surface of the substrate. 103 'is arranged to form a magnetic loop circuit with the magnetic impedance effect 1', and a negative feedback coil 6 'and a bias magnetic field coil 7' are wound around the iron core 103 '(Patent Document) 3).
JP 7-181239 A JP-A-6-283344 JP 2002-289940 A

In the magneto-impedance effect element with a coil shown in FIG. 6 (a), even if a magnetic flux enters from the middle of the element in the axial direction of the element as indicated by h ', an eddy current is generated in the coil and the magnetic flux cancels out. Therefore, the magnetic flux mainly passes from both ends of the magneto-impedance effect element in the element axial direction.
On the other hand, in the magneto-impedance effect element with a coil shown in FIG. 6B, the magnetic flux passes not only at both ends of the element but also from the intermediate surface of the element in the axial direction of the element.
Therefore, the magneto-impedance effect element with a coil shown in FIG. 6B has a larger amount of magnetic flux to be detected and has better detection sensitivity than the magneto-impedance effect element with a coil shown in FIG. . Further, the area that can be magnetically detected by one magneto-impedance effect element is vast.

By the way, the length of the magneto-impedance effect element is restricted in production. For example, in order to connect both ends of a magneto-impedance effect element to an electrode, a welding method is used in which a welding electrode is energized by contacting a + electrode on one end of the magneto-impedance effect element and a-electrode on the other end. The length of the element is limited. Usually 6 mm or less.
Therefore, even in the magneto-impedance effect element with a coil shown in FIG. 6B, there is a limitation in improving the detection sensitivity and expanding the detection area.

  An object of the present invention is to improve the detection sensitivity of a magneto-impedance effect sensor and expand the detection region.

In the magneto-impedance effect sensor head according to claim 1, the iron core is provided on the magneto-impedance effect element so as to form a magnetic loop circuit, and a negative feedback coil and a bias magnetic field coil are wound around the iron core. A plurality of magneto-impedance effect elements with coils, the magneto-impedance effect elements arranged in tandem, and the mutual spacing in the magnetosensitive axis direction of the magneto-impedance effect elements is made shorter than the length of the magneto-impedance effect element And
The magneto-impedance effect sensor head according to claim 2 is the magneto-impedance effect sensor head according to claim 1, wherein the mutual interval in the magnetosensitive axis direction of the magneto-impedance effect element is ¼ or less of the length of the magneto-impedance effect element. It is characterized by.
A magneto-impedance effect sensor according to claim 3 comprises the magneto-impedance effect sensor head according to claim 1 or 2, wherein a magneto-impedance effect element with a coil is connected in series to detect a detected magnetic field applied to the magneto-impedance effect element. The magnetic impedance effect sensor head is connected to a main body portion on which a circuit to be detected is mounted by a conductor joint.
A magneto-impedance effect sensor according to a fourth aspect includes the magneto-impedance effect sensor head according to the first or second aspect, wherein there are two magneto-impedance effect elements with coils, and a detected magnetic field applied to each magneto-impedance effect element is detected. The magneto-impedance effect sensor head is connected to a main body having a circuit for differentially amplifying and detecting the detection by a conductor joint.
A magneto-impedance effect sensor according to claim 5 comprises two magneto-impedance effect sensor heads according to claim 1 or 2, wherein the magneto-impedance effect of each sensor head is connected in series, and is applied to the magneto-impedance effect element of each sensor head. Magnetism characterized in that the magneto-impedance effect sensor head is connected to a body portion having a circuit for detecting a detected magnetic field and differentially amplifying and detecting the detected wave in the same direction and at different positions by conductor joints. Impedance effect sensor.
The magneto-impedance effect sensor according to claim 6 is the magneto-impedance effect sensor according to any one of claims 3 to 5, wherein the magneto-impedance effect element in the magneto-impedance effect sensor head is attached to the surface to be magnetically inspected. It is characterized in that the side surfaces face each other.
The magnetic inspection method according to claim 7 is a method of magnetically inspecting a magnetic impedance effect sensor head in proximity to a magnetic inspection surface and moving the magnetic impedance effect sensor relative to the magnetic inspection surface. The magneto-impedance effect sensor according to any one of claims 3 to 6 is used, and the direction of the magneto-impedance effect element of the magneto-impedance effect sensor head is a direction perpendicular to the moving direction.

