Real-time measurements of size, speed, and dielectric property of liquid segments using a microwave microfluidic sensor

This paper describes the use of microfluidic microwave sensors for measuring the length, volume, speed and dielectric properties of different liquids in a segmented flow. The sensor is a variant of the split ring resonator, operating around 4 GHz, realized in a microstrip implementation. Changes of the resonant frequency and quality factor are performed when a segment enters the sensing region, in this case the gap regions. Two different geometries of resonators were used for the sensors, each with two gaps to accommodate a planar microfluidic channel. The segments consisted of mineral oil and water. Sensor simulations were performed using COMSOL Software, which compare favorably with the experimental measurements.