Electrets: recent developments

Recent progress in the field of electret research is reviewed. In particular, new developments relating to charge storage and charge transport, piezoelectric electrets with cellular or porous structure, ferroelectric polymers, nonlinear optical polymer electrets, and silicon oxide/nitride electrets are discussed. Much of the progress achieved over the past years is due to new developments in materials technology in the sense that novel or improved materials have opened up additional avenues for the advancement of electret science.