Measuring coil assembly for vibrating sample magnetometer

Abstract

The invention discloses a measuring coil assembly for a vibrating sample magnetometer, which consists of four coils which are divided into two groups and are arranged on a pair of electromagnet pole heads. The two coils on the electromagnet pole heads on the same side are arranged up and down in the vibration direction of the sample and cling to each other, and the coils on the opposite side are located at the same height. The projection of each coil on the plane of the electromagnet pole head is not circular, and the ratio of the width of the projection in the vibration direction of the sample to the width perpendicular to the vibration direction of the sample is smaller than 1, namely the ratio of the width in the Z direction to the width in the Y direction is smaller than 1. According to the invention, the sensitivity of the measuring coil group is improved by increasing the coverage area of the measuring coil near the height of the vibration center of the sample, and meanwhile, the measuring coil is properly stretched along the Y direction, so that the error of the measuring result caused by the transverse deviation of the position of the sample along the X and Y directions is reduced, and the accuracy and repeatability of the measuring result are improved.

Description

Technical Field

[0001] The invention relates to the field of magnetic measurement, in particular to a measuring coil group used for a vibrating sample magnetometer. Background Art

[0002] The vibrating sample magnetometer is a widely used magnetic measurement device, which is used to study the relationship between the magnetic moment of a material and the external magnetic field and temperature. The measuring coil assembly is an important component of the vibrating sample magnetometer, and its measurement principle is as follows:

[0003] Under the excitation of a DC power supply, a pair of electromagnet poles generate a magnetic field along the X direction. The sample to be tested is fixed on a non-magnetic rigid rod, placed in the center area of ​​the magnetic field, and driven by it to vibrate slightly along the Z axis. On the electromagnet poles on both sides of the sample rod, two pairs of upper and lower measuring coils are arranged along the Z axis. The vibration center of the sample coincides with the center point of the coil group. As the magnetized sample vibrates up and down, the magnetic flux in the measuring coil changes alternately, and then an AC induced voltage signal is output. Under the condition that the vibration frequency and amplitude of the sample are constant, the intensity of the induced voltage signal is proportional to the magnetic moment of the sample to be tested. The amplitude of the induced voltage signal output by the measuring coil group under the conditions of unit vibration frequency, amplitude and sample magnetic moment is defined as the sensitivity of the measuring coil group.

[0004] Improving the sensitivity of the measuring coil group is conducive to improving the signal-to-noise ratio and resolution of the vibrating sample magnetometer and reducing the dependence on high-performance amplifier circuits. The conventional method is to wind the coil with extremely fine enameled wire, which can increase the number of turns of the coil without changing the volume of the coil, but this will increase the difficulty of processing the coil and maintaining the consistency of the actual parameters of the coil; the height of the coil along the X direction can also be increased, but this will occupy the space between the electromagnet poles, which may affect the use of measurement accessories such as the temperature control cavity. If the distance between the electromagnet poles is widened to accommodate the above accessories, the magnetic field strength between the electromagnet poles will be reduced.

[0005] For traditional circular coil groups, when the inner and outer radii of the measuring coils and the horizontal and vertical spacing of the coils satisfy a specific mathematical relationship, a small uniform sensitivity zone may appear at the center of the coil group. However, the spacing between the electromagnet poles of most vibrating sample magnetometers is designed to be adjustable by the user. Therefore, in most actual usage scenarios, the ideal uniform sensitivity zone does not exist, and the magnetometer is very sensitive to slight deviations between the center of sample vibration and the center of the measuring coil group. This places high demands on the position calibration accuracy of the standard sample and the sample to be measured, otherwise it is difficult to ensure the accuracy and repeatability of the measurement.

[0006] In view of the above problems, the present invention proposes a measuring coil assembly for a vibrating sample magnetometer. Compared with the traditional circular coil assembly, it can not only significantly improve the sensitivity of the measuring coil, but also reduce the influence of the positioning deviation of the standard sample and the sample to be measured relative to the center of the coil assembly on the measurement result. Summary of the invention

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A measuring coil group for a vibrating sample magnetometer comprises four coils, which are arranged in groups of two on a pair of electromagnet poles. The two coils on the electromagnet poles on the same side are arranged up and down along the vibration direction of the sample, and the two coils on the opposite side are located at the same height and are also arranged up and down along the vibration direction of the sample.

[0009] In particular, the outer contour and inner contour of the projection of each coil on the plane of the electromagnet pole head are not circular;

[0010] And the ratio of the width of the projection along the vibration direction of the sample to the width perpendicular to the vibration direction of the sample is less than 1.

