Radio-Mechanical Characterization of Epidermal Antennas During Human Gestures

Recent developments in Materials and Radiofrequency Identification (RFID) technologies are currently boosting the development of new class of flexible and elastic epidermal devices for the wireless remote monitoring of biophysical parameters. As tightly bio-integrated with the skin, epidermal antennas are subjected to mechanical deformation during the natural movements and gestures of the human body. The experienced effect is a degradation of the communication performance of the RFID link. In this contribution, we evaluate the stiffness and the change of the radiation gain of on-skin UHF antennas in common gestures by a combined mechanical-electromagnetic model to provide a database and a modelling methodology to improve the design of deformation-tolerant skin antennas. The deformation of the skin is firstly quantified by using a contactless 3D scanner and then the communication impact is predicted by means of an electromagnetic analysis of stretched antennas for some relevant cases of thin-wire layouts. Preliminary numerical simulations and experimentations demonstrated that constraints over low stiffness and insensitivity of radiation gain could be not always compatible. An epidermal antenna may undergo up to 3-4 dB of gain degradation that converts to 30% reduction of the read distance for the strain orientation producing the minimum mechanical stiffness. The derived deformation database could be useful to improve the design of more robust epidermal antennas.