Terfenol-D Composites Research Articles

A self-consistent magnetoelectric coupling model for GaN-based /Terfenol-D composites

A magnetoelectric composites is designed and investigated, which combines GaN-based semiconductor and magnetostrictive Terfenol-D. In this work, we study the polarization charge and strain of the multilayer composites under an applied magnetic field and prestress. In order to quantitatively describe the response of composites under different loading environments, a nonlinear magneto-electric self-consistent coupling model is established based on nonlinear constitutive equation, Schrodinger equation, and Poisson equation. The validity of this model is well-proven by comparing experimental data and numerical results under different magnetic fields. The results demonstrate that the giant magnetostriction effect of Terfenol-D offered large tensile strain to decrease the polarization charge and strain in GaN-based semiconductor layer. These conclusions will be of great help to the basic research of piezomagnetic composite materials as well as guidance for the future device design.

A Self-Consistent Magnetoelectric Coupling Model for Gan-Based /Terfenol-D Composites

A Self-Consistent Magnetoelectric Coupling Model for Gan-Based /Terfenol-D Composites

Analysis of nonlinear piezomagnetism for magnetostrictive terfenol-D composites

This study presents two micromechanics formulations to investigate the nonlinear piezomagnetism for magnetostrictive Terfenol-D composites subjected to large magnetic driving fields. A simplified unit-cell micromechanics method that hypothesizes the composite microstructure forming a periodic array is developed, and the well-known Mori-Tanaka micromechanics model is reformulated for nonlinear composite problems. This work elucidates the nature of the approximation in applying the unit-cell and Mori-Tanaka micromechanics models to magnetostrictive composites insofar as the concentration tensors are concerned. A first moment secant linearization but conventional tangent linearization is employed for nonlinear magneto-elastic constitutive laws in order to obtain a unified and linearized constitutive equation. Later, a homogenization process on the nonlinear responses of magnetostrictive composites is performed via numerical iterations in order to minimize errors from the linearization process. Different composites comprising of unidirectional Terfenol-D fiber, particle, and lamina reinforcements are studied, respectively. For nonlinear piezomagnetic strain responses simulated in this work, the predictions given by the unit-cell and Mori–Tanaka schemes are in good agreement with the experimental data available in the literature. Numerical results are also presented to illustrate the performance of each micromechanics model for common composite connectivity, i.e., 1–3, 0–3, and 2–2 types. Depending on Terfenol-D geometry, volume fraction, and applied magnetic field, the magnetostrictive composites could exhibit various degrees of nonlinear piezomagnetism. The presented micromechanics models can further be served as composite constitutive equations to analyze smart composite structures such as beams commonly utilized in sensor and actuator applications.

Simulation and experimental study of FBG-based magnetic field sensors with Terfenol-D composites in different geometric shapes

In this paper, we report a study on optical sensors based on fiber Bragg gratings (FBG) and magnetostrictive composites of Terfenol–D applied to magnetic field measurement. The study consisted in determining the sensor's sensitivity influenced by the shape of the magnetostrictive composite with an embedded FBG. The proposed sensors were designed and simulated using finite element method (FEM) in cylindrical, hyperbolic, and conical shapes in order to determine the geometric configuration for best sensitivity using the less amount of Terfenol-D. One prototype of each designed shape was manufactured using powdered Terfenol-D with 200–300 µm grain size and epoxy resin. The experimental results showed that the shape of the magnetostrictive composite influences up to 59% in the sensitivity of the sensors. The results also showed that the smaller sensor, a ∅1.5 mm × 16 mm cylinder using only 0.052 g of Terfenol-D was the best shape and achieved the highest sensitivity.

Nanoscale domain structure evolution and magnetoelectric coupling for PMN-33PT/Terfenol-D multiferroic composite

Multiferroic composites of Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystal and Tb0.3Dy0.7Fe2 (Terfenol-D) possess strong magnetoelectric (ME) coupling at room temperature and hold promises as magnetic field sensors, and energy harvesting devices, etc. The nanoscale domain structure evolution upon the applied magnetic field determines the ME coupling. Via introducing of the PLM (Polarized Light Microscope) into the commercialized Piezoelectric Force Microscope (PFM) (named as PLM-PFM system), in-situ observations of domain structure evolution and ME coupling are investigated for [001]-oriented PMN-33PT/Terfenol-D composites. Upon the magnetic loadings, via strain transfer, domains of orthorhombic (O) phase first expands in area, and then a phase transition from O to monoclinic (M) phase takes place in PMN-33PT. Correspondingly, modulation of the electric field-induced displacement (or the inverse piezoelectric response) can be achieved by the magnetic field. Finite-element simulations are performed to calculate the magnetic field-induced displacement, which demonstrate its dependence on the piezomagnetic coefficient of Terfenol-D. The results provide insight into the magnetic field induced domain switching in nanoscale and magnetoelectric coupling for the PMN-PT/Terfenol-D multiferroic composites.

