Influence Of Structure On Magnetoelectric Effects Of Laminated Magnetoelectric Composites

The magnetoelectric effect includes the direct and the converse magnetoelectric effects.Compared with single phase magnetoelectric materials,the laminated magnetoelectric composites have larger magnetoelectric effect,so they have been extensively studied and applied.In this thesis,we fabricate some kinds of magnetoelectric composites by bonding or electroless deposition to investigate the effects of constituent and structure on magnetoelectric performance.The magnetoelectric effect of FeCo/Pb?Zr,Ti?O₃/Ni and Ni/Pb?Zr,Ti?O₃/FeCo trilayered long cylindrical composites prepared by electroless deposition is investigated.The mean diameter,height and sequence of Ni and FeCo layers of the trilayered long cylindrical composites have strong impacts on the magnetoelectric effect.Keeping the height fixed,the resonant frequency and the maximum magnetoelectric voltage coefficient decrease with the mean diameter of the cylinder increasing,while the optimal bias magnetic field remains approximately constant.When the diameter is fixed,the optimal bias magnetic field is also constant with the height increasing,while the maximum magnetoelectric voltage coefficient increases and the resonant frequency decreases.Meanwhile,the magnetoelectric voltage coefficients of the FeCo/Pb?Zr,Ti?O₃/Ni cylinder are enhanced and superior to those of the Ni/Pb?Zr,Ti?O₃/FeCo in both modes.FourmagnetoelectriccompositeswiththestructuresofNi-Terfenol-D-Ni/PZT,Terfenol-D-Ni-Terfenol-D/PZT,Ni/PZT and Terfenol-D/PZT have developed by bonding the negative magnetostrictive Ni and positive magnetostrictive Terfenol-D plates on the piezoelectric PZT plate.Compared with the other three composites,Ni-Terfenol-D-Ni/PZT has a larger magnetoelectric coefficient at low bias magnetic field and resonance frequency which is attributed to the fact that Ni can concentrate more flux and enhance its stress-interaction with the magnetostrictive Terfenol-D.Furthermore,the converse magnetoelectric effect of Ni-Terfenol-D-Ni/PZT and Terfenol-D/PZT laminate composite has also been investigated.Compared with the conventional Terfenol-D/PZT magnetoelectric composites,the Ni-Terfenol-D-Ni/PZT laminate composite with three remarkable resonance frequencies has a better converse magnetoelectric effect and its maximal CME coefficient can reach 6.2×10-⁷ s/m under the electric field frequency of 42 kHz and a bias magnetic field of 230Oe.It is useful for multifrequency operation and the low resonance frequency can bring an advantage for decreasing the eddy current loss of the magnetoelectric composites.