A DC current sensor based on disk-type magnetoelectric laminate composite

We have found that small long-type magnetoelectric (ME) laminate composites of magnetostrictive Tb1−xDyxFe2−y and piezoelectric Pb(Zr,Ti)O3 are quite sensitive to small dc magnetic field (Hdc) variations, when driven by a constant ac magnetic field. The sensitivity limit is Hdc<10−3Oe (10−7Tesla) using a constant amplitude low frequencies drive, and Hdc<10−4Oe (10−8Tesla) under resonant drive. In addition, an unusual ME switching effect—a 180° phase shift—was observed, in response to changes in the sign of a small Hdc.

We report the effect of epoxy adhesion layers with different mechanical or physical property on a magnetoelectric (ME) composite laminate composed of FeBSi alloy (Metglas)/single-crystal Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3/Metglas to achieve an improved ME conversion performance. Through theoretical simulation, it was revealed that the Young's modulus and the thickness of interfacial adhesives were major parameters that influence the conversion efficiency in ME composites. In the experimental evaluation, we utilized three epoxy materials with a distinct Young's modulus and adjusted the average thickness of the adhesion layers to optimize the ME conversion. The experimental results show that a thin epoxy layer with a high Young's modulus provided the best performance in the inorganic-based ME conversion process. By tailoring the interfacial adhesion property, the ME laminate generated a high conversion coefficient of 328.8 V/(cm Oe), with a mechanical quality factor of 132.0 at the resonance mode. Moreover, we demonstrated a highly sensitive alternating current magnetic field sensor that had a detection resolution below 10 pT. The optimization of the epoxy layers in the ME laminate composite provided significant enhancement of the ME response in a simple manner.

A novel analytical model for magnetoelectric (ME) laminate composites made of piezoelectric (PE) and piezomagnetic (PM) phases is proposed. The multiphysics equations are applied to all four possible laminate configurations (TT, LT, TL, and LL), with appropriate boundary conditions. Closed form, explicit formulas are derived for the calculation of the intrinsic ME charge coefficient, ME voltage coefficient, and ME coupling factor as a function of material properties of both phases and the PM volume fraction. The predicted ME voltage coefficient is in agreement with previous work and experimental data. A new approach is proposed to take into account the conductivity of the PM phase resulting in calculated ME charge coefficients within 30% of experimental data, which is a major departure from the available approaches that either require to impose an additional constraint on the model or simply ignore the conductivity of the PM phase. To assess the conversion of magnetic work into electric work, a novel approach is developed to calculate the ME coupling factor in closed form by using the calculated properties of the ME composite structure, thus avoiding the equivalent circuit assumption, and furthermore novel coupling factor formulas are developed for all four polarization/magnetization configurations and taking into account the strain coupling in both inplane directions. Using actual material properties, conclusions are drawn regarding the optimal configuration and PM volume fraction necessary to achieve maximum charge, voltage, and work conversion.

Magnetoelectric (ME) composites have demonstrated high sensitivity for magnetic field sensor applications. Here, we report a ME laminate heterostructure consisting of magnetostrictive Tb0.3Dy0.7Fe1.92 (Terfenol-D) alloy and piezoelectric polyvinylidene fluoride (PVDF) layers, both operated in shear mode. We show that the shear mode ME sensor exhibits a marked improved ME effect compared with the traditional ME composites operated in longitudinal and transverse piezoelectric and magnetostrictive modes using the same materials. A giant ME coefficient of 7.93 V/(cm·Oe) is obtained under a DC magnetic bias of 2300 Oe. The improved ME coefficient derives from the shear-mode heterostructure design, which allows both the Terfenol-D and PVDF to operate in shear mode that has maximum magnetoelectrical coupling coefficient.

Resonance magnetoelectric (ME) responses are investigated for the ME laminate heterostructure consisting of positive magnetostrictive material FeCuNbSiB, negative magnetostrictive material Ni and piezoelectric material PZT-8. On one hand, both a built-in magnetic field induced by the strong magnetic interactions between positive magnetostrictive and negative magnetostrictive materials and an intrinsic anisotropic field with obvious hysteresis and remnant magnetization in Ni layer result in a large zero-biased ME effect. The corresponding zero-biased ME voltage coefficient reaches 10.12 V/Oe (126.5 V/cm Oe), which is about 3 times larger than that of traditional Ni/PZT-8 (NP) laminate. On the other hand, the additional stress produced by the high magnetic permeability FeCuNbSiB layer enhances the magnetostriction of Ni layer and ME response. The corresponding maximum ME voltage coefficient (dV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ME</sub> /dH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</sub> ) is 12.09 V/Oe (150.87 V/cm Oe) at bias magnetic field H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> = 4 Oe. It is further found that even a step change of ac magnetic field less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> T can be clearly distinguished by the proposed ME composite. The value of ME voltage sensitivity to dc magnetic fields (dVME/dHdc) reaches ~76.7 mV/Oe at H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> = 5 Oe and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</sub> = 0.1 Oe. Correspondingly, the proposed laminate heterostructure is able to possess both strong ac and dc magnetic field sensitivities.

