Extreme Sound Confinement From Quasibound States in the Continuum

Extreme confinement of incident acoustic waves remains challenging, because of the conflict between weak dissipation and eliminating reflection. Help might be found in $b\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}d$ $s\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}s$ $i\phantom{\rule{0}{0ex}}n$ $t\phantom{\rule{0}{0ex}}h\phantom{\rule{0}{0ex}}e$ $c\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}m$ (BICs), resonances with zero leakage and zero linewidth (infinite quality factor) within a continuum of radiating states. This study presents an acoustic quasi-BIC supported by two detuned resonant cavities, a system featuring compensating very low rates of radiative and dissipative decay, to completely trap incoming waves for a long time. This work opens an avenue to study intriguing physics, and may find application in sensing, filtering, absorption, or energy harvesting.