Miniaturized microwave microfluidic sensor based on quarter-mode 2.5-D spoof plasmons

This paper proposes a miniaturized microwave microfluidic sensor based on quarter-mode 2.5-D spoof localized surface plasmons for detecting liquid permittivity. An active amplification circuit is inherited to increase the resonance quality factor and thereby improve the sensor resolution. The sensor has a double-layer structure and uses microstrip feed. The quarter-mode structure is only one quarter of the full-mode case, and the liquid amount is reduced. The introduction of 2.5-D structure can further reduce the resonator size, improve the slow-wave effect and enhance the field confinement. A polydimethylsiloxane chip with a microfluidic channel is placed directly above the resonator. The injected liquid sample flowing through the channel would induce resonant frequency shift, thus achieving the ability of detecting the liquid permittivity. The prototype is manufactured using printed circuit board technology, and the measured sensor sensitivity for characterizing water reaches 0.16% on average, which is in general agreement with the simulated result. The proposed sensor can be expected to play an important role in biomedicine, environmental monitoring, food hygiene and other fields.