Active fiber composites (AFCs) find applications in a variety of industrial, commercial, and aerospace markets as both actuators and sensors. Among the key attributes of AFCs relative to conventional monolithic piezoceramic actuators are high strain energy density, unidirectional response, conformability, and robustness. Recently, performance enhancements in AFCs have been demonstrated through the use of a modified injection molding process to produce piezoceramic modules with multiple identical fibers of a uniform rectangular cross section. AFC actuators made from Type II PZT fiber modules exhibit free micro-strains of 1830 ± 30 ppm at a peak-peak E-field drive of 26.1 kV/cm, and show exceptional part-to-part uniformity. In addition, AFCs made from injection molded PMN-PT fiber modules show a low-field d<sub>33</sub> of 650 pm/V. The successful incorporation of PMN-PT materials into AFCs also demonstrates the viability of using highly textured ceramic PMN-PT piezofibers, for which even larger increases in strain response are expected.
The property enhancement offered by single crystal relaxor ferroelectrics combined with the manufacturability advantages offered by injection molding has the potential of producing single crystal 1-3 piezocomposites at an affordable production-viable rate. Two methods of texturization/recrystallization are being evaluated: an integrated multi-seed process and epitaxial growth. The integrated seed approach involves incorporation of oriented single crystal PMN-PT seeds into injection molding feedstock prior to fabrication of 1-3 ceramic preforms. After sintering, an additional texturization and growth step is carried out. This step is intended to drive recrystallization at multiple sites within the ceramic body extending the oriented texture throughout the matrix. The epitaxial growth approach involves nucleation and growth in the dense ceramic body initiated from a compatible external seed crystal. Recrystallization is achieved through direct contact between a ceramic preform and a seed substrate coupled with appropriate thermal and atmospheric growth conditions.
Ceramics injection molding technology is being adapted for the fabrication of net shape piezoelectric actuators of lead zirconate titanate (PZT) and lead magnesium niobate (PMN). INjection molding offers low cost, high quality actuator components with a high degree of part-of-part reproducibility. Configurations under investigation include a proprietary high displacement linear element, air acoustic actuators, tube array actuators, benders, and various multilayer designs. Applications include conformable unidirectional patches for active noise and vibration control, high displacement bender actuators for active vortex generators and synthetic jets, high force-high displacement actuators for rotorblade flaps, and air acoustic actuators for active noise reduction.
Electric field induced antiferroelectric (AFE) to ferroelectric (FE) phase transformations are accompanied by large strain and significant hysteresis. The properties of these materials can be tailored to fit specific applications such as high strain actuators and charge capacitors. As an attempt to reduced hysteresis, Barium and Strontium A-site substitution of the phase transformation behavior of (Pb<SUB>0.98-(delta</SUB> )La<SUB>0.02</SUB>A<SUB>(delta</SUB> )) (Zr<SUB>x</SUB>Sn<SUB>y</SUB>Ti<SUB>z</SUB>)O<SUB>3</SUB> (A equals Ba, Sr) ceramics have been investigated. The ceramic samples in this study produced 0.2% to 0.3% strain level. Barium proved to be a strong FE stabilizer with decreasing both switching field and hysteresis, while Strontium proved to be a strong AFE stabilizer. Some practical data, including temperature stability and current requirements, are also to be discussed.