Fig. 6: Experimental demonstration of skin modes and odd micropolar moduli.
From: Realization of active metamaterials with odd micropolar elasticity
a Experimental schematic. Flexural waves are generated in the active metabeam from either the right or left side using piezoelectric actuators (yellow), see “Methods”. A scanning laser Doppler vibrometer (SLDV) measures the transverse velocity of the surface of the active metabeam. b, c Unidirectional amplification of waves. A metamaterial consisting of 9 unit cells is actuated from either the right (blue) or left (red) with a 2 kHz tone burst signal (gray). The output velocity is normalized by the maximum velocity observed when the experiment is performed with no active feedback. d Observation of the non-Hermitian skin effect. Experiments are performed between 1.5 kHz and 4 kHz for right to left (blue) and left to right (red) traveling waves. A 2D FFT shows the intensity of the observed spectrum. The intensity is normalized by its maximum value. e The inverse decay length. In d, e the solid theoretical curves are based on the transfer matrix method. In d the gray dashed curves are theoretical predictions with no activity. f A plot of arg(P) as a function of frequency. At ω = ω0 (= 3 kHz), arg(P) = −π/2, indicating that the system is pseudo-Hermitian and accordingly we observe κ = 0 at ω = ω0.
