Multi-Frequency Electrical Response of a Planar Interdigital Capacitive Sensor for Honey–Syrup Mixture Assessment

A planar copper-on-epoxy interdigital capacitor (IDC) was investigated as a direct multi-frequency electrical transducer for assessing honey–syrup mixtures. Eleven nominal syrup levels from 0% to 100% were measured at 100 Hz, 1 kHz, 10 kHz, 100 kHz, 1 MHz, and 2 MHz using a MATRIX MCR-8200H LCR meter in parallel-capacitance/dissipation-factor (Cp–D) mode. Five technical readings were averaged at each level and frequency, and the measured Cp was treated as the equivalent response of the complete IDC–sample system. Among the six frequencies, 1 kHz showed the strongest individual linear relation with nominal syrup level. Under leave-one-out cross-validation, the 1-kHz linear model yielded R2=0.9325, RMSE=8.22 percentage points, and MAE=7.34 percentage points. Six-frequency PLSR did not improve prediction, whereas SVR achieved R2=0.9519, RMSE=6.93 percentage points, and MAE=5.66 percentage points. The results indicate that the frequency-dependent capacitance pattern contains composition-related information beyond the strongest single-frequency response and can be exploited by nonlinear regression. Because the analysis is based on eleven concentration-level observations from one preparation series, further validation with independently prepared batches is required to establish between-batch reproducibility and external predictive performance.