Air-pressure-driven TENG embedded in the insole. (a) The layer-by-layer structural design of the TENG and a photograph of the as-fabricated smart insole. (b) 3D illustration of the working mechanism of the TENG. (c) Signals reflecting the release (off) of foot pressure (on), on the sole. (d) The mechanical durability of the TENG after continuously working about 1000 cycles. (e) Demonstrations of the smart insoles for warning of fall down. (f) A smart shoe recording normal walking monitoring and a sudden fall. Reproduced with permission from [51
]. Copyright Wiley-VCH, 2018.