Reader antenna including resonators for HF RFID detection

Abstract

In this article, HF RFID reader antenna including small resonant coil, operating with the magnetic coupling with the reader coil, is reported. The proposed system is used to improve surface and volume of small tag detection. The performances of such system are validated by maximization of input impedance (load modulation principle) and equivalent mutual inductance between the reader dual-coils and the tag coil compared to a conventional RFID reader antenna. Analytical formulas of theses parameters are developed. The proposed system is validated by detection measurements in parallel and perpendicular configurations between the reader and the tag coils.

Equivalent input and output impedances in HF RFID system including resonator

“…Preliminary results of the proposed design confirm its interest in improving both surface (in the case of lateral misalignment of the tag above the reader antenna surface) and distance of detection [4] [5]. The difficulty is the need of adjusting the impedance of the matching circuit of the reader antenna according to the electrical properties of the resonator in order to maintain the resonance frequency at 13.56MHz [5].…”

“…The voltages V 1 , V res and V 3 in the circuit (b) satisfy the following relations (1), with M ij =M ji being the mutual inductances between coils 1, 2, 3, (1<i,j<3)) The equivalent impedance matrix (Z IO matrix) of the MCRRC system (b) is given by (the complete calculation of the equivalent matrix is developed in [5]): The parameters of the Z IO matrix can be expressed as:…”

“…In this case, the reader antenna has to be changed in multi-loop reader antenna to ensure detection [2][3] [4]. In this study the proposed concept is to changed reader antenna on magnetically coupled reader resonator coils (MCRRC), the link between the reader including resonator and the tag depends on the equivalent mutual impedance [5] [6] [7] [8]. Preliminary results of the proposed design confirm its interest in improving both surface (in the case of lateral misalignment of the tag above the reader antenna surface) and distance of detection [4] [5].…”

“…In this study the proposed concept is to changed reader antenna on magnetically coupled reader resonator coils (MCRRC), the link between the reader including resonator and the tag depends on the equivalent mutual impedance [5] [6] [7] [8]. Preliminary results of the proposed design confirm its interest in improving both surface (in the case of lateral misalignment of the tag above the reader antenna surface) and distance of detection [4] [5]. The difficulty is the need of adjusting the impedance of the matching circuit of the reader antenna according to the electrical properties of the resonator in order to maintain the resonance frequency at 13.56MHz [5].…”

“…Coils 1 and 2 present respectively a radius of 50 mm and 15 mm. In [5] the calculation of the equivalent impedance parameters is given, the work concerns the improvement of the equivalent mutual impedance (as link between the reader multi-coil and the tag coil) at 13.56MHz.…”