Fast and Accurate Full-Field Out-of-Plane Displacement Measurement Using MIMO-SAR-Based Microwave Interferometry

The microwave radar-based full-field displacement measurement technology offers appealing advantages in harsh environments. However, the traditional 2-D microwave imaging-based full-filled displacement measurement suffers from layover and foreshortening imaging effects and commonly requires corner reflectors to identify and track multiple measurement points. Microwave 3-D imaging can eliminate these drawbacks while limited in high time-consuming sampling and algorithmic complexity. Furthermore, the phase interpolation of traditional microwave 3-D imaging method 3-D range migration algorithm (RMA) reduces the interferometry accuracy. In this article, take the advantage of short data acquisition time and low complexity with the combination of synthetic aperture radar (SAR) and multiinput multioutput (MIMO), the MIMO-SAR-based microwave interferometry is proposed to realize full-filled displacement measurement. We proposed an interpolation-free 3-D microwave imaging algorithm, which reduces the computational complexity to at least 1/2 of the 3-D RMA while achieving similar imaging results. In experimental validations, the proposed method is not only compared with the common microwave 3-D imaging algorithms but also compared with the traditional vision-based method 3-D digital image correlation (DIC). The results show that MIMO-SAR-based MI is more accurate than the 3-D DIC at the same level of measurement points without artificial marking.