Microfluidic Microwave Sensor for Simultaneous Dielectric and Magnetic Characterization

Herein, we demonstrate a method for simultaneously quantifying the electric and magnetic properties of liquid systems confined within a capillary. This is based upon an optimized perturbation of a microwave-frequency coaxial resonator, chosen to maximize the spatial separation of the two fields and to minimize the depolarization of the liquid. A capillary is passed through the center of the resonator so the sample occupies either maximum electric field (zero magnetic field) or maximum magnetic field (zero electric field) depending on whether an odd or even TEM mode is interrogated. This allows electric and magnetic effects to be distinguished at multiple discrete frequencies. We demonstrate this capability through the quantification of varying ionic content of saline solutions, which interact with both the electric and magnetic fields via several polarization mechanisms. The distinction of different cations and anions is also demonstrated.