Method for evaluating magnetostrictive member and method for selecting magnetostrictive member

Abstract

[Problem] To provide a method for evaluating magnetostriction characteristics by which magnetostriction characteristics can be easily evaluated and in which stable magnetostriction characteristics not affected by the size of a magnetostrictive member are used; and to provide a method for selecting a magnetostrictive member using said evaluation method. [Solution] A method for evaluating a magnetostrictive material includes: an excitation step of generating a magnetic field with a predetermined strength; an impedance measurement step of measuring the impedance of a coil which is placed in the magnetic field and into which a magnetostrictive material has been inserted; and a calculation step of calculating a characteristic of the magnetostrictive material from the impedance measurement results. The calculation step includes calculating a half-value frequency coupling coefficient (= kf1f2) in accordance with the following equation by using a half value (= f1) of a resonance frequency and a half value (= f2) of an anti-resonance frequency obtained from the impedance measurement results.

Description

Method for evaluating magnetostrictive members and method for selecting magnetostrictive members

[0001] The present invention relates to a method for evaluating magnetostrictive members and a method for selecting magnetostrictive members.

[0002] Magnetostrictive materials are characterized by an inverse magnetostrictive effect, in which magnetization changes significantly when stress is applied, and have attracted attention as functional materials. For example, Fe-Ga alloys, which are iron-based alloys, are materials that exhibit both magnetostrictive and inverse magnetostrictive effects, and exhibit large magnetostrictions of approximately 100 to 350 ppm. For this reason, they have recently attracted attention as vibration-powered energy harvesting materials, and are expected to be applied to wearable devices, sensors, and other devices.

[0003] The properties of magnetostrictive members can be evaluated in several ways. For example, as described in Patent Document 1, they can be evaluated using the magnetostriction amount or magnetostriction constant. When a magnetic field is applied parallel to the <100> direction of the magnetostrictive member, positive magnetostriction appears (hereinafter referred to as "parallel magnetostriction"). On the other hand, when a magnetic field is applied perpendicular to the <100> direction, negative magnetostriction appears (hereinafter referred to as "perpendicular magnetostriction"). When the strength of the applied magnetic field is gradually increased, the parallel magnetostriction amount or the perpendicular magnetostriction amount will each saturate. The magnetostriction constant (3 / 2λ １００ ) is determined by the difference between the saturated parallel magnetostriction amount and the saturated perpendicular magnetostriction amount, and is calculated by the following formula (A): １００ = ε ( / / ) - ε (⊥) ...Formula (A) 3 / 2λ １００ : Magnetostriction constant ε ( / / ): Parallel magnetostriction amount when saturated by applying a magnetic field parallel to the <100> direction ε (⊥): Perpendicular magnetostriction amount when saturated by applying a magnetic field perpendicular to the <100> direction

[0004] The amount of magnetostriction at this time is measured by a strain gauge method in which a strain gauge is attached to the magnetostrictive member with an adhesive and the amount of strain that varies when a magnetic field is applied thereto is measured.

[0005] Furthermore, as disclosed in Patent Document 2, one method for evaluating the properties of magnetostrictive materials is an evaluation method using an electromechanical equivalent circuit analysis (impedance measurement). In this analysis (impedance measurement) using an electromechanical equivalent circuit, a bias magnetic field is generated by an excitation coil using a DC (direct current) power supply, as shown in Figure 1, to magnetize the magnetostrictive material. With the magnetostrictive material placed inside the measurement coil, the impedance of the measurement coil is measured, and a force coefficient α is calculated from the measurement results, which is then used to evaluate the magnetostrictive properties. The force coefficient α is the degree of coupling between the mechanical system and the electrical system, and is an index of the energy conversion efficiency from mechanical energy to electrical energy, and is positively correlated with the power generation output of a vibration power generation device.

[0006] JP 2015-517024 A JP 2020-063997 A

[0007] Jung Jin Park, Suok-Min Na, Ganesh Raghunath, and Alison B. Flatau., AIP ADVANCES 6, 056221(2016)

[0008] The magnetostrictive member, an Fe-Ga alloy, has an easy axis of magnetization in the <100> direction of the crystal, and can exhibit large magnetostriction in this direction. Conventionally, magnetostrictive members of Fe-Ga alloys have been manufactured by cutting a single crystal portion oriented in the <100> direction from an Fe-Ga polycrystal to the desired size, but because the crystal orientation has a significant effect on the magnetostrictive properties, it is thought that a single crystal in which the direction in which magnetostriction is required and the <100> direction in which the crystal magnetostriction is maximized are aligned is the optimal material for a magnetostrictive member.

