Hi-tech security windows

A special polymer window coating can detect and identify potential building break-ins

Potential burglars will have less chance of breaking into buildings through hi-tech security windows developed by researchers in Germany.

The team from the Fraunhofer Institute in Germany has developed a unique security system that enables window panes to detect movements with a special polymer coating.

The coating, developed at the Fraunhofer’s Applied Polymer Research department in Potsdam-Golm, contains nanoparticles that convert light into fluorescent radiation.

A UV lamp illuminates the window panes and generates fluorescent radiation in the coating. This radiation is channelled to the edges of the window where it is detected by sensors. Several of these sensors are installed on four sides of the window frame.

The sensors, which are regular solar cells, convert photons from the UV lamp into current. When a person steps in front of the window, it prevents the light from reaching some of the sensors and therefore their current stops. The sensors wirelessly relay this currency information to a computer program, which alerts security officials of the potential intruder.

Tonino Greco, one of the Fraunhofer researchers involved with the development, said: ‘If several sensors are used, you can determine from where and how fast a person or thing has gone past the window.’

The sensors can also help determine the size of an object. A small object, such as a bird, would only affect a few sensors, while a person would affect many more. Therefore, the system is less prone to false alarms.

Additionally, built-in software prevents the sensors from reacting to light from passing cars. The software, developed by Fraunhofer researchers at the Institute’s Computer Architecture and Software Technology FIRST department in Berlin, enables the system to distinguish between the frequency of the UV lamp and the slowly changing light from a passing headlight.

Greco added: ‘The UV light has a certain frequency modulation and that modulation can be seen in the resulting current. The headlights from a passing car have a different frequency and the software program filters out this frequency so that only the radiation from the lamp is detected.’

The Fraunhofer team has received patents for its technology, but Greco said there are still some details his group would like to keep secret. One particularly sensitive portion of the technology is the window’s special polymer coating. Greco explained that it was a challenge for his team to find the right nanoparticles to incorporate into the plastic.

‘We needed nanoparticles that absorb only in the UV light and radiate in the visible light,’ he said. ‘There are many nanoparticles that absorb in the visible light but those particles would give the coating a colour. We needed the coating to be completely transparent.’

The researchers also had to develop a way to incorporate the nanoparticles into the coating. ‘Nanoparticles usually tend to agglomerate,’ Greco added. ‘When they agglomerate they form bigger particles — this causes the polymer to haze and lose its transparency.’

Greco said the team has developed a technique that mitigates this problem so that such polymer coatings can be applied to windows during the manufacturing process or retrofitted later. The cost-efficient process works by spraying the coating onto windows by airbrush or gluing it on as a film. The team has developed a demonstrator system and now plans to optimise the dyes and their concentration in the coating.

Siobhan Wagner