Three-dimensional phononic crystal with ultra-wide bandgap at megahertz frequencies

Phononic crystals have attracted wide attention in diverse scientific communities due to their ability to efficiently reflect, focus, and guide acoustic and elastic waves. Their use in ultrasonic applications such as medical imaging, however, remains elusive since three-dimensional phononic crystals with lattice constants in the range of hundreds of micrometers are required to operate with MHz ultrasound, smaller than what most additive manufacturing solutions can provide. This work presents a three-dimensional phononic crystal with a cubic symmetry having an experimental ultra-wide complete bandgap extending from 0.6 MHz to 7.5 MHz. Crystal specimens are manufactured using two-photon lithography at the microscale, with a lattice constant of 300 μm, and are characterized using heterodyne interferometry.