Windows and doors as sensors

Charles T. Troy, charlie.troy@laurin.com

A motion sensor developed by two Fraunhofer institutes, Applied Polymer Research (IAP) in Potsdam-Golm and Computer Architecture and Software Technology (FIRST) in Berlin, offers a novel security method. The technology enables windowpanes and glass doors to detect movement, thanks to a special coating. If anything changes in front of the pane, or if a person sneaks up to it, an alarm signal is sent to security.

“The glass is coated with a fluorescent material,” said IAP group manager Dr. Burkhard Elling. “The coating contains nanoparticles that convert light into fluorescent radiation.”

Here’s how it works: A UV lamp “illuminates” the windowpanes, generating fluorescent radiation in the coating. The radiation is channeled to the edges of the window, where it is detected by sensors. Simple applications require only one sensor. As with a light barrier, if someone steps into the beam, less light reaches the coating and less fluorescent radiation is produced. When several sensors are installed on all four sides of the window frame, conclusions can be drawn as to how fast and in what direction an object is moving. Size, too, can be estimated by the sensors. The threshold for the alarm can be set so that small moving objects – for instance, birds – do not trigger an alarm.

The sensors also do not react to light from passing cars because the researchers at FIRST developed a software application that can interpret light signals. This enables the system to distinguish between the frequency of the UV lamp and the slowly changing light from a passing car’s headlights.

The system also has other advantages: It does not infringe on anyone’s personal rights because it detects only the change in radiation, not the person who triggered it. And, because the coating can be sprayed onto the windows by airbrush or glued on as a film, it is cost-efficient.

A demonstrator system already exists, and the researchers now plan to optimize the dyes and their concentration in the coating.