|
|
1.INTRODUCTIONGiant magnetostrictive material (GMM) has the advantages of high driving accuracy, high mechanical and electrical conversion efficiency, fast response speed, large magnetostrictive coefficient, etc. The giant magnetostrictive ultrasonic guided wave transducer uses GMM rod to generate mechanical vibration under the bias magnetic field and high-frequency alternating driving magnetic field, so as to realize the conversion between electricity-magnetic field-mechanical energy 1,2. The mechanical vibration is loaded into the pipeline with defects to generate ultrasonic guided wave, which can be combined with the receiving transducer to complete the defect detection. Yang X.L et al.3 conducted a simulation analysis on the giant magnetostrictive electrohydrostatic actuator (GMEHA) and compared the bias magnetic field provided by DC coil and permanent magnet. The experiment showed that the bias magnetic field provided by permanent magnet had a low displacement peak, but the difference was small and the heat dissipation was good.It can greatly improve the control accuracy and working time of GMEHA, and provide a reference for the selection of magnetic field bias mode in the subsequent research.Chen S et al.4 compared the open and closed state of the magnetic circuit and verified that the magnetic field in the GMM bar of the closed magnetic circuit has greater intensity, greater uniformity and smaller fluctuation range, and that the permanent magnet can provide a stable magnetic field to avoid the phenomenon of “frequency doubling”.Liu Q et al.5 used the finite element software to optimize the magnetic circuit gap size of the giant magnetostrictive transducer. The results showed that the magnetic field strength and uniformity decreased with the increase of the gap, and the groove width of the optimal magnetic cylinder was determined through experiments.Yan H.B et al.6 compared the thickness, radius and other parameters of permanent magnets in the biased magnetic field with the magnetic field of the closed magnetic circuit, obtained the distribution uniformity of the axial magnetic field in the GMM rod, selected the best response parameter values, verified the corresponding relationship between the output displacement and the magnetic field uniformity, and further optimized the magnetic field uniformity.Gao X.H et al.7 used Ansoft Maxwell simulation software to design magnetic conductive end caps at both ends of magnetic circuits to suppress magnetic leakage. By changing the diameter and thickness of the end caps, the functional relationship between these two parameters and the maximum magnetic field intensity was compared and analyzed, and the end cap parameters at the maximum magnetic field intensity were obtained.Du G.X et al.8 built a test platform for the characteristics of giant magnetostrictive bars, which could measure the B-H curve and Young’s modulus of GMM bars and other properties and parameters, providing feasible experimental support for the finite element simulation test. According to the current research status, giant magnetostrictive transducers are mostly involved in machining, micro-displacement sensing system and other fields9-11. While there are few reports on the application of giant magnetostrictive transducers to ultrasonic guided waves for defect detection. Due to the high frequency response required by ultrasonic detection, the magnetic field uniformity is required to be higher.So the study of bias magnetic field is of great significance. 2.STRUCTURE ANALYSIS AND MODEL ESTABLISHMENT OF TRANSDUCER2.1Structural analysis of transducerCommon giant magnetostrictive transducers are mainly composed of driving magnetic field, GMM rod, bias magnetic field, output rod and prestressed device. Figure 1 shows two models of giant magnetostrictive transducers with different structures. Figure 1 shows two models of giant magnetostrictive transducers with different structures. Figure 1 (a) shows the biased magnetic field provided by the DC coil. The magnetic field intensity of this structure can be adjusted by the current, but it is not suitable for long-term use due to its complex structure, large eddy current and high heat generated by the coil; The other is the bias magnetic field provided by the permanent magnet, as shown in Figure 1(b). The size of the bias magnetic field generated by this method is not adjustable, but it is more suitable for small transducers by taking advantage of the large magnetic product energy, relatively simple structure and low cost of the permanent magnet. Figure 1.