Complex Permittivity Measurement Based on Planar Microfluidic Resonator Sensor

In this paper, a microfluidic sensor is proposed using a microwave planar multiple split-ring resonator (MSRR). The main objective of this real time non-destructive microfluidic sensor is to detect and analyse the dielectric properties of materials using extremely small amount of liquid volumes $(2.5\mu \mathrm {L})$. The sensing mechanism of the proposed microfluidic sensor is based on frequency shifting and amplitude changing of material under test. An MSRR is employed using a Rogers RT/Duroid 5880 substrate. Then, a microcapillary made from glass material is loaded on the outer ring slot to observe the perturbation response. The microcapillary is filled with several common solvents and the ideal value of those solvents are used as a reference result. The resonant frequency of the structure with microcapillary is observed to be 2.1 GHz. The functionality and reliability of the proposed sensor are successfully demonstrated through full-wave simulations and measurements. The resonant frequency of the loaded microcapillary showed a shift of 125.5 MHz and 25 MHz when compared to empty microfluidic. Our proposed microfluidic sensor is nondestructive and reliable. Furthermore, it is low cost and fabricated using simple and easy design procedures.