Three-Dimensional Ultrasound Full-Matrix Imaging and Its Application in Online Monitor of Injection Molding Process

Full-matrix capture (FMC) of matrix phased array has raised widespread attention in 3-D ultrasound imaging, while research on the imaging methods mainly concentrates on the total focusing method (TFM). However, the TFM simplifies wave beams into rays to estimate the propagation time, so its imaging accuracy is limited, and it has difficulties in adapting to the media with complex sound speed distribution. In this article, a 3-D ultrasound full-matrix imaging method is developed based on the frequency-domain reverse-time migration. Through the discretization of the 3-D wave equation in the frequency domain, the source and receiving wavefields are reconstructed simultaneously, and then, the imaging condition is implemented to recover the imaging result as the spatial reflectivity distribution. Moreover, online frequency-domain reverse-time migration is proposed to process the online FMC datasets efficiently. Herein, Green functions are initialized for the measurement region, through which the source and receiving wavefields are reconstructed efficiently with low memory consumption. Experiments show that the proposed method can image the defects in the components clearly, and the imaging accuracy and resolution of the proposed method are, respectively, 2 and 1.5 times higher than those of the TFM. In addition, the proposed method is applied to image the melt front during the injection molding process, where the merging process of the melt fronts from two sprues was first visualized in situ. Therefore, the proposed method shows great potential in the detection of defects in the components and online inspection of the manufacturing process.