[0009] Because the device characteristics of magnetostrictive vibration power generation devices and the like are affected by the magnetostrictive properties of the magnetostrictive member, magnetostrictive members are required to have high magnetostrictive properties and little variation in the magnetostrictive properties. Against this background, it was thought that if the crystal orientation of a single crystal of an Fe—Ga alloy was <100> and the Ga concentration was uniform, a magnetostrictive member with a uniform magnetostrictive constant could be obtained. However, as described in Non-Patent Document 1, it has been disclosed that the above device characteristics are influenced not only by the magnetostrictive constant but also by the parallel magnetostriction. As a result of the inventor's investigation, it was found that magnetostrictive members manufactured as described above have variation in the parallel magnetostriction (or perpendicular magnetostriction) even if the magnetostrictive constant is uniform, and that the magnetostrictive constant itself varies. For this reason, it has been necessary to evaluate and select magnetostrictive members for use in vibration power generation devices and the like that have high magnetostrictive constants and parallel magnetostriction, or a high force coefficient, which is a magnetostrictive property.

[0010] However, as described above, the strain gauge method is a method for evaluating magnetostrictive properties, requiring a lot of man-hours because a strain gauge must be attached to each magnetostrictive member. Furthermore, the strain gauge method limits the size of the magnetostrictive member, so there are some magnetostrictive members that cannot be measured, and this method is not suitable as an evaluation method for selecting magnetostrictive members.

[0011] In the evaluation method of magnetostrictive properties, analysis using an electromechanical equivalent circuit (impedance measurement) is easier to perform than the strain gauge method, and it is possible to reduce the measurement time. In the analysis using an electromechanical equivalent circuit, for example, evaluation can be performed using the force coefficient, which is the conversion efficiency from mechanical energy to electrical energy as mentioned above. However, it has been revealed that the force coefficient depends on the size and material of the magnetostrictive member. For this reason, it has been necessary to set an appropriate value for the force coefficient for each size and material of the magnetostrictive member.

[0012] Therefore, the present invention aims to provide a method for evaluating magnetostrictive properties that can easily evaluate magnetostrictive properties and that uses stable magnetostrictive properties that are not affected by the size or material of the magnetostrictive member, and a method for selecting magnetostrictive members using this evaluation method.

[0013] According to an aspect of the present invention, a method for evaluating a magnetostrictive member includes a magnetization step of generating a magnetic field with a predetermined intensity, an impedance measurement step of measuring the impedance of a coil in which a magnetostrictive material placed in the magnetic field is inserted, and a calculation step of calculating the characteristics of the magnetostrictive material from the impedance measurement results, in which the calculation step uses the half value of the resonance frequency (= f1) and the half value of the anti-resonance frequency (= f2) obtained from the impedance measurement results to calculate a half value frequency coupling coefficient (= k ｆ１ｆ２ The present invention provides a method for evaluating a magnetostrictive member, which includes calculating the magnetostrictive force (Mn) of the magnetostrictive member.

[0014] In addition, in the method for evaluating a magnetostrictive member, the excitation step, the impedance measurement step, and the calculation step are repeated while changing the predetermined intensity, and the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is the maximum value of the half-maximum frequency coupling coefficient (= k ｆ１ｆ２ｍａｘ ) and the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is maximized, and the optimum magnetic field strength is the predetermined strength at which the half-maximum frequency coupling coefficient (= ｋｆ１ｆ２ｍａｘ ) Alternatively, the optimum magnetic field strength may be set as a characteristic value of the magnetostrictive member.

[0015] According to another aspect of the present invention, there is provided a method for selecting magnetostrictive members, which includes the above-described method for evaluating magnetostrictive members, and further includes: ｆ１ｆ２ｍａｘ ) or a method for selecting magnetostrictive members using the optimum magnetic field intensity as a criterion for determining whether the properties of the magnetostrictive member are good or bad.

[0016] Furthermore, the half-maximum frequency coupling coefficient (= k ｆ１ｆ２ｍａｘ ) is 0.5 or more, the magnetostrictive member may have good properties.

