SURFACE-ROUGHNESS EVALUATION VIA ULTRASONIC-SCANNING

Despite extensive applications of ultrasonic waves to various nondestr uctive testing and evaluation of materials, scattering of focused ultr asonic waves due to surface roughness has not been fully investigated. This paper presents an analytical and experimental evaluation of surf ace roughness measurement using focused ultrasonic beams. The characte ristics of focused ultrasonic waves are analyzed by using the impulse response method with a sine-modulated Gaussian pulse as source. First, the beam profile in the focal plane of the focused ultrasonic transdu cer is analyzed both numerically and experimentally. Second, peak ampl itude distribution and reflected waveforms from a flat surface with va rious incident angles are analytically generated and compared with exp erimental results. Then, the peak amplitudes of the ultrasonic waves r eflected from cusped surfaces which are easily found among machined su rfaces are analyzed and compared with experimental data for the first time. The analysis shows good agreement between analytical and experim ental results. The excellent correlation between the measurements usin g a profilometer and the proposed ultrasonic system demonstrates a goo d potential for surface roughness measurement by ultrasonic sensing.