(a) A double frequency parametric resonator included a rectangular conductor with a center conductor. Its top and bottom gaps were filled by variable capacitors. (b) A single frequency resonator with the same dimension was tuned by two capacitors. (c) The two resonators were overlapped through a substrate. (d) The modulator was placed on top of a phantom containing 1% agarose, before being inserted into the center of a 7T magnet. During MR signal acquisition, pumping power was applied on the antenna to activate the modulator whose oscillation signal was received by the volume coil.

When the relative SNR of MR images was measured at different distance separations, the amplified resonator (gray) could retain constant sensitivity for transmission attenuation up to 21 dB (at 4.5 cm separation). In comparison, the frequency modulator (yellow) could retain constant sensitivity for transmission attenuation up to 34 dB (at 11 cm separation).