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Figure 5. Environmental energy transfer systems. (A) A low-impedance magnesium coil for wireless energy harvesting^[99]; (B) A wirelessly rechargeable implantable zinc-ion battery^[105]; (C) Body-conforming ultrasound receiver enabling efficient and stable wireless charging in deep tissues^[106]; (D) Near-infrared tandem organic photodiodes for future application in artificial retinal implants^[109]. Reproduced with permission from American Association for the Advancement of Science (A), Springer Nature (B), and Wiley (C and D).