Near-Field Ranging Using Dual Mode Magnetic Induction

We propose a novel method of ranging by using an antenna's common and difference mode utilizing magnetic induction (MI). Localization through MI has several practical advantages such as its resilience to multipath and its straightforward implementation. We do this through a modified near-field MI implementation, using a pair of loop antennas which generate common and difference modes. Analytical analysis shows that these generated modes have unique dependencies on distance; therefore, we show that by only measuring the field strength, the range can be accurately estimated without prior calibration. This unique feature arises because the common and difference modes have similar characteristics within the same propagation medium. The proposed method is implemented in the very low frequency spectrum at 6 kHz, which has minimal attenuation and larger penetration depth. The feasibility of the presented approach has been verified through analytical, numerical and experimental results where 20% higher accuracy is obtained compared to the conventional single mode MI approach. Moreover, this methodology overcomes several conventional MI limitations such as the difficulty in obtaining proper calibrations, complex computations, and sensitivity to conductive media. Therefore, our modified MI approach enables ranging in applications such as those in mining safety characterized by lossy propagation channels.