. 7 6 http://www.radiomuseum.org/ 7 http://www.oldtechnology.net/components.html Physical Layer Connectivity Figure 2.4 1942 Radio with a printed circuit board. Reproduced by permission of the Science Museum/SSPL 10 439 336. Similarly, valve-based two-way radios can still be found operating in some markets or in the hands of enthusiastic collectors. However, although valve performance continued to improve there was a general recognition by the middle of the 1930s that a lower-cost way to generate, amplify and switch signal energy would be needed to achieve a step function reduction in delivery cost both in wireline and wireless networks. The answer was to find a way to harness the unique properties of semiconductors, materials that can act as a conductor and an insulator. 1876 a German physicist Ferdinand Braun, 8 a 24-year-old graduate of the University of Berlin demonstrated a rectification effect that could be created at the point of contact between metals and certain crystal materials, in effect a semiconductor device. Just over 70 years later in 1947 John Bardeen and Walter Brattain built the first transistor, a device with a gate that could be used to control electron flow. Eleven years later in 1958 Jack Kilby invented the integrated circuit and in 1961 Fairchild Semiconductors produced the first planar transistor in which components could be etched directly onto a semiconductor substrate. Fifty years later these devices remain at the heart of every electronics and telecommunications product. So, we have a historical time span of one hundred and seventy years from the 1840s to the present that takes us from Cooke and Wheatstone's telegraph to the modern internet all based on the mechanics of moving electrons around or more accurately harnessing and transferring the releasing the power of electrons in electronic circuits. http://www.computerhistory.org/semiconductor/timeline/1874-semiconductor.html Making Telecoms Work 2.6.1 Graphene - The New Enabler? At some stage substitutes for silicon may also become a