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An acoustic transducer consisting of a magnetostrictive Terfenol-D composite and electrostrictive PMN-PT stack connected in mechanical series is presented. A broadband velocity response is possible in this transducer when the two sections are connected in electrical parallel. A linearly coupled electromechanical model is formulated through mechanical vibrations, classical electroacoustics, and linear piezoelectricity and piezomagnetism. The linear model is used to analytically calculate the head mass velocity of the transducer in response to white noise voltage excitation. The analytical solutions are shown to correlate well with measurements, while providing a framework for calculation of material properties under the same dynamic conditions found during operation, as opposed to quasistatic conditions.

A.P. MORTENSEN and M.J. Dapino, “Hybrid acoustic transducer employing magnetostrictive composite and ferroelectric material,” Journal of Sound and Vibration, Vol. 307, pp. 983991, 2007.

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A magnetomechanical model based on continuum thermodynamics is presented which describes the sensing effect in single-crystal ferromagnetic shape memory Ni–Mn–Ga. The model quantifies the stress and magnetization dependence on strain at different values of bias fields under isothermal conditions. A magnetic Gibbs energy is considered as the thermodynamic potential with Zeeman, magnetostatic, and anisotropy energy contributions. Constitutive equations for stress and magnetization are obtained in the isothermal case after restricting the process through the Clausius-Duhem inequality for the second law of thermodynamics. Mechanical dissipation and the microstructure of Ni–Mn–Ga are incorporated in the continuum model through the internal state variables volume fraction, domain fraction, and magnetization rotation angle. Closed-form solutions describing the evolution of the internal state variables are developed. The model requires only seven parameters identified from simple experiments: stress-strain curve at zero field, and easy-axis and hard-axis magnetization curves.

N.N. SARAWATE and M.J. Dapino, “Continuum thermodynamics model for the sensing effect in ferromagnetic shape memory Ni-Mn-Ga,” Journal of Applied Physics, Vol. 101, No. 12, 123522, 15 June 2007.