Long-range over-a-meter NFC link budget with distributed large-area coils

Abstract

Near-field communication is considered to have a high level of hardware security protection owing to its natural short-range wireless operation, which makes a man-in-the-middle attack impossible. Here we question this statement by demonstrating a several-meter range NFC communication channel, supported by resonance-tuned large-area distributed coils. Typical NFC antenna architectures encompass multi-turn wires, forming flat resonant coils. Being several centimeters across, those devices cannot provide reliable communication between items, situated more than a fraction of a meter apart. An appealing approach to the range extension is to enlarge the coil area, thus spreading the magnetic field over larger distances. However, in this case, the overall length of folded conducting wires becomes wavelength comparable, nevertheless, the overall size of the coil remains electrically small, considering the 13.56 MHz operation frequency. Here we demonstrate several coil designs and establish a reliable NFC channel over several-meter distances. Adaptive impedance matching is implemented to maintain an energy power transfer between resonant coils, thus further extending the communication channel and making it robust to clutter. The ability for long-range NFC communication raises security concerns in sensitive contactless operations like wireless payments, prompting the need for enhanced countermeasures due to potential hardware vulnerabilities.