Unobtrusive long-range detection of passive RFID tag motion

This paper presents a novel method for detecting the motion of passive radio-frequency-identification (RFID) tags within the field of a detecting antenna. The method allows the unobtrusive detection of human interactions with RFID-tagged objects without requiring any modifications to existing communications protocols or RFID hardware. We use the response rate (a metric in lieu of the true received RF-signal intensity) at the reader to study the impact of tag translation, rotation, and coupling, as well as environmental effects. Performance is improved by introducing the idea of multiple tags/readers. Movement-detection algorithms are developed and integrated into the RFID monitoring system, and verified by experiments that demonstrate excellent results.