UHF RFID tag design for AC current sensing

This study reports the development of an ac current sensing technique using a capacitance sensing UHF RFID tag which is integrated with a current transformer (CT). A new tag antenna design is created to integrate with the CT housing while maintaining the tag link. The terminals of the capacitance sensing RFID chip are connected to a tuning circuit with a reactance controlled by the current flow in the primary of the CT. A prototype tag was tested to validate the battery-free compact tag that streams current measurement data over a read range of about 5 m using the European RFID UHF band at 868 MHz. The tag could be used for wirelessly sensing the load current of an individual domestic appliance and where a single reader could simultaneously monitor multiple tags, enabling smart reading of electricity consumption across multiple devices in smart homes.