Hc. Kim et al., Influence of the microstructure on the ultrasonic backscattered energy from a liquid/solid interface at the Rayleigh angle, JPN J A P 1, 38(1A), 1999, pp. 260-267
The scattered ultrasonic energy from a liquid/solid interface at the Raylei
gh angle, E-s, was theoretically derived by considering the interaction bet
ween the energy: bf the penetrated Rayleigh wave, E-0, and the microstructu
re in the subsurface within the Schoch displacement. Delta(s), as E-s = 0.2
5 alpha(s)Delta(s)E(0), where alpha(s) is the attenuation coefficient due t
o scattering. The backscattered ultrasonic energy, E-Bs, at the Rayleigh an
gle was also derived as E-Bs proportional to D(3)f(3) in the Rayleigh scatt
ering region and E-Bs proportional to Df in the stochastic scattering regio
n, where D is the average grain size and f is the frequency. The grain size
and the frequency dependence of the backscattered ultrasonic energy at the
Rayleigh angle were obtained by both, integration and power spectrum analy
sis of the backscattered signals from the interface between the water/stain
less steel plates with the average grain size varying between 5.6 and 40.5
mu m. The exponents of the grain size and the frequency dependence obtained
by both methods were about 3.5 and 2 in the region of lambda(R) greater th
an or equal to 6 pi D and lambda(R) less than or equal to 6 pi D, respectiv
ely. The deviation of the exponents is attributed to the direct scattering
from the surface irregularities in the region of lambda(R) greater than or
equal to 6 pi D and the stochastic scattering due to grain size distributio
n in the region of lambda(R) less than or equal to 6 pi D. This implies tha
t the exponents depend on the ratio of the average size of the scatterer to
the wavelength of the Rayleigh wave. The results suggested that the backsc
attered ultrasonic wave at the Rayleigh angle was built up predominantly by
the scattering from the grain boundaries in the subsurface within the Scho
ch displacement and the direct scattering from the irregularities on the su
rface.