Magnetostrictive Mechanism Research Articles

A new theoretical model for high-order harmonics of SH0 mode ultrasonic guided waves based on magnetostrictive mechanism

In recent years, it was found that magnetostrictive ultrasonic guided wave transducers experimentally excited nonlinear harmonic components under a certain combination of dynamic and static magnetic fields. However, a satisfactory model for the relevant excitation mechanisms is not available. In this study, a new magnetostrictive guided wave excitation model was established and the causes for harmonics generation were analyzed. In addition, the calculation results of the model were obtained under different magnetic field parameters. We firstly changed the calculation conditions of magnetostrictive strain in the model and then theoretically calculated the odd and even harmonics of SH0 mode ultrasonic guided waves for the first time. Furthermore, the accuracy of the model was experimentally verified. By changing the strength ratio of the dynamic magnetic field to the static magnetic field (HD/HS), the excitation amplitudes of odd and even harmonics could be regulated with a magnetostrictive sensor. As the ratio of HD/HS increased, the normalized amplitude of the second harmonic firstly increased and then decreased, whereas the normalized amplitude of the third harmonic showed an exponential growth with different curvatures. This study enriched the theory of magnetostrictive guided wave excitation and provided a theoretical basis for the applications of magnetostrictive sensors.

Precision positioning based on temperature dependence self-sensing magnetostrictive actuation mechanism

The self-sensing actuator that integrates both actuation and sensing functions is an effective way to simplify the structure of electromechanical systems. This paper proposes a temperature-dependent self-sensing actuation strategy based on a self-sensing giant magnetostrictive actuator (SSGMA) by sensing online stiffness. Utilizing the developed model considering temperature-dependent hysteresis nonlinearity, the self-sensing output characteristics of SSGMA are first evaluated. The self-sensing based control system is then designed in detail. The relationship between the self-sensing signal and the output displacement of SSGMA at different temperatures is constructed by General Regression Neural Network (GRNN) model for fast recognition by the controller. On this basis, a composite control scheme that takes into account rate-dependent asymmetric hysteresis nonlinearities and combines an adaptive feedforward controller with PID feedback controller is proposed for precision actuation of SSGMA. Finally, a temperature-controlled experimental platform is assembled for verification. Experimental results demonstrate that, based on the developed model, the SSGMA is capable of accurate self-sensing output at temperatures of 22 °C, 40 °C, and 70 °C, respectively. The SSGMA with the proposed control method enables the synchronous and precise self-sensing positioning of step and multiple-frequency sinusoidal expectations at different temperatures.

A Review of Power Transformer Vibration and Noise Caused by Silicon Steel Magnetostriction

As an important hub equipment in the power system, the power transformer has increasingly higher requirements for its reliability and safety with the rapid development of the power industry. However, the vibrations and noise generated during its operation not only cause a series of issues such as loose windings, core wear, and fatigue of fasteners, but also lead to anxiety and unease among nearby residents, severely affecting their physical and mental health. Therefore, the generation mechanism and control measures of vibration and noise in power transformers have attracted extensive attention from scholars. The magnetostrictive effect of silicon steel sheets is one of the important factors in the causes of transformer vibration and noise. This paper focuses on the magnetostrictive effect of silicon steel sheets. Firstly, the micro mechanism of magnetostriction is introduced. Secondly, based on current research status, the vibration and noise mechanism caused by magnetostriction are summarized, and the influencing factors, measurement, modeling, and noise reduction methods based on magnetostriction are summarized. Finally, based on the current research status and future development trends, prospects are proposed, aiming to provide references for subsequent research on transformer vibration and noise.

Understanding the intrinsic mechanism of the giant magnetostriction in binary and alloyed FeGa solid solutions

Understanding the intrinsic mechanism of the giant magnetostriction in binary and alloyed FeGa solid solutions

Impact of magnetostriction mechanism on frequency manipulation ultrasonic steering in electromagnetic acoustic transducers

AbstractIn this paper, the impact of the magnetostriction mechanism is considered as the focus. An axisymmetric FEM model of the spiral‐coil electromagnetic acoustic transducers (EMAT) is established to conduct the simulation. The simulation results demonstrate that the directivity of ultrasonic wave can be controlled by manipulating the frequency. Furthermore, it is found that the direction of the dominant Lorentz force in the rail varies with time, while the magnetostrictive force compels the ultrasonic wave generated by the Lorentz force towards the axis. It effectively illustrates that the combined power of two mechanisms surpasses that of the Lorentz‐force mechanism alone, particularly at low frequencies.

