JP2007248134A - Strain sensor and pressure measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a strain sensor capable of classifying and measuring pressures of compressing direction and pulled direction of a magnetic layer. <P>SOLUTION: The strain sensor comprises a flexible substrate 11 formed of a glass plate, the magnetic layer 12 formed on the surface of the substrate 11 using a magnetostriction material, and a pair of electrodes 13a and 13b connected to the magnetic layer 12. In the magnetic layer 12, one-axial magnetic anisotropy is added by forming it in a uniform magnetic field, and the angle of an easy-to-magnetize axis with respect to the current direction is specified at 45°. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a strain sensor having a magnetic layer formed of a magnetostrictive material, and a pressure measuring device including the strain sensor.

  As this type of strain sensor, a strain sensor disclosed in Japanese Patent Laid-Open No. 2000-356505 is known. This strain sensor includes a substrate and a magnetic layer (ferromagnetic material layer) formed on the substrate using a magnetostrictive material, and detects the pressure applied to the substrate by utilizing the inverse magnetostriction effect of the magnetic layer. It is configured to be possible. The inverse magnetostriction effect of a magnetic layer is, for example, when the shape of the magnetic layer changes due to pressure when it is compressed or pulled, and the magnetization direction (direction of the easy axis of magnetization) previously applied to the magnetic layer changes. Refers to the phenomenon. The magnetic layer also has a characteristic that the magnetic permeability changes with a change in magnetization direction, and the impedance changes with the change in magnetic permeability.

In the strain sensor described above, the magnetic layer is set so that the easy axis of magnetization is orthogonal to the current direction (or parallel to the current direction), using the above-mentioned effects and the characteristics of the magnetic layer. Then, a change in impedance of the magnetic layer with respect to compressive strain or tensile strain is detected, and pressure is detected based on the change in impedance.
JP 2000-356505 A (page 2-4, Fig. 2-3)

  However, the above strain sensor has the following problems. That is, in this strain sensor, the magnetic layer is set so that its easy axis is perpendicular to the current direction (or parallel to the current direction), so that the easy axis when subjected to compressive strain is used. The rotation direction and rotation angle of the easy magnetization axis when subjected to the same amount of tensile strain as the compressive strain are based on the direction orthogonal to the current direction (or the direction parallel to the current direction). As a result, the rotation direction is opposite and the rotation angles are substantially the same. In this case, the magnetic layer has substantially the same magnetic permeability when subjected to compressive strain and tensile strain. As a result, the impedance of the magnetic layer is also approximately the same in each case. Therefore, this strain sensor has a problem that the pressure in the direction in which the magnetic layer is compressed cannot be measured separately from the pressure in the direction in which the magnetic layer is pulled.

  The present invention has been made to solve such problems, and has as its main object to provide a strain sensor and a pressure measuring device capable of separately measuring the pressure in the direction in which the magnetic layer is compressed and the direction in which the magnetic layer is compressed. .

  In order to achieve the above object, a strain sensor according to claim 1 includes a flexible substrate, a magnetic layer formed on the surface of the substrate using a magnetostrictive material, and a pair of electrodes connected to the magnetic layer. In the magnetic layer, the angle of the easy magnetization axis with respect to the current direction is defined to be 45 ° or approximately 45 °.

  According to a second aspect of the present invention, there is provided a pressure measuring device comprising: a flexible substrate; a magnetic layer formed on the surface of the substrate using a magnetostrictive material; a pair of electrodes connected to the magnetic layer; A measurement unit for supplying a current between the pair of electrodes and measuring a potential difference between the pair of electrodes at the time of supplying the current and calculating an impedance of the magnetic layer based on a current value of the current and the potential difference; An arithmetic unit that calculates a pressure applied to the substrate based on the calculated impedance and a reference impedance, and the magnetic layer defines an angle of an easy axis of magnetization with respect to a current direction as 45 ° or approximately 45 °. Has been.

  According to the strain sensor and the pressure measuring device according to claim 1, since the angle of the easy axis of magnetization with respect to the current direction in the magnetic layer is defined to be 45 ° or almost 45 °, the pressure in the direction in which the magnetic layer is compressed and the magnetic The magnitude of pressure in both directions can be measured while distinguishing from the pressure in the direction in which the layer is pulled. In addition, according to the strain sensor and the pressure measuring device, in the region where the pressure in both directions is small, the impedance change rate changes almost linearly, and the degree of change is large, so that a small pressure can be measured with high accuracy. .

