Wireless window contacts benefit from energy harvesting sensors

October 10, 2011 // By Paul Buckley
Research scientists at the Fraunhofer Institute for Microelectronic Circuits and Systems IMS in Duisburg have now developed wireless window contacts which indicate when a house's windows are open or closed.  The fail-safe system uses sensors that harvest the energy they need to run from ambient radio signals.

The window contacts can make life easier and give peace of mind. The little electronic helpers are fitted onto window handles, and they can tell from the position of the handle whether the window is wide open, tilted open or closed. The sensors transmit this information to a base station, and the house's occupants can then see at a glance which windows are open.

The German researchers have now developed a version of the sensor arrangement that is particularly reliable and easy to use and which needs no wiring or batteries.

“Our wireless window contacts draw all their energy from ambient radio signals,” explained Dr. Gerd vom Bogel, a scientist at the IMS. Until now, wireless models have been reliant on either batteries or solar cells, but both of these approaches have drawbacks. Batteries need to be changed regularly to keep window contacts operational. Solar-powered systems avoid this problem, but they too are liable to fail: all it takes is for the sunlight to be blocked by something casting an unintentional shadow over the solar cell. Solar systems are also aesthetically less pleasing because they cannot be tucked away in a dark corner of the window. Which leaves the classic setup: window contacts with cable connections. Such systems have been on the market for years. The main argument against these is the effort it takes to install them – quite apart from the fact that it is often impossible to retrofit them to existing buildings.

The new system, however, can be fitted with little effort – and they can be positioned discreetly. Aside from window contacts, each room is equipped with a room controller. The transmitter module not only receives the data from individual window contacts, it also actively provides the sensors with energy via its radio signal. The room controller also has the function of passing the sensor data on to a central base station in the building, from