| Since single-phase materials have weak magnetoelectric(ME)coupling at room temperature,the ME composites consisting of magnetostrictive and piezoelectric phases become the main research object of ME device design and preparation.The main factors affecting the ME effect of composites are properties of constituents,interfacial mechanical coupling and the way of combination.In order to improve the ME effect of composites,strong ME effect was observed in the disk-ring and cylindrical structures due to interfacial coupling through normal stress instead of shear stresses.On the other hand,magnetostrictive effect has not made much progress since the observation of giant magnetostrictive effect in rare-earth ferromagnetic alloys in 1950s,making the ME effect relied on magnetostrictive effect difficult to get much improvement.Moreover,the properties of the interfacial coupling in the composites hasn't been solved effectively,which stimulates people to look for some new methods to improve ME effect,such as using magnetic force to drive piezoelectric plate.Based on the two methods mentioned above,this paper will research enhanced ME effect in composites theoretically and experimentally,with the main contents as following:1?With the governing equations of materials,based on elastodynamics equations of continuum media and combined with the boundary conditions,the expressions of the ME coefficients were presented for magnetostrictive-piezoelectric disk-ring/cylindrical composite structure with the PE ring polarized radially.Then the theoretical model was applied for Ni/PZT/Ni cylindrical and Terfenol-D/Pb(Zr,Ti)O3 disk-ring heterostructures to research geometric dimension dependence of low frequency ME coefficients,resonant frequency,resonant ME coefficients,which has good agreement with the experimental results.2?Based on the different vibration modes of the PZT strip such as stretch mode and bending mode,several ME devices with different structures were prepared using Mn-Zn-ferrite/PZT composite,where the ME effect arose from piezoelectric effects driven by magnetic force between ferromagnets.Experiments show that the ME effects in these devices are much stronger than that observed from the samples relied on magnetostrictive effect.Furthermore,ME voltage coefficient as high as 7 Vcm-1Oe-1 with zero bias magnetic field was observed in the device with cantilever structure.In addition,the influence of different structures on ME effect,optimum bias field,resonant frequency and other parameters were compared,and the influence of ferrite permeability on the magnetoelectric effect was also studied.3?Compared with single cantilever,bi-cantilever can keep horizontality more enduringly and work more stably due to its both-ends-f.ixed structure.In addition,the bi-cantilever structure is advantageous for integrationTherefore,bi-cantilever structure can be regarded as an improvement of single cantilever structure.The resonance frequency in Mn-Zn-Ferrite/PZT bi-cantilever composite is higher than that in single cantilever with similar size.The ME voltage coefficient in bi-cantilever is still high enough though it was a little lower than that in single cantilever.When the magnetic gap is relatively big,the ME voltage coefficient can achieve 6.2 Vcm-1Oe-1 at resonance under optimum bias field Hm=1030 Oe;when the magnetic gap is relatively small,strong ME effect can be observed at lower bias field.Therefore,the magnetic gap size is an important parameter in the application of magnetic force driven ME devices.Our theoretical and experimental researches for enhanced ME effect in special-shaped composite materials can provide theoretical basis for the potential application of ME effect in sensors,transducers,energy harvesting devices et al. |
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