Fig. 4: Modeling of experimental AC resistance and demonstration of a low-power respiratory tracker.
a Experimentally measured resistance during stretching and the predicted resistances from a mathematical model as a function of stretching at different frequencies (DC, 1 MHz, and 3 MHz) for a liquid metal wire with 1.5mm diameter. Error bars denote ± 1 s.d. b A Wheatstone bridge circuit incorporating the liquid metal sensor as Rsensor. c Simulated signal-to-noise ratio (SNR) as a function of power consumption from the bias current of the Wheatstone bridge at different excitation frequencies (DC, 2 MHz, and 10 MHz). An instrumentation amplifier, shown in the inset, is proposed to collect differential voltage measurements of the liquid metal sensor. d Liquid metal AC sensor-based system is placed on the human chest area to collect and process respiratory data. e AC signal as a function of time for (i) low frequency (0.1 MHz) and for (ii) high-frequency (10 MHz) input signal for breathing phases (exhalation and inhalation). f Vrms vs. time for corresponding breathing phases at low frequency (0.1 MHz) and high frequency (10 MHz).