Enhancement of capacitive type magnetoimpedance effect in ring-type magnetoelectric transducers vibrator via size-dependent resonance frequency

A magnetically tunable magnetoelectric transducer vibrator made of ring-type Pb(Zr,Ti)O3 (PZT)/Terfenol-D (TDF) composite has been developed. We investigated the size effects of the vibrator resonance frequency. The relative effective permittivity and relative effective permeability of magnetoelectric composite are related to the size of ferromagnetic material. Improvements of about 469%, 176% and 696% of magnetoimpedance, magnetoinductance and magnetocapacitance have been achieved at anti-resonance of the vibrator, respectively. The dramatic change in the magnitude of capacitive type magnetoimpedance, magnetoinductance and magnetocapacitance shows that their responses depend on the size of the magnetostrictive ring in the transducer composite vibrator. The capacitive type magnetoimpedance effect can be substantially enhanced via properly designing the inner radius of magnetostrictive ring, which providing an alternative avenue for increasing magnetically tunable sensitivity.

Magnetic field-induced ferroelectric domain structure evolution and magnetoelectric coupling for [110]-oriented PMN-PT/Terfenol-D multiferroic composites

Magnetic field-induced polarization rotation and magnetoelectric coupling effects are studied for [110]-oriented (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3/Tb0.3Dy0.7Fe2(PMN-xPT/Terfenol-D) multiferroic composites. Two compositions of the [110]-oriented relaxor ferroelectric single crystals, PMN-28PT and PMN-33PT, are used. In [110]-oriented PMN-28PT, domains of rhombohedral (R) and monoclinic (MB) phases coexist prior to the magnetic loadings. Upon the applied magnetic loadings, phase transition from monoclinic MB to R phase occurs. In [110]-oriented PMN-33PT, domains are initially of mixed orthorhombic (O) and MB phases, and the phase transition from O to MB phase takes place upon the external magnetic loading. Compared to PMN-28PT, the PMN-33PT single crystal exhibits much finer domain boundary structure prior to the magnetic loadings. Upon the magnetic loadings, more domain variants are induced via the phase transition in PMN-33PT than that in PMN-28PT single crystal. The finer domain band structure and more domain variants contribute to stronger piezoelectric activity. As a result, the composite of PMN-33PT/Terfenol-D manifests a stronger ME coupling than PMN-28PT/Terfenol-D composite.

On wave characteristics of piezoelectromagnetics

This report gives a discussion of a new wave characteristic as a material parameter for a composite with the magnetoelectric effect. The new parameter depends on the material constants of a piezoelectromagnetic composite. It can be implemented on: (A) mechanically free, electrically and magnetically open surface and (B) mechanically free, electrically and magnetically closed surface. These theoretical investigations are useful for researchers in the fields of acousto-optics, photonics and opto-acousto-electronics. Some sample calculations are carried out for BaTiO3–CoFe2O4 and PZT-5H–Terfenol-D composites of class 6 mm. Also, the first and second derivatives of the new parameter with respect to the electromagnetic constant α are graphically shown.

Magnetostrictive properties of titanate coupling agent treated Terfenol-D composites

As a kind of composites, the bond strength between the polymer matrix and the Terfenol-D particles affects the performance of magnetostrictive composites. By observing the fracture morphologies, the bond strength of the magnetostrictive composites prepared with untreated Terfenol-D was proved weak. Titanate coupling agent was used for particles to improve the bond strength. Contact angle analysis indicates the work of adhesion of the epoxy resin to the treated Terfenol-D is larger than that to the untreated Terfenol-D. Different magnetostrictive composites with 20%, 35% and 50% particle volume fractions were prepared with treated and untreated Terfenol-D particles. Their static and dynamic magnetostriction was tested without pre-stress at room temperature. The results indicate titanate coupling agent treating increases the magnetostrictive properties of magnetostrictive composites, that is probably because the bond strength improves due to the particle treating.

