Meta-screens and near-field antenna-arrays: A new perspective on subwavelength focusing and imaging

This article reviews some of the recent progress made in the field of near-field focusing and near-field imaging. In particular, it addresses the “meta-screen” that produces a subwavelength focal spot from an incident plane wave, as well as the near-field antenna arrays that have been used to demonstrate two-dimensional subwavelength imaging. The significance of these contributions is that subwavelength operation occurs at a relatively long working distance (a quarter-wavelength) from the screen or array elements. To analyze and design such structures, a spatially shifted beam theory was introduced for enhancing the evanescent field. Several meta-screen and antenna array structures will be discussed, with simulation and experimental results presented to illustrate the focusing and imaging behavior.

► Shifted-beam theory is used to design arrays for subwavelength focusing and imaging.
► Subwavelength features are synthesized at a distance of a quarter-wavelength.
► A slotted “meta-screen” demonstrates two-dimensional subwavelength focusing.
► Antenna array probes achieve imaging resolutions of almost a quarter-wavelength.
► Imaging is performed on objects in free-space as well as buried within a dielectric.