Remote characterization of surface slots by enhanced laser-generated ultrasonic Rayleigh waves.

Characterization of surface features is essential in many industrial applications, especially for features with large depths, high aspect ratios or under extreme conditions. This work presents a non-contact method to characterize surface slots with large lengths using ultrasonic Rayleigh waves generated by a pulsed laser. A delay-and-sum superposition technique is applied to enhance the signal to noise ratio of transmitted Rayleigh waves.

Laser-Induced Full-Matrix Ultrasonic Imaging of Complex-Shaped Objects.

We present laser-induced full-matrix imaging of complex-shaped objects that combines the advantages of noncontact laser ultrasound inspection and high-contrast array imaging based on total focusing method (TFM). Full-matrix data were acquired by synthesizing a laser ultrasonic array through an alternate scanning of the generation and detection laser beams. Taking advantage of the simultaneous generation of all wave modes, surface Rayleigh waves were extracted for surface profiling, and longitudinal waves were utilized for imaging.

Deep-subwavelength control of acoustic waves in an ultra-compact metasurface lens.

Space-coiling acoustic metasurfaces have been largely exploited and shown their outstanding wave manipulation capacity. However, they are complex in realization and cannot directly manipulate acoustic near-fields by controlling the effective path length. Here, we propose a comprehensive paradigm for acoustic metasurfaces to extend the wave manipulations to both far- and near-fields and markedly reduce the implementation complexity with a simple structure, which consists of an array of deep-subwavelength-spaced slits perforated in a thin plate.

On-Line Corrosion Monitoring of Plate Structures Based on Guided Wave Tomography Using Piezoelectric Sensors.

Corrosion is a major safety and economic concern to various industries. In this paper, a novel ultrasonic guided wave tomography (GWT) system based on self-designed piezoelectric sensors is presented for on-line corrosion monitoring of large plate-like structures. Accurate thickness reconstruction of corrosion damages is achieved by using the dispersive regimes of selected guided waves and a reconstruction algorithm based on full waveform inversion (FWI).