From Gordon Gould we move on to John Ambrose Fleming this week, whose invention is considered as a milestone in engineering. If Gould was involved in formulating the early ideas of a device which he named laser, Fleming was instrumental in creating the Fleming valve, also known as the thermionic valve or vacuum tube — a device that is perceived as a marker for the birth of modern wireless electronics.
Born at Lancaster in 1849, Fleming was the oldest of seven children. He didn’t take to schooling until he was ten, till which time he was tutored at home by his mother. Once at school, he realised that he wanted to become an engineer.
Even at the young age of 11, Fleming set out to work from his own workshop. He built boats and engines and was even successful in making his own camera. His family’s financial situation, however, meant that he couldn’t be trained to become an engineer. What he lacked monetarily, he decided to make up for it through his work.
After completing his B.S. degree, he earned a doctorate from the University of Cambridge. He taught at Cambridge University and the University of Nottingham and also went on to become the first professor and chair of electrical engineering at the University of Nottingham and University College of London, a position that he held for over four decades.
Edison Effect Before we delve into the Fleming valve, however, we would first have to look into Edison Effect. In 1883, following his groundbreaking work on incandescent lamps, Thomas Alva Edison began experimenting with it. On introducing an electrode into the bulb, Edison realised that it could carry a current when it was a positive potential relative to the filament.
Fleming, who worked as a consultant for the Edison Electric Light Company and also an advisor for Marconi’s Wireless Telegraphy Company, was well aware of the Edison Effect and had also investigated the same himself. He used this to rectify a weak wireless signal.
The Eureka moment In October 1904, Fleming had what he describes as “a sudden, very happy thought”. He knew that the oscillations of a wireless signal were too rapid and it was for this reason that the meters indicated zero, which was the mean value.
He realised that if the currents were rectified (converting alternating current, which reverses direction, into direct current, which is unidirectional), the signal can be read. Fleming had his assistant test out this idea of his based on Edison Effect and it worked.
On November 16, 1904, Fleming applied for a patent for this device which he initially named oscillation valve, but later came to be known as Fleming valve. This diode was an important precursor to the three-element triode, created by American engineer Lee DeForest in 1906.
Fleming is often called the father of modern electronics because the vacuum tube that he had invented was the ancestor for all electronic tubes. These tubes laid the basis for radio communications and the electronics industry, before eventually being replaced by transistors in the second half of the 20th century.
Reach the writer at ganesh.a.s.@thehindu.co.in