A negative feedback is applied to the magneto-impedance effect element and a bias magnetic field is applied. However, since the negative feedback coil and the bias magnetic field coil are not directly wound around the magneto-impedance effect element, the element is arranged in the axial direction of the magneto-impedance effect element. The magnetic flux of the detected magnetic field passes not only from both ends but also from the intermediate surface.
Even if the length of the magneto-impedance effect element itself is constrained, increasing the number of columns of the magneto-impedance effect element can substantially increase the total length of the magneto-impedance effect element and increase the amount of magnetic flux pick-up of the detected magnetic field. The detection sensitivity can be increased.
In addition, since the interval in the magnetic sensitive axis direction between the tandem elements is sufficiently narrowed, the detection area can be sufficiently suppressed from being cut off and enlarged.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1-1 shows an example of a circuit diagram of a magneto-impedance effect sensor according to the present invention.
1-1, 1a and 1b are magneto-impedance effect elements with a coil, 1 is the magneto-impedance effect element, 6 is a coil for a bias magnetic field, 7 is a coil for negative feedback, and A is a magneto-impedance effect with two coils. A magneto-impedance effect sensor head in which elements 1a and 1b are connected in series is shown.
1-2 (a) is a side view showing an example of the coiled magneto-impedance effect element, FIG. 1-2 (b) is a bottom view, and FIG. 1-2 (c) is FIG. 1-2. It is a ha sectional drawing in (b).
In FIG. 1-2, 100 is a board | substrate chip and can use a ceramic board, for example. Reference numeral 101 denotes an electrode provided on one side of the substrate piece, and includes a magneto-impedance effect element connecting projection 102. This electrode can be provided by printing and baking a conductive paste, for example, a silver paste. 1x is a magneto-impedance effect element connected by welding between the protrusions 102 and 102 of the electrodes 101 and 101, and an amorphous wire, amorphous ribbon, sputtered film, or the like having zero or negative magnetostriction can be used. 103 is a C-type iron core made of iron or ferrite, 6 is a negative feedback coil wound around the C-type iron core, 7 is a bias magnetic field coil, and the magneto-impedance effect element 1 and the C-type iron core 103 The both ends of the C-shaped iron core 103 are fixed to the other surface of the substrate piece 100 with an adhesive or the like so as to constitute a loop magnetic circuit. The iron core material may be a magnetic material having a small residual magnetic flux density. Examples thereof include permalloy, ferrite, iron, amorphous magnetic alloy, magnetic powder mixed plastic, and the like.

The magneto-impedance effect element 1 includes a zero magnetostrictive or negative magnetostrictive amorphous alloy wire 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 a domain wall. used. The inductance voltage component in the output voltage between both ends of the wire generated when a high-frequency excitation current is passed through 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 due to the magnetization of the easily magnetizable outer shell in the circumferential direction. Accordingly, the circumferential magnetic permeability μθ depends on the circumferential magnetization of the outer shell. Thus, when a signal magnetic field is applied in the axial direction of the amorphous wire being energized, the outer shell portion having the easily magnetizable property in the circumferential direction is obtained by synthesizing the circumferential magnetic flux and the signal magnetic field magnetic flux by the energization. The direction of the magnetic flux acting on the magnetic field is deviated from the circumferential direction, and magnetization in the circumferential direction is less likely to occur, the circumferential permeability μθ is changed, and the inductance voltage is changed. This fluctuation phenomenon is called a magnetic inductance effect, which can be said to be a phenomenon in which the high-frequency excitation current (carrier wave) is modulated by a detected magnetic field (signal wave). Further, when the frequency of the energizing 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 conductivity. (Resistivity, w indicates angular frequency) varies with μθ, and μθ varies with the signal magnetic field as described above, so the resistance voltage component in the output voltage across the wire also varies with the signal magnetic field. . This fluctuation phenomenon is called a magneto-impedance effect, which can be said to be a phenomenon in which the high-frequency excitation current (carrier wave) is modulated by a signal magnetic field (signal wave).

  In the magneto-impedance effect sensor head A, the magneto-impedance effect elements 1 and 1 are arranged in tandem, and the distance between the magneto-impedance effect elements in the magnetosensitive axis direction is shorter than the length of the magneto-impedance effect element. Is preferably ¼ or less of the length of the magneto-impedance effect element. For example, the interval is set to 1 mm for a length of 5 mm of the magneto-impedance effect element.

  1-1, 2 is a high frequency current source circuit for applying a high frequency excitation current to the magneto-impedance effect element, and 3 is a detected magnetic field H (signal wave) acting in the axial direction of the magneto-impedance effect element. A detector circuit for demodulating the modulated wave modulated by (carrier wave), 4 an amplifier circuit for amplifying the demodulated wave, 5 an output terminal, 60 a negative feedback circuit, and 70 a bias magnetic field + Vcc power source.

