A system comprising: a transmitter that includes at least three coils, thetransmitter configured to generate magnetic fields； a sensor that includes atleast threecoils, the sensor configured to provide sensor signals that correspond to themagneticfields generated by the transmitter； and a computing device in communicationwith thetransmitter and the sensor, the computing device configured to compare a firstsensorsignal and a second sensor signal, and based on the comparison, determinewhether anyof the sensor coils are locked to a corresponding frequency out-of-phase.
