A Passive Wireless Sensor Network for Temperature Mapping Inside a Shielded Coaxial Enclosure

This contribution addresses the electromagnetic feasibility of the wireless temperature monitoring inside a coaxial cavity resembling a portion of a high-power high-frequency cyclotron auto-resonance maser for plasma heating in the new generation of DEMO TOKAMAK machines. The scenario is investigated as a potential communication channel for a ultrahigh-frequency radiofrequency identification (RFID) sensor network where cavity probes are used to both excite the coaxial cavity and to collect the temperature data scattered back by sensor antennas. By using a theoretical near-field analysis of a simplified model of the cavity and of the reader/sensor devices it is demonstrated that a two-probes architecture is suitable to interact with more than N = 16 equally spaced RFID temperature sensors (having power sensitivity of -8.3 dB mW) over the surface of a 0.5 m tube by using less than 20 dB mW power emitted by the reader. The theoretical results are corroborated by experimental data with a mock-up of the cavity and realistic prototypes of miniaturized RFID radio-sensors and excitation probes.