Electret generator

Suzuki Y (2011) Recent progress in MEMS electret generator for energy harvesting. lEEJ Trans Electr Electron Eng 6 101-111... 

Jefimenko and Walker (1978) developed a 6 inch diameter 2-pole generator and obtained 25 mW at 6000 rpm, which is similar with flie eletret motor. Tada (1992) developed a complete model of rotational electret generators and obtained 1 mW at 5000 rpm with a 90 mm diameter 4-pole generator. More recently, Boland et al. (2003) derived a simple analytical formula for the output power by neglecting the parasitic capacitance and obtained 25 pW with an 8 mm diameter 4-pole generator fabricated with MEMS technologies. 

Lo and Tai (2008) developed an electret generator without tefliers. The rotor can slide freely relative to the stator, and then induced charges on the electrodes vary with toe position of the rotor. With a rotor coated with parylene... 

Fig. 12 Gap-closing electret generator with out-of-plane vibration (Takahashi 2013) (Reproduced with permission from IEEE)...

Fig. 13 In-plane electret generator fabricated with precision machining (Masaki 2011) (Courtesy of Dr. T. Seki)...

There have also been reports on the preparation of polar materials by a photo-electro-poling technique that combines the optically induced quadrupolar depletion of chromophores in the direction of the light electric vector with an additional field-induced orientation of dipolar chro-mophores. The latter allows the preparation of cold electrets, which are interesting for nonlinear optical applications, such as optical harmonic generation, wave mixing, etc. ... 

Electret materials are meanwhile used in a large number of modern high-tech applications including microphones, acoustic sensors, transducers, radiation and pollution dosimeters, power generators, filters, and many more. Additionally, electret technology is of great interest in the field of biomaterials, for instance in callus formation and wound healing [10, 11], When used in cellular or in multilayer sandwich structures, polymer electrets can exhibit piezoelectricity. Such materials are ferroelectrets, as they show typical features of ferroelectric materials such as piezo-and pyroelectricity [12-17],... 

Electrical charges generated by static electrization scatter not only over the surface but across the material bulk as well. The direct consequence of friction-induced electrization process in polymers is the emergence of the electret state. 

The presence of dispersed fillers in the polymer material in low amounts may intensify electrization, increase the residual charge and change the friction coefficient. Introduction of the filler in the electret state exerts a still stronger effect on polymer electrization on frictional interaction with metals. Depending on the direction of the field intensity vector formed by the filler particles, the field generated by triboelectrization can be attenuated or intensified. This means that the principle of the electret-triboelectrization superposition is realized [49], which can be used to regulate the parameters of frictional interactions. Thus, by the introduction of the electret filler, e.g. mechanically activated F-3 powder, it is possible to decrease the friction force (Fig. 4.9). 

Besides the previously mentioned piezoelectric material, the second one lies in electret that can preserve the induced charges for a long time. It can not only be used in the fabrication of piezoelectric generators but also triboelectric generators based on electrostatic induction effect. The electret and related devices are discussed further. Here we mainly focus on PVDF and its copolymers in polymer based-piezoelectric transducer/generator. 

The particle collection efficiency of these air filters can be enhanced by the static charging of the fibres, " and this can be realised by using mixed fibres of various layouts of electret filters " such additional filtration mechanism is more useful for filters used in respiration devices.The ionic species generated by the negative polarity corona (CO, ) seem to be more effective for corona charging of a PP nonwoven... 

Also, new polymer elechet materials have been added to the family of electrets, i.e., parylene HT (referred to as polymer AF-4 ) and the amorphous perfluorinated polymer CYTOP. The development of such high-performance electrets is mainly motivated by the apphcation in micro electret power generators (Suzuki 2011 Yang... 

Arakawa Y, Suzuki Y, Kasagi N (2004) Micro seismic power generator using electret polymer film. 

Lo HW, Tai YC (2008) Parylene-based electrets power generators. J Micromech Microeng 18 104006... 

Yang ZH, Wang J, Zhang JW (2012) Research and development ofmicro electret power generators. SCIENCE CHINA Technol Sci 55(3) 581-587... 

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