Electrostatic modulator for control of flow of charged particles

Abstract

A system for controlling the flow of charged particles and for modulated aperture electrostatic printing. An apertured screen having substantially the entire surfaces formed of a dielectric material is charged with like charges over substantially all of its surfaces to develop fringing fields in the apertures. The charge distributed across one side of the screen is selectively dissipated in accordance with the pattern to be reproduced, thereby modifying the fringing fields to form an electrostatic latent image for controlling a flow of charged particles directed to the screen. The screen is initially pre-image charged to carry a higher potential V.sub.A on one face than on the other V.sub.B to provide a potential difference V.sub.A - V.sub.B through the screen apertures. This is accomplished by constructing the screen to have a lower insulator capacitance on side A than on side B; or, to have a greater insulator resistance on side A than on side B; or by selecting the insulator material on side B to have a non-linear resistance characteristic at all voltage levels above the desired value for V.sub.B ; or, to have combinations of two or more of such characteristics. The pre-image charge is modified in accordance with an image to be reproduced, and, in some regions of the screen V.sub.A is reduced to less than V.sub.B. Full modulation control of particle flow is thereby possible with a single selective charge dissipation.