1-3 (a) is a front view showing a magneto-impedance effect sensor provided with the circuit of FIG. 1-1, and (b) in FIG. 1-3 is a side view of the same.
In FIG. 1-3, B is a main body board, on which the high-frequency current source circuit 2, the detection circuit 3, the amplifier circuit 4, the output terminal 5, the negative feedback circuit, the bias magnetic field + Vcc power source and the like are mounted.
A is a sensor head, and the magneto-impedance effect elements 1a and 1b with coils are arranged on the head substrate C so that the magneto-impedance effect elements 1 and 1 are exposed. The distance between the magneto-impedance effect elements in the magnetosensitive axis direction is set to 1/4 or less of the length of the magneto-impedance effect element, and the relative movement of the sensor along the electromagnetic detection surface is The magneto-impedance effect element 1 of the sensor head A is connected to the sensor main body substrate B by a conductor joint d,.

2 (a) [plan view] and FIG. 2 (b) [ro-ro sectional view of FIG. 2 (a)] are magnetic fields using the magneto-impedance effect sensor described with reference to FIGS. In this example, the magneto-impedance effect element of the sensor head is moved close to the electromagnetic inspection surface in the X direction.
As electromagnetic inspection objects, detection of reinforcing bar position of reinforced concrete, detection of defects in iron structures such as iron pipes or plates, detection of needle mixed positions in clothing, detection of residual position of inspection needles in livestock meat The inspection object is detected by picking up the axial component of the magnetic field generated from the remanence of the inspection object with respect to the magneto-impedance effect element. The magnetic impedance effect sensor may be fixed and the electromagnetic inspection object may be moved.
As described above, according to the magneto-impedance effect sensor according to the present invention, it is possible to increase the amount of pick-up magnetic flux, and to apply a strong detected magnetic field to the magneto-impedance effect element by approaching the inspection surface of the magneto-impedance effect element of the sensor head. Therefore, highly sensitive detection is possible. Of course, in order to increase the residual magnetism of the inspection object, it is possible to magnetize it.

In the above embodiment, the magneto-impedance effect elements with coils are arranged in a straight line so that the mutual interval in the magneto-sensitive effect direction of the magneto-impedance effect elements is smaller than the length of the magneto-impedance effect element. While maintaining the mutual axial distance smaller than the length of the magneto-impedance effect element, the magnetic impedance effect element can be shifted in a direction other than the magneto-sensitive axis direction and arranged in tandem.
In the above embodiment, the number of columns of the magneto-impedance effect elements with coils is two, but it can be three or more.

In the above embodiment, the magneto-impedance effect elements with coils are connected in series, and the output of the series-connected elements is detected by the detection circuit. As shown in FIG. Are detected by the detection circuits 3a and 3b, the detection outputs are differentially amplified by the differential amplifier circuit 40, and the differential amplification outputs of the magneto-impedance effect elements 1a and 1b with coils are respectively detected. Negative feedback can be provided to the negative feedback coils 6 and 6.
In this case, noise such as geomagnetism can be removed because the geomagnetism acting on both magnetoimpedance effect elements and the noise magnetic field emitted from the surrounding iron-based structure are equivalent.

In the magneto-impedance effect sensor according to the present invention, two magneto-impedance effect sensor heads, each of which is a series-connected magneto-impedance effect element with coils in a straight line, are used, and the modulation wave at the output end of each sensor head is detected by each detection circuit. These detection outputs are differentially amplified by a differential amplifier circuit, and the differential amplification outputs are negatively fed back to the negative feedback coils of the magneto-impedance effect element with each coil so that the directions of both sensor heads are the same. It can also be connected by a conductor joint.
In this case, it is possible to equalize the geomagnetism acting on both sensor heads and the noise magnetic field generated from the surrounding iron-based structure, so that noise such as geomagnetism can be removed.

  In the magneto-impedance effect sensor according to the present invention, an amorphous ribbon, an amorphous sputtered film, or the like can be used as the magneto-impedance effect element in addition to zero magnetostrictive or negative magnetostrictive amorphous wires.

In the magneto-impedance effect sensor according to the present invention, the magneto-impedance effect element 1 includes an alloy of transition metal and non-metal having a non-metal composition of 10 to 30 atomic%, particularly an alloy of transition metal and non-metal. An amount of 10 to 30 atomic% can be used, and the transition metal is Fe and Co and the nonmetal is B and Si or the transition metal is Fe and the nonmetal is B and Si. For example, the composition Co _70.5 B ₁₅ Si ₁₀ Fe _4.5 , length 2000 μm to 6000 μm, outer diameter 30 μm to 50 μmφ can be used.

  For the high-frequency excitation current, a normal high frequency such as a continuous sine wave, a pulse wave, or a triangular wave can be used. As the high-frequency excitation current source, for example, a Hartley oscillation circuit, a Colpitts oscillation circuit, a collector tuned oscillation circuit, a base tuned oscillation circuit In addition to the normal oscillation circuit, a square wave generator that integrates the square wave output of a crystal oscillator through a DC cut capacitor and an integration circuit and amplifies the triangular wave of this integration output using an amplification circuit, and uses a CMOS-IC as the oscillation unit Can be used.

