Piezoelectric-electrostrictive monolithic bi-layer composite flextensional actuator

We propose a new type of flextensional actuator comprised of an electromechanically active element which is a piezoelectric-electrostrictive monolithic bi-layer composite (PE-MBLC) capped by truncated thin brass sheets. The PE-MBLC contains equal amounts of 0.65{Pb(Mg_1/3Nb_2/3)O₃}-0.35PbTiO₃ and 0.9{Pb(Mg_1/3Nb_2/3)O₃}-0.1PbTiO₃ by volume, and is obtained by a co-sintering process. With applied E_max = 10 kV/cm unipolar drive, the maximum axial displacement (u₃₃) produced by the uncapped and capped PEMBLC is 11 and 21 mum, respectively. The hysteresis in unipolar u₃₃ at 0.5 E_max is 4.6% for the uncapped PE-MBLC, while that for the capped one is 11%. Under bipolar excitation, the maximum u₃₃ for uncapped is 11.6 mum at +E_max and 6.6 mum at -E_max with an asymmetry factor (xi)of 1.75 for which u₃₃ < 0 for all E < 0. Under bipolar excitation, the maximum u₃₃ at +E_max for the capped PE-MBLC is 19 mum while that for -E_max is 8 mum with xi = 2.4, for which u₃₃ > 0 at +E_max but is smaller than the u₃₃ at +E_max. The origins of the observed asymmetry in u₃₃ are discussed in the context of symmetry superposition and deformation mechanics of the endcaps.