Charges and polarization in insulators, a long history with a promising future

Electrets are closely associated with the development of philosophy, electromagnetism and physics in general. The first experiments in this field were reported over a few thousand years ago and, as is well known, they led to the name electron. A significant change in the rate of discoveries took place in the eighteenth century with the development of techniques to generate and store electric charges. Applications started to be considered particularly in connection with the human body and mind... However, it was during the nineteenth century that events accelerated with much important progress being made in relation to electricity and also... with the birth of the word "electret". During the twentieth century, the remarkable properties associated with space charge and polarization in solids began to inspire innovators. Many proposals were made. While some of these proposals did not lead to industrial products, some became quite successful giving way to extremely large-scale applications, in fields as diverse as telecommunications, non destructive testing, medical imaging, automation, safety, biological sciences, etc. Devices are now made by the tens of billions per year and the story is certainly not yet over.