Wearable RF Sensor Array Implementing Coupling-Matrix Readout Extraction Technique

This paper presents a novel single-port multi-pole resonant sensor array fabricated on a novel Frame-Flex flexible substrate for a wearable epidermal ethanol sensor system, in which individual sensors carrying different functional polymers are brought together to share the same electrical input and output, and their resonance behavior along with inter-resonator coupling are captured through the single reflected array response curve (${S} _{11}$). The coupling-matrix readout extraction (CMRE) technique is then further proposed to determine, from the ${S} _{11}$ response, the changes in the diagonal-coupling coefficient, $\Delta M _{ii}$, which are used to identify different chemical analytes as the coupling signature. Two sensor arrays implementing different functional polymer sets—one with siloxane-based polymers and the other with crystalline-based polymers—are fabricated and tested under two selected mechanical loading conditions. The CMRE technique is then employed to obtain the coupling signatures of ethanol, methanol, acetone, and benzene on the arrays. It is successfully shown that the array response analyzed through the CMRE technique can clearly distinguish the presence of ethanol from other chemical interferents. For complicated mixtures of ethanol and other unwanted analytes, the distinctive coupling signatures obtained by CMRE can be used as a reliable data source fed to post-readout multi-variant analysis for pattern recognition.