Chung Ming Leung

Importance of composite parameters in enhanced power conversion efficiency of Terfenol-D/PZT magnetoelectric gyrators

A gyrator that is capable of current-to-voltage conversion can be realized with a magnetoelectric (ME) composite of ferromagnetic and ferroelectric phases placed in a coil. Here, we report the dependence of the power conversion efficiency (PE) on the relative thickness of the two ferroic phases in a gyrator of Terfenol-D and PZT. Both experimental and theoretical results on PE as a function of composite parameters, such as thickness ratio of the ferroic layers (n), magnetic field bias (HBias) and several gyrator parameters, such as the resistance load (RL), were discussed. By decreasing the thickness ratio of Terfenol-D to composite (nu2009=u20090.28) in coil-ME gyrators, a high power efficiency of 73.9% was found at a fundamental resonance frequency of 72.5u2009kHz under a HBias of 1000u2009Oe and RLu2009=u20092.6u2009kΩ in experiments. At the same time, the non-linear mechanical loss was reduced by decreasing the value of n which resulted in a flat response over a wide HBias range. This improved power efficiency promises ME gyrato...

Power conversion efficiency and resistance tunability in coil-magnetoelectric gyrators

The power efficiency and resistance tunability of magnetoelectric (ME) gyrators consisting of two-phase magnetostrictive-piezoelectric ME longitudinal-transverse (L-T) mode sandwich laminates and coils, have been studied. The copper wire coil provided an inductance-based coil port (CoilP) and the piezoelectric layer of the ME laminate provided a capacitance-based ME port (MEP). The device behaved as a 2-port 4-wire ME gyrator. The current-to-voltage and voltage-to-current (I-V and V-I, respectively) conversion ratios, resistance-inductance/capacitance tunabilities (TR-L and TR-C, respectively) and direct/converse power efficiencies (PED and PEC, respectively) were measured. Maximum values of 1454u2009V/A and 0.468u2009mA/V for the I-V and V-I conversion ratios, 76u2009μH/Ω and 0.17u2009pF/Ω for TR-L and TR-C coefficients, and ∼35% for both PED and PEC were found by measuring the performance characteristics. Compared with the electromagnetic and piezoelectric transformers, ME gyrators have good input and output characteri...

Upper limit for power conversion in magnetoelectric gyrators

We characterized the magnetomechanical conversion abilities of Ni-Zn ferrite, cobalt ferrite, and Metglas by constructing a magnetic power path with two winding coils. We found that under high power drive, a portion of the mechanical power re-transformed to the magnetic form and was captured by the receiver coil, which resulted in a decrease in the magnetomechanical conversion ability of the coil-magnetostriction structure. This presents an upper limit of the power conversion characteristics of magnetoelectric gyrators. Furthermore, the efficiency of a Metglas/Pb(Zr,Ti)O3 gyrator was characterized by varying the values of the resistive load, magnetic bias, and power density. The maximum measured efficiency for the power transferred across an optimal resistor load was greater than 90% under low drive conditions and 89% with a power density of up to 30u2009W/in.3

Enhanced stability of magnetoelectric gyrators under high power conditions

In this study, three different coil-based magnetoelectric (ME) gyrators of different geometries, including gyrators with high power output, have been designed and characterized. These included two magnetostrictive/piezoelectric/magnetostrictive (M-P-M) and one piezoelectric/magnetostrictive/piezoelectric (P-M-P) type ME gyrators, which consisted of nickel zinc ferrite (NZFO) and lead zirconate titanate (PZT) ceramic plates. Compared with M-P-M ME gyrators, the P-M-P ones exhibited a higher power efficiency (η) of 85% when operated at resonance under an optimal magnetic bias field (HBias) of 40u2009Oe at low power conditions. It retained a relatively high efficiency of ηu2009=u200979% under a high input power density of 2.87u2009W/cm3. A low reduction in the magnetomechanical coupling and mechanical quality (k33,m and Qm) factors of the NZFO ferrite layer in the ME gyrator explains the resilience of the P-M-P type structure with increasing power drive. The findings open the possibility of using ME gyrators in high power a...

Highly efficient solid state magnetoelectric gyrators

An enhancement in the power-conversion-efficiency (η) of a magneto-electric (ME) gyrator has been found by the use of Mn-substituted nickel zinc ferrite. A trilayer gyrator of Mn-doped Ni0.8Zn0.2Fe2O3 and Pb(Zr,Ti)O3 has ηu2009=u200985% at low power conditions (∼20 mW/in3) and ηu2009≥u200980% at high power conditions (∼5u2009W/in3). It works close to fundamental electromechanical resonance in both direct and converse modes. The value of η is by far the highest reported so far, which is due to the high mechanical quality factor (Qm) of the magnetostrictive ferrite. Such highly efficient ME gyrators with a significant power density could become important elements in power electronics, potentially replacing electromagnetic and piezoelectric transformers.

Magnetoelectricity of CoFe 2 O 4 and tetragonal phase BiFeO 3 nanocomposites prepared by pulsed laser deposition

The coupling between the tetragonal phase (T-phase) of BiFeO3 (BFO) and CoFe2O4 (CFO) in magnetoelectric heterostructures has been studied. Bilayers of CFO and BFO were deposited on (001) LaAlO3 single crystal substrates by pulsed laser deposition. After 30u2009min of annealing, the CFO top layer exhibited a T-phase-like structure, developing a platform-like morphology with BFO. Magnetic hysteresis loops exhibited a strong thickness effect of the CFO layer on the coercive field, in particular along the out-of-plane direction. Magnetic force microscopy images revealed that the T-phase CFO platform contained multiple magnetic domains, which could be tuned by applying a tip bias. A combination of shape, strain, and exchange coupling effects are used to explain the observations.

