Progress in Electrical Engineering was always dependent on progress in materials. For quite some time, electrical engineering meant electromechanicalengineering, and electrical products were made from "trivial" materials, as seen from a modern point of view. What was needed were cables, insulators, ferromagnetic sheet metal for transformers and generators, and a lot of metal for the general mechanics. A few applications centered around some mysterious materials - out of that grew electronics and electronic materials. But even then there were key materials:
- Cu wires of all kinds. Not so trivial - how do you make a insulated but still flexible wire?
- Insulating materials - plastics didn't quite exist yet. Mica was one of the key materials - there were mines for it!
- Graphite and tungsten were important, whenever things got hot, like the filament in the light bulb or in a vacuum tube.
- The "tube of Braun" - the "Braunsche Röhre" as it was known in Europe - the first cathode ray tube (CRT) in other words - needed complicated glass work and some ZnS as electroluminescent material
- Strange compounds like "phosphor bronze" were developed for contacts.
- And Selenium (Se) was important for rectifiers, although nobody quite understood how it worked.
The essential break through in the thirties was the vacuum tube; with it came electronics: Rectifiers, amplifiers, radio, black-and white TV, colour TV. It's not that long ago, but obviously long enough for some not to remember! The next break-through was called transistor; it happened in 1947. Integrated circuits followed around 1970, and since then we witness exponential growth with growth rates in the complexity of electronics (at constant prices) of up to 40% a year! A good (german) book covering this development in some detail is Hans Queissers "Kristallne Krisen".