Magnetoelectric Transducer Research Articles

Nonlinear modeling, design and parametric study of an effective harvester in large amplitude vibration using magnetoelectric transducer

Interest in vibration energy harvesting techniques in wireless sensors networks and small devices has been increased in the last decade. Among various types of energy harvesters, those that employ magnetoelectric transducers have attracted researchers in recent years. When these harvesters vibrate with large amplitudes, the frequency bandwidth is broadened because of nonlinear effects and the performance of harvesters is increased. Therefore, design, modeling and parametric study of the mentioned harvesters in large amplitude vibration are necessary. In this paper, the nonlinear finite element model of the magnetoelectric harvester with considering nonlinear magnetic force is developed. Obtained results in this paper are verified by comparing with available theoretical and experimental results in the literature. Furthermore, a magnetoelectric harvester that is effective in large deflections is designed. The proposed harvester includes one cantilever beam, four permanent magnets, two magnetic yokes, one added mass, and one magnetoelectric transducer. One of the specific features of the designed harvester is frequency-doubling which helps the harvester to generate more power. Finally, the effect of various parameters including the amplitude of excitation, load resistance, the thickness of the beam and added mass on frequency bandwidth, and output power of the harvester are evaluated.

Magnetoelectric wireless power transfer for biomedical implants: Effects of non-uniform magnetic field, alignment and orientation

This article presents experimental validation of a generalized equivalent two-port model for a magnetoelectric-based wireless power transfer system (WPTS) that utilizes a circular multi-turn coil as a transmitter, with a focus on potential application to biomedical implantable devices. The central objective of the work is to investigate the performance of the power delivered to a resistive load under uncertainties in magnetoelectric receiver position and orientation. In addition, the effects of a non-uniform applied magnetic field are considered. For the particular experimental system being studied, a maximum transferred power of 4.91 mW is obtained at a distance of 3 cm between the centers of the coil and the magnetoelectric (ME) transducer, in which the corresponding magnetic flux density is 225.8 μT. As the distance increases to 6 cm, the generated power drops to 1.97 mW. Furthermore, we find that the output power is proportional to the squared cosine of the misorientation angle, compared to the power achieved at the nominal (zero-angle) position. Meanwhile, as expected, the delivered power is less sensitive to misalignment since the width of the receiver is relatively small in comparison with the diameter of the transmit coil. In general, the power produced at the load is a quadratic function of the effective magnetic field that is projected onto the operating direction of the ME laminated composite (i.e., the longitudinal axis in this case). All findings are expected to provide a universal comprehensive picture of the dynamics and performance of the ME WPTS. The presented device concept could open an alternative pathway for powering implants.

A magnetically levitated magnetoelectric vibration generator using a Halbach array

This paper proposes a magnetoelectric (ME) vibration generator based on magnetic levitation. The generator uses a Halbach array and a magnet bar to constitute the suspending magnet structure of the magnetic levitation system. The Halbach array employs three NdFeB magnet rings with a particular magnetization pattern, which produces concentrated magnetic field on the outer side where the ME transducer array is placed. Consequently, the ME transducer array undergoes larger magnetic field variations and more vibration energy is converted into electrical energy. An analytical model is developed based on the solution of the kinetic equation and the equivalent circuit of the ME transducer array. Experiments have been conducted and the analytical model is validated by the experimental results. The generator produces a maximal power of 957.8μW with an optimal load resistance of 1.45MΩ at the acceleration of 0.6 g. The proposed device using a Halbach array exhibits a ∼2.5 times higher output power than that of the harvester employing a conventional suspending magnet bar.

Experimentally validated model and power optimization of a magnetoelectric wireless power transfer system in free-free configuration

This article presents a thorough analysis and an equivalent circuit model of a wireless power transfer system utilizing magnetoelectric (ME) effects. Based on two-port theory, explicit analytical solutions of, (i) the ME coefficient (defined by the derivative of the generated electric field with respect to the applied magnetic field), and (ii) the power transferred to a load resistance, are derived and rigorously validated by experiments. The compact closed-forms of the optimal load and its corresponding maximum output power are developed. In our particular experimental system, a power of ∼10 mW is attained at an applied magnetic flux density of 318.9 µT with a laminated composite made by two Galfenol and one PZT layers. While is widely used in the literature as a standard criterion to evaluate the performance of a ME transducer, we reveal that larger does not always ensure higher optimum power delivered to the load. Instead, we quantify the essential influences of each magnetostrictive and piezoelectric phases on the maximum obtainable power. We show that the transduction factor between the magnetic and mechanical domains is often more critical for power optimization than the mechanical-electrical transduction factor as it determines and limits the maximum power available for transfer to a resistive load.

