# Application of Broadband Microwave Near-Field Sensors for Glucose Monitoring in Biological Media
###### Abstract
The authors considered their sensor to be exact, safe, and fast, providing continuous readings in fractions of a second. Interesting data on measurements of glucose concentration in real time were reported in [13; 14]. The authors used a sensor consisting of a dielectric resonator coupled with a probe-tip. Based on measurement of the reflection coefficient, they observed small changes in the glucose concentration in the range 0-300 mg/mL. At the working frequency changing from 4 to 5 GHz, they succeeded in tracing changes in the glucose concentration with a resolution of 1 mg/mL. The measured signal/noise ratio was about 37 dB, and the minimal detectable signal was about 0.003 dB/(mg/mL). The theory [15] and practice [16] of near-field resonant microwave sensing of different biological media have recently been developed very intensively. Scientists from the Institute for Physics of Microstructures of the Russian Academy of Sciences have demonstrated convincingly that the method permits determining the filling degree of blood in the small vessels of human bodies and tissues and that the corresponding measuring complex is sensitive to any, even minor, changes in the blood flow in tissues rich with blood vessels. This method has already been partially implemented in clinical practice. It is pertinent to note that the developed resonant measuring systems provide penetration depths from 0.1 to 5 mm (in this case, the natural resonant frequencies of sensors were about 600 MHz, and their Q-factors were of the order of 150). Exactly these circumstances allow us to conclude that the method of near-field microwave sensing can be used for non-invasive determination of the blood glucose level in a patient. From the foregoing it follows that to develop a reliable method of non-invasive microwave monitoring of the glucose level, further theoretical and experimental investigations of the physical processes of the interaction of electromagnetic fields with biological tissues containing blood vessels at small depths are required. In the present work, an approach is proposed aimed at developing a near-field microwave sensing system for regular non-invasive monitoring of the glucose level. The paper is organized as follows. In the beginning of the paper, results of simulations of dependences of real parts of the dielectric permittivities \(\varepsilon^{\prime}\) of blood, fat, muscles, and bones at frequencies of electromagnetic oscillations in the range from 10 MHz to 10 GHz are discussed. Then the results of a computer simulation of the interaction of the wideband near-field probe having a special design with phantoms of different biological tissues are presented. This part of our research has allowed us to establish the special features of the attenuation of sensing radiation power density in the near-field zone in the above-indicated tissues. Based on the experimental investigations, opportunities for measuring the glucose content in phantoms of biological tissues (physiological solutions with different dextrose contents) are investigated. Finally, prospects for practical implementation of this approach are briefly discussed. It should be noted that the ideological basis of our work was provided by pioneer research [17] in which the new concept of microwave tomography of absorbing media was proposed. Within the framework of this concept, essential changes in the near-field phase state of the probe in the vicinity of the so-called causal surface are effectively used for sensing of the medium.