Technikatörténeti szemle 20. (1993)

TANULMÁNYOK - Tihanyi Glass, Katalin: The Iconoscope: Kalman Tihanyi and the Development of Modern Television

linearly with the frequency of the radiation, „that is for each incident photon an electron is ejected," under the storage effect a photoconductive and photovoltaic phenomenon occurs where („apart from the liberation of electrons from metals") when photons are absorbed in a p-n junction (in a semiconductor) or metal-semiconductor junction, „new free charge carriers are produced," (photoconductive effect) and where „the electric field in the junction region causes the new charge carriers to move, creating a flow of current in an external circuit without the need for a battery," (photovoltaic effect) (27). The Concise Dictionary of Physics under the heading, ..Photoelectric Cells," differentiates between „the original photocells" (which utilized photoemission from a photosensitive surface and their attraction by the anode) and Jhe more modern photocells which utilize the photoconductive and photovoltaic effect" (28). The advent of storage based television Simply put, the essence of storage technology is that the television signal, rather than being the equivalent to the input charges and the product of primary electron emission, is produced by the secondary emission resulting from several stages of amplification. Contrary then to early electronic television devices which, as we have seen, rely on the minute local capacity of the photoelectric layer — even under conditions where the image carrier is exposed to the light from the image during the entire scansion cycle — a number of major innovations have been added that make true storage possible: 1. the addition of the third electrode, a positively charged grid before, or as part of the screen. This grid electrode opens „the valve," so to say, to the continuous flow of electrons — taking over the control of the electron flow passing from the photosensitive layer through a partially conducting dielectric layer to the collecting electrode, the so-called ..signal plate" throughout the scansion cycle — and acts as an amplifier. The time available for accumulation of charges is on the order of the number of picture elements; 2. the replacement of (Zworykin's) high insulation with the partially conducting dielectric layer which also allows continuous electron flow, and produces an increase in the capacitance of the condenser — i.e. new free charge carriers are produced In the semiconductor and in the metal-semiconductor junctions of the screen — and thus a further increase of