Effect of added resonators in RFID system at 13.56 MHz

In this study, a reader antenna including resonators is proposed to improve detection of a small moving tag in the case of tracking a radiofrequency identification (RFID) system. The near-field RFID technology is based on load modulation, the input impedance on the reader coil and the mutual inductance between the reader and tag coils are the main parameters for performing detection. They are calculated from the impedance matrix parameters. The added resonators change all the parameters of the impedance matrix consequently the input impedance and mutual inductance are also changed. In this study, analytical formulation defining the equivalent impedance matrix parameters is developed. These formulae are used to evaluate the performance of the proposed design according to the tag misalignment (lateral and angular). From the calculation and simulation results, a frequency shift in the equivalent input impedance is found. To avoid this problem, optimising the positioning of the resonators on the reader coil is performed. This study is confirmed by measures of RFID detection for a reader prototype (with and without resonators) and a small commercial tag. Both the surface and volume of detection of the small moving tag (lateral and angular misalignment) are improved by the principle of added resonators

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

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 co-planar 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

Detecting range and coupling coefficient tradeoff with a multiple loops reader antenna for small size RFID LF tags

International audienceThis paper summarizes some tests with Low Frequency (LF, 125 kHz) RFID tags of two types: Card and Token. These tests were done in order to evaluate the feasibility of an identification/traceability of tags which size is constrained and supposed to be detected inside a delimited volume of 40×40×10 cm 3 . As the size of the antenna tag is supposed to be very small, we improve the detection range and volume of definition by designing different reader antennas. Reader antennas presented are of two types whether they are based on single (SL) or multiple loops (ML). Detection range was evaluated for planar antennas (3 SL and one ML). Volume of definition for the detection was estimated by designing two-level prototypes of ML antennas. Results are discussed about the optimization possibility of detection range and volume thanks to ML

Detection tube for small HF RFID tags, based on mutual coupling with a coil resonator

This communication concerns the detection of 13.56 MHz (HF) RFID “small” tags. Herein, the term “small” refer to an effective area below 1 cm2 and the detection principle is in volume, especially inside a tube of 9 cm in diameter and 2m in length. The ability to detect the “small” tags in the tube is achieved by using a coil resonator conformed on the tube surface, following a principle of multiple magnetic coupling, also referred as magnetic field guide. Theoretical considerations on mutual coupling formula and electrical model fit to CST simulations and VNA measurements concerning the evaluation of impedance and coupling factors range. Detection tests with an RFID reader (from IB technology) and NXP SLI-X chip confirm the possibility of detection by providing a first result of 2 cm range. This detection was impossible inside the tube without using the resonator. Perspectives of improvement evocated at the end of the paper are numerous for that structure

Design of 1cm2 coils for HF RFID instruments tracking with detection range improvement

This paper concerns an application of magnetic coupling RFID technology at 13.56 MHz (HF band) for tracking devices such as instruments. The tag size is defined to be ergonomically small compared to the hand, and fixed inside a maximum surface of 1 cm 2. The case of multiple detections is considered, and consequently the reader surface of control is considered wide enough to include several instruments at the same time during a logistic control process. The use of such a small RFID tag is almost impossible using a large reader loop of 15×30 cm 2, as chosen for the tests. The key idea of the paper is then the addition of a resonator that enables to create the mandatory physical link by means of magnetic coupling between the tag coil and the resonator coil and between the resonator coil and the reader loop. Finally the detection range is highly improved by the presence of this resonator and results demonstrate that it is possible to detect these small RFID “1 by 1 cm 2 tags” at a distance of 1.5 cm to 3 cm, depending on their orientations

LF RFID chequered loop antenna for pebbles on the beach detection

This paper focus on low frequency (125 kHz) RFID by magnetic coupling, more precisely using glasstag type of tags in the context of pebble detection on the beach. The challenge is to detect over a wide area very small size tags which are highly sensitive to the orientation of the magnetic field. To improve the detection ability of the reader loop antenna, the paper proposes to exploit the principle of complementary loops. Theoretical simulations with MATLAB show the potential increase by means of mutual inductance value along a displacement of the tag. A prototype of a chequered loop structure is presented and tested with a classical low power RFID reader to demonstrate the improvement without increasing the current in LF reader loops. The detection performances reach 12,8% for a 900 cm 2 surface of a prototype reader loop, whatever the orientation of the glasstag

Coaxially distributed diameter sub-coil twisted loop antenna in HF RFID

This paper proposes an HF (High Frequency) transmitting coil less sensitive to the angular and position misalignments of the small receiving coil. The DDC (Distributed Diameter Coil) shape and TLA (Twisted Loop Antenna) allow respectively minimizing the disturbance of the magnetic link due to the lateral misalignment and the relative tilting direction of the transmitting coil to the receiving coil. The magnetic coupling link obtained from DDC TLA coils is illustrated by comparison with conventional TLA in the case of HF RFID

Active wideband antenna for underwater tomography (1 GHz)

International audienceA new active antenna has been designed to measure electromagnetic fields in water. It combines a differential wideband amplifier and a dipole, the characteristics of which have been designed to provide a constant gain on the bandwidth of the antenna. The small size of the dipole reduces the mask effect. The designed antenna is a symmetrical reception antenna for the electromagnetic field measurement in water in the frequency range of 100 MHz to 1 GHz and it introduces few disturbances. A possible application will be the microwave imaging of immersed objects

Antenne active et retournement temporel pour l'imagerie micro-onde sous-marine

Le système d'imagerie micro-onde d'objets immergés du laboratoire des signaux et systèmes (L2S) a été récemment perfectionné sur deux points. La conception d'une antenne active large bande spécifique a permis de réduire sensiblement les perturbations dues au système de mesures. En outre, une méthode originale basée sur le principe du retournement temporel permet d'estimer rapidement la position de l'objet immergé et est en cours de validation expérimentale

Antenne active et retournement temporel pour l'imagerie micro-onde sous-marine

Le système d'imagerie micro-onde d'objets immergés du laboratoire des signaux et systèmes (L2S) a été récemment perfectionné sur deux points. La conception d'une antenne active large bande spécifique a permis de réduire sensiblement les perturbations dues au système de mesures. En outre, une méthode originale basée sur le principe du retournement temporel permet d'estimer rapidement la position de l'objet immergé et est en cours de validation expérimentale