Research On Preparation And Properties Of Cylindrical Layered Magnetoelectric Composites

Magnetoelectric(ME)composites are room-temperature functional materials for magnetic-electric energy conversion,which can be applied in microwave devices,memories,energy harvesters,ME sensors and so on.The ME composites integrating piezoelectric and magnetostrictive phases have the ME effect originating from the product of the piezoelectric and magnetostrictive effects.ME laminates have shown much higher room-temperature ME coefficients than other ME composites with other phase connectivity.Meanwhile,the ME laminate preparation is simple and low-cost.Thereinto,the compact cylindrical layered composites are beneficial for ME device miniaturization.The ME voltage coefficient peaks at the electromechanical anti-resonance and the ME effect distribution varies with different vibration modes,so it is essential to focus on vibration modes of the ME composites in the utilization of ME devices.There is little research on ME effect distribution on cylindrical layered ME composites.In the dissertation,different patterns and multi-electrode cylindrical layered ME composites were investigated:For different layer-sequenced Ni/PZT/Ni,Ni/PZT and PZT/Ni cylindrical layered ME composites,both the ME resonance frequencies and optimal magnetic bias increase with the electrodeposited Ni layer thickness.High order ME resonances are more affected by the layer sequence than the main ME resonances under axial magnetic fields,while there are only main ME resonances under vertical magnetic fields.Among the three cylinders of difference thickness,the PZT/Ni cylinder has the best ME performance because of the highest axial ME voltage coefficient,the highest vertical ME voltage coefficient when Ni layer thickness≥600 μm and the lowest optimal magnetic bias in both axial and vertical modes.A multi-electrode PZT/Ni cylindrical layered ME composite was prepared by electrodepositing.The electroplated Ni layers were arrayed as four arcs on the PZT cylinder inner surface.Due to the cylinder symmetry,the four Ni arc layers are equivalent under axial magnetic fields and the corresponding four units have the same ME response as the complete-electrode cylindrical ME composite.Moreover,when the four units were connected in series,the ME voltage increased multiplicatively with unchanged overall size.For the multi-electrode PZT/Ni cylinder in vertical mode,both the ME voltage coefficient and the corresponding phase suggest that the ME effect is omni-directional at the fundamental extensional vibration mode of the PZT ring and directional at the third extensional mode,which is excited by the quartering electrodes.The directionality in both amplitude and phase of the ME voltage is helpful to determine the direction of the magnetic field in the ME sensor.The electrode array also influences the ME resonances in multi-electrode ME laminates.Unlike the cylinder,the ME effect in multi-electrode ME laminates are anisotropic under magnetic field in the width direction.The ME voltage shows saddle-shaped distribution in bilayered ME laminate owing to the flexural strain,while the ME voltage presents umbrella-shaped distribution in sandwiched symmetric ME laminate.In multi-electrode ME laminates,although the ME phase is almost same for each unit,the ME voltage cannot remain increasing when units are connected in series since different units have different impedances.The Lorentz force-piezoelectric coupled ME effect and the piezomagnetic-piezoelectric coupled ME effect are compared based on the ME voltage coefficient and the corresponding phase of the piezoelectric/non-piezomagnetic metal and piezomagnetic metal cylindrical layered composites.Both linear Hoc dependence of the ME voltage coefficient and phase of approximately-90° demonstrated the Lorentz force-piezoelectric ME effect for PZT/metal cylindrical layered composites under axial mode.Both ME effect mechanisms work on the ME voltage output for the PZT/Ni cylinder in axial mode.In low field,the ME voltages from the two mechanisms incline to antiphase,but the piezomagnetic-piezoelectric ME effect is much higher than the Lorentz force-piezoelectric ME effect,the ME voltage coefficient shows the trend of the piezomagnetic-piezoelectric ME effect;in high field,there is only the Lorentz force-piezoelectric ME effect.For the PZT/Ni cylinder under the axial mode,the ME voltage coefficient is rather high in the whole magnetic field range,so it can be used to detect both low and high magnetic field.