Research On Preparation And Performance Of Sandwich FEP/THV/FEP Electret Membrane

The electrets have been widely applied in acoustic electric sensors such as microphones and other actuators due to their lasting and stable electrostatic field. Recently, the research focuses on the application of micro-electro-mechanical systems(MEMS), especially on electret generator for energy harvesting applications, in which the vibration energy can be changed into electrical energy by means of the relative displacement between two electret layers when vibrating. Many configuration of electret generator have been proposed, in which the theoretical power output is proportional to the surface charge density of electret materials, therefore, developing an electret materials with an extremely high surface charge density and the long-term stability is crucial for electret generators with a large power output. Based on existing research status of electret material, this parper proposes a idea that preparing a multilayer composite membrane consisting of materials with different electret properties and to make use of their heterogeneous interface structures in order to improve the charge density and charge storage characteristics. The electret hybrid film consisting of Teflon FEP/THV/FEP is prepared with melting method in high temperature and hot polarization charging,the charge storage stability is investigated by means of isothermal surface potential measurements.The main work of this paper and results are as follows:(1)The influence of charging condition on the charge storage stability is investigated, it shows that the surface potential of hybrid film increases with increasing hot polarization temperature and charging voltage,hybrid film electret obtains best charge storage performance on charging condition of 130℃/-3kv,the surface potential of FEP film electret changes little with charging condition;the variation of the surface potential after charging indicates that,after charging,the surface potential of the FEP film electret remain a stable value after a small margin decay,while the hybrid film electret shows a stable value after a small margin increase.(2)Although FEP monolayer film and FEP /THV/FEP hybrid film show good charge storage stability after storage at room temperature,but when do destructive alcohol scrub on different samples surfaces,it was found that the surface potential of the hybrid film can be quickly restored and the single FEP film can not be recovered(3)We study the piezoelectric effect of excellent performance in charge storage sandwich composite membrane FEP/THV/FEP electret material. Piezoelectric constant d33 can be measured, and the maximum is 57.8p C/N, which is three times of the conventional polymer PVDF. these indicate that the composite membrane electret have good prospect in application of piezoelectricity.(4)Sandwich composite membrane FEP/THV/FEP electret is investigated by means of thermally stimulated discharge analysis, research shows that the surface potential decay curve of the composite membrane electret has a peak value due to the phenomenon of non-polar- Polarity- non-polar type electret film, which is different with decay of a single membrane electret surface potential.and relate to and dipole polarization charges are each stored in the FEP layer and THV layer at the same time.(5)We propose a sandwich FEP/THV FEP composite membranes charge storage model, a preliminary analysis shows that sandwich FEP/THV/FEP composite film electret stores three charges: external injection, interfacial polarization and orientation of internal dipole(dipole charge). Therefore displays unique electret properties.