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An ultrasonic phased array consists of multiple ultrasonic probes arranged in a certain regular order, and the delay time of the excitation signal sent to each array element is controlled electronically. The testing system model based on ultrasonic propagation theory is established to obtain a controllable and focused sound field, which has theoretical and engineering guiding significance for the calculation and analysis of ultrasonic array sound fields. Perfecting array theory and exploring array imaging methods can obtain rich acoustic information, provide more intuitive and reliable research results, and further the development of ultrasonic phased-array systems. This paper reviews the progress of research on the application of ultrasound arrays for non-destructive testing (NDT) and brings together the most relevant published work on the application of simulation methods and popular imaging techniques for ultrasonic arrays. It mainly reviews the modeling approaches, including the angular spectrum method (ASM), multi-Gaussian beam method (MGB), ray tracing method, finite element method (FEM), finite difference method (FDM), and distributed point source method (DPSM), which have been used to assess the performance and inspection modality of a given array. In addition, the array of imaging approaches, including the total focusing method (TFM), compression sensing imaging (CSI), and acoustic nonlinearity imaging (ANI), are discussed. This paper is expected to provide strong technical support in related areas such as ultrasonic array testing theory and imaging methods.

Liquid crystal (LC) metasurfaces have attracted lots of attention recently due to their superior performance, tunability, and relatively simple fabrication. Conventional LC metalenses work either at multiple discrete wavelengths or continuous wavelength band with complicated combinations of multielements. Here, we propose and demonstrate achromatic imaging in the continuous broadband wavelength range with a single coded LC metalens. A cubic coded phase is imposed to the conventional phase profile in the plane of a metalens by manipulating the orientations of LC molecules via photopatterning from which a Pancharatnam–Berry (P–B) phase can be generated. Both theoretical and experimental results show that the phase-coded LC lens exhibits great achromatic imaging behaviors in the broadband wavelength range and wide field of view (FOV) in which a bandwidth of 134 nm and FOV of 24° can be achieved in the visible wavelength range with a phase coding parameter of 30π. This work provides a new and practical way of designing liquid crystal metasurfaces for broadband achromatic imaging with advantages of ultrathin, light weight, integrability, and tunability but less fabrication complexity.

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