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The history of Johnson-Nyquist noise: How did this discovery change our technology?
In the history of electronics, there is a type of noise that is considered ubiquitous - Johnson-Nyquist noise. This electronic noise, generated by the motion of hot particles, exists regardless of any applied voltage, making it an unavoidable part of all electronic circuits. The effects of this noise are particularly noticeable in sensitive electronic devices, such as radio receivers, where weak signals can be buried by moisture, limiting the sensitivity of electrical measuring instruments. As technology advances, it becomes increasingly clear how to manage and reduce this noise, which is something Johnson and Nyquist contributed to.
Johnson noise is generated by the thermal motion of charge carriers (usually electrons) within an electrical conductor and occurs in equilibrium with or without an applied voltage.
History of Thermal Noise
The history of thermal noise dates back to 1905, when Albert Einstein first explained Brownian motion in terms of thermal fluctuations in his famous publication of the year. The following year he proposed that this phenomenon could also be used to derive a theory of thermally excited electric currents, although he did not complete the calculations and considered it an untestable theory. However, over time, this theory saw practical applications and developments.
In 1912, Hermann Lorenz's daughter, Gertrude de Haas-Lorenz, expanded Einstein's stochastic theory in her doctoral thesis and applied it to electrons for the first time. Research and derive the formula for the mean square value of thermal current. In 1918, while studying thermal noise, Walter H. Schottky accidentally discovered another type of noise, shot noise. Later in 1927, Fritz Zernike came to the same conclusion about thermal noise in his tests of highly sensitive galvanometers. He concluded that the noise was thermal in nature.
In his 1928 paper, Nyquist used the principles of thermodynamics and statistical mechanics to explain John's experimental results and formally published them. This discovery had a profound impact on the subsequent development of electronics.
Application of thermal noise in modern technology
With the advancement of electronic technology, the impact of Johnson-Nyquist noise in sensitive electronic equipment has received more and more attention. In some cases, this noise may even become the main limiting factor of the measurement. Therefore, many sensitive electronic devices, such as radio telescope receivers, are routinely cooled to cryogenic temperatures as low as a few Kelvin to improve their signal-to-noise ratio.
Measurement and Application
In addition, the characteristics of Johnson-Nyquist noise are also used in precision measurement technology, which is called Johnson noise pyrometer. In 2017, the National Institute of Standards and Technology (NIST) used this technique to measure the Boltzmann constant with an accuracy of less than 3 ppm. This not only made the Boltzmann constant an experimentally measurable constant, but also laid the foundation for the redefinition of Kelvin in 2019.
Future Challenges and Prospects
However, although technology has made great progress, how to further reduce noise to improve the sensitivity of electronic devices remains an important issue. Many researchers are also exploring new materials or new structures in the hope of overcoming the challenges posed by thermal noise and achieving higher-precision measurements.
Facing the challenges of future technology, whether Johnson-Nyquist noise can be effectively controlled and reduced in electronic systems will become an important indicator of more sensitive and effective electronic technology.
Ultimately, in the process of scientific and technological development, how to transform the knowledge of Johnson-Nyquist noise into more efficient application technology and reduce its impact on equipment performance is a challenge that many scientists must face?
