Identifying RF Identification Cards From Measurements of Resonance and Carrier Harmonics

We show that careful measurements of the unloaded resonance frequency and quality factor of RF identification proximity cards allow identification of different card models and, for the set of cards we studied, identification with minimal error of individual cards of the same model. Furthermore, we show that card identification performance is improved by considering an electromagnetic signature that combines measurements of the energy at carrier harmonics during a reader/card transaction together with measurements of unloaded resonance frequency and quality factor.