  Hereinafter, the best mode of a strain sensor and a pressure measuring device according to the present invention will be described with reference to the accompanying drawings.

  First, the configuration of the pressure measuring device 1 will be described with reference to the drawings.

  1 includes a strain detection element 2, a support unit 3, a measurement unit 4, a storage unit 5, a calculation unit 6, and an output unit 7, and can detect the pressure applied to the strain detection element 2. It is configured.

  The strain detection element 2 is a strain sensor according to the present invention, and is configured, for example, in a gas pipe so as to be able to detect the inflow pressure of the gas. As shown in FIGS. And a pair of electrodes 13a and 13b. In this case, the board | substrate 11 is formed in the flat rectangular parallelepiped which has flexibility as an example. Specifically, the substrate 11 is composed of a metal plate, a glass plate, or the like. When a conductive metal plate is used, a metal plate having an insulating layer formed on the surface is used.

  The magnetic layer 12 is formed on the surface of the substrate 11 using a magnetostrictive material. Further, the magnetic layer 12 is formed in a rectangular shape in plan view as an example, and is formed so that its longitudinal direction is parallel to the longitudinal direction of the substrate 11. In this case, it is preferable to use a ferromagnetic material having a magnetostrictive effect as the magnetostrictive material. The magnetostrictive material may be a magnetostrictive material having a negative magnetostriction constant or a magnetostrictive material having a positive magnetostriction constant. Specifically, a NiFe alloy or a CoSiB alloy can be used as the magnetostrictive material having a negative magnetostriction constant, and a FeSiB alloy can be used as the magnetostrictive material having a positive magnetostriction constant. In this example, as an example, the magnetic layer 12 is formed of a NiFe alloy having a negative magnetostriction constant. The magnetic layer 12 is formed so that its thickness is about 0.1 μm.

  The magnetic layer 12 is formed by a known manufacturing method such as a plating method or a sputtering method. In this case, the magnetic layer 12 is formed in a uniform magnetic field, and as shown in FIGS. 2 and 3, the longitudinal direction (magnetic layer 12) in a plane parallel to the substrate 11 when the stress is zero. The uniaxial magnetic anisotropy is such that the angle θ of the easy axis with respect to the current direction in FIG. 4 is a predetermined angle θ1 (within 45 ° ± 15 ° (approximately 45 ° in the present invention: 45 ° as an example)). Has been granted.

  The pair of electrodes 13 a and 13 b are formed on both sides of the magnetic layer 12 in the longitudinal direction on the substrate 11 and are electrically connected to corresponding end portions of the magnetic layer 12. In the strain detecting element 2 configured as described above, one end side of the substrate 11 is fixed to the support portion 3 as shown in FIG. Thereby, when the strain detection element 2 receives the pressure F on the other end side of the substrate 11 as a free end, according to the direction, the strain detection element 2 uses the one end side of the substrate 11 as a fulcrum, and the surface side (A Direction) and back side (B direction).

  The measurement unit 4 is connected to the electrodes 13a and 13b via a pair of electric wires 4a and 4b, and measures an impedance Z (impedance between the electrodes 13a and 13b) Z in the longitudinal direction of the magnetic layer 12 to calculate the calculation unit. 6 is output. As an example, the measurement unit 4 includes a constant current supply circuit, a voltage measurement circuit, and an impedance calculation circuit (all not shown). In this case, the constant current supply circuit supplies a constant current (DC constant current or AC constant current) between the electrodes 13a and 13b, that is, to the magnetic layer 12 via the pair of electric wires 4a and 4b. The voltage measuring circuit measures a voltage (a voltage between both ends) generated between the pair of electric wires 4a and 4b by the constant current, that is, between both ends in the longitudinal direction of the magnetic layer 12. The impedance calculation circuit calculates the impedance Z between both ends of the magnetic layer 12 in the longitudinal direction based on the current value of the constant current supplied from the constant current supply circuit and the voltage value measured by the voltage measurement circuit. Output.

