Passive distance sensing through measurements of mode splitting in coupled magnetic resonators

The monostatic backscattered magnetoquasistatic field measured at the terminals of a resonant loop due to a nearby resonant loop can be modeled using coupled mode theory. Due to close proximity of the monostatic resonant loop and the nearby resonant loop, the backscattered energy is distributed over a set of two orthogonal modes of positive energy that can be described using classical coupled mode theory. The center frequencies of the two orthogonal modes are separated by an amount known as the coupled mode frequency split, which is strongly dependent on coupling and thus distance. Measurements of this frequency split is inverted for passive distance measurements with an RMS distance error of 1.5 cm for distances up to 1 m.