Measurement of Surface Roughness of Painted & Unpainted Metallic Objects using a THz Profilometer
摘要
This paper reports the design aspects of 3D profilometer in terahertz (THz) frequency domain in reflection geometry employed for surface roughness measurements of painted and unpainted metallic objects. We also discuss the selection of correct combination of incident angle and frequency-based modalities for getting best results in terms of signal strength from coated and underneath rusted surfaces at discrete terahertz frequencies. The study focuses on the surface scattering properties, which directly affects the quality and strength of the reflected THz signal. The signal was recorded at frequencies of f = 0.5, 1.0, 1.5 and 2.0 THz, respectively. The measured 3D surface roughness profiles of old painted and unpainted metallic objects ranged from 15–100 μm range for the given THz frequency range . It was observed that the values of reflection coefficient decreased with increasing surface roughness in the 10–20 μm range Furthermore ,frequencies between 0.5and 1.5 THz range exhibited the highest reflection coefficient for surface roughness values below 50 μm. However, the reflected signal at 2.0 THz frequency shows experimental decay up to 120 μm range. The study was focused on the recording of 3D surface roughness profile and reveal that the exponential decay behavior of the reflected signal can be extended for highly rough surfaces by increasing the angle of incidence at lower frequency.