Design of wearable sensors for measuring 5G and beyond signals for health risk assessment

This thesis investigates the feasibility of a compact, low-cost wearable device for the assessment of electromagnetic field (EMF) exposure levels in prospective 6G scenarios in the 14.8–15.35 GHz frequency range. The work is motivated by the intention to anticipate future measurement requirements by developing a solution specifically conceived for frequency bands and propagation conditions that are expected to play a significant role in next-generation wireless systems, thus contributing, at least in part, to the mitigation of one of the main issues that may hinder the early deployment of new communication technologies, namely the lack of adequate instruments for measuring the EMF associated with the signals of interest. To this end, the main characteristics of previous generations of mobile communication systems were first examined in order to gain a deeper understanding of RF-EMF exposure and of the challenges that newer generations, such as 5G and prospective 6G systems, pose to researchers involved in the development of new measurement and modeling techniques. Standardized and non-standardized measurement protocols for the assessment of RF-EMF exposure levels were then presented, together with the main characteristics of the different types of devices that may be employed for this purpose, so as to identify useful insights supporting the achievement of the main objectives of the present work. Furthermore, since the characterization of 6G signal levels is expected to raise challenges similar to those already posed by 5G signals, two real-environment measurement campaigns were discussed in order to examine the solutions currently adopted for the characterization of exposure levels associated with 5G signals. The considerations drawn from this analysis led to the definition of a proof-of-concept architecture based on a planar radiating element, an RMS RF power detector, and a digital acquisition section. Particular attention was devoted to the design and validation of the antenna, which represents the most critical and original element of the system, since its radiation characteristics, physical footprint, and fabrication cost directly affect both the measurement performance and the overall compactness and economic viability of the proposed device. More precisely, in order to satisfy the main requirements of the target application in terms of compactness, cost-effective manufacturability, polarization behavior, and radiation performance, a single-microstrip-fed circularly polarized patch antenna, operating at 15 GHz on a 0.508 mm-thick Rogers RO4003C substrate and occupying an overall area of 22.00 mm × 12.70 mm, was designed and optimized through extensive numerical simulations carried out with CST Studio Suite. On the basis of the obtained design, the antenna prototype was fabricated and experimentally characterized in a semi-anechoic chamber in order to verify whether it was capable of reproducing the behavior predicted by the electromagnetic simulations performed on the numerical model of the antenna. Overall, the obtained results validate the proposed proof-of-concept design and demonstrate the practical feasibility of a compact, low-cost wearable personal exposimeter for prospective 6G applications. In this sense, the work contributes to the development of devices specifically aimed for long-term personal EMF exposure assessment in realistic scenarios.