WAVE-DIODE EFFECT EXPLOITING DISCRETELY MODULATED PHONONIC WAVEGUIDES

Space-time varying phononic materials have drawn great interest in the research community, due to their ability to break time reversal symmetry, therefore achieving one-way wave propagation in elastic structures. In analogy with their electric counterparts, these new devices are generally referred as acoustic wave diodes. In this manuscript we study discretely modulated beams, whose spatiotemporal unitary cells are made of sub-cells with time-varying elastic modulus. This new class of materials is able to break the mirror symmetry in the momentum space, which is necessary to achieve the acoustic wave-diode effect. Non-reciprocal Bloch diagram is computed using a generalization of the Plane Wave Expansion Method (PWEM) which can be applied to any modulation that can be written in a spacetime Fourier basis. In this context, we show that the frequency spectrum is characterized by full and directional bandgaps, that are linked with the harmonic content of the spatiotemporal unit cell.