A system and device for harvesting various frequencies and polarizations
of ambient radio frequency (RF) electromagnetic (EM) energy for making a
passive sensor (tag) into an autonomous passive sensor (tag) adapted to
collect and store data with time-stamping and some primitive computation
when necessary even when an interrogating radio frequency identification
(RFID) reader is not present (not transmitting). A specific source of
ambient RF EM energy may include wireless fidelity (WiFi) and/or cellular
telephone base stations. The system and device may also allow for the
recharging of energy storage units in active and battery assisted passive
(BAP) devices. The system could be a "smart building" that uses passive
sensors with RF EM energy harvesting capability to sense environmental
variables, security breaches, as well as information from "smart
appliances" that can be used for a variety of controls and can be
accessed locally or remotely over the Internet or cellular networks.