A Simple Technique for Liquid–Liquid Percentage Determination Using Single-Frequency Amplitude Measurements

This letter presents a novel technique for the liquid–liquid percentage reading based on the measurement of the transmission amplitude at a single frequency in a cavity resonator with a small pipe where the liquids flow. The proposed approach represents an alternative to the conventional technique based on the determination of the resonance frequency shift and presents a number of advantages. First of all, the proposed technique requires just an oscillator and a power meter at a fixed frequency, instead of the complex equipment needed for the broadband measurement of the scattering parameters of the circuit, as in the conventional technique. Consequently, the proposed method is well-suited for the implementation of low-cost embedded sensors. Moreover, by avoiding the frequency sweep, the reading is instantaneous and therefore the real-time determination of the characteristics of flowing liquids is possible. Experimental results have been performed with a substrate-integrated waveguide (SIW) cavity operating around the frequency of 2.48 GHz industrial scientific and medical (ISM) band, by comparing the performance of the proposed approach and the conventional one in the determination of the liquid–liquid percentage of mixtures of acetone and isopropanol.