Microwave Glucose Sensing Using Double Circular Split Ring Resonators for Improved Sensitivity: The Role of Artificial Blood Plasma and Deionized Water

In 2021, approximately 537 million people were diagnosed with diabetes mellitus. With rates expected to rise, health expenditures are projected to reach one trillion USD by 2030. Thus, measuring glucose levels is essential for rationalizing the costs of public health systems. In this context, this article presents two major contributions. First, it demonstrates that using deionized water (DI-water) as a reference for glucose sensing is not a reliable approach for representing human blood plasma (BP), as it lacks ions and suppresses essential effects such as losses. As an alternative, we investigate the use of an artificial BP solution (ABPS) that closely resembles real human BP. Characterized over a range from 500 MHz to 10 GHz, ABPS shows marginal differences in real permittivity but significant differences in imaginary permittivity compared to DI-water. The second contribution is the design of a highly sensitive microwave (MW) sensor based on double concentric circular split ring resonator (DCCSRR) on a $49\times 45$ mm ROGERS 5880 TM substrate. This sensor can differentiate glucose concentrations from 0 to 400 mg/dL, exceeding the relevant range for diabetic individuals (50–300 mg/dL). The DCCSRR operates at 2.48 GHz and can detect minimal concentration variations of 25 mg/dL in low concentrations, representing a significant advancement in the field. Different from most sensitive approaches available to date, this structure operates in a nonlicensed band and a fully passive form, offering flexibility for implementation and low cost. These characteristics position it as a state-of-the-art solution in MW glucose sensors.