Far-Field Subwavelength Acoustic Computational Imaging with a Single Detector

Acoustic imaging techniques suffer from the diffraction limit due to the loss of evanescent waves that carry subwavelength information of objects. To overcome the diffraction limit, the evanescent components have to be collected and measured. Most of the existing methods targeting this task rely on expensive detector arrays and inefficient near-field point-by-point scanning. Here, we propose and experimentally demonstrate the realization of a far-field acoustic subwavelength imaging method based on a single stationary detector. Specifically, we utilize a series of masks to structure the detected field, so that the evanescent wave information is encoded into the propagating waves due to spatial frequency convolution between the object and masks. Our study shows that, by combining the principles of computational imaging and metalens, high-quality images of a subwavelength object can be reconstructed in the far field, even in the presence of unwanted scatterers. Our work provides a robust method for far-field acoustic subwavelength imaging, which could bring possibilities for acoustic microscopy and could further be applied to medical ultrasonography, underwater sonar, and ultrasonic nondestructive evaluation.