Figure 1a:

(a) WAND device implanted within an animal couples inductively to two external loops (Loop 1 and Loop 2). Loop 2 couples power via the pumping signal to the WAND at ω₃ to convert the weak MR signal at ω₁ into an amplified output at the idler frequency ω₂. The idler current at ω₂ mixes again with the pumping signal at ω₃ to amplify the current at ω₁, which couples out to loop 1 connected to the MR imaging system. (b) Schematic of the WAND implemented as a double resonant circuit coupled inductively to the external loops. (c) Photograph of the PDMS-encapsulated WAND device (see text for discussion of L₁, C₁, L₂, and C₂). (d) The phantom test arrangement with the WAND device placed on the surface of a 1% agarose gel. Loop 1 and loop 2 are both 22 mm in diameter and are mounted concentrically above the gel.