Magnetostriction Of Terfenol-D Research Articles

Dynamic/static displacement sensor based on magnetoelectric composites

This study presents a dynamic/static displacement sensor based on both end fixed Terfenol-D/PZT (lead zirconate titanate) magnetoelectric composites. Owing to the fixed boundary condition, the magnetostriction of Terfenol-D under the magnetic field is limited and the stress acts on PZT through mechanical coupling, and finally, an induced voltage is generated due to the piezoelectric effect in PZT. The magnetic field applied on the magnetoelectric composites varies with the displacement of the permanent magnet which represents the displacement to be measured. In that case, the determination of displacement can be transformed into determining the variation of the magnetic field. The experimental results manifest that the frequency of magnetoelectric voltage is the same as the frequency of displacement. The dynamic displacement sensitivity of this sensor increases with the increase in the input frequency in the low frequency range and the decrease in the length of the air gap. The sensitivity is 6.549 mV/μm with a 0.75 mm air gap for dynamic displacement at 10 Hz and 0.84 μV/μm with a 2.5 mm air gap and an external magnetic field at 1 kHz for static displacement. It can be concluded that the displacement measuring mechanism based on the magnetoelectric effect is a promising robust and accurate method.

A vibration amplitude model for the giant magnetostrictive ultrasonic processing system

For the purposes of estimation and control of the vibration amplitude in rotary ultrasonic machining, the relation between vibration amplitude and excitation signal was examined. The mechanical components outside the Terfenol-D were regarded as a single-degree-of-freedom mass spring damping system, and an equivalent mechanical model of the giant magnetostrictive ultrasonic processing system was addressed. After that, the vibration amplitude was modeled as a function of the frequency and amplitude of the excitation current by considering both magnetization and magnetostriction of Terfenol-D and ultimately achieved through parameter identification using the methods of impedance analysis and nonlinear least-squares fitting. In addition, the relation between resonant frequency of the giant magnetostrictive ultrasonic processing system and the magnitude of the excitation current was studied so that the vibration amplitude model was improved. Thus, the vibration amplitude of the giant magnetostrictive ultrasonic processing system excited by various electric signals with different frequencies and amplitudes can be calculated. As demonstrated by comparison with experimental results, the vibration amplitude model can accurately estimate the vibration amplitude of the giant magnetostrictive ultrasonic processing system. It indicates that the model is meaningful for the design and control of the giant magnetostrictive ultrasonic processing system.

The effect of field-orientation on the magnetoelectric coupling in Terfenol-D/PZT/Terfenol-D laminated structure

The field-orientation dependent magnetoelectric coupling is experimentally studied for a rectangular Terfenol-D/PZT/Terfenol-D laminated structure. The considered magnetic field, namely the dc-bias magnetic field or the ac-excitation magnetic field, is allowed to be spatially re-orientated between two orthogonal geometric dimensions of the composite. In the study, the direction of the excitation can be fixed in the longitudinal (Scheme-I) or thickness (Scheme-II) directions, while considering the bias orientation. Alternatively, the bias field can be restricted to the longitudinal (Scheme-III) or thickness (Scheme-IV) directions, while the excitation orientation is considered. The variation in magnetoelectric coefficient as a function of the bias magnitude is studied with special attention paid to the field-orientation dependency. For the testing schemes of I and II, the direction of the dc-bias field can be re-oriented by forming an angle with the fixed direction of the ac-excitation field. As the angle changes from 0° to 90°, the magnetoelectric coupling evolves from L-T mode to S-T surface shear for Scheme-I, and from T-T mode to S-T thickness shear for Scheme-II. The bias-field-orientation dependence demonstrates a complex pattern due to the varying overall state of anisotropy in Terfenol-D. In Scheme-I with low bias magnitude, the orientation dependence can be represented by the measured effective longitudinal piezomagnetic coefficient. In addition, the optimal bias field for maximum magnetoelectric coefficient is observed to linearly increase with the bias orientation angle. Alternatively, the orientation dependence in Schemes III and IV is more predictable due to the barely changed overall state of anisotropy. In this case, Scheme-III shows that the magnetoelectric coefficient decreases monotonically with the orientation angle and Scheme-IV indicates that the maximum coefficient is attained at around 60°. The dependence of the magnetoelectric coupling on the excitation-filed orientation can be understood via analysis of the resultant magnetostriction in Terfenol-D with assumed effective magnetization, which may depart from the bias field due to the strong demagnetization effect. The analysis is supported by the computed field-orientation dependence of the magnetostriction in Terfenol-D.

Effect of the induced anisotropy axis on altering domain alignment and magnetostriction of Terfenol-D

The present work investigates quantitatively the effect of induced anisotropy axis on magnetostriction of Terfenol-D, exploring a possible method of tailoring flexibly magnetostriction for a particular purpose. It is found that the induced anisotropy axis shows significant effect on the initial domain state, magnetization process, and thus the magnetostriction. Magnetostriction behaviors for a specific induced anisotropy axis are discussed and compared with the experimental observations. The critical case for the expected 90° domain alignments has been also analyzed quantitatively. Diagrams of domain state evolutions are established, shining some light on understanding magnetostriction tunability and developing magnetostrictive material.

A multi-field domain rotation model for giant magnetostrictive materials

A magneto-mechanical-thermal model based on a domain rotation mechanism is developed in this paper. An energy distribution parameter related to prestress and temperature is induced, which can be determined by simple experiments. Magnetization and magnetostriction of Terfenol-D at different temperatures and prestresses are calculated and estimated, which are consistent with experiments. The model can be applied to estimate prestress effects to magnetization. The results show that compressive prestress can increase to maximum using temperature of giant magnetostrictive materials.

