Theoretical And Experimental Research On Nonlinear Magnetoelectric Coupling In Bi-Layer Asymmetric Magnetoelectric Laminates

Magnetoelectric laminates has attracted much attention for their magnetoelectric coupling characteristics,which means they can achieve the conversion between magnetic and electric energy,therefore,they are widely used in the design of magnetoelectric devices,such as magnetoelectric transformers,sensors and energy harvesters.There are lots of researches on symmetric magnetoelectric laminates composed of magnetostrictive material and piezoelectric material,however,the symmetric structure has a relatively larger size and there is a large loss near the resonance frequency of the symmetric structure.In order to solve the problems mentioned above,bi-layer asymmetric magnetoelectric laminates is selected as the research object.In addition,one-dimension nonlinear magneto-elastic coupled constitutive relations of magnetostrictive materials,magnetoelectric coupling effect and converse magnetoelectric effect of bi-layer magnetoelectric material have been researched.First of all,through Gibbs free energy,the relationship between stress and strain and the relationship between magnetization and magnetic field with the polynomial form were obtained with the help of thermodynamic relations.In the process of describing the magnetostriction and magnetization,a new nonlinear function is introduced to describe the strain dependent on domain rotation under different stresses,which overcomes the shortcoming of the difference of expressions between tensile and compressive stress.Besides,introducing a new magnetization relationship has overcome the other shortcoming that explicit magnetization relationship is inconvenience to get,therefore,a nonlinear magneto-elastic constitutive with simple form is obtained.The comparisons between the prediction and the experimental data of different magnetostrictive materials,such as Terfenol-D,Metglas and Ni show that the model can be used to accurately predict the magnetostrictive strain and magnetization of different magnetostrictive materials under different compressive stresses and magnetic fields.Therefore,the new model can well describe magnetostrictive and magnetic characteristics both in low field and high field,not only for positive magnetostrictive material,but also for negative magnetostrictive material.Moreover,the model can fully reflect the nonlinear magneto-elastic characteristics of magnetostrictive material and well explain(35)E effect.Secondly,based on the one-dimension nonlinear magneto-elastic constitutive relation,the piezomagnetic constitutive with the form of variable coefficient is further obtained,and the linear piezoelectric constitutive is used to describe the relationship between stress,strain,electric field,electric displacement.Assuming the existence of a neutral plane without strain in the bi-layer structure,curvature is introduced to describe bending deformation caused by the asymmetric structure,then according to the force and moment balance,the curvature and position of the neutral plane are obtained,eventually a theoretical model of static magnetoelectric effect considering bending deformation is establish.To validate the model,the predicted nonlinear dynamic material parameters are compared with the experimental results to verify the applicability of the derived parameter model for magnetostrictive material,then,the static magnetoelectric coefficient of Terfenol-D/PZT bi-layer laminates are measured,and the predictions with the parameter same as that in experimental measurement are compared with experimental results,the comparison shows good agreement.On this basis,the impact of stress and magnetic field on static magnetoelectric coefficient are predicted by the model,and the predicted results show that improving tensile stress appropriately can increase magnetoelectric coupling and reduce the optimal applied magnetic field,which provides a theoretical basis for the design and application of miniaturized magnetoelectric devices.Finally,in order to further understand the characteristics of the converse magnetoelectric effect in magnetoelectric laminates,the bi-layer structure prepared by bonding magnetostrictive material Terfenol-D and piezoelectric PZT adhesive is measured.At first,the converse magnetoelectric coefficient at the quasi-static state is measured,then,changing the environmental temperature of the laminates,the variation of the converse magnetoelectric coefficient under different temperatures is also researched.According to the measured results,we know that temperature does not change the trend of the converse magnetoelectric coefficient curve,while,with the increase of temperature,magnetostrictive material internal non-180 ° magnetic domain gradually disintegrate,and the performance of the magnetostriction is correspondingly affected,so the polarization in piezoelectric layer produced by the magnetostrictive strain is restrained,which makes the maximum of converse magnetoelectric coefficient gradually reduce with the increase of the temperature.Besides,the impact of the alternating frequency on converse magnetoelectric coefficient is explored,especially for the frequencies near bending resonance frequency.The measured results show that apparent dual-peak phenomenon of resonance magnetoelectric effect generates for bi-layer magnetoelectric laminates,the appearance of dual-peak phenomenon improves the magnetoelectric coefficient,which provides possibility for achieving giant magnetoelectric coupling effect.