Research Of Magnetostrictive/Piezoelectric Composite On The Elastic Amplitude Transformer

Magnetostrictive/elastic amplitude transformer/piezoelectric composite is constructed by bonding magnetostrictive and piezoelectric material on the amplitude transformer which has a high mechanical quality factor (Qm). The magnetoelectric effect of the composite is obtained due to magneto-mechanical-electric coupling. The magnetostrictive layer will actuate the amplitude transformer to vibrate due to the alternative magnetic field. When the driving frequency of magnetic field is equal or near to the natural frequency of the amplitude transformer, the composite will vibrate at resonance. The strain of the magnetostrictive layer is amplified in the max strain area of the amplitude transformer, and consequently the produced voltage in piezoelectric layer bonded at the max strain area of the amplitude transformer will reach maximum. The composite with simple structure and easy fabrication can realize transduction between magnetic and electrical energies effectively.The substrate with an optimal shape, which is a stepped amplitude transformer, is chosen based on analyzing strain amplification mechanics of the amplitude transformer. Based on the composite's design feature, the magnetostrictive/piezoelectric composite on the stepped amplitude transformer is divided into four parts: the magnetostrictive layer and the stepped elastic substrate which are with the same length, the piezoelectric layer and the stepped elastic substrate which are with the same length as well as the rest two parts of the substrate. By using equivalent circuit, the equivalent circuits of four parts are developed. The equivalent circuit of the composite is given by coupling the equivalent circuits of the four parts based on displacement continuum and force equilibrium in the interfaces of the adjacent parts.By using the complex parameter method, the losses which are mainly the mechanical loss and the dielectric loss of the composite are taken into consideration in the equivalent circuit. The eddy current loss can be neglected due to intense bias magnetic field. The theoretical expression of magnetoelectric voltage coefficient is given, where the main losses are all taken into consideration. The expression also indicates the relationship between the magnetoelectric voltage coefficient and the materials'parameters as well as geometry parameters of the composite.The magnetoelectric response of the Terfenol-D/Be-bronze/PZT-5H using the formula derived above is calculated and compared with the experimental. It is indicated that the theoretical response shows a similar variation tendency to the experimental in spite of the difference at resonant frequencies and the values of the magnetoelectric voltage coefficients, which is resulting from ignorance of the glue behavior. The composite on the stepped substrate and the composite on the rectangular substrate are also compared, which is indicated that the former has a higher magnetoelectric voltage coefficient. The main factors, which influence the characteristics of the composite, are further discussed, including the material property parameters and lengthes of individual phases, the thickness ratios and the cross-sectional area coefficient of the amplitude transformer. The optimal size of the composite is obtained, which provides a theoretical ground for design of the composite device.