RFID Tag Coupled with a Magnetic Sensor for Wireless Sensing of Home Electrical Devices

A novel solution for sensing the activity of different electrical devices connected to the home power line, based on the use of a long-range UHF RFID system, is proposed. The solution uses a 3-axis magnetometer, coupled with a flexible RFID tag wrapped around the power cord of an electrical device to be sensed. The time varying magnetic field, generated by the AC current carried by the power cord, is sensed by the magnetometer attached to the RFID tag and utilized for determining the state (ON or OFF) of the electrical device. In addition to the state, the identification of the device is also possible thanks to the unique identification property of the RFID tag. Preliminary measurements were performed using an open development environment based on STM32 microcontroller STNucleo kit, then a prototype of the RFID sensor using a magnetometer chip mounted together with the RFID tag on a flexible substrate holding the RFID antenna, connected to a PCB board including an ultra-low power microcontroller, for necessary data processing, have been realized and successfully tested. A sensing range of approximately 7-8 m using a standard RFID Reader operating in the UHF band have been achieved, despite the close proximity of the power-cord.