Date of Graduation

2016

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Ever J Barbero

Committee Co-Chair

Fritz Campo

Committee Member

Victor Mucino

Committee Member

Xueyan Song

Committee Member

Eduardo Sosa

Abstract

Novel models to predict magnetoelectric (ME) properties of composites made of piezoelectric (PE) and piezomagnetic (PM) phases is proposed. Two different composite arrangements are used: laminate and particulate. ME properties for laminate arrangement are obtained by applying the multiphysics equations for all four possible laminate configurations (TT, LT, TL, and LL), with appropriate boundary conditions. Closed form, explicit formulas are derived for the calculation of the ME charge and voltage coefficients as a function of material properties of both phases and PM volume fraction. A new coefficient, the ME coupling factor, is proposed in order to assess the conversion of magnetic work into electric work. The predicted ME voltage coefficient is in agreement with previous work and experimental data. A new approach is proposed to take into account the conductivity of the PM phase, resulting in calculated ME charge coefficients within 30\% of experimental data. The voltage, current, and electric power generated by unit of magnetic field applied to the composite define the intrinsic voltage, current, and power conversion factors. Since the PM phase of the composite has a higher magnetic permeability than the surrounding medium, a far filed magnetic field is not fully utilized due to demagnetization. Thus, novel explicit equations are developed here to calculate the extrinsic voltage, current, and power conversion factors accounting for demagnetization. The proposed formulation is applied to various materials and geometries to illustrate the process of material and device-geometry selection leading to an optimum design. The magnetoelectric (ME) properties of particulate composites are calculated using Eshelby theory and two homogenization techniques: dilute approximation and Mori-Tanaka mean field theory. A method that allows the calculation of all ME properties under any boundary conditions is proposed. These boundary conditions are dictated by the experimental configuration, e.g. films on a substrate, free-standing composites, etc. Predictions are compared with calculations reported by Harshe et al. and Nan et al., and good correlation is obtained with those, but to achieve good correlation with experimental data, the conductivity of the piezomagnetic (PM) phase must be taken into account, and a method is proposed to that effect. Percolated composites do not have any piezoelectric (PE) or ME properties because the charge leaks through the conductive PM phase. The experimental parameters that influence the percolation threshold are discussed and the best particulate composite design is proposed. Unlike previous models that did not account for conductivity, correlation between the proposed model and experimental data is much better.

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