A sensor, in particular for determining the oxygen content in exhaust gases of internal combustion engines, is provided. The polycrystalline film of silicon can be used to form an electronic device, such as a monolithically integrated solar cell having ohmic contacts formed on opposed surfaces or on the same surface of the film. The lower electrode is comprised of a metal film embedded in an electrode groove formed in an insulating film over the main surface of a semiconductor substrate; and the upper electrode is comprised of a film stack of a TiN film and a Ti film formed over the TiN film. For initial fracturing with relatively large particle sizes, the power spectral density of each stimulator output is down-shifted toward the lower resonant frequencies of large particles. The process is carried out to improve a level of disinfection andor denutrification of the effluent.