Characterisation of RF propagation in metal pipes for passive RFID systems

Abstract: In this paper we extend the theory of Radio Frequency (RF) propagation as it relates to propagation within metal circular pipes. This work is motivated by a need to understand the operation of UHF Radio Frequency IDentification (RFID) systems when the tags are placed within the pipes. These circular pipes are shown to be similar to metal tube waveguides which are hollow. We derive the Bessel function that is used to identify the propagation constants, the different transverse electric and transverse magnetic modes, cut-off frequencies and the multimode attenuation. These parameters are used within the theory to identify operating limitations of passive RFID systems in hollow metal pipes. A comprehensive general theory is developed to enumerate the workings of passive RFID systems in circular metal pipes. Analytical evaluations are used to visualise the tags within the metal pipes and to validate the theory presented in this paper.