High-Resolution PEDOT:PSS-Based Planar Microwave Resonator Sensor

This work presents a polymer-based, high-resolution microwave split-ring resonator (SRR), where metal microstrip lines of the SRR were replaced by poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as a conductive polymer and equipped with an active feedback circuitry to enhance the -3dB quality factor of polymer-based SRR from similar to 1.5 to similar to 600. The PEDOT:PSS passive tag was designed with the effective length of 46 mm, the width of 2 mm, and the gap length of 2 mm, operating at similar to 2 GHz with a resonant amplitude of -20 dB. By controlling the gain of a low-noise amplifier (LNA) and the phase of a phase shifter, PEDOT:PSS-based SRR with adjustable quality factor was achieved. As a proof of concept, the proposed structure was investigated for sensing materials in different states of solid, gas/vapor, and liquid, at different quality factors of 120, 200, and 500, respectively. The enhanced resolution organic microwave resonator (OMR) with a quality factor of 500 showed a great performance detecting standard liquids with relative permittivity ranging from 10 to 80 and loss tangents from 0.1 to 1. The proposed PEDOT:PSS-based SRR with high quality factor demonstrated the potential of integrating organic microwave components with conventional electronic components such as amplifiers and oscillators toward all organic microwave devices. Furthermore, due to the water solubility of the proposed PEDOT:PSS-based SRR, fabricated structures could be modified or repaired with less complexity and less environmental footprint than its metal-based counterparts.