 More recently, it has been applied to study cake buildup on porous membrane surfaces.Scanning versions can determine the topology of a solid/soft-solid surface immersed in a liquid environment, in an analogous manner to an atomic force microscope, but exploiting the principles of fluid mechanics.Key features of the technique are that it can study soft deposit layers without touching them, relies on relatively simple operating principles, can be used in a completely opaque liquid, and does not rely on knowledge of the fluid or deposit properties.