Reducing stress gradients within piezoelectric actuators

Abstract

Piezoelectric actuators of the type comprising a stack of layers of ferroelectric material and intervening electrodes which extend only part-way across the adjacent ferroelectric layers suffer differential remanent stress when electric fields are applied across the layers. To overcome this, a tensile stress is applied to the actuator along an axis substantially perpendicular to the layers of piezoelectric material in the actuator, which tensile stress is sufficient to mechanically align the dipoles, thus giving rise to a remanent strain which is uniform throughout the actuator. The actuator is advantageously heated while the tensile stress is applied, so as to increase the difference between the tensile strength of the material and the applied tensile stress. An alternative arrangement involves subjecting the actuator to a multidirectional stress and reducing the stress along the axis substantially perpendicular to the layers of piezoelectric material in the actuator. The entire process is performed on completed actuators. Under suitable temperature and load conditions no tensile margin fractures form and electrode tip discontinuity is reduced.