An Ultracompact Spoof Surface Plasmon Sensing System for Adaptive and Accurate Detection of Gas Using a Smartphone

Resonantly enhanced dielectric sensing has superior sensitivity and accuracy because the signal is measured from relative resonance shifts that are immune to signal fluctuations. For applications in the Internet of Things (IoT), accurate detection of resonance frequency shifts using a compact circuit is in high demand. We proposed an ultracompact integrated sensing system that merges a spoof surface plasmon resonance sensor with signal detection, processing, and wireless communication. A software-defined scheme was developed to track the resonance shift, which minimized the hardware circuit and made the detection adaptive to the target resonance. A microwave spoof surface plasmon resonator was designed to enhance sensitivity and resonance intensity. The integrated sensing system was constructed on a printed circuit board with dimensions of 1.8 cm × 1.2 cm and connected to a smartphone wirelessly through Bluetooth, working in both frequency scanning mode and resonance tracking mode and achieving a signal-to-noise ratio of 69 dB in acetone vapor sensing. This study provides an ultracompact, accurate, adaptive, sensitive, and wireless solution for resonant sensors in the IoT.