研究目的
To develop a new algorithm for terahertz computed tomography that accounts for beam profile intensities, refraction, and reflection, enabling nondestructive testing of materials transparent to X-rays by reconstructing deviations from a known CAD model.
研究成果
The proposed MCSRT model and linearized reconstruction algorithm effectively handle THz tomography for nondestructive testing, outperforming existing methods like FRT in simulating beam propagation and reconstructing defects. Experiments show successful detection and localization of defects, though limitations exist in blind zones and for non-central defects. Future work should include model updates during reconstruction, incorporation of diffraction, and enhanced acquisition techniques to address blind zone issues.
研究不足
The method assumes small deviations from the CAD model; large defects or high refraction losses may not be accurately reconstructed. Defects in blind zones (due to refraction) lead to missing information and reconstruction inaccuracies. The model does not account for diffraction effects, and computational expense increases for 3D extensions. Early stopping in iterative reconstruction can reduce artifacts but may compromise accuracy.
1：Experimental Design and Method Selection:
The study involves designing a THz tomography system using a Monte Carlo Slash Ray Tracing (MCSRT) model to simulate THz beam propagation, accounting for Gaussian intensity profiles, refraction, and reflection. The reconstruction algorithm linearizes around a CAD model using the SART iterative method.
2：Sample Selection and Data Sources:
Cylindrical objects made of materials like polyoxymethylene (POM), polycarbonate (PC), and acrylonitrile butadiene styrene (ABS) with known defects (e.g., holes or inclusions) are used. Projections are acquired by rotating and translating the objects.
3：List of Experimental Equipment and Materials:
A 106 GHz THz source, lenses (L1 to L5), translation and rotation stages, a THz detector, and various cylindrical samples. Materials include POM, PC, ABS, and air for defects.
4：Experimental Procedures and Operational Workflow:
The THz beam is emitted, collimated, focused on the object, and detected after propagation. Projections are measured at different angles and positions. Simulations use MCSRT with 100,000 rays to model beam interactions.
5：Data Analysis Methods:
Error criteria (mean square error, mean absolute error, max absolute error) compare simulated and acquired data. The SART algorithm reconstructs deviation images, with analysis of artifacts and defect characteristics.
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