Contact-Based Glucose Measurements Without Any Vector Network Analyzer

Most experimental RF/microwave glucose sensors have to operate in conjunction with a vector network analyzer (VNA). Not only is a VNA bulky and expensive, but the process of a VNA-based glucose measurement is extremely tedious. For the first time, a fully customized system has been developed to demonstrate the feasibility of contact-based glucose measurement without any VNA. Method: A sweeping RF synthesizer (LMX2595) was used for scanning a specific range of frequencies that covered the perturbed frequencies of a membrane-supported glucose sensing head (MSSH), which was around 1.3 GHz. During the frequency sweeping process, a gain–phase detector (AD8302) was used to capture the gain, which was one of the parameters for determining the MSSH’s reflection coefficients (S11). During the frequency sweeping process, the measured voltage gains and phases from the AD8302 module were serially sent to a computer, where the reflection coefficients were retrieved and smoothed with a Savitzky–Golay filter augmented with a multilevel neural network implemented in PyTorch 2.13.0. Results: The proposed system was able to conduct continuous measurements on glucose concentrations from 0 to 111 mg/dL with no VNA and no manual intervention. Moreover, it was able to generate highly reproducible results consistent with those of a commercial VNA. Conclusion: The proposed non-VNA glucose sensing system was able to continuously measure the concentrations of a glucose–water solution with results consistent with those of a VNA.