A pair of high voltage switching circuits associated with first and second sources of voltage supply are connected with a pin-shaped record electrode through a resistor and an electrostatic induction plate, respectively. The electrostatic induction plate is disposed very closely adjacent the record electrode...http://www.google.de/patents/US4030107?utm_source=gb-gplus-sharePatent US4030107 - Electrographic recording devices employing electrostatic induction electrodes
