# Application of Broadband Microwave Near-Field Sensors for Glucose Monitoring in Biological Media
###### Abstract  
The paper presents results of numerical simulation and experimental testing of a microwave sensor for non-invasive glucose monitoring. The sensor represents a conical horn with a conical conductor inside expanding toward the horn aperture. Such a sensor has a significantly wider passband in comparison with sensors of other designs. It is essential that the sensor geometry provides formation of an extended near-field zone with high electric field strength near the sensor aperture. A clear relationship between the dielectric permittivity of the phantom biological tissue and the frequency dependence of the parameter S11 of the sensor is observed at frequencies in the range from 1.4 to 1.7 GHz. This circumstance can be used to develop a procedure for measuring the glucose level in blood that correlates with the parameter S11 of the sensor. From the viewpoint of monitoring of the glucose content in blood, the most convenient body sensor location is on the hands or feet, in particular, wrists. diabetes; dielectric permeability; electromagnetic fields; glucose concentration; near-field sensor; non-invasive measurements; microwave sounding +
Footnote †: journal: Medical  
to resolve small blood vessels. It is also important that the sensors are equipped with special nanocomposite films providing good matching with the probed skin. It is stated that this guarantees the reliability of measurements in all patients, irrespective of race, age, and skin type. The glucose meter has good ergonomic characteristics. It is expected that after a cycle of clinical tests, it can be commercialized successfully. At the same time, there is no information on the accuracy of the glucose meter and its advantages over other known meters. In addition to the abovementioned review, more reviews have recently been published (for example, see [2; 3; 4]). It is remarkable that in these reviews, attention is focused on radio wave methods of measurements that have undeniable advantages over other methods. It should be noted that attempts to develop productive technologies for measuring and monitoring the glucose level in the human body using microwave radiation have been undertaken already for a long time. For example, detailed experimental studies reported in master dissertations [5; 6] culminated in a thoughtful publication [7] where an open-terminated spiral-shaped microstrip line was used as a resonant probe for non-invasive determination of blood glucose level. The resonant probe was built into the device for express analysis. An analysis is carried out by pressing the thumb of the patient on the microstrip line. The potential of this probe for estimating the blood glucose level was theoretically investigated in [8] by a numerical simulation method. Malaysian scientists specializing in neural networks of artificial intelligence proposed a super-wideband system for reliable non-invasive determination of the blood glucose level. The system used a pair of microstrip antennas and ensured, according to the developers, an 82% accuracy when determining the blood glucose concentration [9]. Neural networks are used for signal processing in this system. However, the neural networks are rather sensitive to the learning sample and do not guarantee an accurate result when measurement conditions change. This is a disadvantage of the proposed system. In a series of publications [4; 10; 11; 12] by the authors from Cardiff University, the design of a microwave non-invasive sensor for continuous monitoring of the blood glucose level was described in detail. The novelty of the design was that the sensor contained two splitting resonators with a gap. One of the resonators responded to changes in the glucose level, and another was used as a reference. The frequency of microwave radiation was about 1.4 GHz for greater penetration of radiation into biological tissues. The required power level did not exceed 1 mW to eliminate ionization processes in tissues.