Development of dual-main excitation mechanism modes electromagnet EMAT for testing ferromagnetic materials

ABSTRACT In the ultrasonic testing of the mechanical properties of ferromagnetic materials, the main excitation mechanism modes of ultrasonic waves are Lorentz force mechanism ultrasonic and magnetostriction mechanism ultrasonic. Lorentz force mechanism ultrasonic mainly detects the conductive characteristics of materials, while magnetostriction mechanism ultrasonic mainly detects the hysteresis characteristics of materials. However, conventional electromagnetic acoustic transducers (EMATs) cannot simultaneously characterise these two characteristics of ferromagnetic materials. In this study, we conclude from the finite element simulation that a quantitative lift-off distance (i.e. the distance between EMAT and the specimen) can change the main mechanism mode of the excited ultrasonic wave. Based on this conclusion, an electromagnet electromagnetic acoustic transducer with dual main excitation modes (DM-E-EMAT) is designed, which can realise the dual mode switching of the main Lorentz force mechanism and main magnetostriction mechanism by adding or removing hollow square gasket. The ultrasonic testing of ferromagnetic materials based on the two main mechanisms of DM-E-EMAT can simultaneously characterise the conductivity and magnetostriction properties of ferromagnetic materials, which enables the characterisations of two types of characteristic parameters with one transducer, improves the efficiency of electromagnetic ultrasonic non-destructive testing of the mechanical properties and reduces the detection errors of ferromagnetic material.

Room temperature ferromagnetic behavior of GaN nanoceramics

It is shown that the GaN nanoceramics fabricated by low-temperature high-pressure technique exhibit ferromagnetic behavior. The measurements reveal that the magnetization of GaN nanoceramics increased with the sintering pressure to 8 GPa applied in the fabrication process of nanoceramics. It is suggested that the magnetostriction mechanism is responsible for the observed increase of ferromagnetism in GaN nanoceramics. The magnetization of GaN nanoceramic measured at 2 K has decreased nonlinearly with applied pressure by orders of magnitude, reaching a minimum at 4 GPa. It was shown that the magnetization of GaN nanoceramics demonstrates hysteresis behavior.

Self-biased characteristics of NZCF/BCZT layered magnetoelectric composites: A novel coupling paradigm in magnetoelectricity

Here, we investigate room temperature magnetoelectric (ME) behavior of ferroelectric Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) and ferrimagnetic Ni0.75Zn0.20Co0.05Fe2O4 (NZCF) layered composites. The ferroelectric ceramics (thickness, t, ∼0.6, 0.8, and 1.0 mm) are stacked at magnetic specimen of fixed t ∼ 1 mm, coupled with conducting silver epoxy. The phase formation, surface morphology, dielectric, magnetic, magnetoelectric and magnetodielectric characteristics of bilayer composites have been studied in the present work. The maximum value of magnetoelectric (ME) coupling coefficient (αME) is found to be 70, 90, and 110 mVcm−1Oe−1 for composite having ferroelectric layer thickness t ∼ 1, 0.8, and 0.6 mm, respectively. More importantly, αME(H→0) remains finite for composite (t ∼ 0.8, and 0.6 mm) in zero magnetic field, which is a clear evidence of self-biasing phenomenon in NZCF/BCZT layered composite. For closer insight about underlying mechanism, we estimate magnetodielectric (MD) coefficient for the layered composite. The MD coefficient is found to be significantly high ∼6.32% for the thickness 0.6 mm. MD% vs magnetic field, H, curves exhibit steeper field dependence in low field region and for H≥2kOe MD possess saturation characteristics. The high saturation characteristics suggest that the magnetoelectricity in layered composite is driven by magnetostriction mechanism and causes robust ME coupling. Further, we obtain electrical signal ∼143 mV with the Hdc ∼250 Oe, as a consequence of interplaying nature of magneto(striction)- piezo(electricity). Such a sizeable response will improve the underlying intimacy between technology and practical application. The study reveals that the pellet based layered composites may be a proven strategy for the realization of self-biased ME devices.

