Theory and Practice of Near-Field Electromagnetic Ranging

This paper illustrates the divergence of phase, signal, and energy velocities in the near field by employing space-time diagrams of the evolution of near-fields. In addition this paper describes near-field link and impedance relations a near-field phase diagram for electrically small quadrature transmitters. Near-field physics enables near-field electromagnetic ranging systems in a variety of modes for a diverse range of applications. This paper summarizes recent results applying near-field electromagnetic ranging to a Signal-of-Opportunity Location Device (SOLD) implementation. Q-Track tested this system in realistic environments including a multi-story building and underground. SOLD yielded an rms accuracy of 26cm when returning to a calibration point and 46cm rms between calibration points.