3D Acoustic Imaging Hitting the Diffraction Limit via Fully Parameter‐Optimized Meta‐Lens and Frequency‐Domain Reconstruction

Abstract Super‐resolution imaging is the long‐sought goal pursued in acoustics. In the past decade, many solutions have been proposed by utilizing various metamaterial devices. For example, in acoustics, the holographic meta‐lens is employed to improve the lateral resolutions of ultrasonic imaging. However, the filtering effect of meta‐lens broadens the acoustic wave pulses, which severely degrades longitudinal resolutions, making the high‐resolution 3D imaging hitherto quite challenging. Here, an innovative solution is proposed by designing and implementing a fully parameter‐optimized meta‐lens. At the fundamental frequency, this meta‐lens can achieve a lateral resolution of 80 µm (≈0.37λ 0 ), successfully breaking the diffraction limit. Through the frequency‐domain reconstruction, the longitudinal resolution is increased to 296 µm (≈1.36λ 0 ). Utilizing the nonlinear effect of ultrasound in water, the acoustic meta‐lens can furtherly optimize its imaging quality at the harmonic frequency, where the lateral resolution is increased to 44 µm (≈0.2λ 0 ) with the longitudinal resolution to 148 µm (≈0.68λ 0 ). The work breaks the bias on meta‐lenses with deteriorated longitudinal resolution for broad applications in functional ultrasonic imaging.