Figure 4.

Comparison between the measured transient velocity variations and their fitted curves based on Equation (3). a) Results obtained using PS microspheres with fixed densities and different diameters d_p . b) Results obtained using HGMs with varying diameters d_p and effective densities ρ_p . The inset displays the measured effective densities ρ_p in relation to their diameters d_p , consistent with the theoretical prediction of Equation (6) represented by the solid curve. c) The increase in effective density ρ_p (blue dashed curve with half solid circles) of an HGM by coating a 40 nm platinum layer is accurately detected by BMT.