Continuous monitoring of UV exposure

UV lamps are used to cure coatings and adhesives in many industrial manufacturing processes. And special sensors are used to measure the intensity of the UV light applied to these surfaces. But because these sensors age too quickly, they can only be used to record intermittent measurements.

Fraunhofer researchers have developed a new generation of sensors capable of continuously monitoring UV intensity. These devices will be presented for the fi rst time at the Sensor + Test trade show in Nuremberg, from May 14 to 16 (Hall 12, Booth 537).

“UV exposure” is a term that tends to ring alarm bells, as most people associate it with unpleasant consequences such as sunburn and the risk of skin cancer. But ultraviolet (UV) light can also be beneficial, or indeed essential: the human body needs it to produce vitamin D. Industry, too, makes use of UV light, for example to cure adhesives or the coatings applied to food packaging, and also to disinfect water. On the other hand, surfaces can be damaged if they are exposed to too much UV light, and poorly regulated UV lamps also waste energy and generate excessive amounts of ozone. UV sensors are therefore used to optimize light intensity.

Usually these sensors are made of silicon or silicon carbide. The problem with silicon sensors is that they only deliver useful results if visible light is excluded from the measurement by external filters. Unfortunately, the filters used are very expensive and not particularly resistant to ultraviolet light. So to reduce aging, measurements can only be taken intermittently, as snapshots. Silicon carbide sensors have the advantage of being able to withstand longer exposure to UV light, but they only operate in a narrow spectral band. In the majority of industrial curing processes, it is the longer wavelengths that are of interest – precisely the area in which these sensors are least accurate.

Researchers at the Fraunhofer Institute for Applied Solid State Physics IAF in Freiburg have now developed a new UV sensor in collaboration with colleagues at the Fraunhofer Institutes for Manufacturing Technology and Advanced Materials IFAM, for Optronics, System Technologies and Image Exploitation IOSB, for Silicon Technology ISIT and for Physical Measurement Techniques IPM. “Our sensor is based on aluminum gallium nitride technology and can withstand continuous exposure to UV light without damage,” says IAF project manager Dr. Susanne Kopta. “This enables it to be used not only for intermittent snapshots but also for permanent inline monitoring.” A sapphire wafer serves as the substrate for the sensors. The researchers apply epitaxial growth to deposit layers of the active material onto the substrate, in other words the layers have a crystalline structure.

More details can be found at the following link: https://cordis.europa.eu/wire/index.cfm?fuseaction=article.Detail&rcn=36129