We investigated the effect of film thickness d on the acoustic response of titanium dioxide (TiO₂) layers deposited on Ti, SiO₂, Al₂O₃, and Si substrates. For each TiO₂ thickness–substrate pair, we computed reflection coefficients and acoustic signatures under normal operating conditions of a conventional scanning acoustic microscope, then deduced the Rayleigh-wave velocity V_R from spectral analysis of the oscillatory layer–substrate signatures. As d increased, V_R either rose or fell, depending on the layer/substrate pair, and eventually approached a saturation value. For TiO₂/SiO₂ and TiO₂/Ti, V_R increased from those of the bare substrates (SiO₂: 3415 m/s; Ti: 2965 m/s) toward 3830 m·s⁻¹, the bulk TiO₂ value. For TiO₂/Al₂O₃ and TiO₂/Si, V_R decreased from the substrate values (Al₂O₃: 5700 m/s; Si: 4712 m/s) toward the same TiO₂ saturation. These dispersion trends are consistent with stiffening (V_R (TiO₂) > V_R (Substrate)) or loading (V_R (TiO₂) < V_R (Substrate)) effects. The resulting V_R–d dispersion charts provide theoretical reference trends relating thickness and Rayleigh-wave velocity for the idealized TiO₂/substrate systems considered here.