A sensor for tissue characterization is provided, comprising: a resonator, configured to be placed proximally to an edge of a tissue for characterization, without penetrating the tissue, the resonator comprising a conductive structure associated with a diameter-equivalent dimension D, in a plane substantially parallel with the edge, and with a feature size d; and at least one conductive lead, for providing communication with an external system, wherein the resonator is configured to resonate at a frequency which corresponds to a free-air wavelength range of between about lambda and about 40 lambda, wherein lambda is at least about ten times the diameter-equivalent D, and wherein upon receiving a signal in the range of between about lambda and about 40 lambda, the sensor is configured to induce electric and magnetic fields, in a near zone, in the tissue, the near zone having a diameter of about D, so that the tissue in the near zone effectively functions as part of the resonator, influencing its resonating values, and so the tissue in the near zone is thereby characterized by its electromagnetic properties, by the resonating response of the resonator.