Piezoelectric polymer for mechanical sensors in smart card applications

Abstract

In this research, lamination technique was used to improve piezoelectric properties of PVDF. Laminated or multilayer system shows unusually high piezoelectricity because of charge interfering at the interface—charge has been accumulated at the interface of each layer. PVDF film and PVDF/Ba₀.₇Sr₀.₃TiO₃ composite film were used to prepare laminate films in different series by compression molding. Solution-casting technique was used to fabricate thin film of PVDF and composite. Ba₀.₇Sr₀.₃TiO₃ was synthesized via sol-gel method. And compression technique was used to laminate PVDF with PVDF/ Ba₀.₇Sr₀.₃TiO₃ layers. Dielectric properties of Ba₀.₇Sr₀.₃TiO₃ ceramic, composite film and laminate film was measured at the frequency range of 1 kHz to 1 MHz by Impedance/Gain-Phase Analyzer. FTIR result showed that mechanical stretching affected to β-crystalline phase of PVDF film as the decreasing of β-phase content. The highest dielectric constant was observed in original casted PVDF film however as stretching ratio was increased, the dielectric loss was improved resulting from the less porosity. By adding Ba₀.₇Sr₀.₃TiO₃ ceramic into the film, the composite film at higher Ba₀.₇Sr₀.₃TiO₃ ceramic content yielded higher dielectric constant at all frequencies. The dielectric properties of laminated films from PVDF film and PVDF/Ba₀.₇Sr₀.₃TiO₃ composite film were improved by less dissipation factor and the effective dielectric constant of the multilayer structure was related to a series connection model of PVDF and PVDF/BST composite layer dielectrics. The hysteresis loop of laminated film was observed showing the ferroelectric behavior.