Voided polymer electrets - new materials, new challenges, new chances

In this review, the development of cellular propylene as an electret-transducer material since the mid-eighties is described, and the accompanying research into the origins of (quasi-)ferro-, pyro- and piezoelectric effects in voided polymer electrets is discussed in some detail. In this context, the most relevant charging and measuring techniques for piezo- and pyroelectric polymer-foam electrets are introduced. Porous fluoropolymer electrets and their investigation as single- or multiple-layer piezoelectrics are considered in view of their better thermal and temporal stabilities. Finally, some proposed applications of voided polymer electrets are mentioned.