Privacy preservation for voice over internet protocol calling is disclosed. In particular, wettability state of formation rock in a subterranean environment is estimated from multi-frequency measurements of rock dielectric constant and conductivity. Between the two types of layers having different refractive indexes, the first layers are composed of high refractive index material, and the second layer is composed of low refractive index material. More particularly, the upper floating gate may include a flat portion on the lower floating gate and a pair of wall portions extending upward from both edges of the flat portion adjacent to the cell device isolation layer. The invention is also directed to a cell culture biomass of adherent cells having increased cell density and microcarrier concentration compared to the respective confluent cell culture.