  The storage unit 5 includes a ROM and a RAM (both not shown). In this case, the ROM stores an operation program for the calculation unit 6. Further, in the ROM, the pressure F is calculated based on the impedance Z (reference impedance Zo) of the magnetic layer 12 when the pressure F applied to the other end of the substrate 11 is zero and the change rate ΔZ / Zo (%) of the impedance Z. And a conversion data table for calculating. ΔZ means (Z−Zo). The RAM is used as a work memory by the calculation unit 6.

  Here, an outline of the conversion data table will be described. First, it has been experimentally and theoretically confirmed that the relationship shown in FIG. 4 is established between the pressure F and the rate of change ΔZ / Zo of the impedance Z. That is, the angle θ formed by the direction of the current flowing in the magnetic layer 12 (current direction) and the easy magnetization axis when the magnetic layer 12 is formed of a NiFe alloy having a negative magnetostriction constant and the pressure F is zero is expressed as an angle θ1 ( = 45 °), when the substrate 11 is bent in the A direction by applying pressure F (pressure in the + direction) to the other end of the substrate 11 as shown in FIG. A compressive stress acts on the magnetic layer 12 formed on the surface of the substrate 11 (the upper surface in the figure). Further, due to the action of this compressive stress, a compressive strain is generated in the magnetic layer 12, and its easy magnetization axis rotates in the C direction as shown in FIG. It is confirmed that the impedance Z becomes larger than the reference impedance Zo as the angle θ approaches the direction parallel to the angle (the angle θ decreases from the angle θ1).

  On the other hand, when the substrate 11 is bent in the B direction by applying a pressure F in the reverse direction (pressure in the negative direction with respect to the A direction) to the other end of the substrate 11, tensile stress acts on the magnetic layer 12. . Further, due to the action of the tensile stress, tensile strain is generated in the magnetic layer 12, and the easy magnetization axis rotates in the D direction and approaches a direction orthogonal to the current direction as shown in FIG. It is confirmed that the impedance θ increases from the angle θ1), and the impedance Z becomes smaller than the reference impedance Zo. That is, as indicated by the solid line in FIG. 4, the rate of change ΔZ / Zo of the impedance Z increases to the + side according to the magnitude (value) of the pressure F when the pressure F in the + direction is applied to the substrate 11. On the other hand, it has been confirmed that when a negative direction pressure F is applied to the substrate 11, it increases to the negative side corresponding to the magnitude of the pressure F. Further, as shown in FIG. 4, since the angle θ1 is defined as 45 °, the change rate ΔZ / Zo of the impedance Z is almost equal in the region W1 where the pressure F is small on both the + side and the − side. It has been confirmed that the degree of change gradually decreases as the pressure F increases in the region W2 in which the pressure F changes linearly and the degree of change is large but the pressure F is large on both the + side and the − side. .

  The relationship as described above exists between the pressure F and the rate of change ΔZ / Zo of the impedance Z, and data indicating this relationship is stored in the conversion data table. Therefore, the pressure F can be calculated from the change rate ΔZ / Zo of the impedance Z by referring to the conversion data table.

  The calculation unit 6 is configured with a CPU. The calculation unit 6 operates according to an operation program stored in the ROM, calculates a change rate calculation process for calculating a change rate ΔZ / Zo of the impedance Z, and calculates a pressure F from the change rate ΔZ / Zo of the impedance Z. A pressure calculation process and an output process for causing the output unit 7 to output the calculated pressure F are executed.

  The output part 7 is comprised with a display apparatus as an example, and displays the pressure F numerically. Note that the output unit 7 may be configured by another output device such as a printing device or a plotter instead of the display device.

  Next, the operation of the pressure measuring device 1 will be described.

  In the pressure measuring device 1, the measuring unit 4 repeatedly measures the impedance Z of the magnetic layer 12 and outputs it to the calculating unit 6. The calculation unit 6 executes a change rate calculation process, a pressure calculation process, and an output process each time the impedance Z is input from the measurement unit 4.

  Specifically, in the change rate calculation process, the calculation unit 6 first reads the reference impedance Zo from the storage unit 5, and then subtracts the reference impedance Zo from the impedance Z to calculate ΔZ (= Z−Zo). . Subsequently, the arithmetic unit 6 calculates the change rate ΔZ / Zo (%) of the impedance Z by dividing this ΔZ by the reference impedance Zo. In the next pressure calculation process, the calculation unit 6 refers to the conversion data table stored in the storage unit 5 to calculate the pressure F corresponding to the calculated change rate ΔZ / Zo of the impedance Z. Next, in the output process, the calculation unit 6 causes the output unit 7 to display the specified pressure F.

