Optimization of magnetoelectricity in thickness shear mode LiNbO3/magnetostrictive laminated composite

Abstract

Magnetoelectric (ME) composites have recently attracted much attention and triggered a great number of research activities, owing to their potential applications in sensors and transducers. Many researches have focused on the enhancement of ME coefficient by choosing suitable composite material and vibration mode based on the coupling between stress and strain. Besides normal stress, another vibration mode, shear mode, is further discussed as a potential high-frequency resonant device for a high frequency magnetic field detector, and it is useful to optimize the shear ME coefficient to broaden the application scope of the compositions. In this paper, an elasticity method is used to calculate ME coefficients of thickness shear mode LiNbO3/magnetostrictive laminated composites for various crystal orientations of LiNbO3, magnetostrictive materials and material sizes. The stretch-shear structure and shear-shear modes of the composite with considering the boundary condition are both discussed and further optimized. According to the structure design of stretch-shear mode composite from the literature, we design a new structure to achieve the uniform and pure shear ME effect, which changes the magnetostrictive phase on the bonding part into rigid material to avoid stretch deformation. We find that in the shear-shear ME composite, the structure should not move in the in-plane direction in order to realize the parallelogram deformation under shear stress, but should be free in the thickness direction to meet the change of thickness with shear deformation. For the stretch-shear mode Metglas/LiNbO3 [(xzlt) x/y], the shear ME coefficient E15 as a function of orientation of LiNbO3 shows that the maximum E15 is 235.1 mV/(cmOe) when x=0 and y=30. The results indicate that optimal shear ME coefficient is obtained at (xzt) 30 LiNbO3, resulting from the maximum shear piezoelectric coefficient dp15. By changing the material size in stretch-shear composite, the shear ME coefficient increases with the increase of thickness of magnetostrictive phase, because the stretch force increases with the increase of the cross-sectional area of magnetostrictive phase. The maximum values of E15 are, respectively, 24.13 V/(cmOe) in the stretch-shear mode Terfenol-D/LiNbO3 and 11.46 V/(cmOe) in the shear-shear mode Metglas/LiNbO3 by the optimization of material sizes. Experimental results are in accordance with calculation results. It is confirmed that LiNbO3 (xzt) 30 is the best choice for achieving the largest shear ME effect, and thicker Terfenol-D can help to achieve a larger ME coefficient in this stretch-shear composite. This work provides a design method to choose the structure and crystal orientation of shear LiNbO3-based ME laminated composite, which shows a prospect of applications in high-mechanical-quality factor Qm and high-frequency magnetic detectors with shear resonant devices.