Origin of multiferroism in Sm[formula omitted]BaCuO[formula omitted

Proposing a microscopic model we have investigated the multiferroic properties of Sm2BaCuO5. The heat capacity shows two peaks at the antiferromagnetic transitions temperatures TN1∼ 5 K and TN2∼ 23 K. For the appearing of the extraordinary polarization ΔP in Sm2BaCuO5 we have considered the single-ion magnetostriction mechanism. ΔP is zero without magnetic field. An external magnetic field h induces an electric polarization ΔP below TN2 which varies linearly with h showing a linear magnetoelectric effect. Below TN1ΔP decreases due to ordering of the Sm-sublattice. There are some discrepancies in the experimental data for ΔP(T,h) which we will try to clarify. In addition, the temperature and magnetic field dependence of the dielectric constant is discussed. The observed maximum value of the peak at TN2 shifts to smaller temperature values and increases with increasing external magnetic field.

Nanoheterogeneity response in large-magnetostriction Fe-Ga alloys: An in-situ magnetic small-angle neutron scattering study

The underlying mechanism of large magnetostriction in Fe-Ga alloys is obviously beyond the conventional domain rotation and twin boundary motion, but has been attributed to the nanoscale magnetic heterogeneities. However, the nanoheterogeneity response as well as the interaction with matrix during magnetization process is still an open question. Through in-situ magnetic small-angle neutron scattering (SANS) study on a Fe81Ga19 alloy, the present work clearly reveals that the reorientation of nanodomains relevant to face-centered-tetragonal L60 nanoprecipitates occurs at relatively lower fields than that of the magnetic domains. These nanoheterogeneities show a larger magnetic correlation length than their size, ensuring the exchange coupling between nanoprecipitates and matrix as well as the flipping of their magnetizations. This process contributes to the low-field-triggered large magnetostriction, unlike that induced by non-180° domain switches in the homogeneous magnetostrictive materials (such as Terfenol-D). Further study reveals that the correlation length can be effectively tuned by simple heat-treatment, which in turn significantly enhances the magnetostriction without enlarging the triggering field. Consequently, this work contributes to uncover the physical mechanism of the large heterogeneous magnetostriction besides the typical magnetic domain theory, and may also provide a general guideline for achieving tunable magnetostriction in heterogeneous ferromagnets.

Atomic-scale insights into ω-variants in Galfenol triggered by displacive-diffusive transformation

Galfenol owing excellent deformation due to lattice softening are regarded as a new generation of smart magnetostrictive materials. However, the lack of direct probes of phase transformation and intermediate phase related to lattice softening blocks the comprehensive understanding of their intrinsic magnetostrictive mechanism and further improvement of their performance. In this work, we firstly report an atomic observation of ω phase transformation in Galfenol under low temperature aging by spherical aberration-corrected transmission electron microscopy. The ω precipitates with two variants are directly probed to be decomposed from FeGa bcc matrix with the assistances of both spinodal decomposition and displacive transformation. Their orientation relationships with the long range ordered bcc structure of D03 can be well indexed into (0003)ω1[112¯0]ω1 || (44¯4¯)D03[01¯1]D03 || (4¯401¯)ω2[112¯0]ω2. Density functional theory calculations unveil the precipitate of ω phase in Galfenol is theoretically possible. Further magnetostrictive measurements reveal the ω phase precipitates deteriorate the magnetostriction of Galfenol as empirically expected. Our work is believed to contribute a further insight of precipitate and structural evolution in Galfenol and is significant to maintain the magnetostriction performance of Galfenol in service.

Large and sensitive magnetostriction in ferromagnetic composites with nanodispersive precipitates

