Optimised inductively coupled reader antennas for smart HF RFID systems

The Internet of things (IoT) refers to uniquely identifiable objects and their virtual representations in an Internet-like structure to be managed and inventoried by computers. Radio-frequency identification (RFID) - a prerequisite for the IoT - is an automatic way for data transaction in object identification and is used to improve automation, inventory control and checkout operations. An RFID system consists of a reader device and one or several tags. Smart reader systems are building blocks for cutting edge applications of RFID and as a subdivision of these systems, RFID smart shelf solutions are started to be implemented for large-scale item-level management where characteristics of reader antennas are critical issue. This work focuses on designing optimised reader antennas for high frequency (HF) RFID smart shelf systems which operate based on inductive coupling between the tag and the reader antennas and have good performance in crowded environments. Firstly, an approach is presented to increase band-width of HF RFID reader antennas to improve the reception of sub-carrier frequencies. A fabricated enhanced band-width antenna at 13.56 MHz is evaluated for its capability in being used for smart shelf applications. The obtained band-width supports sub-carrier frequencies for all the HF RFID standards to be detected easier and thus leads to increased identification range. It is shown the HF RFID technology is capable of identifying the distance of tagged books based on the received magnetic field intensity. Secondly, multi turn small self resonant coil (MT SSRC) antennas are introduced and analysed as a new model of inductively coupled reader antennas. Based on the analysis, two turn planar SSRC (TTP SSRC) antennas having similar dimension with the current HF RFID reader antennas are investigated. Fabricated TTP SSRC antenna operating at 13.56 MHz is resulted to optimised Q factor and more uniform near field pattern in comparison with the similar antennas. Also, a number of TTP SSRC antennas operating at a distinct frequency, 13.56MHz, are fabricated on different substrates and it is shown the desired Q factor and antenna dimension can be obtained based on the dielectric characteristics of the substrate.

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