[0017] According to the present invention, it is possible to provide a method for evaluating magnetostrictive properties that can be easily evaluated and that uses stable magnetostrictive properties that are not affected by the size of the magnetostrictive member, and a method for selecting magnetostrictive members that uses this evaluation method.

[0018] 1 is a diagram showing an example of a device for measuring the characteristics of magnetostrictive materials. FIG. 2 is a graph showing the results of Example 1, illustrating the relationship between the half-value frequency coupling coefficient, electromechanical coupling coefficient, and force factor and magnetic field strength. FIG. 3 is a graph showing the relationship between the half-value frequency coupling coefficient, electromechanical coupling coefficient, and force factor. FIG. 4 is a graph showing the results of Example 2, illustrating the relationship between the half-value frequency coupling coefficient, electromechanical coupling coefficient, and force factor and magnetic field strength. FIG. 5 is a graph showing the results of Example 3, illustrating the relationship between the maximum half-value frequency coupling coefficient and force factor for each size of member. FIG. 6 is a graph showing the result of Example 4, illustrating the relationship between the maximum half-value frequency coupling coefficient and force factor.

[0019] Specific embodiments of the present invention will be described in detail below. The present invention is not limited to the following embodiments, and can be modified as appropriate without departing from the spirit of the present invention. In the drawings, some or all of the drawings are shown schematically and the scale is changed as appropriate. In the following description, the expression "A to B" means "A or more and B or less."

[0020] [Configuration of the Magnetostrictive Material Property Measuring Apparatus] The magnetostrictive material evaluation method of this embodiment is performed using a magnetostrictive material property measuring apparatus (hereinafter sometimes abbreviated as "property measuring apparatus"). FIG. 1 is a diagram showing an example of the property measuring apparatus. The property measuring apparatus includes a measurement coil, an excitation coil, an impedance analyzer, a direct current (DC) power supply, a PC, and a yoke. The DC power supply and the impedance analyzer are connected to the PC. The PC performs various calculation processes and controls each part of the property measuring apparatus. A known device can be used as the impedance analyzer. An excitation coil connected to the DC power supply is wound around the underside of the yoke, and a measurement coil connected to the impedance analyzer is fixed in the gap of the yoke. In the property measuring apparatus, a magnetic field generated by the excitation coil connected to the DC power supply magnetizes the magnetostrictive material via the yoke, and the impedance of the measurement coil with the magnetized magnetostrictive material inserted is measured by the impedance analyzer. The properties of the magnetostrictive material are evaluated based on the measurement results. Note that the property measuring apparatus is not limited to the apparatus shown in FIG. 1 , and known devices may also be used, such as the device described in Patent Document 2.

[0021] [Method for calculating the electromechanical coupling coefficient] In magnetostrictive and piezoelectric materials, the electromechanical coupling coefficient is generally used as an evaluation method to indicate the efficiency with which electromagnetic energy is converted into mechanical energy, i.e., the degree of coupling between electrical and mechanical quantities.

[0022] Electromechanical coupling coefficient (= k ｆｒｆａ ) can be expressed by the following equation (1) using the resonance frequency (= fr) and anti-resonance frequency (= fa) obtained from the above-mentioned impedance measurement.

[0023] The inventors used the above-mentioned characteristic evaluation device to calculate and compare the force coefficient and electromechanical coupling coefficient of a magnetostrictive member. As a result, they found that the force coefficient also changes when the magnetic field strength is changed, as shown in Figures 2 and 3. Specifically, as shown in Figure 2, when the magnetic field strength applied to the magnetostrictive member is gradually increased, the force coefficient also increases accordingly, reaching a maximum at a specific magnetic field strength value, and then decreasing. The magnetic field strength at which the force coefficient is at its maximum can be considered the optimal magnetic field strength. At the optimal magnetic field strength, the magnetostrictive member maximizes the output of the device when incorporated into it. The electromechanical coupling coefficient, calculated simultaneously with the force coefficient, showed values ​​of 0.15 to 0.3, as shown in Figure 3 (coupling constant in Figure 3). Because the difference between the minimum and maximum values ​​was small and the correlation with the force coefficient was low, the optimal magnetic field strength could not be determined.

[0024] Therefore, the inventors have conducted a study and, as will be explained below, have found that the electromechanical coupling coefficient (= k ｆｒｆａ ) and change it to the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) can be used to improve the above problem.

