*Article* **Non-Invasive Determination of Glucose Concentration Using a Near-Field Sensor**

**Aleksandr Gorst, Kseniya Zavyalova \* and Aleksandr Mironchev**

> Radiophysics Faculty, Tomsk State University, 634050 Tomsk, Russia; gorst93@gmail.com (A.G.); mironchev42@mail.ru (A.M.)

**\*** Correspondence: ksu.b@mail.ru

**Abstract:** The article presents a model of a near-field sensor for non-invasive glucose monitoring. The sensor has a specific design and forms a rather extended near-field. Due to this, the high penetration of electromagnetic waves into highly absorbing media (biologic media) is achieved. It represents a combined slot antenna based on a flexible RO3003 substrate. Moreover, it is small and rather flat (25 mm in diameter, 0.76 mm thick). These circumstances are the distinguishing features of this sensor in comparison with microwave sensors of other designs. The article presents the results of numerical modeling and experimental verification of a near-field sensor. Furthermore, a phantom of human biological media (human hand) was created for experimentation. In the case of numerical modeling, the sensor is located close to the hand model. In a full-scale experiment, it is located close to the phantom of the human hand for the maximum interaction of the near-field with biological materials. As a result of a series of measurements for this sensor, the reflection coefficient is measured, and the dependences of the reflected signal on the frequency are plotted. According to the results of the experiments carried out, there is a clear difference in glucose concentrations. At the same time, the accuracy of determining the difference in glucose concentrations is high. The values of the amplitude of the reflected signal with a change in concentration differ by 0.5–0.8 dB. This sensor can be used for developing a non-invasive blood glucose measurement procedure.

**Citation:** Gorst, A.; Zavyalova, K.; Mironchev, A. Non-Invasive Determination of Glucose Concentration Using a Near-Field Sensor. *Biosensors* **2021**, *11*, 62. https://doi.org/10.3390/bios11030062

Received: 31 January 2021 Accepted: 23 February 2021 Published: 26 February 2021

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**Keywords:** sensor; combined slot antenna; diabetes; dielectric permeability; electromagnetic fields; glucose concentration; near-field sensor; non-invasive measurements; microwave sounding
