Long-wave infrared cameras have the disadvantage that the sensor used in them requires constant cooling, which adds to the cost and complexity of the device. Now a new type of detector has been developed that functions at room temperature.

Traditional infrared cameras for wavelengths above five micrometers like it cold – the sensor used inside them has to be constantly cooled down to about -193°C. Uncooled imagers for the long-wave infrared range do already exist today, but they are mainly used in the military sphere.

 
This is now set to change thanks to research scientists at the Fraunhofer Institute for Microelectronic Circuits and Systems IMS in Duisburg, who have succeeded in producing an imaging sensor for the long-wave infrared range that functions at room temperature. ’We could be the first in Germany to offer this technology,’ said Dr Dirk Weiler, a 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 analogue signal and then digitised using an analogue/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’, Weiler explained. Because of that, complex and costly cooling is no longer required, opening up new areas of application for such devices.

’Mobile devices should benefit from the new development,’ said Weiler. The fact that the cooling mechanism is no longer needed will not only save weight; the battery power required will be reduced and the operating time of a mobile device will increase because no energy is needed for cooling. The potential uses of such mobile infrared cameras include fire fighting, where they could detect hidden hotspots or locate people in smoke-filled buildings.’

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