Fig. 4: Devices for optical sensing.
From: Skin-interfacing wearable biosensors for smart health monitoring of infants and neonates
a Illustration of a cap-mounted device for measuring PPG at the forehead. The sensor sits above the eyebrow. Reproduced under the terms of the Creative Commons CC BY 4.0 license from ref. 48. b Wireless PPG device bending around a glass cylinder. Reproduced under the terms of the Creative Commons CC BY 4.0 license from ref. 33. c Schematic and photographs of a wireless limb unit for measuring PPG. Reproduced with permission17. Copyright 2020, Springer Nature.
