A UHF/UWB Hybrid RFID Tag With a 51-m Energy-Harvesting Sensitivity for Remote Vital-Sign Monitoring

• Published in: IEEE transactions on microwave theory and techniques Vol. 68; no. 11; pp. 4886 - 4895
• Main Authors: Lyu, Hongming, Wang, Zeyu, Babakhani, Aydin
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.11.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antenna-and-rectifier codesign; CMOS; Dipole antennas; Energy harvesting; Far fields; far-field power transfer; Impedance; Integrated circuits; Internet of Things (IoT) sensor; Monitoring; Power consumption; Power management; Radio frequency identification; radio frequency identification (RFID); Remote monitoring; Remote sensors; RFID tags; Sensitivity; UHF antennas; Ultrahigh frequencies; ultrahigh frequency (UHF); Ultrawideband; ultrawideband impulse radio (IR-UWB); vital-signal monitoring; wearable device; Wearable technology
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2020.3017674

A novel ultrahigh frequency (UHF)/ultrawideband (UWB) hybrid radio frequency identification (RFID) tag is reported for object-specific remote vital-sign monitoring application. The tag achieves a record energy-harvesting sensitivity at the UHF band by codesigning a meander dipole antenna and a passive rectifier. The especially high quality-factor makes the frontend sensitive to near-field motions such as heartbeats and respiration in a wearable setting. The custom CMOS integrated circuit (IC) of approximately 1-<inline-formula> <tex-math notation="LaTeX">\mu \text{W} </tex-math></inline-formula> power consumption builds around a low-power UWB transmitter and converts the variations in the supply voltage to the impulse repetition rate. The tag consisting of the IC and UHF/UWB antennas requires no other discrete components and features a size of 4.2 cm <inline-formula> <tex-math notation="LaTeX">\times2.9 </tex-math></inline-formula> cm and a weight of 0.93 g. A long-distance experiment verifies that the tag can be wirelessly powered up at 51 m from a 4-W effective-isotropic-radiation-power UHF transmitter. Remote vital-sign monitoring is validated on a human subject, in which the UHF power source is placed 2 m away from the subject with a power emission of less than 20 dBm. This work proposes a first-of-its-kind remote vital-sign monitoring solution based on a passively powered noncontact wearable tag. The design of the far-field energy-harvesting frontend with a record sensitivity serves as a reference for future works on battery-free remote sensors.