Electrostatic deflection of charged droplets with asymmetrical injection: unexpected optimal design

Abstract

Continuous inkjet printers selectively direct charged droplets to the target medium or into a gutter for recycling by deflecting the stream with an electric field. While this is a well-known and mature technology, it sometimes is useful to revisit the underlying science. We have done this in the similar case of electron beam deflection and results are counterintuitive. Traditionally, to avoid the edge effects at the entrance as much as possible, charged streams have been injected symmetrically into the gap between two oppositely charged conductive plates. However we found that optimal deflection occurs when the stream is injected about 1/3 of the way toward the attracting plate. The stream can be quite wide - about 1/3 of the gap is acceptable. Under these conditions, deflection angles can be much larger than the 10 degrees or so previously considered maximum. For example it is possible to cleanly deflect a charged stream by up to 50 degrees or so. Optimal asymmetrical injection allows the stream to follow equipotentials so that the deflection force is normal to the trajectory and relatively uniform over the entire droplet avoiding break-up. There may be useful design advantages using optimal offset deflection technology in continuous inkjet printing.