This work investigates the sensitivity of surface-wave dispersion characteristics in periodic phononic structures with two types of scatterers: cylindrical pillars and finite-depth circular holes. We develop high-fidelity finite element models of square unit cells with Bloch boundary conditions and analyse the effect of geometric parameters (diameter and height/depth) on eigenfrequencies at a Brillouin zone high-symmetry point. A global sensitivity analysis based on the one-factor-at-a-time method is performed to quantify parameter influence and non-linear interactions. The results show that, for pillar-type structures, the pillar height dominates the dynamic response, while for hole-type structures both diameter and depth have comparable effects. Large geometric variations lead to mode reordering and narrow frequency separations, which is critical for bandgap-oriented optimisation. The approach outlines a route towards tunable phononic platforms for wave-based imaging applications.
