Harry Nyquist (1889–1976) was a Swedish-American physicist and electrical engineer whose theoretical contributions to telecommunications laid essential groundwork for the digital age. His sampling theorem and work on signal transmission directly influenced Claude Shannon’s information theory and remain fundamental to modern digital technology.
Early Life and Education
Nyquist was born on February 7, 1889, in Nilsby, Sweden. In 1907, at age 18, he emigrated to the United States, part of the great wave of Scandinavian immigration to America. He earned a Bachelor of Science (1914) and Master of Science (1915) in electrical engineering from the University of North Dakota[1].
Continuing his education, Nyquist received his Ph.D. in physics from Yale University in 1917. That same year, he joined the American Telephone and Telegraph Company (AT&T), beginning a 37-year career that would profoundly shape telecommunications.
The Sampling Theorem
Nyquist’s most famous contribution came through two landmark papers. In 1924, he published “Certain Factors Affecting Telegraph Speed,” analyzing the relationship between telegraph transmission speed and signal values. His 1928 paper “Certain Topics in Telegraph Transmission Theory” established what became known as the Nyquist-Shannon sampling theorem[2].
The theorem states that to accurately reconstruct a continuous signal from discrete samples, the sampling rate must be at least twice the highest frequency component in the signal. This principle—the Nyquist rate—is fundamental to:
- Digital audio: CD quality requires sampling at 44.1 kHz (twice the ~20 kHz upper limit of human hearing)
- Digital video: Frame rates and resolution depend on Nyquist principles
- Telecommunications: All digital communication systems use Nyquist sampling
- Medical imaging: MRI, CT scans, and ultrasound rely on proper sampling
Influence on Information Theory
Nyquist’s papers, along with work by R.V.L. Hartley, are cited in the opening paragraph of Claude Shannon’s revolutionary 1948 paper “A Mathematical Theory of Communication.” Shannon himself noted that Nyquist stated the sampling theorem, while Shannon later provided the mathematical proof[3].
Other Major Contributions
Thermal Noise
Nyquist derived the formula for calculating thermal noise (also called Johnson-Nyquist noise) generated by resistors—essential for designing low-noise amplifiers and sensitive electronic circuits.
Nyquist Stability Criterion
In 1932, Nyquist developed a method for determining when negative feedback amplifiers are stable. The Nyquist stability criterion became crucial to control systems engineering and was used during World War II for artillery targeting systems.
Facsimile Technology
Nyquist developed an early method for transmitting photographs over telephone lines—the principles underlying modern fax machines.
Recognition and Legacy
Nyquist received the IEEE Medal of Honor in 1960 “for fundamental contributions to a quantitative understanding of thermal noise, data transmission and negative feedback.” He held 138 patents related to telecommunications[1].
He died on April 4, 1976, in Harlingen, Texas. The Nyquist rate, Nyquist frequency, Nyquist plot, and Nyquist-Shannon sampling theorem all bear his name—testaments to contributions that made the digital revolution possible.
Sources
- Britannica. “Harry Nyquist.” Biography and achievements.
- Wikipedia. “Nyquist-Shannon sampling theorem.” History and mathematical foundations.
- IEEE Information Theory Society. “Claude E. Shannon.” Nyquist’s influence on Shannon.