a, Interference between the primary coil and NFC antennas. Shown are schematic illustrations of a primary coil with (left) or without (right) four NFC antennas along the Z direction of the transmission antenna. b, Comparison of experimental (E) and theoretical (T) results of voltage induced by a single primary coil versus a primary coil with four NFC antennas. c, d, Transmission antennas used for operating the VR devices: c, small size, 318 mm × 338 mm; and d, large size, 620 mm × 852 mm. e, An transmission antenna placed in the X–Y plane. f, The magnetic field strength (H) in the Z–X plane (the middle plane of the coil) for the small (left) and large (right) transmission antennas (RF readers). g, Theoretical results show that the small and large transmission antennas are suitable for short (<24 cm) and long (>24 cm) working distances, respectively. h, i, Output power of the serpentine primary coil of the epidermal VR device as a function of distance to the small transmission antenna (h), and the large transmission antenna (i). The error bars correspond to the calculated standard deviation.