  This work compares different linear and nonlinear RF energy harvesting
models, including limited or unlimited sensitivity, for simultaneous wireless
information and power transfer (SWIPT). The probability of successful SWIPT
reception under a family of RF harvesting models is rigorously quantified,
using state-of-the-art rectifiers in the context of commercial RFIDs. A
significant portion of SWIPT literature uses oversimplified models that do not
account for limited sensitivity or nonlinearity of the underlying harvesting
circuitry. This work demonstrates that communications signals are not always
appropriate for simultaneous energy transfer and concludes that for practical
SWIPT studies, the inherent non-ideal characteristics of the harvester should
be carefully taken into account; specific harvester's modeling methodology is
also offered.
