An impedance matched interdigital capacitor at 1.5 GHz for microfluidic sensing applications

Abstract

In this paper, a novel microwave sensor is realized by double stub matching a deionized (DI) water loaded interdigital capacitor to 50 Ω to create a minimum in reflection coefficient around 1.5 GHz. Glucose, l-proline and glycine solutions with different concentrations are loaded into the sensor and consequently impact the frequency of the minimum reflection coefficient. The proposed sensor achieves a linear correlation between its minimum reflection coefficient frequency and permittivity of the loaded solutions. Mixtures between fetal bovine serum (FBS) and phosphate-buffered saline (PBS) having FBS volume fractions of 0%, 20 %, 40 %, 60 %, 80 % and 100 % are also loaded into the proposed sensor. A linear relationship between the volume fractions of the loaded mixtures and the minimum reflection coefficient frequency point of the proposed sensor is as well achieved. Measurement results demonstrate the potential of the proposed miniaturized sensor, coupled with the dislocated-of-the-chip and space-consuming supporting microwave circuitry, for applications such as sample preparation at the microfluidic scale.