###### Abstract  
The article investigates the near-field probe of a special design to account for changes in glucose concentration. The probe is designed in such a way that it emits radiation in both directions from its plane. In this paper, it was proposed to modernize this design and consider the unidirectional emission of the probe in order to maximize the signal and reduce energy loss. We have done extensive research for both bidirectional and unidirectional probe designs. Numerical simulations and field experiments were carried out to determine different concentrations of glucose (0, 4, 5,3, 7.5 mmol/L). Numerical modeling of a unidirectional probe showed that the interaction of radiation generated by such a probe with a multilayer structure simulating a human hand showed a better result and high sensitivity compared to a bidirectional probe. Further, based on the simulation results, a phantom (physical model) of a human hand was recreated from layers with dielectric properties as close as possible to the properties of materials during simulation. The probe was constructed from a copper tube and matched both the geometric and physical parameters of the model. The experimental measurement was carried out using a vector network analyzer in the frequency range 2-10 GHz. The experimental measurement was carried out using a vector network analyzer in the frequency range 2-10 GHz for the unidirectional and bidirectional probes. Further, the results of the experiment were compared with the results of numerical simulation. According to the results of multiple experiments, it was found that the average deviation between the concentrations was 2 dB for a unidirectional probe and 0.4 dB for a bidirectional probe. Thus, the sensitivity of the unidirectional probe was 1.5 dB/(mmol/L) for the bidirectional one 0.3 dB/(mmol/L). Thus, the improved design of the near-field probe can be used to record glucose concentrations. glucose measurement; non-invasive method; near-field probe; microwave probe; glucose concentration; glucose monitoring; diabetes; relative permittivity +
Footnote †: journal: Applied Sciences
effective non-invasive glucometers is still very urgent. The best known are electrochemical methods [3; 4; 5], optical methods [6; 7], transdermal methods [8], microwave or radio frequency methods [9; 10; 11; 12; 13; 14; 15; 16]. The development of contact lenses based on the measurement of tears, a liquid containing glucose, is also gaining popularity [17]. A large number of works in the direction of radio frequency methods are associated with the fact that microwave radio waves penetrate deep enough into biological tissues, however, due to small wavelengths, they are lost with significant distortions due to small inhomogeneities, and also it are sensitive to the integral parameters of the medium. In this case, the concentration of glucose affects the integral electrical characteristics. Most of the work in this area is based on the analysis of the frequency shift of the signal reflected from blood analog samples with different glucose concentrations [14] using microstrip antennas. The disadvantage of this approach is a small change in frequency with a large change in glucose concentration. The electrochemical method is the most accurate of the above methods, but it has a significant drawback, namely: glucose is measured by piercing the skin to take a blood sample. Besides the fact that this procedure is extremely unpleasant and unsafe, this method requires a lot of additional material, such as test strips. The latter, taking into account the fact that monitoring of glucose in the blood must be carried out very often leads to significant costs. In addition, accuracy is critical to creating an effective continuous glucose monitoring device. Optical methods are quite accurate today. The authors of [7] have shown that the use of a 6 \(\times\) 6 mm sensor made with hollow silicone microneedles allows a sufficiently accurate result to be achieved.