WISP-based Smart Bed
The sensing elements in our system are WISP active RFID tags that combine passive UHF RFID technology with sensors to balance energy independence with sensing potential. The device’s antenna and power harvesting circuitry enable off the shelf EPC “Gen 2” RFID readers to power and read from it. To a RFID reader, a WISP appears as a normal RFID tag, but inside the WISP, the harvested energy is operating a 16-bit fully programmable ultra low-power microcontroller. The microcontroller can sample a variety of sensing devices including 3-dimensional accelerometers, lights, and temperature sensors. In our system, we only use 3D accelerometer readings. The WISP tags report these readings by encoding them as part of their identifiers that are read by a RFID reader.
We have designed a WISP based smart bed for sleep monitoring by attaching 3 WISP tags to the mattress of the bed for sleep monitoring. We place the tags in such a way that when someone lies on the bed, there is one tag on each side of his body and one tag near the legs. We used two antennas for reading from the tags. One disadvantage of using the WISP tags is that they need to be placed within 1 − 2 meters of the antenna of the reader. To meet the read-range requirement and to keep the equipment away from obstructing a resident’s movement, we placed the antennas below the bed. The antennas were wired to the reader which was connected with the laptop.
WISP based Smart Bed
Monitoring Body Positions and Movements During Sleep using WISPs. ACM Wireless Health.. 2010.