The Dependence of Acoustic Emission Performance on the Crystal Structures, Dielectric, Ferroelectric, and Piezoelectric Properties of the P(VDF-TrFE) Sensors

To clarify the influence of various molar concentrations of vinylidene fluoride (VDF) on the piezoelectric and acoustic emission (AE) reception performances of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] sensors, we systematically investigated the crystal structures and the dielectric and ferroelectric properties of P(VDF-TrFE) films with different compositions of VDF and TrFE monomers and found that low proportion (<30 mol%) TrFE as a wedge inserted into molecular chains of P(VDF-TrFE) will not only improve the fraction of regular
$\beta $
-phase crystal grains but also decrease the dielectric constant (
$\varepsilon _{r}$
) of these copolymers, which favors the piezoelectric voltage coefficient (
${g}_{{33}}$
) of this P(VDF-TrFE) film. As such, a considerable remanent electric polarization (
${P}_{r}\sim {11.4} ~\mu \text{C}$
/cm
²
) under 200 MV/m and a large piezoelectric coefficient (
${d}_{ {33} }\sim -{25}$
pC/N) are obtained in P(VDF-TrFE) 80/20-mol% films. It is worth noting that a sensor made from P(VDF-TrFE) 80/20 mol% shows an attractive AE reception property of approximately 84 dB, a high signal voltage of above 10 mV from time-domain analysis, and a large signal voltage of above 4 mV from frequency-domain analysis, which are close to standard lead zirconate titanate (PZT) sensors. Considering its unique characters of flexibility, no required stretching, easily shaped, having high thermal Faille temperatures (
${T}_{c}\sim {135.7}~{\circ }\text{C}$
), etc., P(VDF-TrFE) piezoelectric film is considered a promising material for sensors, actuators, and energy transfer units.