Abstract
A new technique that enables passive ultra high frequency (UHF) radio frequency identification (RFID) tags to be read when they are placed in close proximity in an array is presented. This paper demonstrates that, in a linear tag array with a tag separation of 1 cm, the interaction between the backscattered waves and incident wave causes a significant degradation in tag sensitivity. It is found that the use of tags that have polarization diversity can improve the read performance when they are placed in close proximity to one another compared with conventional linear tags. Two ways of achieving polarization diversity are studied in this paper, namely: 1) using a circularly polarized tag and 2) using a cross-polarized tag pair. Both methods show an improvement in close proximity read performance and it is experimentally demonstrated that by using cross-polarized tag pairs in an array, one achieves on average a 2.6-dB increase in read power margin for a 57-tag array with 1 cm separation compared with using conventional linearly polarized tags.
Highlights
I N RECENT years, radio frequency identification (RFID) technology has been used in a wide range of mainstream applications [1]–[3] and passive ultra high frequency (UHF) RFID tags are increasingly replacing current barcode systems due to their longer range, high data capacity, faster read speed, and programmability [4]
We have demonstrated that, using both EM simulation software and a theoretical model that for a tag array with separation of 1 cm, the interference between backscattered waves from tags and the incident wave from the reader causes significant degradation in tag sensitivity
We study the use of tags with polarization diversity in close proximity in a tag array to improve the read performance
Summary
I N RECENT years, radio frequency identification (RFID) technology has been used in a wide range of mainstream applications [1]–[3] and passive ultra high frequency (UHF) RFID tags are increasingly replacing current barcode systems due to their longer range, high data capacity, faster read speed, and programmability [4]. Passive UHF systems operate on the principle of backscatter communications with the tag antenna gathering energy from the electromagnetic wave transmitted by the reader, and using the energy to power a microchip. For many commercial passive UHF RFID applications, a circularly polarized reader antenna is employed to achieve orientation diversity, and the RFID tags are designed with a dipole or microstrip-type antennas with linear polarization [16]. In this case under free space transmission conditions, only half of the potential power transmitted from the reader can be received by the tag antenna as the polarization efficiency is −3 dB. Both the methods are demonstrated through experiment or simulation showing that the tag read performance is greatly improved when such tags are placed close to each other in an array compared to the conventional case that uses linearly polarized passive tags
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