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Acoustic metamaterial concepts, such as metalenses and hyperlenses, have been studied with much interest for super-resolution imaging. However, the physics of wave scattering by sub-wavelength sized defects is still not very well understood. Here, we present studies on acoustic wave interactions with circular defects of sizes varying from over a wavelength to sub-wavelength scale. Near- and far-field scattering patterns of single circular defects are presented, connecting them to analytical frameworks. Scattering field signatures produced by two identical circular defects of different sizes placed side by side are then discussed. The separation distance between the defects is among the parameters varied to understand the effects of geometric features in successful imaging. Experimental results are presented to support the predictions reported in the paper. The insights have important implications for sub-wavelength imaging using acoustic metamaterials. [ABSTRACT FROM AUTHOR]