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

Area of Science:

• Electrical Engineering
• Biomedical Engineering
• Radio-Frequency Engineering

Background:

• Remote vital-sign monitoring is crucial for healthcare, but current methods often require invasive sensors or limited range.
• Existing wearable sensors face challenges with power supply and long-term continuous monitoring.
• Developing non-contact, battery-free solutions for vital-sign detection is a significant technological goal.

Purpose of the Study:

• To develop a novel hybrid ultra-high frequency (UHF)/ultra-wideband (UWB) RFID tag for object-specific remote vital-sign monitoring.
• To achieve record energy-harvesting sensitivity for battery-free operation in wearable applications.
• To demonstrate a non-contact method for detecting physiological signals like heartbeats and respiration.

Main Methods:

• Co-design of a meander dipole antenna and a passive rectifier for enhanced UHF energy harvesting.
• Development of a custom CMOS integrated circuit (IC) with a low-power UWB transmitter and voltage-to-rate converter.
• Integration of UHF and UWB antennas with the CMOS IC into a compact, component-free tag.
• Experimental validation of long-distance wireless power transfer and remote vital-sign monitoring.

Main Results:

• The hybrid RFID tag achieved record energy-harvesting sensitivity at the UHF band.
• The tag demonstrated wireless power-up at a distance of 51 meters from a 4-W EIRP UHF transmitter.
• Remote vital-sign monitoring was successfully validated on a human subject using the non-contact wearable tag.
• The tag has a compact size (4.2 cm × 2.9 cm) and low weight (0.93 g) with approximately 1-μW power consumption.

Conclusions:

• This work presents a first-of-its-kind remote vital-sign monitoring scheme using a noncontact wearable RFID tag.
• The developed far-field energy-harvesting frontend with record sensitivity offers a new reference for battery-free remote sensors.
• The hybrid UHF/UWB tag technology holds significant potential for unobtrusive, long-term health monitoring.