Foil electrets

Fig.1 Foil electret microphone (Sessler and West 1973) (Reproduced with permission from AIP)... 

Sessler GM et al (1973) New touch actuator based on the foil-electret principle. IEEE Trans Com 21 (l) 61-65... 

Fig. 7.22 Thermally stimulated current spectra of FEP electret foils (aluminium, coated on one side) immediately after polarisation. The heating rate was 4 C min"1. Reproduced with permission of the American Institute of Physics from Sessler and West (1971).

A relatively recent development in radon gas monitoring is the electret system (Kotrappa et al, 1988). In effect this is an ionization chamber with an electret foil in the chamber, into which radon gas diffuses through a filter. The electret is a plastic foil which carries a permanent electric charge and therefore an electric potential. The decay of Rn and RnD in the chamber ionises the air, and the electric field caused by the potential on the electret attracts these ions to the electret. The electret loses its charge proportionally to the number of ions collected. The charge, or voltage on the electret is... 

Wild, J. Stranathan, J. (1957). Influence of External Treatments on Electret Behavior. The Journal of Chemical Physics, Vol.27, Nq5, pp. 1055-1059 Yovcheva, T. Avramova, L Mekishev, G. Marinova, T. (2007). Corona-charged polypropylene electrets analyzed by XPS. Journal of Electrostatics, Vol.65, pp. 667-671 Zhongfu, X. Yuda, W. Guamao, Y. Ximin S. (1991). Corona Charging at Elevated Temperature and Charge Transport for Mylar PETP Foils. 7th Int Symp. on Electrets... 

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