As the detection circuit, for example, a configuration in which a modulated wave is half-wave rectified by an operational amplifier circuit and the half-wave rectified wave is processed by a parallel RC circuit or an RC low-pass filter to obtain an envelope output of the half-wave rectified wave, the modulated wave The half-wave rectified wave is processed by a diode, and the half-wave rectified wave is processed by a parallel RC circuit or an RC low-pass filter to obtain an envelope output of the half-wave rectified wave.
Further, it is possible to use tuning detection in which a signal wave is sampled by multiplying the modulated wave by a square wave having a frequency fs tuned to the modulated wave (frequency fs).
In the above embodiment, the detected magnetic field (signal wave) is extracted by demodulating the modulated wave. However, the present invention is not limited to this, and the high frequency excitation modulated by the signal magnetic field (signal wave) acting on the magneto-impedance effect element. As long as the signal magnetic field can be detected from the current wave (carrier wave), an appropriate detection means can be used.

It is a circuit diagram of one Example of the magneto-impedance effect sensor based on this invention. It is drawing which shows the magneto-impedance effect with a coil of the magneto-impedance effect sensor of FIGS. 1-1. It is drawing which shows the external appearance of the magneto-impedance effect sensor of FIGS. 1-1. 1 is a view showing a magnetic inspection method according to the present invention. It is a circuit diagram of another example of the magneto-impedance effect sensor according to the present invention. It is drawing which shows the output characteristic of a magneto-impedance effect element. It is a circuit diagram which shows the conventional magnetic impedance effect sensor. It is drawing which shows the input / output waveform in various places in the conventional magnetic impedance effect sensor. 6 is a view showing a magneto-impedance effect element with a coil of a conventional magneto-impedance effect sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetoimpedance effect element 1a Magnetoimpedance effect element 1b with a coil Magnetoimpedance effect element 2 with a coil Excitation current source 3 Detection circuit 3a Detection circuit 3b Detection circuit 4 Amplification circuit 40 Differential amplifier 5 Detection output terminal 6 Negative feedback magnetic field coil 7 Bias magnetic field coil A Sensor head B Body substrate C Sensor head substrate d Conductor joint

Claims (7)

A plurality of magneto-impedance effect elements with coils, in which an iron core is provided on the magneto-impedance effect element so as to form a magnetic loop circuit, and a negative feedback coil and a bias magnetic field coil are wound around the iron core, A magneto-impedance effect sensor head, characterized in that the impedance effect elements are arranged in tandem and the mutual interval in the magnetic sensitive axis direction of the magneto-impedance effect element is made shorter than the length of the magneto-impedance effect element. 2. The magneto-impedance effect sensor head according to claim 1, wherein the magneto-impedance effect element has a mutual interval in the magnetosensitive axis direction of ¼ or less of the length of the magneto-impedance effect element. A main body having a magneto-impedance effect sensor head according to claim 1, wherein a magneto-impedance effect element with a coil is connected in series, and a circuit for detecting and detecting a detected magnetic field applied to the magneto-impedance effect is mounted A magneto-impedance effect sensor, wherein the magneto-impedance effect sensor heads are connected by a conductor joint. A magneto-impedance effect sensor head according to claim 1 or 2, wherein there are two magneto-impedance effect elements with coils, a detected magnetic field applied to each magneto-impedance effect element is detected, and the detection is differentially amplified. A magneto-impedance effect sensor, wherein the magneto-impedance effect sensor head is connected to a main body having a circuit for detection by a conductor joint. Two magneto-impedance effect sensor heads according to claim 1 or 2 are provided, the magneto-impedance effect elements of each sensor head are connected in series, the detected magnetic field applied to the magneto-impedance effect element of each sensor head is detected, and the detection is performed. A magneto-impedance effect sensor, characterized in that the magneto-impedance effect sensor head is connected to a main body provided with a circuit for differential amplification and detected at different positions in the same direction by conductor joints. 6. The surface of the magneto-impedance effect sensor head on which the magneto-impedance effect element is attached faces the detected surface to be magnetically inspected. Magnetic impedance effect sensor. 7. A magnetic impedance test method according to claim 3, wherein the magnetic impedance effect sensor head is brought close to the magnetic surface to be inspected and the magnetic impedance effect sensor is moved relative to the magnetic surface to be inspected for magnetic inspection. A magnetic inspection method characterized in that an effect sensor is used and the direction of the magneto-impedance effect element of the magneto-impedance effect sensor head is set to a direction perpendicular to the moving direction.

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