Free-Space Imaging Beyond the Diffraction Limit Using a Veselago-Pendry Transmission-Line Metamaterial Superlens

Focusing using conventional lenses relies on the collection and interference of propagating waves, but discounts the evanescent waves that decay rapidly from the source. Since these evanescent waves contain the finest spatial details of the source, the image suffers a loss of resolution and is referred to as ldquodiffraction-limited.rdquo Superlensing is the ability to create an image with fine features beyond the diffraction limit, and can be achieved with a ldquoVeselago-Pendryrdquo lens made from a metamaterial. Such a Veselago-Pendry superlens for imaging in free space must be stringently designed to restore both propagating and evanescent waves, but meeting these design conditions (isotropic
n
= epsiv
_r
= mu
_r
= -1) has proven difficult and has made its realization elusive. We demonstrate free-space imaging with a resolution over three times better than the diffraction limit at microwave frequencies using a Veselago-Pendry metamaterial superlens based on the negative-refractive-index transmission-line (NRI-TL) approach, which affords precise control over its properties and is also less susceptible to losses than other approaches. A microwave superlens can be particularly useful for illumination and discrimination of closely spaced buried objects over practical distances by way of back-scattering, e.g., in tumour or landmine detection, or for targeted irradiation over electrically small regions in tomography/hyperthermia applications.