The Depth of Penetration Into the Metal Longitudinal-Surface (Head) Acoustic Wave

The depth distribution of the amplitude of the longitudinal displacement components in an inhomogeneous longitudinal-surface acoustic wave has been experimentally studied. A steel sample was used to protect the studied signal from extraneous types of waves. The distribution, plotted for depths from zero to 10 mm, in a smoothed form represents a smooth curve with a maximum at a depth of 6.5 mm, which corresponds to an angle of 12.3° to the metal surface. Deviations from the smoothed curve do not exceed 1.8 dB. A longitudinal-surface wave excites a longitudinal subsurface wave. Due to their common cylindrical front, the signals in the vertical section lag behind the signal on the surface for a time increasing with depth. The depth at which this time is equal to 0.1 of the oscillation period of the signal can be considered the penetration depth of the longitudinal-surface wave.