Ceramic actuators : Part 1: Materials

The field of solid-state ceramic actuators is reviewed and shown to be very diverse and growing rapidly. In the last 15 years, there have been a number of new actuator configurations developed such as rainbows' and 'moonies' which afford the designer greater opportunity for much higher displacement at a given applied field than is possible with the conventional monolithic devices. In addition, there have also been developments in the actuator materials themselves. No longer is it necessary to rely on various polycrystalline piezoelectric materials based typically on lead zirconate/titanate (PZT), lead titanate (PT) or barium titanate (BT) with their moderate strain-field behaviour and high hysteresis. Other materials have been developed which offer dramatically different displacement-field characteristics such as polycrystalline 'shape memory' and 'digital displacement' compositions and also several electrostrictor materials such as lead magnesium niobate (PMN) and lead zinc niobate (PZN) that have dramatically reduced strain-field hystereses have appeared and are starting to be commercially available. Perhaps most remarkable of all, in the last three years, it has been shown that up to an order of magnitude greater strain can be generated when the polycrystalline electrostrictor materials are replaced by the single crystal form. These recent developments in both material behaviour and device configuration are leading to an increase in market growth rates. Even before the realization of the very high strain developed by single crystal electrostrictor materials such as PMN and PZN, the over $1 billion/year North American market for actuator materials has been projected to grow at 8-10% annually over the next four years. With the recent announcement of the development of solid state fuel injectors for diesel engines to reduce noise and NO x , that growth rate is likely to increase even further over the next few years.