Research of anapole modes in ring-shaped subwavelength periodic structures fabricated on thin free-standing metal film

Over recent years, numerous designs of metamaterials with diverse functionalities have emerged from various research groups, including negative-refractive-index materials, electromechanical metamaterials, chiral materials, photonic crystals, electromagnetic cloaks, and optical metamaterials [1], [2]. Based on the type of electrical conductivity involved, metamaterials can be categorized into those utilizing metals and those relying on the dielectric optical properties of materials. Ultrathin planar metamaterials composed of periodic subwavelength structures are meticulously arranged to show remarkable electromagnetic characteristics, where the anapole states are of particular interest seeking to realize nonradiating electromagnetic sources [3], [4].