Sharkskin-inspired design principle of the magnetoactive reconfigurable acoustic metamaterials. (a) Schematics to show the sharkskin denticles for switchable flow drag via reversibly tilting the denticles. (b, c) Schematic and sample of the vertical Mie resonator pillar array. Inset in (b) shows the cross-section of the pillar. (d, e) Schematic and sample of the pillar array with two pillars bent via a magnetic field. The red arrows indicate the direction of the magnetic field. The selective actuation of the central two pillars is because of their higher iron volume fraction (18.48% by weight, Fig. S8a
). (f, g) Schematic and sample of the pillar array when the magnetic field is turned off. (h) The acoustic transmissions of samples corresponding to (c), (e), and (g) in functions of the frequency. (i) The applied magnetic field intensity and the corresponding acoustic pressure at 9100 Hz within two switching cycles. The scale bars in (c), (e), and (g) represent 1 cm. The photo credit of the shark in (a) comes from Braulio Lopez Gonzalez Jr.