Quasi-Bound States in the Continuum in Terahertz Trimer-Based Metamaterials

Bound states in the continuum (BICs) are waves confined localized with an infinite quality (Q) factor and zero bandwidth resonance in the frequency spectrum, and quasiBICs preserves their high Q-factor characteristics with limited resonance bandwidth which facilitates observation. Here, we propose a method utilizing terahertz trimer-based metamaterials to generate different numbers of quasi-BICs via changing the spacings between the primitive unit structures while keeping their geometric parameters consistent, and we discuss the relation between the number of equal spacings and the number of quasi-BICs. We prove that 0, 1 and 2 quasi-BICs could be generated when 0, 2 and 3 spacings of all the three spacings in the trimer are unequal, respectively. We also discuss the relevance of quasi-BICs generated in different cases that all the three spacings are unequal and only two spacings are equal.