Uniform High Magnetostrictive Properties of Terfenol-D Composites Prepared by a Dry Process

Magnetostrictive composites were usually fabricated using a wet process. The settlement of particles in liquid polymers due to the gravity results in the inhomogeneous and low magnetostrictive properties. To solve the problem, magnetostrictive composites were prepared using a dry process, and their properties were tested in this paper. Measurement of magnetostriction on different positions along the length direction of the material indicates the magnetostrictive composites prepared by the dry process present uniform properties due to the uniform distribution of the active particles in the polymer matrix. The saturation magnetostriction and the maximum dynamic magnetostriction of the [1-3] Terfenol-D composites prepared in the study was 1005ppm and 4.08nm/A, respectively, which was larger than the [0-3] ones.

Bonded Terfenol-D composites with low eddy current loss and high magnetostriction

Bonded Terfenol-D composites, with high electrical resistivity and low eddy current loss, can be used in an alternating magnetic field with high frequency. However, the nonmagnetic binder impairs the magnetostriction of the composites. To achieve high magnetostriction and low eddy current loss, the mixture of the alloy powder and binder was compressed at low pressure in an oriented magnetic field. After this, the aligned samples were recompressed by cold isostatic pressing (CIP). Besides, the effect of particle size on the magnetostriction of the bonded Terfenol-D composites was also studied. The results showed that the bonded Terfenol-D composites had excellent magnetostriction when the particle size was 50–80 μm. The oriented magnetic field and CIP could improve the magnetostriction of the bonded composites, which reaches 1020×10−6. The bonded Terfenol-D composites had good compact structure and high density (7.24 g/cm3). The magnetic loss of the bonded Terfenol-D composites was 192 mW/cm3 at a frequency of 100 kHz in a magnetic field of 960 A/m, which was about one third of that of casting Terfenol-D alloys.

Fabrication of Tb 0.3Dy 0.7Fe 2/epoxy composites: Enhanced uniform magnetostrictive and mechanical properties using a dryprocess

To improve the uniformity of the magnetostrictive properties of Terfenol-D composites along the field direction, a dry method is developed in the present study. We examined the compaction pressure, particle volume fraction, particle size and composite configuration as factors that affected the magnetostrictive properties of the composites. The experimental results indicated that the magnetostrictive properties were improved with the increase of compaction pressure and particle volume fraction. In addition, larger average particle size was shown to result in more pronounced magnetostrictive properties. The particle alignment due to the orientation field is beneficial for the promotion of the magnetostrictive properties. The largest saturation magnetostriction and the maximum piezo-magnetic coefficient in the absence of a mechanical preload was obtained at 1005 ppm and 4.08 nm/A, respectively, for the aligned composite including a particle volume fraction of 77% and an average particle size of 210 μm.

Magnetoelectric effect in lead-free BNKLBT ceramic/terfenol-D continue fiber composite laminates

A magnetostrictive-piezoelectric laminated composite has been developed by sandwiching a lead-free BNKLBT ceramic plate polarized in the thickness direction between two terfenol-D continuous fiber composite plates. This lead-free magnetoelectric (ME) laminated composite has a large ME voltage sensitivity of 2.5 V/Oe at the resonance frequency of 130.9 kHz under a low magnetic bias field (HBias) of 0.6 kOe. This work shows the potential of BNKLBT lead-free ceramics in ME sensing application.

Predicting performance of polymer-bonded Terfenol-D composites under different magnetic fields

Considering demagnetization effect, the model used to calculate the magnetostriction of the single particle under the applied field is first created. Based on Eshelby equivalent inclusion and Mori–Tanaka method, the approach to calculate the average magnetostriction of the composites under any applied field, as well as the saturation, is studied by treating the magnetostriction particulate as an eigenstrain. The results calculated by the approach indicate that saturation magnetostriction of magnetostrictive composites increases with an increase of particle aspect and particle volume fraction, and a decrease of Young's modulus of the matrix. The influence of an applied field on magnetostriction of the composites becomes more significant with larger particle volume fraction or particle aspect. Experiments were done to verify the effectiveness of the model, the results of which indicate that the model only can provide approximate results.

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.