  In this case, when a pressure F in the A direction (see FIG. 1) is applied to the other end side of the substrate 11, compressive stress acts on the magnetic layer 12, and the easy axis of magnetization of the magnetic layer 12 and the current direction Becomes smaller than the angle θ1 (= 45 °), and the impedance Z of the magnetic layer 12 becomes larger than the reference impedance Zo. Therefore, the calculation unit 6 calculates the change rate ΔZ / Zo of the impedance Z having a positive sign, and outputs the pressure F (positive value) calculated based on the change rate ΔZ / Zo of the impedance Z to the output unit 7. To display.

  Conversely, when a pressure F in the B direction (see FIG. 1) is applied to the other end side of the substrate 11, tensile stress acts on the magnetic layer 12, and the easy axis of magnetization of the magnetic layer 12 and the current direction are Is larger than the angle θ1 (= 45 °), and the impedance Z of the magnetic layer 12 is smaller than the reference impedance Zo. Therefore, the calculation unit 6 calculates the change rate ΔZ / Zo of the impedance Z having a negative sign, and outputs the pressure F (negative value) calculated based on the change rate ΔZ / Zo of the impedance Z to the output unit 7. To display.

  As described above, according to the pressure measuring device 1 and the strain detection element 2, the angle of the easy axis of magnetization with respect to the current direction in the magnetic layer 12 is set to 45 °. The magnitude (value) of the pressure F in both directions can be measured while distinguishing the pressure F in the direction in which the magnetic layer 12 is pulled based on the positive and negative signs displayed on the output unit 7. Further, according to the pressure measuring device 1, as shown in FIG. 4, in the region W1 where the pressure F in both directions is small, the rate of change ΔZ / Zo of the impedance Z changes almost linearly, and the degree of change is large. A small pressure F can be measured with high accuracy.

  In addition, this invention is not limited to said structure. For example, the example in which one end side of the substrate 11 in the strain detection element 2 is fixed to the support portion 3 has been described above, but both ends of the substrate 11 are fixed by the two support portions 3 and the pressure F is received by the central portion so that the substrate 11 A bending configuration can also be employed. Moreover, although the example which employ | adopted the structure which directly measures the impedance Z of the magnetic layer 12 was demonstrated, the structure which incorporates the distortion | strain detector 2 in a bridge circuit and measures the impedance Z can also be employ | adopted. In addition, although the example in which the angle of the easy axis of magnetization with respect to the current direction in the magnetic layer 12 is defined as 45 ° has been described, the present invention is not limited thereto, and can be defined as approximately 45 ° (within 45 ° ± 15 °). . However, in order to achieve the above effect, it is preferable to define within the range of 45 ° ± 10 °, and more preferably within the range of 45 ° ± 5 °.

1 is a configuration diagram showing a configuration of a pressure measuring device 1. FIG. 3 is a perspective view of a strain detection element 2. FIG. 2 is a plan view of a magnetic layer 12. FIG. FIG. 6 is a relationship diagram illustrating a relationship between a pressure F and a change rate ΔZ / Zo of an impedance Z.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pressure measuring device 2 Strain detection element 4 Measuring part 6 Calculation part 11 Board | substrate 12 Magnetic layer 13a, 13b Electrode F Pressure Z Impedance Zo Reference impedance

Claims (2)

A flexible substrate, a magnetic layer formed on the surface of the substrate using a magnetostrictive material, and a pair of electrodes connected to the magnetic layer,
The magnetic layer is a strain sensor in which an angle of an easy magnetization axis with respect to a current direction is defined as 45 ° or approximately 45 °. A flexible substrate, a magnetic layer formed using a magnetostrictive material on the surface of the substrate, a pair of electrodes connected to the magnetic layer, and supplying current between the pair of electrodes and supplying current Measuring a potential difference between the pair of electrodes at the time and calculating an impedance of the magnetic layer based on a current value of the current and the potential difference, and based on the calculated impedance and a reference impedance A calculation unit that calculates the pressure applied to the substrate,
The magnetic layer is a pressure measuring device in which an angle of an easy magnetization axis with respect to a current direction is defined as 45 ° or approximately 45 °.

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