Quantitative Evaluation of Two Kinds of Surface Roughness Parameters Using Air-Coupled Ultrasound

Abstract

Air-coupled ultrasound technique using broadband capacitance transducers with a center frequency of 0.5 MHz is applied to the roughness evaluations of material surfaces having a relatively wide range of roughness, i.e., the rms roughness Rq and the surface correlation length λ0, up to 244 and 445 µm, respectively. To carry out quantitative determinations of the two kinds of roughness parameters, i.e., Rq that represents height information of a surface profile and λ0 that represents lateral information, simple methods using a Kirchhoff-based scattering model are proposed. The two parameters are basically determined from the coherent and diffuse components of the scattered waves of air-coupled ultrasound. The roughness parameters determined by the developed ultrasonic method are generally in agreement with those determined by the conventional stylus method. The effects of frequency, incident, and reflection angles on measurement accuracy are examined.