In some embodiments an apparatus includes an amplifier, a first inverter having an input coupled to an output of the amplifier, and a second inverter having an input coupled to an output of the first inverter and an output, where the output of the second inverter is fed back to an input of the amplifier. Also provided are methods for designing such coils, as well as coils generating arbitrary field profiles. The translation engine is configured to translate the pre-translation event to obtain a first translated event, prepare the first translated event for transmission to a first tracking system, and send the first translated event to the first tracking system.