(a) Coil biased magnetic field transducer, (b) permanent magnet biased magnetic field transducer  Permanent magnet biased magnetic field can be divided into cylinder type and cylindrical type according to different structural forms, as shown in Figure 2. The selection of permanent magnet type affects the structure of magnetic circuit and the size and uniformity of magnetic induction intensity in GMM bar. Generally, the uniformity of cylindrical magnetic field is greater than that of cylindrical magnetic field. The selection and optimization of bias magnetic field are carried out through simulation and comparison test. 2.2Theoretical analysis of the transducerThe magnetic field and external pressure of the GMM rod in the transducer change, resulting in magnetostrictive deformation and magneto-mechanical coupling effect.Changes in applied pressure will also cause magnetic field changes in magnetostrictive materials, thus generating mechanical-magnetic coupling effect. The constitutive relation of this effect under static magnetic field condition12 is: Type:λ ismaterial strain;d33 piezomagnetic coefficient;EHy is the elastic modulus;H is the magnetic field intensity;σ is the compressive stress of GMM bar;μσ is the relative permeability of the GMM bar under a given pressure.B is magnetic induction intensity. According to Formula (1) and Formula (2), it can be obtained: By the formula (3), on the assumption that d33,EH y,μσ is constant, the quantitative σ for a specific value. The linear correspondence equation can be used to describe the relationship between the strain λ and the magnetic induction B of the magnetostrictive material. Therefore, the magnitude and uniformity of magnetic induction in the GMM rod will affect the magnitude of strain. 2.3Transducer model establishment and analysisThe magnetostrictive module in COMSOL Multiphysics was used for modeling, and the magnetic field uniformity in GMM rod was analyzed according to different magnetic loops composed of different structures and materials. Firstly, the magnetic field uniformity was simulated and compared with the structural selection of two permanent magnets.As the transducer has an axisymmetric structure, two-dimensional modeling is conducted, as shown in FIG. 3. The main material parameters in the model are shown in Table 1. Table 1.Main material related parameters of the transducer model
Define ψ for magnetic field uniformity coefficient of uniformity is the higher the coefficient is small, the larger the coefficient that the magnetic induction intensity near 1 say more uneven.Where Hmax is the maximum axial or radial magnetic induction in the GMM bar and Hmin is the minimum axial or radial magnetic induction in the GMM bar. Then the coefficient ψ can be written as: The magnetic induction intensity distributions of two permanent magnets are shown in Figure 4. The field inequality coefficient of the cylindrical permanent magnet transducer is recorded as ψ1, and the cylindrical inequality coefficient is recorded as ψ2. The comparison of axial magnetic induction intensity of GMM rod is shown in Figure 4 (a),Calculated by the male type (4) can get ψ1 = 66.72%, ψ2= 98.55%. It is proved that the magnetic field uniformity of the cylindrical transducer is obviously higher than that of the cylindrical permanent magnet transducer, and the magnetic induction intensity in the cylindrical transducer GMM rod is also greater than that in the cylindrical transducer GMM rod except near the two ends of the GMM rod. As shown in FIG. 4 (b), the radial magnetic induction intensity at the center of GMM rods of the two structures does not change significantly, and the optimization focuses on the axial direction.According to Formula (4), the radial magnetic field inequality of cylindrical GMM rod is 0.15%, and that of cylindrical permanent magnet is 10.29%. The magnetic field uniformity of cylindrical permanent magnet is higher in both radial and axial direction than that of cylindrical permanent magnet, and the magnetic induction intensity generated by cylindrical permanent magnet in GMM rod is too small, which cannot meet the requirements of transducer on magnetic field intensity. The cylindrical permanent magnet is preferred to optimize the magnetic circuit design. 3.TRANSDUCER MAGNETIC CIRCUIT OPTIMIZATION3.1Transducer magnetic circuit designThe magnetic circuit design of the transducer directly affects its working performance. A good closed magnetic circuit can reduce magnetic leakage and make the magnetic induction intensity and uniformity conform to the linear working range of magnetostrictive materials.
