In the research by Swartzendruber et al, they noted
some specific problems we intended to overcome. They placed
RFID tags on a patient’s limb and prosthetic device in different
locations, and noted the signal collision problems related to
the RFID high-frequency tags, where signals coming from
multiple tags would cause interference between themselves.
They also noted that there were specific problems related to
relative orientation of the transmitting antenna and the RFID
tags in question. Their solution was to switch to an ultrahigh-
frequency RFID system [2]. Our system uses NFC which
operates at 13.56 MHz, and as such, signal blocking issues
were not prevalent unless the devices were located within
about 3 cm of each other.