2.5. Thermoelectric self-powered ion skin (T-iskin)
Given the excellent thermoelectrochemical performance of the ionogel, a thermoelectric self-powered ion skin (T-iskin) was constructed for health monitoring (see the Figure 6 a for its explosion diagram of structure). The T-iskin harnesses its inherent thermoelectric effect, enabling it to function as a self-powered source for strain detection, eliminating the requirement for an external power supply. Rf is the load resistor in parallel, and the change in output voltage of the thermoelectric pressure sensor is reflected by testing the relative resistance change of this resistance (Figure 6b), which is obviously easy to see that by applying different pressure (2, 8, and 30 kPa), the relative resistance change of the load resistor changes significantly.
As commonly acknowledged, humans are homoiothermal creatures with a typical body temperature of approximately 37 ℃. During winter, the standard room temperature ranges from 18 ℃ to 25 ℃, while in summer, it varies from 23 ℃ to 28 ℃. Consequently, the temperature gradient is easily generated by the differences between the body’s temperature and that of the surrounding environment. The ionogel previously studied can generate a voltage of about 75 mV and a current of about 25 μA at a temperature of 8 K (Figure S14), which can be used to drive the T-iskin for the monitoring of human physiological movements. Self-powered and synchronized sensing capabilities in natural environments were further demonstrated by a T-iskin attached to a finger (Figure 6c-i). As the fingers perform a sequential motion cycle of straightening-bending-stretching, each peak in the signal output curve detected by T-iskin represents a finger movement, facilitating precise identification of individual finger activity. Thus, it holds potential for monitoring the health status of the knuckles. Similarly, the T-iskin is placed on the wrist and calf to detect the movement action (Figure 6c-ii-iii), and the results show that the waveform and amplitude in the curves are well maintained, and the voltage signals possess an excellent match with the movement. Motion monitoring from the above three physiological sites revealed different peaks and peak shapes of motion signals in varied sites, which were related to the temperature of the place and the force during action. This research offers a research basis for the utilization of low-order thermal energy in the human body.