An epidermal radiofrequency identification technology (RFID) sensor consists of a flexible antenna provided with a radiofrequency identification and sensing microchip directly stuck over the human skin by means of a sub-millimeter bio-compatible membrane. A compact-size epidermal RFID thermometer is here proposed and extensively experimented concerning its electromagnetic and thermal performance in case of battery-less and battery-assisted configurations. The antenna element embeds a mechanism for a post-manufacturing frequency retuning in order to adapt its response to the specific placement over the body. When attached over the skin, the sensor is readable from up to 0.7 m in battery-less mode and 2.3 m in battery-assisted mode. A calibration procedure improved the accuracy of the IC sensor down to 0.18 °C. The time constant evaluated by the first-order response of the IC to impulse heating (photo-flash) resulted in 4.3 s. The epidermal wireless thermometer was experimented in both supervised applications (manual reading) and in un-supervised architectures where users were continuously monitored by a fixed remote antenna or during the crossing of a surveillance gate. In all the considered cases, the reliability of the interrogation link was experimentally quantified and resulted robust for health monitoring applications in clinical and domestic settings and even for the automatic detection of anomalous temperature peaks of people walking within airports and at country border crossing.

The present work deals with the measurement of thermo-physical properties of a freestanding sheet of graphene (thermal diffusivity and thermal conductivity), and their dependence on sample density as result of uniform mechanical compression. Thermal diffusivity of graphene nano-platelets (thin slabs) was measured by the pulse flash method. Obtained response data were processed with a specifically developed least square data processing algorithm. GNP specific heat was assumed from literature and thermal conductivity derived from thermal diffusivity, specific heat and density. Obtained results show a significant difference with respect to other porous media: the thermal diffusivity decreases as the density increases, while thermal conductivity increases for low and high densities, and remain fairly constant for the intermediate range. This can be explained by the very high thermal conductivity values reached by the nano-layers of graphene and the peculiar arrangement of platelets during the compression applied to the samples to get the desired density. Due to very high thermal conductivity of graphene layers, the obtained results show that thermal conductivity of conglomerates increases when there is an air reduction due to compression, and consequent density increases, with the number of contact points between platelets also increased. In the intermediate range (250 ≤ ρ ≤ 700 kg·m^-3) the folding of platelets reduces density, without increasing the contact points of platelets, so thermal conductivity can slightly decrease.