Fig. 4.

Unidirectional pulse amplification. a–e Contour plots of the angular displacement vs. space coordinate and time for a feedback parameter α = 0 (ab) and α = 0.62 (de), upon pulse excitation on the left (ad) and right (be) edge of the metamaterial. (cf) Instantaneous maximum magnitude of the propagation pulse vs. time for a feedback parameter α = 0 (c) and α = 0.62 (f). The points correspond to the experimental data, the thin solid lines to the numerical model without any fit parameters. (f-inset) Decay rate δ derived from exponential fits of the form exp(−δt) on the maximum amplitude of pulses propagating from left to right for different values of the feedback parameter. See also Supplementary Video 2