Figure 1

Genetic representation of a matrix antenna. Left: artistic three-dimensional view of an example bow-tie nanoantenna consisting of eight gold cubes. Right: top view indicating the transition to a $5\times 5$ matrix representation, where each “1” denotes the presence of a $10\times 10\times 11{\mathrm{nm}}^3$ block of gold.Reuse & Permissions

Figure 2

Comparison at $\lambda =647\mathrm{nm}$ between a resonant linear dipole nanoantenna built from two 10-nm separated rectangular arms of $46\times 30\times 11{\mathrm{nm}}^3$ and a structure obtained with the EA described in the text. (a) shows the geometry of both structures from the $+z$ direction. The blue spot denotes the position of the near-field optimization by the EA. The spectra in (b) are taken at this marked position during a broadband Gaussian excitation. (c) shows the logarithmic near-field intensities at $\lambda =647\mathrm{nm}$ when the structures are illuminated by a monochromatic Gaussian focus with $NA=1$. The scales are normalized and not comparable. In (d) the the change of near-field enhancement at the optimization position is shown for each single block when it is toggled. (e) is a zoom of the central part of the EA antenna, showing the strength and direction of the currents.Reuse & Permissions

Figure 3

(a) Geometry and dimensions of the examined split-ring antenna. (b) Near-field intensity enhancement of the structure in (a), showing highly concentrated fields towards the open end of the gap. The blue point denotes the point of the measurement for the spectrum figured in (c). The $Q\approx 25$ for the SRA grey (red online) is comparable to that of the reference antenna (black). (d) shows an overlay of the squared current density and the current direction inside the material as well as the magnetic near-fields outside the structure.Reuse & Permissions

Figure 4

Wavelength shift of the extinction cross section resonance for the combined two-wire antenna and the $n=1$ split-ring resonance, as the conductive link between the two antenna rods and the split-ring (see inset) increases in thickness (marked thick dashed). Also visible are the bonding and antibonding $n=3$ modes, which also shift slightly into the blue and get very weak (marked thin dashed). The sketches at the bottom show the geometries of the fully disconnected and fully connected structures, together with the position and sign of their mode’s charge density maxima.Reuse & Permissions