Large and sensitive magnetostriction (large strain induced by small magnetic fields) is highly desired for applications of magnetostrictive materials. However, it is difficult to simultaneously improve magnetostriction and reduce the switching field because magnetostriction and the switching field are both proportional to the magnetocrystalline anisotropy. To solve this fundamental challenge, we report that introducing tetragonal nanoprecipitates into a cubic matrix can facilitate large and sensitive magnetostriction even in random polycrystals. As exhibited in a proof-of-principle reference, Fe–Ga alloys, the figure of merit—defined by the saturation magnetostriction over the magnetocrystalline anisotropy constant—can be enhanced by over 5-fold through optimum aging of the solution-treated precursor. On the one hand, the aging-induced nanodispersive face-centered tetragonal (FCT) precipitates create local tetragonal distortion of the body-centered cubic (BCC) matrix, substantially enhancing the saturation magnetostriction to be comparable to that of single crystal materials. On the other hand, these precipitates randomly couple with the matrix at the nanoscale, resulting in the collapse of net magnetocrystalline anisotropy. Our findings not only provide a simple and feasible approach to enhance the magnetostriction performance of random polycrystalline ferromagnets but also provide important insights toward understanding the mechanism of heterogeneous magnetostriction.

A flexible and noncontact guided-wave transducer based on coils-only EMAT for pipe inspection

Ultrasonic guided wave testing technique, with its advantages of long propagation distance, low attenuation and high testing efficiency, has been widely used in nondestructive testing and structure health monitoring for pipes. In this paper, a flexible and noncontact guided-wave transducer based on a novel and coils-only electromagnetic acoustic transducer (EMAT) is proposed. In this new transducer, a planar magnetic coil of racetrack shape fed with rectangular-pulsed current is used to produce a quasi-static magnetic field, while a planar meander coil fed with RF-pulse current is used for pulsing and receiving guided-wave signals. Based on the magnetostrictive mechanism, the proposed transducer can generate and receive guided wave of L(0,2) mode in ferromagnetic metal pipes without coupling medium. Electromagnetic fields for the two coils and the induced ultrasonic waves are studied by simulation. Both the simulation and experimental results show that the proposed transducer is effective for generating and receiving ultrasonic guided wave of L(0,2) mode in ferromagnetic pipes, and can be applied on detection for corrosion. Due to the flexible, noncontact feature, and compact configuration of the proposed transducer, it can be conveniently applied for pipes in different diameter with rusty surface or coating in narrow space.

An improved analytical model of the magnetostriction-based EMAT of SH0 mode guided wave in a ferromagnetic plate

The accuracy of electro-acoustic energy transfer efficiency (EAETE) model directly determines the optimization results of an electromagnetic acoustic transducer (EMAT). In this study, the EMAT model of SH0 mode generation based on magnetostriction mechanism is re-examined. In the existing magnetostriction-based EMAT (MEMAT) analytical model, an approximate method of dynamic magnetic field was employed. Thus the effects of the tested ferromagnetic materials on the dynamic magnetic field in the air is ignored and the boundary condition between air and material is not exact. As a result, the calculated dynamic magnetic field inside the tested ferromagnetic materials is incorrect, thus leading to the calculation errors of magnetostriction body force and the final EAETE of MEMAT. The rigorous analytical solutions for calculating the dynamic magnetic field are derived based on Maxwell equations and boundary conditions in this study. The prediction results of improved analytical model were consistent with previously reported experimental results. Compared with existing analytical models, the improved model showed the higher prediction accuracy of several parameters, including dynamic magnetic field, magnetostriction force and the EAETE.

Study of a spiral-coil EMAT for rail subsurface inspection

The novelty of this paper is that a spiral-coil EMAT (electromagnetic acoustic transducer) is applied to rail subsurface inspection. To study the spiral-coil EMAT for rail subsurface inspection, the dominant mechanism is investigated emphatically. The interaction between the Lorentz-force mechanism and the magnetostriction mechanism is analyzed corresponding to the magnetic flux density and the frequency which has a significant effect on the magnetostriction mechanism. The effect of frequency on beam divergence is further discussed about the rail subsurface inspection using spiral-coil EMAT as well. A 2D FEM (finite element model) of spiral-coil EMAT is established and the simulation is carried out to analyze these issues. Besides, the experiments to inspect the subsurface crack of steel plate are carried out at various frequencies to verify the feasibility of the application. The experimental results demonstrate that the rail subsurface inspection by using the spiral-coil EMAT is feasible and the high frequency can contribute to distinguish the echo signal from the rail subsurface crack.

