Figure 3.

Strain measurement of flexible antenna sensor. (a) Schematic of sensor bending under compression and tension. (b) Representative images of GAF sensor conformed to poly(lactic acid) (PLA) rings with different radii. (c, d) Reflection coefficient of antenna as a function of frequency under compressive bending (c) and tensile bending (d) for different central angles. (e) Normalized resonant frequency of flexible antenna sensor as a function of the central angle. The measured results of the antenna with these two statuses (compressive bending and tensile bending) display a similar trend.