Instabilities of intrinsic thermoacoustic modes in a thermoacoustic waveguide with anechoic terminations

A recent study [H. Hao and F. Semperlotti, Phys. Rev. B 104, 104303 (2021)] investigated the dynamic behavior of an infinite one-dimensional (1D) thermoacoustic waveguide (TAWG) illustrated its ability to sustain nonreciprocal near zero-index sound propagation behavior; these properties can be very beneficial in design acoustic devices, including diodes, amplifiers, cloaks. Nevertheless, it is critical realize that when this concept implemented a finite-length waveguide, instabilities may occur either drastically reduce or completely hinder TAWG control manipulate sound. In work, we uncover investigate occurrence evanescent intrinsic (ITA) modes 1D with anechoic terminations. The stability analysis clearly distinguishes two types highlights their different origin rooted thermoviscous effects. Numerical results reveal ITA anechoic-terminated are strictly connected acoustic-driven modes, evolve towards unstable as TA coupling strength increased. This have important implications for practical novel manipulating devices enabled by elements. conclusions drawn also shed lights on effective suppression TAWGs.