Microwave imaging sensor system using metamaterial lens for subwavelength resolution

Abstract

Lenses made of negative refractive index metamaterials can overcome the diffraction-limited resolution of imaging at working distances in the far-field. This paper describes a novel negative index metamaterial (NIM) lens imaging sensor system for subwavelength microwave nondestructive evaluation (NDE) using homodyne detection measurements. The split-ring resonator (SRR) - wire based NIM lens is optimized to work at 6.3 GHz (wavelength λ = 48 mm). Coherent homodyne detection scheme provides a simple, low-cost, and highly sensitive NIM lens imaging sensor system that can be used in the field under practical conditions. Imaging of an omnidirectional source using negative refraction is shown using the proposed system. A focal spot of size 0.62λ was obtained in the image plane of the metamaterial lens with a source to image distance of 1.67λ. The focal spot position was further shifted in the azimuthal plane by simple movement of the source. The study demonstrates unique focus-scanning capability of NIM lenses for target localization without the need for complex tuning mechanisms. The feasibility of the system to image subwavelength defects inside dielectric materials in reflection mode is also investigated for its potential application as an NDE sensor. Defects comprising subwavelength hole of diameter 0.25λ and a groove of dimensions 0.31λ x 0.1λ placed at the focal plane of the lens was imaged using the proposed sensor system.