Wirelessly-Charged UHF Tags for Sensor Data Collection

We present the WISP passive data logger (PDL), an RFID sensor data logging platform that relies on a new, wirelessly-charged power model. A PDL has no battery yet (unlike a passive sensor tag) is able to collect data while away from an RFID reader. A PDL senses and logs data using energy stored in a capacitor; the capacitor can be wirelessly recharged (unlike active tags), and data can be uploaded whenever the PDL is near a reader. Standard EPC generation 2 readers are used for WISP-PDL charging, ID-reading, and sensor data transfer. This allows WISP-PDLs to operate using commercial RFID readers as the only support infrastructure (for both data and power), and allows WISP-PDLs to co-exist with standard RFID tags. We describe the design and implementation of a prototype WISP-PDL, and report results from a short demonstration study that shows it can monitor the temperature and fullness of a milk carton as it is used over the course of a day.