RFID Loop Tags for Merchandise Identification Onboard Ships

Radio frequency identification (RFID) is one of the most actual techniques employed to control the circuit of merchandises, as an alternative to the classical barecode. RFID tags should be cheap and easy to reproduct on a multitude of dielectric supports. There are several types of RFID systems, depending on whether tag and/or reader are active or passive. For cost reasons, merchandise identification should use active reader and passive tag, as the latter might be manufactured on a cheap FR4 support or printed directly on paper, by using a conductive ink. Passive tags can be shaped as straight dipoles, meandered dipoles, or loops. When a small area is required, loops are more appropriated. Codes are made different one from another by using on the same tag antennas with different resonance frequencies. Another advantage of loops is that they can be placed one inside other, so the occupied area is even smaller compared to other multi-resonant tags. Firstly, a single loop is analyzed, in order to model the resonant behaviour, correlated to the loop geometry and size. Open and closed loops are studied; the lowest resonance frequency for a given loop length is achieved for the open loop. In that case, the loop is resonating as a dipole. Next, a tag with three concentric loops is investigated. Separately, a small loop is used on the tag, in order to couple the received power in a resistor. When the tag is close to the reader, the latter is triggered if power is absorbed simultaneously on the three expected frequencies. The proposed tag was simulated and manufactured. Results show a good agreement between measured and simulated data. Finally, a block diagram for the reader was proposed.