Far-field super-resolution focusing with weak side lobes and defect detection via an ultrasonic meta-lens of sharp-edge apertures

Breaking the diffraction limit to achieve super-resolution focusing is a long-sought goal in the field of acoustic imaging and detection. Here, we demonstrated super-resolution focusing of high-frequency ultrasound (5 MHz) based on an acoustic meta-lens with four centrosymmetric dart-like sharp-edge apertures. For the diffracted ultrasound carrying high spatial frequencies, super-resolution focusing is generated in the far field with mainlobe size breaking the diffraction limit (<1.22λ). Different from previous far-field super-resolution focusing, where the sidelobe intensity is close to or even larger than the mainlobe intensity, the sidelobe intensity in our case is weak. We further conducted fine defect detection (∼200 μm) by utilizing our designed far-field super-resolution focusing to verify its nondestructive testing performance.