A magnetically actuated dynamic labyrinthine transmissive ultrasonic metamaterial

Currently, space-coiling acoustic metamaterials are static, requiring manual reconfiguration for sound-field modulation. Here, we introduce an approach to enable active reconfiguration, using standalone dynamic space-coiling unit cells called dynamic meta-bricks. Unlike their static counterparts, these meta-bricks, house an actuatable soft robotic-inspired magnetorheological elastomeric flap. This flap operates like a switch to directly control the transmitted ultrasound. For scalability, we present a hybrid stacking method, which vertically combines static and dynamic meta-bricks. This allows us to form a surface-integrated metasurface through concatenating variations of either fully static or hybrid stacks. By actuating dynamic metasurface sections, we experimentally demonstrate accurate modulation of λ/4 (≈2 mm) between two acoustic twin traps. We shift a levitated bead between the traps, validating that full-array operational dynamicity is achievable with partial, localised actuation. This work showcases the synergy between active and passive reconfigurability, opening possibilities to develop multifunctional metamaterials with additional degrees of freedom in design and control.