Multi-objective optimisation of frequency offset and quality factor in semi-conical microwave resonant cavity for syrup brix measurement

Abstract

Accurate measurement of syrup brix is essential for automated sucrose production because it significantly influences the quality and efficiency of the production process. The microwave resonant cavity method, an effective approach for syrup brix measurement, imposes special performance requirements on the cavity structure design, potentially necessitating unique shapes to capture the properties of the target substance. Traditional empirical design methods for these sensors have significant limitations with nonconventional shapes, often requiring further tuning and analysis of the parameters to adapt to complex geometries and achieve optimal performance. Previous studies have indicated that syrup brix variation can be predicted by the electromagnetic field characteristics of the resonant cavity, specifically the resonant frequency and quality factor, thereby allowing this relationship to be leveraged for sensor optimisation. Therefore, this study presents a systematic multi-objective optimisation approach using electromagnetic simulation software (ANSYS Electronic HFSS) and an Adaptive Reference-based Non-Dominated Sorting Genetic Algorithm (ARNSGA-II), which optimises the frequency offset and quality factor to enhance the sensor sensitivity and accuracy. Experimental comparisons between the optimised and conventional cavity designs demonstrate substantial improvements, with a 60.8% increase in the frequency offset and a 67.2% enhancement in the quality factor. Furthermore, applying the optimised design to a predictive model reduced the mean absolute error to 1.43°Bx, representing a 38.4% improvement compared to the empirical design-based resonant cavity. Results demonstrated that this study provides a robust framework for optimising complex cavity structures and offers valuable insights for the development of high-precision microwave sensors tailored for syrup brix measurements.