Three dimensional surface depression profiling using focused air coupled ultrasonic pulses

Surface topography is an important variable in the performance of many indu strial components and is normally measured with diamond tip profilometry ov er a small area or by using optical scattering methods for larger area meas urement. This article shows quantitative surface topography profiles as obt ained using 1 MHz focused air coupled ultrasonic pulses. The profiles were obtained using a system developed by NASA Glenn Research Center and Sonix, Inc., via a formal cooperative agreement. The method is simple and reproduc ible because it relies mainly on knowledge and constancy of the sound veloc ity through the air. The air transducer is scanned across the surface and s ends pulses to the sample surface where they are reflected back from the su rface along the same path as the incident wave. Time of flight images of th e sample surface are acquired and converted to depth/surface profile images using the simple relation (d = V x t/2) between distance d, time of flight t and the velocity of sound in air V. In this article, resolution is deter mined and results are shown for platelike and cylindrical (curved) samples. Impressive results were obtained for all samples when compared with diamon d tip profiles and measurements from micro thickness gages. The method is c ompletely nondestructive, noninvasive, noncontact and does not require ligh t reflective surfaces.