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By Ernst Burger, Brian Woods, Johan Huysamen, Rensheng Sun, and C.J. Reddy, EM Software & Systems - S.A. (Pty) Ltd.

Modern radio frequency identification (RFID) applications were made a commercially viable reality with Harry Stockman's landmark 1948 paper titled "Communication by Means of Reflected Power." The title of this paper succinctly summarizes the character of passive RFID systems:

• A tag antenna passively waiting for power from a carrier signal to power its associated electronics that modulates the reradiated signal to convey information about the tag.
• An interrogating device that radiates a carrier signal to power tags in its vicinity and listens for modulated returns from these devices before processing the returned data into a usable format.

Compared to low-frequency (LF) and high-frequency (HF) RFID systems (which operate through near-field inductive coupling and thus have relatively short read range), ultra high frequency (UHF) RFID systems operate through farfield backscattering, have larger read range, and have been widely used in supply chain management and inventory control. However, very often the electromagnetic (EM) performance of the reader/tag systems could be significantly degraded due to the complex physical environments. With the aid of full-wave or hybrid numerical simulation tools, such situations can be analyzed and optimized to improve the performance of RFID systems.

This article presents options for the EM characterization of such systems with the aid of a commercial EM analysis tool. The numerical techniques are applied to the analysis of RFID tags, readers, tag placement, tag/reader coupling, and tag/reader systems in complex environments.

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•Full Article: Understanding UHF RFID Systems With The Aid Of Computational Electromagnetics