Integrated liquid–liquid percentage determination microwave sensor exploiting single‐frequency transmission amplitude measurement technique

This letter presents an integrated liquid-liquid percentage determination system exploiting the single-frequency transmission measurement technique. The system is composed of an oscillator, working at a single-frequency (f0), a circular substrate-integrated waveguide (SIW) cavity resonator perturbed at the center to accommodate a glass pipe with the liquid under test (LUT), and a power detector to measure the transmission amplitude variation due to the presence of different LUTs. This system is a great solution for locally embedded and inexpensive applications by avoiding bulky and expensive scattering parameter measurement devices such as vector network analyzers. Furthermore, its single-frequency measurement capability makes it an excellent candidate for real-time measurements. The system is designed to work at 2.47 GHz, which falls into the Industrial, Scientific, and Medical regime. The discrepancies between the proposed model and the measurements are compensated using a proper error calibration method, leading to a significant reduction in the percentage reading errors.