Real-time accurate quantification of nanoliter ethanol using performance-optimized micro-fabricated microwave resonant sensor

Abstract

The inherent trade-off among the level of sensing electromagnetic (EM)-energy and the performance parameters, and consequently, the inevitable nonlinearity at high-sensitivity renders the performance-optimization of a micro-fabricated microwave resonant sensor very difficult. This paper presents a shunt capacitor-based EM-energy splitting technique to generate three distinct levels of coupled EM-energies in micro-fabricated microwave LC resonant ethanol sensors and investigate the quantitative correlation among the resulting energy level, sensitivity, linearity, and signal-to-noise ratio (SNR). Gallium arsenide (GaAs)-based micro-fabrication technique is used to implement the proposed microwave LC resonators employing an air-bridged circular spiral inductor and meandered-line coupling capacitors. The experimental results reveal that the performance-optimized sensor rapidly and accurately quantifies the wide range of nanoliter (200 nl) ethanol concentrations (5%–50% vol.) with a high-sensitivity (1.817 MHz/% vol.), good linearity, and SNR; thus, highlighting the significance of the proposed method to develop a high-performance ethanol sensor. In addition, ethanol-dependent complex permittivity, which is calculated using the measured central frequencies and loaded-quality factors, reveals a negative correlation between the real-permittivity and ethanol concentration of the aqueous solution.