Fig. 3: Sharp tips do not enhance broadband NFRHT.

For NFRHT, an important question is whether the optimal structure might be (a) patterned with sharp cones, or (b) planar structures without any patterning. c Numerical simulations of the scattered fields from an electrostatic dipole source between two-dimensional conducting wedges, either at the source location (red, distance d from either tip) or near the tip (gray, distance 0.1d). Near-tip scattered fields (gray) exhibit the lightning-rod effect, increasing with tip sharpness. But frequency-integrated energy transfer is proportional to the scattered field at the source (red), which increases with wedge angle, consistent with domain monotonicity. Out of all possible sub-domains, planar half-spaces must have the largest frequency-integrated response.