a real smart socks, lead zirconate titanate (PZT) chips are thinned down t o 50um t o make a flexible force sensor which is small enough t o be embedded into socks without losing the comfortability. FIG. 13 shows a comparison of output voltage and (b) current between PEDOT:PSS coated socks and non-coated socks - FIGs. 13(a) and 13(b) respectively. FIG. 12(c) shows the power curve of smart socks within the shoes, under walking and jumping conditions. Similarly, FIG. 13(d) shows the power curve of smart socks without shoes and while under walking and jumping conditions. 

[084] Smart socks as motion, gait, and force sensor 

[085] Based on the working principle of the triboelectric effect, the physical sensor can also be realized by integrating multiple electrodes into socks or shoes. In FIG. 14, by designing a PTFE insole with four electrodes, gait and the position can be identified with larger pressure through the signal peaks. In addition, as shown in FIG. 14c, the embedded thin PZT force sensor can provide more quantitative pressure analysis from movements, due t o its high sensitivity. Relevantly, FIG. 14 shows, for a triboelectric sensor: FIG. 14(a) gait monitoring by multiple electrodes, toe and heel contact, FIG. 14(b) output voltage vs. force calibration, and for PZT piezoelectric force sensors: and FIG. 14(c) output signals from 2 corresponding positions during walking, compare t o theoretical foot pressure mapping. 

[086] Smart socks as sweat sensor 

[087] Triboelectric performance is related t o humidity, in terms of output. To utilize this feature, a sweat sensor is developed together with piezoelectric sensors. More specifically, both contact force and humidity can affect the triboelectric power generation. To eliminate the influence of force fluctuation, the PZT force sensor will act as a baseline, since it will not vary with humidity. Therefore, as shown in FIG. 15, by measuring the triboelectric and piezoelectric signals simultaneously, w e can obtain a rough data about the sweat status of foot, for further sports monitoring or healthcare use. Relevantly, FIG. 15 shows the output voltage of the PZT sensor and triboelectric sensor in either separate, closely positioned devices, or in the same device (e.g. a garment such as a sock) under increasing sweat conditions. 0.9wt% of NaCI solution is used t o mimic sweat. 

[088] The first generation of such smart textiles only used the textile as a substrate that was integrated with rigid and miniaturized electronic components. Intrinsically flexible and wearable sensors based on textile or fabric have emerged, t o realize a seamless integration of multi-function sensors and textiles. The common sensing mechanism of the textile-based flexible or stretchable sensors is based on the resistance change which still cannot bypass the essential issue of power consumption. To solve this matter, fabric based TENG has emerged 

