Researchers in Germany have developed a battery-free internet sensor that is powered via a special solar cell for indoor use, enabling tens of thousands of connected mini-sensors to transmit measurement values directly to the internet via WLAN or GSM. This development will help to reduce cost and maintenance in applications such as museums, libraries and archives, where precision monitoring of temperature, humidity or air pressure is crucial.
There is no need for a base station - data can be logged via the internet and alarm messages are sent to designated persons automatically via email or SMS. The research group, which is led by Dr. Tolgay Ungan, presented the sensor for the first time in at the recent Exponatec show in Cologne. The newly founded endiio is a spin-off from the Department of Microsystems Engineering at the University of Freiburg, Germany.
Tens of thousands of mini-sensors awoken as required
The internet sensor uses patented wake-up wireless technology, which rouses tens of thousands of sleeping mini-sensors so they can collect measurement data. This makes the system far more energy efficient than conventional wireless solutions. Both the internet sensor and the mini-sensors are supplied with energy from the interior use solar cell and can be operated in poor light conditions. A minimum of 50 Lux is required but, with an ambient light less than 50 Lux, several decades of operating time can be ensured using an integrated energy buffer.
Simplicity meets economy
As well as no additional costs for a base station or spare batteries, a further new feature is the use of special coatings on the solar cell, which enable the colour of the components to be adapted to the exhibition rooms. The monitoring system uses latest generation multi-sensors by Bosch Sensortec, which require no recalibration, opening up new possibilities for low cost, zero maintenance monitoring of climatic conditions in museums. The gas sensors can even be used to monitor visitor flows.
"We held intensive discussions about use of the sensors in practice with the Deutsches Museum," explained Ungan. Requirements cited by experts in these discussions have already been incorporated during its development.
At the Institute for Microsystems Technology at the University of Freiburg, research has been conducted on what are known as ‘energy harvesting technologies’ for a long time now. The goal of this is to enable microsystems to operate self-sufficiently without the use of any batteries so they can be supplied with energy from the environment, thereby recording sensor values and transmitting these wirelessly. To date microsystems of this type could be developed where energy was supplied from mechanical motion, temperature differences (Peltier effect), light (solar cells) or even blood sugar (fuel cells), but such systems were only able to transmit a radio signal to a permanently available base station once power had been accumulated for a very long time.