On the Effect of Force, Displacement and Voltage on the Capacitance of Piezoelectric Stack Actuators for Self-Sensing Applications

Capacitance-based self-sensing of piezoelectric actuators (PEAs) is a method used to estimate their displacement and force by measuring their apparent capacitance. However, the physics and limitations of this measurement technique are poorly understood, making it difficult to apply the technique to different boundary conditions. The analysis and experimentation in this study show that apparent PEA capacitance between structural resonances can be used for measuring changes in displacement, when external forces are constant, or for measuring external forces when displacement is constant. For simultaneously measuring force and displacement, the capacitance measurement between resonances can be augmented with a measurement of the shift in capacitance resonance frequencies.