What Is a Bolometer?

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  • Written By: J.M. Willhite
  • Edited By: C. Wilborn
  • Last Modified Date: 16 April 2015
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A bolometer is an instrument used to detect and measure minute quantities of electromagnetic radiation. Also called actinic balances, bolometers measure electromagnetic radiation in its various forms, from radio waves to ultraviolet radiation and gamma rays. The operational principle of the bolometer has also been adapted for use in physics and particle detection.

Invented by American astronomer Samuel Pierpont Langley in the late 19th century, the first bolometer was used in conjunction with a telescope to measure infrared radiation on astronomical objects, namely the Moon. The prototype was basic in design. It consisted of two chambers outfitted with platinum strips which formed a Wheatstone bridge connected to a galvanometer and battery. Soot covered strips, forming the bridge, were arranged such that one was left exposed while the other was shielded from radiation exposure. The exposed strip's temperature would increase when it came into contact with the electromagnetic radiation, altering its electrical resistance and essentially creating a temperature sensor.

A cold electron bolometer (CEB) is a highly sensitive device that detects cosmological radiation. The bolometer's superconducting-insulator-normal (SIN) metal tunnel junction is what sets it apart from other bolometers, because its energy loss is used to cool the absorber. A hot electron bolometer (HEB) is a device used to measure sub-millimeter and far-infrared radiation which cannot be measured by the cold electron bolometer.


A microbolometer is type of bolometer adapted to function as an infrared detector in a thermal camera, commonly known as a Forward Looking Infrared (FLIR) camera. This type of camera works on the same principle as the traditional bolometer, and measures infrared radiation with wavelengths between 8 and 13 microns. The electrical resistance recorded by the camera is translated into temperatures, which are used to create an image.

There are two main disadvantages associated with the bolometer, and both involve residual energy. Lacking discriminatory properties, this device does not differentiate between ionized and non-ionized particles. When used as a thermal detector, a bolometer does not directly dispel the energy collected by the absorber and, therefore, does not immediately reset.

A branch of physics known as particle physics, which studies the basic elements of radiation, uses the term bolometer in reference to an instrument known as a particle detector. The particle detector works on the same principle as Langley's bolometer, and is used to identify high-energy particles. Calorimeters, scintillation counters, and gaseous ionization-type particle detectors are typically used for the purpose of measuring energy associated with radiation and particle characteristics.



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I wonder if this could be used to measure electric power at 60 cycles flowing next to a conductor.

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