Distance Determination of Active Tag Location in the Near Field of Two Coils on NFC Standard Frequency

This paper describes a method for determining the location of an active tag operating at 13.5 MHz, in the form of a flat spiral antenna (tag), placed between two receiver coils, with the possible presence of obstacles. Signal amplitude values are used as input parameters. The ability to determine the position is based on the preservation of the transfer (target) function of the “active tag-receiver coils” system, despite variations in the physical parameters of obstacles. Numerical calculations of the coil field distribution are performed, and the coefficients of the target function polynomials approximating the real dependencies are calculated. An estimation of potential location determination errors in the absence and presence of obstacles between coils is provided. The coil system and the data processing technique allow for one-dimensional spatial localization of the signal source, which can be applied in practical RFID-based applications.