Wearable Near Field Communication Platform with a Battery-Free Skin-Interfaced Tag for Continuous Temperature and Impedance Monitoring

Battery-free skin-interfaced sensing requires lightweight passive tags that can operate with wearable readers. Here, we report a flexible NFC platform combining a passive circular FPCB tag with a flexible TRF7970A-based reader for temperature and impedance monitoring. The tag integrates an RF430FRL152H transponder, skin-contact impedance electrodes, an analog front end for impedance measurement, and an STS41 temperature sensor. The tag maintained stable data readout within 25 mm, and preserved its response under 1 cm bending. A status-gated, duty-cycled ISO 15693 workflow enabled 0.1 Hz temperature and impedance updates with BLE smartphone visualization.