“…In this case, experimental data are used to obtain a fitted expression b = kE n of the specimen, where k and n are constants and exponents without physical meaning, respectively. Numerous studies indicated that the properties of the electret, such as dielectric constant, conductivity, thickness, and the ability to trap the ion species, have a great impact on the charging results [ 11 , 34 , 35 , 36 ].…”