Hexa Cell Triangular CSRR for the Non Invasive Detection of Blood Glucose

The authors propose a compact metamaterial microwave sensor named the Hexa Cell Triangular Complementary Split-ring Resonator (HC-TCSRR), sized <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$60\times 20 \times 1.5\ \text{mm}^{3}$</tex>, designed for non-invasive monitoring of blood glucose levels ranging from 50 to 1000 mg/dL. This unique structure is novel in this application. The theoretical analysis and numerical modelling of the HC-TCSRR sensor were conducted using Computer Simulation Technology (CST) software. When the sensor's sensitivity was demonstrated through simulation in the range of 70–1000 mg/dL, the results exhibited a distinct leftward frequency shift in the transmission response. The sensor showed a maximum sensitivity of up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$13.35 \times 10^{-2}\text{dB}/(\text{mg}/\text{dL})$</tex> and 4.53 MHz/(mg/dL) in simulations. In vitro tests using deionized aqueous glucose solutions (50–200 mg/dL) also showed a left shifts in the resonant frequency of the transmission response. The fabricated HC-TCSRR prototype achieved a maximum sensitivity of 10.24 MHz /(mg/dL). To the best of our knowledge, distinct frequency shifts at lower glucose concentrations (70, 100, 120 mg/dL) and high concentration of 1000 mg/dL with the same sensor have not been reported till now. Furthermore, with its affordability, compact size, operational versatility across various glucose concentrations, and enhanced sensitivity, this sensor concept is a promising candidate for wearable non-invasive continuous blood glucose monitoring devices.