[0025] [Method for calculating half-value frequency coupling coefficient] In this embodiment, the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) can be expressed by the following formula (2) using the half value of the resonance frequency (= f1) and the half value of the anti-resonance frequency (= f2) obtained from the impedance measurement.

[0026] The half-frequency coupling coefficient is calculated from the impedance measurement as described above. The half-frequency coupling coefficient is measured multiple times by varying the excitation strength of the excitation coil. The excitation strength is set multiple times within a range from no magnetic field to magnetic field saturation. This magnetic field saturation can be defined as the state in which the half-frequency coupling coefficient reaches a peak, then drops and becomes nearly constant. The excitation strength varies depending on the material, size, and thickness of the magnetostrictive material, so it is set appropriately. For example, for an FeGa alloy with a thickness of 2 mm and an excitation coil, a magnetic field of 0.2 to 3.6 kA / m can be set (see Figure 4). The measurement interval should be set to a current value of 5 to 10 mA flowing through the excitation coil to achieve a resolution that allows the peak position to be determined. The impedance is measured in a frequency range of, for example, 10 kHz to 200 kHz. The measurement frequency range is set to the frequency range in which resonance and antiresonance occur.

[0027] In contrast to conventional electromechanical coupling coefficients, the method of this embodiment uses the half-value of the resonance frequency (= f1) and the half-value of the anti-resonance frequency (= f2) obtained from impedance measurements. This improves the correlation with the force coefficient because the magnetostrictive material has the maximum energy absorption at the half-value frequency. In addition, because the force coefficient is derived using the half-value frequency, the correlation with the half-value frequency coupling coefficient is improved.

[0028] As with the force coefficient, the half-value frequency coupling coefficient was calculated in the range from no magnetic field to the magnetic field saturation, and the results are shown in Figures 2 and 3. As shown in Figure 2, the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) reaches a maximum value at a predetermined magnetic field strength, similar to the force coefficient. In this embodiment, this half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is calculated by dividing the maximum value of the half-maximum frequency coupling coefficient (= k ｆ１ｆ２ｍａｘ ) and the magnetic field strength at this time is set as the optimum magnetic field strength for the half-value frequency coupling coefficient.

[0029] 4 and 5 show the correlation between the force coefficient and the half-value frequency coupling coefficient. The data in Figs. 4 and 5 show data using magnetostrictive members of different sizes from those used in Figs. 2 and 3. As shown in Figs. 4 and 5, the correlation between the force coefficient and the half-value frequency coupling coefficient (= k ｆ１ｆ２) shows a nearly positive correlation. As shown in Figure 4, the optimum magnetic field strength when the force coefficient is maximized is almost the same as the optimum magnetic field strength when the half-value frequency coupling coefficient is maximized.

[0030] As shown in Figures 2 and 4, the behavior of the change in force factor as a function of magnetic field strength is significantly more correlated with the behavior of the half-frequency coupling factor as a function of magnetic field strength than the behavior of the electromechanical coupling factor as a function of magnetic field strength. As shown in Figures 3 and 5, the correlation between the half-frequency coupling factor and the force factor is significantly higher than the correlation between the electromechanical coupling factor and the force factor. From the results shown in Figures 2 to 5, it can be seen that although the force factor differs depending on the size of the magnetostrictive member, in all of the cases shown in Figures 2 to 5, the half-frequency coupling factor and the force factor show a high correlation.

[0031] FIG. 6 is a diagram showing the force coefficient and half-maximum frequency coupling coefficient for each size of magnetostrictive member. The force coefficient tends to increase as the size and thickness of the magnetostrictive member increase. In contrast, the half-maximum frequency coupling coefficient (= k ｆ１ｆ２ｍａｘ ) is not affected by size and is stable at a high value of 0.65 to 0.85. ｆ１ｆ２ｍａｘ ) is significantly superior to the conventional method.

[0032] [Method for evaluating magnetostrictive members] Hereinafter, each step of the method for evaluating magnetostrictive members of this embodiment will be described. In the following description of the method for evaluating magnetostrictive members of this embodiment, the description of the already-mentioned parts will be omitted or simplified as appropriate, but the matters described in this specification can be applied as appropriate.

[0033] The method for evaluating a magnetostrictive member of this embodiment is a method for evaluating a magnetostrictive member, and includes an excitation step, an impedance measurement step, and a calculation step.

