Variation of signal strength and electromagnetic field pattern in conveyor-based radio frequency identification systems

Abstract

In this paper, we study the characteristics and variation of RF signal strength and electromagnetic (EM) field pattern in a conveyor-based RFID application, and their impact on readability of passive UHF RFID tags. Read-rate (number of reads per second) and received signal strength indicator (RSSI) are employed as a measure of the signal strength within the EM field. It is shown that EM field patterns significantly change depending on the position of tagged case(s) containing metal products, and the number of cases within the read zone. The presence of metal can create read null points in proximity distance to the reader resulting from multipath reflections from objects in the conveyor system environment. Understanding how such significant factors affect the signal strength and EM field pattern is essential for designing an optimised RFID system to achieve a desired level of performance.