Fundamental Issues in Magnetoelectric Transducers: Magnetic Field Sensing Versus Wireless Power Transfer Systems

This paper presents theoretical analysis on fundamental performances of two configurations of magnetoelectric transducers that are used the most in practice, longitudinal-longitudinal and longitudinal-transverse modes, with a focus on magnetic field sensing and wireless power transfer applications. Based on equivalent circuit models and two-port network theory, we derive explicit closed-form solutions for the magnetoelecitric voltage coefficient and the power delivered to a load. We reveal that although the former configuration exhibits some advantages of utilizing as a sensing system, there is no difference in the maximum output power obtained from the two methods. The question on how to reach the upper bound on transferred power is also discussed. The findings can be used as a generalized framework to design an optimal system, depending on desired applications.

Design study of a magnetoelectric-electromagnetic vibration energy converter for energy harvesting

The aim of this paper is to design a combination of a magnetoelectric-electromagnetic (ME-EM) vibration converter in order to reach an improved energy outcome. In this paper, the influence of magnets polarization and magnetoelectric transducer and coil direction are investigated. For this purpose, a finite element model is developed using one coil, one ME transducer in a magnetic circuit. Simulation results show that a better magnetic field distribution and variation is reached, if the magnetic circuit magnets are placed in attraction. Radial polarization shows decisive advantages in comparison with axial polarization. The placement of coil parallel to the magnetic circuit direction and the magnetization of the ME transducer along its width is the optimal direction relative to the magnetic circuit.

A magnetoelectric vibration converter with tunable resonance frequency / Magnetoelektrischer Vibrationswandler mit einstellbarer Resonanzfrequenz

Abstract Integration of smart materials to harvest energy from low vibration sources for powering wireless sensor networks has been of significant interest and still is. Owing to large magnetostriction and energy density of Terfenol- D, the use of piezoelectric/Terfenol-D composites exhibit great potential for the realization of vibration converters. In this work, a magnetoelectric vibration converter is dpresented. The interaction between the magnetic circuit and the magnetoelectric transducer is employed to tune the resonance frequency of the converter.

Magnetoelectric Transducer Designs for Use as Wireless Power Receivers in Wearable and Implantable Applications.

As the size of biomedical implants and wearable devices becomes smaller, the need for methods to deliver power at higher power densities is growing. The most common method to wirelessly deliver power, inductively coupled coils, suffers from poor power density for very small-sized receiving coils. An alternative strategy is to transmit power wirelessly to magnetoelectric (ME) or mechano-magnetoelectric (MME) receivers, which can operate efficiently at much smaller sizes for a given frequency. This work studies the effectiveness of ME and MME transducers as wireless power receivers for biomedical implants of very small (<2 mm3) size. The comparative study clearly demonstrates that under existing safety standards, the ME architecture is able to generate a significantly higher power density than the MME architecture. Analytical models for both types of transducers are developed and validated using centimeter scale devices. The Institute of Electrical and Electronics Engineers (IEEE) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) standards were applied to the lumped elements models which were then used to optimize device dimensions within a 2 mm3 volume. An optimized ME device can produce 21.3 mW/mm3 and 31.3 μW/mm3 under the IEEE and ICNIRP standards, respectively, which are extremely attractive for a wide range of biomedical implants and wearable devices.

Studies on mechanical loss in converse magnetoelectric effect under multi-physical field

By means of the technic for measuring resonant converse magnetoelectric (CME) effect, the mechanical loss of PZT/Terfenol-D/PZT tri-layer symmetric magnetoelectric laminated composites under multi-physical field loads such as bias magnetic field, driven voltage and ambient temperature is systematically measured in this paper. The experimental results show that the mechanical loss in CME effect increases initially with the increase of the bias magnetic field, and approaches to a broad maximum value at 250–500 Oe. Further increasing bias magnetic field leads to the decrease of mechanical loss. The mechanical loss increases rapidly with the increase of driven voltage amplitude, especially in the medium magnitude of the bias magnetic field. While, there is little influence of voltage on the mechanical loss under the higher bias magnetic fields. Importantly, the mechanical loss increases monotonically as the increase of ambient temperature. The research results of the mechanical loss under multi-physics fields in this paper can provide a basic principle of CME improvement by reducing the mechanical loss. Therefore, this research is quite significant to the CME based applications, such as, magnetoelectric transducers, magnetoelectric microwave devices, multiferroic antennas and so on.

