Acoustic time-domain reflectometry for irregular surface recognition

The theoretical scattering of acoustic wave pulses from irregular surfaces is studied by using time-domain analysis. The purpose has been to examine the application of acoustic time-domain reflectometry (ATDR) to the nondestructive testing of surface geometry characteristics. A finite-difference time-domain (FDTD) stimulation method is used to obtain the reflected wave response from irregular success to an incident short pulse by calculating the scattered field and determining the net pressure at an acoustic sensing transducer. Various configurations pertinent to nondestructive testing of irregular surfaces are considered and the relationships between the transducer output waveform and the surface feature are investigated. A strong correlation between the pulse width of the reflected pulse and the surface roughness is established for important configurations of interest. Results are determined for a range of surface conditions extending from the Kirchhoff limit where single scattering approximation is accurate to cases where complex multiple scattering effects become important. Conditions for departure from the single scattering limit are identified from simulations. (C) Acoustical Society of America.