Research On Acoustic Emission Sensing Performance Of P(VDF-TrFE) Piezoelectric Film

Polyvinylidene fluoride-trifluoroethylene(P(VDF-TrFE))is a polar polymer material with strong piezoelectric effect.P(VDF-TrFE)can be used to prepare piezoelectric sensors,transducers and other devices for its good piezoelectric,thermoelectric and ferroelectric properties.In order to study the piezoelectric properties of P(VDF-TrFE)polymer when it is applied as the acoustic emission sensors,this paper prepared P(VDF-TrFE)films by solution casting method,and followed that the films are treated at different annealing temperatures.Then we systematically compared the differences in the crystallization,dielectric,piezoelectric and ferroelectric properties of five groups of P(VDF-TrFE)piezoelectric films with different VDF contents.Based on that,the acoustic emission performance of the polarized piezoelectric film is tested by the pencil lead break acoustic emission sensor experiment.The main results are listed as follows:1)By using DSC,XRD and FTIR,the structures of P(VDF-TrFE)films treated at different annealing temperatures are characterized.It is found that 150? annealing is more conducive to the crystallization of P(VDF-TrFE)film.XRD results also show that the crystalline regions of P(VDF-TrFE)50/50mol%and P(VDF-TrFE)55/45mol%thin films contain two conformations of 3/1-helical phase and all-trans,? phase.The crystalline regions of P(VDF-TrFE)films with VDF/TrFE of 70/30mol%,75/25mol%and 80/20mol%are dominated by the ? phase of all-trans conformation.DSC results show that with the increase of VDF content,the P(VDF-TrFE)film Curie temperature Tc moves to a high temperature direction,and the melting point Tm moves to a low temperature direction.P(VDF-TrFE)80/20mol%film has the highest Tc,reaching 135.7?,indicating that this sample has a higher service temperature than other components of P(VDF-TrFE)film.2)The dielectric properties of the P(VDF-TrFE)film before and after polarization are compared by dielectric spectrogram characterization.It is found that the relative dielectric constant ?r of the polarized P(VDF-TrFE)thin film increases.Especially,?r of P(VDF-TrFE)50/50mol%has a highest increase,and it reaches 24.8 at a frequency of 100 Hz.However,the dielectric loss tan? is significantly reduced and besides that a significant loss peak appears at a high frequency of 100 kHz.From the dielectric temperature spectrum,we find that all P(VDF-TrFE)films have an extreme peak corresponding to the temperature of the ferroelectric-paraelectric phase transition(F-P).Moreover,the trend of the phase transition temperature with the VDF content is consistent with the DSC analysis results.3)Comparing the change of the piezoelectric strain constant(d33)of P(VDF-TrFE)with the polarization electric field,we find that the d33 gradually increased with the increase of the polarization electric field strength.When the polarization electric field increases to 150 MV/m,d33 of all P(VDF-TrFE)films reaches its maximum value.Moreover,the ferroelectricity of the film is tested by hysteresis loop,and it is found that the saturation polarization(Ps)and residual polarization of P(VDF-TrFE)film increased with the increase of VDF content.The Ps and Pr of P(VDF-TrFE)80/20mol%film under the electric field of 200 MV/m reaches to 15.1 ?C/cm2 and 11.4 ?C/cm2,respectively.4)The polarized piezoelectric film is used to test the pencil lead break emission sensor,and the response of different piezoelectric films to the pencil lead break signal was compared.It is found that the signal amplitude of the P(VDF-TrFE)80/20mol%piezoelectric film is the largest and it reaches to·83.49dB in average.Moreover,the range of amplitude is 5 dB,and the obtained signal is more stable than that of PZT.In addition,the peak voltage of the waveform is also the largest,reaching to 14 mV.The peak frequency is mainly distributed in the interval of 20?40 kHz,the frequency peak is the sharp,and the noise of the lead-off signal obtained is less.The results show that when the piezoelectric P(VDF-TrFE)favors of is an excellent sample to make the acoustic emission sensor.Especially,P(VDF-TrFE)80/20mol%film has the more favorable advantages in crystallization,ferroelectric and piezoelectric properties than that of films with other components of VDF/TrFE.Therefore,the P(VDF-TrFE)80/20mol%piezoelectric film is expected to become the core component of the flexible acoustic emission sensor.