Fuente: Wipo "precision agriculture" Subharmonic tags for passive far-field sensing are provided having at least one antenna configured to receive an interrogation signal having a plurality of interrogation frequencies, a passive LTI network in electrical communication with the at least one antenna, and two or more resonators, each resonator having a different resonant frequency and a corresponding trigger frequency different than the resonant frequency, wherein the passive LTI network is configured such that the tag only produces a response signal for trigger frequencies that are different from any of the resonant frequencies of the resonators, each resonator of the subharmonic tag configured to produce a response signal having a different frequency than the trigger frequency, the subharmonic tag configured to produce an output signal responding to the interrogation signal, the output signal including one or more of the response signals.