[0011] Preferably, the coils on the electromagnet pole heads on the same side are tightly attached up and down.

[0012] Preferably, the projection of the coil on the plane of the electromagnet pole head is in the shape of a racetrack.

[0013] Preferably, the projection of the coil on the plane of the electromagnet pole head is a hollow semicircle.

[0014] Preferably, the racetrack-shaped outer contour of the coil is tangent to the contour of the maximum circular area allowed at the central position of the electromagnet pole head.

[0015] Preferably, the semicircular outer contour of the coil is tangent to the contour of the maximum circular area allowed at the central position of the electromagnet pole head.

[0016] Compared with the prior art, the present invention has the following characteristics:

[0017] On the plane of the electromagnet pole head, in the area near the height of the vibration center, the change in magnetic flux density caused by the vibration of the sample is the largest. The closer the measuring coil is to this area, the higher the induced voltage output per unit area and number of turns under the same sample amplitude. The traditional circular double coil cannot fully cover this area. The present invention can efficiently utilize the area near the height of the vibration center on the plane of the electromagnet pole head by changing the shape of the coil, stretching it appropriately along the Y direction, and clinging it up and down at the center of the plane of the electromagnet pole head, thereby improving the sensitivity of the measuring coil. The present invention also reduces the influence of the horizontal deviation of the sample vibration center point along the X and Y directions on the sensitivity of the measuring coil, thereby improving the accuracy and repeatability of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following is an exemplary description of the present invention, which does not constitute a limitation of the embodiments. In the drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0019] Figure 1 It is a schematic diagram of the three-dimensional structure of a hollow semicircular specific embodiment of a measuring coil assembly for a vibrating sample magnetometer of the present invention;

[0020] Figure 2 It is a projection diagram of a circular measuring coil assembly in the prior art on the plane of the electromagnet pole head;

[0021] Figure 3 It is a projection diagram of a racetrack-shaped specific embodiment of a measuring coil assembly for a vibrating sample magnetometer of the present invention on the plane of the electromagnet pole head;

[0022] Figure 4 It is a projection diagram of a hollow semicircular specific embodiment of a measuring coil group for a vibrating sample magnetometer of the present invention on the plane of the electromagnet pole head;

[0023] Figure 5 It is a graph showing the percentage improvement of the sensitivity of two specific embodiments of the present invention compared with the circular measuring coil assembly of the prior art;

[0024] Figure 6 A comparison diagram of the sensitivity of the circular measuring coil assembly of two specific embodiments of the present invention and the deviation of the sample along the X-axis direction;

[0025] Figure 7 A comparison diagram of the sensitivity of the circular measuring coil assembly of two specific embodiments of the present invention and the deviation of the sample along the Y-axis direction;

[0026] Figure 8 A comparison diagram of the sensitivity of the circular measuring coil assembly of two specific embodiments of the present invention and the deviation of the sample along the Z-axis direction;

[0027] Explanation of reference numerals: electromagnet pole 1, sample rod 2, sample 3, four coils 4, 5, 6, 7 (the coils are the same, 4, 5, 6, 7 represent the four coils respectively). DETAILED DESCRIPTION

[0028] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation of the present invention is described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. Figure 1, including an electromagnet pole 1, a sample rod 2, a sample 3, and coils 4, 5, 6, and 7. The up and down arrows in the figure represent the vibration direction of the sample. The coils 4, 5 and coils 6, 7 on the same side of the electromagnet pole are arranged up and down along the vibration direction of the sample and are close to each other. The coils 4, 7 and coils 5, 6 on the opposite side are at the same height. The outer contour and inner contour of the projection of each coil on the plane of the electromagnet pole are not circular, and the ratio of the width of the projection along the vibration direction of the sample to the width perpendicular to the vibration direction of the sample is less than 1, that is, the ratio of the width in the Z direction to the width in the Y direction is less than 1.

[0029] Figure 2 It is a circular measuring coil group of the prior art. In order to increase the enclosed area of ​​the measuring coil 8, the thickness of the coil can be adjusted so that the outer contour of the coil 8 is tangent to the maximum circular area allowed. The thickness of the coil 8 is the difference between the inner and outer edges of the coil 8. The maximum circular area allowed is usually limited by the position of the magnetic flux density sensor installed on the electromagnet pole head 1, or by the size of the electromagnet pole head 1. As an example, the radius of the maximum circular area allowed is uniformly set to R = 10mm, the height of the coil 8 along the X direction is 1.5mm, the thickness of a single circular coil 8 is r1 = 4.5mm, and the inner diameter d = 1mm. See Figure 2 The conventional circular measuring coil 8 has a low coverage rate for the high-sensitivity area 9 near the center of the electromagnet pole head 1 due to its arc-shaped outer edge. Figure 2 The shaded part is indicated in the figure.

