Characterizing the mechanics of periodic scaffolds used for bone tissue repair, while maintaining their structural integrity, is a challenging problem. By leveraging concepts arising from the bulk phononic crystal community, here we investigate the reflection of elastic waves propagating through a water-immersed biphasic architectured medium in the ultrasonic regime. Towards this goal, Bloch–Floquet analysis is applied on a 2D unit cell made of a soft inclusion embedded in a hard matrix, to recover its corresponding phononic band structure. Exploring the modal conversion at the boundary between the homogeneous incident medium and the architectured one allows identifying a bandgap within the considered frequency range, which exhibits a significant sensitivity to varying volume fraction of the soft phase. Conducting further numerical analyzes, which account for the viscoelasticity of the two constituent phases, along with the finite-size and bounded nature of the architectured medium, shows that a sudden amplitude rise of the reflection coefficient takes place at a frequency that is closely related to the upper limit of this bandgap. This hypothesis is experimentally verified on 3D-printed bio-mimicking samples, which exhibit an in-plane periodicity at a length scale of a few hundred micrometers. Altogether, the reported results suggest that tracking prohibited frequency bands via the measurement of the reflection coefficient allows for the monitoring of micro-architectured media like scaffolds.