Mirror image force



See also notes on test3d30.


This option to include this force in ray tracing is accessed from the bottom of the sheet /databuilder/tracing rays/advanced options/.


See also notes on static mirror image force.


When a particle of charge q is at a distance x from a conducting surface the attractive force is

F = -k/x**2,

where k = q**2/(4*pi*epsilon*(2*x)**2).

For example, when q = e, x = 1 micron, then F = E*q, where E = 0.34 V/mm.

This force is therefore usually negligible, except for systems that involve highly charged small composite particles that are near to surfaces (or touching them), such as carbon toner particles.


In evaluating the image force, only the mirror charge in the nearest electrode is considered. There might therefore be a small error near edges and corners.


The image force for a particle outside a medium of dielectric constant K is reduced by

u = (K - 1)/(K + 1).

This is included in CPO3D/Dielectric, and it is always assumed that the particle is in a medium of dielectric constant 1.