Thermopile

A thermopile is a device that converts thermal energy into electrical energy using the Seebeck effect. It consists of many thermocouples connected in series, with the hot junctions mounted on a common surface that absorbs or is heated by incident energy and the cold junctions held at a reference temperature. When a temperature difference exists between the hot and cold junctions, each thermocouple generates a small voltage, and the series connection sums these voltages to produce an output proportional to the absorbed heat flux or radiant power.

In infrared radiometry, thermopiles act as detectors. An infrared-absorbing surface on the hot side converts incident infrared radiation into heat, triggering the thermocouples. The device typically includes cold-junction compensation and signal-conditioning electronics to yield a stable DC output, often in the millivolt range, suitable for amplification and measurement. Thermopiles are used as non-contact infrared thermometers, gas analyzers, flame detectors, and energy-monitoring sensors, as well as for calorimetric and radiant-heat measurements.

Construction features vary, but most thermopiles comprise many junctions bonded to a substrate, enclosed in a housing with an optical window or filter. They offer robustness, operate without cooling, and cover wide temperature ranges, making them practical for handheld devices and industrial sensors. Their main limitations include modest response speed compared with some photodetectors, low output voltage requiring amplification, and the need for calibration and temperature compensation to maintain accuracy.