Brief History of the Seebeck Effect
Thermocouple Principles—the Seebeck Effect and Seebeck Coefficient
one day ago by Dr. Steve Arar
Learn about the Seebeck effect, the Seebeck coefficient, and their relationship with temperature.
Thermocouples are often one the most commonly used temperature sensors today. A thermocouple consists of two dissimilar conductors soldered or welded together at one end. These ubiquitous devices use the Seebeck effect to measure temperature.
This article takes a look at the Seebeck effect, laying the foundation for a discussion of thermocouples in the next article in this series.
Brief History of the Seebeck Effect
In 1822, Thomas Seebeck, a German physicist, noticed that a loop created by connecting two semicircular pieces of bismuth and copper can deflect a nearby compass when there is a temperature gradient along the loop (Figure 1).
A high-level representation of Seebeck's accidental thermo-magnetism discovery.
Figure 1. A high-level representation of Seebeck's accidental thermo-magnetism discovery. Image used courtesy of Analog Devices and Linear Technology
Seebeck’s friend, Hans Christian Oersted, who had published his discovery of the connection between electricity and magnetism in 1820, suggested that the needle should have been moved by a magnetic field generated by an electric current flowing through the loop. This was the first thermoelectric effect discovered. At that time, it was not easy to develop an explaining theory for the observed physical phenomenon because even basic concepts such as voltage, current, and resistance were not clearly formulated then. In fact, the mechanisms of this phenomenon were not well understood until the discovery of electrons in 1897.
It is also worthwhile to mention that the experiments conducted by Luigi Galvani, the discoverer of animal electricity, were also related to the Seebeck effect. In 1786, Galvani observed that the muscles of a dissected frog contract when touched by dissimilar metal probes.
Temperature Effects on Electrons—Electron Redistribution
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TECHNICAL ARTICLE
Thermocouple Principles—the Seebeck Effect and Seebeck Coefficient
one day ago by Dr. Steve Arar
Learn about the Seebeck effect, the Seebeck coefficient, and their relationship with temperature.
Thermocouples are often one the most commonly used temperature sensors today. A thermocouple consists of two dissimilar conductors soldered or welded together at one end. These ubiquitous devices use the Seebeck effect to measure temperature.
This article takes a look at the Seebeck effect, laying the foundation for a discussion of thermocouples in the next article in this series.
Brief History of the Seebeck Effect
In 1822, Thomas Seebeck, a German physicist, noticed that a loop created by connecting two semicircular pieces of bismuth and copper can deflect a nearby compass when there is a temperature gradient along the loop (Figure 1).
A high-level representation of Seebeck's accidental thermo-magnetism discovery.
Figure 1. A high-level representation of Seebeck's accidental thermo-magnetism discovery. Image used courtesy of Analog Devices and Linear Technology
Seebeck’s friend, Hans Christian Oersted, who had published his discovery of the connection between electricity and magnetism in 1820, suggested that the needle should have been moved by a magnetic field generated by an electric current flowing through the loop. This was the first thermoelectric effect discovered. At that time, it was not easy to develop an explaining theory for the observed physical phenomenon because even basic concepts such as voltage, current, and resistance were not clearly formulated then. In fact, the mechanisms of this phenomenon were not well understood until the discovery of electrons in 1897.
It is also worthwhile to mention that the experiments conducted by Luigi Galvani, the discoverer of animal electricity, were also related to the Seebeck effect. In 1786, Galvani observed that the muscles of a dissected frog contract when touched by dissimilar metal probes.
Temperature Effects on Electrons—Electron Redistribution
Thanks to the efforts of many great minds in the history of science, we have a better understanding of physical phenomena such as the Seebeck effect. A detailed discussion of the theory behind the thermoelectric effects is beyond the scope of this article; however, a simplified intuitive explanation can still provide us with a basic understanding of this effect.
Today, we know that an electric field or thermal energy can liberate some electrons from the valence band to the conduction band of a conductor. While the valence electrons are bound too tightly to atoms to contribute to the electric current, the electrons in the conduction band have enough energy to move freely in the material. When a temperature difference exists between the two ends of a metal bar, the hot region produces more free electrons. The electrons at the hot end are also more thermally agitated than the electrons at the colder end of the conductor. These thermally agitated electrons diffuse more rapidly than lower-energy electrons.
A higher concentration of the thermally agitated electrons in the hot end of the wire causes the diffusion of electrons from the hot end to the cold region. As a result of this thermally-induced electron diffusion, the hot region becomes positively charged compared to the opposite end of the conductor. Figure 2 shows how a temperature difference redistributes electrons and makes them travel from the hotter region to the colder end.
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