A comparative study of ultrasonic micro-motors based on single crystal PMN-PT and polycrystalline PZT ceramics

Abstract

A comparative study has been made to explore the potential benefits of newly available single-crystal ferroelectric materials when used in a practical device, in this case an ultrasonic micro-motor. This type of micro-motor exhibits exceptional powerto-weight characteristics, which could be exploited beneficially, for example, in unmanned air-vehicle (UAV) systems. The operating principles of a range of commercial and experimental motor designs were evaluated objectively in order to identify areas of performance that can potentially be enhanced using PMN-PT single-crystal piezoelectric ceramics. Based on this analysis a practical motor design was selected for construction and experimentation. Detailed numerical analysis indicated that a motor constructed from single crystal PMN-PT could be expected to provide an improvement in motor stall-torque by up to a factor of 2.8 and a no-load speed improvement by a factor of 1.5 when compared with motors based on standard polycrystalline lead-zirconate-titanate (PZT) ceramics. In practice single-crystal versions of the motor were found to produce double the power output of their polycrystalline counterparts. Overall efficiency was found to be improved two-fold. There were significant discrepancies between the numerical predictions for the single-crystal devices and their measured performance, whereas the polycrystalline devices were found to perform closely in line with predictions.

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“…PMN-PT material is a solid solution of lead, magnesium and niobium doped with lead titanate oxide Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 . PMN-PT-based materials are characterized by high dielectric permeability, high piezoelectric properties, and are suitable for applications in multilayer capacitors, actuators, sensors, and electro-optical devices such as piezoelectric motors made with MEMS technology [39].…”