Fibrous and granular filters with electrically enhanced dust capturing efficiency: Dedicated to Prof. B. Gross

It is shown that electric charging of a filter material greatly improves its capturing efficiency. The charge can be due to built-in charges (electret filter) or can be achieved by polarization in an external electric field. Various aspects of the two types of filters are discussed: design, choice of material, and filtration characteristics. In addition, the mathematical modelling of electret filters is discussed, in particular filtration with the fibres used in commercially available electret filters. Some applications of electrified filters are also briefly described (personal protection, vacuum cleaners, liquid filtration, etc.).