PVDF-TrFE copolymer piezo film has higher coupling factor (>0.30) than piezo PVDF film (~0.15) due to its lower dielectric constant (~8.0) and higher Young's modulus (>3 GPa). It is usually used in thickness mode (d33) for ultrasound transducers where it is used to generate acoustic wave under electrical excitation (actuator) and at the same time to measure the acoustic wave response (piezo sensor).
It shall be pointed out most PVDF-TrFE copolymer piezo film has much lower d31 and d32 than PVDF as the PVDF piezo film is usually oriented in the "1" direction with high d31 (>25 pC/N)
Even though many people think piezo film and sensors are simple, unfortunately there are lots of mis-information in academic publications and books written by "experts" who never tested a commercial piezo PVDF film. We have seen many university professor and engineers in Fortune 500 companies who do not understand what they are looking for and who do not have a correct specifications. Most of them "learned" piezo film technologies from reading incorrect academic publications and have wasted months' time before talking with us. Email us firstname.lastname@example.org if you need technical support when developing a new product to avoid unnecessary mistakes. We also provide consulting service in designing sensors and other piezo devices.