Magnetoelectric Laminate Composites Research Articles

Thin Film Magnetoelectric Sensors Toward Biomagnetism: Materials, Devices, and Applications

AbstractSince the discovery of strong magnetoelectric (ME) coupling in two‐phase ME laminate composites, strain mediated ME heterostructures have found practical applications in magnetic sensors, tunable inductors, tunable filters, miniaturized antennas, magnetic memories, and nanoscale motors. Thin film ME sensors, in particular, have become promising candidates in biomagnetic sensing, due to their high sensitivity, CMOS compatibility, room temperature operation, and high spatial resolution. In this article, an overview is presented on different types of thin film ME sensors and their applications in biomagnetic measurement. First, the coupling structures, materials selection, and fabrication processes are introduced. Three different mechanisms of recently emerged ME sensors, including the magnetic modulation, electrical modulation, and delta‐E effect are presented. Their performance and noise analysis are also compared and discussed. Finally, real‐time applications of ME sensors in the detection of magnetic fields from different part of human body are presented and discussed. The review concludes with an outlook on future perspectives and challenges of thin film ME sensors for biomagnetic applications.

Smart hybrid sensor for magnetic field and vibration detection based on PMN-PT/Terfenol-D magnetoelectric composites and suspended magnetic vibrator

A smart hybrid sensor for magnetic field and vibration detection is presented. We propose a novel structure of the hybrid sensor consisting of two longitudinally magnetized and thickness polarized mode (L–T mode) Terfenol-D alloy 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystal (PMN–PT) magnetoelectric laminate composites and a suspended magnetic vibrator which can convert external vibration to internal alternating magnetic field. The hybrid sensor exhibits a giant vibration responsivity of 12 V/g at 400 Hz and a useful magnetic field responsivity of 6 mV/μT at 23 Hz. The detection limit for AC acceleration and magnetic field is as low as 8.16 ng/Hz1/2 at 400 Hz and 16.4 pT/Hz1/2 at 23 Hz, respectively. The sensor output shows linear response with low distortion both to AC acceleration and magnetic field. In the end, the sensor's capability for detection of magnetic and non-magnetic moving target has been proven to be useful in intelligent transportation by an outdoor (open) test.

Polymer conformation-dependent piezoelectric properties and self-bias magnetoelectric responses in adhesive-free laminate composites of Ni-foam/PVDF/Ni-foam

In the past decade, polymer-based magnetoelectric (ME) laminate composites have been developed for feasible applications such as flexible energy harvesters and wearable sensors. The 2-2-type ME laminate composites have been typically prepared by epoxy adhesion of piezoelectric and magnetostrictive layers, which is a drawback that disrupts strain transfer from the magnetostrictive phase to the piezoelectric phase due to its strong hardness after epoxy curing. In this study, to overcome the disadvantage of insufficient strain transfer due to the adhesive layers, we designed adhesive-free laminate composites consisting of porous magnetostrictive nickel foam (NF) and soft poly (vinylidene fluoride) (PVDF) films, which exhibited good physical coupling via the sandwich hot-pressing of NF/PVDF/NF. In addition, the self-bias ME effect could be expected from NF, since it exhibits butterfly-shaped magnetostrictive hysteresis loops. Therefore, NF/annealed PVDF(AP)/NF and NF/hot-pressed PVDF(HP)/NF were prepared for investigating the polymer conformation during the fabrication process of ME laminates. Polymer conformation-dependent piezoelectric properties were investigated after annealing and hot-pressing, respectively. The NF/AP/NF laminates (mM/mP = 0.88) were found to exhibit a β/α phase ratio of 2.07, degree of crystallinity (χc) of 46.5%, piezoelectric charge constant (d33) of 17.7 pC/N, and self-bias ME response of 1.88 mV/cm Oe (94% of the maximal ME response at Hbias = 20 Oe). The NF/HP/NF laminates (mM/mP = 1.26) were found to exhibit a β/α phase ratio of 1.40, χc of 32.2%, d33 of 12.4 pC/N, and self-bias ME response of 2.27 mV/cm Oe (92% of the maximal ME response at Hbias = 10 Oe). The high β/α phase ratio were carried out sufficient stretching effect during hot-press laminating process. The optimal piezoelectric properties of β/α phase ratio and χc were induced by predominant stretching of PVDF chains rather than recrystallization during the hot-press. Further, reliable self-bias ME responses were obtained in the adhesive-free laminate composites by enhancement of coupling effect between magnetostrictive and piezoelectric phases. As a result, the sandwich laminate composites of NF/PVDF/NF were successfully prepared via hot-pressing and reliable ME responses were obtained without requiring the electroding process. This demonstrates the feasibility of ME laminate composites for use in wearable energy harvesters or sensors through removal of the hard adhesive layer.

