Defocussing of charged particle beams transmitted through meshes

A mesh that separates two regions of different electrostatic field strength exerts a “micro-lensing” effect on charged particles that are transmitted through the mesh, causing the directions of the particles to change. A computational study has been carried out to establish magnitudes of the directional changes for four types of mesh that are commonly used, square holes in thin and thick plates, welded and woven.