Low-power bed / seat occupancy sensor based on EMFi

Ambient Assisted Living (AAL) systems demand is raising. The use of bed seat occupancy sensors is imperative for this kind of ubiquitous monitoring systems. Pressure mats are a first way to solve this feature, but several environmental dependencies make them weak to be an efficient and reliable solution for large volume deployments. Solutions based on force-to-resistor transducer seems to imply a too high power consumption to be integrated on wireless sensor nodes. A force-capacitive transducer based sensor has been proposed, implemented and tested in this paper. This sensor, based on Electro-Mechanical Films (EMFi) is able to detect force variations in a quasi-passive way. This detection is used to trigger an active mechanism to measure the weight by means of the transducer capacity. A low-power wireless sensor node prototype including this new sensor has been assembled and tested with a wide range of weights. The occupancy detection was successful and the power consumption of the node was increased at less that a 15%. © 2011 Springer-Verlag Berlin Heidelberg.