The history of thermopiles

General information about thermopiles and thermopile sensors is provided below. Some terms are linked to the the free internet encyclopedia www.wikipedia.org, where more cross-referenced information can be found.

The figure above illustrates the principle of a thermocouple. Two different thermoelectric materials (could be metals, alloys or semiconductor materials) are combined into a circuit.

Thermopiles convert thermal energy (temperature differences) to electrical energy. Thermopiles are built from a series of so called thermocouples, i.e. two leads (also referred to as legs) of different/disparate materials (typically metal/alloy or semiconductor materials) attached to each other at two junctions. When the junctions are held at different temperatures, an electrical voltage is produced in the circuit. The physical principle of this is called the thermoelectric effect, or the Seebeck effect. This voltage is proportional to the applied temperature difference. Hence, the thermoelectric circuit can be used as a heat flux sensor, a differential temperature sensor, or a thermal generator. They are also commonly used as thermal radiation sensors for infrared light. Depending on the application, other thermal radiation sensors, such as bolometers and pyrometers, can be used.

In 1821 Thomas Johan Seebeck found out that a magnetic field was produced when a thermal gradient was applied to a circuit built from two metals. Later, he found out that the reason for this was that an electrical current was generated in the circuit. The Italian physicist Leopoldo Nobili invented the first thermopile device in 1835. The purpose was to measure radient heat, and his thermocouple leads were built from antimony and bismuth metals. Several further constuctions soon followed. Of the many different motivations, one interest purpose was to be able to convert heat (from fire or gas) into electricity to obtain a simple electrical energy source.