Magnetoelectric gradiometer with enhanced vibration rejection efficiency under H-field modulation

A magnetoelectric (ME) gradiometer consisting of two Metglas/Pb(Zr,Ti)O3 fiber-based sensors has been developed. The equivalent magnetic noise of both sensors was first determined to be about 60 pT/√Hz while using an H-field modulation technique. The common mode rejection ratio of a gradiometer based on these two sensors was determined to be 74. The gradiometer response curve was then measured, which provided the dependence of the gradiometer output as a function of the source-gradiometer-normalized distance. Investigations in the presence of vibration noise revealed that a ME gradiometer consisting of two ME magnetometers working under H-field modulation was capable of significant vibration rejection. The results were compared to similar studies of ME gradiometers operated in a passive working mode. Our findings demonstrate that this active gradiometer has a good vibration rejection capability in the presence of both magnetic signals and vibration noise/interferences by using two magnetoelectric sensors ...

Power conversion process in magnetoelectric gyrators

We have investigated the power conversion and loss processes in magnetoelectric gyrators. Two types of loss mechanisms were identified by using a transformer-gyrator structure, which transfers power between magnetic and magnetomechanical forms. A missing portion of the power in a gyrator was then identified to be a returned power from the load resistor under low drive conditions. Under high drive conditions, decreases in both the magnetostriction and mechanical quality factor resulted in additional inefficiencies. Power transfer efficiencies of greater than 70% and 50% were achieved for magnetoelectric (ME) gyrators based on Metglas/Pb(Zr,Ti)O3 laminated composites under low power drive and high power density drive (60u2009W/in.3) conditions, respectively.

Stability enhancement of yttrium substituted nickel zinc ferrite/PZT magnetoelectric gyrators under high power conditions

The influence of yttrium (Y) ion substitution on the magneto-mechanical properties of nickel-zinc ferrite (Ni0.7Zn0.3YxFe2-xO4) or NZFO-Y and the power efficiency (η) of magnetoelectric (ME) gyrators consisting of NZFO-Y/Pb(Zr, Ti)O3 layers were studied. X-ray diffraction (XRD) of polycrystalline samples of NZFO-Y indicated that yttrium incorporated into the crystal lattice resulted in an enlargement of the lattice parameter. Also, the density and ionic hopping length were increased, and the porosity was decreased. Together, these resulted in significant changes in the magneto-mechanical coupling (k33,m) and mechanical quality (Qm) factors. It was found that k33,m decreased with the increasing Y content for 0u2009≤u2009xu2009≤u20090.08, whereas Qm was increased. For xu2009>u20090.05, the values of k33,m and Qm were found to be nearly stable with increasing input power density (PD-Ms) up to 47u2009W/in3. Under this high power driving condition for 20u2009min, we found that the power conversion stability of ME gyrators was increased with the increasing Y content in the ferrite and that a maximum power conversion efficiency occurred near 77%. These findings offer the potential for ferrite-based ME gyrator applications in power electronic conversion devices.The influence of yttrium (Y) ion substitution on the magneto-mechanical properties of nickel-zinc ferrite (Ni0.7Zn0.3YxFe2-xO4) or NZFO-Y and the power efficiency (η) of magnetoelectric (ME) gyrators consisting of NZFO-Y/Pb(Zr, Ti)O3 layers were studied. X-ray diffraction (XRD) of polycrystalline samples of NZFO-Y indicated that yttrium incorporated into the crystal lattice resulted in an enlargement of the lattice parameter. Also, the density and ionic hopping length were increased, and the porosity was decreased. Together, these resulted in significant changes in the magneto-mechanical coupling (k33,m) and mechanical quality (Qm) factors. It was found that k33,m decreased with the increasing Y content for 0u2009≤u2009xu2009≤u20090.08, whereas Qm was increased. For xu2009>u20090.05, the values of k33,m and Qm were found to be nearly stable with increasing input power density (PD-Ms) up to 47u2009W/in3. Under this high power driving condition for 20u2009min, we found that the power conversion stability of ME gyrators was increased with ...

Nanopillars with E-field accessible multi-state (N ≥ 4) magnetization having giant magnetization changes in self-assembled BiFeO 3 -CoFe 2 O 4 /Pb(Mg 1/3 Nb 2/3 )-38at%PbTiO 3 heterostructures

We have deposited self-assembled BiFeO3-CoFe2O4 (BFO-CFO) thin films on (100)-oriented SrRuO3-buffered Pb(Mg1/3Nb2/3)0.62Ti0.38O3 (PMN-38PT) single crystal substrates. These heterostructures were used for the study of real-time changes in the magnetization with applied DC electric field (EDC). With increasing EDC, a giant magnetization change was observed along the out-of-plane (easy) axis. The induced magnetization changes of the CFO nanopillars in the BFO/CFO layer were about ΔM/MrDCu2009=u200993% at EDCu2009=u2009−3u2009kv/cm. A giant converse magnetoelectric (CME) coefficient of 1.3u2009×u200910−7u2009s/m was estimated from the data. By changing EDC, we found multiple(Nu2009≥u20094) unique possible values of a stable magnetization with memory on the removal of the field.