Super-Resolution in Near-Field Acoustic Time Reversal Using Reverberated Elastic Waves in Skull-Shaped Antenna

We investigate the potential of using elastic waves for near-field acoustic time reversal, and in doing so evaluate the possibility of reconstructing sound source positions at below-wavelength distances from a skull-shaped acoustic antenna. Our work is based on a conceptual processing model that translates elastic waves conducted and reverberated in an elastic object into source position, through a time reversal analysis. Signals are recorded by passive sensors glued on a replica of a human skull, measuring solely its mechanical vibrations, and not sensitive to airborne sound. The sound source is placed along the azimuthal and sagittal planes for distances to the skull between 5 and 100 cm. We reconstruct the source position for signals with frequencies in the physiological hearing range with a resolution indirectly proportional to the distance between source and skull across all measurements in the far-field. Measurements in the near-field show –3 dB widths smaller than half a wavelength (super-resolution) with highest resolutions of down to λ/15 measured in front of the orbital cavities. We infer that these anatomical details give rise to complex features of the skull's Green's function, that in turn enhance resolution in a direction-dependent manner.