Investigation on Passive Booster for Improving Magnetic Coupling of Metal Mounted Proximity Range HF RFIDs

In this paper, the design methodology, fabrication, and measurement of a passive circuit for increasing the read range of the near-field-communications (NFCs) gadget in handheld devices to read miniature metal mounted radio-frequency identification (RFID) are discussed. Since, the impedances at source and load are unknown, the conventional methods are not helpful for designing a proper communication. The proposed circuit is fabricated on thin flexible polyimide film hence; it can be simply attached to the back of handheld devices with arbitrary shape. Having only one discrete component in the circuit is another step toward low-cost devices. The magnetic coupling between the small metal mounted high-frequency (HF) RFID and the NFC coil are improved by adding two coils connected in parallel to each other resonating at 13.56 MHz. One coil is designed to be coupled to the NFC coil and the other one to the HF RFID. The operability of the system is investigated not only by standard measurement equipment like vector network analyzer but also utilizing different smartphones. The agreement between the simulation and practical results shows that the booster improves the read range significantly.