Setup-Independent UHF RFID Sensing Technique Using Multidimensional Differential Measurement

Ultrahigh frequency radio-frequency identification (UHF RFID) technology using transducer-integrated antennas provides a cost-effective option for sensing. A novel setup-independent UHF RFID sensing system that can overcome challenges caused by the measurement setup with a priori unknown mutual distance and orientation between the tag and the read/write device (RWD) is proposed. The concept is based on using off-the-shelf radio-frequency identification (RFID) chips having self-tuning capability, which maximizes power transfer coefficient between RFID chip and RFID antenna. An ON-OFF differential (OOD) measurement is implemented to provide setup-independent sensing. The OOD parameters form a 3-D vector that can support more sensing states than prior art using single-dimensional information. Power transfer efficiency (PTE) and tag sensor efficiency (TSE) are defined, where PTE is the minimal power transfer coefficient in all sensing states and TSE is the minimal pairwise Euclidean distance of the OOD parameters. The RFID antenna layout is optimized by optimizing PTE and TSE simultaneously so as to offer sensing robustness without sacrificing communication performance in all sensing states. A water filling-level sensor has been designed and evaluated. Theoretical predications are favorably compared with experimental results under different measurement setups, having different relative distances and orientations between the tag and RWD.