Bound States in the Continuum in Single Microwave Resonators

Bound states in the continuum (BICs) enable extreme wave-matter interaction, which can be utilized in many applications such as lasing, sensing and energy harvesting. One inherent problem of BICs is that they require large periodic structures and/or materials with exotic properties such as epsilon-near-zero materials. In this work, we realize a localized BIC supported in a single resonator, which is based on simple and abundant materials. The localized BIC is realized by imposing suitable boundary conditions around the resonator effectively achieved with a simple rectangular waveguide, and holds strong potential in sensing of small perturbations and impurities in tiny drops of water.