Fig. 3. Experiments of the response of a high-density energy-harvesting metamaterial device under various wave size conditions.

a schematic of the experimental rig; b photographs of the experimental rig: (i) oscilloscope, which shows the energy-harvesting metamaterial plate output voltage; (ii) computer; (iii) signal controller, which generates sinusoidal signals; (iv) power amplifier;(v) triaxial shakers that provide excitation in the x-, y- and z-directions;(vi) flume, which simulates the ocean wave environment; c motion state analysis and output voltage of a rolling magnetic ball in a metamaterial energy-harvesting device under various wave conditions:(i), (ii): a = 0.1 g, f = 2 Hz, x-direction excitation; (iii), (iv): a = 0.5g, f = 2 Hz, x -direction excitation; (v), (vi): a = 1.0 g, f = 2 Hz, x-direction excitation; (vii), (viii): a = 1.5 g, f = 2 Hz, z-direction excitation; when the energy harvesting metamaterial plate is in the multi-direction excitation state; (ix), (x): a = 1.5g, f = 2 Hz, x-y-direction excitation, when the energy harvesting metamaterial plate is in the multi-direction excitation state; (xi), (xii): a = 2.0 g, f = 2 Hz, z-direction excitation, when the energy harvesting metamaterial plate is in the overturning state; where (i)–(vi) simulate the motion state and energy output of the rolling ball in the metamaterial energy harvester in a steady wave environment, (vii)–(xii) simulate the motion state and energy output of the rolling ball in the metamaterial energy harvester in a harsh environment.