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

Abstract

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.

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

“…In the case of RFID, the volume to prospect could be wide in comparison with the object to detect. This latter one could be oriented arbitrary and can be displaced; for instance, tagged pebbles [7] with a movable reader coil on sea-beach, clinical patient in a hospital [8] or surgeon devices sliding in an inclined tube [9]. A solution could be to design a planar transmitting antenna that generates magnetic field with the same intensity over the entire surface of the reader antenna but several orientations versus the zone of the reader antenna.…”

Enhanced Hf Rfid Detection Area of Mobile Small Tag via Distributed Diameter Coil Resonator

“…Whenever the prospecting surface or volume is large, and the tagged object is small, moved and oriented randomly, we have to realize an efficient link. We can cite for instance applications such as a patient moving in a large room [2], surgeon devices inserted in a box on a movable tray or sliding in an inclined tube [3], or tagged pebbles when the reader is moved onto the beach [4]. RFID systems can be classified into two categories: far-field radiation for RF and microwave systems and nearfield magnetic induction for LF and HF bands [5].…”

“…There are in fact two types of near-field magnetic induction: IC (Inductive Coupling) and MRC (Magnetic Resonant Coupling). MRC [6] provides longer range and larger TX and RX size than IC with higher efficiency [3,[7][8][9].…”