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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, cutoff 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.

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This paper describes the environmental effects and performance analysis of 2.45 GHz Surface Acoustic Wave (SAW) based RFID systems. Piezoelectric materials and their underlying principles are reviewed to describe the nature of SAWs. A performance analysis is conducted to measure the readability and read range for individual tags, compared to multiple tags in a field environment. On the other hand, effects of temperature, humidity, altitude and vibration on the readability and operability of the system are described. Finally, a conclusion is drawn with regards to the performance of SAW-based RFID systems.