Spin waves (SWs), or magnons, are collective excitations of magnetization in magnetic materials arising from electron spins. They have attracted considerable attention as information carriers and have shown promise in logic circuits, memory devices and physical neural networks. Among the emerging platforms for manipulating SWs are magnonic crystals (MCs), engineered magnetic materials with periodic structures designed to control magnon propagation. These periodic structures give rise to magnonic band structures and mode profiles, much like semiconductor crystals control electron transport.