Characterization of Deep Sub-wavelength Sized Horizontal Cracks Using Holey-Structured Metamaterials

Image resolution in classical wave applications is limited by the diffraction limit which corresponds to half the operating wavelength ( λ ). To achieve higher resolution, ways of overcoming the natural diffraction limits are of interest. In this paper, an experimental demonstration of deep sub-wavelength resolution in the ultrasonic regime using a metamaterial lens is presented. Metamaterial lenses effectively transfer the evanescent waves to the imaging plane, which carry the details of the sub-wavelength features. The successful transmission of the decaying evanescent waves which contain much larger wave vectors than the propagating waves enables to overcome the diffraction limit set by the operating wavelength. We report an imaging technique using optimized holey-structured metamaterial lens to characterize a horizontal crack of size λ /25 in a layered aluminium sample.