Magneto-Electric Hybrid Generator for Simultaneously Harvesting Vibration and Stray Magnetic Field Energy

An array-based magneto-electric hybrid generator is presented which can respond to vibration and stray magnetic fields. Using the magnetic levitation mechanism, the generator can extract vibration energy in three axes, and the use of a magneto-electric array improves the output power. The nonlinear magnetic force on the suspending magnets is analyzed during vibration, and a nonlinear dynamical equation is established. A law for the time-varying displacement of the suspending magnets is obtained after solving the dynamical equation. The magnetic field on the magneto-electric transducer array under dual excitations is analyzed, and a theoretical model is developed. A prototype is fabricated to conduct the energy-harvesting experiments. The results demonstrate the feasibility of the generator under dual excitations.

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.

Experimental study of magnetoelectric transducers for power supply of small biomedical devices

This paper presents experiment results of an energy transducer based on the magnetoelectric composites. Various configurations of the layered structure composed of the Terfenol-D or/and the Metglas with the PZT-5H have been investigated. The impact of Metglas on the performance of the transducer is outlined. The high output voltage coefficient and the significant deliverable power of the combination Terfenol-D/Metglas/PZT-5H makes it as an ideal energy transducer candidate for wireless powering of embedded device in biomedical applications.

Flexible magnetoelectric transducer with high magnetic field sensitivity based on Metglas/poly(vinylidene fluoride) heterostructures

In this paper, the flexible magnetoelectric (ME) transducer consisting of FeSiB (Metglas)/poly(vinylidene fluoride) (PVDF) is presented, whose ME coupling characteristics and ME sensing performance under different bend status have been investigated. It is found that an appropriate size of transducers is propitious to the ME coupling characteristics due to the demagnetization effect. In addition, with increase the bending angle (θ) of transducers from 0° to 50°, the magnetoelectric voltage coefficient (MEVC) shows a reduction from 240.42 to 26.44 V/cm·Oe and 13.1 to 2.11 V/cm·Oe, at the resonance and low-frequency (1 kHz), respectively. Meanwhile, the induced ME voltage have an excellent linear relationship to ac magnetic field. An ultrahigh magnetic field sensitivity of 1.22 V/Oe and 0.11 V/Oe have been found under θ = 0° and 50°, respectively, which are positively comparable to the highest reported in the most recent polymer-based ME transducers. Moreover, the transducers can maintain the MEVC stable after an additionally bending cycles up to 1000 times, indicating the full flexibility and high stability of the mentioned transducers. Obviously, it demonstrates that the proposed FeSiB/PVDF transducers have great potential of being applied to wearable devices.

Strain coupling optimization in magnetoelectric transducers

The mechanical behavior of magnetoelectric transducers consisting of piezoelectric-magnetostrictive bilayers has been modeled. The effect of the aspect ratio of the transducer as well as the influence of non-active surrounding layers has been modeled, including a passivation layer surrounding the active device, a clamping layer above the active device, and an interfacial layer that might be inserted between the magnetostrictive and the piezoelectric layers. Strategies to control and maximize the strain magnitude and orientation based on material selection and device design are proposed.

Investigation on magnetoelectric behavior of (80Bi0.5Na0.5TiO3-20Bi0.5K0.5TiO3)-CoFe2O4 particulate composites

Particulate magnetoelectric (ME) ceramics constituted by (1-x)(80Bi0.5Na0.5TiO3-20Bi0.5K0.5TiO3)-xCoFe2O4 [(1-x)BNKT-xCFO] (x=0, 0.1, 0.2, 0.3, 0.4 and 1.0) were synthesized by an powder-in-sol precursor hybrid processing method and their structure, magnetic, ferroelectric, magnetodielectric (MD) and ME properties have been investigated. Results showed that the ceramics consisted of only two chemically separated phases and had homogeneous microstructure. The introduction of CFO into BNKT matrix led to the weakening of ferroelectric and dielectric properties whereas the strengthening magnetic and MD properties. The observation of the MD effect revealed the evidence of the strain-induced ME coupling and the MD value is well scaled with M2. A maximum value of ME output of 25.07mV/cm·Oe was achieved for the 0.7BNKT-0.3CFO composite. The improved ME response together with the linear MD effect makes the ceramics promise for use in magnetic field controllable devices or magneto-electric transducers.

Temperature and frequency dependence of the dielectric and piezoelectric response of P(VDF–TrFE)/CoFe2O4 magnetoelectric composites

CoFe2O4 nanoparticles embedded in polyvinylidene fluoride–trifluoroethylene (P(VDF–TrFE)) matrix show suit­able properties for practical applications as piezoelectric and magnetoelectric transducers. The knowledge about the dielectric and electromechanical responses of the multiferroic films in a broad frequency and temperature range is essential for applicability. The purpose of this work is to investigate the dielectric, ferroelectric and piezoelectric properties of multiferroic composites based on P(VDF–TrFE) as a host matrix and CoFe2O4 as a magnetic filler. Free-standing films with a different concentration of the filler were investigated. The polarization switching was demonstrated for all the compositions. The polarization displacement hysteresis was achieved at different temperatures. The piezoelectric coefficient d33 is not affected by different concentration of ferrite. On the other hand, the composition with the largest weight % of CoFe2O4 shows higher coercive fields which is not favourable for applications. This indicates that the optimal content of the filler must be determined and taken into account when optimizing both ferroelectric and magnetoelectric properties.

