Ferroelectric film-based stretch sensor with successive stretch and release motions characterized by a combined piezoelectric and electrostrictive effect

A stretch sensor fabricated from a hydrothermally grown ferroelectric PZT film on titanium foil was developed. The unique sensor structure effectively converts the stretching motion of the PZT film to an out-of-plane deformation with a linear strain variation. An experiment with a strain-stretch displacement of more than 10% was conducted using the sensor anchored on a silicone rubber plate. The induced polarization of the PZT film was linearly converted into a voltage output through the sensing circuit. The combined piezoelectric and electrostrictive effects are proposed to characterize the experimental results. Based on both the elastic Gibbs energy and piezoelectric theory, we derive a mathematical equation relating the strain and polarization of the PZT film. The measured stretch displacement and voltage data exhibited an excellent fit with the derived equation. An identical repeated motion can be sequenced by the memorized function of the sensor using the constant term of the fitting curve. With the characterized results, the computed displacement matched well with the measured displacement for repeated cyclic motions, with a correlation coefficient greater than 0.99. Compared with the simple piezoelectric effect, the more accurate displacement obtained via the detected voltage will significantly benefit wearable stretch sensors based on ferroelectric films.