A Twisted Loop Antenna to enhance HF RFID detection for different tag positioning

Abstract

In this paper, a new LF/HF RFID reader loop antenna design is proposed and tested, in order to increase detection areas of the tags. The studied structure is a Twisted Loop Antenna (TLA) which is based on a modified distribution and orientation of the magnetic field lines. Our structure fruitfully uses the complementary antenna principle in a coplanar configuration. This offers more possibilities of tag detection whatever the tag position and orientation. The antenna performances are evaluated by optimizing the equivalent mutual inductance between reader antenna and tag antenna. Results are presented firstly in simulation (MATLAB and HFSS electromagnetic calculator) and secondly by experimental tests at different distances and misalignments, for the two possible tag orientations: parallel and perpendicular.

Sub-coil in reader antenna for HF RFID volume detection improvment

“…Complementary coils [3] increase magnetic coupling in the intersection of the coils when the transponder is perpendicular to the reader surface (VM mode in Fig.1.b) and Distributed Diameter Coil [4] allows especially the detection in HM mode, i.e. when the transponder is placed parallel (Fig.1.a).…”

“…In this study, sub-coils [2] in complementary coils [3] are combined to improve the RFID detection for a small tag (in comparison with the size of the reader coil). The complementary coils allow detection of a tag placed perpendicularly to the reader plane (defined as VM mode), not only on the edges of the loop but also in the center of the structure.…”

Calculation of the equivalente mutual impedance in complex HF RFID systems

“…Tn the following step of the calculus, the capacitors C1 and C3 are inserted in order to find the final Z,o-matrix of the entire system: a conversion from impedance matrix to chain matrix is used. (6) Where (j3( 1)) and (j3( 3)) are the chain matrix of both capacitors C1 and C3• 7The final ZIO matrix, considering the capacitors C1 and C3, has the following terms:…”

“…In the case of weak coupling, the detection performance of the tag is fruitfully evaluated by the mutual inductance as a figure of merit [1] [2][3] [4]. A current challenge in HF RFID is to increase the surface and, if possible, the volume of detection by customizing the shape of the reader antenna [5] [6] [7]. More precisely, a way of improvement is studied and obtained by the addition of a small resonator coil.…”

Array sub-loops reader antenna for HF RFID tracking

“…In this case, optimizing the tag detection is currently done by changing the shape of the conventional (circular or rectangular) reader coil. In the context of small misaligned tag, several studies are proposed to improve RFID detection [6][7][8][9][10][11][12]. In [12] reader antenna including resonator is proposed.…”