Generally speaking, air filters are physically simple but technically complex devices. Whether they are particulate or gas phase filters, they rely on a complex set of mechanisms to perform their function satisfactorily. In many cases, more than one of these mechanisms comes into play.
Many new technologies have been employed in the effort to improve the quality and performance of air filters, and in some cases to reduce their cost. The most notable areas where advancement has been pursued are reduction in pressure drop and elimination of biological contaminants in the filter media. It is important to consider whether applying new technologies to air filter products is necessary and functional. In many cases it is, but in some cases it's not. Certain technologies, like ionic air cleaners, may produce by-products that can be harmful to people or the environment.
Mechanical air filters remove particles from the air stream because particles come into contact with the surface of fibres in the filter media and adhere to the fibres.
The mechanisms by which the particles come into contact with the fibres in the filter media are Straining (sieving), Interception, Diffusion, Inertial seperation and Electrostatic attraction. The first of these mechanisms applies mainly to mechanical filters and is influenced by particle size. Electrostatic filtration is obtained by charging the media as a part of the manufacturing process.