Highly Sensitive Impedance-Matched Microwave Dielectric Sensor for Glucose Concentration Measurements

This article presents a highly sensitive microwave dielectric sensor for determining glucose concentration using a novel metamaterial-inspired interdigital capacitor (IDC)–complementary split-ring resonator (CSRR) structure. The sensor’s sensitivity is improved by a factor of 80 when used as a one-port impedance-matched structure compared to a conventional two-port configuration. By utilizing a digitally controlled step capacitor, we were able to achieve impedance matching at the two distinct frequencies of 3.69 and 4.38 GHz while conserving the resonant mode of the IDC-CSRR. Both matched frequencies were then used for glucose concentration measurements, resulting in a maximum sensitivity of 8.727 dB/mg/mL and 53.01 kHz/mg/mL. Principal component regression (PCR) was used to predict glucose concentration with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}}$ </tex-math></inline-formula> of 0.9997 and a mean average error (MAE) of only 0.045 mg/mL, achieving a resolution of 0.42 mg/mL, corresponding to the minimum detected concentration difference between the two measured samples. The proposed setup demonstrates substantial improvements over conventional two-port sensors, surpassing the performance of more complex interferometric systems.