Complete history of microwave technology (part 3). Turn of the century, detailing discoveries made by J.A. Fleming (diode tube) and J.C. Bose (short electromagnetic waves).

A lot was happening in microwaves around the previous turn of the century. J.A. Fleming, who had worked with Maxwell, Marconi, and Thomas Edison, invented an electrical valve', better known today as a diode tube. Fleming also came up with an equation that expressed the impedance characteristics of high frequency transmission lines in terms of measurable effects of electromagnetic waves.

Up until this point, focus had been on sending and receiving communication signals. As the new century progressed, scientists worked with longer and longer wavelengths to achieve greater and greater distances.

In India, however, J.C. Bose was working with shorter and shorter waves. In 1895, Bose gave his first public demonstration of electromagnetic waves, using them to ring a bell remotely and to explode some gunpowder.

The wavelengths he used ranged from 2.5 cm to five mm. He was playing at 60 GHz over one hundred years ago! Bose's investigations included measurement of refractive index of a variety of substances. He also made dielectric lenses, oscillators, receivers, and his own 'polarization device.'