THz-TDS-SAFT for the detection of inherent discontinuities in dielectric materials

Today X-ray tomography and Ultrasound Synthetic Aperture Focusing Techniques are representative examples for defect imaging in the field of nondestructive testing. THz time domain spectroscopy (TDS) operates with short electromagnetic pulses. The sensitivity of the pulses to optical material property changes makes THz-TDS attractive for the detection of flaws in dielectric materials. Unfortunately, the X-ray computed tomography (CT) model holds only for THz-TDS reconstruction if minor refraction index differences between the inhomogeneities and the surrounding material matrix exist. A Time Domain SAFT algorithm has been developed to overcome the restrictions. THz time domain measurement on representative sample sets with inherent artefacts were performed to use them for the image reconstructions. The results will be presented and compared with optical surface images of the used test objects to evaluate the SAFT algorithm in relation to the reconstruction quality.