IR Imaging at Room Temperature

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Because infrared cameras are able to register thermal radiation, such as body heat, they would be ideal for improving visibility while driving an unlit country road. The problem is that for wavelengths ranging above 5 µm these cameras like it cold — a constant cool-down temperature of –193 ºC — adding to the cost and complexity of the device. While uncooled imagers for the long-wave IR range do exist, they are mainly used in the military and are not readily available in the commercial market, but according to research scientists at the Fraunhofer Institute for Microelectronic Circuits and Systems (Fraunhofer IMS), this is about to change.

This photo was taken by an infrared camera equipped with a temperature-sensitive detector. The image shows the various temperature fields. (Image: Fraunhofer IMS)

The research team out of Duisburg, Germany, has succeeded in producing an imaging sensor for the long-wave infrared range at room temperature. “We could be the first in Germany to offer this technology,” said Dr. Dirk Weiler, scientist at the IMS.

At the heart of the IRFPA (infrared focal plane array) sensor is a microbolometer — a temperature-sensitive detector that absorbs long-wave infrared light. To produce a two-dimensional image, several microbolometers are combined to form an array. If the microbolometer absorbs light from a heat source, its interior temperature rises and its electrical resistance changes. A readout chip then converts this resistance value directly into a digital signal. Previously this was not possible without a further intermediate step — normally the electrical pulse is first translated into an analog signal and then digitized using an analog/digital converter.

“We use a very specific type of converter, a sigma-delta converter, in our imager. This has enabled us to produce a digital signal directly,” said Weiler.

As complex and costly cooling is no longer required, further areas of application become feasible beyond the automotive sector. “Mobile devices in particular should benefit from the new development,” he added.

The fact that the cooling mechanism is no longer needed not only saves weight, but also saves energy. The potential uses of mobile IR cameras include firefighting, where they could detect hidden hotspots or locate people in smoke-filled buildings.

Initial laboratory tests with the new sensor element were successful. The research scientists have already been able to produce a number of infrared images.

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Published: July 2010
thermal radiation
The emission of radiant energy in which the energy emitted originates in the thermal motion of the atoms or molecules of the source material.
absorbing lightbody heat temperaturecamerasdefenseDr. Dirk WeilerEuropefive micrometersFraunhofer Institute for Microelectronic Circuits and Systems IMSGermanyImaginginfrared camerasinfrared imaginglow-wave infrared rangemicrobolometersminus 193 degrees CelsiusResearch & TechnologySensors & Detectorssigma-delta converterthermal radiation

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