Design of an Out-Folded Patch Antenna With a Zeroth-Order Resonance for Non-Invasive Continuous Glucose Monitoring

This article proposes an out-folded patch antenna with a zeroth-order resonance (ZOR) that is robust to a high-dielectric condition of a human body for noninvasive continuous glucose monitoring (CGM). The proposed antenna has two faces of a tapered section and a rectangular patch separated by a gap, and those faces are connected through vias at two corners near the gap. Two identical antennas are fabricated on a flexible printed circuit board (FPCB), and the properties of ZOR are compared with those of the fundamental mode to demonstrate the feasibility. The ZOR of the proposed antenna exhibits a negligible frequency shift, and its quality factor is 2.9 times higher than the fundamental mode, when attached to the skin. The evaluation is further extended to a human experiment using the two antennas for real-time estimation of coupling strength according to the change in glucose concentration. The trend of measured coupling strength well describes that of the glucose concentration obtained from a glucose meter with a mean absolute relative difference of 12.23%. The results demonstrate that the proposed concept has a great potential to improve the accuracy of noninvasive estimation in microwave spectrum.