Process Could Make IR Lenses up to 70 Percent Cheaper

A new fabrication process that lowers the cost of infrared lenses for thermal cameras by 70 percent could make such devices more attractive for integration into cars as driver warning systems.

Current thermal imagers, used mostly in luxury-class vehicles, cost around €2000. These devices detect infrared rays — for instance, the heat emitted from an animal crossing the road — and warn drivers of danger ahead through an acoustic signal or warning light.

Normally, infrared lenses are made of crystalline materials like germanium, zinc selenide or zinc sulfide. These materials are very expensive and can only be processed mechanically — it takes grinding, polishing or diamond-turning to shape them correctly, which involves high processing costs.

(Above) Thermal image, taken with pressed lenses in a test camera. (Below) Pressed lenses made of chalcogenide glass. (Image: © Fraunhofer IWM)

Now researchers at the Fraunhofer Institute for Mechanics of Materials (IWM) have turned to amorphous chalcogenide glass to manufacture these microbolometer infrared lenses.

“Instead of crystalline materials, we use the amorphous chalcogenide glass, said Dr. Helen Müller, a scientist at IWM. “Its softening temperature — that is, the temperature at which it can be formed — is low. Therefore, we can form it using non-isothermic hot stamping.”

The chalcogenide glass is formed between two pressing tools, similar to a waffle iron, that determine the form of the required lenses. In contrast to conventional processed optics, it does not require further refining. The lenses manufactured this way exhibit the same optical imaging quality as those that are polished.

The scientists now want to refine the process further toward cost-effective mass production.

Applications for the microbolometers are not limited to the automotive market. They could also send an alarm to relatives when an elderly person has fallen at home; they could also oversee and monitor the production process of various products to ensure that necessary temperatures are maintained and to warn employees who are spending time in danger zones. In residential buildings, the device could detect energy leaks.

For more information, visit: www.fraunhofer.de