Reducing the equivalent magnetic noise of Metglas/Mn-PMNT laminate composites via annealing treatment

The variation of dielectric loss in [1 1 0] -oriented Mn-doped 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (Mn-PMNT) single crystals after different annealing treatments, as well as their influence on equivalent magnetic noise (EMN) for magnetoelectric laminate composites, were investigated in this study. Dielectric loss can be reduced significantly in oxygen-sufficient atmosphere and high annealing temperature, and dielectric constant varies little in this annealing process, which is favorable to the decrease of the dielectric loss noise. The temperature dependence of dc conductivity was used to characterize the change of dc conductivity and activation energy, which indicated that oxygen vacancies in Mn-PMNT single crystals can be reduced by the annealing treatment, leading to the decrease of dielectric loss. For the influence of magnetoelectric laminate composites, the EMN is clearly reduced in low frequency range (10 < f < 100 Hz) after annealing treatment, which is in good agreement with the simulation results.

A passive isolator realized by magnetoelectric laminate composites

This work demonstrates a passive isolator realized by magnetoelectric laminate composites. The proposed isolator consists of a magnetoelectric gyrator, two impedance matching networks, and a load impedance. The equivalent circuit model of the isolator is developed. Good agreement has been obtained between the measured and computed results based on the proposed equivalent circuit model. The measured forward insertion loss and reverse isolation of the proposed isolator are 4.7 dB and 19 dB, respectively. A figure-of-merit which determines the performance of the isolator is proposed, which can be used to guide the design of such isolators.

Comprehensive investigation on direct and converse magnetoelectric effects in longitudinally magnetized and polarized laminate composites by equivalent circuit and experiments

Asymmetrical equivalent circuits, making φmH as magnetic part for the direct magnetoelectric (DME) effect of magnetoelectric laminate composites of longitudinally magnetized and poled (L–L) mode, have been reported recently. In this paper, we developed a symmetrical magnetic–mechanical–electric equivalent circuit to study both the DME and converse magnetoelectric (CME) effects equivalently, predicting the DME and CME coefficients near the resonance frequency. The theoretical values are in good agreement with the corresponding experiments. The L–L mode laminate composites have higher DME voltage coefficient and CME coefficient in comparison with the longitudinally magnetized and transversely poled (L–T) mode. In particular, its voltage coefficient is almost ten times as large as that of the L–T mode composite. The results are significant for the fabrication of magnetoelectric transducer, energy capture device, electronically controlled magnetometers and magnetic field sensors.

Giant zero-biased flexible magnetoelectric laminate composites for wearable magnetic sensor

Flexible magnetoelectric (ME) laminate composites consist of polyvinylidene fluoride (PVDF) and nanocrystalline alloy (FeCuNbSiB) were prepared. The ME coupling properties under different bending angle (θ) at zero dc bias magnetic field (Hdc) were investigated. The experimental results demonstrate the optimum zero-biased resonant ME voltage coefficient (MEVC) of ME laminate composites can reach 17.65 V/(cm·Oe). This is mainly due to the large permeability and low saturation magnetostrictive coefficient of the nanocrystalline alloy. The induced zero-biased ME voltages of ME laminate composites show an excellent linear relationship to ac magnetic field at bending states over a wide range. This laminate composite shows promising applications for high-sensitivity and small-size wearable magnetic sensors without bias.

Magnetoelectric laminate composites: an overview of methods for improving the DC and low-frequency response

Magnetoelectric (ME) composite materials have a stronger ME coupling effect in resonant states than in non-resonant states. Typically, these resonant states appear at frequencies of several tens of kHz or even MHz. However, for DC and low-frequency applications of ME composites, obtaining a high ME response is critical. In recent years, many studies have attempted to improve the DC and low-frequency ME performance of ME composite materials at frequencies below 1 kHz. This article reviews the research and major progress in this field and investigates the application of other methods.

