Figure 3.

Results for (a) the difference spectra $D\left(f\right)$ and (b) the normalized difference spectra $nD\left(f\right)$ for all transducers (2.25, 5, 7.5, and 10 MHz) and all three choices of gate separation (${\tau }_s=0$, $5/f_c$, and $10/f_c$). Individual data series were generated by averaging all measurements from all specimens for each choice of transducer and gate separation.