THz-CT System Based on FMCW

Terahertz waves combine the penetration capability of microwaves with the fingerprint spectral characteristics of infrared light, making them an emerging imaging and detection modality. This paper proposes and implements a Terahertz Computed Tomography (THz-CT) method based on a Frequency-Modulated Continuous Wave (FMCW) signal to leverage its non-destructive and safe advantages. Based on Radon transform and the Fourier slice theorem, this work establishes an imaging model for FMCW THz-CT, deriving the key equation that correlates the amplitude attenuation of the echo signal with the line integral projection of the object's interior. The experimental system employs a 14-17 GHz fundamental frequency source, which is multiplied by a factor of 12 to generate a 168-204 GHz terahertz signal. A 4f quasi-optical system achieves beam focusing (with a full width at half maximum of approximately 7 mm at the focal point), and a high-precision rotation-translation scanning mechanism is used to acquire multi-angle projection data. Imaging experiments conducted on a sample consisting of two polytetrafluoroethylene (PTFE) cylinders successfully reconstructed their internal structure, validating the method's effectiveness. The experimental results also reveal significant terahertz wave scattering and diffraction effects at the sample edges caused by the geometric curvature, which are identified as a critical factor affecting imaging quality. This study provides a foundation for the theory and system implementation of terahertz FMCWCT technology, demonstrating its potential in the fields of non-destructive testing and security screening. Future work will focus on optimizing the compensation for scattering effects and refining the image reconstruction algorithm.