Large piezoelectric effects in charged, heterogeneous fluoropolymer electrets

Large piezoelectric d(33) coefficients around 600 pC/N are found in corona- charged non-uniform electrets consisting of elastically "soft" (microporous polytetrafluoroethylene PTFE) and "stiff" (perfluorinated cyclobutene PFCB ) polymer layers. The piezoelectric activity of the two-layer fluoropolymer stack exceeds the d(33) coefficient of the ferroelectric ceramic lead zirc onate titanate (PZT) by more than a factor of two and that of the ferroelec tric polymer polyvinylidene fluoride (PVDF) by a factor of 20. Soft piezoel ectric materials may become interesting for a large number of sensor and tr ansducer applications, in areas such as security systems, medical diagnosti cs, and nondestructive testing.