Non-Invasive Microwave Sensors for Biomedical Applications: New Design Perspectives

The basic operation principles of non-invasive microwave sensors are summarized in this work, with specific emphasis on health-care systems applications. Design criteria to achieve reliable results in terms of biological parameters detection are specifically highlighted. In particular, the importance to adopt accurate frequency models for the complex permittivity (in terms of both dielectric constant as well as loss tangent) in the synthesis procedure of the microwave sensor is clearly motivated. Finally, an application example of the outlined new perspectives in the framework of glucose monitoring to face diabete disease is deeply discussed

Application of CRLH Transmission Line Metamaterial in Micro-bio Sensing for Non-invasive Continuous Glucose Monitoring

Department of Electrical EngineeringIn recent decades, the emergence of metasurface has attracted considerable attention due to the unusual properties not commonly found in nature. These unique properties are caused by the left-handed materials (LHM) that usually have negative permittivity (???) and permeability (???). These LH properties can be modeled by the transmission line (TL) approach through the combination of shunt inductance and series capacitance. In reality, a purely left-handed (PLH) structure is not possible for realization due to the unavoidable RH properties of conventional TL structures, defined by series inductance and shunt capacitance per-unit-length. Therefore, the general model of composite right/left-handed (CRLH) structures, including RH properties, is often used in practice to develop several novel applications. This thesis focused on utilizing the novel concept of CRLH TL materials in micro bio-sensing for noninvasive continuous glucose monitoring. Both standing wave and traveling waves mechanisms are analyzed for medical applications to realize the zeroth-order resonating (ZOR) antenna and the leakywave antenna (LWA), respectively. Using CRLH TL approaches, the two antenna types are designed at 2.5 GHz to investigate the interaction with a high-dielectric condition of a human body for non-invasive sensors. Then, the excellent candidate of the ZOR antenna is chosen for the actual body experiment to evaluate the feasibility. The proposed ZOR antenna has two faces of a tapered section and a rectangular patch separated by a gap, and those faces are connected through vias at two corners near the gap. Two identical antennas are fabricated on a flexible printed circuit board (FPCB), and the properties of the zeroth-order resonance are compared with those of the fundamental mode to demonstrate the feasibility. The zerothorder resonance of the proposed antenna exhibits a negligible frequency shift, and its quality factor is 2.9 times higher than the fundamental mode when attached to the skin. The evaluation is further extended to a human experiment using the two antennas for real-time estimation of coupling strength according to the change in glucose concentration. The trend of measured coupling strength well describes the glucose concentration obtained from a glucose meter with a mean absolute relative difference of 12.23%. The results demonstrate that the proposed concept has a great potential to improve the accuracy of the non-invasive estimation in the microwave spectrum. Besides, the LWA concept is also studied and designed in software simulation. The proposed antenna has a radiating region from 2.35 GHz to 2.65 GHz in accordance with the continuous scanning angle from backward to forward without the open stopband. The wide-range steering angle shows a promising approach to keep verifying the characteristics of the antenna in the change of glucose level.ope