Packaged angle-sensing device with magnetoelectric laminate composite and magnetic circuit

A packaged angle sensor consisting of four PZT/FeGa/PZT magnetoelectric (ME) laminate composites, four magnetic accumulation arcs, a magnetic accumulation (MA) ring, a multi-polar magnetic ring (MPMR), a shaft, and necessary shells is fabricated and characterized. The ME laminate composite with a slim shape is placed between the MA arc and the MA ring. The MPMR fixed on the shaft is used to apply a magnetic field associated with angle information to the ME laminate composites. Under the role the MA parts, the magnetic field applied to the ME laminate composites can be enhanced about 7 times. With the increasing of the rotational speed, the frequency of the sensor’s output signal is increased linearity, which can be used to measure the rotational speed. The amplitude of the output signal is increased as well and finally reached a stable value of 45.3 Vpp. In order to realize static test without the participation of an excitation coil, one of the ME laminate composites has been used as a piezoelectric transformer. In experimental, a resolution of 0.2° and a favorable stability with a standard deviation in population of ∼40 μVpp are achieved from this sensor. These characteristics show that the packaged sensor can be successfully used in rotational parameters testing and has the potential to establish self-powered wireless angle-sensing devices.

Theoretical modeling and experimental study of dielectric loss of the multi-push-pull mode magnetoelectric laminate composites

In this work, we establish a dielectric loss model for multi-push-pull mode ME laminate composites. It deduces that the total dielectric loss of the ME composites equals the linear average of the dielectric loss of piezoelectric plate and epoxy resin. But further analysis of this model has indicated that we can ignore the dielectric loss of epoxy resin. To verify this model, we use three kinds of epoxy resin with different dielectric loss to fabricate multi-push-pull mode PMNT/Metglas ME laminate composites respectively. It turns out that the different kinds of epoxy resin have little influence on the total dielectric loss, capacitance and piezoelectricity of the composites, which demonstrates that our model conforms to the practical case. Therefore, we can pay more attention to the mechanical properties of epoxy resin rather than its dielectric loss on fabricating the ME laminate composites.

Equivalent circuit model for plate-type magnetoelectric laminate composite considering an interface coupling factor

We describe the modeling of magnetoelectric (ME) effect in the plate-type Terfenol-D/PZT laminate composite by introducing a newly proposed interface coupling factor into the equivalent circuit model, aiming at providing a guidance for designing, fabricating and using the ME laminate composite based devices, such as current sensor, magnetic sensor, energy harvester, and wireless energy transfer system. Considering that the strains of the magnetostrictive and piezoelectric layers are not equal in actual operation due to the epoxy resin adhesive bonding condition, the equivalent circuit models of magnetostrictive and piezoelectric layers are created based on the constitutive equation and the equation of motion, respectively. An interface coupling factor kc is introduced which physically reflects the strain transfer condition between the magnetostrictive and piezoelectric phases. Specifically, the respective equivalent circuit models of magnetostrictive and piezoelectric layers are combined with an ideal transformer whose turn-ratio is just the interface coupling factor. Furthermore, the theoretical expressions containing kc for the longitudinal ME voltage coefficient v and the optimum thickness ratio noptim to which the maximum ME voltage coefficient corresponds are derived from the modified equivalent circuit model of ME laminate, where the interface coupling factor acts as an ideal transformer. To explore the influence of mechanical load on the interface coupling factor kc, two sets of weights, i.e., 100 g and 500 g, are placed on the top of the ME laminates, each with the same thickness ratio n in the sample fabrication for comparison. A total of 12 L-T mode plate-type ME laminate samples with different-thickness configurations are fabricated. The interface coupling factors determined from the measured v and the DC bias magnetic field Hbias are 0.15 for 500 g pre-mechanical load and 0.10 for 100 g pre-mechanical load, respectively. Furthermore, the measured optimum thickness ratios are 0.57 for kc=0.15 and 0.50 for kc=0.10, respectively. Both the measured ME voltage coefficient v and optimum thickness ratio containing kc agree well with the corresponding theoretical predictions. The relationship between the optimum thickness ratios under two different mechanical loads remains unchanged, i.e., the measured optimum thickness ratio for kc=0.15 is larger than for kc=0.10. The experimental results verify the reasonability and correctness of the introduction of kc in the modified equivalent circuit model. The possible reasons for different interface coupling factors under different loads are also qualitatively discussed in this paper.