[0034] The excitation step includes generating a magnetic field with a predetermined intensity. In the excitation step, for example, a magnetic field is generated by an excitation coil connected to a DC power supply using the characteristic evaluation device shown in FIG. 1 described above. At this time, in the characteristic evaluation device, a measurement coil with a magnetostrictive material inserted therein is placed in the magnetic field generated by the excitation coil. The wire diameter, number of turns, DC resistance value, etc. of the excitation coil and measurement coil are arbitrary and are set appropriately. The excitation conditions are not particularly limited and are as described above.

[0035] The impedance measurement step includes measuring the impedance of a coil in which a magnetostrictive material is inserted and placed in a magnetic field. The impedance measurement step measures the impedance of a measurement coil in which a magnetostrictive material magnetized by the magnetic field generated in the excitation step is inserted, using an impedance analyzer. The impedance measurement step acquires impedance and data related to the impedance. The resonant frequency (= fr) and antiresonant frequency (= fa) can be determined, for example, by the impedance analyzer. The conditions for the impedance measurement are as described above.

[0036] The calculation step includes calculating the characteristics of the magnetostrictive member from the measurement results of the impedance step. The calculation step uses the half value of the resonance frequency (= f1) and the half value of the anti-resonance frequency (= f2) obtained from the impedance measurement results, and calculates the half value frequency coupling coefficient (= k ｆ１ｆ２ ) is calculated. Note that the calculation step may calculate data other than the above. For example, the calculation step may calculate a half-value frequency coupling coefficient (= k ｆ１ｆ２ ) may be calculated.

[0037] In the evaluation method of the magnetostrictive member of this embodiment, as described above, the half-value frequency coupling coefficient (= k ｆ１ｆ２ ), the magnetostrictive material has the maximum energy absorption at the half-power frequency, and therefore the correlation with the force coefficient is improved. In addition, since the force coefficient is derived using the half-power frequency, the correlation with the half-power frequency coupling coefficient is improved. In this embodiment, the calculated half-power frequency coupling coefficient (= k ｆ１ｆ２ ) the properties of the magnetostrictive member can be evaluated based on the above.

[0038] Subsequently, the excitation step, impedance measurement step, and calculation step are repeated while changing the predetermined intensity. After the repetition, the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is the maximum value of the half-maximum frequency coupling coefficient (= k ｆ１ｆ２ｍａｘ ) and the half-value frequency coupling coefficient (= k ｆ１ｆ２ In the method for evaluating a magnetostrictive member of this embodiment, the optimum magnetic field strength is calculated, which is the predetermined strength when the maximum half-value frequency coupling coefficient (= ｋｆ１ｆ２ｍａｘ ) or preferably includes setting the optimum magnetic field strength as a characteristic value of the magnetostrictive member.

[0039] In the evaluation method of the magnetostrictive member of this embodiment, as described above, the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) can be used to evaluate the characteristics of the magnetostrictive member, which allows for a more stable evaluation of magnetostrictive characteristics that is less affected by the size or material of the magnetostrictive member than when evaluating the characteristics of a magnetostrictive member using the conventional electromechanical coupling coefficient. ｋｆ１ｆ２ｍａｘ ), or the optimum magnetic field strength, and by using these as characteristic values ​​of the magnetostrictive member, it is possible to more reliably achieve the effect of evaluating the magnetostrictive properties stably without being affected by the size or material of the magnetostrictive member. Furthermore, the evaluation method of the magnetostrictive member of this embodiment does not require setting an appropriate value for the force coefficient for each size or material of the magnetostrictive member, and measurement is easier than with the strain gauge method, and the measurement man-hours can be reduced, so the magnetostrictive properties can be evaluated easily.

[0040] [Method for selecting magnetostrictive members] The method for selecting magnetostrictive members of this embodiment will be described below. The method for selecting magnetostrictive members of this embodiment includes the method for evaluating magnetostrictive members of this embodiment described above, and is ｆ１ｆ２ｍａｘ ) or the optimum magnetic field strength is used as a criterion for determining whether the properties of the magnetostrictive member are good or bad.

