Electrets charge stability

Rychkov D, Gerhard R, Ivanov V, Rychkov A (2012a) Enhanced electret charge stability on polyethylene films treated with titanium-tetrachloride vapor. IEEE Trans Dielectr Electr Insul... 

Hence, the preliminarily placement of the electrets at low pressure for a certain period of time can be used as an effective method for stabilizing the electrets charge depending on their applications. 

Xia, Z., Gerhard-Multhaupt, R., Nunstler, W. K, Wedel, A. Danz, R. "High surface-charge stability of porous polytetrafluoroethylene electret films at room and elevated temperatures", J. Phys. D Appl. Phys., Vol.32, pp.L83-85, (1999)... 

Electrets are dielectric materials capable of quasi-permanently storing electric charges at their surface or in their bulk. This chapter presents a brief history of electret research, followed by a classification and introduction of the most important electret materials. The chapter also discusses ferroelectrets and recent developments in charge stability. 

Electret Polymer Ferroelectret Dipole Charge Stability... 

Another way of investigating the depth in energy to which charges are trapped (a measure of the stability towards thermal decay) may be obtained by thermally stimulated currents (TSC). In this technique, electrodes on the two sides of the electret are connected via a sensitive current meter and the specimen is then heated at a constant, slow rate (1 Cmin-1, say). Discrete current peaks are observed as a function of temperature as successively more deeply trapped charges are released (Fig. 7.22). Dipolar relaxation may also give peaks in the TSC spectrum (van Turnhout, 1975). 

In this section, a systematic evaluation of the charge storage behavior of PPE/PS blends is provided to develop tailored electrets with enhanced temperature stability and processability. 

The materials and methods presented in this review allow access to charge storage materials with extraordinary high temperature stability which can be employed for instance in microphones, sensor devices, and electret filters. In addition, such excellent electrets are of fundamental importance for piezoelectric devices within the rapidly emerging field of energy harvesting. 

In contrast to charge electrets with their stored real charges, dipole electrets are characterized by a preferential orientation of their molecular dipoles. Here amorphous and semicrystalline dipole electrets are distinguished. Amorphous dipole electrets are characterized by a quasi-permanent dipole polarization in the amorphous phases (Fig. 3a), whereas semicrystalline ones show a permanent dipole orientation in the crystalline phases and additionally contain Maxwell-Wagner compensation charges at the interfaces between amorphous and crystalline regions for stabilizing the polarization (Fig. 3b) (Mopsik and Broadhurst 1975 Broadhurst et al. 1978 Sessler et al. 1992). 

Besides, high-performance polymer electrets, sueh as Parylene HT and certain types of CYTOP, were introduced to the family of electret materials. They exhibit not only excellent electret properties (high surfaee charge density with exceptional long-term and thermal stability) but also good compatibility with MEMS fabrication process. 

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