Laminated magnetoelectric (ME) composites consisting of magnetostrictive and piezoelectric materials have been investigated and proved to realize strong ME coupling, which shows great benefits to fabricate high sensitivity ME magnetic sensors. In this work, optimized L–T mode ME composites consisting of heat-treated Metglas ribbons and [110]-oriented Mn-doped 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (Mn-doped PMN-PT) single crystal fibers were reported, which achieves giant ME coupling and ultrahigh ME electric field coefficient of 4.26 × 104 V cm−1 Oe−1 at the electromechanical resonance. The equivalent magnetic noise of the ME sensor based on the proposed ME composites is only 2.89 fT Hz−1/2 at the electromechanical resonance, which exhibits great prospect in the application of precision magnetic field detection. Based on the characterization of heat-treated Metglas samples and the finite element simulation of the ME composites, the improved performance of the ME composites and ME sensors can be attributed to the enhanced properties of heat-treated Metglas (higher piezomagnetic coefficient d 33,m, higher induced magnetic flux density and lower mechanical loss) due to the enhancement of nanocrystallization and the stronger magnetic flux concentration effect corresponding to the dimension of the Metglas ribbons.

Magnetoelectric (ME) composites have drawn increasing interest in recent years due to advancements in the technology resulting in enhanced ME coupling coefficients, stable room-temperature operation, sub-nanoTesla noise floor, low- and zero-biased operation, and fabrication of compact, miniaturized devices. Now, more than ever, practical use of ME devices in commercial magnetometry applications is feasible, while continued development of numerous other applications, such as voltage-tunable magnetic field generators, voltage-tunable inductors, and magnetically-tunable capacitors, bolster the overall usefulness of ME composites as a valuable technology. This dissertation focuses on development and characterization of tube-topology ME composites as magnetic field sensors. The novel topology is most notable for demonstrating high zero-external-bias sensitivity, low noise floor, low-frequency bandwidth, and self-powered, stable room temperature operation. Numerous characterization studies are included in this work where several devices are analyzed as a function of test-field, DC-bias field, geometry, material choice, and more. The overall conclusions drawn upon these results indicate strongly that the tube-topology ME magnetic field sensor holds promise to compete with existing hall-effect and flux-gate magnetometers. ME composites are at the tipping point of commercialization for use in magnetometry applications and are emerging as a valuable technology for use in numerous creative ways.

Since the piezoelectric/magnetostrictive laminate composite exhibits a strong magnetoelectric (ME) effect, it provides a novel method for detecting ac magnetic field. There are a number of researches on the development of ME composites and their applications in detecting magnetic fields. Dong et al. demonstrates the possibility of fabricating ac magnetic field sensors with high performances[1]. Especially, ME composite sensor can achieve the passive sensing of magnetic field and possesses high sensitivity, which greatly enhances the competitiveness of ME composite sensor against traditional magnetic sensors. ME voltage coefficient varies with H dc owing to the piezomagnetic coefficient's variation as a function of H dc , which shows a peak behavior near an optimum dc bias magnetic field H dc, opti . Hence, the ME composite sensor requires an external dc bias magnetic field to obtain the high ME sensitivity. However, the bias magnetic field is usually generated by using permanent magnets. It will increase the electromagnetic noise and increase the size of the sensor greatly, which is disadvantageous for the realization of high-sensitivity miniature magnetic sensors. Furthermore, the peak point is sharp and fixed, correspondingly small fluctuations of the optimum dc bias magnetic field will lead to a remarkable decrease of the ME voltage coefficient and degrade the ME composite performance significantly. In addressing these issues, the study of self-biased ME composite has provoked a great number of research activities and made progress [2-3]. However, these efforts have not obtained a wide range of dc bias response.

A low-frequency magnetoelectric (ME) response model of magnetostrictive/piezoelectric laminate composites based on multi-parameter analysis is presented. This model, taken the shear effect as the basis, analyzes the stress and strain of the magnetostrictive and piezoelectric layers by the stress function. The interlayer shear stress and the low-frequency ME response characteristics of ME laminate composites are obtained by using Hamilton principle of minimum energy and in consideration of the influence of stored magnetic field energy of magnetostrictive layer. The theoretical results show that the ME voltage coefficient is related with the magnetic permeability, Poisson ratio, magnetomechanical coupling coefficient, thickness ratio of magnetostrictive material and the Poisson ratio and electromechanical coupling coefficient of piezoelectric material. The influence of these parameters is analyzed. The experimental results show that analytical results are also compared to experimental test data with excellent correlation and their errors are less than 6%.

