Observation and interpretation of mode splitting in positive rayleigh wave dispersion characteristics

In this paper, we investigate the positive dispersive behavior of Rayleigh velocity for several layer/substrate combinations: Cr/quartz, SiO
₂
/Mo, SiO
₂
/stainless steel and Cr/Mo. The simulation conditions were those usually used in conventional acoustic microscopy. It was found that a second mode appears next to that of Rayleigh, unlike the usual unique dispersive curve. Moreover, this new mode has a negative dispersive behavior which is not likely to happen in the rigidity effect. This unusual phenomenon is interpreted by the acoustic impedance mismatching between layers and substrates.