Figure 6.(a)Axial magnetic induction intensity of GMM bar with different permeability blocks. (b)Axial magnetic field unevenness of GMM bar with different materials.  3.2Comparative analysis of transducer magnetic circuit optimizationFigure 9 (a) shows the overall optimized distribution of the transducer’s bias magnetic field. Compared with the non-optimized state in Figure 5 (b), most of the magnetic induction lines generated by the permanent magnet enter the GMM rod through the magnetic conductive block, and the magnetic leakage is significantly reduced. The magnetic induction lines are evenly distributed at both ends of the GMM rod and the center point.Figure 9(b) shows the comparison curve before and after optimization. Before optimization, the magnetic field unevenness is 66.72%, and the mean magnetic induction intensity is 0.272T.After optimization, the non-uniformity is 6.89% and the mean magnetic induction intensity is 0.356T. The magnetic field uniformity and magnetic induction intensity were increased by 59.83% and 0.084T, respectively, and the two optimization indexes were improved. 4.CONCLUSIONIn this paper, the characteristics of two magnetostrictive ultrasonic guided wave transducers with different biased magnetic field structures are compared. Based on the magnetostrictive theory under static magnetic field, the finite element software is used to conduct simulation research on the magnetostrictive ultrasonic guided wave transducers, and the optimal biased magnetic field structure form is selected by numerical comparison of specific magnetic induction intensity and non-uniformity. The non-ferromagnetic material is determined as the transducer shell.The influence of the magnetic block on the overall magnetic induction line distribution of the transducer was studied. The variation trend of the axial magnetic field uniformity of the GMM bar with different permeability of the magnetic block was analyzed, and the material and arrangement of the magnetic block were determined. The axial magnetic field ununiformity of the GMM bar was reduced to 10.98%.By changing the axial length of permanent magnet, the optimal structural size of permanent magnet is determined to be 36mm, and the magnetic field non-uniformity is further reduced to 6.89%, while the average magnetic field intensity is also increased by 0.084T, which verifies the effectiveness of this experiment. ACKNOWLEDGMENTSProject Research on pipeline defect identification and visualization method under complex working conditions based on ultrasonic guided wave and structured light vision(62161042) supported by National Natural Science Foundation of China and Research on methods for identifying minor defects in Hydrogen high-pressure pipelines based on helical guided wave(NJZY23074) supported by Scientific research project of colleges and universities in Inner Mongolia Autonomous Region. REFERENCESLiu,Y., Dang, X. A., Yang L. J.,
“Improvement and motion analysis of powder laying device of direct metal Sintering rapid forming machine,”
Hot Working Art, 19 207
–209
(2012). Google Scholar
Xue, G. M., He, Z. B., Li, D. W., Li, Y. L., Yang, C. S.,
“Modeling of magnetic field Strength of Giant Magnetostrictive Rod and Coil Optimization Analysis[J],”
Nanotechnology and Precision Engineering, 12
(02), 85
–90
(2014). Google Scholar
Yang, X. L., Zhu, Y. C., Fei, S. S,et al.,
“Magnetic Field Analysis and Optimization of Giant Magnetostrictive electrohydrostatic Actuator,”
Journal of Aerospace Power, 31
(09), 2210
–2217
(2016). Google Scholar
Chen, S., Zhao, L. D., Zhou, J, et al.,
“Magnetic Circuit Design and Simulation of Rare Earth Giant Magnetostrictive Transducer,”
Machinery Design & Manufacture, 02 43
–46
(2018). Google Scholar
Liu, Q., Li, P. Y., Xu, G. Y, et al.,
“Magnetic circuit optimization Design of isomogiant magnetostrictive ultrasonic transducer,”
Journal of Beijing University of Aeronautics and Astronautics, 45
(8), 1639
–1645
(2019). Google Scholar
Yan, H. B., Gao, H., Niu, Y, et al.,
“Magnetic Circuit Design and Simulation of Giant Magnetostrictive Actuator,”
Machinery Design & Manufacture, 02 242
–246+251
(2022). Google Scholar
Gao,X.H.,Liu,Y.G and Pei,Z.C.,
“Magnetic Circuit Optimization Design of Giant Magnetostrictive Actuator,”
Journal of Harbin Institute of Technology, 48
(09), 145
–150
(2016). Google Scholar
Du, G. X., Yang, X., Wei, Y. F, et al.,
“Optimization and Experimental Study of Rare Earth Giant Magnetostrictive Bar Characteristics Test Platform,”
Transactions of China Electrotechnical Society, 36
(18), 3867
–3875
(2021). Google Scholar
Li, P. Y., Liu, Q., Zhou, L. X.,
“Design and analysis of giant Magnetostrictive ultrasonic Transducer,”
Chinese Journal of Basic Science and Engineering, 25
(05), 1065
–1075
(2017). Google Scholar
Liu, J., Zhang, T. L., Wang, J. M, et al.,
“Advances in Giant Magnetostrictive Materials and Their Applications,”
Materials Advances in China, 31
(04), 1
–12+25
(2012). Google Scholar
Zhai, P., Xiao, B. H., He, K, et al.,
“Compound Feedback Control of Giant Magnetostrictive Actuator and Its Application in Precision Machining of Variable Elliptic Pin Hole,”
Optics and Precision Engineering, 24
(06), 1389
–1398
(2016). https://doi.org/10.3788/OPE. Google Scholar
Tu, J. W., Liu, Z. F., Li, Z,
“Magnetic Circuit Optimization Design and Finite Element Analysis of Giant Magnetostrictive Actuator,”
Journal of Chongqing University, 44
(04), 52
–63
(2021). Google Scholar
|
