PMN-PT piezoelectric-electrostrictive bi-layer composite actuators.

摘要

In the past few decades, significant advances have been achieved to replace the conventional actuators, including hydraulic, shape memory alloy, electromagnetic and linear induction, with piezoelectric actuators since they are light weight and small in size, have precision positioning capabilities, offer a wide range of generative force, consume less power, and provide higher durability and reliability. The strain produced by bulk polycrystalline piezoelectric ceramics and single crystals are typically in the range of 0.1 to 1%, respectively, which is still low for many applications. Therefore, various strain amplification designs including multilayer, bimorph, unimorph, flextensional actuators (Moonie and cymbal), co-fired and functionally graded ceramics have been proposed to enhance the displacement.;In this investigation, Piezoelectric/Electrostrictive Bi-Layer Monolithic Composites (PE-MBLC) were fabricated by co-pressing and co-sintering of the piezoelectric (PMN-PT 65/35: P) and electrostrictive (PMN/PT 90/10: E) powders. Flat and dome shaped of PE-MBLCs were obtained by optimizing processing conditions such as pressing pressure and sintering temperature. In addition, poling conditions of bilayer composite actuators were thoroughly studied to maximize their electromechanical properties. It was found that composites had lower d33eff and Keff values than the calculated values. This was attributed to a significant difference between relative permittivities of P and E materials as well as the presence of induced stresses in both P and E layers after sintering that hindered domain switching within piezoelectric layer during poling.;The shape change (planar to dome), electromechanical properties, and actuation performance of PE-MBLC actuators were examined as a function of volume percent of piezoelectric phase. The highest displacement ∼15 mum was obtained from PE-MBLC actuator with 50 volume % piezoelectric phase due to the transverse strain response of piezoelectric and electrostrictive layers, the geometry of the composites, and the domain reorientation.;Two designs of the flextensional actuators were also fabricated. In the first design, two truncated thin metal caps were attached to a flat PE-MBLC. In the second design, dome-shaped PE-MBLC actuators with various volume fraction of piezoelectric phase were attached to a flat metallic plate. The actuation evaluation showed that ∼21 to 70 mum displacement could be achieved by such designs.