Towards a Compact UHF RFID Reader for Wearable Bio-sensing Devices

We present a compact, Ultra High Frequency Radio Frequency Identification (UHF RFID) Bio-sensing system, which operates in the 865 - 868 MHz band. The proposed system was designed, using custom and commercial off-the shelf (COTS) components. The main system blocks consist of: (1) A compact, low power UHF RFID reader, with an effective isotropic radiated power (EIRP) level of 10.82 mW (+10.34 dBm), (2) A 16×15×1 mm
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custom designed electrically small antenna (ESA), fabricated on an FR4 substrate, and (3) A battery free UHF RFID sensor tag, with an internal temperature sensor. Wireless connectivity and power transfer, between the UHF RFID reader ESA assembly and the battery free sensor tag, were achieved at a distance of 31 cm. The reader assembly successfully recorded sensor tag localised ambient temperature measurements. Sensor tag temperature measurements were performed using its internal temperature sensors and compared to a reference temperature sensor. Both sensor tag and reference sensor measurements were performed concurrently, in a temperature-controlled environment. The reader-ESA assembly has a mass of approximately 20 g, suitable for portable applications. Low EM emissions, from the proposed system, are at a safer level for operation in proximity to sensitivity electronic medical devices, such as pacemakers. Healthcare practitioners can use this system, to remotely monitor infants localised body temperature in neonatal or transitional care wards, when performing routine patient checks.