Magnetization and magnetostriction of Terfenol-D near spin reorientation boundary

Magnetization and magnetostriction behaviors of quasi-binary TbxDy1−xFe2 alloys (Terfenol-D) near spin reorientation boundary (SRB) between 〈111〉 and 〈100〉 easy axes are studied by computer simulation of magnetic domain rotations under increasing magnetic field and compressive stress along [112] growth direction. The simulation results reveal coexistence of 〈111〉 and 〈100〉 domains near SRB and show that the switching field first decreases then increases when crossing the SRB from the 〈100〉 region into the 〈111〉 region of the quasi-binary phase diagram, while the magnetostriction first increases then saturates, thus providing an optimal combination of large magnetostriction and low switching field near the SRB as desired for actuator application. This finding has general implications for other magnetostrictive quasi-binary alloys that also exhibit spin reorientation phenomenon, allowing material design for improved magnetostrictive property near SRB, in analogy to morphotropic phase boundary ferroelectrics.

Effects of magnetocrystalline anisotropy constant K2 on magnetization and magnetostriction of Terfenol-D

Magnetocrystalline anisotropy constant K2 is found to produce significant effects on the magnetization and magnetostriction behaviors of Terfenol-D crystals through magnetic domain rotation mechanism. Such effects have often been neglected in previous studies. Considering different values of K2 in the magnetization rotation of ⟨111⟩ easy-direction domains under external magnetic field and compressive uniaxial stress applied along [1¯1¯2] direction, it is shown that a change in K2 causes significant changes in both magnetization and magnetostriction curves. Therefore, K2 is an important parameter that must be considered in magnetoelastic behaviors of Terfenol-D.

The inverse magnetostrictive effect in Tb0.3Dy0.7Fe2

The inverse magnetostrictive effect, also called magnetomechanical effect, in Terfenol-D material, has been investigated in this paper. Based on Stoner-Wohlfarth (SW) model, taking into account magnetocrystalline and stress-induced anisotropy energy, and following the free energy minimization procedure, direction cosines of magnetization in Terfenol-D single crystal in demagnetized state have been obtained as a function of the compressive stress. The nonlinear equations for equilibrium have been solved numerically. The results indicated that under compressive stress, magnetic anisotropy in Terfenol-D is determined by a competition between magnetocrystalline and stress-induced anisotropy energy, and changes from cubic symmetry to uniaxial. A comparison between experimental and numerical results showed that there is a maximum magnetostriction in Terfenol-D at a certain stress. According to our numerical results, experimental observations that compressive stress makes Terfenol-D hard to be magnetized and leads to the maximum magnetostriction can be explained. The computation in this paper presents a more accurate approach to similar investigations, and its numerical results would be helpful for a better understanding of magnetization process of similar materials.

The effect of magnetic field heat treatment on magnetostriction of Terfenol-D 2-2 composites

Based on the analysis of the magnetostriction for Terfenol-D composites, Terfenol-D 2-2 magnetostrictive composites have been prepared with laminations perpendicular to [1 1 2] axes. Then one of the samples was annealed in the vacuum at 423 K for 15 min at the magnetic field of 240 kA/m, which is along the direction of laminations and vertical to the [1 1 2] axes of the specimen. The static magnetostriction λ and dynamic magnetostrictive coefficient d 33 of samples were measured under the compressive stress of 0, 2, 4, 6 and 8 MPa. Effects of the compressive stress and the magnetic field heat treatment on the magnetostriction λ have been investigated. It is found that the magnetostriction of 2-2 composites can be improved under the compressive stress when the magnetic field is larger than 20 kA/m. The magnetostriction of 2-2 composites with the magnetic field heat treatment increases under compressive stress, and it can reach 1390×10 −6 at the magnetic field of 200 kA/m and under the compressive stress of 4 MPa, much larger than the value of 860×10 −6 without the magnetic field heat treatment. The highest magnetostriction of the 2-2 composite with the magnetic field heat treatment can reach 1530×10 −6. The dynamic magnetostrictive coefficient d 33 of 2-2 composites with the magnetic field heat treatment have been improved, compared with that without magnetic field heat treatment. The maximum value of d 33 of the sample with magnetic field heat treatment is 71% larger than that without magnetic field heat treatment.

Enhanced magnetoelectric effect in Terfenol-D and flextensional cymbal laminates

A magnetoelectric (ME) laminate configuration was fabricated using a flextensional cymbal located between two magnetostrictive Terfenol-D (Tb1−xDyxFe2) plates. The laminate, operating in transverse magnetized/transverse polarized mode, has a ME voltage coefficient of 56.8mV∕Oe under a magnetic bias field of 1kOe, which is larger than that of conventional Terfenol-D/PZT/Terfenol-D configuration. It is believed that the enhancement of ME effect is due to the coupling between the magnetostriction of Terfenol-D and the high piezoelectric response of cymbal.

Barkhausen effect and discontinuous magnetostriction in Terfenol-D

Measurements of magnetostriction λ, magnetic Barkhausen effect (MBE), and magnetic induction B have been made as a function of magnetic field H in a number of specimens of Tb0.3Dy0.7Fe1.9 prepared recently at Ames Laboratory. These results showed marked variations in properties from specimen to specimen. For example, the saturation magnetostriction of the materials under a compressive load of 14 MPa (2000 psi) varied from 1500 to 2200×10−6. However, it was noticed that in the high-performance, high-magnetostriction specimens a common feature was a very rapid change in magnetostriction with field in the range 400–500 Oe. Barkhausen measurements taken on two extreme specimens from the group also revealed very different signals, in particular the high-performance material was found to have a distinctive double peak in Barkhausen activity, one peak of which corresponded to the rapid change in magnetostriction, while the other occurred at the flat region of the magnetostriction versus field curve, corresponding to little or no change in magnetostriction.