Thermal camera lenses measures temperature differences in a scene by imaging each resolved point to a corresponding pixel in a camera sensor. Each pixel is sensitive to radiant thermal energy, which changes the electrical resistance and enables measurement of scene temperature. These sensors are typically made using silicon CMOS technologies and are called micro-bolometers.
Bolometers were invented more than a century ago – the rise of semiconductor technologies led to the practical realization of arrays of pixels (µbolometers) that could be used to provide thermal contrast images of a scene. Honeywell invented the technology in the 1970s under a classified contract with the U.S. Department of Defense, which led to the development of long-wave infrared cameras (LWIR) for ISR (Intelligence, Surveillance, Reconnaissance). Portions of the technology were de-classified in the early 1990s and transferred to multiple commercial entities. Today, thermal camera lenses serves applications ranging from surveillance (defense and border control), medical diagnostics and remote temperature monitoring (fever detection) to nighttime driving.
Micro-bolometers are sensitive in the 7.5 – 14 µm wavelength range of thermal radiation. This part of the spectrum is invisible to human eyes and visible cameras (which rely on incident light or photons). Animals and humans have body temperatures that are typically different from other natural or artificial objects in the scene. Measuring these temperature differences can provide unique perception capabilities in various lighting and obscuration conditions, critical in automotive applications where pedestrian and animal detection at long range is essential for safety and autonomy.