Passive UHF RFID-Based Knitted Wearable Compression Sensor

One of the major challenges faced by passive on-body wireless Internet-of-Things sensors is the absorption of radiated power by tissues in the human body. We present a batteryless, wearable knitted ultrahigh frequency (UHF, 902-928 MHz) radio frequency identification compression sensor (Bellypatch) antenna and show its applicability as an on-body respiratory monitor. The antenna radiation efficiency is satisfactory in both free-space and on-body operations. We extract radio-frequency (RF) sheet resistance values of three knitted silver-coated nylon fabric candidates at 913 MHz. The best type of fabric is selected based on the extracted RF sheet resistance. Simulated and measured performance of the antenna confirm the suitability for on-body applications. The proposed Bellypatch antenna is used to measure the breathing activity of a programmable infant patient emulator mannequin (SimBaby) and a human subject. The antenna is highly sensitive to respiratory compression and relaxation. Fluctuations in the backscatter power level/received signal strength indicator in both cases range from 6 to 15 dB. The improved on-body read range of the proposed sensor antenna is 5.8 m, about ten times higher than its predecessor wearable knitted strain sensing Bellyband antenna (0.6 m). The maximum simulated specific absorption rate on a human torso model is 0.25 W/kg, lower than the maximum allowable limit of 1.6 W/kg.

Automated summary

A batteryless, wearable antenna designed for on-body respiratory monitoring is proposed in this study. Through extracting RF sheet resistance values and conducting simulated and measured performance tests, the antenna's suitability for on-body applications is confirmed. The antenna shows high sensitivity to respiratory activities and an improved read range compared to its predecessor.