Polar state induced by block-type lattice distortions in BaFe2Se3 with quasi-one-dimensional ladder structure

Temperature dependent crystal structures of the quasi-one-dimensional ladder material BaFe2Se3 are examined. Combining the optical second harmonic generation (SHG) experiments and neutron diffraction measurements, we elucidate the crystal structure with Pmn2_1 space group in the low-temperature phase below Ts2 = 400 K, further above Neel temperature. This low-temperature phase loses the spatial inversion symmetry, where a resultant macroscopic polarization emerges along the rung direction. The transition is characterized by block-type lattice distortions with the magneto-striction mechanism. Change in the electrical resistivity and the magnetic susceptibility across the polar-nonpolar transition also suggests a modification of the electronic states reflecting the structural instability. Consistency and discrepancy with the existing theory are discussed.

Magnetodielectric Relaxation in Ho2Ti2O7 and Dy2Ti2O7 Spin Ice

Materials having magnetoelectricity is one of the highest priority research topics for the development of novel multifunctional materials. Recently, Ho2Ti2O7 and Dy2Ti2O7 pyrochlores show the coexistence of ferroelectricity with complex magnetism. The present study shows that these spin ices show an anomalous nature of relaxation taking place at ~ 4 K. Arrhenius nature of frequency dispersion behavior and order of characteristic relaxation time τ0 suggest that observed relaxation is associated with non-interacting electric dipoles induced by lattice distortions. These lattice distortions are associated with prevailing 3in-1out spin structure via magnetostriction mechanism, thus enabling the control of ferroelectricity though magnetism.

Facile synthesis of magnetic rubber foam with cellular structure by one-step solution foam processing for application in giant magnetostriction

Generally, magnetostriction elastomer were based on magnetic field-induced strains of elastomer matrix, resulting from the rotation of magnetic particle in elastomer matrix. However, such magnetostriction was relatively small and large hysteresis. Here, a new class magnetic rubber foam with cellular structure was developed and synthesized by the one-step solution foam processing. The magnetic rubber foam did not only show larger magnetostriction value of ca.11.0% comparing to previous magnetostriction elastomer, but also was few remanent magnetostriction and rapid response (ca. 1.0s). Furthermore, a new mechanism of magnetostriction was proposed for explaining the high performance magnetostriction. These provide a universal route for the rational design of magnetostriction materials with high performance for various applications.

A study of magnetostriction mechanism of EMAT on low-carbon steel at high temperature

The Electromagnetic acoustic transducer (EMAT) is used in a number of non-destructive testing applications [1–5]. The EMAT's operation is principally based on one of two mechanisms; the Lorenz force and magnetostriction mechanism [6–9]. The magnetostriction mechanism of an EMAT at elevated temperatures is reported in this paper. An optimized model is developed to describe the magnetostriction of polycrystalline iron, which is based on Brown's magnetic domain wall movement model [10] and Lee's magnetic domain rotation model [11]. The magnetostriction curves of polycrystalline iron for the temperature range 300 K–900 K are predicted, which reveal that the saturated magnetostriction coefficient changes from −4×10−6 to approximately 12×10−6. A non-linear, isotropic magnetostriction, finite element model is developed to simulate the Lamb waves generated in 4 mm thick steel plate by an EMAT, and the results show that the amplitude of S0 Lamb wave is greatly enhanced with an increase of temperature. In the experiments, a magnetostriction-based EMAT is used to generate Lamb waves in 4 mm thick steel plate. Experimental measurements verify that the contribution of the magnetostriction mechanism on steel rises as temperature increases in the range 298 K–873 K, while the contribution to ultrasonic generation from the Lorenz force mechanism decreases, as expected.

Designs for improving electromagnetic acoustic transducers’ excitation performance

The main drawback of electromagnetic acoustic transducers (EMATs) is their low energy transition efficiency. For the purpose of increasing the amplitude of the received signal, a ferrite core (FC) and a bias magnet (BM) are utilized respectively to improve the EMAT’s excitation performance in this paper. It indicates that the new configurations can increase the peak-to-peak amplitude of the received signal by a factor of 2.7 and 2.9, respectively. The reasons for the signal enhancement are also investigated through simulation and experimental methods. For the FC EMAT, improvement is achieved due to the enhancement of the dynamic magnetic field and the increase of coil inductance. In comparison, the change of the magnetostrictive transduction mechanism leads to the signal enhancement for the BM EMAT. The bias magnet magnetized the surface of the steel plate, which changes the signal excitation mechanism from domain wall movement to reversible domain rotations.