Selectively exciting quasibound states in the continuum in open microwave resonators using dielectric scatters

Bound states in the continuum (BICs) are wave modes that remain in the continuous spectrum of radiating waves that carry energy; however, they remain perfectly localized and nonradiating. BICs, or embedded eigenmodes, exhibit high quality factors that have been observed in optical and acoustic waveguides, photonic structures, and other physical systems. However, there are limited means to manipulate these BICs in terms of the quality factor and their excitation. In this work, we show that quasi-BICs (QBICs) in open resonators can be tailored by introducing embedded scatters. Using microwave cavities and dielectric scatters as an example, QBICs are shown to be capable of being repeatedly manipulated by tuning the geometry of the structure and the specific locations of the dielectric scatters. Using coupled mode theory and numerical simulations, we demonstrate by altering dielectric and structural parameters that tuning the quality factor as well as selective excitation and suppressing of specific QBIC modes can be achieved. These results provide an alternative means to control BICs in open structures and may be beneficial to applications including sensors and high-Q resonators that need confined fields and selectivity in frequency.