Magnetic field sensors based on the foil of amorphous cobalt alloy and NiMnGa martensite single-crystals

The problem of creation of small size wideband sensitive sensors of magnetic field with a narrow directional diagram and a small coefficient of thermal drift is actual and requires searching for new magnetic materials. We present the results of the development of the flux-gate sensors with the 20μm magnetic core of amorphous foils of ММ-3Со and ММ-5Со cobalt alloys and magnetoelectric transducers with magnetic field sensitive element of NiMnGa martensite single-crystal. The peculiarities of our sensors are the usage of the parametric amplification and related to it the strong nonlinearity of the dependences of magnetic permeability of amorphous foil and NiMnGa single-crystal magnetostriction on the magnetic field amplitude.

A Three-Dimensional Magneto-Electric Vibration Energy Harvester Based on Magnetic Levitation

A three-dimensional vibration energy harvester employing a magneto-electric (ME) transducer was developed for wireless sensor networks. It uses a magnetic levitation unit to convert ambient vibration in arbitrary directions into the motion of a central suspended magnet. The ME transducer generates output power in response to magnetic field variations. Experiments verify the feasibility of the device. For a vertical acceleration of 0.8 g, the harvester has a bandwidth of 1.9 Hz and a maximum power of 514.5 μW. The average output power varies with the angle between the acceleration and the horizontal plane. The average output power varies from 386.1 to 495.4 μW when the exciting angle increases from 30° to 60°.

A Novel Magnetic Energy Harvester Using Spinning Magnetoelectric Transducer

Over recent years, there has been a growing interest in the held of energy harvesters and their applications across a wide range of areas. In the context of harvesting ambient stray magnetic energy, a magnetoelectric (ME) transducer based on piezoelectric transduction has attracted most scientihc attention. Though the ME transducers based on the electromagnetic (EM) induction mechanism promises are highly efhcient and much more easier to be integrated, research on this specihc type of ME transducer has been scarcely reported. This paper presents the design, fabrication, and experimental results of a novel EM energy harvester. Unlike other EM harvesters that linearly vibrate, the proposed one operates in a rotatory mode, making use of a specially designed magnet array to convert the horizontal ac magnetic held into a vertical spinning magnetic held, as well as the printing coils to scavenge energy from the rotatory magnetic held. In this paper, the influence of the load, the applied magnetic held, and the magnet's spatial arrangement are studied analytically, and the experimental results obtained by our fabricated prototype are consistent with the simulation results. The fabricated harvester prototype is able to generate 23.1 μW under a 2 Oe magnetic held at a resonant frequency of 10 Hz, corresponding to a power density of 14.2 μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Simulation and experimental results show that miniaturizing the harvester (i.e., reducing both the volume of magnet array and the area of printing coils) as well as increasing the coil turns can bring about a higher resonant frequency and a higher power density, which makes the micro-machined EM harvester a better ht for the ubiquitous 60 Hz ambient magnetic energy.

A Non-Resonant Magnetoelectric Energy Converter for Scavenging Magnetic Field Energy From Two-Wire Power Cords

A non-resonant magnetoelectric (ME) energy converter is presented for scavenging power-frequency magnetic field energy from two-wire power cords. The device is composed of a Terfenol-D/Pb(Mg1/3Nb2/3)O3-PbTiO3(PMNT)/Terfenol-D ME transducer, a NdFeB manget, and E-shaped magnetic yokes. The ME transducer, the magnet, and the magnetic yokes constitute a magnetic circuit, and the bias magnetic field of the ME transducer can be tuned by adjusting the contact area between the magnet and the magnetic yokes to obtain optimal power output. Meanwhile, the power-frequency magnetic field of the power cord is concentrated to the ME transducer by the magnetic yokes, which can potentially improve the power output of the device. Experiments were undertaken to evaluate the potential of energy scavenging from nearby power cords. When coupled to an appliance power cord carrying a current of 16 A, the device generated a rms voltage of 2.46 V and a maximum power of $6.05 \times 10^{\mathrm {-6}}$ W with a matching load resistance of $\sim 1~\text{M}\Omega $ . At a duration of 205 ms, the device can supply power for a temperature-humidity wireless sensor through an up-conversion management circuit with the power consumption of 90 mW at transmitting and 18 mW at receiving.