[0041] FIG. 7 shows the results of preparing multiple magnetostrictive members whose magnetostrictive properties are thought to vary, measuring the half-maximum frequency coupling coefficients of the magnetostrictive members, and selecting magnetostrictive members based on the results. For confirmation, the force coefficient was also measured at the same time. Based on the results, a diagram is shown of the correlation between the half-maximum frequency coupling coefficient and the force coefficient. There is a positive correlation between the half-maximum frequency coupling coefficient and the force coefficient of each magnetostrictive member, and by using the half-maximum frequency coupling coefficient as an index for selection, it is possible to select magnetostrictive members as members with a predetermined force coefficient. As shown in International Publication No. 2021 / 100467, the magnetostrictive properties may vary, for example, when no grooves are formed in the magnetostrictive member. In such cases, it is necessary to select members with high magnetostrictive properties, and by using the half-maximum frequency coupling coefficient as an index, it is possible to easily select magnetostrictive members with high magnetostrictive properties. For example, in the magnetostrictive member selection method of this embodiment, as shown in FIG. 7, the half-maximum frequency coupling coefficient (= k ｆ１ｆ２ｍａｘ ) is within a predetermined range, the properties of the magnetostrictive member may be deemed to be good. This predetermined value may be 0.5 or more, preferably 0.6 or more, and more preferably 0.7 or more. Furthermore, if the optimal magnetic field strength is used as the criterion for determining whether the properties of the magnetostrictive member are good or bad, the magnitude of the optimal magnetic field strength of the magnetostrictive member is proportional to the size of the magnet to be incorporated into a device such as a vibration power generation device, so by determining the optimal magnetic field strength, the size of the magnet can be determined in advance. The value (index value) of the optimal magnetic field strength used as the criterion for determining whether the properties are good or bad can be set as appropriate.

[0042] As described above, according to this embodiment, it is possible to provide a method for evaluating magnetostrictive properties that can be easily evaluated and that uses stable magnetostrictive properties that are not affected by the size of the magnetostrictive member, and a method for selecting magnetostrictive members that uses this evaluation method.

[0043] (Example 1) As shown in International Publication No. 2021 / 100467, a magnetostrictive member was prepared by grinding the surface of the magnetostrictive member using a surface grinder to form grooves, and a member with high and stable magnetostriction characteristics with a parallel magnetostriction amount of around 300 ppm was prepared. In addition, a magnetostrictive member that had been heat-treated after grinding was used to stabilize the optimal magnetic field strength. The size of the magnetostrictive member was 16 mm x 4 mm x 0.5 mm (length x width x thickness).

[0044] Using the characteristic evaluation device shown in Figure 1, the impedance of the prepared magnetostrictive member was measured under conditions of a magnetic field strength (applied magnetic field) of 1.1 kA / m to 8.8 kA / m and a measurement frequency of 10 kA / m to 200 kHz, and the force coefficient, electromechanical coupling coefficient, and half-value frequency coupling coefficient were calculated from the measurement results. The results are shown in Figures 2 and 3.

[0045] (Example 2) The size of the magnetostrictive member was 64 mm x 16 mm x 2 mm. Other details were the same as in Example 1. Using the characteristic evaluation device described above, the impedance of the magnetostrictive member was measured under conditions of a magnetic field strength of 0.2 kA / m to 3.5 kA / m and a measurement frequency of 10 kA / m to 200 kHz, and the force coefficient, electromechanical coupling coefficient, and half-value frequency coupling coefficient were calculated from the measurement results. The results are shown in Figures 4 and 5.

[0046] (Example 3) As shown in International Publication No. 2021 / 100467, the magnetostrictive member was ground with a surface grinder to form grooves on the surface of the magnetostrictive member, and the parallel magnetostriction amount was around 300 ppm. Multiple members with high and stable magnetostrictive characteristics were prepared for each size of the magnetostrictive member. The prepared magnetostrictive members were three 16 mm x 4 mm x 0.5 mm members, two 32 mm x 8 mm x 1 mm members, two 64 mm x 16 mm x 2 mm members, and four 96 mm x 24 mm x 3 mm members.

[0047] Using the characteristic evaluation device described above, the impedance of each magnetostrictive member was measured, and the force coefficient, electromechanical coupling coefficient, and half-maximum frequency coupling coefficient were calculated from the measurement results, and the maximum force coefficient and half-maximum frequency coupling coefficient for each magnetostrictive member were determined. The relationship between the maximum force coefficient and half-maximum frequency coupling coefficient for each magnetostrictive member is shown in Figure 6.

[0048] (Example 4) As shown in WO 2021 / 100467, the magnetostrictive member was prepared by not grinding the surface of the magnetostrictive member with a surface grinder, and the amount of parallel magnetostriction was unstable. Six magnetostrictive members were prepared, each measuring 16 mm x 4 mm x 0.5 mm.

