Thermopile detectors are used to measure the temperature of objects at a distance by converting infrared (IR) radiation into an electrical signal. This single main functionality serves a raft of functions across industry and science, enabling high-precision non-contact temperature measurements of a near-limitless range of substrates. High-sensitivity thermopile sensors also compare favourably with other types of temperature sensor modules in terms of durability and stability, making them ideal for intensive and routine applications alike.

This article will explore the working principle of thermopile detectors and the various applications they serve in multiple industries.

What is the Working Principle of a Thermopile Detector?

Understanding thermopile detectors requires a cursory understanding of thermocouple technology. Thermocouples–the most prevalent type of electrical temperature-sensing element–comprise two dissimilar metal wires bonded to form a “hot junction” and a “cold junction”. When the joint is heated or cooled, it generates a weak voltage (V), also known as the Seebeck voltage, which corresponds to the change in temperature. There is also a proportionality factor to consider, but for the purposes of this article, it is enough to know that the voltage generated is directly proportional to the temperature difference between the hot and cold junctions.

Thermopile detectors comprise an array of thermocouples connected in a series. The underlying idea is to multiply the effect of each individual element. They can be considered a group of miniature thermocouple junctions–similarly divided into hot and cold junctions–which are composed of alternating n-type and p-type materials, referred to as “arms”.

The arm materials vary with different thermopile types. Thin film systems, for example, tend to comprise arms of antimony and bismuth, while silicon thermopiles comprise alternating n-type and p-type Poly-Silicon or n-type and Gold or Aluminum. The cold junctions are generally connected to the detector package and around the perimeter, while the hot junctions–which define the active area–are located in the center and coated with an energy absorber. These hot junctions are suspended on a thin membrane to thermally isolate them from the rest of the package. So, how does the array work?

As mentioned, the multiple thermocouples in a thermopile detector are connected in series, which means that the voltage difference generated by each one is added together to produce a total voltage output. This total voltage output is proportional to the temperature of the object being measured. Since the Seebeck effect is a relatively weak signal, thermopile detectors are equipped with voltage amplifiers to ensure the signal can be read by a meter or data acquisition (DAQ) system. A calibration factor or transfer function is then used to convert the signal into a legible temperature measurement.

Applications of Thermopile Detectors

Thermopile detectors have various applications in various industries due to their accuracy, stability, and durability. Some of the critical applications of thermopile detectors are listed below:

• Energy: Thermopile detectors are used for temperature control in boilers and heating systems. They are also used in solar panels for monitoring the temperature of the panels, ensuring that they operate at the optimal temperature for maximum efficiency.
• Automotive: Thermopile detectors are used for temperature sensing in engines, exhaust systems, and catalytic converters. They are also used for temperature monitoring in battery packs in electric vehicles.
• Aerospace: Thermopile detectors are used for temperature monitoring in spacecraft and satellites. They are also used in aircraft engines for temperature sensing and control.
• Medical: Thermopile detectors are used for temperature measurement in medical equipment, such as infrared thermometers. They are also used in non-invasive temperature monitoring in the human body, such as in fever detection.
• Industrial: Thermopile detectors are used for temperature control and monitoring in various industrial processes, including drying, baking, and heat treating. They are also used in industrial ovens and furnaces for temperature control.

Looking for Thermopile Detectors?

At Dexter Research Center, we lead the way in delivering infrared sensing solutions for various detection applications. For more information about thermopile detectors, refer to the technical papers section of our M5 Thin Film-based thermopile detector product page for a full Introduction to Thermopile Detectors. Should you have any further questions or require assistance, our knowledgeable team is here to help.