Experimental Observation of Nonreciprocal Waves in a Spatiotemporally Modulated Phononic Chain

Mechanical devices that break time-reversal symmetry are highly desirable for sound and vibration insulation, because they allow non-reciprocal wave transmission. Here, we show the first experimental demonstration of non-reciprocity in a one-dimensional phononic chain, obtained from spatio-temporal modulation of local stiffness and resonance. The modulation is controlled by electro-magnets in a discrete chain of magnetic masses connected by weakly nonlinear springs. This biased modulation breaks time-reversal symmetry and opens a bandgap in the dispersion relation, which allows uni-directional sound transmission. This work provides opportunities to build nonreciprocal devices in 1D, without using 2D topological mechanical systems.