A Sensor Measuring a Gradient Tensor of the Magnetic Field for Localization of a Magnetic Dipole.

In ubiquitous computing, localization of an radio frequency identification (RFID) tag attracts great attention, since it is a key to interfaces with location awareness such as haptic interfaces and navigations for blind people/mobile robots. Since an RFID tag with carrier frequencies of 135kHz or 13.56MHz has a loop antenna, the tag's position estimation is reduced to localization of a magnetic dipole. So far, dipole localization has been conducted using an array of loop coils (e.g. 3x3 array of loop coils with diameter of 50mm) and nonlinear optimization algorithms which need iterative computations. In this paper, we develop 1) a closed-form localization formula without iteration, and 2) a spatially compact sensor.