Research On Capacitive Magnetic Impedance Effect Based On Magnetoelectric Composite Oscillator

Magneto-impedance effect ( MI ) (i.e., a large change in ac impedance of a magnetic conductor with an ac current when subjected to an applied dc magnetic field), which is related to the relative permeability and relative dielectric constant. The relatively effective permeability of magnetic material with higher permeability changes with magnetic field and then leads to change of impedance, which is referred to an inductive type magneto-impedance. And the main materials of inductive type magneto-impedance are amorphous metallic alloys,amorphous metallic ribbons and magnetic thin films. Recently, with the development of magnetoelectric composite materials, one can also find that the impedance of composite materials will change with the variation of external dc magnetic field. However, the reason of the impedance change is that the dielectric constant of the composite (capacitance) changes with the magnetic field, which called capacitive type magnetic impedance. Researches show that the MI effect of capacitive type is more than inductive type magneto-impedance in single-phase magnetic materials.In this paper, a significant capacitive type magnetoimpedance effect of piezoelectric-magnetostrictive composite resonator is presented at room temperature.Based on the magnetic-force-electricity coupling effect, a theoretical analysis of the capacitive type magnetoimpedance effect is provided below.(1) Magnetoelectric composite materials composed of circular piezoelectric vibrator (PZT) and circular or strip magnetostrictive (Terfenol-D). We investigated the size effect of magnetoimpedance, magnetocapacitance and resonance frequency.Based on the magnetic-force-electricity coupling effect, a theoretical analysis of the capacitive type magnetoimpedance effect in magnetoelectric composite are showed. It was found that the variations of relatively effective permittivity of the composite with a dc magnetic field are responsible for the capacitive type magnetoimpedance effect.Addition,we also investigated the effect of polarization direction of piezoelectric ring for magnetoimpedance.(2) On the basis of the above theory and experiment, we designed different three-layer magnetoelectric laminates of Terfenol-D/PZT/Terfenol-D to study the impedance, capacitance and the shift of the resonance frequency under a single dc magnetic field at room temperature. Experimental and theoretical proved that not only the change in Young's modulus for the ferromagnetic phase due to magnetostriction( the AE effect) but also the effect of the elastic constant of the piezoelectric phase, via electrostriction will leading to the multiferroic composite resonance frequency shift. A detailed analysis also indicates that the volume fraction of piezoelectric phase play an important role in ME composite resonance frequency shift. Since the volume fraction of magnetostriction Terfenol-D is smaller than that of piezoelectric PZT will leading to the monotonic variation of resonance frequency;Otherwise, the shift of frequency with the magnetic field is nonmonotonic.