Methods and Apparatus for Evaluating Downhole Conditions with RFID Mems Sensors

Goodwin, S., Roberson, M., Bartee, C., McGuire, K., Roddy, C., Rothrock, G., & Ravi, K. (2016). Methods and Apparatus for Evaluating Downhole Conditions with RFID Mems Sensors (Patent No. 9,494,032.)

A radio frequency identification (RFID) tag can include a die attached to an inductive-capacitive (LC) circuit including a capacitive element coupled to an inductive element. The LC circuit can have a resonant frequency that varies according to properties of fluid proximate the RFID tag. The RFID tag can further include a coating material disposed around the die to form an outer surface of the RFID tag. The coating material may have a thickness over a portion of the LC circuit, to permit a conductivity property of a fluid proximate the outer surface to affect the resonant frequency of the LC circuit such that the resonant frequency shifts to a second resonant frequency. Additional apparatus, systems, and methods are disclosed.