[0030] The following describes a first embodiment of the present invention, a racetrack-shaped measuring coil assembly. Figure 3 On the basis of the circular measuring coil group in the prior art, the measuring coil 4 is appropriately stretched along the Y direction, and the thickness of the coil 4 is adjusted so that the outer contour of the coil 4 is tangent to the maximum circular area allowed, thereby increasing the enclosed area of ​​the measuring coil 4. Then, the outer edges of the straight segments of the upper and lower pairs of coils 4 of the same side electromagnet pole head 1 are made to be close to each other to the greatest extent possible, so as to cover the high-sensitivity area 9 in the center of the electromagnet pole head 1 to the greatest extent possible. The high-sensitivity area 9 near the center of the electromagnet pole head 1 is Figure 3 In this embodiment, the radius of the maximum circular area allowed is uniformly set to R=10 mm, and the height of the coil 4 along the X direction is 1.5 mm. Using finite element simulation, the optimal solution for the thickness of the coil 4 in this example is obtained to be r2=4.15 mm.

[0031] The second embodiment of the present invention is described below: Figure 4On the basis of the track-shaped measuring coil assembly of the first embodiment, the coil 4 is appropriately stretched along the Z direction, and the thickness of the coil 4 is adjusted so that the outer contour of the coil 4 fills the maximum allowable circular area to the greatest extent, thereby increasing the enclosed area of ​​the measuring coil. Then, the outer edges of the straight segments of the upper and lower pairs of coils 4 of the same-side electromagnet pole head 1 are made to be close to each other to the greatest extent, so as to cover the high-sensitivity area 9 at the center of the electromagnet pole head 1 to the greatest extent. The high-sensitivity area 9 near the center of the electromagnet pole head 1 is Figure 4 In this embodiment, the radius of the maximum circular area allowed is set to R=10 mm, and the height of the coil 4 along the X direction is 1.5 mm. Using finite element simulation, the optimal solution for the thickness of the coil 4 in this example is obtained to be r3=4 mm.

[0032] Under the condition that the vibration frequency and magnetic moment of the sample are constant, finite element simulation is used to examine the corresponding relationship between the change in magnetic flux generated by the vibrating sample in the measuring coil group and the sample amplitude, and the sensitivity of Example 1 and Example 2 of the present invention and the traditional circular measuring coil group can be compared. In order to simplify the simulation parameters and make the comparison results more intuitive, the electromagnet used to magnetize the sample is omitted in the finite element simulation, and a permanent magnet sample with a constant residual magnetic flux density is used. As an example, the permanent magnet sample is an N48 spherical permanent magnet with a radius of 1mm, which is magnetized along the X-axis. The sample space spacing in the X-axis direction of the measuring coil group is set to 16, 20, and 24mm, and the sample amplitude is set to 1-3mm. See. Figure 5 The sensitivity of the racetrack-shaped coil group in the first embodiment is increased by about 40-46% compared with the traditional circular coil group, and the sensitivity of the semicircular coil group in the second embodiment is increased by about 60-72% compared with the traditional circular coil group.

[0033] Using finite element simulation, we investigate the ΔΦ of the measuring coil dvi / ΔΦ mid The correspondence between the deviation distance of the vibration center point of the sample relative to the center point of the measuring coil group can be used to compare the degree to which the sensitivity of this scheme and the traditional circular measuring coil group is affected by the positioning deviation of the sample. dvi It is the change in magnetic flux generated by the vibrating sample in the measuring coil group when the sample vibration center deviates from the center of the measuring coil group along the X, Y and Z axes. mid It is the change in magnetic flux generated by the vibrating sample in the measuring coil group when the sample vibration center coincides with the center of the measuring coil group. As an example, the sample space spacing in the X-axis direction of the measuring coil group is set to 16mm, and the sample amplitude is set to 2mm.

[0034] See also Figure 6The error caused by the lateral deviation of the sample vibration center along the X direction by plus or minus 1 mm is 7.04% for the traditional circular measuring coil group, and is reduced to 6.33% for the runway-shaped measuring coil group in Example 1, with a relative reduction ratio of 9.94%; and is reduced to 5.79% for the semicircular measuring coil group in Example 2, with a relative reduction ratio of 19.63%.

