Imaging surface roughness with continuous-wave ultrasound reflectometry.
Farid G. Mitri, James F. Greenleaf, Mostafa Fatemi · The Journal of the Acoustical Society of America · 2008
Measurement of surface roughness irregularities is an important indicator of product quality for many nondestructive testing industries. Many techniques exist; however, because of their qualitative, time-consuming and direct-contact modes, it is of some importance to work out new experimental methods and efficient tools for quantitative estimation of surface roughness. Continuous-wave ultrasound reflectometry (CWUR) is presented here as a novel nondestructive modality for imaging and measuring surface roughness in a noncontact mode. In CWUR, voltage variations due to phase shifts in the reflected ultrasound waves are recorded and processed to form an image of surface roughness. An acrylic test block with surface irregularities ranging from 4.22 to 19.05 μm as measured by a coordinate measuring machine (CMM) is scanned by an ultrasound transducer having a diameter of 45 mm, a focal distance of 70 mm, and a central frequency of 3 MHz. It is shown that CWUR technique gives very good agreement with the results obtained through CMM inasmuch as the maximum average percent error is around 11.5%.