A Novel Microstrip Band-Stop Filter at 5.5 GHz for Non-Invasive Blood Glucose Monitoring

This work presents a novel compact size and sensitive band-stop filter, whose notch frequency is 5.5 GHz, and it is suggested to estimate the concentration of blood glucose non-invasively. The filter is made on FR-4, with the size of the entire structure being 15 mm × 25 mm × 1.6 mm. A human finger-phantom model, comprising layers of skin, fat, blood, and bone, is built in an EM simulation environment (HFSS) to assess the sensing performance of the human finger-phantom. The glucose content in the blood layer is kept at a range of 0 to 500 mg/dL, with the ratio of the resonant frequency shift being assessed by placing the finger phantom on the proposed filter structure. The sensing principle is based on the fact that the resonant frequency of the microwave sensor changes with changes in glucose concentration in the tissue, and this is due to the changes in the dielectric properties of the tissue. The shifts obtained in the study are used for the evaluation of glucose concentration in blood as a non-invasive technique. This work explores five microstrip band-stop filters noted as Designs I, II, III, IV, and V. In these filters, better results of minimum and maximum frequency shifts of 0.1 and 1.4 MHz in Design I and 0.1 and 2 MHz in Design IV are observed. The simulated results of Design IV are verified with measured results. Good matching is also noted at the lower frequencies. The filters are compact, cost-effective, and give better sensitivity performance. Hence, the proposed design can be used for glucose monitoring in blood samples involving a non-invasive method.