Fraunhofer reveals chip-scale solar-powered wireless sensor node German lab Fraunhofer IMS has created a self-contained solar-powered wireless chip-scale IC that can warn when windows are left open.
At 10mm across, the chip is small enough to be installed inside double glazing on the frame that separate the two glass panes.
�Thanks to this window space, the solar cell obtains adequate light, even in the darkness of winter,� said Fraunhofer.
On the chip are magnetic and acceleration sensors that measure how far the window is open, and radio that communicates this information to a basestation.
Challenge one, was to deposit a solar cell directly on a die, over the uneven metal layers. �This is why we had to find a means of filling in and evening the surface prior to coating it with the solar cell,� said engineer Dr Gerd vom Bögel, who lead the team with physicist Dr Andreas Goehlich.
Secondly, the chip needed to run from a tiny solar cell, in the winter, and through the night.
�By keeping both processor and chip extremely small, the latter is extremely frugal. In addition, the researchers constructed switches that consume little energy, and engineered very short radio protocols,� said Fraunhofer. �Adding to the overall conservation of power is the fact that the sensor always switches to sleep mode. Depending on the user preferences, the sensor can be set so that it wakes up every few minutes, or even seconds, and takes a measurement.�
�We have extracted every possible µA,� added vom Bögel.
Currently, the prototypes can store enough power for up to 30 hours of darkness, and the lab predicts products will emerge over the next two years that can run through two weeks of darkness.
In the window application, sensors on the chip measure tilt, and report if it is open � so the associated system could warn if a window is open while the heating is on, for example.
The chip also detects shock, and Fraunhofer claims can differentiate between a ball hitting the glass and a crowbar levering open the window.
�The applications of the radio chip are diverse. It can remind homeowners to ventilate regularly or warn if a window is still open when they leave the home. In addition, it offers reliable protection from intruders even for closed windows,� said the lab.
Impetus came from Israeli firm Solchip which approached IMS for on-die solar cells two years ago. Solchip has plans to use them to monitor street traffic and the climate in vine-yards.
 
�There are a lot of application areas,� said vom Bögel. �Production costs are minimal because the application of the solar coating is directly connected to the production process of the chips. Only a handful of additional production steps are needed so that manufacturing can also be accomplished in high quantities.�
The solar radio sensor chip is on show this week at the BAU trade fair in Munich (Hall C2, Stand 119).