Applications of electrets

It has been said that the applications of electrets are unlimited. We will show that there is a great deal of truth, in this statement. The variety of applications is due first to the availability of three types of electrets: normal ones purely based on charge storage, piezo- and pyro-active ones and light-sensitive ones. Secondly, there are three ways of using electrets; one can use (a) its inductive power, (b) the forces it generates, and (c) sacrifice its charge, for instance for measuring radiation. Electrets can convert e.g. mechanical to electrical, electrical to mechanical, thermal to electrical and optical to electrical signals. They are or can be used in audio systems, for measuring and testing, in the medical and maritime field, for security and surveillance, etc. In this paper the emphasis will be on recent advances and developments, particularly those which have found large-scale application.