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.