Evaluation of shielding materials for low frequency RFID systems

When RFID reader antennas are placed in a parallel line configuration, proper shielding is indispensable to prevent the readout of tags in a different line. However, placing electrically conductive or magnetically permeable shielding materials in the vicinity of a loop antenna influences the magnetic field strength and self inductance of the antenna, thus affecting the readout range. This paper evaluates the effects of different shieldings on the magnetic field strength, the readout range of an RFID tag and the self inductance of the antenna. The considered shieldings consist of copper or a combination of copper with a layer of highly or lowly permeable ferrite on top. First, the influences of these materials are compared to a free space setup in FEM simulations. These results are subsequently verified in an experimental setup. The configuration with a copper plate covered with a highly permeable ferrite layer increases the magnetic field strength, readout range and self inductance of the antenna, in contrast to the other configurations. Due to the efficient shielding, erroneous readout events of tags in a parallel line are suppressed.