Vladimir Zworykin is -- or should be- -famous for his achievements in the field of Opto-Electronics.
WHO? Never heard of him? Well, it's certainly true that Zworykin, a pioneer of electronic television, isn't as well known on this side of the Atlantic as he is on the other, but that's not really an excuse.
Zworykin was born in 1889 in Imperial Russia and during the first part of World War One served with distinction in the Radio Corps of the Imperial Russian Army. Then came the Revolution, the army was disbanded in confusion and, like many others, Zworykin escaped while escape was still possible. Emigrating to the USA in 1919, he joined the Westinghouse Electric Corporation in Pittsburg, and launched his brilliant research career. In 1923, he patented the device which provided the first genuine electronic television service. It was the Iconoscope -- the first TV camera tube.
The Iconoscope has long been out of date and only survives in a few museums, but it was the mainstay of TV broadcasting from 1936 until well after the second World War. Briefly, the idea was that an image of a scene was projected on to a photosensitive sheet of material inside an evacuated tube. The sheet (or target) wasn't continuous but consisted of tiny dots of conducting material surrounded by insulation, so that each dot became electrically charged by the action of the light falling on it. A beam of electrons was then scanned across the sheet and the differences in charge at various places on the conducting target caused the electron beam to be modulated at the final anode, after the beam had been reflected from the target.
Problems
The principle was fairly simple, though not well understood at the time and depended on being able to construct a target with just the right amount of leakage between conducting sections. This was not possible then, though if a bit more development work had been done, television wouldn't have been sidetracked into mechanical methods left over from the 1880's.
Zworykin, totally committed to all-electronic television, patented a receiver in 1924 and continued development work at Westinghouse. A patent for a colour TV system followed in 1928 and, in 1929, RCA were so impressed by Zworykin's improved working model of a receiver that they offered him the plum job of Director of Research at their Princeton research centre (now at Camden). The years that followed were extremely exciting for the future of TV. Demonstrations of mechanical systems had caused considerable sums of money to flow into a method which would prove to be a dead end. This had the twin effects of making fewer resources available for research into electronic TV and at the same time convincing many people that television simply wasn't worth having. At RCA, however, Zworykin assembled a team whose objective was to ensure that they came up with the first all-electric TV Meanwhile in Hayes, Middlesex, the EMI Company (then HMV) was working on precisely the same project, with the advantage of having two outstanding research engineers- - McGee and Blumlein. McGee (now Professor McGee) was in charge of camera tube development, Blumlein was in charge of circuit development.
Everyone a Winner Who won? We all did. One of the remarkable things about that period was the way in which everything went in synchronism (almost) at the two places. If we take the end of the race as being the first public TV broadcast then the EMI team, with the close co operation of the BBC, just made it. No-one on the other side of the pond is ever going to admit that, though! As in so many other cases, however, RCA was able to produce and sell TV receivers on a scale which greatly outstripped the UK (there were about 700 receivers in London in 1939) and it was Zworykin's team that undoubtedly made the true mass production of TV receivers a reality.
By the outbreak of war between Japan and the USA, Zworykin had taken out another significant patent. It was for a device which he called an 'electric eye', but which we now recognize as an electron microscope. The development of the electron microscope did not progress much further until after the War, but the basic principles remain those laid out in Zworykin's patent. Our understanding of materials, particularly the nature of semiconductors, owes much to this remarkable instrument.
The onset of war inevitably caused research laboratories to turn away from television. Zworykin's team worked extensively on infra-red imaging tubes, the 'sniperscopes' which can sometimes still be bought as 'war surplus'. The basic principle, illustrated in Figure 1, was remarkably simple. A photocathode was made which was sensitive to infra-red (heat) radiation so that electrons were emitted from any part of the photocathode struck by infra red. These electrons could then be accelerated by a high voltage and used to form a visible image on a phosphor screen. Using a lens to focus the infra-red rays onto the photocathode, the tube produced a visible image from the invisible infra-red.
Early sniper scopes were relatively insensitive but were quite capable of detecting hot engines or guns, allowing artillery to be aimed at night. Towards the end of the war more sensitive versions were developed, capable of detecting human bodies against a colder background. The most recent devices allow us to see with almost the same resolution and contrast range as we would expect from television!
1. Principle of the 'sniper scope'. A photocathode emits electrons when struck by infra-red (heat) rays. The electrons are accelerated to a phosphor screen to produce a visible image, allowing the user to literally "see in the dark".
Images Intensified
It was Zworykin's work which made this and so many other modern light detectors possible. Secondary emission multiplication, a method of noiseless amplification and another first for Zworykin, makes use of an effect which takes place when a fast moving electron hits the surface of an insulator or conductor. When both the speed of the electrons and the voltage between the source of the electrons and the surface are correctly adjusted, each electron which hits a surface can knock off several others. This is where the 'multiplier' comes from; each time this happens, the number of electrons in the beam is being multiplied. Several stages of multiplication can change of current from a fraction of a micro-amp to one of several milliamps and without any noise signal being introduced. This principle was to be the key to the more sensitive camera tube, the image orthicon, which superseded the iconoscope and its offspring, the super-iconoscope. Scientific investigation was also to benefit from photomultiplier light detectors, which also use the secondary emission effect.
Zworykin's lifetime of research was not overlooked by his colleagues or by RCA He was appointed an Honorary Vice President of the company in 1950 and became Director of the Rockefeller Medical Electronics Institute (now Rockefeller University) in New York City. As the final seal of esteem, in 1967 the National Academy of Sciences awarded him their highest honor, the National Medal of Science.
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(adapted from: Hobby Electronics magazine)
Also see:
- Switched Tuned Radio
- Quick Project: SIMPLE TIMER
- INTELLIGENT NI-CAD CHARGER
- INTRUDER CONFUSER