[0049] The maximum half-value frequency coupling coefficient was calculated for each magnetostrictive member in the same manner as in Example 1. Using this half-value frequency coupling coefficient as an index, magnetostrictive members were selected based on a standard of 0.5 or more. One member with a half-value frequency coupling coefficient of 0.5 or more was selected from the six members. For confirmation, the force coefficient was also calculated. Figure 7 shows the relationship between the maximum half-value frequency coupling coefficient and the maximum force coefficient. Magnetostrictive members with a half-value frequency coupling coefficient of 0.5 or more had a force coefficient of 100 or more, making it possible to select magnetostrictive members with high magnetostrictive properties.

[0050] From the results of the examples, as shown in Figures 2 and 4, it can be seen that the behavior of the change in force factor in response to magnetic field strength is significantly more correlated with the behavior of the half-value frequency coupling factor in response to magnetic field strength than the behavior of the electromechanical coupling factor in response to magnetic field strength. As shown in Figures 3 and 5, it can be seen that the correlation between the half-value frequency coupling factor and the force factor is significantly higher than the correlation between the electromechanical coupling factor and the force factor. From the results shown in Figures 2 to 5, it can be seen that although the force factor differs depending on the size of the magnetostrictive member, in all of the cases shown in Figures 2 to 5, the half-value frequency coupling factor and the force factor show a high correlation. Furthermore, as shown in Figure 6, the force factor tends to increase as the size and thickness of the magnetostrictive member increase, but the maximum half-value frequency coupling factor (= k ｆ１ｆ２ｍａｘ ) is not affected by size and remains stable at a high value of 0.65 to 0.85.

[0051] As described above, it has been confirmed that the magnetostrictive property evaluation method of this embodiment and the magnetostrictive member selection method using this evaluation method are significantly superior to conventional methods in that they can easily evaluate magnetostrictive properties and use stable magnetostrictive properties that are not affected by the size of the magnetostrictive member.

[0052] The technical scope of the present invention is not limited to the aspects described in the above-mentioned embodiments. One or more of the requirements described in the above-mentioned embodiments may be omitted. Furthermore, the requirements described in the above-mentioned embodiments may be combined as appropriate. Furthermore, to the extent permitted by law, the disclosures of Japanese Patent Application No. 2024-018142 and all documents cited in the above-mentioned embodiments are incorporated by reference or incorporated herein as part of the present description.

Claims

1. A method for evaluating a magnetostrictive member, comprising: an excitation step of generating a magnetic field of a predetermined strength; an impedance measurement step of measuring the impedance of a coil into which a magnetostrictive material placed in the magnetic field is inserted; and a calculation step of calculating the characteristics of the magnetostrictive material from the impedance measurement results, wherein the calculation step uses the half-value of the resonance frequency (= f1) and the half-value of the anti-resonance frequency (= f2) obtained from the impedance measurement results to calculate a half-value frequency coupling coefficient (= k ｆ１ｆ２ ) calculating the magnetostrictive member strength.

2. Repeat the excitation step, the impedance measurement step, and the calculation step while changing the predetermined intensity, and calculate the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is the maximum value of the half-maximum frequency coupling coefficient (= k ｆ１ｆ２ｍａｘ ) and the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is maximized, and the optimum magnetic field strength is the predetermined strength at which the half-maximum frequency coupling coefficient (= ｋｆ１ｆ２ｍａｘ 2. The method for evaluating a magnetostrictive member according to claim 1, further comprising: determining the optimum magnetic field intensity as a characteristic value of the magnetostrictive member; 3. A method for selecting magnetostrictive members, comprising the method for evaluating magnetostrictive members according to claim 2, wherein the maximum half-value frequency coupling coefficient (= k ｆ１ｆ２ｍａｘ ) or a method for selecting magnetostrictive members, in which the optimum magnetic field intensity is used as a criterion for judging whether the properties of the magnetostrictive members are good or bad.

4. The half-maximum frequency coupling coefficient (= k ｆ１ｆ２ｍａｘ 4. The method for selecting magnetostrictive members according to claim 3, further comprising determining that the properties of the magnetostrictive member are good when the ratio (ratio) of the magnetostrictive member to the surface area of the magnetostrictive member is 0.5 or more.

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