High magnetostriction polymer-bonded Terfenol-D composites

Different magnetostrictive composites that contain Terfenol-D particles in a polyurethane elastomer matrix were prepared by changing the ratio of the hard/soft segment ( F) of the polyurethane, and modifying the amount of Terfenol-D particles, from 30 to 50 wt%. The magnetostrictive behaviour, as well as the mechanical properties of the magnetic composites, has been investigated. The magnetostriction was measured at room temperature with strain gauges (and parallels) in magnetic fields up to 1 T. The magnetostrictive response improves when the magnetic particles are oriented in different magnetic fields (0.05, 0.5 and 1 T) and reaches ≈700 microstrains for an oriented F = 1 and 50% of Terfenol-D sample. On the other hand, the effect of the matrix on the magnetostrictive response has been examined, obtaining the highest response for a F = 1.5 polyurethane and 50 wt% of Terfenol-D oriented with a magnetic field of 0.5 T.

Magnetostrictive Properties of Polymer-Bonded Terfenol-D Composites

Magnetostrictive Properties of Polymer-Bonded Terfenol-D Composites

Interfacial stiffness dependence of the effective magnetostriction of particulate magnetostrictive composites

Terfenol-D composites attract much attention recently due to their large magnetostriction, small eddy energy loss and large operation frequency bandwidth. Binder layer in the composite usually mechanically weakens the composite and reduces the effective properties. A typical kind of magnetostictive composite is composed of Rare Earth metallic compound powder, matrix material and resin binder. The binder, which is usually flexible and forms mechanically weak interface in the composite, inevitably influences the overall magnetostriction of composites. In this paper, a theoretical model was developed to treat a simple deformation case of this kind of mechanically weak interface, in which the flexible layer has low stiffness to withstand deformation but no de-bonding or cracking. An infinite magnetostrictive plane with a circular inclusion was considered, where the matrix and inclusion are all general magnetostrictive materials which can be modeled by the standard square constitutive relation of magnetostriction. The binder layer of a certain thickness was modeled as a set of springs with no thickness but with an equivalent stiffness. The mathematical formulation was brought into the complex variable framework. The magnetoelastic field was solved and the effective magnetostriction was explicitly obtained. Comparisons with experimental results were also presented. In terms of this analysis, the interfacial stiffness has significant influences on the overall magnetostriction of composite. Increasing the interfacial stiffness can lead to large magnetostriction of composites. The measure for improving the interfacial stiffness includes increasing the binder modulus and reducing its thickness.

Magnetoelectric effect in sputtered composites

The magnetoelectric effect in millimeter size PMN-PT∕Terfenol-D composites is known. In an effort towards miniaturization, we report on the magnetoelectric effect in micrometer-size sputtered composites. Multilayers of TbFe∕FeCo with a thickness of 4μm were sputter deposited on both sides of PMN-PT piezoelectric single crystals. The magnetoelectric voltage of samples was measured and reached values of 13mV∕(Oecm) at dc bias fields of 2mT, a linear dependence of magnetoelectric voltage on ac amplitude was detected in the range from 1mT to 1nT.

Magnetostrictive 1-3 Composites With Internal Field Biasing

1-3 composites comprising an array of square Terfenol-D rods continuous in the direction of actuation and separated by an epoxy matrix have been produced. The benefits of a Terfenol-D 1-3 composite over bulk Terfenol-D and powder composites has been investigated. A higher frequency capability is realized while maintaining a greater coupling coefficient, k/sub 33/, to that of powder composites. 1-3 composites were produced containing between 40% and 70% volume fraction of Terfenol-D. Magnetic biasing was achieved using Nd/sub 2/Fe/sub 14/B powder located within the epoxy matrix at 40% volume fraction. Internal bias fields of 75 and 45 kA/m were measured for the 1-3 composites containing 40% and 70% Terfenol-D, respectively. A coupling coefficient of 0.53 was measured for the composites filled with epoxy alone while the coupling coefficient varied from 0.33 to 0.48 for the biased composites with between 40% and 70% volume fraction of Terfenol-D, respectively. The acoustic impedance was determined using the radial resonance and observed to decrease with decreasing Terfenol-D volume fraction. A 50% volume fraction Terfenol-D 1-3 composite containing microspheres within the epoxy had the lowest measured acoustic impedance of 6.8 Mrayl, making this composite the most suitable for coupling acoustic energy into tissue/water for ultrasound/SONAR applications.