Investigation of magnetoelectric multilayer laminate composites with series and parallel electrical connections

AbstractThis paper investigates the performance of magnetoelectric composites composed of multilayer magnetostrictive and piezoelectric laminates in which the series and parallel electrical connections are applied. The multiphysics simulations have been performed according to the different longitudinal and transversal magnetization and polarization modes using a numerical model based on the finite element method and an analytical formulation based on the equivalent circuit model. The obtained results highlight the limitation of the analytical formulation to model the multilayer composites when an alternative opposing polarization between each neighboring piezoelectric layer is applied.

Large resonance magnetoelectric response in Ni(Terfenol-d)/Pb(Zr,Ti)O3 bilayer laminate composites

In this work we report magnetoelectric laminate composites made up of negative magnetostrictive Ni plates, positive magnetostrictive Tb0.3Dy0.7Fe2 (Terfenol-d) plates and piezoelectric Pb(Zr,Ti)O3 (PZT) plates, in which negative and positive magnetostrictive plates are bonded on the piezoelectric plate and conjugate longitudinally with various orders. Both Ni-Terfenol-d-Ni/PZT and Terfenol-d-Ni-Terfenol-d/PZT composites are constructed and compared with Ni/PZT and Terfenol-d/PZT composites. The bias magnetic field and the frequency dependences of the magnetoelectric coefficient suggest that Ni-Terfenol-d-Ni/PZT is an optimal configuration with excellent magnetoelectric effects such as a large magnetoelectric coefficient at a low bias magnetic field and a low resonance frequency at which the maximum ME voltage coefficient appears. Besides, compared with most of other bulk composites configuration with Terfenol-d plates, the Ni-Terfenol-d-Ni/PZT composite reduces the Terfenol-d usage. We believe that the Ni-Terfenol-d-Ni/PZT composite is useful for the application due to its simple configuration and large resonance magnetoelectric response at a low frequency.

Cellulose-based magnetoelectric composites

Since the first magnetoelectric polymer composites were fabricated more than a decade ago, there has been a reluctance to use piezoelectric polymers other than poly(vinylidene fluoride) and its copolymers due to their well-defined piezoelectric mechanism and high piezoelectric coefficients that lead to superior magnetoelectric coefficients of >1 V cm−1 Oe−1. This is the current situation despite the potential for other piezoelectric polymers, such as natural biopolymers, to bring unique, added-value properties and functions to magnetoelectric composite devices. Here we demonstrate a cellulose-based magnetoelectric laminate composite that produces considerable magnetoelectric coefficients of ≈1.5 V cm−1 Oe−1, comprising a Fano resonance that is ubiquitous in the field of physics, such as photonics, though never experimentally observed in magnetoelectric composites. The work successfully demonstrates the concept of exploring new advances in using biopolymers in magnetoelectric composites, particularly cellulose, which is increasingly employed as a renewable, low-cost, easily processable and degradable material.

Equivalent Circuit Model of Low-Frequency Magnetoelectric Effect in Disk-Type Terfenol-D/PZT Laminate Composites Considering a New Interface Coupling Factor.

This paper describes the modeling of magnetoelectric (ME) effects for disk-type Terfenol-D (Tb0.3Dy0.7Fe1.92)/PZT (Pb(Zr,Ti)O3) laminate composite at low frequency by combining the advantages of the static elastic model and the equivalent circuit model, aiming at providing a guidance for the design and fabrication of the sensors based on magnetoelectric laminate composite. Considering that the strains of the magnetostrictive and piezoelectric layers are not equal in actual operating due to the epoxy resin adhesive bonding condition, the magnetostrictive and piezoelectric layers were first modeled through the equation of motion separately, and then coupled together with a new interface coupling factor kc, which physically reflects the strain transfer between the phases. Furthermore, a theoretical expression containing kc for the transverse ME voltage coefficient αv and the optimum thickness ratio noptim to which the maximum ME voltage coefficient corresponds were derived from the modified equivalent circuit of ME laminate, where the interface coupling factor acted as an ideal transformer. To explore the influence of mechanical load on the interface coupling factor kc, two sets of weights, i.e., 100 g and 500 g, were placed on the top of the ME laminates with the same thickness ratio n in the sample fabrication. A total of 22 T-T mode disk-type ME laminate samples with different configurations were fabricated. The interface coupling factors determined from the measured αv and the DC bias magnetic field Hbias were 0.11 for 500 g pre-mechanical load and 0.08 for 100 g pre-mechanical load. Furthermore, the measured optimum thickness ratios were 0.61 for kc = 0.11 and 0.56 for kc = 0.08. Both the theoretical ME voltage coefficient αv and optimum thickness ratio noptim containing kc agreed well with the measured data, verifying the reasonability and correctness for the introduction of kc in the modified equivalent circuit model.

