Dipole Estimation from the Magnetic Field Gradient for RFID Tag Localization†

This paper presents a simple sensor and algorithm to estimate the position of a magnetic dipole for localization of an RF-ID tag. Acquisition of the tag position, in addition to the ID information, opens up various applications with location awareness. A key point of our method is the use of spatial gradients of the magnetic field, created by the RF-ID tag. First we show a deterministic algorithm to express the tag position, irrespective of its posture, in terms of the combination of the fields and their first order spatial derivatives. Then, we show a sensor unit that can measure the spatial gradients efficiently.