General Framework of Bound States in the Continuum in an Open Acoustic Resonator

Bound states in the continuum (BICs) provide a viable way of achieving high-Q resonances both photonics and acoustics. In this work, we propose general method constructing Friedrich-Wintgen (FW) BICs accidental coupled acoustic waveguide-resonator system. We demonstrate that FW can be achieved with arbitrary two degenerate closed resonator, regardless whether they have same or opposite parity. Moreover, their eigenmode profiles arbitrarily engineered by adjusting position attached waveguide. This suggests an effective continuously switching nature from to symmetry-protected BICs. Also, such are sustained system shapes as rectangles, ellipses, rhomboids. These interesting phenomena well explained two-level non-Hermitian Hamiltonian, where strongly modes play major role forming Additionally, find open also supports geometry space instead momentum via tuning waveguide, which is attributed quenched coupling between waveguide eigenmodes cavity. Finally, fabricate series three-dimensional resonator waveguides experimentally verify existence measuring transmission spectra. Our results complement current BIC library acoustics nice routes for designing devices, absorbers, filters, sensors.