mple, in the 1880s in the USA Thomas Alva Edison was experimenting with different types of filament to try and create a light bulb that would last more than a few hours, deciding by a process of trial and error and observation that the best option was a carbon filament operating in a near vacuum. Edison, however, also famously observed and questioned why an uneven blackening OC- curred within the glass bulb particularly near one terminal of the filament. Adding an extra electrode within the bulb he observed that a negative charge flowed from the filament to the electrode and that the current from the hot filament increased with increasing voltage. Al- though the phenomenon that came to be known as thermionic emission had been observed a few years earlier by Frederick Guthrie in Britain, Edison was the first to measure it. The effect was then explained and given a name (the electron) by JJ Thomson in 1897 but was referred for a number of years as the Edison effect. Edison was also witnessing the effect of photonic energy. This could be regarded as a light-bulb moment in more senses than one. The British physicist John Ambrose Fleming working for the British Wireless Telegraphy company then discovered that the Edison effect could be used to detect radio waves and produced the first two element vacuum tube known as the diode, patented in November 1904 and shown in Figure 2.1. Three years later the concept was improved upon by the American Lee de Forest by adding an additional grid between the anode and cathode to produce a device, the triode valve that could either amplify or oscillate. This is shown in Figure 2.2. The telecoms industry now had an enabling component technology that meant that tuned circuits could be built that would be capable of concentrating transmission energy within a discrete radio channel, the foundation of the radio broadcasting industry and two-way radio communication. 5 It might be argued that man-made materials are fundamentally combinations of natural ingredients. Physical Layer Connectiv