[0035] See also Figure 7 The error caused by the lateral deviation of the sample vibration center along the Y direction by plus or minus 1 mm is -2.74% for the traditional circular coil group, and is reduced to -1.64% for the runway-shaped measurement coil group in Example 1, with a relative reduction ratio of 39.96%; and is reduced to -1.27% for the semicircular measurement coil group in Example 2, with a relative reduction ratio of 53.4%.

[0036] See also Figure 8 The error caused by the deviation of the sample vibration center position along the Z direction by plus or minus 1mm is -4.14% for the traditional circular coil group, -4.56% for the runway-shaped measurement coil group in Example 1, and the relative increase ratio is 10.09%; the error for the semicircular measurement coil group in Example 2 is -4.39%, and the relative increase ratio is 6.11%.

[0037] Compared with the traditional circular coil assembly, the runway-shaped measurement coil assembly of the first embodiment of the present invention and the semicircular measurement coil assembly of the second embodiment both significantly reduce the error caused by the deviation of the sample along the Y direction on the measurement result. The present invention implements two semicircular measurement coil assemblies, and the relative reduction ratio (19.63% and 53.4%) of the error caused by the deviation of the sample along the X and Y directions is much higher than the relative increase ratio (6.11%) of the error caused by the deviation of the sample along the Z direction.

[0038] In the actual use environment, the vibration center of the sample may deviate from the center of the measuring coil group in the three directions of X, Y, and Z. If other interference factors are ignored and the effects of the deviation of the vibration center of the sample in the three directions of X, Y, and Z on the measurement results can be considered independent of each other, the relative error E(M) of the measured magnetic moment M can be obtained by the formula It is inferred that E(X), E(Y) and E(Z) are the measurement errors when the vibration center of the sample deviates only in one of the X, Y and Z directions and does not deviate in the other two directions. When the deviation of the sample in the three directions of X, Y and Z is plus or minus 1 mm, the relative error of the measurement result of the traditional circular coil group is 8.61%. The relative error of the measurement result of the racetrack-shaped coil group in Example 1 is 7.97%, which is 7.43% lower than that of the traditional circular coil group. The relative error of the measurement result of the semicircular coil group in Example 2 is 7.38%, which is 14.29% lower than that of the traditional circular coil group.

[0039] The above sensitivity data only represent the optimization effects of the two embodiments of the present invention compared with the traditional circular coil group under the following parameter setting conditions: the radius of the maximum circular area allowed by the coil group is R=10mm, the height of the coil along the X direction is 1.5mm, the sample space spacing in the X-axis direction of the coil group is 16, 20, 24mm, the sample amplitude is 1-3mm, the circular coil thickness r1=4.5mm, the racetrack coil thickness r2=4.15mm, and the semicircular coil thickness r3=4mm. The above relative error data only represent: based on the above parameters, and under the conditions of the sample space spacing in the X-axis direction of the coil group is 16mm, and the sample amplitude is 2mm. When the above parameter settings change, the optimization effects of the obtained sensitivity and relative error also change accordingly, but the optimization trend still exists.

[0040] The above are only some embodiments of the present invention and should not be construed as limiting the present invention. Without departing from the concept of the present invention, various changes and improvements made by ordinary technicians in this field to the technical solution of the present invention are within the protection scope of the present invention.

Claims

1. A measuring coil assembly for a vibrating sample magnetometer, comprising four coils, arranged in pairs on a pair of electromagnet poles, the two coils on the same side of the electromagnet poles being arranged up and down along the vibration direction of the sample, and the two coils on the opposite side being at the same height and also arranged up and down along the vibration direction of the sample, Features : The outer contour and inner contour of the projection of each coil on the plane of the electromagnet pole head are not circular; And the ratio of the width of the projection along the vibration direction of the sample to the width perpendicular to the vibration direction of the sample is less than 1.

2. A measuring coil assembly for a vibrating sample magnetometer according to claim 1, Features: The coils on the electromagnet pole head on the same side are tightly attached up and down.

3. A measuring coil assembly for a vibrating sample magnetometer according to claim 1, Features: The projection of the coil on the plane of the electromagnet pole head is in a racetrack shape.

4. A measuring coil assembly for a vibrating sample magnetometer according to claim 1, Features: The projection of the coil on the plane of the electromagnet pole head is a hollow semicircle.

5. A measuring coil assembly for a vibrating sample magnetometer according to claim 3, Features: The racetrack-shaped outer contour of the coil is tangent to the contour of the maximum circular area allowed at the center of the electromagnet pole head.

6. A measuring coil assembly for a vibrating sample magnetometer according to claim 4, Features: The semicircular outer contour of the coil is tangent to the contour of the maximum circular area allowed at the center of the electromagnet pole head.

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