High-Sensitivity Metasurface-Based Sensor With Intrinsic Microchannel for Liquid Permittivity Measurement

Achieving high sensitivity and structural integration in metamaterial sensors for liquid permittivity measurement remains a significant challenge, primarily due to limited electromagnetic (EM) coupling with the liquid under test (LUT) and the complexity of microchannel fabrication. In this work, we propose a high-sensitivity metasurface-based sensor with an intrinsically integrated microchannel, fabricated by bonding an etched 0.5-mm-thick metal pattern onto a dielectric substrate. Unlike traditional designs that separate the sensing element and fluidic channel, our design achieves dual functionality—resonant sensing and microchannel integration—within a single patterned metal layer, reducing overall fabrication complexity by approximately 40%. To evaluate the performance, polyethylene glycol 200 (PEG200)–water mixtures were used to establish the permittivity-sensing model. The sensor exhibited a maximum normalized sensitivity of 5.71% per unit dielectric constant for pure PEG200, corresponding to the lowest permittivity in the test range. Importantly, the overall sensitivity curve is consistently higher than that of conventional designs across the full permittivity range ( $\varepsilon _{\text {r}} =4$ –80), nearly doubling the performance of previously reported microwave microfluidic sensors. Further validation using PEG200–glycerol (GLY) mixtures showed excellent agreement with reference data, with a maximum deviation of less than 3.1%. The effective electric field distribution around the microchannel enhances the interaction with the LUT, enabling accurate permittivity characterization. This work provides an integrated, high-performance solution for dielectric sensing across diverse biomedical and chemical applications.