Origin of Large Phase Shift and Magnetoelectric Resonance in Magnetoelectric Laminate Composite

Magnetoelectric composites enjoy large magnetoelectric transfer efficiency at resonance frequency, accompanying a large phase shift. We prepared two magnetoelectric laminate composites to research the origin of large phase shift and magnetoelectric characteristics by electric-field-induced strain and magnetic-field-induced strain. The piezoelectric part plays a dominant role in both the direct and converse magnetoelectric resonances. The electromechanical resonance inspires direct and converse magnetoelectric resonant peaks, and results in the magnetoelectric phase shift of near $\pi $ around the resonance frequency. However, the magnetostrictive part is difficult to inspire the magnetoelectric resonance and phase shift.

Equivalent magnetic noise reduction at high frequency range due to polarized direction optimization in Terfenol-D/Pb(Mg1/3Nb2/3)O3-PbTiO3 magnetoelectric laminate sensors

In this paper, we investigate the responsivities and output voltage noise power spectral densities of magnetoelectric (ME) laminate sensors, consisting of length magnetized Terfenol-D alloys and transverse/width poled Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMNT) crystals (i.e. L-T mode and L-W mode respectively), which are directly integrated with custom-build low noise charge amplifier circuits. Both the theoretical analyses and experimental results prove that the L-W mode sensor with the optimized polarized direction of the PMNT plate possesses lower magnetic detection limit at the interested high frequency range of 10kHz≤f≤50kHz. The equivalent magnetic noise (EMN) of the L-W mode sensor is 0.78pT/Hz1/2 at 30kHz, which is about 1.7 times lower than the 1.35pT/Hz1/2 for conventional L-T mode sensor. Furthermore, an effective method of using operational amplifiers with low equivalent input noise voltage and employing ME laminate composites with high voltage coefficient to reduce the EMNs of the ME laminate sensors at high frequency range has been established.

Multiphysics Modeling of Thin-Layer Magnetoelectric Laminate Composites Using Shell Element

This paper proposes to use the nodal shell element in a finite-element multiphysics formulation to simulate the magnetoelectric (ME) laminate composites constituted of the thin magnetostrictive layers. The multiphysics model considers the nonlinearity of the thin-layer magnetostrictive material as well as the electrical load effects of the ME laminate composites. A trilayer ME Metglas/PZT/Metglas problem is solved in order to prove the efficiency of the proposed method. This paper provides the basis to study the ME devices composed of laminated thin layers.

Macro fiber composite-based low frequency vibration energy harvester

In this paper, we present a vibration energy harvester using a spherical permanent magnet as springless proof mass and a magnetoelectric laminate structure composed of MSMA (magnetic shape memory alloy) and MFC (macro fiber composite) in d31 or d33 operational modes. Combination of transduction mechanisms, including magnetoelectric effect and impact-induced vibration of the magnetoelectric laminate composite, generates power from low frequency excitation such as human-body-induced motion. Two different types of magnetoelectric laminate composite based power generators have been fabricated, tested and compared. Moreover, the contributions of individual transduction mechanisms have been analyzed experimentally. Maximum peak-to-peak open circuit voltage of 16.4V has been obtained in response to a 3g vibration at 15Hz for device with d33 mode MFC. Device with d31 mode MFC generated maximum output power of 11.2μW in vibration exciter test and 82.5μW in manual vibration test across an 800Ω load. Based on the experimental observations, an impact-based harvester with d31 mode MFC has been proposed, which generated improved output power of 245.6μW.

Charge, voltage, and work-conversion formulas for magnetoelectric laminated composites

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.