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Exploring conditions required for the subwavelength focusing of sound in the near field of an array of resonators using time reversal

This presentation will discuss the time reversal focusing of audible sound over an array of Helmholtz resonators. The presence of the resonators modifies the phase speed of waves, thereby lowering the effective wavelength, in the near field of the focus. It is shown experimentally what conditions are necessary to obtain super resolution. Frequencies above the resonators’ resonance frequency do not result in super resolution. In order to achieve super resolution in the plane of the resonators, the focused waves must be confined to propagate only in the plane of the resonators. When waves converged in three dimensions, super-resolution was not observed but when a 2-D waveguide was used, and super-resolution was observed.