Influence of poling and ageing on high-frequency dielectric and piezoelectric response of PVDF-type polymer foils

Polyvinylidene fluoride (PVDF) based films offer a wealth of practical application as pyroelectric and piezoelectric transducers. Crucial for these applications is knowledge about the dielectric response of the films which can be modified by an external DC electric field (poling) and by a heat treatment (ageing). Here, we present our studies of the dielectric response of PVDF foils in the frequency range of 1 MHz–1 GHz using a coaxial line and HP-4191A impedance analyzer. For corona-charged PVDF foils of thickness 24 μm a dielectric absorption in the range 2–3 MHz, piezoelectric resonance near 50 MHz and its harmonics as well as a high-frequency absorption at ∼800 MHz were found. From analysis of dielectric spectrum the relaxation and resonance frequencies as well as the electromechanical coupling coefficient were estimated. Influence of the annealing conditions on these parameters was investigated. Annealing in the temperature Ta⩾150°C causes a disappearance of the piezoelectric resonance.