An Engineering Equation for Corona Devices

Electrostatic engineering is concerned with the creation, movement, and control of charges to produce beneficial results. In many applications the first step is the creation of charges within the product itself, as, for example, in the electrostatic air cleaner or precipitator used to clean the air in a home or in the photocopy machine used to reproduce a document in the office. In the electrostatic precipitator, charges (gas ions) are created around a fine wire held at a high electrical potential, and then these charges are moved into the surrounding gas, where they become attached to pollutant particles. This allows the pollutants to be removed from the gas by an imposed electric field. Likewise, in the photocopy machine charges are created around a fine wire and deposited on a drum that has a photosensitive coating. Light reflected off a document varies in intensity based on the reflective properties of the document, and when this light shines on the photosensitive coating, the segments of the photo-conductive drum which receive the light become conductive and the deposited charges are selectively removed. This leaves a latent electrostatic image on the surface of the drum which is further processed to eventually give a reproduction of the document.