Fig. 4.

Impedance spectra of ICE based touch sensors. a Schematic diagram of uncovered touch sensor at different states. Plots of impedance magnitude (|Z|) and negative phase angle (−ϕ) versus testing frequency of uncovered touch sensor (b, c) at different states (original, black line; stretched, yellow line; touched, blue line; stretched and touched, magenta line). d Nyquist plots of impedance spectra of uncovered touch sensor at different states. e Repeatedly detected data of uncovered touch sensor at a single frequency (f = 20 KHz) in impedance complex plane (original, black dots; stretched, yellow dots; touched, blue dots; stretched and touched, magenta dots). f Schematic diagram of insulating film covered touch sensor. Plots of impedance magnitude (|Z|) and negative phase angle (−ϕ) versus testing frequency of insulating film covered touch sensor (g, h), varies thickness of insulating film were tested (100 μm, black line; 200 μm, yellow line; 500 μm, blue line; 1000 μm, magenta line; 2000 μm, green line; untouched, deep blue line). i Nyquist plots of impedance spectra of insulating film covered touch sensor. j Repeatedly detected data of insulating film covered touch sensor at a single frequency (f = 10 KHz) in impedance complex plane. Green circle, untouched, purple circle, touched