Magnetoelectric (ME) composites exhibit the magnetoelectric effect, which is a coupling phenomenon resulting from the interaction between the magnetostrictive and piezoelectric phases. This makes ME composites useful as multifunctional devices in a variety of applications. In this work, a press-fit epoxy-free nested ring structured ME composite has been fabricated, in which nickel and FeNi form the magnetostrictive phase and PZT-5A constitutes the piezoelectric phase. To conduct a comparative study, epoxy bonded conventional bilayered and trilayered ME composites of the same material constituents and similar volume fractions have also been made. Magnetostriction measurements are done on individual magnetostrictive materials at varying temperatures in longitudinal and transverse directions. Measurement of the ME coefficient is done on all the prepared composites and their relative response at elevated temperatures is presented. Self-biased behavior of the ME composites resulting out of the applied prestress is also captured. A 2D hysteretic model including the temperature and prestress effects that can capture the behavior of epoxy-free ring composites has also been formulated. The results from the model are in agreement with the experimental results at all the temperatures. The obtained experimental results highlight the suitability of epoxy-free ring composites to be used in high temperature microdevices.

Electrical, magnetic, and direct and converse magnetoelectric properties of (1− x )Pb(Zr 0.52 Ti 0.48 )O 3 −( x )CoFe 2 O 4 (PZT–CFO) magnetoelectric composites

The structural, magnetic, ferroelectric, and magnetoelectric (ME) properties of lead-free ferroelectric phase (0.45)Ba0.7Ca0.3TiO3-(0.55)BaTi0.8Zr0.2O3 (BCZT) and rare earth modified Co-Mn ferrite phase Co0.7Mn0.3Fe1.95Dy0.05O4 (CMFDO) magnetoelectric (ME) composites are reported. X-ray diffraction confirms the presence of a crystal structure corresponding to both the ferroelectric and ferrite phases, which was further confirmed by Raman spectroscopic measurements. Scanning electron micrograph imaging along with the elemental mapping reveals the distribution of CMFDO grains in a BCZT matrix. The variation of dc resistivity with temperature indicates a semiconducting nature of the ME composite. The ME composite shows usual dielectric dispersion behavior with a higher dielectric constant value in the low frequency region compared to the individual ferroic phases, due to the space charge effects. Frequency dependent ac conductivity reveals that the conduction process in the ME composite is due to the small polaron hopping mechanism. Also, the variation of dielectric constant with temperature reveals the presence of two dielectric anomalies corresponding to ferroelectric phase transitions, i.e., from orthorhombic (O) to tetragonal (T) phases (∼298–323 K) and tetragonal (T) to cubic (C) phases (∼400 K). The ME composite exhibits both the ferroelectric [i.e., polarization (P) vs electric field (E)] and ferrimagnetic [i.e., magnetization (M) vs magnetic field (H)] hysteresis loops that confirm its multiferroic nature. The P-E hysteresis loop indicates the significant changes in remanent polarization (ΔPr ∼ 54%) after magnetic poling, confirming the presence of strong magnetoelectric coupling in the ME composite. Further, the strength of the ME coupling calculated was ∼54%, which is remarkable. Thus, the ME composite prepared in the present study may be a suitable candidate for applications in magnetic field sensors and multistate memory devices and may be suitable alternatives for single phase multiferroics.

Magnetoelectric (ME) composites have recently received extensive attention due to their much higher ME coefficients and relatively high operating temperatures compared to single-phase ME materials. However, the ME coefficients of ME composites depend on the external magnetic field, and high ME coefficients usually require the presence of a biased external DC magnetic field. In this work, we propose a hybrid magnetoactive elastomer, which is a rubber matrix embedded with both soft iron particles and hard NdFeB particles. It is found that such a hybrid MAE shows a nonzero piezomagnetic coefficient even as the applied magnetic field approaches zero. Based on this phenomenon, we further propose a soft ME material with a self-bias effect and experimentally demonstrate that the self-bias effect can be tailored by changing the residual magnetization of the hybrid MAE and the charge density of the electret layer. This work successfully demonstrates a new mechanism of the self-bias effect for magnetoelectric materials and introduces a new member to the family of ME materials.

Tremendous progress has been made in boosting the realization of magnetoelectric (ME) magnetometers based on the direct ME effect (DME) for bulk ME laminates. In this work, we studied the potential of an electrically driven bulk magnetic field sensor based on the converse ME effect (CME). Starting from a discussion about the dependence of the induced voltage from the pickup coil on coil parameters and the CME coupling process, we then experimentally measured the optimized bias field in the off resonance region and observed the double-peak phenomenon that occurred within the resonance window. More importantly, the optimization with respect to the sample's dimension, excitation voltage, and frequency was conducted to improve the sensing capability for low-frequency magnetic fields. It was experimentally found that a limit of detection (LoD) of ∼115 pT for a magnetic field of 10 Hz and ∼300 pT for a magnetic field of 1 Hz was achieved when exciting the ME laminate at 1 V without any bias field. In this case, the power consumption for the ME laminate is only 0.56 mW, which is much lower compared to tens of milliwatts (10–100 mW) for optically pumped or flux gate sensors (excluding the power consumption from the electronics) and also shows advantages over conventional ME magnetic field sensors based on DME with a current pump.

Piezoelectric and magnetoelectric behaviors of multifunctional cement-based laminated composites