Computer simulation of the diffraction of millimeter electromagnetic waves to detect internal defects of products made using additive technology

The article describes the computer model of using electromagnetic waves with lengths from $0.1$ mm to $1$ mm for detection of internal defects of products made by additive technology.
Now additive technology and 3D printing use materials transparent for terahertz waves (frequency $3\cdot 10^{11}$–$3\cdot10^{12}$ Hz, wave length $0.1$–$1$ mm). At the same time, defects in 3D printed products have sizes like a terahertz wave’s length. Thus the Fresnel diffraction can be observed during illumination of a product with the same defects by monochromatic milliwaves.
Thereby the simulated diffraction method for 3D printed products quality checking can be applied. In this article the checking scheme, the diffraction pattern modeling algorithm using the Rayleigh – Sommerfeld integral, and the computer programme for this algorithm are described. The determination of sizes and positions of defects in products using diffraction patterns is shown.
The proposed diffraction method is fully automated and low-cost, uses safety electromagnetic radiation and can compete with tomography methods.