A new measurement method for ultrasonic surface roughness measurements

This study proposes the application of Doppler-based ultrasonic method to surface roughness measurements. The fabricated prototype measures the slope of the under-test surface at small holes to evaluate the roughing parameters and this makes for more precise measurement. The device comprises an ultrasonic transmitter emits sound pulses that travel across to the under-test surface. The reflected wave is separated into many weak sounds, a few of which are received by the receiver. The Doppler effect caused the frequency of the received wave to be shifted with respect to the surface roughness at the reflecting point. The relationship between the Doppler shift and the roughing slope is mathematically analyzed.Compared to the transit-time based techniques, the dependency of the sensor on the sound speed in air is decreased by a factor of 2 and therefore a more precise measurement is achieved. The fabrication of a prototype device and experimental verification of the analytical results are reported.