Experimental Study On Mechanical Properties And Piezoelectric Effect Of PVDF Thin Films

As a novel piezoelectric polymer material,the sensors made of PVDF(polyvinylidene fluoride)piezoelectric film have the advantages of high sensitivity,wide frequency band,low acoustic impedance,high voltage output,and can be processed into specific shapes,which are widely applied in various fields.In this paper,the basic mechanical properties,the vibration characteristics under different temperature fields,and the piezoelectric effect of silver-coated PVDF piezoelectric films were studied experimentally and analyzed.The specific research contents and conclusions are as follows:First,the PVDF piezoelectric films with different thickness of 40 ?m,64 ?m,and 122 ?m(the thickness of coated silver on the upper and lower surfaces is 6?m)were prepared.The tensile samples of PVDF piezoelectric film were tested in two directions using a fiber tensile tester,i.e.,parallel(1 direction)and perpendicular(2 direction)to the molecular chains,and the corresponding stress-strain curves were obtained.The experimental results show that: in the elastic stage,the mechanical properties of the two directions are practically identical,however,in the plastic stage,the mechanical properties of the two directions are significantly different,showing a strong anisotropy.Next,PVDF cantilever specimens with thicknesses of 40?m,64?m and 122?m were prepared respectively.The non-contact vibration test system was used to test the vibration characteristics of the PVDF cantilever beam under different temperature fields,and its first-order natural frequency was obtained.The experimental results show that the first-order natural frequency of the PVDF cantilever beam decreases with increasing temperature.In the initial heating stage,the frequency decreases more slowly,and when the temperature rises to a certain degree,it declines rapidly.Besides,the smaller the PVDF film thickness is,the greater its natural frequency is affected by the temperature.Finally,based on the non-contact vibration test system,the piezoelectric effect of PVDF was investigated experimentally.The experimental results of three different thickness PVDF cantilever plates show that the voltage-frequency curve is in good agreement with the amplitude-frequency response curve,and the excitation frequency corresponding to the peak output voltage is consistent with the resonance frequency of the PVDF cantilever plate,indicating the sensor's output voltage has a good linear relationship with the input strain and is suitable for strain measurement.In the same time,the sensor made of smaller thickness has higher sensitivity.In this paper,the basic properties of PVDF piezoelectric films were experimentally researched and analyzed,which provides the basic data reference for the design and optimization of PVDF piezoelectric sensors and has much significance in engineering application.