Microwave Planar Resonant Solutions for Glucose Concentration Sensing: A Systematic Review

Abstract

The measurement of glucose concentration finds interesting potential applications in both industry and biomedical contexts. Among the proposed solutions, the use of microwave planar resonant sensors has led to remarkable scientific activity during the last years. These sensors rely on the changes in the dielectric properties of the medium due to variations in the glucose concentration. These devices show electrical responses dependent on the surrounding dielectric properties, and therefore the changes in their response can be related to variations in the glucose content. This work shows an up-to-date review of this sensing approach after more than one decade of research and development. The attempts involved are sorted by the sensing parameter, and the computation of a common relative sensitivity to glucose is proposed as general comparison tool. The manuscript also discusses the key points of each sensor category and the possible future lines and challenges of the sensing approach.

Development of a Microwave Sensor for Solid and Liquid Substances Based on Closed Loop Resonator

“…The values of dielectric shift in Table 14 was calculated from the simulation graph in Figure 21 corresponding to the frequency shift observed when loading different samples. The sensitivity and normalized sensitivity [48] of the loaded samples is presented in Table 14. Sensitivity is computed as per Equation ( 6) and normalized sensitivity is com-puted as per Equation (7), where S N is the normalized sensitivity, ∆ f is the frequency shift, f r is the resonant frequency and ∆ε r is the shift in dielectric permittivity.…”

“…When considering RF planar sensors, the sensitivity parameter may depend upon one or more parameters. From literature, we can find sensors based on resonant frequency, insertion/return loss, phase or quality factor (Q) [48]. The resonant frequency is an important parameter that has a direct relation with the sensitivity of the resonator structures [49][50][51].…”

Commercial and Scientific Solutions for Blood Glucose Monitoring—A Review

“…Well-known methods are for example Raman spectroscopy, optical polarimetry (OP) or optical coherence tomography (OCT) [77]. The millimeter and microwave sensing and bioimpedance spectroscopy utilize the dielectric properties of glucose [28,77]. Both techniques are applied mostly over the skin.…”

“…These approaches can be classified according to the applied glucose sensing method. The primary sensing methods for NI methods are the electrochemical [24,25] and the electromagnetic-based methods [26][27][28]. In electrochemical NI glucose sensors, a probe of saliva [29], tear drop [30] or the exhaled breath [31] is analyzed.…”

A Sensor for Characterisation of Liquid Materials with High Permittivity and High Dielectric Loss

“…The general description of this type of sensor can be found in Ref. [21] and a good review on this topic can be found by Juan et al [31]. When materials are placed on top of the resonator, interaction between fields and samples will modify the resonant frequency f r and the corresponding quality factor Q.…”