A Terahertz 3-D Imaging Method for Complex Internal Structure of Object

Terahertz (THz) technology is a promising technology in recent years due to its great potential for non-destructive testing (NDT) of specific materials. This article proposes a THz 3-D imaging method for the internal structure of materials, which is widely needed in NDT applications. First, a "rotating arrays" method for THz scanning is proposed. With rotating the conventional 2-D arrays, the "rotating arrays" method solves the problem that THz reflected waves from complex structures are hardly received by the probe. After that, a "two-step reconstruction" (TSR) THz data processing method is proposed. The first step is the "primary reconstruction" (PR), in which the sample is reconstructed without considering the refractive index of itself. Then, "secondary reconstruction" (SR) is used for refraction correction of the internal structure based on the refractive index of the material and the data obtained in the PR. The experimental results verify that compared with the conventional THz imaging method, the method proposed in this article can image the interfaces, air gaps, and complex geometric structures inside the measured object with satisfactory accuracy and can image the overall internal structure in 3-D.