Figure 4.

Application of flexible antenna sensor for human motion detection. (a, b) Photographs of a flexible antenna sensor attached to the back of the hand in the initial (a) and bending (b) states. (c, d) Photographs of flexible antenna sensor attached to the wrist in the initial (c) and bending (d) states. (e) Response of normalized frequency varying with initial and bending states in the two cases. The normalized frequency changes abruptly but always restores to its original frequency after each bending cycle.