Application of Ultrasonic Guided Waves for Surface Roughness Measurement

Surface roughness is inherently a product of manufacturing process and is often undesirable. In surface metrology, the term “roughness” is typically applied to the highfrequency and short-wavelength parameters of a finished surface. In practical applications, the surface roughness is directly associated with the quality of the manufacturing. This study proposes the use of ultrasonic surface guided waves to characterize the surface roughness amplitude and frequency during the manufacturing process. Finite element modeling (FEM) of acoustic wave propagation along a rough surface has revealed that there is a cut-off threshold for Rayleigh wave propagation, which is indicative of the surface roughness description. This cut-off occurs for a particular ratio of the spatial surface waviness and the acoustic wavelength, and the detection of the resulting wave attenuation and decay characterizes the surface roughness. If such a measurement system can be used in-line with the production process then it could signal adjustment of the material deposition rate when needed to achieve the required product quality.