Two-dimensional Localization of an RFID Tag by Using a Weighted Integral Sensor on a Square Boundary

This paper presents a novel method for the localization of a passive Radio Frequency Identification (RFID) tag in two-dimensional (2D) space. First, in a 2D square domain inside which an RFID tag is freely placed and moved, we show that a line on which the RFID tag exists can be estimated from the weighted integrals of the magnetic field created by the tag along the boundary of the domain. Then, for measuring them, we develop a square-shaped magnetic sensor composed of three coils only: two pairs of oppositely-wound rectangle coils connected in series on the parallel sides of the squared domain, and four bow-tie-shaped coils connected in series on all sides. Using the developed sensor with the side length of 200 mm, a low frequency (135 kHz) RFID tag was localized in the square area 160 mm on the side with the average error 3.6 mm at 80 points.