Experimental verification of subwavelength acoustic focusing using a near-field array of closely spaced elements.

A linear array of closely spaced sound transducers is presented that can produce a subwavelength-focused intensity profile at a distance of a quarter wavelength. This work is related to research on super-resolution using metamaterials in both the acoustic and optical domains. It is designed using the principle of shifted beams, a near-field antenna array theory developed for the subwavelength focusing of electromagnetic waves. Once the spatial sound pattern is characterized for each source, the optimal weights for a minimum beam width can be calculated. An experiment operating at 4 kHz was able to successfully construct a super-focused beam.