This conference paper presents some experimental results using the concept of an multi-loaded enhanced RFID tag capable of switching between different loads to fully determine the input impedance of the RFID tag antenna which can then be used for sensing applications.
Capdevila, S. [et al.]. Enhancing RFID sensing capabilities: multi-load backscattering. A: IEEE International Symposium on Antennas and Propagation. "Proceedings of the IEEE Antennas and Propagation Society". Orlando: 2013, p. 2315-2316.