Modern Control Engineering

Harry Nyquist was born in Nilsby, Sweden in 1889. In 1907 he entered the United States to commence undergraduate study at the University of North Dakota. After graduating he moved on to Yale where he was awarded a Ph.D. in Physics in 1917. He then entered the Bell telephone Laboratories where he remained until he retired in 1954. Between 1920 and 1940 he published a series of papers on research in telecommunications which are arguably the most outstanding set of scientific contributions since Newton (apart from Einstein!).

At least three of his contributions would have been contenders for Nobel Prizes (if he had not been an Engineer).

The first of these was his work on 'Certain Topics in Telegraph Transmission Theory' (1928). In this he solved virtually all the fundamental problems in digital transmission. He set out the limitations for digital transmission over physical transmission paths, he showed how to design a transmission path to optimise digital transmission, and through his 'sampling theorem' he showed how to convert analogue signals such as telephony and television into digit streams and how to recover them again after transmission.

In the same year, with Johnson as joint author, he published the fundamental theory of the origins of noise in transmission systems. At about the time as he retired later workers in the Bell Laboratories succeeded in detecting the signature of the creation of the Universe, the radio noise generated by the 'Big Bang'. This work was dependent on Nyquist's earlier theoretical analysis of noise.

Finally, Harry Nyquist was engaged in studies of feedback amplifiers, which led to a simple method of assessing their stability, and also explained the phenomena of conditional stability. We now come across this work in the Nyquist Diagram and the Nyquist Stability Criterion.