NFC/RFID Patch Coil Curvature Effect and Shielding for Medical Applications Wirelessly Powered

This paper presents the design of a flexible 4×4 cm
²
square coil for a medical wearable NFC/RFID patch. In such application, the coil is connected to an IC which can power supply an embedded medical sensor. This energy harvesting ability is achieved by inductive resonant coupling using NFC technology at 13.56 MHz. As the patch is fixed on human body (arm), the influence of the human tissue, the need of patch flexibility as well as the interest of a shielding must be investigated. This work focuses herein on the influence of the patch curvature on the coil ability to capture magnetic fields and thus on the recovered energy. This influence, related to the mistuning of the coil, is studied with and without shielding, by means of magnetic and conductive material layers. Measurements show the possible recoverable power level using a NFC chip (NXP NT3H) as the dedicated IC.