Fig. 1: Design diagram of wave energy harvesting and self-powered health monitoring system in OIoT.

a Schematic of a metamaterial energy harvester harvesting wave energy from the ocean environment.the red dashed circle illustrates the electromagnetic energy harvesting cell and the blue dashed circle illustrates the resonant cell; b (i) Schematic of the energy concentration phenomenon of the metamaterial with defects under wave excitation; (ii) Simulated displacement clouds of metamaterial plates with point defects when excited by ocean waves, c schematic design of a self-powered ocean environmental health monitoring system: (i) high-density wave energy harvesting metamaterial panels. The green circle illustrates the resonant cell and the red circle illustrates the energy harvesting cell, (ii) rectifier module (AC → DC);(iii) Series/parallel conversion module for energy storage elements. (S is a single-patch double-throw switch (ADG719-EP) integrated into the circuit to achieve series/parallel conversion of the energy storage element. When S₁ is closed, the capacitors are connected in parallel and the energy storage element is charged; when S₂ is closed, the capacitors are connected in series and the energy storage element is discharged); This series/parallel coversion modulue allows the system to be able to charge the storage at low voltages and supply power to sensing subsystems at higher voltages, enhancing the energy harvesting capability; (iv) energy storage module; (v) environmental condition monitoring module (e.g. pH, temperature, and water quality); (vi) monitored information receiving module; and (vii) charge/discharge curves of the energy storage modules.