Experimental Verification of Overcoming the Diffraction Limit with a Volumetric Veselago-Pendry Transmission-Line Lens

A fully printed Veselago-Pendry lens (isotropic $n=-1$, ${\epsilon }_r=-1$, ${\mu }_r=-1$) is presented which is based on transmission-line metamaterials. The lens is constructed in a parallel-plate environment at 1.569 GHz and without any embedded sources and achieves a resolution better than the diffraction limit (full width half power of $0.235\lambda$). Because the lens is low loss ($<0.3\mathrm{dB}$ per unit cell), the focused fields are dominated by the evanescent components which dictates that subwavelength tightening of the beam is achieved only in the transverse and not the longitudinal direction. The demonstrated lens is quarter-wavelength thick thus allowing ample “working distance” between the subject/image and the lens.

Figure 1

Volumetric NRI-TL unit cell.

Figure 2

Volumetric shunt-node NRI-TL slab shown in (a) and the printed features shown in (b).

Figure 3

Simulated transmission coefficient (red or gray lines) and reflected coefficient (blue or dark gray lines) from full-wave finite-element method solver Ansoft HFSS (solid lines) and the MTL theory (dotted lines) shown in (a) and the extracted effective material parameters $\epsilon$ and $\mu$ from $S$ parameter, shown in (b).

Figure 4

Side view plot of the magnitude of the electric field along the plane crossing the central line of the NRI-TL metamaterial slab at 1.50 GHz. The electric field is highly confined within the substrate.

Figure 5

The fabricated one layer shunt-node NRI-TL slab lens, consisting of $21\times 4$ fully printed unit cells, as shown in (a) and the demonstration of the focusing experiment setup shown in (b).

Figure 6

The measured magnitude of the vertical electric field detected at the image region at 1.569 GHz. The plot has been normalized to its maximum value. The enhancement of the evanescent waves in magnitude is evident near the exit face of the NRI-TL lens. The dashed line lies at 24 mm away from the rear side of the lens, where the image plane is expected. The solid line demonstrates a magnitude contour plot, of which the phase center lies at the image plane approximately.

Figure 7

The measured phase of the vertical electric field detected at 1.569 GHz. A lack of phase progression is evident near the exit face of the NRI-TL lens where the evanescent waves dominate. (a) shows the phase plot at the entire image region and (b) shows the phase plots at the transverse planes with 1 mm (solid line), 12 mm (dashed line), 24 mm (dotted line), 36 mm (dash-dotted line), and 48 mm (dash-crossed line) away from the lens, respectively.

Figure 8

The measured vertical electric field (red or gray solid line) along with the diffraction-limited image (blue or dark gray dashed line) at the image plane at 1.569 GHz and at a distance of 24 mm away from the exit surface of the lens. The measured electric field is normalized to its maximum value.