Improving LF reader antenna volume of detection for RFID token tag thanks to Identical Coaxial Loops (ICLs) and in/out-of phase multiple-loops structures

Abstract

This work concerns the prototyping of a low cost PCB based multiple loops antenna for LF 125 kHz RFID application. The multiple loops structure is considered for the context of small tags traceability, for example token tags such as circular HitagS (1-2 cm of diameter). The targeted volume is 20×20×10 cm3 for the moment. The position of the tag can be parallel or orthogonal to the reader antenna plane, with a variation of the angle position, and is moving inside the volume of detection (small objects in a storage basket in practice). The dedicated conception of a reader antenna is necessary because the application targets a volume of detection rather than maximum range detection. Additionally, the position of the tag is not known. The design considerations are based on a combination of Identical Coaxial Loops (ICL) and in/out-of phase loops structures whose advantages are discussed in terms of mutual inductance in the simulation part. An optimum diameter of 7,5 cm is noticed for square loops case. The realization of this structure shows qualitatively good results for our objectives and emphasizes a tradeoff between the two effects of coupling due to the two structures combined. As the tag is moving inside the volume, with an orientation (tag position test) unknown, our observations drive to the conclusion that the detection will be effective. Some perspectives are also clearly identified to improve the structure in the future.